Abstract P262: Receptor-Ligand Functional Interaction Between CD44 and Osteopontin During Calcific Aortic Stenosis: A Molecular Mechanism for Accelerated Biomineralization of Bicuspid Aortic Valve

Abstract

Introduction: Calcific aortic valve degeneration (CAVD) is the most common indication for surgical valve replacement in the US. The calcification starts with a Tricuspid Aortic Valve (TAV) or with a Bicuspid Aortic Valve (BAV). Initial phases of the disease, include thickening of the valve, a condition known as aortic valve sclerosis (AVSc), whereas advanced stages, aortic valve stenosis (AVS), are associated with leaflets biomineralization. The biomineralization process, occurring in an accelerated manner in BAV, has not been described in its molecular mechanisms. We reported that Osteopontin (OPN) is implicated in the calcification of dystrophic and ectopic sites. Here we investigate the interaction between OPN, and one of its functional regulators, CD44, during valve degeneration in TAV and BAV patients. Methods: Five groups of 10 subjects each (TAV: control, AVSc, AVS; BAV: control and AVS) were selected from our tissue biorepository according to echocardiographic analysis, inclusion/exclusion criteria, and/or intra-op observations. Histological studies, cellular and molecular analysis, and in situ proximity-ligation-assay (PLA) on surgically resected tissues were used to investigate the functional interaction between OPN and CD44. Results: 1) In vitro calcification assays shows that OPN protects against calcification through CD44 interaction. 2) OPN and CD44 levels are elevated in the leafelts of BAV patients, both stenotic patients and controls. In TAV, AVSc and AVS patients shows elevated levels of OPN and CD44 when compared to controls. 3) In situ PLA assay displayed a direct interaction between CD44 and OPN in BAV patients, in both stenotic patients and controls, and in TAV AVSc and AVS patients. Healthy, non-calcified TAV subjects, shows barely detectible OPN-CD44 interaction. Conclusion: OPN-CD44 direct interaction correlate with the severity of biomineralization in TAV patients. Conversely, in BAV we demonstrate a direct interaction between OPN and CD44 in both stenotic and non-calcified tissues. These results are aims to elucidate the mechanisms behind the accelerated biomineralization of BAV compared to TAV, and generate important insights into the development of diagnostic and therapeutic approached for CAVD.