Differentiated Smooth Muscle Cells Generate a Subpopulation of Resident Vascular Progenitor Cells in the Adventitia Regulated by Klf4

Rationale:The vascular adventitia is a complex layer of the vessel wall consisting of vasa vasorum microvessels, nerves, fibroblasts, immune cells, and resident progenitor cells. Adventitial progenitors express the stem cell markers, Sca1 and CD34 (adventitial sca1-positive progenitor cells [AdvSca1]), have the potential to differentiate in vitro into multiple lineages, and potentially contribute to intimal lesions in vivo. Objective:Although emerging data support the existence of AdvSca1 cells, the goal of this study was to determine their origin, degree of multipotency and heterogeneity, and contribution to vessel remodeling. Methods and Results:Using 2 in vivo fate-mapping approaches combined with a smooth muscle cell (SMC) epigenetic lineage mark, we report that a subpopulation of AdvSca1 cells is generated in situ from differentiated SMCs. Our data establish that the vascular adventitia contains phenotypically distinct subpopulations of progenitor cells expressing SMC, myeloid, and hematopoietic prog...