Disruption of HSD17B12 in mouse hepatocytes leads to reduce body weight and defect in the lipid droplet expansion associated with microvesicular steatosis
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE255345 | GEO | 2024/09/18
REPOSITORIES: GEO
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Project description:Non-alcoholic fatty liver disease (NAFLD) is a major public health burden and it covers a spectrum of diseases. NAFLD starts with the accumulation of lipid droplets (LDs) within hepatocytes (steatosis). Part of the challenge of studying the mechanistic processes involved in LD accumulation and their implications on the pathogenesis of human NAFLD is due to the available models. Investigating hepatic LDs in humans is challenging and relies on liver biopsies, meaning only cross-sectional data be obtained. On the other hand, LD patterns in in vitro models are poorly defined and rarely reported. Diacylgylcerol acyltransferase (DGAT)2 is one of two enzymes that carry out the final committed step in triacylglycerol (TAG) synthesis. It is unclear whether the enzymes are able to compensate for each other or whether they have distinct roles. It has been hypothesised that DGAT1 primarily utilises exogenous fatty acids and DGAT2 uses de novo-derived fatty acids. Given the important role of this enzyme in TAG synthesis and accumulation, the aims of this study are first to create a cellular model of intrahepatocellular TAG accumulation by manipulating nutritional substrates and to investigate intracellular metabolism in wildtype and DGAT2 knockout cells under these conditions. The experimental workflow for this study is as follows: Huh7 cells (either wild type or knockout) were grown in media containing 11 mM glucose and 2% human serum (HS) for seven days before additional sugars and fatty acids (FAs) were added for a further seven days. All treatments contained 11 mM glucose and 2% HS, either with 200 µM FAs (low fat low sugar; LFLS), 5.5 mM fructose + 200 µM FAs (low fat high sugar; LFHS) or 5.5 mM fructose + 800 µM FAs (high fat high sugar; HFHS). FA metabolism, lipid droplet characteristics and transcriptomic signatures were investigated.
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Project description:Methionine adenosyltransferase (MAT) enzymes generate SAMe (S-adenosylmethionine), the main biological methyl donor. There are two MAT encoding genes in mammals (Mat1a and Mat2a), which show different activities and cellular distribution. Mat1a encodes the enzyme mainly expressed in normal liver. Mat1a ablation in mice results in the spontaneous development of non-alcoholic steatohepatitis (NASH). We observed that SAMe depletion in Mat1a KO mice had three main effects on hepatic lipid metabolism: 1) impaired TG (triglyceride) export via VLDL; 2) impaired mitochondrial FA (fatty acid) oxidation (as evidenced by membrane depolarization, downregulation of Phb1 (prohibitin 1, a mitochondrial chaperone protein) and Mcj/Dnajc15 (endogenous mitochondrial repressor of respiratory chain), and accumulation of long-chain acylcarnitines); and 3) increased FA uptake. The convergence of these three factors induced TG accumulation in LD (lipid droplets). LD expansion confronts hepatocytes with a high demand of PC (phosphatidylcholine) molecules to cover the LD surface since other phospholipids, such as PE (phosphatidylethanolamine), cannot stabilize LD and prevent coalescence. In Mat1a KO this situation is aggravated, since SAMe-dependent PC synthesis via PE methylation is decreased, the PC/PE ratio reduced and mitochondrial FA oxidation impaired. To put a brake to this drain of PC molecules to LD, FA are rerouted in Mat1a KO mice liver to other catabolic (endoplasmic reticulum and peroxisome oxidation) and biosynthetic (ceramides synthesis) pathways, causing oxidative stress, inflammation and fibrosis. SAMe treatment for two months in 8-9 month old Mat1a KO mice ameliorated mitochondrial dysfunction (reduces membrane depolarization, improves Phb1 and Mcj expression, and increases SAMe transport to mitochondria) improving FA oxidation efficiency (FA and acylcarnitine levels decrease), which results in a drastic reduction in TG accumulation. SAMe treatment in Mat1a KO mice resulted in more PC available for proper membrane function, improving liver lipid homeostasis, histology (H&E, Sudan red, Sirius red) and liver injury (ALT, AST).
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Project description:Controlling fatty acid uptake, lipid production and storage, and metabolism of lipid droplets (LDs), is closely related to lipid homeostasis, adipocyte hypertrophy and obesity. We report here that stomatin, a major constituent of lipid rafts, participates in adipogenesis and adipocyte maturation by modulating related signaling pathways. In adipocyte-like cells, increased stomatin promotes LD growth or enlargements by facilitating LD-LD fusion, as well as fatty acid uptake from extracellular environment by recruiting effector molecules, such as FAT/CD36 translocase, to lipid rafts to promote internalization of fatty acids. Stomatin transgenic mice fed with high-fat diets exhibit obesity, insulin resistance and hepatic impairments; however, such phenotypes are not seen if feeding the transgenic animals with regular diets. Inhibitions of stomatin by gene knockdown or OB-1 pharmacological treatments inhibit adipogenic differentiation and LD growth through downregulation of PPARγ pathway. Effects of stomatin on PPARγ involve ERK signaling; however, an alternate pathway may also exist.
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