title: Flavin-Containing Monooxygenase 3 Reduces Endoplasmic Reticulum Stress in Lipid-Treated Hepatocytes.
abstract: Isoforms of flavin-containing monooxygenase (FMO) are involved in xenobiotic metabolism but have also been implicated in the regulation of glucose and lipid homeostasis and in the development of atherosclerosis. However, we have recently shown that improved insulin action is associated with increased FMO expression in livers of protein kinase C-deficient mice. Here, we investigated whether FMO3 expression affected insulin signaling, glucose metabolism, and endoplasmic reticulum (ER) stress in hepatocytes. HepG2 and IHH hepatocytes were transfected with FMO3 cDNA for overexpression, or small interfering RNA for knockdown. Cells were treated with palmitate to induce insulin resistance and insulin signaling, phosphoenolpyruvate carboxykinase (PEPCK) gene expression and ER stress markers were examined by immunoblotting and RT-PCR. Glycogen synthesis was measured using [(14)C]glucose. Palmitate treatment reduced insulin signaling at the level of Akt phosphorylation and glycogen synthesis, which were little affected by FMO3 overexpression. However, the fatty acid also increased the levels of several ER stress markers and activation of caspase 3, which were counteracted by FMO3 overexpression and exacerbated by FMO3 knockdown. Although FMO3 expression did not reverse lipid effects on protein thiol redox in hepatocytes, it did prevent up-regulation of the gluconeogenic enzyme PEPCK by pharmacological ER stress inducers or by palmitate. ER stress and PEPCK levels were also reduced in livers of fat-fed protein kinase Cδ-deficient mice. Our data indicate that FMO3 can contribute to the regulation of glucose metabolism in the liver by reducing lipid-induced ER stress and the expression of PEPCK, independently of insulin signal transduction.
authors.affiliation: Diabetes and Metabolism Division (B.M.L., S.A.M., W.E.H., C.S.-P.), Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia; and St. Vincent's Hospital Clinical School (W.E.H., C.S.-P.), Faculty of Medicine, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Bing M
authors.initials: BM
authors.lastname: Liao
authors.affiliation: Diabetes and Metabolism Division (B.M.L., S.A.M., W.E.H., C.S.-P.), Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia; and St. Vincent's Hospital Clinical School (W.E.H., C.S.-P.), Faculty of Medicine, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Sophie A
authors.initials: SA
authors.lastname: McManus
authors.affiliation: Diabetes and Metabolism Division (B.M.L., S.A.M., W.E.H., C.S.-P.), Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia; and St. Vincent's Hospital Clinical School (W.E.H., C.S.-P.), Faculty of Medicine, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: William E
authors.initials: WE
authors.lastname: Hughes
authors.affiliation: Diabetes and Metabolism Division (B.M.L., S.A.M., W.E.H., C.S.-P.), Garvan Institute of Medical Research, Sydney, New South Wales 2010, Australia; and St. Vincent's Hospital Clinical School (W.E.H., C.S.-P.), Faculty of Medicine, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Carsten
authors.initials: C
authors.lastname: Schmitz-Peiffer
mesh_terms: D000818:Animals; D059305:Diet, High-Fat; D059865:Endoplasmic Reticulum Stress; D004794:Enzyme Repression; D015870:Gene Expression; D005943:Gluconeogenesis; D006003:Glycogen / Q000096:biosynthesis; D057809:HEK293 Cells; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D007328:Insulin / Q000502:physiology; D008297:Male; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010105:Oxygenases / Q000235:genetics / Q000378:metabolism*; D010169:Palmitic Acids / Q000494:pharmacology; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D007328:Insulin; D010169:Palmitic Acids; D017382:Reactive Oxygen Species; D006003:Glycogen; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming); C497259:Prkcd protein, mouse; D051745:Protein Kinase C-delta; C000597251:PCK2 protein, human; D019764:Phosphoenolpyruvate Carboxykinase (ATP)