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!

A central problem in genetic epidemiology is to identify and rank genetic markers involved in a disease. Complex diseases, such as cancer, hypertension, diabetes, are thought to be caused by an interaction of a panel of genetic factors, that can be identified by markers, which modulate environmental factors. Moreover, the effect of each genetic marker may be small. Hence, the association signal may be missed unless a large sample is considered, or a priori biomedical data are used. Recent advances generated a vast variety of a priori information, including linkage maps and information about gene regulatory dependence assembled into curated pathway databases. We propose a genotype-based approach that takes into account linkage disequilibrium (LD) information between genetic markers that are in moderate LD while modeling gene-gene and gene-environment interactions. A major advantage of our method is that the observed genetic information enters a model directly thus eliminating the need to estimate haplotype-phase. Our approach results in an algorithm that is inexpensive computationally and does not suffer from bias induced by haplotype-phase ambiguity. We investigated our model in a series of simulation experiments and demonstrated that the proposed approach results in estimates that are nearly unbiased and have small variability. We applied our method to the analysis of data from a melanoma case-control study and investigated interaction between a set of pigmentation genes and environmental factors defined by age and gender. Furthermore, an application of our method is demonstrated using a study of Alcohol Dependence.

Inflammation-associated pigmentation changes are extremely common, but the etiology underlying this clinical observation remains elusive. Particularly, it is unclear how the myriad of cytokines known to be involved in inflammatory skin processes affect epidermal melanocytes. We sought to determine how IL-17 and tumor necrosis factor (TNF) influence normal human melanocytes, as these two cytokines have been implicated in various skin diseases. IL-17 and TNF jointly stimulated broad inductions of cytokines, including melanoma mitogens CXCL1 and IL-8. Moreover, IL-17 and TNF synergistically inhibited pigmentation-related signaling and melanin production, and induced keratinocyte production of beta-defensin 3, an antagonist for melanocortin 1 receptor. When analyzing psoriasis lesions that are known to overexpress IL-17 and TNF, we observed an increase in melanocyte number and a simultaneous decrease in pigmentation signaling. Furthermore, therapeutic neutralization of TNF and IL-17 with mAbs resulted in a rapid recovery of pigment gene expression in psoriasis lesions. These results demonstrate that IL-17 and TNF can affect both the growth and pigment production of melanocytes, which may contribute to the pigmentation changes associated with psoriasis. These findings may allow the development of novel therapeutics for pigmentary disorders and bring new insights into the immune milieu surrounding melanocytes and related neoplasms.

Accumulation of proteins in the endoplasmic reticulum (ER) typically induces stress and initiates the unfolded protein response (UPR) to facilitate recovery. If homeostasis is not restored, apoptosis is induced. However, adaptation to chronic UPR activation can increase resistance to subsequent acute ER stress. We therefore investigated adaptive mechanisms in Oculocutaneous albinism type 2 (Oca2)-null melanocytes where UPR signaling is arrested despite continued tyrosinase accumulation leading to resistance to the chemical ER stressor thapsigargin. Although thapsigargin triggers UPR activation, instead of Perk-mediated phosphorylation of eIF2alpha, in Oca2-null melanocytes, eIF2alpha was rapidly dephosphorylated upon treatment. Dephosphorylation was mediated by the Gadd34-PP1alpha phosphatase complex. Gadd34-complex inhibition blocked eIF2alpha dephosphorylation and significantly increased Oca2-null melanocyte sensitivity to thapsigargin. Thus, Oca2-null melanocytes adapt to acute ER stress by disruption of pro-apoptotic Perk signaling, which promotes cell survival. This is the first study to demonstrate rapid eIF2alpha dephosphorylation as an adaptive mechanism to ER stress.

Pigmentation disorders span the genetic spectrum from single-gene autosomal recessive disorders such as oculocutaneous albinism (OCA), the autosomal dominant disorder piebaldism to X-linked ocular albinism and multifactorial vitiligo. OCA connotes a group of disorders that result in hypopigmented skin due to decreased melanin production in melanocytes and loss of visual acuity. There are four non-syndromic forms, OCA1-4, which are classified based on the gene that is mutated (tyrosinase, OCA2, tyrosinase-related protein 1 and SLC45A2, respectively). Despite the fact that multiple genes account for the various forms of OCA, the phenotypes of all four forms result from disruption in the maturation and trafficking of the enzyme tyrosinase. OCA2 is the most prevalent autosomal recessive disorder among southern African blacks, affecting 1/3 900 individuals; while OCA3, although rare, is most prevalent in southern Africa. Another common pigmentation disorder in southern Africa is vitiligo, which affects 1 - 2% of people worldwide. Vitiligo is a complex, acquired disorder in which melanocytes are destroyed due to an autoimmune response. The aetiology underlying this disorder is poorly understood, although recent genetic association studies have begun to shed light on the contributing factors. Pigmentation disorders have significant psychosocial implications and co-morbidities, yet therapies are still lacking. Recent progress in our understanding of the pathobiology of both albinism and vitiligo may herald novel treatment strategies for these disorders.

BACKGROUND: Oculocutaneous albinism type 2 (OCA2) is caused by mutations of the OCA2 gene. Individuals affected by OCA2 as well as other types of albinism are at a significantly increased risk for sun-induced skin-cancers, including malignant melanoma (MM). OBJECTIVE: To identify the molecular etiology of oculocutaneous albinism in a previously uncharacterized melanoma pedigree and to investigate the relationship between two OCA2 variants and melanoma predisposition in this pedigree. METHODS: DNA and RNA were isolated from the peripheral blood of seven patients in a familial melanoma pedigree. Electron microscopy was performed on the individual with clinical oculocutaneous albinism. OCA2, TYRP1, MC1R, CDKN2A/p16, CDKN2A/p19ARF, and CDK4 genes were sequenced in affected individuals. The relationship between OCA2 variants and melanoma was assessed using a pedigree likelihood-based method. RESULTS: The proband was determined to be an OCA2 compound heterozygous mutation carrier with a previously reported conservative missense mutation (V443I) and a novel non-conservative missense mutation (L734R). The pedigree contained individuals diagnosed with both cutaneous and iris melanoma. Based on co-segregation analysis, the odds of these OCA2 variants being high penetrance loci for melanoma was: 1.3-to-1 if we include the iris melanoma as affected and 6.5-to-1 if we only consider cutaneous melanoma as affected. CONCLUSION: The discovery of this novel OCA2 variant adds to the body of evidence on the detrimental effects of OCA2 gene mutations on pigmentation, supports existing GWAS data on the relevance of the OCA2 gene in melanoma predisposition, and may ultimately assist in the development of targeted molecular therapies in the treatment of OCA and melanoma.