Endogenously formed reactive oxygen species continuously damage cellular constituents including DNA. These challenges, coupled with exogenous exposure to agents that generate reactive oxygen species, are both associated with normal aging processes and linked to cardiovascular disease, cancer, cataract formation, and fatty liver disease. Although not all of these diseases have been definitively shown to originate from mutations in nuclear DNA or mitochondrial DNA, repair of oxidized, saturated, and ring-fragmented bases via the base excision repair pathway is known to be critical for maintaining genomic stability. One enzyme that initiates base excision repair of ring-fragmented purines and some saturated pyrimidines is NEIL1, a mammalian homolog to Escherichia coli endonuclease VIII. To investigate the organismal consequences of a deficiency in NEIL1, a knockout mouse model was created. In the absence of exogenous oxidative stress, neil1 knockout (neil1 ؊/؊ ) and heterozygotic (neil1 ؉/؊ ) mice develop severe obesity, dyslipidemia, and fatty liver disease and also have a tendency to develop hyperinsulinemia. In humans, this combination of clinical manifestations, including hypertension, is known as the metabolic syndrome and is estimated to affect >40 million people in the United States. Additionally, mitochondrial DNA from neil1 ؊/؊ mice show increased levels of steady-state DNA damage and deletions relative to wild-type controls. These data suggest an important role for NEIL1 in the prevention of the diseases associated with the metabolic syndrome.DNA repair ͉ fatty liver disease ͉ mitochondria ͉ obesity ͉ oxidative stress A fter exposure to reactive oxygen species (ROS), the major purine lesions are 8-oxoguanine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 4,6-diamino-5-formamidopyrimidine (1-5). To reverse the potentially deleterious effects of oxidative DNA base lesions, cells primarily use the base excision repair (BER) pathway to restore the DNA to its undamaged state (6). The BER pathway is initiated by lesion-specific DNA glycosylases that catalyze bond scission and release the damaged base from the deoxyribose sugar.Unlike nucleotide excision repair, which functions only on nuclear DNA, the BER pathway is operative on both nuclear DNA and mitochondrial DNA (mtDNA). Although BER in the mitochondria repairs normal endogenous oxidant-induced DNA damage, expression of mitochondrially targeted DNA glycosylases that are specific for the repair of oxidatively induced DNA lesions leads to enhanced repair and increased survival after ROS challenge (7-10). These data emphasize that maintenance of the mitochondrial genome is a delicate balance of mtDNA copy number and BER capacity.To initiate repair of oxidative lesions, mammalian cells primarily use the products of the ogg1, nth1, neil1, and neil2 genes (11). These corresponding proteins have somewhat overlapping substrate specificities that may explain, at least partially, the absence of obvious phenotypes in ogg1-and nth1-null mice. NEIL1 has a strong sub...

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.

Ultraviolet (UV) light causes DNA damage in skin cells, leading to more than one million cases of non-melanoma skin cancer diagnosed annually in the United States. Although human cells possess a mechanism (Nucleotide Excision Repair, NER) to repair UV-induced DNA damage, mutagenesis still occurs when DNA is replicated prior to repair of these photoproducts. While human cells have all the enzymes necessary to complete an alternate repair pathway, Base Excision Repair (BER), they lack a DNA glycosylase that can initiate BER of dipyrimidine photoproducts. Certain prokaryotes and viruses produce pyrimidine dimer-specific DNA glycosylases (pdgs) that initiate BER of cyclobutane pyrimidine dimers (CPDs), the predominant UV-induced lesions. Such a pdg was identified in the Chlorella virus PBCV-1 and termed Cv-pdg. The Cv-pdg protein was engineered to contain a nuclear localization sequence (NLS) and a membrane permeabilization peptide (TAT). Here, we demonstrate that the Cv-pdg-NLS-TAT protein was delivered to repair-proficient keratinocytes and fibroblasts, and to a human skin model, where it rapidly initiated removal of CPDs. These data suggest a potential strategy for prevention of human skin cancer.