Vitamin D treatment prevents uremia-induced reductions in aortic microRNA-145 attenuating osteogenic differentiation despite hyperphosphatemia

Abstract

In chronic kidney disease, systemic inflammation and high serum phosphate (P) promote the de-differentiation of vascular smooth muscle cells (VSMC) to osteoblast-like cells, increasing the propensity for medial calcification and cardiovascular mortality. Vascular microRNA-145 (miR-145) content is essential to maintain VSMC contractile phenotype. Because vitamin D induces aortic miR-145, uremia and high serum P reduce it and miR-145 directly targets osteogenic osterix in osteoblasts, this study evaluated a potential causal link between vascular miR-145 reductions and osterix-driven osteogenic differentiation and its counter-regulation by vitamin D. Studies in aortic rings from normal rats and in the rat aortic VSMC line A7r5 exposed to calcifying conditions corroborated that miR-145 reductions were associated with decreases in contractile markers and increases in osteogenic differentiation and calcium (Ca) deposition. Furthermore, miR-145 silencing enhanced Ca deposition in A7r5 cells exposed to calcifying conditions while miR-145 overexpression attenuated it, partly through increasing α-actin levels and reducing os-terix-driven osteogenic differentiation. In mice, 14 weeks after the induction of renal mass re-duction, both aortic miR-145 and α-actin mRNA decreased by 80% without significant elevations in osterix or Ca deposition. Vitamin D treatment from week 8 to 14 fully prevented the reductions in aortic miR-145 and attenuated by 50% the decreases in α-actin despite uremia-induced hyper-phosphatemia. In conclusion, vitamin D was able to prevent the reductions of aortic miR-145 and α-actin content induced by uremia reducing the alterations in vascular contractility and osteogenic differentiation despite hyperphosphatemia.