title: Cytosolic aspartate aminotransferase, a new partner in adipocyte glyceroneogenesis and an atypical target of thiazolidinedione.
abstract: We show that cytosolic aspartate aminotransferase (cAspAT) is involved in adipocyte glyceroneogenesis, a regulated pathway that controls fatty acid homeostasis by promoting glycerol 3-phosphate formation for fatty acid re-esterification during fasting. cAspAT activity, as well as the incorporation of [(14)C]aspartate into the neutral lipid fraction of 3T3-F442A adipocytes was stimulated by the thiazolidinedione (TZD) rosiglitazone. Conversely, the ratio of fatty acid to glycerol released into the medium decreased. Regulation of cAspAT gene expression was specific to differentiated adipocytes and did not require any peroxisome proliferator-activated receptor gamma (PPARgamma)/retinoid X receptor-alpha direct binding. Nevertheless, PPARgamma is indirectly necessary for both cAspAT basal expression and TZD responsiveness because they are, respectively, diminished and abolished by ectopic overexpression of a dominant negative PPARgamma. The cAspAT TZD-responsive site was restricted to a single AGGACA hexanucleotide located at -381 to -376 bp whose mutation impaired the specific RORalpha binding. RORalpha ectopic expression activated the cAspAT gene transcription in absence of rosiglitazone, and its protein amount in nuclear extracts is 1.8-fold increased by rosiglitazone treatment of adipocytes. Finally, the amounts of RORalpha and cAspAT mRNAs were similarly increased by TZD treatment of human adipose tissue explants, confirming coordinated regulation. Our data identify cAspAT as a new member of glyceroneogenesis, transcriptionally regulated by TZD via the control of RORalpha expression by PPARgamma in adipocytes.
authors.affiliation: Inserm U530, Université Paris Descartes, F-75006, Paris, France.
authors.forename: Joan
authors.initials: J
authors.lastname: Tordjman
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Leroyer
authors.forename: Geneviève
authors.initials: G
authors.lastname: Chauvet
authors.forename: Joëlle
authors.initials: J
authors.lastname: Quette
authors.forename: Caroline
authors.initials: C
authors.lastname: Chauvet
authors.forename: Céline
authors.initials: C
authors.lastname: Tomkiewicz
authors.forename: Charles
authors.initials: C
authors.lastname: Chapron
authors.forename: Robert
authors.initials: R
authors.lastname: Barouki
authors.forename: Claude
authors.initials: C
authors.lastname: Forest
authors.forename: Martine
authors.initials: M
authors.lastname: Aggerbeck
authors.forename: Bénédicte
authors.initials: B
authors.lastname: Antoine
mesh_terms: D017667:Adipocytes / Q000201:enzymology* / Q000378:metabolism; D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism; D000818:Animals; D001219:Aspartate Aminotransferases / Q000737:chemistry / Q000502:physiology*; D001483:Base Sequence; D003600:Cytosol / Q000378:metabolism*; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D047495:PPAR gamma / Q000378:metabolism; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000737:chemistry; D015534:Trans-Activators / Q000378:metabolism
chemical_list: D007004:Hypoglycemic Agents; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D047495:PPAR gamma; C539738:RORA protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D045162:Thiazolidinediones; D015534:Trans-Activators; D000077154:Rosiglitazone; C089946:2,4-thiazolidinedione; D001219:Aspartate Aminotransferases