3D Contractile and Remodeling Behaviors of Functionally Normal and Prolapsed Human Mitral Valve Interstitial Cells

Abstract Mitral valve prolapse (MVP) can lead to heart failure, arrhythmia, and death. The only treatments available for MVP are replacement or repair; alternative therapies remain elusive due to lack of knowledge of the underlying pathological processes. The goal of the present study was thus to explore how MVP affects human mitral valve interstitial cell (hMVICs) extracellular matrix (ECM) remodeling and basal contractility characteristics. Isolated MVP and physiologically normal hMVICs were embedded in poly(ethylene) glycolbased hydrogels containing fluorescent fiducial markers and 3D traction force microscopy via inverse modeling was employed to determine the local change in hMVIC hydrogels due to enzymatic degradation and collagen deposition. Results indicated pronounced hydrogel softening occurred generally further from the hMVICs, whereas stiffening occurred in close proximity to hMVICs due to collagen deposition as verified by collagen-staining. MVP hMVICs induced greater hydrogel stiffening and less degradation than normal hMVICs. Interestingly, even though MVP hMVICs had higher basal contractile displacements, their corresponding traction forces and hydrogel strain energy densities were significantly lower than those of normal hMVICs. These findings elucidate, for the first time, that MVP hMVICs have significantly altered biophysical contractile and ECM remodeling behaviors compared to normal hMVICs. Simple Summary When a mitral heart valve gets thick, stiffened, and degraded, it can flip backwards (prolapse), causing blood to flow the wrong way. This can cause heart failure, arrhythmia, or even death. The only treatment for mitral valve prolapse (MVP) is surgery. To pave the way for a medication, this study aimed to understand how cells that maintain the mitral valve, mitral valve interstitial cells (MVICs), act on their surrounding tissue. The mechanical properties of the MVICs were tested, including how much they contract and how much they pull on their surroundings. Also, the mechanical properties that the MVICs place on their surroundings were tested, like how much they stiffen and degrade the tissue and how much energy is stored in the tissue as the MVICs contract. Compared to normal MVICs, we found that MVP MVICs stiffen their surroundings more and degrade their surroundings less. We also found that even though MVP MVICs contract more than normal MVICs, the energy that they place on their surroundings is less than that of normal MVICs, indicating that MVP MVICs are less mechanically effective. This is the first time that this ineffectiveness has been seen and may be key to targeting MVP with future medications. Competing Interest Statement The authors have declared no competing interest. Footnotes gf2375{at}cumc.columbia.edu Abbreviations - 3D-TFM - three-dimensional traction force microscopy - αSMA - alpha-smooth muscle actin - CytoD - cytochalasin-D - dPBS - Dulbecco’s phosphate buffered saline - ECM - extracellular matrix - MVP - mitral valve prolapse - ERK - extracellular signal regulated kinase - GPR - Gaussian process regression - HBSS - Hank’s buffered salt solution - hMVICs - human mitral valve interstitial cells - MAPK - mitogen-activated protein kinase - MMP - matrix metalloproteinase - MR - mitral regurgitation - MV - mitral valve - MVICs - mitral valve interstitial cells - MVP - mitral valve prolapse - Norm - physiologically normal - PEG - poly(ethylene) glycol - RhoA - ras homolog gene family, member A, GTPase - ROCK - rho-associated coiled-coil kinase - SMAD - SMA/MAD homologous protein - TDR - traction-to-displacement ratio - TGFβ - transforming growth factor β - WGA - wheat germ agglutinin