Regulation of Melanogenesis in Skin Epidermal Keratinocytes via Activation of α7 Nicotinic Acetylcholine Receptor on the Expression of α‐Melanocyte‐Stimulating Hormone

UV irradiation stimulates the production of pro-opiomelanocortin (POMC) and its derived peptides, for example, α-melanocyte stimulating hormone (α-MSH), from keratinocytes that subsequently stimulate melanin production in melanocytes. The idea of "skin synapse" describes the interplay between keratinocytes and melanocytes being modulated by cholinergic signaling, in which acetylcholine (ACh) release is induced by UV irradiation, regulating the process of pigmentation. ObjectiveHere, the role of the cholinergic system in regulating α-MSH production in keratinocytes during UV-induced skin pigmentation was identified. α7 Nicotinic acetylcholine receptor (nAChR) agonists and antagonists, Ca²⁺ chelator BAPTA-AM, and α7 nAChR shRNA were applied onto HaCaT keratinocytes to evaluate the expression of POMC and production of α-MSH following UVB induction. Moreover, the conditioned medium collected from the treated HaCaT keratinocytes was added to cultured B16F10 melanoma cells to assess melanogenesis. Inhibiting α7 nAChR by its antagonist, or Ca²⁺ influx by Ca²⁺ chelator, suppressed the UVB-induced POMC expression and α-MSH production in cultured keratinocytes. Genetic silencing α7 nAChR expression hindered the UVB-induced POMC expression. Besides, the conditioned medium collected from keratinocytes being treated with α7 nAChR antagonist and UVB downregulated melanogenesis, as implied by the reduced expression of melanogenic enzymes, indicating the suppressing effect of α7 nAChR antagonist on the production of α-MSH in keratinocytes. The result suggests that α7 nAChR mediates the regulation of melanogenesis through the modulation of UVB-induced POMC transcription and α-MSH production in keratinocytes.