Role of pericytes in vascular calcification: a review

Pericytes are defined by their location in vivo; the pericyte partially sur rounds the endothelial cell of the microvessel and shares a common basement membrane with it. As an integral part of the microvasculature, pericytes p lay a fundamental role in maintaining local and tissue homeostasis, Current evidence also suggests that pericytes function as progenitor cells capable of differentiating into a variety of different cell types including osteob lasts, chondrocytes and adipocytes. It is now apparent that cells resemblin g microvascular pericytes, and termed 'pericyte-like' cells, have a widespr ead distribution in vivo. Pericyte-like cells have been identified in the i nner intima, the outer media, and in the vasa vasora of the adventitia of l arge, medium and small human arteries (1,2). Moreover, recent studies have suggested that these cells may be responsible, at least in part, for mediat ing the calcification commonly associated with atherosclerosis (1, 3, 4). I n this review, we a) examine the evidence that microvascular pericytes depo sit a bone-like mineralised matrix in vitro, b) compare the morphological a nd biochemical properties of microvascular pericytes, calcifying vascular c ells (CVCs) and 'classical' smooth muscle cells (SMCs) isolated from bovine aorta, c) demonstrate that microvascular pericytes deposit a well-organise d matrix of bone, cartilage and fibrous tissue in vivo, and d) discuss rece nt studies designed to gain a better understanding of how pericyte differen tiation is regulated.