Melatonin attenuates dermal fibroblast senescence with suppression of CXCL9-associated inflammatory signaling and mitochondrial stress.

Skin aging is driven by intrinsic and extrinsic factors that promote fibroblast senescence and dermal extracellular matrix degradation. Melatonin has potent antioxidant and anti-inflammatory activities. Here, we investigated the anti-aging effects of melatonin in human dermal fibroblasts and aged mouse skin, focusing on the pro-inflammatory chemokine CXCL9. Replicative-, irradiation-, and doxorubicin-induced senescence models of human dermal fibroblasts were used to assess the effects of melatonin. Melatonin significantly reduced the proportion of senescence-associated β-galactosidase-positive cells (38.5%-41.6%) and suppressed the expression of senescence markers, such as p16INK4a and γH2AX, and the senescence-associated secretory phenotype (SASP) factors IL1A and IL6. Additionally, melatonin lowered intracellular reactive oxygen species levels (50.8%-87.7%), restored mitochondrial membrane potential, ATP levels, and reduced STAT1 phosphorylation. CXCL9 was markedly upregulated in senescent fibroblasts and was suppressed by melatonin treatment. siRNA-mediated CXCL9 knockdown mimicked the anti-senescence effects of melatonin, whereas the melatonin receptor antagonist luzindole attenuated these effects. Furthermore, melatonin pretreatment protected young fibroblasts against irradiation-induced senescence. In vivo, intradermal melatonin administration increased dermal thickness by 97% and collagen density by 23%, while reducing SASP factor expression. Collectively, these findings suggest that melatonin attenuates dermal fibroblast senescence in association with reduced CXCL9 expression and preservation of mitochondrial homeostasis.