Impact of sustained de novo lipogenesis on mitochondrial dysfunction and hepatocellular redox during fatty liver disease

Abstract

Dysfunctional mitochondrial metabolism and sustained de novo lipogenesis are characteristic of non-alcoholic fatty liver disease (NAFLD), a common comorbidity of obesity and type 2 diabetes. We hypothesize that sustained de novo lipogenesis, through its biochemical relationships with mitochondria (e.g., tri-carboxylic acid (TCA) cycle) can contribute to dysfunctional oxidative flux during NAFLD. In study 1, male mice (C57BL/6JN) were fed either a low-fat (LF; 10% fat Kcal), high-fat (HF; 60% fat Kcal), or high-fructose/HF diet (HFr/HF; 34.9% fructose Kcal, 25% fat Kcal) for 24-wks. Liver mitochondria were utilized to determine oxygen consumption and were incubated in a buffer (for 5-min) to determine changes in TCA cycle intermediates, using gas chromatography-mass spectrometry (GC-MS). Plasma and liver samples were utilized for GC-MS based metabolomics and determination of gene and protein expression. In study 2, C57BL/6JN mice were provided 30% fructose in drinking water (FW) for 2-wks to induce hepatic de novo lipogenesis vs. mice given regular water (RW). Liver mitochondria were incubated in a buffer containing 1mM [ 13 C 3 ]pyruvate or 2.5mM [ 13 C 4 ]malate for 5-min. Isotopomer distribution of the TCA cycle intermediates were determined using GC-MS. Both HF and HFr/HF diets resulted in similar degrees of hepatic steatosis. However, lipogenic gene expression ( Scd1, Acyl, Fasn) and fasting plasma β-hydroxybutyrate levels were higher (p<0.001) in HFr/HF vs. HF group. Further, the feeding-to-fasting induction of genes involved in lipid oxidation ( Cpt1α, Lcad, Hmgcs2) was higher (p ≤0.01) in HFr/HF vs. HF livers. After 5-min of incubation, the HFr/HF liver mitochondria had higher (p<0.05) TCA cycle intermediates vs. the HF. The HFr/HF mitochondria also had higher expression of oxidative phosphorylation proteins and higher oxygen consumption rates (OCR), vs. the HF (p<0.05). In study 2, fructose in drinking water induced hepatic de novo lipogenesis. Induction of lipogenesis was also accompanied by higher mitochondrial OCR, higher reactive oxygen species, and higher TCA cycle metabolism (p<0.05). Gene expression of components of the mitochondrial nutrient shuttles ( SLC25A13, MPC1, MPC2, ME1) was upregulated in lipogenic livers (p<0.05). Incorporation of 13 C from [ 13 C 4 ]malate into pyruvate and α-ketoglutarate, indices of malic enzyme and TCA cycle activity, were higher (p<0.05) in lipogenic livers. Similarly, incorporation of 13 C from [ 13 C 3 ]pyruvate into aspartate and citrate, indices of pyruvate carboxylase and pyruvate dehydrogenase activity, were also higher (p<0.05) in lipogenic livers. These results demonstrate that the induction of several facets of mitochondrial oxidative metabolism and de novo lipogenesis accompany a carbohydrate-rich dietary milieu and NAFLD. Sustained induction of both de novo lipogenesis and mitochondrial oxidative function could contribute to the progression of metabolic dysfunction during NAFLD. National Institutes of Health R01 DK112865 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.