AKT-independent activation of p38 MAP kinase promotes vascular calcification

Vascular calcification is prevalent in patients with atherosclerosis, and oxidative stress promotes pathogenesis of atherosclerosis. We have previously reported that activation of AKT by oxidative stress induces vascular calcification. Using sodium dichloroacetate (DCA), a previously reported small molecule inhibitor of AKT, the present studies uncovered an AKT-independent mechanism in regulating vascular calcification. We found that DCA dose-dependently induced calcification of vascular smooth muscle cells (VSMC) in vitro and aortic rings ex vivo. Furthermore, DCA markedly enhanced vascular calcification in atherosclerotic ApoE knockout mice in vivo. DCA-induced VSMC calcification was associated with increased Runx2, but not via activation of AKT, a key upstream signal that upregulates Runx2 during VSMC calcification. In contrast, DCA inhibited AKT activation and induced activation of p38 MAPK in calcified atherosclerotic lesions in vivo and calcified VSMC in vitro. Using a pharmacological inhibitor and shRNA for p38 MAPK, we demonstrated that inhibition of p38 MAPK blocked DCA-induced Runx2 upregulation and VSMC calcification. Furthermore, Runx2 deletion attenuated DCA-induced VSMC calcification. Immunoprecipitation analysis revealed association of p38 MAPK with Runx2, which was enhanced by DCA treatment. Knockdown p38 MAPK inhibited DCA-induced Runx2 transactivity, supporting the function of p38 MAPK in regulating Runx2 transactivity. Our studies have uncovered a new function of DCA in regulating vascular calcification, via AKT-independent activation of p38 MAPK. Furthermore, we have identified novel interaction between p38 MAPK and Runx2 enhances Runx2 transactivity, thus promoting VSMC calcification. These results revealed a novel signaling mechanism underlying DCA-induced vascular calcification, and offer opportunities to identify new therapeutic targets.