title: Differing endoplasmic reticulum stress response to excess lipogenesis versus lipid oversupply in relation to hepatic steatosis and insulin resistance.
abstract: Mitochondrial dysfunction and endoplasmic reticulum (ER) stress have been implicated in hepatic steatosis and insulin resistance. The present study investigated their roles in the development of hepatic steatosis and insulin resistance during de novo lipogenesis (DNL) compared to extrahepatic lipid oversupply. Male C57BL/6J mice were fed either a high fructose (HFru) or high fat (HFat) diet to induce DNL or lipid oversupply in/to the liver. Both HFru and HFat feeding increased hepatic triglyceride within 3 days (by 3.5 and 2.4 fold) and the steatosis remained persistent from 1 week onwards (p<0.01 vs Con). Glucose intolerance (iAUC increased by ∼60%) and blunted insulin-stimulated hepatic Akt and GSK3β phosphorylation (∼40-60%) were found in both feeding conditions (p<0.01 vs Con, assessed after 1 week). No impairment of mitochondrial function was found (oxidation capacity, expression of PGC1α, CPT1, respiratory complexes, enzymatic activity of citrate synthase & β-HAD). As expected, DNL was increased (∼60%) in HFru-fed mice and decreased (32%) in HFat-fed mice (all p<0.05). Interestingly, associated with the upregulated lipogenic enzymes (ACC, FAS and SCD1), two (PERK/eIF2α and IRE1/XBP1) of three ER stress pathways were significantly activated in HFru-fed mice. However, no significant ER stress was observed in HFat-fed mice during the development of hepatic steatosis. Our findings indicate that HFru and HFat diets can result in hepatic steatosis and insulin resistance without obvious mitochondrial defects via different lipid metabolic pathways. The fact that ER stress is apparent only with HFru feeding suggests that ER stress is involved in DNL per se rather than resulting from hepatic steatosis or insulin resistance.
authors.affiliation: Molecular Pharmacology for Diabetes Group, Health Innovations Research Institute and School of Health Sciences, RMIT University, Melbourne, Victoria, Australia.
authors.forename: Lu-Ping
authors.initials: LP
authors.lastname: Ren
authors.forename: Stanley M H
authors.initials: SM
authors.lastname: Chan
authors.forename: Xiao-Yi
authors.initials: XY
authors.lastname: Zeng
authors.forename: D Ross
authors.initials: DR
authors.lastname: Laybutt
authors.forename: Tristan J
authors.initials: TJ
authors.lastname: Iseli
authors.forename: Ruo-Qiong
authors.initials: RQ
authors.lastname: Sun
authors.forename: Edward W
authors.initials: EW
authors.lastname: Kraegen
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Cooney
authors.forename: Nigel
authors.initials: N
authors.lastname: Turner
authors.forename: Ji-Ming
authors.initials: JM
authors.lastname: Ye
mesh_terms: D050156:Adipogenesis; D000818:Animals; D015153:Blotting, Western; D004041:Dietary Fats / Q000008:administration & dosage; D059865:Endoplasmic Reticulum Stress; D005234:Fatty Liver / Q000209:etiology / Q000503:physiopathology*; D005632:Fructose / Q000008:administration & dosage; D018149:Glucose Intolerance / Q000209:etiology / Q000503:physiopathology; D007333:Insulin Resistance; D050356:Lipid Metabolism / Q000502:physiology*; D050155:Lipogenesis; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress
chemical_list: D004041:Dietary Fats; D005632:Fructose