High fat diet causes hepatic lipid accumulation by programming lipid synthesizing genes via gene body methylation
A high-fat diet (HFD) has been shown to cause more hepatic lipid accumulation as compared to a low-fat control (C) diet. However, it is still unclear what role epigenetic mechanisms play in hepatic lipid accumulation. We hypothesize that a HFD will cause greater hepatic lipid accumulation through increased lipid synthesizing gene expression via decreased gene methylation. The objective of this study is to determine the role of methylation in hepatic lipid synthesizing genes as an outcome of hepatic lipid accumulation due to a HFD. Two models were used to address the following: the direct effects of a post-weaning HFD on hepatic lipid synthesizing genes as well as the indirect effects of a maternal HFD. Timed-pregnant Sprague-Dawley rats were given either a C (16% fat) or HFD (45% fat) during gestation and lactation. Pups from both C mothers were weaned onto either a C or HFD and the pups from the maternal HFD were weaned onto a HFD, creating three offspring groups: C/C, C/HF, and HF/HF. Model 1 compared the C/C group to the C/HF group, while model 2 focused on the comparison of the C/HF group to the HF/HF group. Rats were sacrificed at 12 weeks of age, and the left lobe of the liver was used for further analysis. In model 1, liver histology showed greater hepatic fat accumulation in the C/HF group. Gene expression data was measured for multiple genes in the following pathways: glycolysis, gluconeogenesis, fatty acid synthesis, and triacylglycerol synthesis. Glycerol-3-phosphate acyltransferase (GPAM), fatty acid synthase (FASN), acetyl CoA carboxylase 1 (ACC1), and glucose-6-phosphotase (G6Pase) showed lower levels of mRNA in the C/HF group as compared to the C/C group. DNA methylation of those genes was analyzed based on data obtained from methyl-DNA immunoprecipitation with high-throughput sequencing (MEDIP-SEQ). Differential methylation was observed for G6Pase, GPAM, and ACC1. GPAM and ACC1 showed decreased average methylation read peaks for C/HF in comparison to the C/C group. The data in model 1 suggest that decreased gene body methylation leads to decreased lipid synthesizing genes. In model 2, liver histology showed greater hepatic fat accumulation in the HF/HF group. Gene expression data were measured in the same pathways as previously stated. GPAM and FASN showed higher levels of mRNA in the HF/HF group. MEDIP-SEQ data showed greater average methylations read peaks for HF/HF along the gene body for GPAM. Methylation specific polymerase chain reaction (MSP) validated these results by showing greater methylation on intron 1, on the 7.2 kilobases (kB) pair region, as well as exon 21, at 59.5 kB pair region on GPAM. The data in model 2 suggest that increased gene body methylation leads to increased lipid synthesizing genes. These studies suggest that there is a positive relationship between gene body methylation and mRNA expression in hepatic lipid synthesizing genes.
Epigenetics, Nutrient-gene interaction, Nonalcoholic fatty liver disease, Obesity
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign