RESUMEN
Dietary and xenobiotic compounds can disrupt endocrine signaling, particularly of steroid receptors and sexual differentiation. Evidence is also mounting that implicates environmental agents in the growing epidemic of obesity. Despite a long-standing interest in such compounds, their identity has remained elusive. Here we show that the persistent and ubiquitous environmental contaminant, tributyltin chloride (TBT), induces the differentiation of adipocytes in vitro and increases adipose mass in vivo. TBT is a dual, nanomolar affinity ligand for both the retinoid X receptor (RXR) and the peroxisome proliferator-activated receptor gamma (PPARgamma). TBT promotes adipogenesis in the murine 3T3-L1 cell model and perturbs key regulators of adipogenesis and lipogenic pathways in vivo. Moreover, in utero exposure to TBT leads to strikingly elevated lipid accumulation in adipose depots, liver, and testis of neonate mice and results in increased epididymal adipose mass in adults. In the amphibian Xenopus laevis, ectopic adipocytes form in and around gonadal tissues after organotin, RXR, or PPARgamma ligand exposure. TBT represents, to our knowledge, the first example of an environmental endocrine disrupter that promotes adipogenesis through RXR and PPARgamma activation. Developmental or chronic lifetime exposure to organotins may therefore act as a chemical stressor for obesity and related disorders.
Asunto(s)
Adipogénesis/efectos de los fármacos , Disruptores Endocrinos/farmacología , Compuestos Orgánicos de Estaño/farmacología , Animales , Biomarcadores , Línea Celular , Dimerización , Homeostasis/efectos de los fármacos , Humanos , Ligandos , Metabolismo de los Lípidos/efectos de los fármacos , Hígado/efectos de los fármacos , Hígado/metabolismo , Ratones , Ratones Endogámicos C57BL , Tamaño de los Órganos/efectos de los fármacos , PPAR gamma/genética , PPAR gamma/metabolismo , Receptor alfa X Retinoide/agonistas , Receptor alfa X Retinoide/genética , Receptor alfa X Retinoide/metabolismo , Transducción de Señal/efectos de los fármacosRESUMEN
Retinoid signaling is important for patterning the vertebrate hindbrain and midaxial regions. We recently showed that signaling through retinoic acid receptors (RARs) is essential for anteroposterior patterning along the entire body axis. To further investigate the mechanisms through which RARs act, we used microarray analysis to investigate the effects of modulating RAR activity on target gene expression. We identified 334 up-regulated genes (92% of which were validated), including known RA-responsive genes, known genes that have never been proposed as RA targets and many hypothetical and unidentified genes (n = 166). Sixty-seven validated down-regulated genes were identified, including known RA-responsive genes and anterior marker genes. The expression patterns of selected up-regulated genes (n = 45) were examined at neurula stages using whole-mount in situ hybridization. We found that most of these genes were expressed in the neural tube and many were expressed in anterior tissues such as neural crest, brain, eye anlagen, and cement gland. Some were expressed in tissues such as notochord, somites, pronephros, and blood islands, where retinoic acid (RA) plays established roles in organogenesis. Members of this set of newly identified RAR target genes are likely to play important roles in neural patterning and organogenesis under the control of RAR signaling pathways, and their further characterization will expand our understanding of RA signaling during development.
