The regulation of vascular calcification by calcifying progenitor cells.

<p>Illustration of calcifying/decalcifying progenitor cells and their proposed roles in noncalcified conditions (A) and atherosclerotic plaques (B). Sca-1⁺ progenitor cells do not express hematopoietic lineage markers but express MSC-like markers. Sca-1⁺/PDGFRα⁻ progenitor cells differentiate into osteoblasts/osteoclasts bidirectionally, whereas Sca-1⁺/PDGFRα⁺ progenitor cells are committed to osteoblastic fates. PPARγ activation can shift the direction of differentiation of Sca-1⁺/PDGFRα⁻ progenitor cells toward osteoclasts, but it cannot change the differentiation of Sca-1⁺/PDGFRα⁺ progenitors. (A) Under homeostatic noncalcified conditions, circulating BM-derived calcifying cells (Sca-1⁺ cells) infiltrated the adventitia through the vasa vasorum. (B) Under pathologic atherosclerotic calcification or therapeutic intravascular cell delivery, these cells might infiltrate into the intima directly from the blood.