Exposure to chronic and acute oxidative stress is correlated with many human diseases, including, but not limited to, cancer, heart disease, diabetes, and obesity. In addition to cellular lipids and proteins, cellular oxidative stress can result in damage to DNA bases, especially in mitochondrial DNA. We previously described the development of spontaneous late-onset obesity, hepatic steatosis, hyperinsulinemia, and hyperleptinemia in mice that are deficient in the DNA glycosylase nei-like 1 (NEIL1), which initiates base excision repair of several oxidatively damaged bases. In the current study, we report that exposure to a chronic oxidative stress in the form of a high-fat diet greatly accelerates the development of obesity in neil1−/− mice. Following a 5-wk high-fat diet challenge, neil1−/− mice gained significantly more body weight than neil1+/+ littermates and had increased body fat accumulation and moderate to severe hepatic steatosis. Analysis of oxygen consumption by indirect calorimetry indicated a modest reduction in total oxygen consumption in neil1−/− mice that was abolished upon correction for lean body mass. Additionally, hepatic expression of several inflammatory genes was significantly upregulated in neil1−/− mice following high-fat diet challenge compared with chow-fed or neil1+/+ counterparts. A long-term high-fat diet also induced glucose intolerance as well as a significant reduction in mitochondrial DNA and protein content in neil1−/− mice. Collectively, these data indicate that NEIL1 deficiency results in an increased susceptibility to obesity and related complications potentially by lowering the threshold for tolerance of cellular oxidative stress in neil1−/− mice
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