Magnesium Activates Calcium-Sensing Receptor (CaSR) to Reduce Osteoblastic Differentiation and Calcification in CKD Vasculature

Background: Vascular calcification is an important risk factor for cardiovascular mortality in CKD. Higher dietary magnesium (Mg2+) intake was shown to reduce vascular calcification; however, the mechanisms of Mg2+ effect remain largely unknown. cAMP is a major driver for osteoblastic differentiation and calcification of vascular smooth muscle cells (VSMC). Extracellular calcium-sensing receptor (CaSR) is a regulator of cAMP pathway and Mg2+ is a CaSR agonist. We hypothesized that CaSR activation is a major mechanism for the protective effects of Mg2+ in vascular calcification. Methods: The effects of Mg2+ and roles of CaSR were studied in cell and animal models of vascular calcification including a CKD model. Results: In a primary mouse aortic VSMC calcification model induced by high Ca2+ and PO42-, increasing Mg2+ concentration to physiological levels (0.1 to 1 mM) reduced severity of calcification by up to 90%. Mg2+ effect was abolished with CaSR inhibitor NPS-2143 treatment. In primary VSMC from VSMC-specific CaSR knockout mice (SM22-Cre; Casr-flox), Mg2+ concentration and CaSR inhibition had minimal effects on calcification. CaSR activation assays showed that Mg2+ is a more potent CaSR agonist than Ca2+ in VSMC at physiological concentrations seen in plasma. 1 mM Mg2+ reduced cAMP levels, CREB phosphorylation and RUNX2 (osteoblastic differentiation marker) expression in VSMC. In adenine-induced CKD model, increasing dietary Mg2+ reduced vascular calcification severity by >90 % in wild-type mice with minimal effect in VSMC-specific CaSR knockouts. Higher Mg2+ intake in CKD model increased serum Mg2+ levels without any changes in serum Ca2+, Pi or BUN. In mouse aorta, vascular calcification reduced CaSR expression by 60%, and high Mg2+ diet administration resulted in preserved CaSR expression. Lastly, physiological Mg2+ concentrations reduced calcification severity by >70% in a primary human aortic VSMC model and Mg2+ effect was abolished with CaSR inhibition. Conclusion: Our results suggest that Mg2+ reduces vascular calcification by activating CaSR and preventing osteoblastic differentiation in VSMC. Mg2+ supplementation can be a simple and safe treatment for preventing vascular calcification in CKD. Funding: NIDDK Support, Private Foundation Support