Smooth muscle diversity in arterial wound repair

Repair of arterial injury results in formation of a new structure, a neointima, that causes luminal narrowing. Smooth muscle cell (SMC) properties required for neointima formation are also found in nascent SMCs of developing blood vessels in the embryo (e.g., proliferation, extracellular matrix synthesis, cell migration). We isolated 2 distinct types of SMC from aortic media of newborn rats that were distinguished by cell shape, secretion of platelet-derived growth factor (PDGF) and insulin-like growth factor-1 (IGF-1), and expression of PDGF-B and PDGF alpha-receptor genes. These two SMC types did not interconvert over many cell generations in vitro. Adult rat aorta yields only one SMC type, suggesting that the "pup" SMC variant is developmentally regulated. However, SMC with the "pup" phenotype reappear in the adult artery wall during neointima formation after balloon catheter injury. These observations raise the possibility that SMC proliferation and arterial remodeling during development, repair and disease of the artery wall might depend upon a SMC subpopulation with special properties.