Digital Theses Archive


Tesi etd-03312021-145207

Type of thesis
Impact of hepatic lipid changes on mitochondrial function and fluidity in nonalcoholic fatty liver disease
Scientific disciplinary sector
Istituto di Scienze della Vita - TRANSLATIONAL MEDICINE
relatore Dott.ssa GASTALDELLI, AMALIA
  • de novo lipogenesis
  • fatty liver
  • Fluxomics
  • Lipidomics
  • metabolism
  • mitochondria
  • TAGneogenesis
Exam session start date
Non-alcoholic fatty liver disease (NAFLD) is associated with lipid accumulation within hepatocytes that can alter liver metabolism and cause lipotoxicity and severe liver damage. It has been hypothesized that in the progression from simple steatosis (NAFL) to steatohepatitis (NASH) lipotoxicity and mitochondrial dysfunction-related to lipid changes play a major role.<br>This thesis addressed the effects of hepatic lipid accumulation on mitochondrial function in two animal models of NAFLD, the high-fat high sucrose (HFHS) and the methionine choline-deficient (MCD) diet, investigating the impact of changes in hepatic and plasma lipidomics on changes in mitochondrial oxidation, membrane fluidity and lipid accumulation as a consequence of NAFLD. Moreover, changes in de novo hepatic lipid synthesis were measured using fluxomic techniques and investigated in the liver and mitochondria.<br>HFHS and MCD diet produced different phenotypes: HFHS led to hepatic fat accumulation, impaired glucose tolerance due to increased body weight and lipotoxicity, increased hepatic and plasma lipids; MCD also led to hepatic fat accumulation despite a decrease in weight and in circulating lipids, with histological evidence of NASH indicating more severe liver disease compared to HFHS. Analysis of plasma and hepatic lipidome showed that the mechanisms leading to hepatic lipid accumulation are distinct between the two diets. Fluxomic analyses showed de novo lipogenesis (DNL) of palmitic acid was unchanged in HFHS and decreased in MCD; however, synthesis of TAG incorporating de novo synthesized fatty acids decreased after HFHS feeding, suggesting adipose tissue fatty acid pool as main precursors for TAG synthesis. <br>Interestingly, in both animal models, hepatic mitochondrial function was not altered despite high TAG accumulation. The intermediate metabolites of the TCA cycle or the products of mitochondrial beta-oxidation were unchanged, suggesting that the excess hepatic lipid accumulation did not lead to mitochondrial dysregulation. However, the dietary challenges altered the lipid composition of the hepatic mitochondrial membrane by decreasing mitochondrial sphingomyelins in both HFHS and MCD diet and altering the phospholipid composition, thus resulting in decreased membrane fluidity.<br>In conclusion, by using lipidomics and fluxomics, we demonstrated that while NAFLD is associated with hepatic alteration in lipid metabolism and major lipid remodelling, hepatic mitochondrial dysfunction is not an early sign of this disease, although major alterations were observed in mitochondrial membrane fluidity.<br>