oa The Role Of BMP/Wnt Signalling In Human Heart Valve Calcification

Aortic valve calcification is a complex process that is characterised by the expression of bone markers in the valve leaflet. The Wnt pathway and bone morphogenetic proteins (BMPs) have been implicated to play a role in vascular and heart valve calcification. This study examines the regulation of Wnt3a by BMPs and the functional effects mediated by Wnt3a in human valve interstitial cells (VICs). Treatment of VICs by BMPs up-regulated the expression of Wnt3a, ALP, RUNX2, and β-catenin, as was shown by Western Blot analysis. Analysis of human pathological specimens by immunohistochemistry showed an increased level of expression of Wnt3a, Msx2 and β-catenin was localised to peri-calcific regions of the tissue. The concentration-dependent proliferation or differentiation of VICs in response to Wnt3a was measured by the incorporation of [3H]-thymidine and activity of alkaline phosphatase (ALP) respectively. Wnt3a-treated VICs proliferated in a concentration-dependent manner. At higher concentrations, Wnt3a caused a significant increase in ALP activity and expression of RUNX2. Lastly, Western blot experiments showed that BMP2 induced RUNX2 up-regulation was mediated through β-catenin/Wnt-signalling and not Smad-signalling. This study demonstrates the important role of Wnt-signalling in valve calcification in response to BMPs. Wnt3a may induce valve calcification by regulating the proliferation and osteogenic differentiation of cells within the valve. These findings may help to identify new therapeutic.