Inhibitory effect and mechanism of action of blue light irradiation on adipogenesis

Blue light can reach the epidermis, dermis, and hypodermis of the skin and affect the physiology of each cell type. However, thus far, most studies have focused on the effects of blue light on the epidermis and dermis; no studies have been conducted on the effects of blue light on the hypodermis. In this study, we attempted to elucidate the effects of blue light on the hypodermis. Specifically, we investigated the effects of blue light on 3T3-L1 adipogenesis and its mechanism of action. In this study, we found that blue light reduced lipid accumulation and GPDH activity, indicating its antiadipogenic properties. Furthermore, blue light inhibited the mRNA and protein levels of peroxisome proliferator-activated receptor γ (PPARγ) and its target genes, such as Fasn and FABP4, and the luciferase activity of the PPRE promoter, suggesting that blue light downregulates the expression of adipogenic genes, leading to suppression of 3T3-L1 adipogenesis. Furthermore, blue light increased the phosphorylation of PPARγ, indicating its anti-adipogenic effect through PPARγ degradation. Blue light upregulates the expression and phosphorylation of transient receptor potential vanilloid 1 (TRPV1). Furthermore, blue light restored calcium influx, which was attenuated by adipogenesis. These data suggest that TRPV1 is involved in the anti-adipogenic effects of blue light. Blue light induced the phosphorylation of AMPK, ACC, and MAPKs, whereas capsazepine, an antagonist of TRPV1, attenuated the effects of blue light. Capsazepine treatment also reduced the blue light-induced anti-adipogenic effects. These results indicate that TRPV1 operates upstream of AMPK or MAPKs in the blue light-induced anti-adipogenesis process, which is mediated by activating the TRPV1-AMPK/MAPK signaling pathways. Meanwhile, inhibition of AMPK and MAPKs reduced the phosphorylation level of PPARγ, indicating that AMPK/MAPK signaling contributes to the phosphorylation of PPARγ. These results suggest the possibility of using blue light as an antiadipogenic agent.