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Karimi A, Aga M, Khan T, D'costa SD, Thaware O, White E, Kelley MJ, Gong H, Acott TS. Comparative analysis of traction forces in normal and glaucomatous trabecular meshwork cells within a 3D, active fluid-structure interaction culture environment. Acta Biomater 2024; 180:206-229. [PMID: 38641184 DOI: 10.1016/j.actbio.2024.04.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 03/26/2024] [Accepted: 04/11/2024] [Indexed: 04/21/2024]
Abstract
This study presents a 3D in vitro cell culture model, meticulously 3D printed to replicate the conventional aqueous outflow pathway anatomical structure, facilitating the study of trabecular meshwork (TM) cellular responses under glaucomatous conditions. Glaucoma affects TM cell functionality, leading to extracellular matrix (ECM) stiffening, enhanced cell-ECM adhesion, and obstructed aqueous humor outflow. Our model, reconstructed from polyacrylamide gel with elastic moduli of 1.5 and 21.7 kPa, is based on serial block-face scanning electron microscopy images of the outflow pathway. It allows for quantifying 3D, depth-dependent, dynamic traction forces exerted by both normal and glaucomatous TM cells within an active fluid-structure interaction (FSI) environment. In our experimental design, we designed two scenarios: a control group with TM cells observed over 20 hours without flow (static setting), focusing on intrinsic cellular contractile forces, and a second scenario incorporating active FSI to evaluate its impact on traction forces (dynamic setting). Our observations revealed that active FSI results in higher traction forces (normal: 1.83-fold and glaucoma: 2.24-fold) and shear strains (normal: 1.81-fold and glaucoma: 2.41-fold), with stiffer substrates amplifying this effect. Glaucomatous cells consistently exhibited larger forces than normal cells. Increasing gel stiffness led to enhanced stress fiber formation in TM cells, particularly in glaucomatous cells. Exposure to active FSI dramatically altered actin organization in both normal and glaucomatous TM cells, particularly affecting cortical actin stress fiber arrangement. This model while preliminary offers a new method in understanding TM cell biomechanics and ECM stiffening in glaucoma, highlighting the importance of FSI in these processes. STATEMENT OF SIGNIFICANCE: This pioneering project presents an advanced 3D in vitro model, meticulously replicating the human trabecular meshwork's anatomy for glaucoma research. It enables precise quantification of cellular forces in a dynamic fluid-structure interaction, a leap forward from existing 2D models. This advancement promises significant insights into trabecular meshwork cell biomechanics and the stiffening of the extracellular matrix in glaucoma, offering potential pathways for innovative treatments. This research is positioned at the forefront of ocular disease study, with implications that extend to broader biomedical applications.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, United States.
| | - Mini Aga
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Taaha Khan
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Siddharth Daniel D'costa
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Omkar Thaware
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, United States
| | - Elizabeth White
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department Integrative Biosciences, School of Dentistry, Oregon Health & Science University, Portland, OR, United States
| | - Haiyan Gong
- Department of Ophthalmology, Boston University School of Medicine, Boston, MA, United States; Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, MA, United States
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department Chemical Physiology & Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, United States
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Karimi A, Aga M, Khan T, D'costa SD, Cardenas-Riumallo S, Zelenitz M, Kelley MJ, Acott TS. Dynamic traction force in trabecular meshwork cells: A 2D culture model for normal and glaucomatous states. Acta Biomater 2024; 175:138-156. [PMID: 38151067 PMCID: PMC10843681 DOI: 10.1016/j.actbio.2023.12.033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2023] [Revised: 12/10/2023] [Accepted: 12/20/2023] [Indexed: 12/29/2023]
Abstract
Glaucoma, which is associated with intraocular pressure (IOP) elevation, results in trabecular meshwork (TM) cellular dysfunction, leading to increased rigidity of the extracellular matrix (ECM), larger adhesion forces between the TM cells and ECM, and higher resistance to aqueous humor drainage. TM cells sense the mechanical forces due to IOP dynamic and apply multidimensional forces on the ECM. Recognizing the importance of cellular forces in modulating various cellular activities and development, this study is aimed to develop a 2D in vitro cell culture model to calculate the 3D, depth-dependent, dynamic traction forces, tensile/compressive/shear strain of the normal and glaucomatous human TM cells within a deformable polyacrylamide (PAM) gel substrate. Normal and glaucomatous human TM cells were isolated, cultured, and seeded on top of the PAM gel substrate with embedded FluoSpheres, spanning elastic moduli of 1.5 to 80 kPa. Sixteen-hour post-seeding live confocal microscopy in an incubator was conducted to Z-stack image the 3D displacement map of the FluoSpheres within the PAM gels. Combined with the known PAM gel stiffness, we ascertained the 3D traction forces in the gel. Our results revealed meaningfully larger traction forces in the glaucomatous TM cells compared to the normal TM cells, reaching depths greater than 10-µm in the PAM gel substrate. Stress fibers in TM cells increased with gel rigidity, but diminished when stiffness rose from 20 to 80 kPa. The developed 2D cell culture model aids in understanding how altered mechanical properties in glaucoma impact TM cell behavior and aqueous humor outflow resistance. STATEMENT OF SIGNIFICANCE: Glaucoma, a leading cause of irreversible blindness, is intricately linked to elevated intraocular pressures and their subsequent cellular effects. The trabecular meshwork plays a pivotal role in this mechanism, particularly its interaction with the extracellular matrix. This research unveils an advanced 2D in vitro cell culture model that intricately maps the complex 3D forces exerted by trabecular meshwork cells on the extracellular matrix, offering unparalleled insights into the cellular biomechanics at play in both healthy and glaucomatous eyes. By discerning the changes in these forces across varying substrate stiffness levels, we bridge the gap in understanding between cellular mechanobiology and the onset of glaucoma. The findings stand as a beacon for potential therapeutic avenues, emphasizing the gravity of cellular/extracellular matrix interactions in glaucoma's pathogenesis and setting the stage for targeted interventions in its early stages.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, USA.
| | - Mini Aga
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | - Taaha Khan
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | - Siddharth Daniel D'costa
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | | | - Meadow Zelenitz
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department Integrative Biosciences, School of Dentistry, Oregon Health & Science University, Portland, OR, USA
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department Chemical Physiology & Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, USA
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Karimi A, Khan S, Razaghi R, Aga M, Rahmati SM, White E, Kelley MJ, Jian Y, Acott TS. Segmental biomechanics of the normal and glaucomatous human aqueous outflow pathway. Acta Biomater 2024; 173:148-166. [PMID: 37944773 PMCID: PMC10841915 DOI: 10.1016/j.actbio.2023.11.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 10/18/2023] [Accepted: 11/02/2023] [Indexed: 11/12/2023]
Abstract
The conventional aqueous outflow pathway, encompassing the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and inner wall endothelium of Schlemm's canal (SC), governs intraocular pressure (IOP) regulation. This study targets the biomechanics of low-flow (LF) and high-flow (HF) regions within the aqueous humor outflow pathway in normal and glaucomatous human donor eyes, using a combined experimental and computational approach. LF and HF TM/JCT/SC complex tissues from normal and glaucomatous eyes underwent uniaxial tensile testing. Dynamic motion of the TM/JCT/SC complex was recorded using customized green-light optical coherence tomography during SC pressurization in cannulated anterior segment wedges. A hyperviscoelastic model quantified TM/JCT/SC complex properties. A fluid-structure interaction model simulated tissue-aqueous humor interaction. FluoSpheres were introduced into the pathway via negative pressure in the SC, with their motion tracked using two-photon excitation microscopy. Tensile test results revealed that the elastic moduli of the LF and HF regions in glaucomatous eyes are 3.5- and 1.5-fold stiffer than the normal eyes, respectively. The FE results also showed significantly larger shear moduli in the TM, JCT, and SC of the glaucomatous eyes compared to the normal subjects. The LF regions in normal eyes demonstrated larger elastic moduli compared to the HF regions in glaucomatous eyes. The resultant strain in the outflow tissues and velocity of the aqueous humor in the FSI models were in good agreement with the digital volume correlation and 3D particle image velocimetry data, respectively. This study uncovers stiffer biomechanical responses in glaucomatous eyes, with LF regions stiffer than HF regions in both normal and glaucomatous eyes. STATEMENT OF SIGNIFICANCE: This study delves into the biomechanics of the conventional aqueous outflow pathway, a crucial regulator of intraocular pressure and ocular health. By analyzing mechanical differences in low-flow and high-flow regions of normal and glaucomatous eyes, this research unveils the stiffer response in glaucomatous eyes. The distinction between regions' properties offers insights into aqueous humor outflow regulation, while the integration of experimental and computational methods enhances credibility. These findings have potential implications for disease management and present a vital step toward innovative ophthalmic interventions. This study advances our understanding of glaucoma's biomechanical basis and its broader impact on ocular health.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, USA.
| | - Shanjida Khan
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, USA
| | - Reza Razaghi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | - Mini Aga
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | | | - Elizabeth White
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department Integrative Biosciences, School of Dentistry, Oregon Health & Science University, Portland, OR, USA
| | - Yifan Jian
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, USA
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA; Department Chemical Physiology & Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, USA
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Karimi A, Razaghi R, D'costa SD, Torbati S, Ebrahimi S, Rahmati SM, Kelley MJ, Acott TS, Gong H. Implementing new computational methods for the study of JCT and SC inner wall basement membrane biomechanics and hydrodynamics. Comput Methods Programs Biomed 2024; 243:107909. [PMID: 37976613 PMCID: PMC10840991 DOI: 10.1016/j.cmpb.2023.107909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Revised: 10/28/2023] [Accepted: 10/30/2023] [Indexed: 11/19/2023]
Abstract
PURPOSE The conventional aqueous outflow pathway, which includes the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and the inner wall endothelium of Schlemm's canal (SC), regulates intraocular pressure (IOP) by controlling the aqueous humor outflow resistance. Despite its importance, our understanding of the biomechanics and hydrodynamics within this region remains limited. Fluid-structure interaction (FSI) offers a way to estimate the biomechanical properties of the JCT and SC under various loading and boundary conditions, providing valuable insights that are beyond the reach of current imaging techniques. METHODS In this study, a normal human eye was fixed at a pressure of 7 mm Hg, and two radial wedges of the TM tissues, which included the SC inner wall basement membrane and JCT, were dissected, processed, and imaged using 3D serial block-face scanning electron microscopy (SBF-SEM). Four different sets of images were used to create 3D finite element (FE) models of the JCT and inner wall endothelial cells of SC with their basement membrane. The outer JCT portion was carefully removed as the outflow resistance is not in that region, leaving only the SCE inner wall and a few µm of the tissue, which does contain the resistance. An inverse iterative FE algorithm was then utilized to calculate the unloaded geometry of the JCT/SC complex at an aqueous humor pressure of 0 mm Hg. Then in the model, the intertrabecular spaces, pores, and giant vacuole contents were replaced by aqueous humor, and FSI was employed to pressurize the JCT/SC complex from 0 to 15 mm Hg. RESULTS In the JCT/SC complex, the shear stress of the aqueous humor is not evenly distributed. Areas proximal to the inner wall of SC experience larger stresses, reaching up to 10 Pa, while those closer to the JCT undergo lower stresses, approximately 4 Pa. Within this complex, giant vacuoles with or without I-pore behave differently. Those without I-pores experience a more significant strain, around 14%, compared to those with I-pores, where the strain is roughly 9%. CONCLUSIONS The distribution of aqueous humor wall shear stress is not uniform within the JCT/SC complex, which may contribute to our understanding of the underlying selective mechanisms in the pathway.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR, United States.
| | - Reza Razaghi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Siddharth Daniel D'costa
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Saeed Torbati
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States
| | - Sina Ebrahimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States.
| | | | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department Integrative Biosciences, School of Dentistry, Oregon Health & Science University, Portland, OR, United States.
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, United States; Department Chemical Physiology & Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, United States.
| | - Haiyan Gong
- Department of Ophthalmology, Boston University School of Medicine, Boston, Massachusetts, United States; Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, Massachusetts, United States.
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Karimi A, Razaghi R, Kelley MJ, Acott TS, Gong H. Biomechanics of the JCT and SC Inner Wall Endothelial Cells with Their Basement Membrane Using 3D Serial Block-Face Scanning Electron Microscopy. Bioengineering (Basel) 2023; 10:1038. [PMID: 37760140 PMCID: PMC10525990 DOI: 10.3390/bioengineering10091038] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 08/01/2023] [Accepted: 08/30/2023] [Indexed: 09/29/2023] Open
Abstract
BACKGROUND More than ~70% of the aqueous humor exits the eye through the conventional aqueous outflow pathway that is comprised of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), the inner wall endothelium of Schlemm's canal (SC). The flow resistance in the JCT and SC inner wall basement membrane is thought to play an important role in the regulation of the intraocular pressure (IOP) in the eye, but current imaging techniques do not provide enough information about the mechanics of these tissues or the aqueous humor in this area. METHODS A normal human eye was perfusion-fixed and a radial wedge of the TM tissue from a high-flow region was dissected. The tissues were then sliced and imaged using serial block-face scanning electron microscopy. Slices from these images were selected and segmented to create a 3D finite element model of the JCT and SC cells with an inner wall basement membrane. The aqueous humor was used to replace the intertrabecular spaces, pores, and giant vacuoles, and fluid-structure interaction was employed to couple the motion of the tissues with the aqueous humor. RESULTS Higher tensile stresses (0.8-kPa) and strains (25%) were observed in the basement membrane beneath giant vacuoles with open pores. The volumetric average wall shear stress was higher in SC than in JCT/SC. As the aqueous humor approached the inner wall basement membrane of SC, the velocity of the flow decreased, resulting in the formation of small eddies immediately after the flow left the inner wall. CONCLUSIONS Improved modeling of SC and JCT can enhance our understanding of outflow resistance and funneling. Serial block-face scanning electron microscopy with fluid-structure interaction can achieve this, and the observed micro-segmental flow patterns in ex vivo perfused human eyes suggest a hypothetical mechanism.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97208, USA; (R.R.); (M.J.K.); (T.S.A.)
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97208, USA
| | - Reza Razaghi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97208, USA; (R.R.); (M.J.K.); (T.S.A.)
| | - Mary J. Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97208, USA; (R.R.); (M.J.K.); (T.S.A.)
- Department Integrative Biosciences, School of Dentistry, Oregon Health & Science University, Portland, OR 97208, USA
| | - Ted S. Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97208, USA; (R.R.); (M.J.K.); (T.S.A.)
