RESUMEN
X-linked adrenoleukodystrophy (X-ALD) is a demyelinating disease due to mutations in the ABCD1 (ALD) gene, encoding a peroxisomal ATP-binding cassette transporter (ALDP). Overexpression of adrenoleukodystrophy-related protein, an ALDP homologue encoded by the ABCD2 (adrenoleukodystrophy-related) gene, can compensate for ALDP deficiency. 4-Phenylbutyrate (PBA) has been shown to induce both ABCD2 expression and peroxisome proliferation in human fibroblasts. We show that peroxisome proliferation with unusual shapes and clusters occurred in liver of PBA-treated rodents in a PPARalpha-independent way. PBA activated Abcd2 in cultured glial cells, making PBA a candidate drug for therapy of X-ALD. The Abcd2 induction observed was partially PPARalpha independent in hepatocytes and totally independent in fibroblasts. We demonstrate that a GC box and a CCAAT box of the Abcd2 promoter are the key elements of the PBA-dependent Abcd2 induction, histone deacetylase (HDAC)1 being recruited by the GC box. Thus, PBA is a nonclassical peroxisome proliferator inducing pleiotropic effects, including effects at the peroxisomal level mainly through HDAC inhibition.
Asunto(s)
Transportadoras de Casetes de Unión a ATP/metabolismo , Adrenoleucodistrofia/genética , Proliferadores de Peroxisomas/farmacología , Peroxisomas/ultraestructura , Fenilbutiratos/farmacología , Regulación hacia Arriba/efectos de los fármacos , Subfamilia D de Transportadores de Casetes de Unión al ATP , Miembro 1 de la Subfamilia D de Transportador de Casetes de Unión al ATP , Transportadoras de Casetes de Unión a ATP/genética , Adrenoleucodistrofia/patología , Animales , Células COS , Células Cultivadas , Chlorocebus aethiops , Fibroblastos , Hepatocitos/metabolismo , Hepatocitos/ultraestructura , Histona Desacetilasas/genética , Histona Desacetilasas/metabolismo , Humanos , Hígado/patología , Neuroglía/metabolismo , Neuroglía/ultraestructura , PPAR alfa/genética , PPAR alfa/metabolismo , Peroxisomas/genética , Peroxisomas/metabolismo , Regiones Promotoras Genéticas , Ratas , Ratas Wistar , Regulación hacia Arriba/genética , Regulación hacia Arriba/fisiologíaRESUMEN
Peroxisome proliferator-activated receptor alpha (PPARalpha) activation by fibrates controls expression of several genes involved in hepatic cholesterol metabolism. Other genes could be indirectly controlled in response to changes in cellular cholesterol availability. To further understand how fibrates may affect cholesterol synthesis, we investigated in parallel the changes in the metabolic pathways contributing to cholesterol homeostasis in liver. Ciprofibrate increased HMG-CoA reductase and FPP synthase mRNA levels in rat hepatocytes, together with cholesterogenesis from [(14)C] acetate and [(3)H] mevalonate. The up-regulation observed in fenofibrate- and WY-14,643-treated mice was abolished in PPARalpha-null mice, showing an essential role of PPARalpha. Among the three sterol regulatory element-binding protein (SREBP) mRNA species, only SREBP-1c level was significantly increased. In ciprofibrate-treated hepatocytes, cholesterol efflux was decreased, in parallel with cholesteryl ester storage and bile acids synthesis. As expected, AOX expression was strongly induced, supporting evidence of the peroxisome proliferation. Taken together, these results show that fibrates can cause cholesterol depletion in hepatocytes, possibly in part as a consequence of an important requirement of cholesterol for peroxisome proliferation, and increase cholesterogenesis by a compensatory phenomenon afterwards. Such cholesterogenesis regulation could occur in vivo, in species responsive to the peroxisome proliferative effect of PPARalpha ligands.
Asunto(s)
Colesterol/metabolismo , Ácido Clofíbrico/análogos & derivados , Hepatocitos/metabolismo , Receptores Citoplasmáticos y Nucleares/metabolismo , Factores de Transcripción/metabolismo , Acetatos/metabolismo , Animales , Ácidos y Sales Biliares/metabolismo , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Isótopos de Carbono , Carboxiliasas/metabolismo , División Celular , Ácido Clofíbrico/farmacología , Proteínas de Unión al ADN/metabolismo , Ácidos Fíbricos , Hepatocitos/efectos de los fármacos , Hidroximetilglutaril-CoA Reductasas/metabolismo , Masculino , Ácido Mevalónico/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proliferadores de Peroxisomas/farmacología , Pirimidinas/farmacología , ARN Mensajero/metabolismo , Ratas , Transducción de Señal , Proteína 1 de Unión a los Elementos Reguladores de Esteroles , Regulación hacia ArribaRESUMEN
Fibrates are hypolipidemic drugs that exert multiple effects on lipid metabolism by activating peroxisome proliferator-activated receptor alpha (PPARalpha) and modulating the expression of many target genes. In order to investigate the link between PPARalpha and cholesterol synthesis, we analysed the effect of fibrates on expression of the farnesyl diphosphate synthase (FPP synthase) gene, known to be regulated by sterol regulatory element-binding proteins (SREBPs), in conjunction with HMG-CoA reductase. In wild-type mice, both fenofibrate and WY 14,643 induced FPP synthase gene expression, an effect impaired in PPARalpha-null mice. A three-fold induction was observed in ciprofibrate-treated rat hepatocytes, in primary culture. This effect was decreased in presence of 5,6-dichlorobenzimidazole riboside (DRB) and cycloheximide (CHX), transcription and translation inhibitors, respectively. Acyl-CoA oxidase (AOX), a bona fide PPARalpha target gene, was induced by ciprofibrate but slower and more strongly than FPP synthase. In addition, induction of FPP synthase gene expression was abolished in the presence of 25-hydroxycholesterol (25-OH Chol). Thus, activation of PPARalpha by fibrates induced FPP synthase gene expression in both hepatocytes in culture and in mouse liver. This effect is likely to be dependent on cellular sterol level, possibly through SREBP-mediated transcriptional activation.