TRPM8 Controls Melanin Synthesis in Human Skin Melanocyte

Transient receptor potential melastatin 8 (TRPM8) is the cold stimulus receptor found as a member of the temperature sensor transient receptor potential (TRP) family in peripheral sensory nerves. Currently, some studies about TRPM8 functions besides the temperature sensor are in progress, but little is known about the role of TRPM8 in human skin melanocytes. Therefore, we examined the function and effect of Geranium robertianum L. on TRPM8 in human skin melanocytes. As a result, mRNA expressions of melanin synthesis-related factors were decreased by this TRPM8 activator. On the other hand, a TRPM8 inhibitor exerted reverse effects. In UVB-irradiated melanocytes, TRPM8 activity and mRNA expression were decreased, and mRNA expressions of melanin synthesis-related factors were increased. Moreover, Geranium robertianum L. increased TRPM8 activity and mRNA expression, and decreased mRNA expressions of melanin synthesis-related factors in human skin melanocytes. On the basis of these results, it was concluded that TRPM8 had a suppressive function for melanin synthesis and the reduction of this function by UVB irradiation induced the acceleration of melanin synthesis in skin melanocytes. Since Geranium robertianum L. enhanced TRPM8 activity and mRNA level, it may prevent and improve pigmentation induced by the excessive synthesis of melanin.