Regulation of Valvular Interstitial Cell Mineralization by Components of the Extracellular Matrix

The composition of the extracellular matrix (ECM) is believed to play a role in heart valve disease, and is highly relevant to the design of heart valve tissue engineering scaffolds, yet the interaction of valvular interstitial cells (VICs) with the ECM environment has not been well characterized. Thus, 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 the 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 and fibronectin, were resistant to calcification, even upon treatment with several mineralization-inducing growth factors. Meanwhile, cultures of VICs on fibrin, laminin, and heparin coatings not only had a high number of calcified nodules, but also elevated levels of ALP and CBFa1. Nodule composition analysis revealed the presence of multiple types of mineralization, including hydroxyapatite. Although apoptotic and necrotic cells were more concentrated in nodules than in other parts of the VIC cultures, the nodules contained a strong majority population of viable cells. By demonstrating this ECM-dependence of VIC calcification, we aim to identify appropriate biomaterial environments for heart valve tissue engineering as well as elucidate mechanisms of valvular disease.