1
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Saccuzzo EG, Youngblood HA, Lieberman RL. Myocilin misfolding and glaucoma: A 20-year update. Prog Retin Eye Res 2023; 95:101188. [PMID: 37217093 PMCID: PMC10330797 DOI: 10.1016/j.preteyeres.2023.101188] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 05/18/2023] [Accepted: 05/19/2023] [Indexed: 05/24/2023]
Abstract
Mutations in the gene MYOC account for approximately 5% of cases of primary open angle glaucoma (POAG). MYOC encodes for the protein myocilin, a multimeric secreted glycoprotein composed of N-terminal coiled-coil (CC) and leucine zipper (LZ) domains that are connected via a disordered linker to a 30 kDa olfactomedin (OLF) domain. More than 90% of glaucoma-causing mutations are localized to the OLF domain. While myocilin is expressed in numerous tissues, mutant myocilin is only associated with disease in the anterior segment of the eye, in the trabecular meshwork. The prevailing pathogenic mechanism involves a gain of toxic function whereby mutant myocilin aggregates intracellularly instead of being secreted, which causes cell stress and an early timeline for TM cell death, elevated intraocular pressure, and subsequent glaucoma-associated retinal degeneration. In this review, we focus on the work our lab has conducted over the past ∼15 years to enhance our molecular understanding of myocilin-associated glaucoma, which includes details of the molecular structure and the nature of the aggregates formed by mutant myocilin. We conclude by discussing open questions, such as predicting phenotype from genotype alone, the elusive native function of myocilin, and translational directions enabled by our work.
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Affiliation(s)
- Emily G Saccuzzo
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA, 30332-0400, USA
| | - Hannah A Youngblood
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA, 30332-0400, USA
| | - Raquel L Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA, 30332-0400, USA.
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2
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Zhou B, Lin X, Li Z, Yao Y, Yang J, Zhu Y. Structure‒function‒pathogenicity analysis of C-terminal myocilin missense variants based on experiments and 3D models. Front Genet 2022; 13:1019208. [PMID: 36267417 PMCID: PMC9577182 DOI: 10.3389/fgene.2022.1019208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2022] [Accepted: 09/16/2022] [Indexed: 11/13/2022] Open
Abstract
MYOC is a common pathogenic gene for primary open-angle glaucoma and encodes the protein named myocilin. Multiple MYOC variations have been found, with different clinical significance. However, the pathogenesis of glaucoma induced by MYOC mutations has not been fully clarified. Here, we analyze the molecular and cellular biological differences caused by multiple variant myocilins, including protein secretion characteristics, structural changes, subcellular localization, cellular autophagic activity and oxidative stress. Denaturing and nondenaturing electrophoresis showed myocilin to be a secreted protein with the tendency to self-oligomerize. The full-length myocilin and its C-terminal cleavage fragment are secreted. Secretion analysis of 23 variant myocilins indicated that secretion defects are closely related to the pathogenicity of MYOC variants. Structural analysis showed that the alteration of steric clash is associated with the secretion characteristics and pathogenicity of myocilin variants. Immunocytochemistry results demonstrated that mutated myocilins are retained in the endoplasmic reticulum and disrupt autophagy. MTT assay, MitoTracker staining, and DCFH-DA staining showed increased oxidative injury in cells expressing MYOC mutants. Taken together, MYOC mutations are able to induce cell dysfunction via secretion defects and intracellular accumulation resulting from steric clash alterations.
