Abstract 3030: Differential Regulation of Valvular Interstitial Cell Dysfunction by Extracellular Matrix Components

Abstract

Calcification is the leading cause of bioprosthetic and native aortic valve failure, but relatively little is known regarding the factors that contribute to the progression of valvular calcification. Because extracellular matrix (ECM) disarray is often observed in explanted diseased valves, we have investigated the role of individual ECM components in the in vitro calcification of valvular interstitial cells (VICs). The transformation of VICs to an osteoblast-like phenotype was quantified in VICs cultured on different types of ECM coatings. The results show that the number and size of calcific nodules formed in VIC cultures, as well as the expression of mineralization markers alkaline phosphatase (ALP) and CBFa1, were highly dependent upon the composition of the culture surface. In fact, VICs cultured on certain ECM components, namely collagen (Coll) and fibronectin (FN), were resistant to calcification, even upon treatment with potent mineralization-inducing growth factors, such as transforming growth factor beta1 (TGFb1). Meanwhile, VIC cultures on fibrin (FB), laminin, and heparin not only had a high number of calcified nodules (p<0.001 vs. Coll, FN), but also elevated levels of ALP and CBFa1 (p<0.02), and the number of nodules on these ‘pro-calcific’ coatings significantly increased upon treatment with exogenous TGFb1 (p<0.05). To explain the ECM-dependence of calcification, the endogenous production of a pro-mineralization factor (TGFb1) was assessed in VICs on anti-calcific (Coll) and pro-calcific (FB) substrates. Quantification of TGFb1 mRNA revealed that VICs on Coll surfaces expressed a significantly lower amount of TGFb1 mRNA than VICs on FB (p<0.01). Furthermore, treatment with a neutralizing antibody to TGFb1 decreased TGFb1 mRNA expression by VICs on Coll in comparison to VICs on FB or polystyrene controls (p<0.02). Thus, we have discovered a strong correlation between VIC calcification and ECM composition. Our findings show that the ECM plays an important role in controlling TGFb1 expression and subsequent calcification of VICs, which may significantly impact the design of biomaterials for valve tissue engineering, understanding of valvular disease, and the development of preventative treatments for valve calcification.