- Department Chemical Physiology & Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR 97208, USA
| | - Haiyan Gong
- Department of Ophthalmology, Boston University School of Medicine, Boston, MA 02118, USA;
- Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, MA 02118, USA
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Karimi A, Crouch DJ, Razaghi R, Crawford Downs J, Acott TS, Kelley MJ, Behnsen JG, Bosworth LA, Sheridan CM. Morphological and biomechanical analyses of the human healthy and glaucomatous aqueous outflow pathway: Imaging-to-modeling. Comput Methods Programs Biomed 2023; 236:107485. [PMID: 37149973 DOI: 10.1016/j.cmpb.2023.107485] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 03/09/2023] [Accepted: 03/13/2023] [Indexed: 05/09/2023]
Abstract
BACKGROUND AND OBJECTIVE Intraocular pressure (IOP) is maintained via a dynamic balance between the production of aqueous humor and its drainage through the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway. Primary open angle glaucoma (POAG) is often associated with IOP elevation that occurs due to an abnormally high outflow resistance across the outflow pathway. Outflow tissues are viscoelastic and actively interact with aqueous humor dynamics through a two-way fluid-structure interaction coupling. While glaucoma affects the morphology and stiffness of the outflow tissues, their biomechanics and hydrodynamics in glaucoma eyes remain largely unknown. This research aims to develop an image-to-model method allowing the biomechanics and hydrodynamics of the conventional aqueous outflow pathway to be studied. METHODS We used a combination of X-ray computed tomography and scanning electron microscopy to reconstruct high-fidelity, eye-specific, 3D microstructural finite element models of the healthy and glaucoma outflow tissues in cellularized and decellularized conditions. The viscoelastic TM/JCT/SC complex finite element models with embedded viscoelastic beam elements were subjected to a physiological IOP load boundary; the stresses/strains and the flow state were calculated using fluid-structure interaction and computational fluid dynamics. RESULTS Based on the resultant hydrodynamics parameters across the outflow pathway, the primary site of outflow resistance in healthy eyes was in the JCT and immediate vicinity of the SC inner wall, while the majority of the outflow resistance in the glaucoma eyes occurred in the TM. The TM and JCT in the glaucoma eyes showed 1.32-fold and 1.13-fold larger beam thickness and smaller trabecular space size (2.24-fold and 1.50-fold) compared to the healthy eyes. CONCLUSIONS Characterizing the accurate morphology of the outflow tissues may significantly contribute to constructing more accurate, robust, and reliable models, that can eventually help to better understand the dynamic IOP regulation, hydrodynamics of the aqueous humor, and outflow resistance dynamic in the human eyes. This model demonstrates proof of concept for determining changes to outflow resistance in healthy and glaucomatous tissues and thus may be utilized in larger cohorts of donor tissues where disease specificity, race, age, and gender of the eye donors may be accounted for.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Devon J Crouch
- Department of Eye and Vision Science, Institute of Life Course and Medical Sciences, Faculty of Health and Life Sciences, University of Liverpool, Liverpool L7 8TX, United Kingdom
| | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States; Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon, United States
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States; Department of Integrative Biosciences, Oregon Health & Science University, Portland, Oregon, United States
| | - Julia G Behnsen
- Department of Mechanical, Materials, and Aerospace Engineering, University of Liverpool, Liverpool, L69 6GB, United Kingdom
| | - Lucy A Bosworth
- Department of Eye and Vision Science, Institute of Life Course and Medical Sciences, Faculty of Health and Life Sciences, University of Liverpool, Liverpool L7 8TX, United Kingdom
| | - Carl M Sheridan
- Department of Eye and Vision Science, Institute of Life Course and Medical Sciences, Faculty of Health and Life Sciences, University of Liverpool, Liverpool L7 8TX, United Kingdom.
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Karimi A, Khan S, Razaghi R, Rahmati SM, Gathara M, Tudisco E, Aga M, Kelley MJ, Jian Y, Acott TS. Developing an Experimental-Computational Workflow to Study the Biomechanics of the Human Conventional Aqueous Outflow Pathway. Acta Biomater 2023; 164:346-362. [PMID: 37072067 DOI: 10.1016/j.actbio.2023.04.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2022] [Revised: 03/29/2023] [Accepted: 04/06/2023] [Indexed: 04/20/2023]
Abstract
The aqueous humor actively interacts with the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and Schlemm's canal (SC) through a dynamic fluid-structure interaction (FSI) coupling. Despite the fact that intraocular pressure (IOP) undergoes significant fluctuations, our understanding of the hyperviscoelastic biomechanical properties of the aqueous outflow tissues is limited. In this study, a quadrant of the anterior segment from a normal human donor eye was dynamically pressurized in the SC lumen, and imaged using a customized optical coherence tomography (OCT). The TM/JCT/SC complex finite element (FE) with embedded collagen fibrils was reconstructed based on the segmented boundary nodes in the OCT images. The hyperviscoelastic mechanical properties of the outflow tissues' extracellular matrix with embedded viscoelastic collagen fibrils were calculated using an inverse FE-optimization method. Thereafter, the 3D microstructural FE model of the TM, with adjacent JCT and SC inner wall, from the same donor eye was constructed using optical coherence microscopy and subjected to a flow load-boundary from the SC lumen. The resultant deformation/strain in the outflow tissues was calculated using the FSI method, and compared to the digital volume correlation (DVC) data. TM showed larger shear modulus (0.92 MPa) compared to the JCT (0.47 MPa) and SC inner wall (0.85 MPa). Shear modulus (viscoelastic) was larger in the SC inner wall (97.65 MPa) compared to the TM (84.38 MPa) and JCT (56.30 MPa). The conventional aqueous outflow pathway is subjected to a rate-dependent IOP load-boundary with large fluctuations. This necessitates addressing the biomechanics of the outflow tissues using hyperviscoelastic material-model. STATEMENT OF SIGNIFICANCE: While the human conventional aqueous outflow pathway is subjected to a large-deformation and time-dependent IOP load-boundary, we are not aware of any studies that have calculated the hyperviscoelastic mechanical properties of the outflow tissues with embedded viscoelastic collagen fibrils. A quadrant of the anterior segment of a normal humor donor eye was dynamically pressurized from the SC lumen with relatively large fluctuations. The TM/JCT/SC complex were OCT imaged and the mechanical properties of the tissues with embedded collagen fibrils were calculated using the inverse FE-optimization algorithm. The resultant displacement/strain in the FSI outflow model was validated versus the DVC data. The proposed experimental-computational workflow may significantly contribute to understanding of the effects of different drugs on the biomechanics of the conventional aqueous outflow pathway.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA
| | - Shanjida Khan
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, Oregon, USA
| | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | | | - Michael Gathara
- Department of Computer Science, University of Alabama at Birmingham, Birmingham, Alabama, USA
| | - Erika Tudisco
- Division of Geotechnical Engineering, Lund University, Lund, Sweden
| | - Mini Aga
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA; Department Integrative Biosciences, School of Dentistry, Oregon Health & Science University, Portland, Oregon, USA
| | - Yifan Jian
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA; Department of Biomedical Engineering, Oregon Health & Science University, Portland, Oregon, USA
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA; Department Chemical Physiology & Biochemistry, School of Medicine, Oregon Health & Science University, Portland, Oregon, USA.
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Karimi A, Halabian M, Razaghi R, Downs JC, Kelley MJ, Acott TS. Modeling the Endothelial Glycocalyx Layer in the Human Conventional Aqueous Outflow Pathway. Cells 2022; 11:cells11233925. [PMID: 36497183 PMCID: PMC9740116 DOI: 10.3390/cells11233925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 11/30/2022] [Accepted: 12/03/2022] [Indexed: 12/07/2022] Open
Abstract
A layer of proteoglycans and glycoproteins known as glycocalyx covers the surface of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and Schlemm's canal (SC) inner wall of the conventional aqueous outflow pathway in the eye. This has been shown to play a role in the mechanotransduction of fluid shear stress and in the regulation of the outflow resistance. The outflow resistance in the conventional outflow pathway is the main determinant of the intraocular pressure (IOP) through an active, two-way, fluid-structure interaction coupling between the outflow tissues and aqueous humor. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex with interspersed aqueous humor was constructed. A very thin charged double layer that represents the endothelial glycocalyx layer covered the surface of the elastic outflow tissues. The aqueous humor was modeled as electroosmotic flow that is charged when it is in contact with the outflow tissues. The electrical-fluid-structure interaction (EFSI) method was used to couple the charged double layer (glycocalyx), fluid (aqueous humor), and solid (outflow tissues). When the IOP was elevated to 15 mmHg, the maximum aqueous humor velocity in the EFSI model was decreased by 2.35 mm/s (9%) compared to the fluid-structure interaction (FSI) model. The charge or electricity in the living human conventional outflow pathway generated by the charged endothelial glycocalyx layer plays a minor biomechanical role in the resultant stresses and strains as well as the hydrodynamics of the aqueous humor.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
- Correspondence:
| | - Mahdi Halabian
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - J. Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - Mary J. Kelley
- Departments of Ophthalmology and Integrative Biosciences, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Ted S. Acott
- Departments of Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
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Karimi A, Razaghi R, Rahmati SM, Downs JC, Acott TS, Kelley MJ, Wang RK, Johnstone M. The Effect of Intraocular Pressure Load Boundary on the Biomechanics of the Human Conventional Aqueous Outflow Pathway. Bioengineering (Basel) 2022; 9:672. [PMID: 36354583 PMCID: PMC9687513 DOI: 10.3390/bioengineering9110672] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2022] [Revised: 10/28/2022] [Accepted: 11/08/2022] [Indexed: 09/29/2023] Open
Abstract
BACKGROUND Aqueous humor outflow resistance in the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway actively contribute to intraocular pressure (IOP) regulation. Outflow resistance is actively affected by the dynamic outflow pressure gradient across the TM, JCT, and SC inner wall tissues. The resistance effect implies the presence of a fluid-structure interaction (FSI) coupling between the outflow tissues and the aqueous humor. However, the biomechanical interactions between viscoelastic outflow tissues and aqueous humor dynamics are largely unknown. METHODS A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex was constructed with elastic and viscoelastic material properties for the bulk extracellular matrix and embedded elastic cable elements. The FE models were subjected to both idealized and a physiologic IOP load boundary using the FSI method. RESULTS The elastic material model for both the idealized and physiologic IOP load boundary at equal IOPs showed similar stresses and strains in the outflow tissues as well as pressure in the aqueous humor. However, outflow tissues with viscoelastic material properties were sensitive to the IOP load rate, resulting in different mechanical and hydrodynamic responses in the tissues and aqueous humor. CONCLUSIONS Transient IOP fluctuations may cause a relatively large IOP difference of ~20 mmHg in a very short time frame of ~0.1 s, resulting in a rate stiffening in the outflow tissues. Rate stiffening reduces strains and causes a rate-dependent pressure gradient across the outflow tissues. Thus, the results suggest it is necessary to use a viscoelastic material model in outflow tissues that includes the important role of IOP load rate.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | | | - J. Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - Ted S. Acott
- Departments of Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Mary J. Kelley
- Departments of Ophthalmology and Integrative Biosciences, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Ruikang K. Wang
- Department of Ophthalmology, University of Washington, Seattle, WA 98195, USA
- Department of Bioengineering, University of Washington, Seattle, WA 98195, USA
| | - Murray Johnstone
- Department of Ophthalmology, University of Washington, Seattle, WA 98195, USA
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Karimi A, Razaghi R, Padilla S, Rahmati SM, Downs JC, Acott TS, Kelley MJ, Wang RK, Johnstone M. Viscoelastic Biomechanical Properties of the Conventional Aqueous Outflow Pathway Tissues in Healthy and Glaucoma Human Eyes. J Clin Med 2022; 11:jcm11206049. [PMID: 36294371 PMCID: PMC9605362 DOI: 10.3390/jcm11206049] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Revised: 10/11/2022] [Accepted: 10/12/2022] [Indexed: 11/16/2022] Open
Abstract
Background: Although the tissues comprising the ocular conventional outflow pathway have shown strong viscoelastic mechanical response to aqueous humor pressure dynamics, the viscoelastic mechanical properties of the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm’s canal (SC) inner wall are largely unknown. Methods: A quadrant of the anterior segment from two human donor eyes at low- and high-flow (LF and HF) outflow regions was pressurized and imaged using optical coherence tomography (OCT). A finite element (FE) model of the TM, the adjacent JCT, and the SC inner wall was constructed and viscoelastic beam elements were distributed in the extracellular matrix (ECM) of the TM and JCT to represent anisotropic collagen. An inverse FE-optimization algorithm was used to calculate the viscoelastic properties of the ECM/beam elements such that the TM/JCT/SC model and OCT imaging data best matched over time. Results: The ECM of the glaucoma tissues showed significantly larger time-dependent shear moduli compared to the heathy tissues. Significantly larger shear moduli were also observed in the LF regions of both the healthy and glaucoma eyes compared to the HF regions. Conclusions: The outflow tissues in both glaucoma eyes and HF regions are stiffer and less able to respond to dynamic IOP.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
- Correspondence:
| | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - Steven Padilla
- Department of Ophthalmology, University of Washington, Seattle, WA 98109, USA
| | | | - J. Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - Ted S. Acott
- Departments of Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Mary J. Kelley
- Departments of Ophthalmology and Integrative Biosciences, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Ruikang K. Wang
- Department of Ophthalmology, University of Washington, Seattle, WA 98109, USA
- Department of Bioengineering, University of Washington, Seattle, WA 98105, USA
| | - Murray Johnstone
- Department of Ophthalmology, University of Washington, Seattle, WA 98109, USA
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Karimi A, Rahmati SM, Razaghi R, Crawford Downs J, Acott TS, Wang RK, Johnstone M. Biomechanics of human trabecular meshwork in healthy and glaucoma eyes via dynamic Schlemm's canal pressurization. Comput Methods Programs Biomed 2022; 221:106921. [PMID: 35660943 PMCID: PMC10424782 DOI: 10.1016/j.cmpb.2022.106921] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 05/17/2022] [Accepted: 05/26/2022] [Indexed: 05/27/2023]
Abstract
BACKGROUND AND OBJECTIVE The trabecular meshwork (TM) consists of extracellular matrix (ECM) with embedded collagen and elastin fibers providing its mechanical support. TM stiffness is considerably higher in glaucoma eyes. Emerging data indicates that the TM moves dynamically with transient intraocular pressure (IOP) fluctuations, implying the viscoelastic mechanical behavior of the TM. However, little is known about TM viscoelastic behavior. We calculated the viscoelastic mechanical properties of the TM in n = 2 healthy and n = 2 glaucoma eyes. METHODS A quadrant of the anterior segment was submerged in a saline bath, and a cannula connected to an adjustable saline reservoir was inserted into Schlemm's canal (SC). A spectral domain-OCT (SD-OCT) provided continuous cross-sectional B-scans of the TM/JCT/SC complex during pressure oscillation from 0 to 30 mmHg at two locations. The TM/JCT/SC complex boundaries were delineated to construct a 20-µm-thick volume finite element (FE) mesh. Pre-tensioned collagen and elastin fibrils were embedded in the model using a mesh-free penalty-based cable-in-solid algorithm. SC pressure was represented by a position- and time-dependent pressure boundary; floating boundary conditions were applied to the other cut edges of the model. An FE-optimization algorithm was used to adjust the ECM/fiber mechanical properties such that the TM/JCT/SC model and SD-OCT imaging data best matched over time. RESULTS Significantly larger short- and long-time ECM shear moduli (p = 0.0032), and collagen (1.82x) and elastin (2.72x) fibril elastic moduli (p = 0.0001), were found in the TM of glaucoma eyes compared to healthy controls. CONCLUSIONS These findings provide additional clarity on the mechanical property differences in healthy and glaucomatous outflow pathway under dynamic loading. Understanding the viscoelastic properties of the TM may serve as a new biomarker in early diagnosis of glaucoma.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
| | | | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA
| | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
| | - Ted S Acott
- Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA.
| | - Ruikang K Wang
- Department of Ophthalmology, University of Washington, Seattle, WA, USA; Department of Bioengineering, University of Washington, Seattle, WA, USA.
| | - Murray Johnstone
- Department of Ophthalmology, University of Washington, Seattle, WA, USA.
