Faculty Bibliography

Vitiligo is characterized by depigmented skin patches due to localized loss of melanocytes. The etiology of vitiligo is not fully understood, particularly the mechanisms that initially trigger depigmentation. Induction of oxidative stress is thought to be a common attribute of trigger events in vitiligo, while autoimmunity contributes to disease progression. In this study we sought to identify mechanisms that link disease triggers and the spread of lesions. A hallmark of melanocytes at the periphery of vitiligo lesions, even when cultured in vitro, is dilation of the endoplasmic reticulum (ER). We hypothesized that oxidative stress caused by trigger events extends to the ER where redox reactions that facilitate protein folding are disrupted and that the subsequent accumulation of misfolded peptides activates the unfolded protein response (UPR). The UPR initially signals a reduction in global protein synthesis, while promoting expression of folding chaperones in order to restore homeostasis. Sustained UPR activation has been implicated in several autoimmune disorders and may play a role in vitiligo. We used 4-tertiary butyl phenol (4-TBP) and monobenzyl ether of hydroquinone (MBEH), phenols known to trigger occupational vitiligo, to study pathways that contribute to melanocyte loss. Expression of key UPR components was increased following exposure of human melanocytes to the phenols. In addition, we observed UPRmediated increases in pro-inflammatory interleukin-6 (IL6) and IL8, which have been shown to be increased in the skin of patients with vitiligo. We next investigated UPR-regulated pathways that may contribute to cytokine production and determined that cross-talk between the UPR and the nuclear factor-kappa B (NFkB) pathway contributes to the increase in expression of IL6 and IL8 following phenol exposure. Identification of the pathways that link exposure to vitiligoinducing triggers and onset of autoimmunity may allow for the development of more effective therapies for this disfiguring di!

Vitiligo is a common disorder characterized by progressive melanocyte death. Vitiligo can be induced in an occupational setting by exposure to vitiligo-inducing phenols (VIPs) such as 4 tert-butyl phenol (4TBP) and monobenzyl ether of hydroquinone (MBEH). These VIPs are believed to specifically target melanocytes due to their structural similarity to tyrosine and competition for binding to tyrosinase, the rate-limiting enzyme for melanin synthesis. By exposing normal melanocytes to VIPs and using microarray analysis and bioinformatics approaches for gene expression profiling, we identified key signaling pathways that are involved in the melanocyte response to VIP exposure. In particular, we hypothesized that exposure of primary human melanocytes to VIPs would result in oxidative stress that triggers antioxidant responses in order to protect melanocytes from cell death. Following melanocyte exposure to VIPs, HO-1 was upregulated (4TBP exposure: 5.49-fold; MBEH exposure: 25.98- fold). HO-1 is a direct target of Nrf2, a key regulator of the Nrf2- ARE antioxidant response. Activation of Nrf2 and its targets, HO- 1 and NQO1, was confirmed by conventional Western blot analysis and quantitative RT-PCR. We are now characterizing the mechanisms that regulate Nrf2 activation in response to VIPs. Additional antioxidants including SOD2 (4TBP: 10.5-fold; MBEH: 38.5-fold), peroxiredoxin 6 (4TBP: 2.44-fold; MBEH: 15.18-fold), and Nrf2 binding partners, MafK (4TBP: 2.12-fold; MBEH: 2.50- fold) and MafF (4TBP: 2.32-fold; MBEH: 3.16-fold) were also upregulated with VIP exposure and are being investigated further. Several studies have revealed dysfunctional antioxidant responses in melanocytes from patients with vitiligo, however the underlying mechanisms that reduce their efficacy are yet to be determined. We hypothesize that investigation of VIP-induced pathways may lead to the characterization of these mechanisms and provide opportunities for development of targeted therapeutics for the treatment of vitiligo