Asunto(s)
Regulación del Desarrollo de la Expresión Génica , Análisis de Secuencia por Matrices de Oligonucleótidos , Receptores de Ácido Retinoico/metabolismo , Xenopus/embriología , Animales , Northern Blotting , Tipificación del Cuerpo , Análisis por Conglomerados , Regulación hacia Abajo , Ácidos Grasos/metabolismo , Hibridación in Situ , Riñón/embriología , Cresta Neural/embriología , Cresta Neural/metabolismo , Retinoides/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal , Esteroides/metabolismo , Factores de Tiempo , Tretinoina/metabolismo , Regulación hacia ArribaRESUMEN
Anteroposterior (AP) patterning of the developing CNS is crucial for both regional specification and the timing of neurogenesis. Several important factors are involved in AP patterning, including members of the WNT and FGF growth factor families, retinoic acid receptors, and HOX genes. We have examined the interactions between FGF and retinoic signaling pathways. Blockade of FGF signaling downregulates the expression of members of the RAR signaling pathway, RARalpha, RALDH2 and CYP26. Overexpression of a constitutively active RARalpha2 rescues the effects of FGF blockade on the expression of XCAD3 and HOXB9. This suggests that RARalpha2 is required as a downstream target of FGF signaling for the posterior expression of XCAD3 and HOXB9. Surprisingly, we found that posterior expression of FGFR1 and FGFR4 was dependent on the expression of RARalpha2. Anterior expression was also altered with FGFR1 expression being lost, whereas FGFR4 expression was expanded beyond its normal expression domain. RARalpha2 is required for the expression of XCAD3 and HOXB9, and for the ability of XCAD3 to induce HOXB9 expression. We conclude that RARalpha2 is required at multiple points in the posteriorization pathway, suggesting that correct AP neural patterning depends on a series of mutually interactive feedback loops among FGFs, RARs and HOX genes.
Asunto(s)
Vértebra Cervical Axis/embriología , Factores de Crecimiento de Fibroblastos/metabolismo , Transducción de Señal , Tretinoina/metabolismo , Xenopus/embriología , Familia de Aldehído Deshidrogenasa 1 , Aldehído Oxidasa , Aldehído Oxidorreductasas/genética , Aldehído Oxidorreductasas/metabolismo , Animales , Vértebra Cervical Axis/metabolismo , Tipificación del Cuerpo/genética , Sistema Enzimático del Citocromo P-450/genética , Sistema Enzimático del Citocromo P-450/metabolismo , Embrión no Mamífero , Epistasis Genética , Proteínas Fetales/genética , Proteínas Fetales/metabolismo , Factor 8 de Crecimiento de Fibroblastos , Factores de Crecimiento de Fibroblastos/genética , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Proteínas Tirosina Quinasas Receptoras/genética , Proteínas Tirosina Quinasas Receptoras/metabolismo , Receptor Tipo 1 de Factor de Crecimiento de Fibroblastos , Receptor Tipo 4 de Factor de Crecimiento de Fibroblastos , Receptores de Factores de Crecimiento de Fibroblastos/genética , Receptores de Factores de Crecimiento de Fibroblastos/metabolismo , Receptores de Ácido Retinoico/genética , Receptores de Ácido Retinoico/metabolismo , Retinal-Deshidrogenasa , Ácido Retinoico 4-Hidroxilasa , Receptor alfa de Ácido Retinoico , Xenopus/genética , Xenopus/metabolismo , Proteínas de Xenopus/genética , Proteínas de Xenopus/metabolismoRESUMEN
We sought to characterize expression of an apically expressed intestinal Na-P(i) cotransporter (Na-P(i)-IIb) during mouse ontogeny and to assess the effects of methylprednisolone (MP) treatment. In control mice, Na-P(i) uptake by intestinal brush-border membrane vesicles was highest at 14 days of age, lower at 21 days, and further reduced at 8 wk and 8-9 mo of age. Na-P(i)-IIb mRNA and immunoreactive protein levels in 14-day-old animals were markedly higher than in older groups. MP treatment significantly decreased Na-P(i) uptake and Na-P(i)-IIb mRNA and protein expression in 14-day-old mice. Additionally, the size of the protein was smaller in 14-day-old mice. Deglycosylation of protein from 14-day-old and 8-wk-old animals with peptide N-glycosidase reduced the molecular weight to the predicted size. We conclude that intestinal Na-P(i) uptake and Na-P(i)-IIb expression are highest at 14 days and decrease with age. Furthermore, MP treatment reduced intestinal Na-P(i) uptake approximately threefold in 14-day-old mice and this reduction correlates with reduced Na-P(i)-IIb mRNA and protein expression. We also demonstrate that Na-P(i)-IIb is an N-linked glycoprotein and that glycosylation is age dependent.