Stimulation of fibroblast collagen and total protein formation by an endothelial cell-derived factor

We investigated the effect of medium conditioned by bovine aortic endothelial cells on collagen accumulation and total protein formation by human embryonic fibroblasts or bovine smooth muscle cells in cultures. The conditioned medium at a 1:10 dilution induced a twofold increase in collagen and total protein accumulation in fibroblast cultures. At low concentration (1:50 dilution), the conditioned medium stimulated collagen accumulation preferentially; at high concentration (1:10 dilution), overall protein synthesis also was increased. The increase in type I collagen accumulation was associated with an increase in the steady-state level of alpha 1 (I) mRNA for collagen. The conditioned medium increased the production of types I and III collagen without affecting the proportion of collagen types in both fibroblast and smooth muscle cell cultures. Partial purification of the endothelial cell-derived factor disclosed it to be a heat-stable protein with an apparent molecular weight of 8-10 kDa. The stimulation of protein formation by this substance was not inhibited by antibodies against transforming growth factor-beta or the insulinlike growth factor I receptor. The partially purified factor stimulated protein production without affecting fibroblast proliferation. This endothelial cell-derived protein may play a role in the remodeling of vascular connective tissue by stimulating collagen synthesis.