Project description:Hepatic fat accumulation has been widely associated with diabetes and hepatocellular carcinoma (HCC). Here, we aim to characterize the metabolic response that high fat availability elicits in livers prior to development of these diseases. We find that, after a short term on high fat diet, otherwise healthy mice show elevated hepatic glucose metabolization, activated glucose uptake, glycolysis and glucose contribution to serine as well as elevated pyruvate carboxylase activity compared to control diet mice. To understand other changes in the liver tissue after high fat diet exposure, we conducted untargeted transcriptomics and proteomics. This glucose phenotype occurred independent from transcriptional or proteomic programming, which identified increased peroxisomal and lipid metabolism pathways. Interestingly, we observe that high fat diet fed mice exhibit an increased lactate production when challenged with glucose. This trait seems to find a parallel in a human cohort, where we observe a correlation between waist circumference and lactate secretion after an oral glucose bolus across healthy individuals. In an in vitro model of hepatoma cells, we found physiologically relevant palmitate exposure stimulated production of reactive oxygen species (ROS) and glucose uptake, a similar glycolytic phenotype to the in vivo study. This effect is inhibited upon interference with peroxisomal lipid metabolism and ROS production. Furthermore, we find that with exposure to an HCC-inducing hepatic carcinogen, continuation of high fat diet enhances the formation of HCC (100% with resectable tumors) as compared to control (50% with resectable tumors) in mice. However, regardless of the dietary background, all murine tumors showed similar alterations in glucose metabolism compared to those identified in fat exposed non-transformed mouse livers. Further, the presence of tumors in high fat diet exposed mice normalized glucose tolerance. Lipidomics analysis of tumor tissue and liver tissue from high fat diet exposed mice identified tumor tissue enrichment of diacylglycerol (DG) and phosphatidylcholine (PC) species. Some of these species were also increased in high fat diet liver tissue compared to control diet liver tissue. These findings suggest that fat can induce similar metabolic changes in non-transformed liver cells than found in HCC, and that peroxisomal metabolism of lipids may be a factor in driving a glycolytic metabolism In conclusion, we show that normal, non-transformed livers respond to fat by inducing glucose metabolism.

Project description:Background: Obesity has become a worldwide concern. Acute respiratory distress syndrome (ARDS) comprises 10.4% of total intensive care unit admissions and is associated with very high mortality. ARDS incidence is increased in obese patients. Exposure of rodents to hyperoxia mimics many of the clinical and pathologic features observed in patients with ARDS. The aim of this study was to determine the impact of high fat diet-induced obesity on the susceptibility to hyperoxic acute lung injury in mice. Methods: Male C57BL/6 mice received 60% fat versus ingredient matched 10% fat diet. Mice were exposed to >95% oxygen to induce lung damage. RNA was isolated from lung homogenates and by comparing RNA sequencing results with mouse Mitocarta, an inventory of genes encoding proteins with mitochondrial localization, we identified fatty acid synthase (FASN), an enzyme catalyzing de novo fatty acid synthesis, as one of the mitochondrial genes significantly changed with diet and with hyperoxia. We generated mice deficient in FASN in alveolar epithelial cells by using a tamoxifen inducible Cre recombinase construct (FASNflox/flox SPC Cre+/-) and subjected them to hyperoxia and high fat diet. Results: Mice receiving 60% fat diet had significantly higher weight, serum cholesterol and fasting glucose. High fat diet mice had significantly reduced survival and increased lung damage, as assessed by BAL protein and LDH, histology and TUNEL staining. By RNA sequencing of lung homogenates we identified FASN as one of the mitochondrial genes significantly reduced in mice receiving 60% compared to 10% fat diet and further reduced with hyperoxia. We confirmed that FASN protein levels in the lung of high fat diet mice were lower by immunoblotting and immunohistochemistry. After 48 hours of hyperoxia FASNflox/flox SPC Cre+/- mice displayed increased levels of BAL protein and LDH and more severe histologic lung injury. FASNflox/flox SPC Cre+/- mice remained more prone to lung injury after hyperoxic exposure even when they received 60% fat diet. Conclusions: These results demonstrate that obesity increases the severity of hyperoxia induced acute lung injury in mice by altering FASN levels in the lung of high fat diet fed rodents. To our knowledge, this is the first study to show that high fat diet leads to altered FASN expression in the lung and that both high fat diet and reduced FASN in alveolar epithelial cells lead to increased lung injury under hyperoxic conditions.

Project description:Purpose: To study the effects of high-fat diet feeding in mouse liver tissues with and without the hepatocellular carcinoma-inducing carcinogen DEN. Here, we used RNA sequencing to identify gene expression patterns associated with high-fat diet feeding. Methods: C57BL/6N mice were injected at 2-weeks of age with vehicle control (PBS) or DEN. At 6 weeks, mice were randomized to control diet, or 60% high-fat diet. After 8-weeks of diet exposure, mice underwent a 13C6-glucose labelling protocol, and liver tissues were extracted for anlaysis (metabolomic, transcriptomic). RNA was isolated from mouse liver tissue using Triazol extraction, purified, and libraries generated using KAPA Stranded mRNA Sequencing kit. After cDNA synthesis, adapter ligation, and final cDNA library generation, samples were sequenced on a flow cell (1x50bp single-end reads) and HiSeq4000 (Illumina). Data processing was conducted in an NGS pipeline (Snakemake) and quality control was performed with FastQC. Trimmed data was analyzed for differential expression (DEseq2) and gene set enrichment analysis (GSEA) to look for KEGG pathways and gene ontologies (GO) of interest. Results: Using 13C6-glucose labelling, we determined there was a glycolytic phenotype caused by high-fat diet exposure. Therefore, we focused on a diet effect in our transcriptomcis dataset. By comparing control diet to high-fat diet liver tissue, we found gene sets invloved in peroxisomes and lipid metabolism to be enriched in high-fat diet exposed livers. These findings were in line with in vitro testing of a liver cell line, showing peroxisomal metabolism of palmitate drives ROS production and a glycolytic phenotype. Conclusions: We found high-fat diet exposed liver exhibits a strong metabolic phenotype towards increased glucose metabolism. At the transcriptome level, we found a lipid-reporgramming signature, and not a glucose metabolism signature. The lipid reprogramming signature was in line with in vitro work using liver cell lines, in which exposure to palmitate stimulated a glycolyitic phenotype that was inhibited by targeting peroxisomal-derived ROS species. In combination with metabolic and lipidomic data after long-term exposure to DEN and subsequent tumor formtion, we discovered that high-fat diet can prime liver tissue for carcinogenesis and tumor development by stimulating a Warburg-like metabolism. These findings suggest that fat can induce similar changes in non-transformed liver cells than found in HCC. In conclusion, we show that normal, non-transformed livers respond to fat by inducing glucose metabolism.

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E-GEOD-16377

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