The role of DNA repair deficiency in lipid accumulation: A proof-of-concept study

Animal models suggest an association between base excision repair (BER) deficiency and increased risk of obesity. To mechanistically investigate the effect of BER deficiency on intracellular lipid accumulation, we studied metabolic activity in in vitro BER knockdown (KD) models, targeting MutY DNA Glycosylase (MUTYH), Nth Like DNA Glycosylase 1 (NTHL1) and 8-Oxoguanine DNA Glycosylase (OGG1). We hypothesized that exposing BER deficient cells to lipids leads to reduced mitochondrial function and enhanced intracellular lipid accumulation. Stable BER KD models were generated in HepG2 cells using lentiviral shRNAs. KD was confirmed by qRT-PCR and BER activity was assessed using a modified comet assay. Upon exposure to a mixture of oleic and palmitic acid, DNA damage and mitochondrial copy number were only altered in NTHL1-KD cells, but all KD cells accumulated more intracellular lipids compared to lacZ control cells as determined by Oil-Red-O (ORO) staining. Compared to control cells, exposure to the fatty acid mixture increased proton leak in MUTYH-KD cells, indicating impaired mitochondrial function. Moreover, all KD cells showed reduced β-oxidation activity when exposed to the fatty acid mixture. Overall, this study shows that BER deficient HepG2 cells are more prone to accumulated lipids, which was associated with impaired mitochondrial function. These findings are relevant in understanding the underlying mechanisms that modulate the sensitivity of a person to accumulate lipids and increase their risk of developing metabolic diseases such as obesity and fatty liver disease.