Are Mural Cells Guardians of Stemness?

In the current issue of Circulation , Dar and colleagues report the healing of ischemic limbs in athymic mice by multipotent progenitors derived from human embryonic stem (ES) cells or reprogrammed adult cells. So far, nothing really original; the excitement comes from the demonstration that these ES cell and induced pluripotent stem cell (iPS)–derived regenerative units exhibit the features of vascular pericytes.1 These observations are timely and remarkable inasmuch as the blood vessel, far from being a mere conduit, has lately gained nobility in the eyes of stem cell biologists for its recognized contribution to diverse cell lineages. On the one hand, it is now well accepted that, from fish to humans, specialized blood-forming endothelial cells in the dorsal aorta and, most certainly, other organs supply the embryo with hematopoietic cells.2–6 Another developmental affiliation has been more recently documented between pericytes, also known as mural cells, which ensheath capillaries, arterioles, and venules and are classically confined to an organizational/structural role in angiogenesis,7 and the elusive mesenchymal stem cell (MSC). Mesenchymal stem cells are adherent multilineage mesodermal progenitor cells spontaneously selected in long-term cultures of unfractionated cell suspensions from diverse tissues. Such a retrospective isolation in vitro has long obscured the native identity, anatomic …