title: Nitric oxide-dependent downregulation of adipocyte UCP-2 expression by tumor necrosis factor-alpha.
abstract: Uncoupling protein-2 (UCP-2) is a mitochondrial protein expressed in adipocytes and has recently been involved in the control of energy dissipation. Because obesity is characterized by an imbalance between energy intake and expenditure and by an enhanced adipocyte-derived secretion of tumor necrosis factor-alpha (TNF-alpha), we asked whether TNF-alpha could directly influence UCP-2 expression in adipocytes. Experiments performed in differentiated 3T3F442A preadipocytes showed that TNF-alpha (10 ng/ml) induced a reduction of UCP-2 trancripts, assessed by Northern blot analysis. A significant decrease in UCP-2 expression (40%) was observed after 12 and 24 h of TNF-alpha stimulation of the cells. The characterization of the mechanisms responsible for the TNF-alpha effect on UCP-2 expression demonstrates an involvement of the TNF-alpha-induced inducible (i) nitric oxide synthase (NOS) expression. Cell treatment with the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 1 mmol/l) significantly diminished the TNF-alpha-mediated sustained downregulation of UCP-2 expression, whereas cell treatment with a nitric oxide (NO) donor (10(-3) mol/l S-nitroso-L-glutathione) mimicked the TNF-alpha effect on UCP-2 expression. Moreover, Western blot analysis clearly showed that TNF-alpha alone induces the expression of iNOS after 12-24 h treatment of differentiated 3T3F442A cells. These experiments demonstrate that TNF-alpha directly downregulates UCP-2 expression via NO-dependent pathways that involve the induction of iNOS expression.
authors.affiliation: Laboratoire de Pharmacologie Médicale et Clinique, Institut National de la Santé et de la Recherche Médicale Unité 317, 31073 Toulouse Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Merial
authors.forename: A
authors.initials: A
authors.lastname: Bouloumie
authors.forename: V
authors.initials: V
authors.lastname: Trocheris
authors.forename: M
authors.initials: M
authors.lastname: Lafontan
authors.forename: J
authors.initials: J
authors.lastname: Galitzky
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D002454:Cell Differentiation; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005978:Glutathione / Q000031:analogs & derivatives* / Q000494:pharmacology; D007473:Ion Channels; D026901:Membrane Transport Proteins; D051379:Mice; D024101:Mitochondrial Proteins; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009573:Nitrites / Q000378:metabolism; D009603:Nitroso Compounds / Q000494:pharmacology; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D026422:S-Nitrosoglutathione; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology; D000071246:Uncoupling Protein 2
chemical_list: D004791:Enzyme Inhibitors; D007473:Ion Channels; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D020030:Nitric Oxide Donors; D009573:Nitrites; D009603:Nitroso Compounds; D011506:Proteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; C000604390:Ucp2 protein, mouse; D000071246:Uncoupling Protein 2; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D005978:Glutathione; D019331:NG-Nitroarginine Methyl Ester