The CAD risk locus 9p21 increases the risk of vascular calcification in an iPSC-derived VSMC model.

BACKGROUND: Coronary artery disease (CAD) is the leading cause of death worldwide. Chromosome locus 9p21 was the first to be associated with increased risk of CAD and coronary artery calcification (CAC). Vascular calcification increases the risk for CAD. Vascular smooth muscle cells (VSMCs) are one of the major cell types involved in the development of vascular calcification. METHODS: So far, mainly animal models or primary SMCs have been used to model human vascular calcification. In this study, a human in vitro assay using iPSC-derived VSMCs was developed to examine vascular calcification. Human iPSCs were derived from a healthy non-risk (NR) and risk (R) donor carrying SNPs in the 9p21 locus. Additionally, 9p21 locus knockouts of each donor iPSC line (NR and R) were used. Following differentiation, the iPSC-derived VSMCs were characterized based on cell type, proliferation, and migration rate, along with calcium phosphate (CaP) deposits. CaP deposits were confirmed using Calcein and Alizarin Red S staining and then quantified. RESULTS: The data demonstrated significantly more proliferation, migration, and CaP deposition in VSMCs derived from the R and both KO iPSC lines than in those derived from the NR line. Molecular analyses confirmed upregulation of calcification markers. These results are consistent with recent data demonstrating increased calcification when the 9p21 murine ortholog is knocked-out. CONCLUSION: Therefore, in conclusion, genetic variation or deletion of the CAD risk locus leads to an increased risk of vascular calcification. This in vitro human iPSC model of calcification could be used to develop new drug screening strategies to combat CAC.

Differentiation of human iPSCs into VSMCs and generation of VSMC-derived calcifying vascular cells.

Vascular calcification displays a major cause of death worldwide, which involve mainly vascular smooth muscle cells (VSMCs). Since 2007, there are increasing numbers of protocols to obtain different cell types from human induced-pluripotent stem cells (iPSCs), however a protocol for calcification is missing. Few protocols exist today for the differentiation of iPSCs towards VSMCs and none are known for their calcification. Here we present a protocol for the calcification of iPSC-derived VSMCs. We successfully differentiated iPSCs into VSMCs based on a modified protocol. Calcification in VSMCs is induced by a commercial StemXVivo™ osteogenic medium. Calcification was verified using Calcein and Alizarin Red S staining or Calcium assays, and molecular analyses showed enhanced expression of calcification-associated genes. The presented method could help to study genetic risk variants, using the CRISPR/Cas technology through the introduction of Knockouts or Knockins of risk variants. Finally, this method can be applied for drug screening.