Project description:cdipt is an essential gene in the synthesis of phosphatidylinositol (PtdIns) in the zebrafish, Danio rerio. The zebrafish mutant cdipt^hi559Tg (ZL782) carries a retroviral insertion which inactivates cdipt. Homozygous mutants exhibit hepatocellular endoplasmic reticulum (ER) stress and non-alcoholic fatty liver disease (NAFLD) pathologies at 5 days post fertilization (dpf). This study reveals a novel link between PtdIns, ER stress, and steatosis. We compared whole animal gene expression profiles of hi559 mutant larvae with phenotypically wild type larvae from a heterozygote incross in triplicate.
Project description:cdipt is an essential gene in the synthesis of phosphatidylinositol (PtdIns) in the zebrafish, Danio rerio. The zebrafish mutant cdipt^hi559Tg (ZL782) carries a retroviral insertion which inactivates cdipt. Homozygous mutants exhibit hepatocellular endoplasmic reticulum (ER) stress and non-alcoholic fatty liver disease (NAFLD) pathologies at 5 days post fertilization (dpf). This study reveals a novel link between PtdIns, ER stress, and steatosis.
Project description:We examined the effect of oral TUDCA treatment on hepatic steatosis and associated changes in hepatic gene expression in ob/ob mice. We administered TUDCA to ob/ob mice at a dose of 500 mg/kg twice a day by gastric gavage for 3 weeks. Body weight, glucose homeostasis, endoplasmic reticulum (ER) stress, and hepatic gene expression were examined in comparison with control ob/ob mice and normal littermate C57BL/6J mice.
Project description:Metabolic dysfunction-associated steatotic liver disease (MASLD) affects one third of the global population. Understanding metabolic pathways involved can provide insights into disease progression and treatment. Untargeted metabolomics of livers from mice with early-stage steatosis uncovered decreased methylated metabolites, suggesting altered one-carbon metabolism. The levels of glycine, a central component of one-carbon metabolism, were lower in mice with hepatic steatosis, consistent with clinical evidence. Stable-isotope tracing demonstrated that increased serine synthesis from glycine via reverse serine hydroxymethyltransferase (SHMT) is the underlying cause for decreased glycine in steatotic livers. Consequently, limited glycine availability in steatotic livers impaired glutathione synthesis under acetaminophen-induced oxidative stress, enhancing acute hepatotoxicity. Glycine supplementation or hepatocyte-specific
ablation of the mitochondrial SHMT2 isoform in mice with hepatic steatosis mitigated
acetaminophen-induced hepatotoxicity by supporting de novo glutathione synthesis. Thus, early metabolic changes in MASLD that limit glycine availability sensitize mice to xenobiotics even at the reversible stage of this disease.
Project description:The unfolded protein response (UPR), induced by endoplasmic reticulum (ER) stress, regulates the expression of factors that restore protein folding homeostasis. However, in the liver and kidney, ER stress also leads to lipid accumulation, accompanied at least in the liver by transcriptional suppression of metabolic genes. The mechanisms of this accumulation are unclear, including which pathways contribute to the phenotype in each organ. We combined gene expression profiling, biochemical assays, and untargeted lipidomics to understand the basis of stress-dependent lipid accumulation, taking advantage of enhanced hepatic and renal steatosis in mice lacking the ER stress sensor ATF6α. We found that impaired fatty acid oxidation contributed to the early development of steatosis in the liver, but not the kidney; while anorexia-induced lipolysis promoted late triglyceride and free fatty acid accumulation in both organs. These findings provide evidence for both direct and indirect regulation of peripheral metabolism by ER stress.
Project description:Hepatic metabolic derangements are key components in the development of fatty liver, insulin resistance, and atherosclerosis. SIRT1, a NAD+-dependent protein deacetylase, is an important regulator of energy homeostasis in response to nutrient availability. Here we demonstrate that hepatic SIRT1 regulates fatty acid metabolism by positively regulating PPAR-alpha. Hepatocyte-specific deletion of SIRT1 impairs PPAR-alpha signaling and decreased fatty acid beta-oxidation in the liver. When challenged with a high-fat diet, liver-specific SIRT1 knockout mice develop hepatic steatosis, hepatic inflammation, and endoplasmic reticulum stress. Taken together, our data indicate that SIRT1 plays a vital role in the regulation of hepatic lipid homeostasis.
