HMGB1 deficiency reduces H₂O₂-induced oxidative damage in human melanocytes via the Nrf2 pathway

Oxidative stress leads to melanocyte death and has been implicated in the pathogenesis of vitiligo. The nuclear factor, E2-related factor 2 (Nrf2), is a critical transcription factor in protecting cells from oxidative damage. High-mobility group box 1 (HMGB1) is a chromatin-associated nuclear protein and an extracellular damage-associated molecular pattern molecule. Extracellular HMGB1 released from activated immune cells, necrotic or injured cells, becomes a proinflammatory mediator through binding to cell-surface receptors of responding cells. In this study, we investigated the role of HMGB1 from melanocytes in the response to oxidative stress and the mechanism involved. We showed that HMGB1 is expressed by primary normal human epidermal melanocytes (NHEMs). H₂O₂ treatment increased cytoplasmic translocation and extracellular release of HMGB1. HMGB1 knockdown by small interfering RNA (siRNA) led to decreased apoptosis of NHEMs. HMGB1 inhibition enhanced the expression of Nrf2 and its target genes. The expression of Nrf2 and its downstream antioxidant genes was downregulated after the supernatant of H₂O₂-treated NHEMs was added to HMGB1-deficient cells. HMGB1 knockdown by siRNA suppressed the expression of the autophagosome marker, LC3, and enhanced p62 expression. Coimmunoprecipitation with Keap1 showed a reduced Nrf2-Keap1 interaction and an increased p62-Keap1 interaction under oxidative stress. These data demonstrated that external stimuli (eg, oxidative stress) may trigger autocrine HMGB1 translocation and release by melanocytes, suppressing the expression of Nrf2 and downstream antioxidant genes to induce melanocyte apoptosis, and thereby participate in the pathological process of vitiligo.