Light-emitting diode 585 nm photomodulation inhibiting melanin synthesis and inducing autophagy in human melanocytes

Background Melasma is a common hyperpigmentation skin disease on face. Light-emitting diode (LED) photomodulation (585 nm) is reported to be effective for the treatment of melasma. However, whether and how LED photomodulation would influence melanogenesis of human epidermal melanocytes (HEMs) is unknown. Objective To evaluate the effects of LED photomodulation (585 nm) on melanogenesis in HEMs. Methods HEMs were irradiated with fluences of 0, 5, 10 and 20 J/cm2 585 nm LED light. After 5-day treatment, cell viability was analyzed by CCK-8 assay, and apoptosis was assessed by Annexin V APC assay. Melanin content and tyrosinase activity were measured by spectrophotometer. Melanosome stage and autophagosomes were determined under transmission electron microscope (TEM). The formation of autophagic punctate structures was observed under confocal microscope. RT-PCR and western blotting were used to assess the expression of relative mRNA and protein levels. Results Yellow light LED 585 nm had no effects on HEMs cell viability and apoptosis. Treatment with LED 585 nm from 5 J/cm2 to 20 J/cm2 inhibited melanosome maturation, decreased melanin content and tyrosinase activity. Inhibition was accompanied by the decreased expression of tyrosinase (TYR), tyrosinase-related protein-1 (TRP-1) and microphthalmia-associated transcription factor (MITF) on both mRNA and protein levels. Autophagosomes were observed under TEM. Autophagic punctate structures of microtubule-associated protein light chain 3 (LC3) proteins were induced by LED 585 nm light. The configuration change of LC3 from LC3-I to LC3-II, and the degradation of p62 protein were observed after LED 585 nm. Furthermore, we also revealed that the anti-melanogenic effect of LED 585 nm photomodulation was reversed by 3-Methyladenine (3-MA), which inhibits autophagy by blocking autophagosome formation via the inhibition of type III Phosphatidylinositol 3-kinases (PI-3K). Conclusions Our finding demonstrated that LED photomodulation with 585 nm wavelength suppressed melanin content in HEMs, and the effect was caused by its dose-dependent inhibition on melanogenesis and the induction of HEMs autophagy. This may provide new insights into the efficacy of LED photomodulation in the treatment of hyperpigmentation disorders.