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Affiliation(s)
- Biting Zhou
- Department of Ophthalmology, The First Affiliated Hospital of Fujian Medical University, Fuzhou, China
| | - Xiaojia Lin
- Department of Ophthalmology, The First Affiliated Hospital of Fujian Medical University, Fuzhou, China
| | - Zhong Li
- Department of Bioengineering and Biopharmaceutics, School of Pharmacy, Fujian Medical University, Fuzhou, China
| | - Yihua Yao
- Department of Ophthalmology, The First Affiliated Hospital of Fujian Medical University, Fuzhou, China
| | - Juhua Yang
- Department of Bioengineering and Biopharmaceutics, School of Pharmacy, Fujian Medical University, Fuzhou, China
- *Correspondence: Yihua Zhu, ; Juhua Yang,
| | - Yihua Zhu
- Department of Ophthalmology, The First Affiliated Hospital of Fujian Medical University, Fuzhou, China
- *Correspondence: Yihua Zhu, ; Juhua Yang,
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3
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Martin MD, Huard DJ, Guerrero-Ferreira RC, Desai IM, Barlow BM, Lieberman RL. Molecular architecture and modifications of full-length myocilin. Exp Eye Res 2021; 211:108729. [DOI: 10.1016/j.exer.2021.108729] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 07/26/2021] [Accepted: 08/12/2021] [Indexed: 01/06/2023]
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4
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Patterson-Orazem AC, Lieberman RL. Antibodies Used to Detect Glaucoma-Associated Myocilin: More or Less Than Meets the Eye? Invest Ophthalmol Vis Sci 2019; 60:2034-2037. [PMID: 31067323 PMCID: PMC6890424 DOI: 10.1167/iovs.19-26843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Antibodies are key reagents used in vision research, indeed across biomedical research, but they often do not reveal the whole story about a sample. It is important for researchers to be aware of aspects of antibodies that may affect or limit data interpretation. Federal agencies now require funded grants to demonstrate how they will authenticate reagents used. There is also a push for recombinant antibodies, enabled by phage display technology awarded the 2018 Nobel Prize in Chemistry, which allow for thorough validation and a fixed DNA sequence. Here, we discuss how issues surrounding antibodies are pertinent to detecting myocilin, a protein found in trabecular meshwork and associated with a portion of hereditary glaucoma. Confirmation of myocilin expression in tissues and cell culture has been adopted as validation standard in trabecular meshwork research; thus, a discussion of antibody characteristics and fidelity is critical. Further, based on our basic structural understanding of myocilin architecture and its biophysical aggregation properties, we provide a wish list for the characteristics of next-generation antibody reagents for vision researchers. In the long term, well-characterized antibodies targeting myocilin will enable new insights into its function and involvement in glaucoma pathogenesis.
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Affiliation(s)
- Athéna C Patterson-Orazem
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
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5
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Lynch JM, Dolman AJ, Guo C, Dolan K, Xiang C, Reda S, Li B, Prasanna G. Mutant myocilin impacts sarcomere ultrastructure in mouse gastrocnemius muscle. PLoS One 2018; 13:e0206801. [PMID: 30395621 PMCID: PMC6218065 DOI: 10.1371/journal.pone.0206801] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 10/19/2018] [Indexed: 11/19/2022] Open
Abstract
Myocilin (MYOC) is the gene with mutations most common in glaucoma. In the eye, MYOC is in trabecular meshwork, ciliary body, and retina. Other tissues with high MYOC transcript levels are skeletal muscle and heart. To date, the function of wild-type MYOC remains unknown and how mutant MYOC causes high intraocular pressure and glaucoma is ambiguous. By investigating mutant MYOC in a non-ocular tissue we hoped to obtain novel insight into mutant MYOC pathology. For this study, we utilized a transgenic mouse expressing human mutant MYOC Y437H protein and we examined its skeletal (gastrocnemius) muscle phenotype. Electron micrographs showed that sarcomeres in the skeletal muscle of mutant CMV-MYOC-Y437H mice had multiple M-bands. Western blots of soluble muscle lysates from transgenics indicated a decrease in two M-band proteins, myomesin 1 (MYOM1) and muscle creatine kinase (CKM). Immunoprecipitation identified CKM as a MYOC binding partner. Our results suggest that binding of mutant MYOC to CKM is changing sarcomere ultrastructure and this may adversely impact muscle function. We speculate that a person carrying the mutant MYOC mutation will likely have a glaucoma phenotype and may also have undiagnosed muscle ailments or vice versa, both of which will have to be monitored and treated.
