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Ohnsorg ML, Mash KM, Khang A, Rao VV, Kirkpatrick BE, Bera K, Anseth KS. Nonlinear Elastic Bottlebrush Polymer Hydrogels Modulate Actomyosin Mediated Protrusion Formation in Mesenchymal Stromal Cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024:e2403198. [PMID: 38655776 DOI: 10.1002/adma.202403198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2024] [Revised: 04/19/2024] [Indexed: 04/26/2024]
Abstract
The nonlinear elasticity of many tissue-specific extracellular matrices is difficult to recapitulate without the use of fibrous architectures, which couple strain-stiffening with stress relaxation. Herein, bottlebrush polymers are synthesized and crosslinked to form poly(ethylene glycol)-based hydrogels and used to study how strain-stiffening behavior affects human mesenchymal stromal cells (hMSCs). By tailoring the bottlebrush polymer length, the critical stress associated with the onset of network stiffening is systematically varied, and a unique protrusion-rich hMSC morphology emerges only at critical stresses within a biologically accessible stress regime. Local cell-matrix interactions are quantified using 3D traction force microscopy and small molecule inhibitors are used to identify cellular machinery that plays a critical role in hMSC mechanosensing of the engineered, strain-stiffening microenvironment. Collectively, this study demonstrates how covalently crosslinked bottlebrush polymer hydrogels can recapitulate strain-stiffening biomechanical cues at biologically relevant stresses and be used to probe how nonlinear elastic matrix properties regulate cellular processes.
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Affiliation(s)
- Monica L Ohnsorg
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, 80308, USA
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, 80308, USA
| | - Kayla M Mash
- Department of Biochemistry, University of Colorado Boulder, Boulder, CO, 80308, USA
| | - Alex Khang
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, 80308, USA
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, 80308, USA
| | - Varsha V Rao
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, 80308, USA
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, 80308, USA
| | - Bruce E Kirkpatrick
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, 80308, USA
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, 80308, USA
- Medical Scientist Training Program, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Kaustav Bera
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, 80308, USA
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, 80308, USA
| | - Kristi S Anseth
- Department of Chemical and Biological Engineering, University of Colorado Boulder, Boulder, CO, 80308, USA
- BioFrontiers Institute, University of Colorado Boulder, Boulder, CO, 80308, USA
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Khang A, Meyer K, Sacks MS. An Inverse Modeling Approach to Estimate Three-Dimensional Aortic Valve Interstitial Cell Stress Fiber Force Levels. J Biomech Eng 2023; 145:121005. [PMID: 37715307 PMCID: PMC10680985 DOI: 10.1115/1.4063436] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 08/18/2023] [Accepted: 08/21/2023] [Indexed: 09/17/2023]
Abstract
Within the aortic valve (AV) leaflet exists a population of interstitial cells (AVICs) that maintain the constituent tissues by extracellular matrix (ECM) secretion, degradation, and remodeling. AVICs can transition from a quiescent, fibroblast-like phenotype to an activated, myofibroblast phenotype in response to growth or disease. AVIC dysfunction has been implicated in AV disease processes, yet our understanding of AVIC function remains quite limited. A major characteristic of the AVIC phenotype is its contractile state, driven by contractile forces generated by the underlying stress fibers (SF). However, direct assessment of the AVIC SF contractile state and structure within physiologically mimicking three-dimensional environments remains technically challenging, as the size of single SFs are below the resolution of light microscopy. Therefore, in the present study, we developed a three-dimensional (3D) computational approach of AVICs embedded in 3D hydrogels to estimate their SF local orientations and contractile forces. One challenge with this approach is that AVICs will remodel the hydrogel, so that the gel moduli will vary spatially. We thus utilized our previous approach (Khang et al. 2023, "Estimation of Aortic Valve Interstitial Cell-Induced 3D Remodeling of Poly (Ethylene Glycol) Hydrogel Environments Using an Inverse Finite Element Approach," Acta Biomater., 160, pp. 123-133) to define local hydrogel mechanical properties. The AVIC SF model incorporated known cytosol and nucleus mechanical behaviors, with the cell membrane assumed to be perfectly bonded to the surrounding hydrogel. The AVIC SFs were first modeled as locally unidirectional hyperelastic fibers with a contractile force component. An adjoint-based inverse modeling approach was developed to estimate local SF orientation and contractile force. Substantial heterogeneity in SF force and orientations were observed, with the greatest levels of SF alignment and contractile forces occurring in AVIC protrusions. The addition of a dispersed SF orientation to the modeling approach did not substantially alter these findings. To the best of our knowledge, we report the first fully 3D computational contractile cell models which can predict locally varying stress fiber orientation and contractile force levels.
