Figure 6.
Smooth muscle cell (SMC) heterogeneity and stem cell differentiation. During vascular development or in response to injury, the media SMCs exhibit a synthetic, proliferative, and migratory phenotype, where they may express some stem cell markers (Sca-1) and also the marker SMα-actin. This is accompanied by a decrease in the expression of SMC differentiation markers, such as calponin and SMMHC (smooth muscle myosin heavy chain). Stem cells (Sca-1+, c-Kit+, CD34+) can differentiate into SMCs in response to vascular injury, and thus, their expression of stem cell markers is decreased, whereas the expression of SMC markers is increased (SMα-actin, calponin, SMMHC). Mature and fully differentiated SMCs express high levels of calponin and SMMHC and show reduced or negligent levels of stem cell markers. These cells present a more elongated morphology and a contractile phenotype, with a low proliferative and migratory rate. Stem/progenitor cell markers can potentially be expressed in dedifferentiated SMCs, which have gone through a dedifferentiation process in atherosclerosis, and which contribute to vessel wall remodeling.