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Title: The dynamics of hepatic lipid metabolism in humans : understanding their role in fatty liver disease
Author: Gunn, Pippa
ISNI:       0000 0004 7960 0104
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2018
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Non-alcoholic fatty liver disease (NAFLD) has become increasingly prevalent. It is associated with changes in hepatic and whole-body fatty acid (FA) metabolism, with the first stage of the disease, steatosis, characterised by excess triacylglycerol (TAG) storage with a specific (macrovesicular) lipid droplet (LD) pattern; the final step in TAG synthesis is catalysed by diacylglycerol acyltransferase (DGAT). Although the pathogenesis of NAFLD is known to include both genetic and lifestyle factors, the sequence of events that precedes lipid accumulation in the liver remains unclear. Human hepatoma cell lines (HepG2 and Huh7 cells) were optimised for use as models of hepatic FA metabolism. Use of human serum in the cell media resulted in reduced de novo lipogenesis (DNL) and improved levels of FA oxidation and secretion in both cell lines; Huh7 cells were used for subsequent experiments. To create a macrovesicular LD pattern, low (glucose only) and high (glucose and fructose) levels of sugar were added to the media in combination with low and high concentrations of FAs. The addition of high fat high sugar (HFHS) media to Huh7 cells caused accumulation of large LDs in a more macrovesicular pattern, which was similar to steatotic primary hepatocytes. Low and high sugar and fat treatments were used on CRISPR-modified Huh7 cells with DGAT2 knocked out; changes in these cells included a reduction in TAG secretion, DNL and glucose uptake from the media. In the HFHS treatment, DGAT2 knockout was associated with signs of oxidative stress and inflammation, suggesting an interaction between substrate availability and DGAT2 function. Recruitment of controls and people carrying a DGAT2 mutation who took part in a sugar overfeeding intervention demonstrated that a change in DGAT2 function may impact systemic glucose disposal, evident by increased carbohydrate oxidation and a resistance to metabolic changes caused by sugar overfeeding. Overall, I developed physiologically-relevant models of hepatocellular metabolism and steatosis. Investigations using these models in parallel with human participants identified altered DGAT2 function as having a potential role in NAFLD.
Supervisor: Hodson, Leanne ; Green, Charlotte ; Karpe, Fredrik Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: NAFLD ; Metabolism ; Medical sciences ; Lipids