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Affiliation(s)
- Alex Khang
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences, Austin, TX 78712; Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229
| | - Kenneth Meyer
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences, Austin, TX 78712; Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229
| | - Michael S Sacks
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences, Austin, TX 78712; Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229
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Tuscher R, Khang A, West TM, Camillo C, Ferrari G, Sacks MS. Functional differences in human aortic valve interstitial cells from patients with varying calcific aortic valve disease. Front Physiol 2023; 14:1168691. [PMID: 37405132 PMCID: PMC10316512 DOI: 10.3389/fphys.2023.1168691] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 05/16/2023] [Indexed: 07/06/2023] Open
Abstract
Calcific aortic valve disease (CAVD) is characterized by progressive stiffening of aortic valve (AV) tissues, inducing stenosis and insufficiency. Bicuspid aortic valve (BAV) is a common congenital defect in which the AV has two leaflets rather than three, with BAV patients developing CAVD decades years earlier than in the general population. Current treatment for CAVD remains surgical replacement with its continued durability problems, as there are no pharmaceutical therapies or other alternative treatments available. Before such therapeutic approaches can be developed, a deeper understanding of CAVD disease mechanisms is clearly required. It is known that AV interstitial cells (AVICs) maintain the AV extracellular matrix and are typically quiescent in the normal state, transitioning into an activated, myofibroblast-like state during periods of growth or disease. One proposed mechanism of CAVD is the subsequent transition of AVICs into an osteoblast-like phenotype. A sensitive indicator of AVIC phenotypic state is enhanced basal contractility (tonus), so that AVICs from diseased AV will exhibit a higher basal tonus level. The goals of the present study were thus to assess the hypothesis that different human CAVD states lead to different biophysical AVIC states. To accomplish this, we characterized AVIC basal tonus behaviors from diseased human AV tissues embedded in 3D hydrogels. Established methods were utilized to track AVIC-induced gel displacements and shape changes after the application of Cytochalasin D (an actin polymerization inhibitor) to depolymerize the AVIC stress fibers. Results indicated that human diseased AVICs from the non-calcified region of TAVs were significantly more activated than AVICs from the corresponding calcified region. In addition, AVICs from the raphe region of BAVs were more activated than from the non-raphe region. Interestingly, we observed significantly greater basal tonus levels in females compared to males. Furthermore, the overall AVIC shape changes after Cytochalasin suggested that AVICs from TAVs and BAVs develop different stress fiber architectures. These findings are the first evidence of sex-specific differences in basal tonus state in human AVICs in varying disease states. Future studies are underway to quantify stress fiber mechanical behaviors to further elucidate CAVD disease mechanisms.