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Karimi A, Razaghi R, Rahmati SM, Downs JC, Acott TS, Wang RK, Johnstone M. Modeling the biomechanics of the conventional aqueous outflow pathway microstructure in the human eye. Comput Methods Programs Biomed 2022; 221:106922. [PMID: 35660940 PMCID: PMC10424784 DOI: 10.1016/j.cmpb.2022.106922] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Revised: 05/16/2022] [Accepted: 05/26/2022] [Indexed: 05/27/2023]
Abstract
BACKGROUND AND OBJECTIVE Intraocular pressure (IOP) is determined by aqueous humor outflow resistance, which is a function of the combined resistance of Schlemm's canal (SC) endothelium and the trabecular meshwork (TM) and their interactions in the juxtacanalicular connective tissue (JCT) region. Aqueous outflow in the conventional outflow pathway results in pressure gradient across the TM, JCT, and SC inner wall, and induces mechanical stresses and strains that influence the geometry and homeostasis of the outflow system. The outflow resistance is affected by alteration in tissues' geometry, so there is potential for active, two-way, fluid-structure interaction (FSI) coupling between the aqueous humor (fluid) and the TM, JCT, and SC inner wall (structure). However, our understanding of the biomechanical interactions of the aqueous humor with the outflow connective tissues and its contribution to the outflow resistance regulation is incomplete. METHODS In this study, a microstructural finite element (FE) model of a human eye TM, JCT, and SC inner wall was constructed from a segmented, high-resolution histologic 3D reconstruction of the human outflow system. Three different elastic moduli (0.004, 0.128, and 51.5 MPa based on prior reports) were assigned to the TM/JCT complex while the elastic modulus of the SC inner wall was kept constant at 0.00748 MPa. The hydraulic conductivity was programmed separately for the TM, JCT, and SC inner wall using a custom subroutine. Cable elements were embedded into the TM and JCT extracellular matrix to represent the directional stiffness imparted by anisotropic collagen fibril orientation. The resultant stresses and strains in the outflow system were calculated using fluid-structure interaction method. RESULTS The higher TM/JCT stiffness resulted in larger stresses, but smaller strains in the outflow connective tissues, and resulted in a 4- and 5-fold larger pressure drop across the SC inner wall, respectively, compared to the most compliant model. Funneling through µm-sized SC endothelial pores was evident in the models at lower tissue stiffness, but aqueous flow was more turbulent in models with higher TM/JCT stiffness. CONCLUSIONS The mechanical properties of the outflow tissues play a crucial role in the hydrodynamics of the aqueous humor in the conventional outflow system.
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Affiliation(s)
- Alireza Karimi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670 University Boulevard, VH 372B, Birmingham, AL 35294, USA.
| | - Reza Razaghi
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670 University Boulevard, VH 372B, Birmingham, AL 35294, USA
| | | | - J Crawford Downs
- Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, 1670 University Boulevard, VH 372B, Birmingham, AL 35294, USA
| | - Ted S Acott
- Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, USA
| | - Ruikang K Wang
- Department of Ophthalmology, University of Washington, Seattle, WA, USA; Department of Bioengineering, University of Washington, Seattle, WA, USA
| | - Murray Johnstone
- Department of Ophthalmology, University of Washington, Seattle, WA, USA
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McDowell CM, Kizhatil K, Elliott MH, Overby DR, van Batenburg-Sherwood J, Millar JC, Kuehn MH, Zode G, Acott TS, Anderson MG, Bhattacharya SK, Bertrand JA, Borras T, Bovenkamp DE, Cheng L, Danias J, De Ieso ML, Du Y, Faralli JA, Fuchshofer R, Ganapathy PS, Gong H, Herberg S, Hernandez H, Humphries P, John SWM, Kaufman PL, Keller KE, Kelley MJ, Kelly RA, Krizaj D, Kumar A, Leonard BC, Lieberman RL, Liton P, Liu Y, Liu KC, Lopez NN, Mao W, Mavlyutov T, McDonnell F, McLellan GJ, Mzyk P, Nartey A, Pasquale LR, Patel GC, Pattabiraman PP, Peters DM, Raghunathan V, Rao PV, Rayana N, Raychaudhuri U, Reina-Torres E, Ren R, Rhee D, Chowdhury UR, Samples JR, Samples EG, Sharif N, Schuman JS, Sheffield VC, Stevenson CH, Soundararajan A, Subramanian P, Sugali CK, Sun Y, Toris CB, Torrejon KY, Vahabikashi A, Vranka JA, Wang T, Willoughby CE, Xin C, Yun H, Zhang HF, Fautsch MP, Tamm ER, Clark AF, Ethier CR, Stamer WD. Consensus Recommendation for Mouse Models of Ocular Hypertension to Study Aqueous Humor Outflow and Its Mechanisms. Invest Ophthalmol Vis Sci 2022; 63:12. [PMID: 35129590 PMCID: PMC8842499 DOI: 10.1167/iovs.63.2.12] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 12/08/2021] [Indexed: 01/07/2023] Open
Abstract
Due to their similarities in anatomy, physiology, and pharmacology to humans, mice are a valuable model system to study the generation and mechanisms modulating conventional outflow resistance and thus intraocular pressure. In addition, mouse models are critical for understanding the complex nature of conventional outflow homeostasis and dysfunction that results in ocular hypertension. In this review, we describe a set of minimum acceptable standards for developing, characterizing, and utilizing mouse models of open-angle ocular hypertension. We expect that this set of standard practices will increase scientific rigor when using mouse models and will better enable researchers to replicate and build upon previous findings.
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Affiliation(s)
- Colleen M. McDowell
- Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | | | - Michael H. Elliott
- University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, United States
| | - Darryl R. Overby
- Department of Bioengineering, Imperial College London, United Kingdom
| | | | - J. Cameron Millar
- Department of Pharmacology & Neuroscience, and North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Markus H. Kuehn
- Department of Ophthalmology and Visual Sciences and Institute for Vision Research, The University of Iowa; Center for the Prevention and Treatment of Visual Loss, Veterans Affairs Medical Center, Iowa City, Iowa, United States
| | - Gulab Zode
- Department of Pharmacology & Neuroscience, and North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Ted S. Acott
- Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Michael G. Anderson
- Department of Molecular Physiology and Biophysics and Department of Ophthalmology and Visual Sciences, The University of Iowa; Center for the Prevention and Treatment of Visual Loss, Veterans Affairs Medical Center, Iowa City, Iowa, United States
| | | | - Jacques A. Bertrand
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Terete Borras
- University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
| | | | - Lin Cheng
- Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States
| | - John Danias
- SUNY Downstate Health Sciences University, Brooklyn, New York, United States
| | - Michael Lucio De Ieso
- Department of Ophthalmology, Duke Eye Center, Duke University, Durham, North Carolina, United States
| | - Yiqin Du
- Department of Ophthalmology, University of Pittsburgh, Pennsylvania, United States
| | - Jennifer A. Faralli
- Department of Pathology and Laboratory Medicine, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | - Rudolf Fuchshofer
- Institute of Human Anatomy and Embryology, University of Regensburg, Regensburg, Germany
| | - Preethi S. Ganapathy
- Department of Ophthalmology and Visual Sciences, SUNY Upstate Medical University, Syracuse, New York, United States
| | - Haiyan Gong
- Department of Ophthalmology, Boston University School of Medicine, Boston, Massachusetts, United States
| | - Samuel Herberg
- Department of Ophthalmology and Visual Sciences, SUNY Upstate Medical University, Syracuse, New York, United States
| | | | - Peter Humphries
- Smurfit Institute of Genetics, Trinity College Dublin, Dublin, Ireland
| | - Simon W. M. John
- Department of Ophthalmology, Columbia University, New York, New York, United States
| | - Paul L. Kaufman
- Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | - Kate E. Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Mary J. Kelley
- Department of Ophthalmology and Department of Integrative Biosciences, Oregon Health & Science University, Portland, Oregon, United States
| | - Ruth A. Kelly
- Ocular Genetics Unit, Smurfit Institute of Genetics, Trinity College Dublin, Dublin, Ireland
| | - David Krizaj
- Department of Ophthalmology, University of Utah School of Medicine, Salt Lake City, Utah, United States
| | - Ajay Kumar
- Department of Ophthalmology, University of Pittsburgh, Pennsylvania, United States
| | - Brian C. Leonard
- Department of Surgical and Radiological Sciences, University of California, Davis, Davis, California, United States
| | - Raquel L. Lieberman
- Department of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
| | - Paloma Liton
- Department of Ophthalmology and Department of Pathology, Duke University, Durham, North Carolina, United States
| | - Yutao Liu
- Department of Cellular Biology and Anatomy, James & Jean Culver Vision Discovery Institute, Augusta University, Augusta, Georgia, United States
| | - Katy C. Liu
- Duke Eye Center, Duke Health, Durham, North Carolina, United States
| | - Navita N. Lopez
- Department of Neurobiology, University of Utah, Salt Lake City, Utah, United States
| | - Weiming Mao
- Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Timur Mavlyutov
- Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | - Fiona McDonnell
- Duke Eye Center, Duke Health, Durham, North Carolina, United States
| | - Gillian J. McLellan
- Department of Surgical Sciences and Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | - Philip Mzyk
- Department of Ophthalmology and Visual Sciences, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | - Andrews Nartey
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Louis R. Pasquale
- Department of Ophthalmology, Icahn School of Medicine at Mount Sinai, New York, New York, United States
| | - Gaurang C. Patel
- Ophthalmology Research, Regeneron Pharmaceuticals, Tarreytown, New York, United States
| | | | - Donna M. Peters
- Department of Pathology and Laboratory Medicine, University of Wisconsin–Madison, Madison, Wisconsin, United States
| | | | - Ponugoti Vasantha Rao
- Department of Ophthalmology, Duke University School of Medicine, Durham, North Carolina, United States
| | - Naga Rayana
- Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Urmimala Raychaudhuri
- Department of Neurobiology, University of California, Irvine, Irvine, California, United States
| | - Ester Reina-Torres
- Department of Bioengineering, Imperial College London, London, United Kingdom
| | - Ruiyi Ren
- Department of Ophthalmology, Boston University School of Medicine, Boston, Massachusetts, United States
| | - Douglas Rhee
- Case Western Reserve University School of Medicine, Cleveland, Ohio, United States
| | - Uttio Roy Chowdhury
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, United States
| | - John R. Samples
- Washington State University, Floyd Elson College of Medicine, Spokane, Washington, United States
| | | | - Najam Sharif
- Santen Inc., Emeryville, California, United States
| | - Joel S. Schuman
- Department of Ophthalmology and Department of Physiology and Neuroscience, NYU Grossman School of Medicine, NYU Langone Health, New York University, New York, New York, United States; Departments of Biomedical Engineering and Electrical and Computer Engineering, New York University Tandon School of Engineering, Brooklyn, New York, United States; Center for Neural Science, College of Arts and Science, New York University, New York, New York, United States
| | - Val C. Sheffield
- Department of Pediatrics and Department of Ophthalmology and Visual Sciences, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States
| | - Cooper H. Stevenson
- Department of Pharmacology & Neuroscience, and North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Avinash Soundararajan
- Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | | | - Chenna Kesavulu Sugali
- Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Yang Sun
- Veterans Affairs Palo Alto Health Care System, Stanford University, Palo Alto, California, United States
| | - Carol B. Toris
- Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska, United States; Department of Ophthalmology and Vision Sciences, The Ohio State University, Columbus, Ohio, United States
| | | | - Amir Vahabikashi
- Cell and Developmental Biology Department, Northwestern University, Chicago, Illinois, United States
| | - Janice A. Vranka
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Ting Wang
- Department of Ophthalmology, Indiana University School of Medicine, Indianapolis, Indiana, United States
| | - Colin E. Willoughby
- Genomic Medicine, Biomedical Sciences Research Institute, Ulster University, Coleraine, Northern Ireland, United Kingdom
| | - Chen Xin
- Beijing Institute of Ophthalmology, Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing, China
| | - Hongmin Yun
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
| | - Hao F. Zhang
- Biomedical Engineering Department, Northwestern University, Evanston, Illinois, United States
| | - Michael P. Fautsch
- Biomedical Engineering Department, Northwestern University, Evanston, Illinois, United States
| | | | - Abbot F. Clark
- Department of Pharmacology and Neuroscience, North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - C. Ross Ethier
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology; Emory University School of Medicine, Emory University, Atlanta, Georgia, United States
| | - W. Daniel Stamer
- Duke Ophthalmology, Duke University, Durham, North Carolina, United States
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Acott TS, Vranka JA, Keller KE, Raghunathan V, Kelley MJ. Normal and glaucomatous outflow regulation. Prog Retin Eye Res 2021; 82:100897. [PMID: 32795516 PMCID: PMC7876168 DOI: 10.1016/j.preteyeres.2020.100897] [Citation(s) in RCA: 63] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 07/28/2020] [Accepted: 07/31/2020] [Indexed: 12/12/2022]
Abstract
Glaucoma remains only partially understood, particularly at the level of intraocular pressure (IOP) regulation. Trabecular meshwork (TM) and Schlemm's canal inner wall endothelium (SCE) are key to IOP regulation and their characteristics and behavior are the focus of much investigation. This is becoming more apparent with time. We and others have studied the TM and SCE's extracellular matrix (ECM) extensively and unraveled much about its functions and role in regulating aqueous outflow. Ongoing ECM turnover is required to maintain IOP regulation and several TM ECM manipulations modulate outflow facility. We have established clearly that the outflow pathway senses sustained pressure deviations and responds by adjusting the outflow resistance correctively to keep IOP within an appropriately narrow range which will not normally damage the optic nerve. The glaucomatous outflow pathway has in many cases lost this IOP homeostatic response, apparently due at least in part, to loss of TM cells. Depletion of TM cells eliminates the IOP homeostatic response, while restoration of TM cells restores it. Aqueous outflow is not homogeneous, but rather segmental with regions of high, intermediate and low flow. In general, glaucomatous eyes have more low flow regions than normal eyes. There are distinctive molecular differences between high and low flow regions, and during the response to an IOP homeostatic pressure challenge, additional changes in segmental molecular composition occur. In conjunction with these changes, the biomechanical properties of the juxtacanalicular (JCT) segmental regions are different, with low flow regions being stiffer than high flow regions. The JCT ECM of glaucomatous eyes is around 20 times stiffer than in normal eyes. The aqueous humor outflow resistance has been studied extensively, but neither the exact molecular components that comprise the resistance nor their exact location have been established. Our hypothetical model, based on considerable available data, posits that the continuous SCE basal lamina, which lies between 125 and 500 nm beneath the SCE basal surface, is the primary source of normal resistance. On the surface of JCT cells, small and highly controlled focal degradation of its components by podosome- or invadopodia-like structures, PILS, occurs in response to pressure-induced mechanical stretching. Sub-micron sized basement membrane discontinuities develop in the SCE basement membrane and these discontinuities allow passage of aqueous humor to and through SCE giant vacuoles and pores. JCT cells then relocate versican with its highly charged glycosaminoglycan side chains into the discontinuities and by manipulation of their orientation and concentration, the JCT and perhaps the SCE cells regulate the amount of fluid passage. Testing this outflow resistance hypothesis is ongoing in our lab and has the potential to advance our understanding of IOP regulation and of glaucoma.
