Coronary artery disease associated gene Phactr1 modulates severity of vascular calcification in vitro

Calcification of vessels is strongly associated with atherosclerosis and leads to coronary artery disease (CAD) and myocardial infarction (MI). Genome-wide association studies (GWAS) revealed several genes that are associated with and contribute to CAD/MI as well as coronary artery calcification (CAC); however, the underlying mechanisms are unknown. PHACTR1, which encodes phosphatase and actin regulator 1, is among these risk genes. The aim of this study was to functionally test whether Phactr1 regulates calcification in vitro using murine embryonic stem cell (mESC)-derived smooth muscle cells (SMCs). Phactr1 was stably up- or down-regulated in mESCs. These mESCs were differentiated into SMCs, and calcification was enhanced using osteogenic medium. Calcium phosphate deposits were detected and quantified. RT-PCR analysis demonstrated that gene expression of Phactr1 correlated with increased calcification in mESC-derived SMCs as well as primary human aortic SMCs. Down-regulation of Phactr1 decreased calcification. Decreased expression of the osteogenic marker osteopontin confirmed this finding at the molecular level. By contrast, overexpression of Phactr1 in calcifying mESC-derived SMCs enhanced mineralization. Taken together, we demonstrated that PHACTR1 gene expression increases with the progression of calcification and that regulation of PHACTR1 in SMCs modulates the severity of vascular calcification.