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Affiliation(s)
- Robin Tuscher
- Department of Biomedical Engineering, James T. Willerson Center for Cardiovascular Modeling and Simulation, The Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, United States
| | - Alex Khang
- Department of Biomedical Engineering, James T. Willerson Center for Cardiovascular Modeling and Simulation, The Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, United States
| | - Toni M. West
- Department of Biomedical Engineering, James T. Willerson Center for Cardiovascular Modeling and Simulation, The Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, United States
| | - Chiara Camillo
- Department of Surgery, The Seymour Cohn Cardiovascular Research Laboratory, Columbia University, New York, NY, United States
| | - Giovanni Ferrari
- Department of Surgery, The Seymour Cohn Cardiovascular Research Laboratory, Columbia University, New York, NY, United States
| | - Michael S. Sacks
- Department of Biomedical Engineering, James T. Willerson Center for Cardiovascular Modeling and Simulation, The Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, TX, United States
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West TM, Howsmon DP, Massidda MW, Vo HN, Janobas AA, Baker AB, Sacks MS. The effects of strain history on aortic valve interstitial cell activation in a 3D hydrogel environment. APL Bioeng 2023; 7:026101. [PMID: 37035541 PMCID: PMC10076067 DOI: 10.1063/5.0138030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 03/13/2023] [Indexed: 04/05/2023] Open
Abstract
Aortic valves (AVs) undergo unique stretch histories that include high rates and magnitudes. While major differences in deformation patterns have been observed between normal and congenitally defective bicuspid aortic valves (BAVs), the relation to underlying mechanisms of rapid disease onset in BAV patients remains unknown. To evaluate how the variations in stretch history affect AV interstitial cell (AVIC) activation, high-throughput methods were developed to impart varied cyclical biaxial stretch histories into 3D poly(ethylene) glycol hydrogels seeded with AVICs for 48 h. Specifically, a physiologically mimicking stretch history was compared to two stretch histories with varied peak stretch and stretch rate. Post-conditioned AVICs were imaged for nuclear shape, alpha smooth muscle actin (αSMA) and vimentin (VMN) polymerization, and small mothers against decapentaplegic homologs 2 and 3 (SMAD 2/3) nuclear activity. The results indicated that bulk gel deformations were accurately transduced to the AVICs. Lower peak stretches lead to increased αSMA polymerization. In contrast, VMN polymerization was a function of stretch rate, with SMAD 2/3 nuclear localization and nuclear shape also trending toward stretch rate dependency. Lower than physiological levels of stretch rate led to higher SMAD 2/3 activity, higher VMN polymerization around the nucleus, and lower nuclear elongation. αSMA polymerization did not correlate with VMN polymerization, SMAD 2/3 activity, nor nuclear shape. These results suggest that a negative feedback loop may form between SMAD 2/3, VMN, and nuclear shape to maintain AVIC homeostatic nuclear deformations, which is dependent on stretch rate. These novel results suggest that AVIC mechanobiological responses are sensitive to stretch history and provide insight into the mechanisms of AV disease.
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Affiliation(s)
- Toni M. West
- James T. Willerson Center for Cardiovascular Modelling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, Austin, Texas 78711, USA
| | - Daniel P. Howsmon
- James T. Willerson Center for Cardiovascular Modelling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, Austin, Texas 78711, USA
| | - Miles W. Massidda
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas 78711, USA
| | | | | | - Aaron B. Baker
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, Texas 78711, USA
| | - Michael S. Sacks
- James T. Willerson Center for Cardiovascular Modelling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, Austin, Texas 78711, USA
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Khang A, Steinman J, Tuscher R, Feng X, Sacks MS. Estimation of aortic valve interstitial cell-induced 3D remodeling of poly(ethylene glycol) hydrogel environments using an inverse finite element approach. Acta Biomater 2023; 160:123-133. [PMID: 36812955 DOI: 10.1016/j.actbio.2023.01.043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Revised: 01/16/2023] [Accepted: 01/19/2023] [Indexed: 02/24/2023]
Abstract
