The role of proopiomelanocortin-derived peptides in skin fibroblast and mast cell functions.

We have previously described proopiomelanocortin (POMC) gene-expression in human normal cultured dermal fibroblasts, and its dose- and time-dependent modulation by transforming growth factor-beta (TGF-beta) and tumor necrosis factor-alpha (TNF-alpha). The aim of the work described here was to investigate POMC-derived peptide release in vitro by cultured fibroblasts following incubation with different concentrations of both TNF-alpha and TGF-beta for 24 hours (1, 5, and 10 ng/ml). The effect of simultaneous addition of both TNF-alpha and TGF-beta (10 ng/ml) was also evaluated. Culture supernatants of human skin fibroblasts were collected to detect adrenocorticotropin hormone (ACTH), alpha-melanotropin (alpha-MSH), and beta-endorphin (beta-EP) levels by specific immunoenzymatic assay. We investigated the in vitro histamine-releasing activity of the POMC-derived peptides, alpha-MSH and beta-EP, on human foreskin mast cells. Detection of cleavage products in supernatants from cultured normal human dermal fibroblasts indicated intracellular processing by POMC protein. We were able to measure detectable levels of all peptides in basal conditions. TNF-alpha addition resulted in an increase in beta-EP and ACTH levels. TGF-beta-stimulated fibroblasts showed no alteration in beta-EP and alpha-MSH levels, whereas ACTH release was significantly enhanced. Both alpha-MSH and beta-EP induced histamine release from human foreskin mast cells in vitro with beta-EP-induced histamine levels as high as those observed with the calcium ionophore, ionomycin. Our data document fibroblast POMC-derived peptide release and modulation by cytokines, suggesting that they have a possible role in extracellular matrix deposit regulation and skin inflammation.