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Affiliation(s)
- Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, 97239, USA; Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR, 97239, USA.
| | - Janice A Vranka
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, 97239, USA
| | - Kate E Keller
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, 97239, USA
| | - VijayKrishna Raghunathan
- Department of Basic Sciences, The Ocular Surface Institute, College of Optometry, Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX, 77204, USA
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR, 97239, USA; Department of Integrative Biosciences, Oregon Health & Sciences University, Portland, OR, 97239, USA
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15
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Li X, Acott TS, Nagy JI, Kelley MJ. ZO-1 associates with α3 integrin and connexin43 in trabecular meshwork and Schlemm's canal cells. Int J Physiol Pathophysiol Pharmacol 2020; 12:1-10. [PMID: 32211117 PMCID: PMC7076326] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 01/14/2020] [Indexed: 06/10/2023]
Abstract
Cellular structures that perform essential homeostatic functions include tight junctions, gap junctions, desmosomes and adherens junctions. The aqueous humor, produced by the ciliary body, passes into the anterior chamber of the eye and is filtered by the trabecular meshwork (TM), a tiny tissue found in the angle of the eye. This tissue, along with Schlemm's canal (SC) inner wall cells, is thought to control intraocular pressure (IOP) homeostasis for normal, optimal vision. The actin cytoskeleton of the tissue plays a regulatory role in maintaining IOP. One of the key risk factors for primary open angle glaucoma is persistent elevation of IOP, which compromises the optic nerve. The ZO-1 (Zonula Occludens-1), extracellular matrix protein integrins, and gap junction protein connexin43 (Cx43) are widely expressed in many different cell populations. Here, we investigated the localization and interactions of ZO-1, α3 integrin, β1 integrin, and Cx43 in cultured porcine TM and SC cells using RT-PCR, western immunoblotting and immunofluorescence labeling with confocal microscopy, along with co-immunoprecipitation. ZO-1 partially co-localized with α3 integrin, but not with β1 integrin, and co-immunoprecipitated with Cx43, as well as with α3 integrin. The association of ZO-1 with α3 integrin and Cx43 suggests that these proteins may form a multiple protein complex in porcine TM and SC cells. Since integrins interact with the actin cytoskeleton via scaffolding proteins, these results implicate junctional and scaffolding protein ZO-1 as a potential control point in regulation of IOP to normal levels for glaucoma therapy.
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Affiliation(s)
- Xinbo Li
- Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science UniversityPortland, Oregon, USA
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science UniversityPortland, Oregon, USA
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science UniversityPortland, Oregon, USA
| | - James I Nagy
- Department of Physiology and Pathophysiology, University of ManitobaWinnipeg, MB, Canada
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health and Science UniversityPortland, Oregon, USA
- Department of Integrative Bioscience, Oregon Health and Science UniversityPortland, Oregon, USA
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16
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Li X, Nagy JI, Li D, Acott TS, Kelley MJ. Gap junction connexin43 is a key element in mediating phagocytosis activity in human trabecular meshwork cells. Int J Physiol Pathophysiol Pharmacol 2020; 12:25-31. [PMID: 32211119 PMCID: PMC7076328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Accepted: 01/16/2020] [Indexed: 06/10/2023]
Abstract
Human trabecular meshwork (TM) cells play pivotal roles in maintaining homeostasis of intraocular pressure via regulation of aqueous humor outflow. These cells are capable of phagocytosis, which is considered to be essential for their regulatory function. In addition, there is a strong expression of the gap junction protein connexin43 (Cx43) in the TM. Here, we investigated functional relationships between phagocytosis activity of TM cells and their expression of Cx43. Phagocytosis was measured by showing the ability of TM cells to engulf inert fluorescent particles consisting of pHrodo. We found that internalized pHrodo was partially co-localized with Cx43 and that the phagocytic activity was dramatically reduced after knockdown of Cx43 using lentiviral Cx43 shRNA. These results suggest that Cx43 is involved in the regulation of phagocytosis by TM cells.
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Affiliation(s)
- Xinbo Li
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science UniversityPortland, Oregon, USA
| | - James I Nagy
- Department of Physiology and Pathophysiology, University of ManitobaWinnipeg, MB, Canada
| | - Davey Li
- University of WaterlooWaterloo, ON, Canada
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science UniversityPortland, Oregon, USA
- Department of Chemical Physiology & Biochemistry, Oregon Health & Science UniversityPortland, Oregon, USA
| | - Mary J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science UniversityPortland, Oregon, USA
- Department of Integrative Biosciences, Oregon Health & Science UniversityPortland, Oregon, USA
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Vranka JA, Staverosky JA, Reddy AP, Wilmarth PA, David LL, Acott TS, Russell P, Raghunathan VK. Biomechanical Rigidity and Quantitative Proteomics Analysis of Segmental Regions of the Trabecular Meshwork at Physiologic and Elevated Pressures. Invest Ophthalmol Vis Sci 2018; 59:246-259. [PMID: 29340639 PMCID: PMC5770183 DOI: 10.1167/iovs.17-22759] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Purpose The extracellular matrix (ECM) of the trabecular meshwork (TM) modulates resistance to aqueous humor outflow, thereby regulating IOP. Glaucoma, a leading cause of irreversible blindness worldwide, is associated with changes in the ECM of the TM. The elastic modulus of glaucomatous TM is larger than age-matched normal TM; however, the biomechanical properties of segmental low (LF) and high flow (HF) TM regions and their response to elevated pressure, are unknown. Methods We perfused human anterior segments at two pressures using an ex vivo organ culture system. After extraction, we measured the elastic modulus of HF and LF TM regions by atomic force microscopy and quantitated protein differences by proteomics analyses. Results The elastic modulus of LF regions was 2.3-fold larger than HF regions at physiological (1×) pressure, and 7.4-fold or 3.5-fold larger than HF regions at elevated (2×) pressure after 24 or 72 hours, respectively. Using quantitative proteomics, comparisons were made between HF and LF regions at 1× or 2× pressure. Significant ECM protein differences were observed between LF and HF regions perfused at 2×, and between HF regions at 1× compared to 2× pressures. Decorin, TGF-β–induced protein, keratocan, lumican, dermatopontin, and thrombospondin 4 were common differential candidates in both comparisons. Conclusions These data show changes in biomechanical properties of segmental regions within the TM in response to elevated pressure, and levels of specific ECM proteins. Further studies are needed to determine whether these ECM proteins are specifically involved in outflow resistance and IOP homeostasis.
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Affiliation(s)
- Janice A Vranka
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Julia A Staverosky
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Ashok P Reddy
- Proteomics Shared Resources, Oregon Health & Science University, Portland, Oregon, United States
| | - Phillip A Wilmarth
- Proteomics Shared Resources, Oregon Health & Science University, Portland, Oregon, United States.,Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon, United States
| | - Larry L David
- Proteomics Shared Resources, Oregon Health & Science University, Portland, Oregon, United States.,Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon, United States
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States.,Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, Oregon, United States
| | - Paul Russell
- Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, California, United States
| | - Vijay Krishna Raghunathan
- Department of Basic Sciences, The Ocular Surface Institute, College of Optometry, University of Houston, Houston, Texas, United States.,Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, Texas, United States
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18
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Keller KE, Bhattacharya SK, Borrás T, Brunner TM, Chansangpetch S, Clark AF, Dismuke WM, Du Y, Elliott MH, Ethier CR, Faralli JA, Freddo TF, Fuchshofer R, Giovingo M, Gong H, Gonzalez P, Huang A, Johnstone MA, Kaufman PL, Kelley MJ, Knepper PA, Kopczynski CC, Kuchtey JG, Kuchtey RW, Kuehn MH, Lieberman RL, Lin SC, Liton P, Liu Y, Lütjen-Drecoll E, Mao W, Masis-Solano M, McDonnell F, McDowell CM, Overby DR, Pattabiraman PP, Raghunathan VK, Rao PV, Rhee DJ, Chowdhury UR, Russell P, Samples JR, Schwartz D, Stubbs EB, Tamm ER, Tan JC, Toris CB, Torrejon KY, Vranka JA, Wirtz MK, Yorio T, Zhang J, Zode GS, Fautsch MP, Peters DM, Acott TS, Stamer WD. Consensus recommendations for trabecular meshwork cell isolation, characterization and culture. Exp Eye Res 2018; 171:164-173. [PMID: 29526795 PMCID: PMC6042513 DOI: 10.1016/j.exer.2018.03.001] [Citation(s) in RCA: 197] [Impact Index Per Article: 32.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 03/01/2018] [Indexed: 12/30/2022]
Abstract
Cultured trabecular meshwork (TM) cells are a valuable model system to study the cellular mechanisms involved in the regulation of conventional outflow resistance and thus intraocular pressure; and their dysfunction resulting in ocular hypertension. In this review, we describe the standard procedures used for the isolation of TM cells from several animal species including humans, and the methods used to validate their identity. Having a set of standard practices for TM cells will increase the scientific rigor when used as a model, and enable other researchers to replicate and build upon previous findings.
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Affiliation(s)
| | | | | | | | | | - Abbott F Clark
- University of North Texas Health Sciences Center, United States
| | | | - Yiqin Du
- University of Pittsburgh, United States
| | | | | | | | - Thomas F Freddo
- Massachusetts College of Pharmacy and Health Sciences, United States
| | | | | | | | | | - Alex Huang
- University of California, Los Angeles, United States
| | | | | | | | | | | | | | | | | | | | - Shan C Lin
- University of California, San Francisco, United States
| | | | | | | | - Weiming Mao
- University of North Texas Health Sciences Center, United States
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - James C Tan
- University of Southern California, United States
| | | | | | | | - Mary K Wirtz
- Oregon Health and Science University, United States
| | - Thomas Yorio
- University of North Texas Health Sciences Center, United States
| | - Jie Zhang
- University of California, Los Angeles, United States
| | - Gulab S Zode
- University of North Texas Health Sciences Center, United States
| | - Michael P Fautsch
- Department of Ophthalmology, Mayo Clinic, 200 1st St SW, Rochester, MN 55905, United States.
| | - Donna M Peters
- Department of Pathology & Laboratory Medicine, University of Wisconsin, 1300 University Ave, Madison, WI 53706, United States.
| | - Ted S Acott
- Department of Ophthalmology, Department of Biochemistry & Molecular Biology, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, United States.
| | - W Daniel Stamer
- Department of Ophthalmology, Duke University, DUMC 3802, Durham, NC 27705, United States.
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19
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Keller KE, Bradley JM, Sun YY, Yang YF, Acott TS. Tunneling Nanotubes are Novel Cellular Structures That Communicate Signals Between Trabecular Meshwork Cells. Invest Ophthalmol Vis Sci 2017; 58:5298-5307. [PMID: 29049733 PMCID: PMC5656416 DOI: 10.1167/iovs.17-22732] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Purpose The actin cytoskeleton of trabecular meshwork (TM) cells plays a role in regulating aqueous humor outflow. Many studies have investigated stress fibers, but F-actin also assembles into other supramolecular structures including filopodia. Recently, specialized filopodia called tunneling nanotubes (TNTs) have been described, which communicate molecular signals and organelles directly between cells. Here, we investigate TNT formation by TM cells. Methods Human TM cells were labeled separately with the fluorescent dyes, DiO and DiD, or with mitochondrial dye. Fixed or live TM cells were imaged using confocal microscopy. Image analysis software was used to track fluorescent vesicles and count the number and length of filopodia. The number of fluorescently labeled vesicles transferred between cells was counted in response to specific inhibitors of the actin cytoskeleton. Human TM tissue was stained with phalloidin. Results Live-cell confocal imaging of cultured TM cells showed transfer of fluorescently labeled vesicles and mitochondria via TNTs. In TM tissue, a long (160 μm) actin-rich cell process bridged an intertrabecular space and did not adhere to the substratum. Treatment of TM cells with CK-666, an Arp2/3 inhibitor, significantly decreased the number and length of filopodia, decreased transfer of fluorescently labeled vesicles and induced thick stress fibers compared to vehicle control. Conversely, inhibiting stress fibers using Y27632 increased transfer of vesicles and induced long cell processes. Conclusions Identification of TNTs provides a means by which TM cells can directly communicate with each other over long distances. This may be particularly important to overcome limitations of diffusion-based signaling in the aqueous humor fluid environment.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - John M Bradley
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Ying Ying Sun
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Yong-Feng Yang
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Ted S Acott
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
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20
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Wang K, Johnstone MA, Xin C, Song S, Padilla S, Vranka JA, Acott TS, Zhou K, Schwaner SA, Wang RK, Sulchek T, Ethier CR. Estimating Human Trabecular Meshwork Stiffness by Numerical Modeling and Advanced OCT Imaging. Invest Ophthalmol Vis Sci 2017; 58:4809-4817. [PMID: 28973327 PMCID: PMC5624775 DOI: 10.1167/iovs.17-22175] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Purpose The purpose of this study was to estimate human trabecular meshwork (hTM) stiffness, thought to be elevated in glaucoma, using a novel indirect approach, and to compare results with direct en face atomic force microscopy (AFM) measurements. Methods Postmortem human eyes were perfused to measure outflow facility and identify high- and low-flow regions (HF, LF) by tracer. Optical coherence tomography (OCT) images were obtained as Schlemm's canal luminal pressure was directly manipulated. TM stiffness was deduced by an inverse finite element modeling (FEM) approach. A series of AFM forcemaps was acquired along a line traversing the anterior angle on a radially cut flat-mount corneoscleral wedge with TM facing upward. Results The elastic modulus of normal hTM estimated by inverse FEM was 70 ± 20 kPa (mean ± SD), whereas glaucomatous hTM was slightly stiffer (98 ± 19 kPa). This trend was consistent with TM stiffnesses measured by AFM: normal hTM stiffness = 1.37 ± 0.56 kPa, which was lower than glaucomatous hTM stiffness (2.75 ± 1.19 kPa). None of these differences were statistically significant. TM in HF wedges was softer than that in LF wedges for both normal and glaucomatous eyes based on the inverse FEM approach but not by AFM. Outflow facility was significantly correlated with TM stiffness estimated by FEM in six human eyes (P = 0.018). Conclusions TM stiffness is higher, but only modestly so, in glaucomatous patients. Outflow facility in both normal and glaucomatous human eyes appears to associate with TM stiffness. This evidence motivates further studies to investigate factors underlying TM biomechanical property regulation.
