RESUMO
BACKGROUND: Hepatic PPARalpha acts as the primary mediator of the adaptive response to fasting by upregulation of a number of genes involved in fatty acid catabolism. Whether carnitine-acylcarnitine translocase (CACT), which mediates the import of acylcarnitines into the mitochondrial matrix for subsequent beta-oxidation of fatty acid moieties, is also regulated by PPARalpha in the liver has not yet been investigated. METHODS AND RESULTS: Herein, we observed that hepatic mRNA abundance of CACT was increased by both, fasting and treatment with PPARalpha agonist WY-14,643 in wild-type mice but not PPARalpha-knockout mice (P<0.05). Cell culture experiments revealed that CACT mRNA abundance was higher in liver cells treated with either WY-14,643 or PPARdelta agonist GW0742, but not with PPARgamma agonist troglitazone (TGZ) than in control cells (P<0.05). In addition, reporter assays revealed activation of mouse CACT promoter by WY-14,643 and GW0742, but not TGZ. Moreover, deletion and mutation analyses of CACT promoter and 5'-UTR revealed one functional PPRE in the 5'-UTR of mouse CACT. GENERAL SIGNIFICANCE: CACT is upregulated by PPARalpha and PPARdelta, probably by binding to a functional PPRE at position +45 to +57 relative to the transcription start site. The upregulation of CACT by PPARalpha and PPARdelta, which are both important for the regulation of fatty acid oxidation in tissues during fasting, may increase the import of acylcarnitine into the mitochondrial matrix during fasting.
Assuntos
Carnitina Aciltransferases/genética , Fígado/metabolismo , PPAR alfa/genética , PPAR delta/genética , Animais , Sequência de Bases , Peso Corporal/efeitos dos fármacos , Carnitina Aciltransferases/metabolismo , Carnitina O-Palmitoiltransferase/genética , Carnitina O-Palmitoiltransferase/metabolismo , Linhagem Celular Tumoral , Sistema Enzimático do Citocromo P-450/genética , Sistema Enzimático do Citocromo P-450/metabolismo , Jejum , Feminino , Regulação Enzimológica da Expressão Gênica/efeitos dos fármacos , Humanos , Fígado/citologia , Fígado/efeitos dos fármacos , Luciferases/genética , Luciferases/metabolismo , Masculino , Camundongos , Camundongos Knockout , Dados de Sequência Molecular , Mutação , PPAR alfa/agonistas , PPAR alfa/metabolismo , PPAR delta/agonistas , PPAR delta/metabolismo , Regiões Promotoras Genéticas/genética , Pirimidinas/farmacologia , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Tiazóis/farmacologia , Transcrição Gênica/efeitos dos fármacosRESUMO
BACKGROUND: Feeding oxidized fats causes activation of peroxisome proliferator-activated receptor alpha (PPARalpha) in the liver of rats. However, whether feeding oxidized fat during pregnancy also results in activation of PPARalpha in fetal liver is unknown. Thus, this study aimed to explore whether feeding oxidized fat during pregnancy causes a PPARalpha response in fetal liver. Two experiments with pregnant rats which were administered three different diets (control; oxidized fat; clofibrate as positive control) in a controlled feeding regimen during either late pregnancy (first experiment) or whole pregnancy (second experiment) were performed. RESULTS: In both experiments pregnant rats treated with oxidized fat or clofibrate had higher relative mRNA concentrations of the PPARalpha-responsive genes acyl-CoA oxidase (ACO), cytochrome P450 4A1 (CYP4A1), L-type carnitin-palmitoyl transferase I (L-CPT I), medium-chain acyl-CoA dehydrogenase (MCAD), and long-chain acyl-CoA dehydrogenase (LCAD) in the liver than control rats (P < 0.05). In addition, in both experiments fetuses of the oxidized fat group and the clofibrate group also had markedly higher relative mRNA concentrations of ACO, CYP4A1, CPT I, MCAD, and LCAD in the liver than those of the control group (P < 0.05), whereas the relative mRNA concentrations of PPARalpha, SREBP-1c, and FAS did not differ between treatment groups. In the second experiment treatment with oxidized fat also reduced triacylglycerol concentrations in the livers of pregnant rats and fetuses (P < 0.05). CONCLUSION: The present study demonstrates for the first time that components of oxidized fat with PPARalpha activating potential are able to induce a PPARalpha response in the liver of fetuses. Moreover, the present study shows that feeding oxidized fat during whole pregnancy, but not during late pregnancy, lowers triacylglycerol concentrations in fetal livers.