Extracellular matrix and control of proliferation of vascular endothelial cells

Abstract

Bovine vascular endothelial cells plated at low cell density in the presence of high (10%) concentrations of serum and maintained on plastic tissue culture dishes proliferate slowly. If the cultures were exposed to fibroblast growth factors (FGF), the cells proliferated actively and, after a week, a monolayer composed of closely apposed and highly contact-inhibited mononucleated cells formed. In contrast to cultures maintained on plastic, cultures maintained on dishes coated with an extracellular matrix produced by corneal endothelial cells proliferated rapidly and no longer required FGF to reach confluence. Addition of FGF to such cultures did not decrease the mean doubling time, which was already at a minimum (18 h), nor did it result in a higher final cell density, which was already at a maximum (700-1,000 cells/mm2). Likewise, although human umbilical vein endothelial cells plated at low density on plastic did not proliferate, they proliferated matrix. However, unlike bovine vascular endothelial cells, they still required FGF if the cultures were to become confluent. The ability of plasma vs. serum to sustain cell proliferation was analyzed using low density bovine-vascular endothelial cell cultures maintained either on plastic or on dishes coated with an extracellular matrix. Cells plated on plastic had a lower growth rate when exposed to plasma than to serum. In both cases, FGF was required for the cultures to become confluent. In contrast, when cells were plated on an extracellular matrix, they proliferated equally well, regardless of whether they were exposed to plasma or serum, and no longer required FGF to become confluent. Because the growth rate of the cultures maintained on extracellular matrix was a direct function of the serum or plasma concentrations to which they were exposed, it is likely that the extracellular matrix had a permissive rather than a direct mitogenic effect on the cells. Therefore, one can conclude that the simple change of substrate from plastic to extracellular matrix will restore the sensitivity of vascular endothelial cells to physiological agents present in plasma or serum.