Magnesium Supplementation Reduces Vascular Calcification by Activating Calcium-Sensing Receptor (CaSR) in Vascular Smooth Muscle Cells

Background: Pathological deposition of calcium-phosphate in the arterial wall leads to vascular calcification, which is an important risk factor for cardiovascular mortality in CKD patients. Higher dietary Mg2+ intake was shown to reduce vascular calcification and cardiovascular mortality in clinical studies, however the mechanisms of Mg2+ effect remain unclear. Extracellular Ca2+-sensing receptor (CaSR) is a protein expressed in many tissues including vascular smooth muscle cells (VSMC). Although Ca2+ is considered as its main physiological agonist, we recently showed that Mg2+ (an often neglected CaSR agonist) is a more potent CaSR activator in certain tissues such as gut and lung. Methods: We studied the roles of CaSR in therapeutic effects of Mg2+ in cell and mouse models of vascular calcification. Results: In both mouse and human primary aortic smooth muscle cells, calcium-phosphate treatment (3 mM Ca2+, 2.5 mM PO43- for 7 days) resulted in marked calcification. Increasing Mg2+ in culture media concentration-dependently reduced calcification by up to 90% at 1 mM. The protective effects of Mg2+ were essentially abolished by CaSR inhibitor NPS-2143. Mg2+ concentration had minimal effects on calcification in primary cells derived from VSMC-specific CaSR knockout mice (SM22-Cre; Casr-flox), confirming key roles of CaSR in its efficacy. CaSR activation assays showed that Mg2+ is 2-5 fold more potent CaSR agonist than Ca2+ in human and mouse primary VSMC. In high dose vitamin D-induced vascular calcification model, mice fed with low (0.02%) Mg2+ diet had severe aortic calcification which was reduced by 32% and 66% in mice fed with normal (0.2%) and high (0.5%) Mg2+ diets, respectively. Aortic CaSR protein expression was found to be reduced by 85% and 60% in mice fed with low and normal Mg2+ diets, respectively, compared to controls. Co-staining showed that CaSR expression was primarily reduced in calcified areas. High Mg2+ diet resulted in largely preserved aortic CaSR expression in mice. Conclusion: These results collectively suggest that Mg2+ is the key CaSR agonist in VSMC for prevention of vascular calcification. Mg2+ deficiency results in reduced CaSR activity and expression, which can be restored by its supplementation. Mg2+ supplementation can potentially be used as a simple, safe and effective treatment for preventing vascular calcification in CKD. Funding: NIDDK Support