Responses of adventitial CD34+ vascular wall-resident stem/progenitor cells and medial smooth muscle cells to carotid injury in rats.

Cell culture and carotid injury studies with SD rats were performed to investigate the roles of CD34+ vascular wall-resident stem/progenitor cells (VRS/Pcs) and vascular smooth muscle cells (SMCs) in neointimal formation. In vitro, the media-isolated SM MHC+ SMCs occupied 93.92±8.62% of total BrdU+ cells, whereas the CD34+ cells, only 2.61±0.82%, indicating that the cell expansion in SMC culture was attributed to SM MHC+ SMCs. The adventitia-isolated CD34+ VRS/Pcs responded to PDGF-BB by differentiating into SMC-like cells which expressed SM22α (an early stage SMC marker), but seldom SM MHC (a late stage SMC marker). In carotid injury model, the CD34+ VRS/Pcs differentiated SMC-like cells migrated in very few numbers into only the outer layer of the media, and this was further confirmed by a cell tracking analysis. While the neointimal cells were consistently SM MHC+ and CD34- SMCs during whole course of the post-injury remodeling. Thus it is speculated that the adventitial CD34+ VRS/Pcs, at least in rat model, do not directly participate in neointimal formation, but function to maintain homeostasis of the media during injury-induced vascular wall remodeling.