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

Abstract

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.

Oxidative Stress–Induced HMGB1 Release from Melanocytes: A Paracrine Mechanism Underlying the Cutaneous Inflammation in Vitiligo

“…In the current study, we found that HMGB1 was abnormally localized in the cytoplasm of the remaining melanocytes in vitiligo perilesional skin. Further in vitro experiments showed that under the treatment with 0.5 mM H 2 O 2 , which is known as the concentration of H 2 O 2 in vitiligo lesion , HMGB1 was translocated from nucleus to cytoplasm in melanocytes and subsequently released into extracellular space, which was consistent with the findings reported by Mou et al (2018). Keratinocytes also failed to release HMGB1 under the same treatment, implicating that melanocytes are the main source of proinflammatory HMGB1 in vitiligo.…”

“…As a classic damage-associated molecular pattern molecule, HMGB1 is involved in the development of many autoimmune skin diseases, including psoriasis (Zhang et al, 2017), atopic dermatitis (Karuppagounder et al, 2015;Wang et al, 2018), and lichen planus (de Carvalho et al, 2018). Recently, some studies have reported that HMGB1 may directly induce the apoptosis of melanocytes in vitiligo (Becatti, 2017;Mou et al, 2018). We found that HMGB1 secreted by melanocytes under oxidative stress was able to promote the secretion of chemokines from keratinocytes, which could induce the cutaneous infiltration of CD8 þ T cells and the maturation of DCs.…”

“…Oxidative stress is a central regulator of the function of HMGB1 (Mou et al, 2018;Petrovi c et al, 2017;Yu et al, 2015). In brief, oxidative stress affects the redox status of cysteines in HMGB1, which determines its proinflammatory activity (Andersson et al, 2018).…”

Glycyrrhizin protects human melanocytes from H2O2‑induced oxidative damage via the Nrf2‑dependent induction of HO‑1

“…1A) on the survival rate and apoptosis of NHEMs treated with H 2 O 2 . Our previous study determined that treatment of melanocytes with 0.5 mM H 2 O 2 for 24 optimal to induce oxidative stress (31). As shown in Fig.…”

“…GR binds to high-mobility group box 1 (HMGB1) protein and inhibits its cytokine activities as an HMGB1 inhibitor (38). Our previous study also showed that oxidative stress stimulation triggers autocrine HMGB1 translocation and release from melanocytes, leading to the suppressed expression of Nrf2 and downstream genes, which induces melanocyte apoptosis (31). GR may also upregulate the Nrf2 pathway by inhibiting HMGB1 and is involved in antioxidant effects.…”