NB-UVB promotes melanogenesis and cell proliferation through downregulating the expression of miRNA-25 in human melanocytes

Objective: To investigate the effect of narrow-band UVB (NB-UVB) on melanocytes proliferation, melanin production, tyrosinase activities and miRNA-25 expression so as to explore the relationship between NB-UVB and miRNA-25 and the possible mechanism of NB-UVB for treatment of vitiligo. Methods: Melanocytes cultured in vitro were treated with 40 mJ/cm² dose of NB-UVB for 72 h, the effects of NB-UVB on cell proliferation, tyrosinase activity and melanin content were investigated. After NB-UVB stimulation for 12 h, the effect of NB-UVB on miRNA-25 expression in melanocytes was detected. Melanocytes were transfected with miRNA-25 mimics, miRNA-25 inhibitor and miRNA-25 mutant, respectively, the changes of cell proliferation, tyrosinase activitiy and melanin content were observed. Cell viability was detected using MTT method. Tyrosinase activities were measured with levodopa as the substrate. NaOH assay was used for the detection of melanin content. Real-time quantitative polymerase chain reaction (qRT-PCR) was used to detect miRNA-25 expression. Results: After NB-UVB of 40 mJ/cm² dose was used for the cells cultured for 72 h, the viability of melanocytes, tyrosinase activities, and melanin content were significantly increased (P<0.05). After NB-UVB stimulation for 12 h, miRNA-25 expression was significantly lower than that in the control group (P<0.05). After knockdown of miRNA-25, the cell proliferation of melanocytes, tyrosinase activities and melanin content were increased, whereas overexpression of miRNA-25 decreased the cell proliferation, tyrosinase activities and melanin production. Overexpression of miRNA-25 partially inhibited the effect of NB-UVB on the treatment of melanocytes. Conclusion: NB-UVB may promote cell proliferation, increase tyrosinase activities and melanin formation through partially downregulating the expression of miRNA-25 in melanocytes.