Project description:Non-alcoholic fatty liver is the most common liver disease worldwide. Here, we show that the mitochondrial protein mitofusin 2 (Mfn2) protects against liver disease. Reduced Mfn2 expression was detected in liver biopsies from patients with non-alcoholic steatohepatitis (NASH). Moreover, reduced Mfn2 levels were detected in mouse models of steatosis or NASH, and its re-expression in a NASH mouse model ameliorated the disease. Liver-specific ablation of Mfn2 in mice provoked inflammation, triglyceride accumulation, fibrosis, and liver cancer. We demonstrate that Mfn2 binds phosphatidylserine (PS) and can specifically extract PS into membrane domains, favoring PS transfer to mitochondria and mitochondrial phosphatidylethanolamine (PE) synthesis. Consequently, hepatic Mfn2 deficiency reduces PS transfer and phospholipid synthesis, leading to endoplasmic reticulum (ER) stress and the development of a NASH-like phenotype and liver cancer. Ablation of Mfn2 in liver reveals that disruption of ER-mitochondrial PS transfer is a new mechanism involved in the development of liver disease.
Project description:Cholesterol and phosphoinositides (PI) are two critically important lipids that are found in cellular membranes and dysregulated in many disorders. Therefore, uncovering molecular pathways connecting these essential lipids may offer new therapeutic insights. We report that loss of function of lysosomal Niemann-Pick Type C1 (NPC1) cholesterol transporter, which leads to neurodegenerative NPC disease, initiates a signaling cascade that alters the cholesterol/phosphatidylinositol 4-phosphate (PtdIns4P) countertransport cycle between Golgi-endoplasmic reticulum (ER), as well as lysosome-ER membrane contact sites (MCS). Central to these disruptions is increased recruitment of phosphatidylinositol 4-kinases-PI4KIIα and PI4KIIIβ-which boosts PtdIns4P metabolism at Golgi and lysosomal membranes. Aberrantly increased PtdIns4P levels elevate constitutive anterograde secretion from the Golgi complex, and mTORC1 recruitment to lysosomes. NPC1 disease mutations phenocopy the transporter loss of function and can be rescued by inhibition or knockdown of either key phosphoinositide enzymes or their recruiting partners. In summary, we show that the lysosomal NPC1 cholesterol transporter tunes the molecular content of Golgi and lysosome MCS to regulate intracellular trafficking and growth signaling in health and disease.
Project description:Background: Diet is a major contributor to metabolic disease risk, but there is controversy as to whether increased incidences of diseases such as non-alcoholic fatty liver disease arise from consumption of saturated fats or free sugars. Our aims were to investigate whether a sub-set of TAGs were associated with hepatic steatosis and whether they arise from de novo lipogenesis (DNL) from the consumption of carbohydrates. </br></br> Results: We conducted direct infusion mass spectrometry of lipids in plasma to study the association between specific triacylglycerols (TAGs) and hepatic steatosis assessed by ultrasound and fatty liver index in volunteers from the UK-based Fenland Study (n=1507), and evaluated clustering of TAGs in the National Survey of Health and Development UK cohort (n=1701). TAGs formed 3 clusters, with those TAGs containing saturated and monounsaturated fatty acids with 16-18 carbons being specifically associated with hepatic steatosis. These TAGs were associated with higher consumption of carbohydrate and saturated fat, hepatic steatosis, and variations in the gene for protein phosphatase 1, regulatory subunit 3b (PPP1R3B), which in part regulates glycogen synthesis. DNL was measured in hyperphagic ob/ob mice, mice on a Western diet (high in fat and free sugar) and in healthy humans using stable isotope techniques following high carbohydrate meals, demonstrating the rate of DNL correlates with increased synthesis of this cluster of TAGs. Furthermore, these TAGs were increased in plasma from patients with biopsy-confirmed steatosis. </br></br> Conclusion: A sub-set of TAGs are associated with hepatic steatosis, even when correcting for common confounding factors. We suggest that hepatic steatosis risk in Western populations is in part driven by increased DNL following carbohydrate rich meals. </br></br> The protocols and data of the murine study of de novo lipogenesis are included in the study MTBLS614. </br><br/> Linked Studies: <a href='https://www.ebi.ac.uk/metabolights/MTBLS614' target='_blank'><span class='label label-success'>MTBLS614</span></a>