Bone‐forming perivascular cells: Cellular heterogeneity and use for tissue repair

Mesenchymal progenitor cells are broadly distributed across perivascular niches—an observation conserved between species. One common histologic zone with a high frequency of mesenchymal progenitor cells within mammalian tissues is the tunica adventitia, the outer layer of blood vessel walls populated by cells with a fibroblastic morphology. The diversity and functions of (re)generative cells present in this outermost perivascular niche are under intense investigation; we have reviewed herein our current knowledge of adventitial cell potential with a somewhat narrow focus on bone formation. Antigens of interest to functionally segregate adventicytes are discussed, including CD10, CD107a, aldehyde dehydrogenase isoforms, and CD140a, among others. Purified adventicytes (such as CD10+, CD107alow, and CD140a+ cells) have stronger osteogenic potential and promote bone formation in vivo. Recent bone tissue engineering applications of adventitial cells are also presented. A better understanding of perivascular progenitor cell subsets may represent a beneficial advance for future efforts in tissue repair and bioengineering. Mesenchymal progenitor cells in the tunica adventitia have a hierarchy of differentiation and proliferation potential. On top of the hierarchy, platelet‐derived growth factor receptor (PDGFR)α+ and aldehyde dehydrogenase (ALDH)High cells show a bipotent differentiation potential into osteogenic and adipogenic cell lineages with high proliferative rate. Conversely, CD10 and CD107a expression separate osteogenic progenitors from adipogenic progenitors, respectively. Moreover, osteoprogenitors can transition into adipogenic phenotype.