The vascular wall is built up of a heterogeneous population of smooth muscle cells, which exhibit not only morphological distinctions but also important differences in the composition of their structural and contractile proteins. "Epithelioid" smooth muscle cells correspond to an intimal-like type and display features associated with immaturity, whereas "spindle-shaped" cells closely resemble the more typical medial smooth muscle population. We have investigated the integration of these two cell types into the vascular architecture of an in vivo wound-healing model. Stably transfected with the beta-galactosidase gene, intima- and media-like cells were injected intravenously into the chicken chorioallantoic membrane, within which superficial foci of granulation tissue had been created by thermal or chemical injury. At 24 to 72 h after injection, cells had honed in on the lesion sites and were observed in juxtaposition to the endothelial lining of the capillaries. They began to deposit laminin, thereby indicating an impending role in the formation of the vascular wall. Intima- and media-like smooth muscle cells did not differ in their capacity to associate with capillaries, and, in so doing, their biochemical lineage characteristics became indistinguishable from one another. However, intima-like cells also penetrated the adventitial and medial layers of arteries. These findings reveal vascular smooth muscle cells to possess an extraordinary degree of plasticity, being able to adapt flexibly to changes in functional demands.
Copyright 1999 Academic Press.