Regulation of valvular interstitial cell phenotype by matrix mechanics involves alpha‐smooth muscle actin

Abstract

Introduction: Remodeling of the extracellular matrix (ECM) is a hallmark of valvular calcification. Remodeling may alter the mechanical properties of the ECM and consequently regulate the fate of valve interstitial cells (VICs) to a pathologic phenotype. Objectives: To determine if matrix stiffness regulates calcification by VICs in vitro, and to investigate the role of alpha‐smooth muscle actin (SMA) in mechanically‐regulated cell responses. Methods: Primary porcine aortic VICs were cultured on topographically identical stiff and compliant Type I collagen matrices. We compared the morphology, proliferation, and differentiation of VICs by (immuno)staining, RT‐PCR, and biochemical analyses. Results: Compared with VICs grown on stiff substrates, VICs grown on compliant substrates proliferated more rapidly and formed more bone‐like nodules (P<0.05) that displayed alkaline phosphatase activity, calcium accumulation, bone gene expression, and viable cells. VICs on stiff substrates expressed abundant filamentous SMA in stress fibres, while those on compliant substrates did not. Disruption of SMA stress fibres with Swinholide A had no effect on VICs on compliant matrices, but further reduced the number of bone‐like nodules on stiff matrices. Conclusion: This study demonstrates for the first time that mechanical cues from the matrix, mediated in part by SMA, determine VIC phenotype.