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MESH Headings
- Animals
- Cytoskeletal Proteins/genetics
- Cytoskeletal Proteins/metabolism
- Disease Models, Animal
- Eye Proteins/genetics
- Eye Proteins/metabolism
- Female
- Gene Expression
- Glaucoma, Open-Angle/genetics
- Glaucoma, Open-Angle/metabolism
- Glaucoma, Open-Angle/pathology
- Glycoproteins/genetics
- Glycoproteins/metabolism
- Humans
- Intraocular Pressure/genetics
- Male
- Mice
- Mice, Mutant Strains
- Mice, Transgenic
- Microscopy, Electron, Transmission
- Muscle, Skeletal/metabolism
- Muscle, Skeletal/ultrastructure
- Mutant Proteins/genetics
- Mutant Proteins/metabolism
- Mutation
- Myocardium/metabolism
- Phenotype
- Recombinant Proteins/genetics
- Recombinant Proteins/metabolism
- Sarcomeres/genetics
- Sarcomeres/metabolism
- Sarcomeres/ultrastructure
- Trabecular Meshwork/metabolism
- Trabecular Meshwork/ultrastructure
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Affiliation(s)
- Jeffrey M. Lynch
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
- * E-mail:
| | - Andrew J. Dolman
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
| | - Chenying Guo
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
| | - Katie Dolan
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
| | - Chuanxi Xiang
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
| | - Samir Reda
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
| | - Bing Li
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
| | - Ganesh Prasanna
- Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, MA, United States of America
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6
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Lynch JM, Li B, Katoli P, Xiang C, Leehy B, Rangaswamy N, Saenz-Vash V, Wang YK, Lei H, Nicholson TB, Meredith E, Rice DS, Prasanna G, Chen A. Binding of a glaucoma-associated myocilin variant to the αB-crystallin chaperone impedes protein clearance in trabecular meshwork cells. J Biol Chem 2018; 293:20137-20156. [PMID: 30389787 DOI: 10.1074/jbc.ra118.004325] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 10/19/2018] [Indexed: 01/09/2023] Open
Abstract
Myocilin (MYOC) was discovered more than 20 years ago and is the gene whose mutations are most commonly observed in individuals with glaucoma. Despite extensive research efforts, the function of WT MYOC has remained elusive, and how mutant MYOC is linked to glaucoma is unclear. Mutant MYOC is believed to be misfolded within the endoplasmic reticulum, and under normal physiological conditions misfolded MYOC should be retro-translocated to the cytoplasm for degradation. To better understand mutant MYOC pathology, we CRISPR-engineered a rat to have a MYOC Y435H substitution that is the equivalent of the pathological human MYOC Y437H mutation. Using this engineered animal model, we discovered that the chaperone αB-crystallin (CRYAB) is a MYOC-binding partner and that co-expression of these two proteins increases protein aggregates. Our results suggest that the misfolded mutant MYOC aggregates with cytoplasmic CRYAB and thereby compromises protein clearance mechanisms in trabecular meshwork cells, and this process represents the primary mode of mutant MYOC pathology. We propose a model by which mutant MYOC causes glaucoma, and we propose that therapeutic treatment of patients having a MYOC mutation may focus on disrupting the MYOC-CRYAB complexes.
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Affiliation(s)
- Jeffrey M Lynch
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139.
| | - Bing Li
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Parvaneh Katoli
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Chuanxi Xiang
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Barrett Leehy
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Nalini Rangaswamy
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Veronica Saenz-Vash
- Analytical Sciences and Imaging, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Y Karen Wang
- Analytical Sciences and Imaging, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Hong Lei
- Laboratory Animal Services, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Thomas B Nicholson
- Chemical Biology and Therapeutics, and Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Erik Meredith
- Global Developmental Chemistry, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Dennis S Rice
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Ganesh Prasanna
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
| | - Amy Chen
- From Ophthalmology, Novartis Institutes for BioMedical Research, Cambridge, Massachusetts 02139
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7
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Patterson-Orazem AC, Hill SE, Fautsch MP, Lieberman RL. Epitope mapping of commercial antibodies that detect myocilin. Exp Eye Res 2018; 173:109-112. [PMID: 29752947 DOI: 10.1016/j.exer.2018.05.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Revised: 04/17/2018] [Accepted: 05/05/2018] [Indexed: 01/26/2023]
Abstract
The presence of myocilin is often used in the process of validating trabecular meshwork (TM) cells and eye tissues, but the antibody reagents used for detection are poorly characterized. Indeed, for over a century, researchers have been using antibodies to track proteins of interest in a variety of biological contexts, but many antibodies remain ill-defined at the molecular level and in their target epitope. Such issues have prompted efforts from major funding agencies to validate reagents and combat reproducibility issues across biomedical sciences. Here we characterize the epitopes recognized by four commercial myocilin antibodies, aided by structurally and biochemically characterized myocilin fragments. All four antibodies recognize enriched myocilin secreted from human TM cell media. The detection of myocilin fragments by ELISA and Western blot reveal a variety of epitopes across the myocilin polypeptide chain. A more precise understanding of myocilin antibody targets, including conformational specificity, should aid the community in standardizing protocols across laboratories and in turn, lead to a better understanding of eye physiology and disease.
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Affiliation(s)
- Athéna C Patterson-Orazem
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332-0400, United States
| | - Shannon E Hill
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332-0400, United States
| | - Michael P Fautsch
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, 55905, United States
| | - Raquel L Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332-0400, United States.
