Role of oxidative stress in melanoma and steatohepaititis

Abstract

During the development of this Thesis, we used zebrafish models to study the impact of Dual Oxidase 1 (Duox1) and Xanthine dehydrogenase (Xdh), two major oxidative stress contributing enzymes, during the progression of melanoma and steatohepatitis. In the first chapter, we report a dual role of DUOX1 in melanoma. We found that high, but not low, DUOX1 transcript levels in early melanoma are associated with poor patient survival, while no statistically significant differences in patient survival were observed in late melanoma. In addition, altered signaling pathways involved in immune system, complement activation and allograft rejection were observed in melanoma expressing low levels of DUOX1, suggesting the importance of oxidative stress balance in melanoma progression. Although we did not find any significant effect of this enzyme in melanocyte transformation and early melanoma progression, allotransplantation experiments in immunocompromised zebrafish recipients revealed that Duox1-deficient melanoma cells showed decreased growth but, paradoxically, generated more metastasis than control. The relevance of DUOX1 in melanoma and in skin chronic inflammatory diseases, point to DUOX1 as a pharmacological target. So, we generated a melanoma cell line that overexpresses both DUOX1 and its maturation factor DUOXA1, to perform pharmacological screening to find specific activators or inhibitors of this enzyme. Among 256 FDA/EMA-approved drugs, we identified several promising candidates that required validation. In the second chapter, we studied the role played by Xdh in steatohepatitis development. We observed accumulation of lipids and increased reactive oxygen species (ROS) production in the liver of larvae fed with high cholesterol diet (HCD), concomitant with liver histological features related with Non-Alcoholic Fatty Liver Disease/Non-Alcoholic Steatohepatitis (NAFLD/NASH) in humans, such as accumulation of lipid droplets and ballooning of hepatocytes. Proteomic analysis of livers of wild type larvae fed with HCD showed downregulation of several enzymes which participates in the cholesterol and lipid biosynthesis pathways. Importantly, Xdh deficiency ameliorated the progression of the disease by decreasing all these pathological alterations associated to NASH progression. One of the most interesting observations of our study is that Xdh deficiency was able to ameliorate NASH progression in larvae fed with HCD and, concomitantly, to promote the downregulation of lipid metabolic pathways, including fatty acid degradation, retinol metabolism and glycerolipid metabolism, and the upregulation of oxidative phosphorylation. Overall, all these results support that Xdh is involved in NAFLD disease progression, explaining the association found between XDH and NAFLD in several clinical studies, and point out to the relevance of the zebrafish larval model fed with HCD to identify novel signaling pathways associated with NAFLD/NASH in humans.