Angiotensin II promotes an osteoblast-like phenotype in porcine aortic valve myofibroblasts.

Objectives: The mechanisms for pathogenesis of cardiac valve calcification were explored by studying the regulation of the Wnt signaling pathway during the transformation from cardiac valvular myofibroblasts to osteoblast-like phenotype.

Methods: Studies were carried on primary cultured porcine aortic valvular myofibroblasts. The cells were randomly divided into four groups and treated with angiotensin II (Ang II) according to the following: Ang II (10(-6) mol/l), Valsartan (Val) (10(-5) mol/l), Ang II plus Val (Ang II 10(-6) mol/l + Val 10(-5) mol/l) or mock treated as the control. Protein expression of Bone morphogenetic protein 2 (BMP2), Alkaline phosphatase (ALP), and Wnt pathway components, Wnt3a and β-catenin, was investigated to assess the activation of the Wnt signaling pathway and determine whether cells undergo the transformation to osteoblast-like phenotype.

Result: Ang II treatment of myofibroblasts led to significant up-regulation of α-SMA expression and activation of the cells. Neither the BMP2 or ALP proteins, nor the mRNA was detectable in the control group or the Val-treated group; however, there was a significant increase in Ang II-treated group (P < 0.01). The Wnt/β-catenin signaling ligand, Wnt3a, was not expressed in the control or Val-treated groups, whereas in Ang II-treated cells, both Wnt3a and β-catenin gene expression were enhanced (P < 0.01).The effect of Ang II can be inhibited by the addition of Val (P < 0.05).

Conclusion: Ang II might act on the Ang II receptor on valvular interstitial cells (VICs) and lead to activation of the Wnt/β-catenin pathway and hence cause the activation, differentiation and proliferation of myofibroblasts, and finally, osteoblast-like phenotype transformation, leading to calcification of heart valves.