RESUMO
Bone morphogenetic protein (BMP) signaling is required for endochondral bone formation. However, whether or not the effects of BMPs are mediated via canonical Smad pathways or through noncanonical pathways is unknown. In this study we have determined the role of receptor Smads 1, 5 and 8 in chondrogenesis. Deletion of individual Smads results in viable and fertile mice. Combined loss of Smads 1, 5 and 8, however, results in severe chondrodysplasia. Smad1/5(CKO) (cartilage-specific knockout) mutant mice are nearly identical to Smad1/5(CKO);Smad8(-/-) mutants, indicating that Smads 1 and 5 have overlapping functions and are more important than Smad8 in cartilage. The Smad1/5(CKO) phenotype is more severe than that of Smad4(CKO) mice, challenging the dogma, at least in chondrocytes, that Smad4 is required to mediate Smad signaling through BMP pathways. The chondrodysplasia in Smad1/5(CKO) mice is accompanied by imbalances in cross-talk between the BMP, FGF and Ihh/PTHrP pathways. We show that Ihh is a direct target of BMP pathways in chondrocytes, and that FGF exerts antagonistic effects on Ihh expression. Finally, we tested whether FGF exerts its antagonistic effects directly through Smad linker phosphorylation. The results support the alternative conclusion that the effects of FGFs on BMP signaling are indirect in vivo.
Assuntos
Proteínas Morfogenéticas Ósseas/fisiologia , Osteogênese/fisiologia , Proteína Smad1/fisiologia , Proteína Smad5/fisiologia , Animais , Diferenciação Celular , Proliferação de Células , Sobrevivência Celular , Condrócitos/citologia , Condrócitos/fisiologia , Condrogênese/genética , Condrogênese/fisiologia , Extremidades/embriologia , Feminino , Fatores de Crescimento de Fibroblastos/fisiologia , Proteínas Hedgehog/fisiologia , Masculino , Camundongos , Camundongos Knockout , Camundongos Mutantes , Osteogênese/genética , Proteína Relacionada ao Hormônio Paratireóideo/fisiologia , Fosforilação , Transdução de Sinais , Proteína Smad1/deficiência , Proteína Smad1/genética , Proteína Smad4/deficiência , Proteína Smad4/genética , Proteína Smad4/fisiologia , Proteína Smad5/deficiência , Proteína Smad5/genética , Proteína Smad8/deficiência , Proteína Smad8/genética , Proteína Smad8/fisiologiaRESUMO
The transforming growth factor beta (TGFbeta) family has critical roles in the regulation of fertility. In addition, the pathogenesis of some human cancers is attributed to misregulation of TGFbeta function and SMAD2 or SMAD4 mutations. There are limited mouse models for the BMP signaling SMADs (BR-SMADs) 1, 5, and 8 because of embryonic lethality and suspected genetic redundancy. Using tissue-specific ablation in mice, we deleted the BR-SMADs from somatic cells of ovaries and testes. Single conditional knockouts for Smad1 or Smad5 or mice homozygous null for Smad8 are viable and fertile. Female double Smad1 Smad5 and triple Smad1 Smad5 Smad8 conditional knockout mice become infertile and develop metastatic granulosa cell tumors. Male double Smad1 Smad5 conditional knockout mice are fertile but demonstrate metastatic testicular tumor development. Microarray analysis indicated significant alterations in expression of genes related to the TGFbeta pathway, as well as genes involved in infertility and extracellular matrix production. These data strongly implicate the BR-SMADs as part of a critical developmental pathway in ovaries and testis that, when disrupted, leads to malignant transformation.
