Extracellular acidosis suppresses calcification of vascular smooth muscle cells by inhibiting calcium influx via L-type calcium channels.

Vascular calcification such as arteriosclerosis, which is characterized by a calcification of the tunica media, is a severe complication of chronic kidney disease (CKD), contributing to the high prevalence of cardiovascular morbidity and mortality in patients with CKD. An essential step during the development of arteriosclerosis is the transdifferentiation/calcification of vascular smooth muscle cells (VSMCs), resembling osteogenesis. Metabolic acidosis, a common clinical manifestation in CKD, is known to decrease vascular calcification. To understand the underlying regulatory mechanisms of acidosis, we investigated whether the acidosis-decreased VSMC calcification involves altered signaling of the LTCC/Ca2+ /Runx2 pathway. Vascular calcifications, calcium content, runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), L-type calcium channel (LTCC) β3 subunits, and calcium influx were measured in vivo or in vitro. Calcified nodules and calcium content increased either in aorta sections of vascular calcified rats or in VSMCs induced by β-GP. The expression of Runx2 and ALP activity markedly rose, accompanied by the increasing expression of LTCC β3 subunits and calcium influx. However, acidosis supplementation successfully attenuated VC and VSMC calcification and inhibited Runx2, ALP, LTCC β3 subunits, and calcium influx. In conclusion, acidosis significantly attenuated vascular calcification in association with downregulation of the LTCC/Ca2+ /Runx2 pathway.