Wnt signaling plays a role in the differentiation as well as the development of melanocytes. Previous studies showed that hyperpigmentary skins of melasma express high levels of frizzled-related protein 2 (sFRP2) and Wnt inhibitory factor-1 (WIF-1) compared to perilesional normal skins. In this study, I investigated the functional roles of sFRP2 and WIF-1 on skin pigmentation.
The present study demonstrated that sFRP2 and WIF-1 were expressed in both melanocytes of normal human skin and in cultured melanocytes, suggesting that these molecules may have physiologic functions in melanocytes as an auto- or paracrine modulator of Wnt signaling. In addition, I found that secreted frizzled-related protein 2 (sFRP2) was overexpressed in the hyperpigmentary skins of not only melasma but also solar lentigo and the acutely UV-irradiated skin in vivo. Therefore, I hypothesized that sFRP2 and WIF-1 could have stimulatory roles for skin pigmentation. As results, sFRP2 and WIF-1 stimulated melanogenesis in normal human melanocytes through the increased expression of MITF and tyrosinase via β-catenin signaling. Moreover, the epidermal pigmentation of human skin was also increased in the presence of recombinant human sFRP2 and WIF-1.
These findings suggest that UV irradiation may stimulate sFRP2 and WIF-1 secretion in the skin, which functions as melanogenic stimulator. This may play an important role in the development of UV-induced hyperpigmentary disorders.
