Fluoxetine activates melanocyte stem cells indirectly through the epithelial 5-hydroxytryptamine (5-HT) receptor...

Melanocyte stem cells (McSCs) serve as the major origin of epidermal melanocytes in adults and fulfill a critical function in skin homeostasis, repair, and regeneration. Preclinical and clinical studies confirm McSCs have therapeutic potential for diseases including vitiligo. This study shows fluoxetine treatment is associated with McSC activation. Using narrow-band UVB (NB-UVB) irradiation as a positive control, we found 14-day fluoxetine treatment was associated with an increased number of epidermal melanocytes in the McSC-depletion mouse model, an effect correlated with upregulated hair follicle McSC activation 1-3 days post-treatment. Consistently, in McSC-specific Tg(-1.1tfap2b:eGFP)^cpu108 zebrafish, we observed increased epidermal melanocyte numbers and McSC activation after 2-day fluoxetine treatment. Notably, at the study timepoint, unlike NB-UVB irradiation, fluoxetine treatment was associated with no oxidative stress, DNA damage, apoptosis, or inflammation in mouse skin. Furthermore, 5-hydroxytryptamine receptor 1A (HTR1A) and Wnt7a colocalized in hair germ epithelial cells on day 3, with both molecules upregulated in fluoxetine-treated group. Conditioned medium from fluoxetine-treated HaCaT cells (24 h) applied to SK-MEL-2 cells (48 h) indicated that fluoxetine indirectly activated Wnt signaling through epithelial HTR1A, regulating melanocyte differentiation. Collectively, this study provides a foundation for investigating the dynamic behavior of early melanocytes and developing skin repair strategies.