Smooth Muscle Cell Phenotype and Proliferation

Intimal thickening, commonly observed in atheromatous lesions, mainly consists of smooth muscle cells. The intimal smooth muscle cells have vastly different characteristics from those of medial smooth muscle cells. The major differences are their rapid growth property, their expression of a scavenger pathway and the autocrine system for growth factor in the intimal smooth muscle cells. The existence of an autocrine system is proved by the secretion of smooth muscle cells derived growth factor (SDGF). Intimal smooth muscle cells are considered to be derived from medial smooth muscle cells through migration from the media and proliferation in intima in vivo. The change from medial to intimal smooth muscle cells was proved by the co-culture system with endothelial cells in vitro. Their rapid growth is observed not only in intimal smooth muscle cells but also in medial smooth muscle cells from the aorta of diabetes mellitus. These findings indicate that smooth muscle cell phenotype change occurs in various stages during the formation of atherosclerosis, and that endothelial cells play an important role in the phenotype change