Aortic valve interstitial cells (AVICs) reside within the leaflet tissues of the aortic valve and maintain and remodel its extracellular matrix components. Part of this process is a result of AVIC contractility brought about by underlying stress fibers whose behaviors can change in various disease states. Currently, it is challenging to directly investigate AVIC contractile behaviors within dense leaflet tissues. As a result, optically clear poly (ethylene glycol) hydrogel matrices have been used to study AVIC contractility via 3D traction force microscopy (3DTFM). However, the local stiffness of the hydrogel is difficult to measure directly and is further confounded by the remodeling activity of the AVIC. Ambiguity in hydrogel mechanics can lead to large errors in computed cellular tractions. Herein, we developed an inverse computational approach to estimate AVIC-induced remodeling of the hydrogel material. The model was validated with test problems comprised of an experimentally measured AVIC geometry and prescribed modulus fields containing unmodified, stiffened, and degraded regions. The inverse model estimated the ground truth data sets with high accuracy. When applied to AVICs assessed via 3DTFM, the model estimated regions of significant stiffening and degradation in the vicinity of the AVIC. We observed that stiffening was largely localized at AVIC protrusions, likely a result of collagen deposition as confirmed by immunostaining. Degradation was more spatially uniform and present in regions further away from the AVIC, likely a result of enzymatic activity. Looking forward, this approach will allow for more accurate computation of AVIC contractile force levels. STATEMENT OF SIGNIFICANCE: The aortic valve (AV), positioned between the left ventricle and the aorta, prevents retrograde flow into the left ventricle. Within the AV tissues reside a resident population of aortic valve interstitial cells (AVICs) that replenish, restore, and remodel extracellular matrix components. Currently, it is technically challenging to directly investigate AVIC contractile behaviors within the dense leaflet tissues. As a result, optically clear hydrogels have been used to study AVIC contractility through means of 3D traction force microscopy. Herein, we developed a method to estimate AVIC-induced remodeling of PEG hydrogels. This method was able to accurately estimate regions of significant stiffening and degradation induced by the AVIC and allows a deeper understanding of AVIC remodeling activity, which can differ in normal and disease conditions.
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Affiliation(s)
- Alex Khang
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229, USA
| | - John Steinman
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229, USA
| | - Robin Tuscher
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229, USA
| | - Xinzeng Feng
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229, USA
| | - Michael S Sacks
- James T. Willerson Center for Cardiovascular Modeling and Simulation, Oden Institute for Computational Engineering and Sciences and the Department of Biomedical Engineering, The University of Texas at Austin, 201 East 24th St, Stop C0200, Austin, TX 78712-1229, USA.
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Mechanosensor YAP cooperates with TGF-β1 signaling to promote myofibroblast activation and matrix stiffening in a 3D model of human cardiac fibrosis. Acta Biomater 2022; 152:300-312. [DOI: 10.1016/j.actbio.2022.08.063] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Revised: 08/25/2022] [Accepted: 08/25/2022] [Indexed: 01/03/2023]
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Hillsley A, Santoso MS, Engels SM, Halwachs KN, Contreras LM, Rosales AM. A strategy to quantify myofibroblast activation on a continuous spectrum. Sci Rep 2022; 12:12239. [PMID: 35851602 PMCID: PMC9293987 DOI: 10.1038/s41598-022-16158-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Accepted: 07/05/2022] [Indexed: 12/04/2022] Open
Abstract
Myofibroblasts are a highly secretory and contractile cell phenotype that are predominant in wound healing and fibrotic disease. Traditionally, myofibroblasts are identified by the de novo expression and assembly of alpha-smooth muscle actin stress fibers, leading to a binary classification: "activated" or "quiescent (non-activated)". More recently, however, myofibroblast activation has been considered on a continuous spectrum, but there is no established method to quantify the position of a cell on this spectrum. To this end, we developed a strategy based on microscopy imaging and machine learning methods to quantify myofibroblast activation in vitro on a continuous scale. We first measured morphological features of over 1000 individual cardiac fibroblasts and found that these features provide sufficient information to predict activation state. We next used dimensionality reduction techniques and self-supervised machine learning to create a continuous scale of activation based on features extracted from microscopy images. Lastly, we compared our findings for mechanically activated cardiac fibroblasts to a distribution of cell phenotypes generated from transcriptomic data using single-cell RNA sequencing. Altogether, these results demonstrate a continuous spectrum of myofibroblast activation and provide an imaging-based strategy to quantify the position of a cell on that spectrum.
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Affiliation(s)
- Alexander Hillsley
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX, USA
| | - Matthew S Santoso
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX, USA
| | - Sean M Engels
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX, USA
| | - Kathleen N Halwachs
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX, USA
| | - Lydia M Contreras
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX, USA
| | - Adrianne M Rosales
- McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, TX, USA.
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