Low-Concentration Hydrogen Peroxide Can Upregulate Keratinocyte Intracellular Calcium and Par-2 Expression in a Human Keratinocyte-Melanocyte Co-Culture System

Hydrogen peroxide (H(2)O(2)) may have a biphasic effect on melanin synthesis and melanosome transfer. High H(2)O(2) concentrations are involved in impaired melanosome transfer in vitiligo. However, low H(2)O(2) concentration promotes the beneficial proliferation and migration of melanocytes. The aim of this study was to explore low H(2)O(2) and its mechanism in melanosome transfer, protease-activated receptor-2 (PAR-2) expression and calcium balance. Melanosomes were fluorescein-labeled for clear visualization of their transfer. The expression of protease-activated receptor-2 (PAR-2) in keratinocytes was determined by western blot analysis. Flow cytometry was employed to evaluate the effects of H(2)O(2) on calcium levels in keratinocytes. Fluorescence microscopy showed the upregulation of melanosome transfer into keratinocytes following 0.3?mM H(2)O(2) treatment in the co-cultures rather than in the untreated control groups, which was associated with higher expression of PAR-2 protein and increased calcium concentration. The addition of a PAR-2 antagonist inhibited the positive activity of H(2)O(2) and calcium flow in keratinocytes. When calcium flow was blocked by a calcium chelator, the addition of H(2)O(2) did not increase the PAR-2 expression level in keratinocytes, therefore, inhibiting dendrite formation and melanosome transfer. Low H(2)O(2) concentration promotes melanosome transfer with increased PAR-2 expression level and calcium concentration in keratinocytes. In addition, the interaction between melanocytes and keratinocytes is more beneficial to enhance calcium levels in keratinocytes which mediate melanin transfer. Moreover, low H(2)O(2) concentration promotes dendrite formation, in which extracellular calcium and Par-2 were involved.