Endothelial cell proliferation during angiogenesis. In vitro modulation by basement membrane components.

Modulation of the behavior of microvascular endothelial cells during angiogenesis has been observed to correlate with changes in the extracellular matrix. These reports prompted a comparison of the growth of microvascular endothelial cells on monolayers of various matrix components in vitro. Over a 5 day period, the proliferation of these cells was significantly greater on laminin than on either plasma fibronectin, the interstitial collagen types I and III, or on the basement membrane collagen type IV. Proliferation of the microvascular endothelial cells was compared with that of bovine aortic endothelial cells and bovine aortic smooth muscle cells on the same matrices. All three cell types grew significantly more rapidly on laminin than on fibronectin. The aortic endothelial cells differed from their microvascular counterparts in that the growth of these large vessel endothelial cells on the collagenous matrices (types I and III, or type IV) was not significantly different from that observed for laminin, but was greater than the relatively slow growth seen on plasma fibronectin. Further comparison of the growth of the microvascular endothelial cells on the two basement membrane components, laminin and type IV collagen, demonstrated that the growth of these cells on laminin can be modulated by the presence of type IV collagen. This was true either if the two matrices were combined as a mixed layer, or if the laminin was specifically bound to a layer of type IV collagen, more closely simulating the distribution of these molecules in a basement membrane. Examination by immunoperoxidase of in vivo model of neovascularization in the murine cornea revealed a temporally staggered appearance of basement membrane components. The appearance of laminin was found to occur throughout the newly formed vessels, as well as in individual cells at the migrating, proliferating tips. In contrast, the appearance of type IV collagen correlated with lumen formation and was not detected at the vessel tips. The results of this study suggest that the temporally ordered synthesis of specific matrix components plays a significant role in orchestrating the growth and differentiation of endothelial cells during the highly integrated set of responses known as angiogenesis.