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8
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Full-length myocilin protein is purified from mammalian cells as a dimer. Protein Expr Purif 2018; 147:38-48. [PMID: 29475084 DOI: 10.1016/j.pep.2018.02.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2018] [Revised: 02/11/2018] [Accepted: 02/15/2018] [Indexed: 12/14/2022]
Abstract
Myocilin (MYOC) is a secreted protein found in human aqueous humor (AH) and mutations in the MYOC gene are the most common mutation observed in glaucoma patients. Human AH analyzed under non-reducing conditions suggests that MYOC is not normally found in a monomeric form, but rather is predominantly dimeric. Although MYOC was first reported almost 20 years ago, a technical challenge still faced by researchers is an inability to isolate full-length MYOC protein for experimental purposes. Herein we describe two methods by which to isolate sufficient quantities of human full-length MYOC protein from mammalian cells. One method involved identification of a cell line (HeLa S3) that would secrete full-length protein (15 mg/L) while the second method involved a purification approach from 293 cells requiring identification and modification of an internal MYOC cleavage site (Glu214/Leu215). MYOC protein yield from 293 cells was improved by mutation of two MYOC N-terminal cysteines (C47 and C61) to serines. Analytical size exclusion chromatography of our full-length MYOC protein purified from 293 cells indicated that it is predominantly dimeric and we propose a structure for the MYOC dimer. We hope that by providing methods to obtain MYOC protein, researchers will be able to utilize the protein to obtain new insights into MYOC biology. The ultimate goal of MYOC research is to better understand this target so we can help the patient that carries a MYOC mutation retain vision and maintain quality of life.
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9
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Jain A, Zode G, Kasetti RB, Ran FA, Yan W, Sharma TP, Bugge K, Searby CC, Fingert JH, Zhang F, Clark AF, Sheffield VC. CRISPR-Cas9-based treatment of myocilin-associated glaucoma. Proc Natl Acad Sci U S A 2017; 114:11199-11204. [PMID: 28973933 PMCID: PMC5651749 DOI: 10.1073/pnas.1706193114] [Citation(s) in RCA: 108] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Primary open-angle glaucoma (POAG) is a leading cause of irreversible vision loss worldwide, with elevated intraocular pressure (IOP) a major risk factor. Myocilin (MYOC) dominant gain-of-function mutations have been reported in ∼4% of POAG cases. MYOC mutations result in protein misfolding, leading to endoplasmic reticulum (ER) stress in the trabecular meshwork (TM), the tissue that regulates IOP. We use CRISPR-Cas9-mediated genome editing in cultured human TM cells and in a MYOC mouse model of POAG to knock down expression of mutant MYOC, resulting in relief of ER stress. In vivo genome editing results in lower IOP and prevents further glaucomatous damage. Importantly, using an ex vivo human organ culture system, we demonstrate the feasibility of human genome editing in the eye for this important disease.
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Affiliation(s)
- Ankur Jain
- Department of Pediatrics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242
| | - Gulab Zode
- North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, TX 76107;
| | - Ramesh B Kasetti
- North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, TX 76107
| | - Fei A Ran
- McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Winston Yan
- McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Tasneem P Sharma
- Stephen A. Wynn Institute for Vision Research, Department of Ophthalmology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242
| | - Kevin Bugge
- Department of Pediatrics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242
| | - Charles C Searby
- Department of Pediatrics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242
| | - John H Fingert
- Stephen A. Wynn Institute for Vision Research, Department of Ophthalmology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242
| | - Feng Zhang
- McGovern Institute for Brain Research, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Abbot F Clark
- North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, TX 76107
| | - Val C Sheffield
- Department of Pediatrics, Carver College of Medicine, University of Iowa, Iowa City, IA 52242;
- Stephen A. Wynn Institute for Vision Research, Department of Ophthalmology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242
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10
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Kwon HS, Tomarev SI. Myocilin, a glaucoma-associated protein, promotes cell migration through activation of integrin-focal adhesion kinase-serine/threonine kinase signaling pathway. J Cell Physiol 2011; 226:3392-402. [PMID: 21656515 DOI: 10.1002/jcp.22701] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The MYOCILIN gene encodes a secreted glycoprotein which is highly expressed in eye drainage structures. Mutations in this gene may lead to juvenile open-angle glaucoma and adult onset primary open-angle glaucoma, one of the leading causes of irreversible blindness in the world. Functions of wild-type myocilin are still unclear. We have recently demonstrated that myocilin is a modulator of Wnt signaling and may affect actin cytoskeleton organization. Here we report that myocilin and its naturally occurring proteolytic fragments, similar to Wnt3a, are able to stimulate trabecular meshwork, NIH3T3, and FHL124 cell migration with the N-terminal proteolytic fragment of myocilin lacking the olfactomedin domain producing the highest stimulatory effect. Stimulation of cell migration occurs through activation of the integrin-focal adhesion kinase (FAK)-serine/threonine kinase (AKT) signaling pathway. Inhibition of FAK by siRNA reduced the stimulatory action of myocilin by threefold. Activation of several components of this signaling pathway was also demonstrated in the eyes of transgenic mice expressing elevated levels of myocilin in the eye drainage structures. These data extend the similarities between actions of myocilin and Wnt proteins acting through a β-catenin-independent mechanism. The modification of the migratory ability of cells by myocilin may play a role in normal functioning of the eye anterior segment and its pathology including glaucoma.
