RESUMO
Skeletal growth and homeostasis require the finely orchestrated secretion of mineralized tissue matrices by highly specialized cells, balanced with their degradation by osteoclasts. Time- and site-specific expression of Dlx and Msx homeobox genes in the cells secreting these matrices have been identified as important elements in the regulation of skeletal morphology. Such specific expression patterns have also been reported in osteoclasts for Msx genes. The aim of the present study was to establish the expression patterns of Dlx genes in osteoclasts and identify their function in regulating skeletal morphology. The expression patterns of all Dlx genes were examined during the whole osteoclastogenesis using different in vitro models. The results revealed that Dlx1 and Dlx2 are the only Dlx family members with a possible function in osteoclastogenesis as well as in mature osteoclasts. Dlx5 and Dlx6 were detected in the cultures but appear to be markers of monocytes and their derivatives. In vivo, Dlx2 expression in osteoclasts was examined using a Dlx2/LacZ transgenic mouse. Dlx2 is expressed in a subpopulation of osteoclasts in association with tooth, brain, nerve, and bone marrow volumetric growths. Altogether the present data suggest a role for Dlx2 in regulation of skeletal morphogenesis via functions within osteoclasts.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Homeodomínio/genética , Família Multigênica/genética , Osteoclastos/metabolismo , Fatores de Transcrição/genética , Fosfatase Ácida/metabolismo , Animais , Diferenciação Celular/genética , Linhagem Celular , Perfilação da Expressão Gênica , Proteínas de Homeodomínio/metabolismo , Isoenzimas/metabolismo , Masculino , Mandíbula/citologia , Mandíbula/enzimologia , Mandíbula/metabolismo , Metaloproteinase 9 da Matriz/metabolismo , Camundongos , Osteoclastos/citologia , Osteoclastos/enzimologia , Osteogênese/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fosfatase Ácida Resistente a Tartarato , Fatores de Transcrição/metabolismo , beta-Galactosidase/metabolismoRESUMO
Infantile malignant osteopetrosis (IMO) is a rare and lethal disease characterized by an absence of bone resorption due to inactive OCLs. Affected patients display an increased bone mass and hematological defects. The osteopetrotic oc/oc mouse displays a bone phenotype similar to the one observed in IMO patients, and the same gene, Tcirg1, is mutated in this model and in the majority of these patients. Therefore, we explored in oc/oc mice the consequences of the perturbed bone microenvironment on hematopoiesis. We show that the myelomonocytic differentiation is increased, leading to an elevated number of OCLs and dendritic cells. B lymphopoiesis is blocked at the pro-B stage in the bone marrow of oc/oc mouse, leading to a low mature B-cell number. T-cell activation is also affected, with a reduction of IFNgamma secretion by splenic CD4(+) T cells. These alterations are associated with a low IL-7 expression in bone marrow. All these data indicate that the lack of bone resorption in oc/oc mice has important consequences in both myelopoiesis and lymphopoiesis, leading to a form of immunodeficiency. The oc/oc mouse is therefore an appropriate model to understand the hematological defects described in IMO patients, and to derive new therapeutic strategies.
Assuntos
Reabsorção Óssea , Hematopoese/fisiologia , Linfopoese/fisiologia , Osteopetrose/patologia , Animais , Linfócitos B/citologia , Medula Óssea/metabolismo , Medula Óssea/patologia , Diferenciação Celular , Células Dendríticas/metabolismo , Células Dendríticas/patologia , Modelos Animais de Doenças , Hematopoese/genética , Interferon gama/metabolismo , Interleucina-7/metabolismo , Ativação Linfocitária , Camundongos , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Camundongos Knockout , Osteoclastos/metabolismo , Osteopetrose/metabolismo , Baço/imunologia , Linfócitos T/citologiaRESUMO
Msx1 is a key factor for the development of tooth and craniofacial skeleton and has been proposed to play a pivotal role in terminal cell differentiation. In this paper, we demonstrated the presence of an endogenous Msx1 antisense RNA (Msx1-AS RNA) in mice, rats, and humans. In situ analysis revealed that this RNA is expressed only in differentiated dental and bone cells with an inverse correlation with Msx1 protein. These in vivo data and overexpression of Msx1 sense and AS RNA in an odontoblastic cell line (MO6-G3) showed that the balance between the levels of the two Msx1 RNAs is related to the expression of Msx1 protein. To analyze the impact of this balance in the Msx-Dlx homeoprotein pathway, we analyzed the effect of Msx1, Msx2, and Dlx5 overexpression on proteins involved in skeletal differentiation. We showed that the Msx1-AS RNA is involved in crosstalk between the Msx-Dlx pathways because its expression was abolished by Dlx5. Msx1 was shown to down-regulate a master gene of skeletal cells differentiation, Cbfa1. All these data strongly suggest that the ratio between Msx1 sense and antisense RNAs is a very important factor in the control of skeletal terminal differentiation. Finally, the initiation site for Msx1-AS RNA transcription was located by primer extension in both mouse and human in an identical region, including a consensus TATA box, suggesting an evolutionary conservation of the AS RNA-mediated regulation of Msx1 gene expression.
