Endothelial Cell Influences on Vascular Smooth Muscle Phenotype

In the normal arterial wall the smooth muscle cells and abluminal surface of the endothelium are surrounded by a basal lamina consisting of (among other substances) laminin, heparan sulfate proteoglycan, and type IV collagen (59, 75). In turn the basal laminae are closely associated with the continuum of collagen, elastin, and proteoglycans of the extracellular matrix. This associa­ tion maintains spatial arrangements of components within the vessel wall (93), but may also regulate the proper homeostatic balance of the cellular con­ stituents. In this article, the relationship between the endothelium, smooth muscle, and an extracellular matrix molecule they produce is explored. In particular, we will discuss the proposal that a heparin-like glycosaminoglycan present in the basal lamina of both smooth muscle and endothelium plays an important role in controlling the phenotype the smooth muscle expresses, and its response to serum mitogens. Change in smooth muscle phenotype leads to many changes in the biology of the cell, and these will also be reviewed.