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Affiliation(s)
- Ke Wang
- Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States
| | - Murray A Johnstone
- Department of Ophthalmology, University of Washington, Seattle, Washington, United States
| | - Chen Xin
- Department of Bioengineering, University of Washington, Seattle, Washington, United States
| | - Shaozhen Song
- Department of Bioengineering, University of Washington, Seattle, Washington, United States
| | - Steven Padilla
- Department of Ophthalmology, University of Washington, Seattle, Washington, United States
| | - Janice A Vranka
- Department of Ophthalmology, Casey Eye Institute, Portland, Oregon, United States
| | - Ted S Acott
- Department of Ophthalmology, Casey Eye Institute, Portland, Oregon, United States
| | - Kai Zhou
- Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States
| | - Stephen A Schwaner
- Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States
| | - Ruikang K Wang
- Department of Bioengineering, University of Washington, Seattle, Washington, United States
| | - Todd Sulchek
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
| | - C Ross Ethier
- Department of Biomedical Engineering, Georgia Institute of Technology/Emory University, Atlanta, Georgia, United States.,George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
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21
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Vranka JA, Acott TS. Pressure-induced expression changes in segmental flow regions of the human trabecular meshwork. Exp Eye Res 2016; 158:67-72. [PMID: 27334250 DOI: 10.1016/j.exer.2016.06.009] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Revised: 06/11/2016] [Accepted: 06/16/2016] [Indexed: 10/24/2022]
Abstract
Elevated intraocular pressure (IOP) is thought to create distortion or stretching of the juxtacanalicular and Schlemm's canal cells and their extracellular matrix (ECM) leading to a cascade of events that restore IOP to normal levels, a process termed IOP homeostasis. The ECM of the trabecular meshwork (TM) is intricately involved in the regulation of outflow resistance and IOP homeostasis, as matrix metalloproteinase (MMP)-initiated ECM turnover in the TM is necessary to maintain outflow facility. Previous studies have shown ECM gene expression and mRNA splice form differences in TM cells in response to sustained stretch, implicating their involvement in the dynamic process of IOP homeostasis. The observation that outflow is segmental around the circumference of the eye adds another layer of complexity to understanding the molecular events necessary to maintaining proper outflow facility. The aim of this work was to identify molecular expression differences between segmental flow regions of the TM from anterior segments perfused at either physiological or elevated pressure. Human anterior segments were perfused in an ex vivo model system, TM tissues were extracted and quantitative PCR arrays were performed. Comparisons were made between high flow and low flow regions of the TM from anterior segments perfused either at normal (8.8 mmHg) or at elevated (17.6 mmHg) perfusion pressure for 48 h. The results are presented here as independent sets: 1) fold change gene expression between segmental flow regions at a single perfusion pressure, and 2) fold change gene expression in response to elevated perfusion pressure in a single flow region. Multiple genes from the following functional families were found to be differentially expressed in segmental regions and in response to elevated pressure: collagens, ECM glycoproteins including matricellular proteins, ECM receptors such as integrins and adhesion molecules and ECM regulators, such as matrix metalloproteinases. In general, under normal perfusion pressure, more ECM genes were enriched in the high flow regions than in the low flow regions of the TM, whereas more ECM genes were found to be enriched in low flow regions of the TM in response to elevated perfusion pressure. Thus it appears that a limited subset of ECM genes is differentially regulated in both high and low flow regions and in response to elevated pressure. Some of these same ECM genes have previously been shown to be involved in the pressure response of stretched TM cells supporting their central role in IOP homeostasis. In general, different ECM gene family members are called upon to produce the response to elevated pressure in different segmental regions of the TM.
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Affiliation(s)
- Janice A Vranka
- Casey Eye Institute, Oregon Health & Science University, Portland, OR, 97239, USA.
| | - Ted S Acott
- Casey Eye Institute, Oregon Health & Science University, Portland, OR, 97239, USA
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22
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Abu-Hassan DW, Li X, Ryan EI, Acott TS, Kelley MJ. Induced pluripotent stem cells restore function in a human cell loss model of open-angle glaucoma. Stem Cells 2015; 33:751-61. [PMID: 25377070 PMCID: PMC4359625 DOI: 10.1002/stem.1885] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Revised: 09/18/2014] [Accepted: 10/11/2014] [Indexed: 11/06/2022]
Abstract
Normally, trabecular meshwork (TM) and Schlemm's canal inner wall endothelial cells within the aqueous humor outflow pathway maintain intraocular pressure within a narrow safe range. Elevation in intraocular pressure, because of the loss of homeostatic regulation by these outflow pathway cells, is the primary risk factor for vision loss due to glaucomatous optic neuropathy. A notable feature associated with glaucoma is outflow pathway cell loss. Using controlled cell loss in ex vivo perfused human outflow pathway organ culture, we developed compelling experimental evidence that this level of cell loss compromises intraocular pressure homeostatic function. This function was restored by repopulation of the model with fresh TM cells. We then differentiated induced pluripotent stem cells (iPSCs) and used them to repopulate this cell depletion model. These differentiated cells (TM-like iPSCs) became similar to TM cells in both morphology and expression patterns. When transplanted, they were able to fully restore intraocular pressure homeostatic function. This successful transplantation of TM-like iPSCs establishes the conceptual feasibility of using autologous stem cells to restore intraocular pressure regulatory function in open-angle glaucoma patients, providing a novel alternative treatment option. Stem Cells2015;33:751–761
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Affiliation(s)
- Diala W Abu-Hassan
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA; Department of Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, Oregon, USA; Department of Biochemistry & Physiology, University of Jordan, Amman, Jordan
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23
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Vranka JA, Kelley MJ, Acott TS, Keller KE. Extracellular matrix in the trabecular meshwork: intraocular pressure regulation and dysregulation in glaucoma. Exp Eye Res 2015; 133:112-25. [PMID: 25819459 DOI: 10.1016/j.exer.2014.07.014] [Citation(s) in RCA: 246] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Revised: 07/14/2014] [Accepted: 07/16/2014] [Indexed: 12/30/2022]
Abstract
The trabecular meshwork (TM) is located in the anterior segment of the eye and is responsible for regulating the outflow of aqueous humor. Increased resistance to aqueous outflow causes intraocular pressure to increase, which is the primary risk factor for glaucoma. TM cells reside on a series of fenestrated beams and sheets through which the aqueous humor flows to exit the anterior chamber via Schlemm's canal. The outer trabecular cells are phagocytic and are thought to function as a pre-filter. However, most of the outflow resistance is thought to be from the extracellular matrix (ECM) of the juxtacanalicular region, the deepest portion of the TM, and from the inner wall basement membrane of Schlemm's canal. It is becoming increasingly evident that the extracellular milieu is important in maintaining the integrity of the TM. In glaucoma, not only have ultrastructural changes been observed in the ECM of the TM, and a significant number of mutations in ECM genes been noted, but the stiffness of glaucomatous TM appears to be greater than that of normal tissue. Additionally, TGFβ2 has been found to be elevated in the aqueous humor of glaucoma patients and is assumed to be involved in ECM changes deep with the juxtacanalicular region of the TM. This review summarizes the current literature on trabecular ECM as well as the development and function of the TM. Animal models and organ culture models targeting specific ECM molecules to investigate the mechanisms of glaucoma are described. Finally, the growing number of mutations that have been identified in ECM genes and genes that modulate ECM in humans with glaucoma are documented.
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Affiliation(s)
- Janice A Vranka
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Mary J Kelley
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Ted S Acott
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA.
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24
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Vranka JA, Bradley JM, Yang YF, Keller KE, Acott TS. Mapping molecular differences and extracellular matrix gene expression in segmental outflow pathways of the human ocular trabecular meshwork. PLoS One 2015; 10:e0122483. [PMID: 25826404 PMCID: PMC4380331 DOI: 10.1371/journal.pone.0122483] [Citation(s) in RCA: 72] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2014] [Accepted: 02/22/2015] [Indexed: 01/09/2023] Open
Abstract
Elevated intraocular pressure (IOP) is the primary risk factor for glaucoma, and lowering IOP remains the only effective treatment for glaucoma. The trabecular meshwork (TM) in the anterior chamber of the eye regulates IOP by generating resistance to aqueous humor outflow. Aqueous humor outflow is segmental, but molecular differences between high and low outflow regions of the TM are poorly understood. In this study, flow regions of the TM were characterized using fluorescent tracers and PCR arrays. Anterior segments from human donor eyes were perfused at physiological pressure in an ex vivo organ culture system. Fluorescently-labeled microspheres of various sizes were perfused into anterior segments to label flow regions. Actively perfused microspheres were segmentally distributed, whereas microspheres soaked passively into anterior segments uniformly labeled the TM and surrounding tissues with no apparent segmentation. Cell-tracker quantum dots (20 nm) were localized to the outer uveal and corneoscleral TM, whereas larger, modified microspheres (200 nm) localized throughout the TM layers and Schlemm’s canal. Distribution of fluorescent tracers demonstrated a variable labeling pattern on both a macro- and micro-scale. Quantitative PCR arrays allowed identification of a variety of extracellular matrix genes differentially expressed in high and low flow regions of the TM. Several collagen genes (COL16A1, COL4A2, COL6A1 and 2) and MMPs (1, 2, 3) were enriched in high, whereas COL15A1, and MMP16 were enriched in low flow regions. Matrix metalloproteinase activity was similar in high and low regions using a quantitative FRET peptide assay, whereas protein levels in tissues showed modest regional differences. These gene and protein differences across regions of the TM provide further evidence for a molecular basis of segmental flow routes within the aqueous outflow pathway. New insight into the molecular mechanisms of segmental aqueous outflow may aid in the design and delivery of improved treatments for glaucoma patients.
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Affiliation(s)
- Janice A. Vranka
- Casey Eye Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, Oregon, United States of America
- * E-mail:
| | - John M. Bradley
- Casey Eye Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, Oregon, United States of America
| | - Yong-Feng Yang
- Casey Eye Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, Oregon, United States of America
| | - Kate E. Keller
- Casey Eye Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, Oregon, United States of America
| | - Ted S. Acott
- Casey Eye Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, Oregon, United States of America
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Aga M, Bradley JM, Wanchu R, Yang YF, Acott TS, Keller KE. Differential effects of caveolin-1 and -2 knockdown on aqueous outflow and altered extracellular matrix turnover in caveolin-silenced trabecular meshwork cells. Invest Ophthalmol Vis Sci 2014; 55:5497-509. [PMID: 25103269 DOI: 10.1167/iovs.14-14519] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
PURPOSE A single nucleotide polymorphism (SNP) identified between caveolin-1 (CAV1) and caveolin-2 (CAV2) on chromosome 7 is associated with glaucoma. One function of CAVs is endocytosis and recycling of extracellular matrix (ECM) components. Here, we generated CAV-silencing lentivirus to evaluate the effects on ECM turnover by trabecular meshwork (TM) cells and to measure the effect on outflow facility in anterior segment perfusion culture. METHODS Short hairpin CAV1 and CAV2 silencing and control lentivirus were generated, characterized, and applied to anterior segments in perfusion culture. Colocalization of CAVs with various ECM molecules in TM cells was investigated using immunofluorescence and confocal microscopy. Western immunoblotting and fluorogenic-based enzyme activity assays were used to investigate ECM protein levels and degradation, respectively. RESULTS Endogenous CAVs colocalized with cortactin at podosome- or invadopodia-like structures (PILS), which are areas of focal ECM degradation. In perfusion culture, outflow rates increased significantly in CAV1-silenced anterior segments, whereas outflow significantly decreased in CAV2-silenced anterior segments. Matrix metalloproteinase (MMP)2 and MMP14, and a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS4) colocalized with both CAVs in TM cells. Protein levels and enzyme activities of MMP/ADAMTS4, fibronectin protein levels, actin stress fibers, and α-smooth muscle actin were all increased in CAV-silenced cells. CONCLUSIONS Caveolin-mediated endocytosis is one mechanism by which TM cells can alter the physiological catabolism of ECM in order to change the composition of the outflow channels in the TM to regulate aqueous outflow resistance. Dysregulation of CAV function could contribute to the pathological changes in ECM that are observed in glaucoma.
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Affiliation(s)
- Mini Aga
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - John M Bradley
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Rohan Wanchu
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Yong-feng Yang
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Ted S Acott
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
| | - Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, United States
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Keller KE, Yang YF, Sun YY, Sykes R, Gaudette ND, Samples JR, Acott TS, Wirtz MK. Interleukin-20 receptor expression in the trabecular meshwork and its implication in glaucoma. J Ocul Pharmacol Ther 2014; 30:267-76. [PMID: 24455976 DOI: 10.1089/jop.2013.0187] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
PURPOSE To determine whether interleukin-20 receptors (IL-20R) are expressed in trabecular meshwork cells and the effect of a T104M mutation in IL-20R2 on downstream cellular functions. METHODS Evaluation of signal transducer and activator of transcription (STAT)3 phosphorylation and generic matrix metalloproteinase (MMP) activity in primary open angle glaucoma (POAG) dermal fibroblasts (pHDF) with the T104M IL-20R2 mutation were compared with normal human dermal fibroblasts (HDF). Expression of IL-20R1 and IL-20R2 in human trabecular meshwork (HTM) cells was determined by immunohistochemistry and western immunoblotting. RESULTS A T104M mutation in IL20-R2 was identified in a large POAG family in which the GLC1C locus was originally mapped. pHDFs harboring this mutation had significantly increased phosphorylated STAT3 (pSTAT3) activity compared with normal HDFs. However, stimulation with either IL-19 or IL-20 for 15 min resulted in significantly decreased levels of pSTAT3 in pHDFs compared with controls. Generic MMP activity was significantly decreased in pHDFs compared with controls after stimulation with IL-20 for 24 h. Both IL-20R1 and IL-20R2 receptors were expressed in HTM cells by western immunoblot and immunofluorescence, and they appeared to be up-regulated in response to cytokine treatment. CONCLUSIONS A T104M mutation in IL-20R2 significantly impacts the function of this receptor as shown by decreased pSTAT3 levels and generic MMP activity. Reduced MMP activity may affect the ability of glaucoma patients to alter outflow resistance in response to elevated intraocular pressure.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health & Sciences University , Portland, Oregon
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Acott TS, Kelley MJ, Keller KE, Vranka JA, Abu-Hassan DW, Li X, Aga M, Bradley JM. Intraocular pressure homeostasis: maintaining balance in a high-pressure environment. J Ocul Pharmacol Ther 2014; 30:94-101. [PMID: 24401029 DOI: 10.1089/jop.2013.0185] [Citation(s) in RCA: 110] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Although glaucoma is a relatively common blinding disease, most people do not develop glaucoma. A robust intraocular pressure (IOP) homeostatic mechanism keeps ocular pressures within relatively narrow acceptable bounds throughout most peoples' lives. The trabecular meshwork and/or Schlemm's canal inner wall cells respond to sustained IOP elevation and adjust the aqueous humor outflow resistance to restore IOP to acceptable levels. It appears that the cells sense IOP elevations as mechanical stretch or distortion of the actual outflow resistance and respond by initiating a complex extracellular matrix (ECM) turnover process that takes several days to complete. Although considerable information pertinent to this process is available, many aspects of the IOP homeostatic process remain to be elucidated. Components and mechanisms beyond ECM turnover could also be relevant to IOP homeostasis, but will not be addressed in detail here. Known aspects of the IOP homeostasis process as well as possible ways that it might function and impact glaucoma are discussed.
