The association of FOXO3A gene polymorphisms with serum FOXO3A levels and oxidative stress markers in vitiligo patients
Introduction
Vitiligo is an acquired depigmenting disease characterized by milky white patches of skin due to local loss of the epidermal melanocytes (Halder and Chappell, 2009, Huang et al., 2002). It occurs with a frequency of 0.1–2% worldwide (Ortonne, 2008). Although its pathophysiology is still unknown, diverse theories have been proposed, including autoimmune, neural, oxidative stress, apoptosis, and genetic factors (Passeron and Ortonne, 2005). Recent studies have suggested that oxidative stress might play a prominent role in the pathogenesis of vitiligo (Maresca et al., 1997, Schallreuter et al., 1991, Schallreuter et al., 1994, Schallreuter et al., 1999). Oxidative stress is defined as a disruption of the delicate balance between the formation of reactive oxygen species (ROS) and the antioxidant defense system (Sies, 1991). ROS, especially superoxide anions and hydrogen peroxide (H2O2), can cause lipid peroxidation and protein and DNA oxidation, as well as alter apoptotic pathways, thereby inducing cellular injury. It has been suggested that some enzyme defects during melanogenesis might cause oxidative stress, with a consequent accumulation of H2O2 (Jimbow et al., 2001). Several clinical studies have demonstrated increased H2O2 levels and decreased antioxidant enzyme activities in vitiligo patients (Beazley et al., 1999, Hazneci et al., 2005, Koca et al., 2004, Schallreuter et al., 1991); high levels of H2O2 are thought to trigger melanocyte degeneration in patients with vitiligo. It has been suggested that ROS such as H2O2 stimulate apoptosis through activation of signaling molecules, including protein kinase C and c-Jun-N-terminal kinase (Essers et al., 2004).
Genetic factors are also thought to have an important role in the etiology of vitiligo (Imran et al., 2012). Recently, single-nucleotide polymorphisms (SNPs) of several candidate genes, including PTPN22, NLRP1, ESR1, FOXP1, CAT, COMT, TLR-2, and TLR-4, were reported to be associated with vitiligo susceptibility (Casp et al., 2002, Imran et al., 2012, Karaca et al., 2013, Shajil et al., 2006). Forkhead box class O (FOXO) proteins are a subclass family of the Forkhead box (FOX) transcription factors, including FOXO1, FOXO3A, FOXO4, and FOXO6, which play a crucial role in diverse cellular processes such as cell cycle regulation, apoptosis, oxidative stress and DNA repair (Brunet et al., 1999, Furukawa-Hibi et al., 2005). Studies have shown that FOXO3A have important roles in the regulation of oxidative stress. Activation of FOXO3A has been shown to induce gene expression of manganese superoxide dismutase (MnSOD) and catalase antioxidant enzymes (Kops et al., 2002, Nemoto and Finkel, 2002), as well as prevent cell integrity against genotoxic agents H2O2 and UV irradiation (Brunet et al., 2004, Klagge et al., 2011). The human FOXO3A gene is located at chromosomal position 6q21 and is comprised of three exons and two introns (Anderson et al., 1998). Thus far, functional SNPs of FOXO3A have been found to be associated with longevity, obesity, and bipolar disorders (Anselmi et al., 2009, Flachsbart et al., 2009, Kim et al., 2006; Li, 2008; Magno et al., 2001, Willcox et al., 2008). However, to the best of our knowledge, there have been no reports regarding the relationship between FOXO3A genetic variants and the risk of vitiligo.
Taking into account the possible effects of oxidative stress and apoptosis in the pathophysiology of vitiligo, we hypothesized that FOXO3A genetic variants might be associated with risk of vitiligo. For this reason, we investigated two functional SNPs (rs2253310, rs4946936) in the FOXO3A gene, as well as its protein levels and superoxide dismutase (SOD) and catalase antioxidant enzyme activities in vitiligo patients and healthy controls. In addition, plasma advanced oxidation protein product (AOPP) levels were evaluated in an effort to understand the possible role of protein oxidation in the etiology of vitiligo.
Section snippets
Methods
This study was approved by the Ethics Committee of the Bulent Ecevit University Faculty of Medicine (protocol no; 2011-63-17/05) and performed in accordance with the guidelines of the Declaration of Helsinki; written informed consent was obtained from all the subjects. Eighty-two vitiligo patients and 81 matched healthy controls, all recruited from the Department of Dermatology at Bulent Ecevit University Hospital, were included in the study. The healthy controls displayed no clinical evidence
Clinical and biochemical variables
The clinical characteristics of the vitiligo patients and the healthy controls are shown in Table 1. No statistically significant differences in median ages between the two groups were observed (p > 0.05). SOD activity and AOPP levels were determined to be significantly higher in the patients with vitiligo than in the healthy control group (p < 0.001; Table 3). Catalase activity and FOXO3A levels of the patients with vitiligo were lower than those of the control group (p < 0.001; Table 3).
Genotype and allele frequencies
The
Discussion
Oxidative stress and genetic predisposition is thought to play an important role in the pathogenesis of vitiligo. To the best of our knowledge, our study is the first to evaluate the association of FOXO3A gene polymorphisms, FOXO3A levels, and protein oxidation with the pathophysiology of vitiligo. We also investigated activities of the main antioxidant enzymes in vitiligo patients and healthy subjects by measuring SOD and catalase activities. In this study, we demonstrated that rs4946936 of
Conflict of interest
The authors report that there is no conflict of interests.
Acknowledgments
This study was supported by the Research Fund of the University Mugla Sitki Kocman (No: 2011/68). We would also like to thank Dr. Seda Sevinc KAYA for her assistance in collecting patient samples.
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