Interactions of vascular wall cells with collagen gels

Culture properties of bovine aortic endothelial cells and bovine aortic smooth muscle cells have been examined in relation to collagen gels. Endothelial cells grown on collagen maintain typical monolayer morphology not only in relationship to the overlying medium but also with respect to the collagen substrate. Endothelial cells placed within a collagen matrix assume a mycelial pattern resembling that of the microvasculature. Overlayment of confluent endothelial cells with collagen induces separation of the cells, changes in morphology, and reinitiation of growth. These shape changes do not require protein synthesis, appear to be independent of fibronectin, are not inhibited by cytochalasin D, but are inhibited by colchicine. Endothelial cell growth can be reinitiated by collagen. This phenomenon appears to be related to a change in cell shape and perhaps to separation of cells at the intercellular junction. In contrast, smooth muscle cells plated on collagen infiltrate the gels and assume a spindle-like, elongated morphologic appearance. Overlayment with collagen does not alter smooth muscle cell shape. Migration into the collagen gels is significantly enhanced when cells are cultured in medium containing platelet-released products, independent of growth stimulation itself. Migration is accompanied by collagen gel degradation. Release of labeled collagen into the medium by smooth muscle cells and appearance of TCA fragments in collagenase assay suggest secretion of collagenase. In summary, endothelial cells, but not smooth muscle cells, are restricted to the surface of collagen gels. The ability of the smooth muscle cells to invade is stimulated by platelet products and may be related to the synthesis of a smooth muscle collagenase.