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Affiliation(s)
- Ted S Acott
- Casey Eye Institute, Oregon Health & Science University , Portland, Oregon
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Affiliation(s)
- Diala W Abu-Hassan
- Casey Eye Institute, Department of Ophthalmology, Oregon Health & Science University, Portland, Oregon, USA
| | - Ted S Acott
- Department of Biochemistry & Molecular Biology, Oregon Health & Science University, Portland, Oregon, USA
| | - Mary J Kelley
- Department of Biochemistry & Physiology, University of Jordan, Amman, Jordan
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Keller KE, Vranka JA, Haddadin RI, Kang MH, Oh DJ, Rhee DJ, Yang YF, Sun YY, Kelley MJ, Acott TS. The effects of tenascin C knockdown on trabecular meshwork outflow resistance. Invest Ophthalmol Vis Sci 2013; 54:5613-23. [PMID: 23882691 DOI: 10.1167/iovs.13-11620] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Tenascin C (TNC) is a matricellular glycoprotein whose expression in adult tissue is indicative of tissue remodeling. The purpose of the current study was to determine the localization of TNC in trabecular meshwork (TM) tissue and to analyze the effects of TNC on intraocular pressure (IOP). METHODS Human TM frontal sections were immunostained with anti-TNC and imaged by confocal microscopy. TNC mRNA and protein levels were quantitated in anterior segments perfused at physiological and elevated pressure. Short, hairpin RNA (shRNA) silencing lentivirus targeting full-length TNC (shTNC) was applied to anterior segment perfusion organ cultures. The IOPs and central corneal thickness (CCT) of wild-type, TNC(-/-), and tenascin X (TNX(-/-)) knockout mice were measured. RESULTS TNC was distributed in the juxtacanalicular (JCT) region of adult human TM, predominantly in the basement membrane underlying the inner wall of Schlemm's canal. Application of shTNC lentivirus to human and porcine anterior segments in perfusion culture did not significantly affect outflow rate. Although TNC was upregulated in response to pressure, there was no difference in outflow rate when shTNC-silenced anterior segments were subjected to elevated pressure. Furthermore, IOPs and CCTs were not significantly different between TNC(-/-) or TNX(-/-) and wild-type mice. CONCLUSIONS TNC does not appear to contribute directly to outflow resistance. However, TNC immunolocalization in the JCT of adult human eyes suggests that certain areas of the TM are being continuously remodeled with or without an IOP increase.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA.
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Keller KE, Yang YF, Sun YY, Sykes R, Acott TS, Wirtz MK. Ankyrin repeat and suppressor of cytokine signaling box containing protein-10 is associated with ubiquitin-mediated degradation pathways in trabecular meshwork cells. Mol Vis 2013; 19:1639-55. [PMID: 23901248 PMCID: PMC3724959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Accepted: 07/22/2013] [Indexed: 11/23/2022] Open
Abstract
PURPOSE Ankyrin repeat and suppressor of cytokine signaling (SOCS) box containing protein-10 (ASB10) was recently identified as a gene that causes primary open-angle glaucoma. Here, we investigated endogenous ASB10 protein expression in human trabecular meshwork (HTM) cells to provide the first clues to the biologic function of this protein. METHODS Primary HTM cells were cultured and immunostained with anti-ASB10 and various biomarkers of the ubiquitin-mediated proteasomal and autophagy-lysosomal degradation pathways. Cells were imaged with confocal and high-resolution structured illumination microscopy. Colocalization was quantified using Imaris Bitplane software, which generated a Pearson's correlation coefficient value. Coimmunoprecipitation of ASB10-transfected cells was performed. RESULTS Immunofluorescence and confocal analysis showed that ASB10 was localized in intracellular structures in HTM cells. Two populations were observed: small, spherical vesicles and larger, less abundant structures. In the ASB10-silenced cells, the number of large structures was significantly decreased. ASB10 partially colocalized with biomarkers of the ubiquitin-mediated proteasomal pathway including ubiquitin and the α4 subunit of the 20S proteasome. However, ASB10 itself was not ubiquitinated. ASB10 also colocalized with numerous biomarkers of specific autophagic structures: aggresomes (histone deacetylase 6 [HDAC6] and heat shock protein 70 [HSP70]), autophagosomes (light chain 3 [LC3] and p62), amphisomes (Rab7), and lysosomes (lysosomal-associated membrane protein 1 [LAMP1]). Pearson coefficients indicated strong colocalization of large ASB10-stained structures with the α4 subunit of the 20S proteasome, K48 and K63-linked ubiquitin antibodies, p62, HSP70, and HDAC6 (Pearson's range, 0.59-0.82). Coimmunoprecipitation assays showed a positive interaction of ASB10 with HSP70 and with the α4 subunit of the 20S proteasome. Super-resolution structured illumination confocal microscopy suggested that the smaller ASB10-stained vesicles aggregated into the larger structures, which resembled aggresome-like induced structures. Treatment of HTM cells with an autophagy activator (MG132) or inhibitors (wortmannin, bafilomycin A1) significantly increased and decreased the number of small ASB10-stained vesicles, respectively. No discernible differences in the colocalization of large ASB10-stained structures with ubiquitin or HDAC6 were observed between dermal fibroblasts derived from a normal individual and a patient with primary open-angle glaucoma carrying a synonymous ASB10 mutation. CONCLUSIONS Our evidence suggests that ASB10 may play a role in ubiquitin-mediated degradation pathways in TM cells.
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Keller KE, Acott TS. The Juxtacanalicular Region of Ocular Trabecular Meshwork: A Tissue with a Unique Extracellular Matrix and Specialized Function. J Ocul Biol 2013; 1:3. [PMID: 24364042 PMCID: PMC3867143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The trabecular meshwork (TM) is a filter-like tissue located in the anterior segment of the eye. It is composed of a series of fenestrated beams through which aqueous humor flows to exit the anterior chamber via Schlemm's canal. The primary function of the TM is to regulate the flow of aqueous humor in order to establish intraocular pressure (IOP). Dysregulated aqueous humor outflow causes elevated IOP, which is a primary risk factor for glaucoma. The region of the TM implicated in establishing IOP lies adjacent to Schlemm's canal and is called the juxtacanalicular tissue (JCT) or cribriform region. Recent advanced light microscopy studies suggest that the JCT can be subdivided into inner and outer zones based on the localization of certain extracellular matrix (ECM) molecules. By comparing the ECM of the JCT to other connectives tissues and disease processes, this review outlines the evidence for two new concepts in TM biology: (1) continuous maintenance ECM remodeling, which may be critical in order to preserve open aqueous humor flow channels by releasing trapped debris and associated ECM fragments from the outflow pathways; (2) the JCT ECM as a barrier to functionally isolate the aqueous outflow channels. The ECM surrounding the outflow channels in the JCT may function to sequester small active regulatory molecules and prevent them from aberrantly modulating outflow resistance. These adaptations point to a distinctive tissue that has evolved transient ECM remodeling processes in order to regulate aqueous humor outflow and maintain rigorous control of IOP.
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Affiliation(s)
- Kate E. Keller
- Address for Correspondence Casey Eye Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA, Tel: 503 494 2366; Fax: 503 418 2399;
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Keller KE, Sun YY, Vranka JA, Hayashi L, Acott TS. Inhibition of hyaluronan synthesis reduces versican and fibronectin levels in trabecular meshwork cells. PLoS One 2012; 7:e48523. [PMID: 23139787 PMCID: PMC3489675 DOI: 10.1371/journal.pone.0048523] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 09/26/2012] [Indexed: 01/08/2023] Open
Abstract
Hyaluronan (HA) is a major component of the extracellular matrix (ECM) and is synthesized by three HA synthases (HAS). Similarities between the HAS2 knockout mouse and the hdf mutant mouse, which has a mutation in the versican gene, suggest that HA and versican expression may be linked. In this study, the relationship between HA synthesis and levels of versican, fibronectin and several other ECM components in trabecular meshwork cells from the anterior segment of the eye was investigated. HA synthesis was inhibited using 4-methylumbelliferone (4MU), or reduced by RNAi silencing of each individual HAS gene. Quantitative RT-PCR and immunoblotting demonstrated a reduction in mRNA and protein levels of versican and fibronectin. Hyaluronidase treatment also reduced versican and fibronectin levels. These effects could not be reversed by addition of excess glucose or glucosamine or exogenous HA to the culture medium. CD44, tenascin C and fibrillin-1 mRNA levels were reduced by 4MU treatment, but SPARC and CSPG6 mRNA levels were unaffected. Immunostaining of trabecular meshwork tissue after exposure to 4MU showed an altered localization pattern of HA-binding protein, versican and fibronectin. Reduction of versican by RNAi silencing did not affect HA concentration as assessed by ELISA. Together, these data imply that HA concentration affects synthesis of certain ECM components. Since precise regulation of the trabecular meshwork ECM composition and organization is required to maintain the aqueous humor outflow resistance and intraocular pressure homeostasis in the eye, coordinated coupling of HA levels and several of its ECM binding partners should facilitate this process.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA.
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Keller KE, Sun YY, Yang YF, Bradley JM, Acott TS. Perturbation of hyaluronan synthesis in the trabecular meshwork and the effects on outflow facility. Invest Ophthalmol Vis Sci 2012; 53:4616-25. [PMID: 22695958 DOI: 10.1167/iovs.12-9500] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
PURPOSE Hyaluronan (HA) is a major component of the aqueous outflow pathway. However, the contribution of HA to human outflow resistance remains unclear. Three HA synthase genes (HAS1-3) have been identified. Here, we evaluate the contribution of each of the HAS proteins to outflow facility in anterior segment perfusion culture. METHODS Two methods were used to reduce HA synthesis: 1 mM 4-methylumbelliferone (4MU) was used to inhibit all HAS synthases and shRNA silencing lentivirus was generated to knock down expression of each HAS individually. Quantitative RT-PCR, Western immunoblotting and an HA ELISA assay were used to assess HAS mRNA and protein levels and HA concentration, respectively. The effects of 4MU treatment and HAS gene silencing on outflow facility were assessed in human and porcine perfusion culture. RESULTS Quantitative RT-PCR and Western immunoblotting showed a reduction of each HAS in response to their respective silencing and 4MU treatment. HA concentration was concomitantly reduced. Treatment with 4MU decreased outflow facility in human anterior segments but increased outflow facility in porcine eyes. Lentiviral delivery of HAS1 and HAS2 silencing vectors caused similar opposite effects on outflow facility. Silencing of HAS3 did not significantly affect outflow resistance in either species. CONCLUSIONS This is the first conclusive evidence for a significant role of HA in the human outflow pathway. HA chains synthesized by HAS1 and HAS2 contribute to outflow resistance, while hyaluronan produced by HAS3 does not appear to play a significant role.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, 97239, USA.
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Pasutto F, Keller KE, Weisschuh N, Sticht H, Samples JR, Yang YF, Zenkel M, Schlötzer-Schrehardt U, Mardin CY, Frezzotti P, Edmunds B, Kramer PL, Gramer E, Reis A, Acott TS, Wirtz MK. Variants in ASB10 are associated with open-angle glaucoma. Hum Mol Genet 2011; 21:1336-49. [PMID: 22156576 DOI: 10.1093/hmg/ddr572] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The molecular events responsible for obstruction of aqueous humor outflow and the loss of retinal ganglion cells in glaucoma, one of the main causes of blindness worldwide, remain poorly understood. We identified a synonymous variant, c.765C>T (Thr255Thr), in ankyrin repeats and suppressor of cytokine signaling box-containing protein 10 (ASB10) in a large family with primary open angle glaucoma (POAG) mapping to the GLC1F locus. This variant affects an exon splice enhancer site and alters mRNA splicing in lymphoblasts of affected family members. Systematic sequence analysis in two POAG patient groups (195 US and 977 German) and their respective controls (85 and 376) lead to the identification of 26 amino acid changes in 70 patients (70 of 1172; 6.0%) compared with 9 in 13 controls (13 of 461; 2.8%; P = 0.008). Molecular modeling suggests that these missense variants change ASB10 net charge or destabilize ankyrin repeats. ASB10 mRNA and protein were found to be strongly expressed in trabecular meshwork, retinal ganglion cells and ciliary body. Silencing of ASB10 transcripts in perfused anterior segment organ culture reduced outflow facility by ∼50% compared with control-infected anterior segments (P = 0.02). In conclusion, genetic and molecular analyses provide evidence for ASB10 as a glaucoma-causing gene.
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Affiliation(s)
- Francesca Pasutto
- Institute of Human Genetics, University Hospital Erlangen-Nuremberg, Erlangen, Germany
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Anderssohn AM, Cox K, O'Malley K, Dees S, Hosseini M, Boren L, Wagner A, Bradley JM, Kelley MJ, Acott TS. Molecular chaperone function for myocilin. Invest Ophthalmol Vis Sci 2011; 52:7548-55. [PMID: 21873671 DOI: 10.1167/iovs.11-7723] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Myocilin is thought to be a stress response protein, but its exact molecular functions have not been established. Studies were conducted to see whether myocilin can act as a general molecular chaperone. METHODS Myocilin was isolated and purified from porcine trabecular meshwork (TM) cell culture media. Its ability to protect citrate synthase, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the restriction endonuclease DrdI from thermal inactivation was evaluated. Light scattering was used to evaluate thermally induced aggregation of citrate synthase. Myocilin induction was assessed after exposure of TM cells to several types of stress treatments. RESULTS Levels of extracellular myocilin expressed by TM cells were increased in response to mechanical stretch, heat shock, TNFα, or IL-1α. Myocilin protected citrate synthase activity against thermal inactivation for 5 minutes at 55°C in a concentration-dependent manner, with nearly full protection of 1.5 μM citrate synthase in the presence of 650 nM myocilin. Myocilin significantly reduced thermal aggregation of citrate synthase to levels 36% to 44% of control levels. Myocilin also protected GAPDH from thermal inactivation for 10 minutes at 45°C. Myocilin at 18 nM was more effective than 1 μM bovine serum albumin at protecting DrdI from thermal inactivation. CONCLUSIONS Myocilin is induced in response to several cellular stresses and displays general molecular chaperone activity by protecting DrdI, citrate synthase, and GAPDH from thermal inactivation. Myocilin also suppresses the thermal aggregation of citrate synthase. One function of myocilin may be to serve as a molecular chaperone.
