Human fibroblasts treated with hydrogen peroxide stimulate human melanoblast proliferation and melanocyte differentiation, but inhibit melanocyte proliferation in serum-free co-culture system

Abstract Background Oxidative stress caused by hydrogen peroxide (H 2 O 2 ) elicits harmful effects on human melanocytes such as DNA damage and cell death. On the contrary, H 2 O 2 is known to possess beneficial effects on melanocytes. However, mechanisms of the beneficial effects of H 2 O 2 on melanocytes have not been fully understood, especially the indirect effects on melanocyte proliferation and differentiation from cells constituting surrounding tissue environment such as fibroblasts. Objective The aim of this study was to clarify whether H 2 O 2 -treated human fibroblasts affect the proliferation and differentiation of human melanocytes using serum-free co-culture system. Methods Epidermal melanoblasts and melanocytes were co-cultured with H 2 O 2 -treated or control fibroblasts in serum-free culture media. The effects of H 2 O 2 -treated fibroblasts were detected by changes in the proliferation and differentiation of melanoblasts/melanocytes. Results H 2 O 2 -treated fibroblasts stimulated the proliferation of melanoblasts and the differentiation, melanogenesis, and dendritogenesis of melanocytes, but inhibited the proliferation of melanocytes. In the melanocytes co-cultured with H 2 O 2 -treated fibroblasts, the expression of tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), and KIT was increased, whereas TYRP2 and microphthalmia-associated transcription factor showed no change. Conclusion These results suggest that H 2 O 2 -treated fibroblasts can produce and release some mitogenic and melanogenic factors toward melanoblasts in addition to some proliferation-inhibiting factors toward melanocytes. The stimulation of melanocyte differentiation seems to be performed through the upregulation of TYR, TYRP1, and KIT.