The effects of endothelin-1 on human dermal fibroblast growth and synthetic activity

Endothelin-1 (ET-1) is the most potent vasoconstricting substance known, and is believed to have a fundamental role in the regulation of blood flow. It is a peptide produced and secreted by endothelial cells in response to hypoxia and injury, as well as by macrophages. These properties suggest that ET-1 may play a role during tissue repair. In this study, we have examined the effects of ET-1 on the growth and synthetic activity of human dermal fibroblasts. ET-1 stimulated DNA synthesis in serum-deprived cultures: this effect reached a mean value of 64% more than control (P < 0.01) at 2.5 ng/ml (10^-9, M) of ET-1. In contrast, the addition of ET-1 to fibroblasts at different densities and in 0, 3, or 10% fetal bovine serum (FBS) failed to increase cell counts. In 1% FBS, a 41% mean increase in cell counts compared to control values was observed in cultures treated with 2.5 ng/ml of ET-1 (P < 0.01). Incubation of dermal fibroblast cultures at 37°C for 1 hr with increasing concentrations of ¹²⁵I-ET-1 resulted in saturable binding and a half-maximal specific binding of 27.5 pM. Scatchard plot analysis of the binding showed a K_d of 224 pM and 11,400 high-affinity binding sites per cell. ET-1 had no effect on [¹⁴C]-glucosamine incorporation by fibroblasts and caused no increase in collagen synthesis, as measured by collagenase-sensitive [³H]proline incorporation and by salt precipitation of ³H-labeled collagen at acid and neutral pH successively. In summary, ET-1 binds to fibroblasts through specific high-affinity surface receptors, but has no obvious direct effect on macromolecular synthesis. ET-1 stimulates [³H]thymidine uptake, but has marginal effects on cell growth. We conclude that any role of ET-1 in tissue repair is probably due to its hemodynamic effects and not as a growth factor.