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Affiliation(s)
- Ann Marie Anderssohn
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239, USA
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Keller KE, Bradley JM, Vranka JA, Acott TS. Segmental versican expression in the trabecular meshwork and involvement in outflow facility. Invest Ophthalmol Vis Sci 2011; 52:5049-57. [PMID: 21596823 DOI: 10.1167/iovs.10-6948] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
PURPOSE Versican is a large proteoglycan with numerous chondroitin sulfate (CS) glycosaminoglycan (GAG) side chains attached. To assess versican's potential contributions to aqueous humor outflow resistance, its segmental distribution in the trabecular meshwork (TM) and the effect on outflow facility of silencing the versican gene were evaluated. METHODS Fluorescent quantum dots (Qdots) were perfused to label outflow pathways of anterior segments. Immunofluorescence with confocal microscopy and quantitative RT-PCR were used to determine versican protein and mRNA distribution relative to Qdot-labeled regions. Lentiviral delivery of shRNA-silencing cassettes to TM cells in perfused anterior segment cultures was used to evaluate the involvement of versican and CS GAG chains in outflow facility. RESULTS Qdot uptake by TM cells showed considerable segmental variability in both human and porcine outflow pathways. Regional levels of Qdot labeling were inversely related to versican protein and mRNA levels; versican levels were relatively high in sparsely Qdot-labeled regions and low in densely labeled regions. Versican silencing decreased outflow facility in human and increased facility in porcine anterior segments. However, RNAi silencing of ChGn, an enzyme unique to CS GAG biosynthesis, increased outflow facility in both species. The fibrillar pattern of versican immunostaining in the TM juxtacanalicular region was disrupted after versican silencing in perfusion culture. CONCLUSIONS Versican appears to be a central component of the outflow resistance, where it may organize GAGs and other ECM components to facilitate and control open flow channels in the TM. However, the exact molecular organization of this resistance appears to differ between human and porcine eyes.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health and Science University, Portland, Oregon 97239, USA
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Last JA, Pan T, Ding Y, Reilly CM, Keller K, Acott TS, Fautsch MP, Murphy CJ, Russell P. Elastic modulus determination of normal and glaucomatous human trabecular meshwork. Invest Ophthalmol Vis Sci 2011; 52:2147-52. [PMID: 21220561 DOI: 10.1167/iovs.10-6342] [Citation(s) in RCA: 247] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
PURPOSE Elevated intraocular pressure (IOP) is a risk factor for glaucoma. The principal outflow pathway for aqueous humor in the human eye is through the trabecular meshwork (HTM) and Schlemm's canal (SC). The junction between the HTM and SC is thought to have a significant role in the regulation of IOP. A possible mechanism for the increased resistance to flow in glaucomatous eyes is an increase in stiffness (increased elastic modulus) of the HTM. In this study, the stiffness of the HTM in normal and glaucomatous tissue was compared, and a mathematical model was developed to predict the impact of changes in stiffness of the juxtacanalicular layer of HTM on flow dynamics through this region. METHODS Atomic force microscopy (AFM) was used to measure the elastic modulus of normal and glaucomatous HTM. According to these results, a model was developed that simulated the juxtacanalicular layer of the HTM as a flexible membrane with embedded pores. RESULTS The mean elastic modulus increased substantially in the glaucomatous HTM (mean = 80.8 kPa) compared with that in the normal HTM (mean = 4.0 kPa). Regional variation was identified across the glaucomatous HTM, possibly corresponding to the disease state. Mathematical modeling suggested an increased flow resistance with increasing HTM modulus. CONCLUSIONS The data indicate that the stiffness of glaucomatous HTM is significantly increased compared with that of normal HTM. Modeling exercises support substantial impairment in outflow facility with increased HTM stiffness. Alterations in the biophysical attributes of the HTM may participate directly in the onset and progression of glaucoma.
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Affiliation(s)
- Julie A Last
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin, USA
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Abstract
PURPOSE Matrix metalloproteinases (MMPs) degrade extracellular matrix (ECM) and increase outflow facility in anterior segment perfusion culture. One group is the ADAMTSs (a disintegrin and metalloproteinase with thrombospondin type 1 motifs). In this study, the authors examined the effects of ADAMTS-1, -4, and -5 on outflow facility and investigated their mRNA levels and protein expression in the trabecular meshwork (TM). METHODS ADAMTS mRNA was quantitated by qRT-PCR in TM cells exposed to TNFalpha, IL-1alpha, TGFbeta2, or mechanical stretch. ADAMTS-4 mRNA was assessed in normal and glaucomatous human anterior segments perfused at physiological or elevated pressure. Immunofluorescence was used to localize ADAMTSs in human TM cells and tissue. Anterior segments in perfusion culture were treated with recombinant ADAMTSs to determine effects on outflow facility. RESULTS Cytokine treatment increased mRNA of all three ADAMTSs. Mechanical stretch increased ADAMTS-4 mRNA but conversely decreased ADAMTS-1 and -5 mRNA. ADAMTS-4 mRNA levels increased in response to pressure elevation in normal eyes and to higher levels in glaucomatous eyes. ADAMTS-4 protein was highly increased in the juxtacanalicular region of the TM in anterior segments perfused at increased pressure. In human TM cells, ADAMTS-4 colocalized with cortactin in podosome- or invadopodia-like structures, but ADAMTS-1 and -5 did not. Recombinant ADAMTS-4 increased outflow facility in human and porcine anterior segments, whereas recombinant ADAMTSs-1 and -5 did not. CONCLUSIONS These results show differential responses and expression of ADAMTS-1, -4, and -5 in human TM cells. Combined, these results suggest that ADAMTS-4 is a potential modifier of outflow facility.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health and Science University, Portland, Oregon 97239-4197, USA
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Keller KE, Aga M, Bradley JM, Kelley MJ, Acott TS. Extracellular matrix turnover and outflow resistance. Exp Eye Res 2008; 88:676-82. [PMID: 19087875 DOI: 10.1016/j.exer.2008.11.023] [Citation(s) in RCA: 180] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 09/15/2008] [Accepted: 11/20/2008] [Indexed: 11/29/2022]
Abstract
Normal homeostatic adjustment of elevated intraocular pressure (IOP) involves remodeling the extracellular matrix (ECM) of the trabecular meshwork (TM). This entails sensing elevated IOP, releasing numerous activated proteinases to degrade existing ECM and concurrent biosynthesis of replacement ECM components. To increase or decrease IOP, the quantity, physical properties and/or organization of new components should be somewhat different from those replaced in order to modify outflow resistance. ECM degradation and replacement biosynthesis in the outflow pathway must be tightly controlled and focused to retain the complex structural organization of the tissue. Recently identified podosome- or invadopodia-like structures (PILS) may aid in the focal degradation of ECM and organization of replacement components.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health and Science University, Portland, OR 97239-4197, USA
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Kelley MJ, Rose AY, Keller KE, Hessle H, Samples JR, Acott TS. Stem cells in the trabecular meshwork: present and future promises. Exp Eye Res 2008; 88:747-51. [PMID: 19061887 DOI: 10.1016/j.exer.2008.10.024] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2008] [Revised: 10/25/2008] [Accepted: 10/28/2008] [Indexed: 12/25/2022]
Abstract
Primary open-angle glaucoma is recognized as a disease of aging, and studies show a relationship between aging and trabecular meshwork (TM) cell density. Human TM cell division occurs primarily in the anterior, non-filtering region. A commonly used glaucoma treatment, laser trabeculoplasty (LTP), triggers and increases cell division, as well as cell migration of these anterior TM cells. These freshly-divided migrating cells repopulate the burned laser sites, suggesting that they are stem cells. Several studies concerning this putative TM stem cell will be discussed.
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Affiliation(s)
- M J Kelley
- Department of Ophthalmology, Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA.
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Keller KE, Bradley JM, Kelley MJ, Acott TS. Effects of modifiers of glycosaminoglycan biosynthesis on outflow facility in perfusion culture. Invest Ophthalmol Vis Sci 2008; 49:2495-505. [PMID: 18515587 DOI: 10.1167/iovs.07-0903] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Glycosaminoglycans (GAGs) have been implicated in the regulation of outflow resistance of aqueous humor flow through the trabecular meshwork (TM). Their role was further investigated by assessment of the effects of chlorate, an inhibitor of sulfation, and beta-xyloside, which provides a competitive nucleation point for addition of disaccharide units, in anterior segment perfusion culture. METHODS Outflow facility was measured in perfused porcine and human anterior organ cultures treated with 20 or 50 mM sodium chlorate, or 1 mM beta-xyloside. Perturbation of extracellular matrix (ECM) components was assessed in paraffin-embedded sections by immunofluorescence and confocal microscopy. Parallel experiments were conducted on cultured TM cells. RESULTS Outflow facility increased in porcine eyes with chlorate (3-fold) and beta-xyloside (3.5-fold) treatments. In human eyes, outflow increased approximately 1.5-fold and took longer (>48 hours) to occur. By confocal microscopy, immunostaining for chondroitin and heparan sulfates was observed on edges of human TM beams in nontreated eyes, with intense staining in the juxtacanalicular tissue (JCT) region. In treated eyes, staining of beam edges was severely reduced and was instead found in plaques. Chlorate treatment resulted in a striated pattern of GAG staining in the human JCT region. Fibronectin immunostaining was altered in beta-xyloside-treated eyes, whereas in cell culture, chlorate induced formation of thick fibronectin fibrils, to which tenascin C colocalized. CONCLUSIONS Disrupting GAG chain biosynthesis increased outflow facility in perfusion culture and induced atypical ECM molecule interactions in cell culture. This study provides direct evidence of the critical role of GAG chains in regulating outflow resistance in human TM.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239-4197, USA
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Aga M, Bradley JM, Keller KE, Kelley MJ, Acott TS. Specialized podosome- or invadopodia-like structures (PILS) for focal trabecular meshwork extracellular matrix turnover. Invest Ophthalmol Vis Sci 2008; 49:5353-65. [PMID: 18641286 DOI: 10.1167/iovs.07-1666] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
PURPOSE There are distinctive areas of colocalization of matrix metalloproteinase (MMP)-2 and -14 on trabecular meshwork (TM) cells that resemble podosomes or invadopodia. Studies were conducted to determine whether TM cells exhibit podosome- or invadopodia-like structures (PILS) and whether they produce focal extracellular matrix (ECM) turnover. METHODS Porcine and human TM cells and perfused anterior segment organ cultures were studied. Localization of PILS components on TM cells and in sections from anterior segments was determined by immunohistochemistry and confocal microscopy. Cells were grown on type I collagen labeled with fluorescein isothiocyanate (FITC) for degradation analysis. Confocal time lapse images were taken of labeled TM cells on FITC-collagen. RESULTS Immunostaining for MMP-2, MMP-14, and the typical PILS components cortactin, caldesmon, alpha-actinin, N-WASP, Arp-3, and cdc42 colocalized on these distinctive structures. Integrin-alphaV and -beta1, fibronectin, and versican colocalized with PILS components. TM cells on FITC-conjugated collagen developed focal regions of degradation. Time-lapse imaging showed dramatic and controlled movement of TM cell processes during this ECM degradation and fragment internalization. MMP-2, MMP-14, and cortactin colocalized at regions that appear to be PILS on cells within the outflow pathway in sections of human anterior segments. CONCLUSIONS TM cells exhibit areas where PILS components colocalize with MMP-2 and -14. Similar structures are found in sections, suggesting that PILS occur in situ in the outflow pathway. The collagen degradation suggests that PILS may serve as focal sites for targeted ECM turnover, an event linked to modifications of aqueous outflow resistance and intraocular pressure homeostasis.
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Affiliation(s)
- Mini Aga
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239-4197, USA
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Abstract
The extracellular matrix (ECM) of the trabecular meshwork (TM) is thought to be important in regulating intraocular pressure (IOP) in both normal and glaucomatous eyes. IOP is regulated primarily by a fluid resistance to aqueous humor outflow. However, neither the exact site nor the identity of the normal resistance to aqueous humor outflow has been established. Whether the site and nature of the increased outflow resistance, which is associated with open-angle glaucoma, is the same or different from the normal resistance is also unclear. The ECMs of the TM beams, juxtacanalicular region (JCT) and Schlemm's canal (SC) inner wall are comprised of fibrillar and non-fibrillar collagens, elastin-containing microfibrils, matricellular and structural organizing proteins, glycosaminoglycans (GAGs) and proteoglycans. Both basement membranes and stromal ECM are present in the TM beams and JCT region. Cell adhesion proteins, cell surface ECM receptors and associated binding proteins are also present in the beams, JCT and SC inner wall region. The outflow pathway ECM is relatively dynamic, undergoing constant turnover and remodeling. Regulated changes in enzymes responsible for ECM degradation and biosynthetic replacement are observed. IOP homeostasis, triggered by pressure changes or mechanical stretching of the TM, appears to involve ECM turnover. Several cytokines, growth factors and drugs, which affect the outflow resistance, change ECM component expression, mRNA alternative splicing, cellular cytoskeletal organization or all of these. Changes in ECM associated with open-angle glaucoma have been identified.
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Affiliation(s)
- Ted S Acott
- Casey Eye Institute, Oregon Health & Science University, 3375 SW Terwilliger, Portland, OR 97239-4197, USA.
