Galanin contributes to ultraviolet irradiation-induced inflammation in human skin

Exposure of the skin to ultraviolet (UV) irradiation causes various consequences such as inflammation and photoageing. Galanin is an active neuropeptide expressed widely in the central nervous system and peripheral tissues including the skin. Galanin promotes or inhibits inflammation in a context-dependent manner, but its role in UV irradiation-induced responses in human skin was still unknown. UV irradiation induced a substantial expression of galanin in primary epidermal keratinocytes in vitro and in human epidermis in vivo. Galanin knock-down by siRNA transfection markedly inhibited UV irradiation-induced expression of matrix metalloproteinase (MMP)-1, interleukin (IL)-1β, IL-6 and cyclooxygenase (COX)-2. Moreover, siRNA-mediated knock-down of GAL₂ , a principal galanin receptor in the skin, led to a considerable decrease in these mediators in keratinocytes. Collectively, our findings suggest that galanin is an important messenger between the neuroendocrine system and UV irradiation-damaged skin.