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Affiliation(s)
- Heung Sun Kwon
- Molecular Mechanisms of Glaucoma Section, Laboratory of Molecular and Developmental Biology, National Eye Institute, NIH, Bethesda, Maryland 20892-9303, USA
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11
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Sohn S, Joe MK, Kim TE, Im JE, Choi YR, Park H, Kee C. Dual localization of wild-type myocilin in the endoplasmic reticulum and extracellular compartment likely occurs due to its incomplete secretion. Mol Vis 2009; 15:545-56. [PMID: 19287508 PMCID: PMC2654785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2008] [Accepted: 03/09/2009] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Wild-type myocilin is known to be secreted extracellularly, but a significant amount of the protein is also present in the endoplasmic reticulum (ER). The present study was undertaken to address whether intracellular myocilin is a true ER resident protein. METHODS Human wild-type myocilin was adenovirally expressed in human trabecular meshwork cells, and general characteristics of both intracellular and extracellular myocilins including molecular weight, pI, glycosylation state, and cleavage site of the signal peptide were examined by biochemical analyses. Topology and decay kinetics of myocilin were also examined by protease protection assay and pulse chase analysis, respectively. The expression pattern and cytopathic effect of myocilin were analyzed in individual cells by immunocytochemistry. RESULTS Intracellular myocilin were very similar to secreted myocilin in characteristics such as molecular weight, pI, glycosylation state, and cleavage site of the signal peptide. The intracellular protein was found to be present in the lumen of the ER where it appeared to be retained without further export to the Golgi apparatus. The kinetics of myocilin turnover clearly showed that it was intrinsically a very stable but incompletely secreted protein. The expression of myocilin was confined to a subset of cells and accompanied by the upregulation of a 78 kDa glucose-regulated protein, suggesting that it was not properly folded or processed in the ER. CONCLUSIONS Based on these findings and the fact that myocilin has no known ER retention signals, the ER localization of wild-type myocilin is likely a consequence of its incomplete secretion due to its misfolding.
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Affiliation(s)
- Seongsoo Sohn
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea
| | - Myung Kuk Joe
- Center for Clinical Research, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, South Korea
| | - Tae Eun Kim
- Center for Clinical Research, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, South Korea
| | - Ji-eun Im
- Center for Clinical Research, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, South Korea
| | - Young Ran Choi
- Center for Clinical Research, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, South Korea
| | - Hwayong Park
- Department of Medical Research, Korea Institute of Oriental Medicine, Daejeon, South Korea
| | - Changwon Kee
- Department of Ophthalmology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea,Center for Clinical Research, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, South Korea
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12
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MacKay EO, Källberg ME, Gelatt KN. Aqueous humor myocilin protein levels in normal, genetic carriers, and glaucoma Beagles. Vet Ophthalmol 2008; 11:177-85. [DOI: 10.1111/j.1463-5224.2008.00617.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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13
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Kato K, Sasaki N, Matsunaga S, Nishimura R, Ogawa H. Cloning of canine myocilin cDNA and molecular analysis of the myocilin gene in Shiba Inu dogs. Vet Ophthalmol 2008; 10 Suppl 1:53-62. [PMID: 17973835 DOI: 10.1111/j.1463-5224.2007.00530.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE To identify canine myocilin cDNA and compare its sequence in glaucomatous and nonglaucomatous Shiba Inu dogs with closed and open iridocorneal angles (ICAs). PROCEDURES Total RNA was extracted from the ciliary body of the eyes of a healthy Beagle, and the canine myocilin gene was cloned and sequenced. Of the Shiba Inu dogs tested, five were glaucomatous with closed ICA, three were nonglaucomatous with open ICA, and two were nonglaucomatous with closed ICA. The genomic DNA of these dogs was extracted from peripheral blood leukocytes. The exons of the canine myocilin gene were amplified using the polymerase chain reaction (PCR), and sequenced. The frequency of mutation in canine myocilin DNA was verified in these dogs by using the myocilin cDNA of a Beagle. RESULTS The canine myocilin cDNA was 1452 bp long and contained the entire open reading frame encoding 483 amino acids. A leucine zipper-like motif and olfactomedin-like domain were conserved in the amino acid residues. The presence of sequence variants in the genomic DNA of Shiba Inu dogs was independent of the occurrence of glaucoma and ICA grading. CONCLUSIONS Myocilin RNA was detected in the ciliary body and trabecular meshwork (TM) of a Beagle. The myocilin sequence of Shiba Inu dogs suggests that myocilin mutations are unlikely to play a significant role in the pathogenesis of primary closed-angle glaucoma in this breed. However, several mutations in the myocilin gene in exon 1 of Shiba Inu dogs may predispose them to an obstruction in the anterior aqueous outflow.
