Imperatorin promotes melanin degradation in keratinocytes through facilitating autophagy via the PI3K/Akt signaling pathway

PurposeMelanin's pivotal role in skin protection and its overproduction leading to hyperpigmentation disorders highlight the necessity of regulating melanogenesis, with autophagy identified as a key degradation pathway. Imperatorin, a compound from Angelica dahurica, has been revealed to reduce melanin in epidermal keratinocytes, with the specific effects and mechanisms unknown. The purpose of this study was to investigate the mechanism by which imperatorin, reduces melanin production in HaCaT cells, with a focus on its potential role in promoting autophagy and regulating the PI3K/Akt signaling pathway.MethodsThe study used HaCaT cells to investigate the effects of imperatorin on melanin production, autophagy, and PI3K/Akt signaling. Melanin content was measured using a spectrophotometric method. Protein levels of PMEL, ATG1, ATG5, and LC3B II were assessed by Western blotting. Autophagy was further visualized by GFP-LC3B puncta formation. The autophagy inhibitor 3-MA, the PI3K/Akt inhibitor LY294002 and PI3K/Akt activator 740 Y-P were used to assess the role of autophagy and PI3K/Akt signaling in imperatorin's effects. Cell viability was monitored to ensure that imperatorin's effects were not due to cytotoxicity.ResultsImperatorin reduced melanin content in HaCaT cells in a dose-dependent manner without compromising cell viability. This reduction in melanin was accompanied by decreased levels of PMEL protein, a key player in melanosome formation. Additionally, imperatorin promoted autophagy in HaCaT cells, as evidenced by increased levels of autophagy-associated markers ATG1, ATG5, and LC3B II, as well as an increase in GFP-LC3B puncta. The autophagy inhibitor 3-MA partially reversed the effects of imperatorin on both autophagy markers and PMEL levels, indicating that autophagy plays a crucial role in imperatorin's depigmentation action. Furthermore, imperatorin inhibited Akt and mTOR phosphorylation, which are downstream targets of PI3K/Akt signaling, enhancing autophagy and further reducing melanin levels. The PI3K/Akt inhibitor LY294002 amplified imperatorin's effects on PI3K and Akt phosphorylation, autophagy, and melanin levels. While, PI3K/Akt activator 740 Y-P reversed imperatorin's effects on these factors.ConclusionsImperatorin reduces melanin in HaCaT cells via promoting autophagy and melanin degradation, possibly via the PI3K/Akt signaling. Taken together, imperatorin has the therapeutic potential for the treatment of hyperpigmentation disorders.