oa Biomechanical Activation of Human Valvular Interstitial Cells from Early Stage of CAVD

Aortic Valve (AV) leaflets are exposed to complex biomechanical stimulations, which has been linked to the progression of Calcific Aortic Valve Disease (CAVD) characterized by valvular interstitial cells (VICs) adopting an osteogenic phenotype, remodeling of the ECM and biomineralization. Initial asymptomatic phases of CAVD, named Aortic Valve Sclerosis (AVSc), include thickening of the cusps whereas advanced stages, Aortic Valve Stenosis (AVS), are associated with severe calcification. Prospective clinical studies of CAVD are hampered by the typically slow and variable progression of the disease. In addition, patients who present with AVS are already in the stage of severe calcification where damage to the AV leaflets is too severe to be reversed by drug therapy. Finally, due to its asymptomatic presentation little is known about the AVSc stage. The aim of this study is to develop tissue- and cell-based models to uncover the biomechanical forces leading to activation of VICs in early, asymptomatic AVSc patients. We investigate the impact of biological (BMP4 pathway) and mechanical (tensile stretch) forces leading to VICs osteogenic transdifferentiation, and biomineralization of the fibrosa layer. Human, surgically resected, AV tissue from AVSc patients were characterized for cellular and extracellular markers and compared to healthy controls and AVS tissues. BMP4 and tensile stretch induce osteogenic marker expression and biomineralization of the fibrosa in non-calcified AVSc-derived tissue. VICs were isolated from patients and induced to transdifferentiate in either 2D cell culture or 3D Tissue Engineering valve model based on decellularized porcine AV scaffold repopulated with human-derived cells. Our results show that the synergistic combination of biological (BMP4) and mechanical (tensile stretch) forces is required to promote SMA, RUNX2, OPN, and ON expression of AVSc-derived cells. These results provide a novel study model of early asymptomatic AVSc that combine biological and mechanical stimulation to induce activation of AVSc-derived VICs and biomineralization of AVSc tissue. This model could be used to unveil the molecular mechanisms lading to VIC activation and to test possible future small drug to control cellular activation and tissue remodeling.