Perivascular Mesenchymal Progenitors for Bone Regeneration.

Mesenchymal progenitor cells reside in all assayed vascularized tissues, and are broadly conceptualized to participate in homeostasis/renewal and repair. The application of mesenchymal progenitor cells has been studied for diverse orthopaedic conditions related to skeletal degeneration, regeneration, and tissue fabrication. One common niche for mesenchymal progenitors is the perivascular space, and in both mouse and human tissues, perivascular progenitor cells have been isolated and characterized. Of these "perivascular stem cells" or PSC, pericytes are the most commonly studied cells. Multiple studies have demonstrated the regenerative properties of PSC when applied to bone, including direct osteochondral differentiation, paracrine-induced osteogenesis and vasculogenesis, and immunomodulatory functions. The confluence of these effects have resulted in efficacious bone regeneration across several preclinical models. Yet, key topics of research in perivascular progenitors highlight our lack of knowledge regarding these cell populations. These ongoing areas of study include cellular diversity within the perivascular niche, tissue-specific properties of PSC, and factors that influence PSC-mediated regenerative potential. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1221-1228, 2019.