Project Summary The demographic shift of populations toward a more obese phenotype in just one or two generations appears to be primarily attributed to environmental or epigenetic mechanisms. Recent research advancements have highlighted the importance of nutrition during fetal and early life development and thus suggest an emerging need to evaluate the impact and risks of maternal diet schemes and understand the molecular mechanism. Our recent published work reported in a murine model that switching from a high-fat (HF) diet to a normal-fat (NF) diet 1 week before pregnancy (H1N group) and maintained NF diet until weaning, was not necessarily beneficial but actually exacerbates the offspring obesity and glucose intolerance, versus the offspring from the dam on a consistent maternal HF diet (HF group) or NF diet (NF group) through weaning. In our follow up study, we evaluated the impacts of different durations of maternal diet transition from a HF to a NF diet, which was 1 week (H1N group), 5 weeks (H5N group) or 9 weeks (H9N group), before pregnancy, on offspring obesity. We found that a longer transition duration led to less severe phenotype of obesity and non-alcoholic fatty liver disease (NAFLD). Our transcriptome data and gene ontology (GO) analysis identified significant association of different maternal diet-switch regimens with biological process involving lipid metabolism, energy utilization, epigenetic regulation and one-carbon pool metabolism and one-carbon transfer. Specifically, the DNA methylation enzymes and the one-carbon pool by folate signaling for methionine cycle was suggested to be affected by different maternal diet transition regimens. We hypothesize that maternal HF diet and a short-term transition from a HF to a NF diet genetically upregulate the hepatic lipid profile through inhibition of DNA methylation associated with disrupted methionine cycle; and a longer term transition allows restoration of the methionine cycle. To test this hypothesis, we propose to determine that hepatic lipid profiles are genetically regulated by different maternal diet transition regimens by lipidomics and signaling pathway analysis on lipid metabolism (Aim1). We will determine that global DNA methylation was differentially altered by different maternal diet transition regimens which lead to differential expression of genes involved in lipid metabolism in liver by bisulfite sequencing and an integrative analysis for identifying lipid metabolism specific DNA methylation by different maternal diet interventions (Aim2). Lastly, we will determine that disrupted methionine cycle caused by maternal HF diet contributes to offspring obesity and NAFLD, which is reversed by a long-term, but not a short-term transition from a HF to a NF diet (Aim3). This proposed study will potentially fill the gap in the field between lipid metabolism and epigenetics in transgeneration and therefore understand how maternal diet interventions would affect offspring health status.