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Affiliation(s)
- Kumiko Kato
- The Laboratory of Veterinary Emergency Medicine, Graduate School of Agricultural and Life Sciences, the University of Tokyo, Tokyo, Japan
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15
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Oezbey S, Stengel C, Schlötzer-Schrehardt U, Ekici A, Rautenstrauss B. Heterologous expression of wildtype and mutant myocilin in High Five insect cells shows comparable effects to cultivated trabecular meshwork cells. ACTA ACUST UNITED AC 2007; 24:313-7. [PMID: 17597001 DOI: 10.1016/j.bioeng.2007.05.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2006] [Revised: 05/11/2007] [Accepted: 05/22/2007] [Indexed: 10/23/2022]
Abstract
Myocilin (MYOC, TIGR) variations are associated with juvenile and primary open angle glaucoma (POAG). To investigate consequences of MYOC wildtype overexpression and selected mutations, we established a heterologous insect cell system (High Five). Wildtype, Pro370Leu, Gln368X and Lys423Glu were cloned into a modified pIB/V5-His (pEXIV) vector with and without downstream GFP in frame fusion. Mutations were introduced by in vitro mutagenesis. Heterologous expression was shown and analysed by RT-PCR, Western blotting, immunocytochemistry and fluorescence microscopy. Extended cultivation (>14 days) resulted in accumulation of MYOC protein for all variants in growing dilated cisterns of the rough endoplasmic reticulum. Finally cell death for overexpressed wildtype and mutants occurs. A direct attachment of ribosomes to these growing vesicles preceding the cell death was observed by electron microscopy. Our observations indicate that this system is suitable to trace the intracellular effects of MYOC mutants.
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Affiliation(s)
- Sevinc Oezbey
- University Hospital Erlangen, Institute of Human Genetics, Schwabachanlage 10, 91054, Erlangen, Germany
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Sakai H, Shen X, Koga T, Park BC, Noskina Y, Tibudan M, Yue BYJT. Mitochondrial association of myocilin, product of a glaucoma gene, in human trabecular meshwork cells. J Cell Physiol 2007; 213:775-84. [PMID: 17516541 DOI: 10.1002/jcp.21147] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The trabecular meshwork (TM), an ocular tissue next to the cornea, is a major site for regulation of the aqueous humor outflow. Malfunctioning of this tissue is believed to be responsible for development of glaucoma, a major blinding disease. Myocilin is a gene directly linked to the most common form of glaucoma. Its protein product has been localized to both intra- and extra-cellular sites in TM cells. This study was to investigate the association of myocilin with mitochondria in TM cells. In vitro mitochondrial import assays showed that myocilin was imported to the TM mitochondria, targeting to mitochondrial membranes and/or the intermembrane space. The targeting was mediated mostly via the amino-terminal region of myocilin. When myocilin expression was induced either by treatment with dexamethasone or transfection with a myocilin construct, the mitochondrial membrane potential in TM cells, as assessed by JC-1 staining, was lowered. Subcellular fractionation and Western blot analyses confirmed that a portion of myocilin sedimented with the mitochondrial fractions. Upon anti-Fas treatment to provoke apoptosis, an increase of myocilin distribution in cytosolic fraction was observed, suggesting that myocilin was partially released from mitochondrial compartments. These results confirmed the association of myocilin with TM cell mitochondria and indicated that myocilin may have a proapoptotic role in TM cells.
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Affiliation(s)
- Hiroshi Sakai
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60612, USA
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Park BC, Shen X, Fautsch MP, Tibudan M, Johnson DH, Yue BYJT. Optimized bacterial expression of myocilin proteins and functional comparison of bacterial and eukaryotic myocilins. Mol Vis 2006; 12:832-40. [PMID: 16902400 PMCID: PMC2077819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023] Open
Abstract
PURPOSE To maximize the expression level of myocilin and its truncated proteins in Escherichia coli (E. coli) and to examine the biological effects of bacterially expressed myocilin as compared to eukaryotic myocilin on cultured human trabecular meshwork (TM) cells. METHODS Myocilin full length (1-504 amino acids) and two truncated proteins, myocilin 1-270 and 271-504, were expressed and purified from an E. coli strain, Rosetta2(DE3)pLysS. The eukaryotic myocilin was purified from cultured medium of a transformed TM cell line (TM5) transduced with feline immunodeficiency virus that contains an internal cassette expressing full length myocilin. The morphology and adhesion of human TM cells plated either on fibronectin alone or on fibronectin/purified myocilin mixtures were assessed by phase contrast microscopy. Actin cytoskeleton was examined using Oregon Green phalloidin. Immunofluorescence staining for paxillin was also performed. RESULTS The expression of full length and truncated myocilin proteins in Rosetta2(DE3)pLysS was markedly increased especially when the bacteria were grown in media supplemented with 1.0% glucose. Cell adhesion was impaired and microspikes were formed when TM cells were plated onto fibronectin/bacterial full length myocilin mixtures. Loss of actin stress fibers and focal adhesions was also observed. This myocilin phenotype was also seen with myocilin 1-270, but not with myocilin 271-504. The eukaryotic full length myocilin produced nearly identical de-adhesive effects as those of the bacterially expressed myocilin. CONCLUSIONS The condition for a high level expression of full length and truncated myocilins in E. coli was optimized. The bacterial and eukaryotic recombinant full length myocilin produced similar biological consequence on TM cells. The myocilin phenotype appears to be largely due to the NH(2)-terminal half of the protein.
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Affiliation(s)
- Bum-Chan Park
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago College of Medicine, Chicago, IL 60612, USA
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Fautsch MP, Vrabel AM, Johnson DH. Characterization of the Felix domesticus (cat) glaucoma-associated protein myocilin. Exp Eye Res 2006; 82:1037-45. [PMID: 16289048 DOI: 10.1016/j.exer.2005.08.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Revised: 08/29/2005] [Accepted: 08/29/2005] [Indexed: 11/18/2022]
Abstract
The domestic cat (Felix domesticus) is a useful model for understanding the implications of long-term expression and function of normal and mutant myocilin. To better understand the role myocilin has in the cat eye, we isolated and characterized cat myocilin. Oligonucleotides designed against conserved nucleotide regions of myocilin mammalian orthologs were used to PCR amplify a partial cat myocilin cDNA clone. Rapid amplification of cDNA ends (5' and 3' RACE) was used to obtain full-length cat myocilin. The 2125 nucleotide cat myocilin cDNA contains a 490 amino acid open reading frame. Comparison of cat myocilin to human myocilin shows a 87% similarity, including conservation of the N-terminal leucine zipper, N-linked glycosylation site, C-terminal olfactomedin domain, and all five cysteine residues thought to be involved in disulfide bond formation. Expression in a transformed human trabecular cell line or in Crandall feline kidney cells showed cat myocilin was secreted from these cells, similar to human myocilin, suggesting cat myocilin contains a functional signal peptide sequence. In contrast, expression of cat myocilin containing a known human glaucoma-associated mutation (Y423H in cat; Y437H in human) was not secreted. Characterization of cat myocilin will enable long-term studies be performed in Felix domesticus to analyze changes to intraocular pressure and the aqueous outflow pathway following expression of myocilin and glaucoma causing mutations.
