Strain and Substrate Stiffness Affect Calcium Accumulation in Aortic Valve Interstitial Cells

The progression of aortic valve (AV) disease is often characterized by the formation of calcific nodules on thickened AV leaflets, limiting the biomechanical function of the valve. Calcification is a major problem that often leads to the failure of bioprosthetic replacement valves [1]. In these cases, the association of extracellular Ca²⁺ with phosphates remaining in cellular debris within the decellularized scaffolds has been proposed to lead to the nucleation and growth of Ca₃(PO₄)₂ nodules. In native tissue, calcification is thought to be a more active process involving AV interstitial cells (AVICs). The exact molecular mechanisms that lead to the formation of these calcific nodules in native tissue remain unclear; however, AVICs have been shown to form nodule-like structures in vitro through differentiation to a phenotype with osteogenic character [2]. Additionally, in vitro nodules are characterized by activated smooth muscle α-actin positive AVICs and high levels of apoptosis [2–3]. Mechanical strain has also been shown to influence nodule formation in excised AV leaflets [4]. Intracellular Ca²⁺ exhibits mechanodependency in cultured cells [5], and heightened levels of intracellular Ca²⁺ have been shown to be associated with apoptosis in many cell types [6] In this study, we assess the role of mechanically-induced changes in intracellular calcium and its function in modulating AVIC behavior. We hypothesized that intracellular Ca²⁺ will increase in strained AVICs and that over time, this will lead to apoptosis. We believe that the results from this study will help illustrate the mechanotransductive role of Ca²⁺ in AVICs and may elucidate early cellular changes that lead to AV calcification.