Evidence for expression of melanocortin-1 receptor in human sebocytes in vitro and in situ

Many lines of evidence indicate that the activity of sebaceous glands can be modulated by neuropeptides. Direct evidence in man, however, is still missing. We show that SZ95 sebocytes, an immortalized human sebaceous gland cell line, express receptors for alpha-melanocyte-stimulating hormone. Reverse transcription polymerase chain reaction with primers against the five melanocortin receptors and immunofluorescence studies using an antibody directed against a peptide corresponding to the amino acids 2-18 of the human melanocortin-1 receptor disclosed specific transcripts and immunoreactivity for melanocortin-1 receptor in these cells. Melanocortin-1 receptor expression was confirmed in sebocytes of normal human skin by immunohistochemistry. In contrast, no immunostaining for the melanocortin-5 receptor could be detected in sebocytes in situ, in accordance with the lack of specific transcripts for this melanocortin receptor in SZ95 sebocytes. As cytokines play an important role in the recruitment of inflammatory cells in acne and related disorders and alpha-melanocyte-stimulating hormone exerts immunomodulatory effects in many other cell types, we investigated the effect of alpha-melanocyte-stimulating hormone on interleukin-8 secretion by SZ95 sebocytes. Treatment with interleukin-1beta resulted in a marked increase in interleukin-8 release that was partially blocked by coincubation with alpha-melanocyte-stimulating hormone in a dose-dependent manner. Taken together, we show here that the melanocortin-1 receptor is expressed in vitro and in situ in human sebocytes. By modulating interleukin-8 secretion, alpha-melanocyte-stimulating hormone may act as a modulator of inflammatory responses in the pilosebaceous unit.