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Affiliation(s)
- Michael P Fautsch
- Department of Ophthalmology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
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Gobeil S, Letartre L, Raymond V. Functional analysis of the glaucoma-causing TIGR/myocilin protein: Integrity of amino-terminal coiled-coil regions and olfactomedin homology domain is essential for extracellular adhesion and secretion. Exp Eye Res 2006; 82:1017-29. [PMID: 16466712 DOI: 10.1016/j.exer.2005.11.002] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2005] [Revised: 11/11/2005] [Accepted: 11/16/2005] [Indexed: 11/29/2022]
Abstract
TIGR/MYOC mutations account for 2-4% of the primary open-angle glaucoma (POAG) patients. More than 90% of the known mutations are located within its carboxy-terminus olfactomedin-homology (Olf) domain (amino acids (aa) 245-504). In vitro and in vivo studies showed that several Olf domain mutations prevented myocilin secretion. To investigate if intracellular sequestration was a characteristic feature shared by a majority of the mutations, we analyzed the secretion status of 36 myocilin variants. These encompassed 26 glaucoma-causing mutations and 10 non-disease associated or undefined polymorphisms. As several variants were found to be secreted, we tested for their adhesion to the extracellular matrix (ECM) and/or cell surface. Myocilin variants were generated by site-directed mutagenesis of a vector encoding the human MYOC cDNA. COS-7 or immortalized human trabecular meshwork cells were transfected with wild-type or mutated MYOC constructs. Myocilin levels were estimated by immunoprecipitation and/or immunoblotting. All variants showed identical behaviors in both cell lines; the truncated R46X polypeptide being the only variant which could not be detected in our assays. Of the 35 variants monitored, 20 remained sequestered intracellularly. All of them encoded disease-causing polypeptides carrying Olf domain mutations. Of the 15 variants secreted into the culture medium, six (6) were POAG mutants (of which three (3) located within the Olf domain) while the remaining nine (9) were non-disease causing or undefined polymorphisms. Three (3) of the six (6) secreted mutations caused familial POAG; these were the R126W, T377M and A427T mutants. Both, the T377M and A427T mutants located within the Olf domain. When cells were cultured at 30 degrees C, a process known to facilitate protein folding, 11 of the 20 sequestered mutants were released in the extracellular medium. Out of the 15 secreted variants tested for their adhesion to the ECM and/or cell surface, only the R82C and L95P polypeptides displayed loss of their adhesive properties. Deletion experiments revealed that the coiled-coil (aa 78-105) and leucine zipper (aa 114-183) motifs were essential for adhesion. These experiments demonstrate that intracellular sequestration might be the primary mechanism contributing to myocilin-related POAG as it was associated with more than 80% of the disease-causing mutants tested in our study. A second mechanism may involve abnormal interaction(s) between myocilin and ECM and/or cell surface proteins. Our data further revealed the importance of the olfactomedin-homology domain for myocilin secretion and the significant role of the N-terminal region for its extracellular interactions.
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Affiliation(s)
- Stéphane Gobeil
- Laboratory of Ocular Genetics and Genomics, Molecular Endocrinology and Oncology Research Center, Laval University Hospital (CHUL) Research Center, 2705 Laurier Boulevard, Room T3-67, Quebec City, Prov. of Québec, Canada G1V 4G2
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Surgucheva I, Park BC, Yue BYJT, Tomarev S, Surguchov A. Interaction of myocilin with gamma-synuclein affects its secretion and aggregation. Cell Mol Neurobiol 2006; 25:1009-33. [PMID: 16392033 DOI: 10.1007/s10571-005-8471-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2005] [Accepted: 04/12/2005] [Indexed: 10/25/2022]
Abstract
Mutations in the gene encoding human myocilin are associated with some cases of juvenile and early-onset glaucoma. Glaucomatous mutations prevent myocilin from being secreted. The analysis of the defects associated with mutations point to the existence of factor(s) in addition to mutations that might be implicated in the development of glaucoma. In the present paper, we found that interaction of myocilin with one of the members of the synuclein family alters its properties, including its ability to be secreted. Results of immunoprecipitation show that myocilin is a gamma-synuclein-interacting protein. Further analysis demonstrated that both myocilin and gamma-synuclein are expressed in human TM cells, immortalized rat ganglion (RGC-5) cells, and HT22 hippocampal neurons. According to Western blotting, in addition to monomeric form with molecular weight 17 kDa gamma-synuclein is present as higher molecular weight forms ( approximately 35 and 68 KDa), presumably dimer and tetramer. Myocilin and gamma-synuclein have partially overlapping perinuclear localization. Dexamethasone upregulates myocilin expression in RGC-5 cells and HT22 hippocampal neurons. We found alterations of myocilin properties as a result of its interaction with gamma-synuclein. In cultured cells, gamma-synuclein upregulates myocilin expression, inhibits its secretion and prevents the formation of high molecular weight forms of myocilin. Although both alpha-synuclein and gamma-synuclein are expressed in HTM cells, only gamma-synuclein interacts with myocilin and alters its properties. We conclude that myocilin and gamma-synuclein interact and as a result, myocilin's properties are changed. Since myocilin and gamma-synuclein have partially overlapping intracellular localization in cell types that are implicated in glaucoma development, their interaction may play an important role in glaucoma.
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Affiliation(s)
- Irina Surgucheva
- Retinal Disease Research Laboratory, Veterans Administration Medical Center, 4801 Linwood Blvd, Kansas City, MO 66148, USA
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