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Kelley MJ, Rose A, Song K, Lystrup B, Samples JW, Acott TS. p38 MAP kinase pathway and stromelysin regulation in trabecular meshwork cells. Invest Ophthalmol Vis Sci 2007; 48:3126-37. [PMID: 17591882 DOI: 10.1167/iovs.06-1375] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Increased expression of stromelysin-1 (matrix metalloproteinase [MMP]-3) by the trabecular meshwork (TM) initiates extracellular matrix turnover and increases aqueous humor outflow facility. Tumor necrosis factor (TNF)alpha and interleukin (IL)-1alpha are efficacious inducers of MMP-3 in TM. To facilitate understanding of the regulation of MMP-3, the authors investigated the involvement of p38 MAP kinase pathway proteins in this process. METHODS Western immunoblots were used to determine the effects of these cytokines and p38 MAP kinase pathway inhibitors on MMP-3 protein levels, p38 MAP kinase isoforms, and phosphorylation levels in human and porcine TM cells. The effects of a dominant-negative p38 MAP kinase construct on MMP-3 expression were evaluated. Morphologic changes in the cells were also examined. RESULTS Both cytokines increased MMP-3 levels. The p38 MAP kinase inhibitor SB202190 diminished MMP-3 induction by TNFalpha at all times and at 24 hours by IL-1alpha but potentiated the IL-1alpha-induced increase in MMP-3 at later times. MMP-3 induction by both cytokines was blocked by dominant-negative p38 MAP kinase constructs. Each cytokine increased phosphorylation of the p38 MAP kinase pathway components and altered TM cell morphology. The p38 inhibitor blocked only the morphologic changes produced by TNFalpha. Human and porcine TM cells expressed p38 alpha, beta, delta, and gamma isoforms, which migrate coincident with bands of specific phosphorylation. CONCLUSIONS The effects of p38 inhibitors and the dominant-negative construct on TNFalpha and IL-1alpha induction of MMP-3 demonstrate an essential role for p38 in this signaling process. Differences between p38 inhibitor effects on TNFalpha and IL-1alpha induction of MMP-3 suggest divergent p38 isoform use, as do the morphologic responses. The anomalous p38 inhibitor effect on IL-1alpha induction of MMP-3 and phosphorylation of p38 delta/gamma suggests complex interactions between p38 MAP kinase isoforms and their differential uses by TNFalpha and IL-1alpha in TM.
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Affiliation(s)
- Mary J Kelley
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239-4197, USA.
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Kelley MJ, Rose AY, Song K, Chen Y, Bradley JM, Rookhuizen D, Acott TS. Synergism of TNF and IL-1 in the induction of matrix metalloproteinase-3 in trabecular meshwork. Invest Ophthalmol Vis Sci 2007; 48:2634-43. [PMID: 17525194 DOI: 10.1167/iovs.06-1445] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE TNF and IL-1 increase matrix metalloproteinase-3 (MMP-3) expression in the trabecular meshwork (TM). TNF-alpha, in combination with IL-1alpha or IL-1beta, produces highly synergistic MMP-3 increases. Possible mechanisms for this synergism in TM cells were investigated. METHODS Porcine and human TM cells were treated with TNF-alpha, IL-1alpha, IL-1beta and their combinations. Western immunoblots were used to evaluate MMP-3, MMP-9, MMP-12, TNF-alpha, IL-1alpha, IL-1beta, IL-6, TNF receptor I (RI), IL-1 RI, and IL-1 RII levels and the phosphorylation of Erk, JNK, and p38 MAP kinases. Dose-response effects for TNF-alpha, IL-1alpha and IL-1beta on MMP-3 were evaluated. Microarray and quantitative RT-PCR were used to determine mRNA levels. MMP-3 transcription rate was assessed by transfecting TM cells with an MMP-3 promoter/reporter construct. Combined cytokine effects on outflow facility were appraised in perfused anterior segment organ culture. RESULTS TNF-alpha, IL-1alpha, and IL-1beta each individually increased MMP-3 levels, whereas TNF-alpha in combination with IL-1alpha or IL-1beta produced highly synergistic increases. MMP-9 and MMP-12 levels were also elevated, but only MMP-12 showed synergism. IL-1alpha, IL-1beta, and IL-6, but not TNF-alpha mRNA or protein level, were elevated by these cytokines. Maximum MMP-3 production for individual cytokines, even at high doses, was far less than with dual cytokine doses. Erk 1 and 2, JNK 1 and 2, and p38 alpha and beta phosphorylation increased, but not synergistically. However, phosphorylation of novel isoforms of JNK and p38 delta and gamma did show synergism. MMP-3 mRNA levels and transcription rates also demonstrated synergism. TNF-alpha significantly increased IL-1 RI levels. Synergism in outflow facility was observed with TNF-alpha and IL-1alpha. CONCLUSIONS TNF-alpha, in combination with IL-1alpha or IL-1beta, produced intense synergistic increases in MMP-3 and MMP-12 but not in MMP-9. Induction of IL-1 RI by TNF-alpha partially explains the synergism. Responses of novel JNK and p38 MAP kinase delta and gamma isoforms also partially account for the synergism. Understanding this strong synergistic effect may provide useful insight into optimizing therapeutic regulation of intraocular pressure in glaucoma.
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Affiliation(s)
- Mary J Kelley
- Casey Eye Institute, Oregon Health and Science University, Portland, Oregon 97239-4197, USA
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Keller KE, Kelley MJ, Acott TS. Extracellular Matrix Gene Alternative Splicing by Trabecular Meshwork Cells in Response to Mechanical Stretching. ACTA ACUST UNITED AC 2007; 48:1164-72. [PMID: 17325160 DOI: 10.1167/iovs.06-0875] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
PURPOSE Elevated intraocular pressure (IOP), sensed as mechanical stretching by trabecular meshwork (TM) cells, triggers extracellular matrix (ECM) remodeling. In addition to changes in gene expression, alternative mRNA splicing may alter ECM protein isoforms. Changes in mRNA expression and alternative splicing of four ECM molecules in response to mechanical stretching of TM cells were investigated. METHODS Porcine TM cells were mechanically stretched for 12, 24, or 48 hours. RNA was isolated, and RT-PCR was performed with primers that flanked alternatively spliced domains. PCR products were identified by DNA sequencing. Quantitative RT-PCR (qRT-PCR) was performed with primers positioned within nonspliced and spliced regions of the genes. RESULTS Total levels of tenascin C, collagen type XII, and CD44 mRNA were increased, whereas versican mRNA levels were decreased in response to the mechanical stretch. In addition, each of these genes expressed alternate mRNA isoforms. Transcripts containing the fibronectin type III domain D of tenascin C, the long NC3 isoform of collagen type XII, the V1 isoform of versican, and exons v7 and v8 of CD44 all increased in response to mechanical stretching. A novel isoform of collagen type XII was observed that resulted in deletion of two exons, a frameshift, and a premature stop codon. This isoform was expressed only by stretched TM cells. CONCLUSIONS These alternative splicing events led to the modulation of potential GAG attachment sites and other ECM-binding motifs. These changes should affect TM cell-ECM and/or protein-protein interactions during the ECM remodeling that occurs coincident with homeostatic restoration of IOP to normal.
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Affiliation(s)
- Kate E Keller
- Casey Eye Institute, Oregon Health and Science University, Portland, Oregon, USA
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Hosseini M, Rose AY, Song K, Bohan C, Alexander JP, Kelley MJ, Acott TS. IL-1 and TNF Induction of Matrix Metalloproteinase-3 by c-Jun N-Terminal Kinase in Trabecular Meshwork. ACTA ACUST UNITED AC 2006; 47:1469-76. [PMID: 16565381 DOI: 10.1167/iovs.05-0451] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
PURPOSE The cytokines TNF and IL-1 mediate the MMP-3 increase that occurs in response to trabecular meshwork (TM) treatment by laser trabeculoplasty. This MMP-3 increase appears to play a key role in the efficacy of this treatment for open-angle glaucoma. Protein kinase Cmu and the Erk mitogen-activated protein (MAP) kinases are essential signaling components in transducing MMP-3 increases produced by treatment of TM cells with these cytokines. Here, the involvement of the JNK-MAP kinase pathway in this process was evaluated. METHODS Porcine TM cells were treated with TNFalpha, IL-1alpha, or IL-1beta. Changes in MMP-3 and MMP-9 protein levels in the media were then determined by Western immunoblot. The effect of JNK inhibitor 2 was evaluated. Changes in the level of phosphorylation of JNK, c-Jun, ATF-2, MKK4, and MKK7 were also determined at various times after TNFalpha or IL-1alpha treatment. A 2.3-kb MMP-3 promoter fragment was cloned into a secreted alkaline phosphatase reporter vector. This reporter construct was cotransfected into TM cells with a mammalian expression vector containing a dominant-negative mutant of JNK. The involvement of JNK activity in the TNFalpha and IL-1alpha induction of MMP-3 expression was then evaluated. RESULTS TNFalpha, IL-1alpha, and IL-1beta increase media MMP-3 and MMP-9 protein levels, and JNK inhibitor 2 blocks these increases. JNK1/2, MKK4, c-Jun, and ATF-2 phosphorylation levels increase in response to TNFalpha and IL-1alpha treatment. JNK inhibitor 2 pretreatment blocks these c-Jun and ATF-2 phosphorylation increases. Dominant-negative JNK dramatically reduces the MMP-3 promoter-driven reporter activity induced by these cytokines. CONCLUSIONS JNK activity is necessary for the induction of MMP-3 and MMP-9 by TNFalpha, IL-1alpha, or IL-1beta in TM cells. Phosphorylation of components of the JNK signaling pathway and of the transcription factors c-Jun and ATF-2 support a role for this pathway in the induction of MMP-3 and MMP-9 in the TM in response to these cytokines. Thus, at least three separate signal transduction pathways are necessary in this signaling event in TM cells.
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Affiliation(s)
- Mojgan Hosseini
- Casey Eye Institute, Oregon Health & Science University, Portland, Oregon 97239-4197, USA
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Schultz DW, Weleber RG, Lawrence G, Barral S, Majewski J, Acott TS, Klein ML. HEMICENTIN-1 (FIBULIN-6) and the 1q31 AMD locus in the context of complex disease: review and perspective. Ophthalmic Genet 2005; 26:101-5. [PMID: 16020313 DOI: 10.1080/13816810590968023] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Age-related macular degeneration (AMD) is the most common blinding disorder in the Western world. Similar to other common diseases in which age is a risk factor (e.g., type II diabetes or Alzheimer's disease), AMD is thought to have a complex etiology. Previously, a Gln5345Arg mutation in HEMICENTIN-1 was found to segregate with AMD in a large family. However, the population frequency of this allele is inconsistent with the large proportion of families shown by linkage studies to map near this gene at 1q31. This review summarizes current knowledge regarding the role of HEMICENTIN-1 in AMD, the results of association studies for the Gln5345Arg mutation, and the linkage evidence for an AMD locus on 1q31. The data can be reconciled through proposing both additional variants in HEMICENTIN-1 and a second genetic risk factor for AMD in the region.
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Affiliation(s)
- Dennis W Schultz
- Macular Degeneration Center, Casey Eye Institute, Oregon Health & Science University, 3375 SW Terwilliger Boulevard, Portland, OR 97239-4197, U.S.A.
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Vittal V, Rose A, Gregory KE, Kelley MJ, Acott TS. Changes in gene expression by trabecular meshwork cells in response to mechanical stretching. Invest Ophthalmol Vis Sci 2005; 46:2857-68. [PMID: 16043860 DOI: 10.1167/iovs.05-0075] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Trabecular meshwork (TM) cells appear to sense changes in intraocular pressure (IOP) as mechanical stretching. In response, they make homeostatic corrections in the aqueous humor outflow resistance, partially by increasing extracellular matrix (ECM) turnover initiated by the matrix metalloproteinases. To understand this homeostatic adjustment process further, studies were conducted to evaluate changes in TM gene expression that occur in response to mechanical stretching. METHODS Porcine TM cells were subjected to sustained mechanical stretching, and RNA was isolated after 12, 24, or 48 hours. Changes in gene expression were evaluated with microarrays containing approximately 8000 cDNAs. Select mRNA changes were then compared by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Western immunoblots were used to determine whether some of these changes were associated with changes in protein levels. RESULTS On the microarrays, 126 genes were significantly upregulated, and 29 genes were significantly downregulated at one or more time points, according to very conservative statistical and biological criteria. Of the genes that changed, several ECM regulatory genes, cytoskeletal-regulatory genes, signal-transduction genes, and stress-response genes were notable. These included several proteoglycans and matricellular ECM proteins composed of common repetitive binding domains. The results of analysis of mRNA changes in more than 20 selected genes by qRT-PCR supported the findings in the microarray analysis. Western immunoblots of several proteins demonstrated protein level changes associated with changes in the level of mRNA. CONCLUSIONS The expression of a variety of TM genes is significantly affected by mechanical stretching. These include several ECM proteins that contain multiple binding sites and may serve organizational roles in the TM. Several proteins that could contribute to the homeostatic modification of aqueous humor outflow resistance are also upregulated or downregulated.
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Affiliation(s)
- Vasavi Vittal
- Casey Eye Institute, Oregon Health and Science University, Portland, OR 97239-4197, USA
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Abstract
PURPOSE Trabecular meshwork (TM) matrix metalloproteinase (MMP), and tissue inhibitor (TIMP) changes in response to mechanical stretching appear to be central to intraocular pressure (IOP) homeostasis. Studies were conducted to define the signal transduction pathway responsible for the increases in MMP-2 and -14 that occur in response to mechanical stretching of TM cells. METHODS Porcine TM cells were subjected to mechanical stretching, and changes in MMP-2 and -14 levels were determined by gelatin zymography and Western immunoblot analysis. Effects of signal transduction pathway inhibitors on MMP levels were analyzed. Phosphospecific antibodies were used to identify phosphorylation changes in select pathway intermediates. In silico secondary structure analysis was conducted on the 5' untranslated regions (UTRs) of MMP-2 and -14 mRNAs. RESULTS The increases in MMP-2 and -14 that occur 24 hours after sustained mechanical stretching of TM cells were blocked by rapamycin. Wortmannin blocked the MMP-2 but not the MMP-14 increase. Protein kinase B (PKB) phosphorylation on S473 and T308 was increased significantly by stretching. Rapamycin-sensitive phosphorylation of T389 in p70/p85 S6 kinase was also increased. The phosphorylations of the translation initiation factor eIF-4E on S209 and of its inhibitory binding protein 4E-BP1 on T70 were both increased by stretch. The calculated free energies of secondary structures of the 5' UTRs of the mRNAs for MMP-2 and -14 were negative and relatively large. MMP-2 also had pyrimidine tracts in the extreme 5' region of its UTR. CONCLUSIONS The increases in TM MMP-2 and -14 protein levels in response to mechanical stretching appear to be transduced at least in part by mTOR, the mammalian target of rapamycin (mTOR). The wortmannin sensitivity implicates phosphoinositide 3-kinase as a modulator of the MMP-2 but not the MMP-14 increase. Integrin-linked kinase (ILK), phosphoinositide-dependent kinase (PDK-1), and PKB are implicated in the MMP-2 increase. Translational initiation involving eIF-4E and its inhibitory binding protein 4E-BP1 appear to be involved in both the MMP-2 and -14 increases with stretching and are normally regulated by mTOR. The high degree of secondary structure in the 5' UTRs of these transcripts is typically an indicator of genes specifically sensitive to regulation through this pathway. P70/p85 S6 kinase is probably involved downstream from mTOR and PKB in regulating translation of MMP-2, which has pyrimidine tracts in its 5' UTR. Manipulation of these transduction pathways may provide new approaches to therapeutic IOP regulation.
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Affiliation(s)
- John M B Bradley
- Casey Eye Institute, Oregon Health and Science University, 3375 SW Terwilliger, Portland, OR 97239-4197, USA
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