High-Phosphate-Induced Calcification Is Related to SM22a Promoter Methylation in Vascular Smooth Muscle Cells

Montes de Oca A, Madueño JA, Martinez-Moreno JM, Guerrero F, Muñoz-Castañeda J, Rodriguez-Ortiz ME, Mendoza FJ, Almaden Y, Lopez I, Rodriguez M, Aguilera-Tejero E
Source: Other
Publication Date: (2010)
Issue: 25(9): 1996-2005
Research Area:
Basic Research
Cells used in publication:
SMC, aortic (AoSMC), human
Species: human
Tissue Origin: aortic
Hyperphosphatemia is closely related to vascular calcification in patients with chronic kidney disease. Vascular smooth muscle cells (VSMCs) exposed to high phosphate concentrations in vitro undergo phenotypic transition to osteoblast-like cells. Mechanisms underlying this transdifferentiation are not clear. In this study we used two in vitro models, human aortic smooth muscle cells and rat aortic rings, to investigate the phenotypic transition of VSMCs induced by high phosphate. We found that high phosphate concentration (3.3?mmol/L) in the medium was associated with increased DNA methyltransferase activity and methylation of the promoter region of SM22a. This was accompanied by loss of the smooth muscle cell-specific protein SM22a, gain of the osteoblast transcription factor Cbfa1, and increased alkaline phosphatase activity with the subsequent in vitro calcification. The addition of a demethylating agent (procaine) to the high-phosphate medium reduced DNA methyltransferase activity and prevented methylation of the SM22a promoter, which was accompanied by an increase in SM22a expression and less calcification. Additionally, downregulation of SM22a, either by siRNA or by a methyl group donor (S-adenosyl methionine), resulted in overexpression of Cbfa1. In conclusion, we demonstrate that methylation of SM22a promoter is an important event in vascular smooth muscle cell calcification and that high phosphate induces this epigenetic modification. These findings uncover a new insight into mechanisms by which high phosphate concentration promotes vascular calcification.