Figure 2. Sources of vascular smooth muscle progenitor cells in adults.

In large arteries (red) and veins (grey), resident SMC progenitors have been identified in the adventitial layer (green cell clusters) ^6,7,9 and in the medial layer (scattered blue cells) ¹⁸⁰. Some reports suggest that SMCs in atherosclerotic plaques and intimal masses can arise from circulating, bone marrow-derived progenitor cells (yellow) ^173,174 while others report finding no evidence to support that possible origin ^175,176. In microvessels, pericytes (purple) have been proposed to have multilineage differentiation potentials ^162,166, and can act as SMC progenitor cells ^159,163.