RESUMO
In this study we analyzed whether other members of the Bcl-2 family are regulated in the absence of Bax during the postnatal development of the striatum and cortex and after striatal excitotoxic lesion. Compared with wild-type animals, Bax knockout mice showed region- and time-dependent increases in pro-apoptotic proteins Bak and Bim(EL). Excitotoxicity induced in the adult striatum increased Bim(EL) in both genotypes whereas Bak and Bcl-x(L) were only increased in Bax knockout mice. However, translocation of Bim(EL) protein to the mitochondrial fraction, cytochrome c release and caspase-3 activation were only observed in wild-type striata. Furthermore, analysis of Bim null mutant mice showed that this protein is not essential to excitotoxicity-induced striatal cell death. In conclusion, our results show that in Bax deficient mice Bim(EL) and Bak are specifically regulated during postnatal development, suggesting that these proteins may participate in the compensatory mechanisms triggered in the absence of Bax. In contrast, Bax is required to induce apoptosis after excitotoxicity in the adult striatum.
Assuntos
Proteínas Reguladoras de Apoptose/biossíntese , Córtex Cerebral/metabolismo , Corpo Estriado/metabolismo , Proteínas de Membrana/biossíntese , Proteínas Proto-Oncogênicas/biossíntese , Regulação para Cima , Proteína Killer-Antagonista Homóloga a bcl-2/biossíntese , Proteína X Associada a bcl-2/deficiência , Animais , Animais Recém-Nascidos , Apoptose/genética , Proteínas Reguladoras de Apoptose/genética , Proteína 11 Semelhante a Bcl-2 , Morte Celular/genética , Córtex Cerebral/crescimento & desenvolvimento , Córtex Cerebral/fisiologia , Corpo Estriado/crescimento & desenvolvimento , Corpo Estriado/fisiologia , Feminino , Masculino , Proteínas de Membrana/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas Proto-Oncogênicas/genética , Ácido Quinolínico/toxicidade , Regulação para Cima/genética , Proteína Killer-Antagonista Homóloga a bcl-2/genética , Proteína X Associada a bcl-2/genéticaRESUMO
The striatum is one of the brain areas most vulnerable to excitotoxicity, a lesion that can be prevented by neurotrophins. In the present study, intrastriatal injection of the N-methyl-d-aspartate receptor (NMDAR) agonist quinolinate (QUIN) was performed in mice heterozygous for neurotrophin-3 (NT3 +/-) or brain-derived neurotrophic factor (BDNF +/-) to analyze the role of endogenous neurotrophins on the regulation of striatal neurons susceptibility to excitotoxic injury. QUIN injection induced a decrease in dopamine- and cyclic AMP-regulated phosphoprotein of 32 kDa (DARPP-32) protein levels that was higher in NT-3 +/- than in BDNF+/- or wild type animals. This enhanced susceptibility was specific for enkephalin- and tachykinin-positive projection neurons, and also for parvalbumin-positive interneurons. However the excitotoxic damage in large interneurons was not modified in NT-3 +/- mice compared with wild type animals. This effect can be related to the regulation of NMDARs by endogenous NT-3. Thus, our results show that there is an age-dependent regulation of NMDAR subunits NR1 and NR2A, but not NR2B, in NT-3 +/- mice. The deficit of endogenous NT-3 induced a decrease in NR1 and NR2A subunits at postnatal day (P) 0 and P3 mice respectively, whereas an upregulation was observed in 12 week old NT-3 +/- mice. This differential effect was also observed after administration of exogenous NT-3. In primary striatal cultures, NT-3 treatment induced an enhancement in NR2A, but not NR2B, protein levels. However, intrastriatal grafting of NT-3 secreting-cells in adult wild type mice produced a down-regulation of NR2A subunit. In conclusion, NT-3 regulates the expression of NMDAR subunits modifying striatal neuronal properties that confers the differential vulnerability to excitotoxicity in projection neurons and interneurons in the striatum.
Assuntos
Corpo Estriado/metabolismo , Regulação da Expressão Gênica/fisiologia , Neurotrofina 3/fisiologia , Receptores de N-Metil-D-Aspartato/metabolismo , Análise de Variância , Animais , Fator Neurotrófico Derivado do Encéfalo/deficiência , Contagem de Células/métodos , Transplante de Células , Células Cultivadas , Corpo Estriado/lesões , Corpo Estriado/patologia , Aminoácidos Excitatórios/toxicidade , Fibroblastos/metabolismo , Fibroblastos/transplante , Regulação da Expressão Gênica/efeitos dos fármacos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Neurotrofina 3/deficiência , Ácido Quinolínico/toxicidade , Ratos , Ratos Endogâmicos F344 , Receptores de N-Metil-D-Aspartato/genética , Transfecção/métodos , Transplante Heterólogo , Ácido gama-Aminobutírico/metabolismoRESUMO
Bone morphogenetic proteins (BMPs) are a set of members of the transforming growth factor-beta superfamily recently described as promoting the differentiation of several neuronal populations within the basal ganglia. This study examined whether a member of this family, BMP-6, could exert neurotrophic effects on the neurons of the striatum, in which BMP-6 mRNA had been previously detected during development. Here we show that BMP-6 increases the number and differentiation of calbindin-positive neurons in vitro. Indeed, BMP-6 increased the total area, the perimeter, and the degree of arborization of this neuronal population. This trophic factor promoted dendritic growth without modifying axonal length or soma area. Furthermore, BMP-6 increased the number of glial fibrillary acidic protein-positive cells while decreasing the number of nestin-positive cells. The suppression of cell proliferation or glial development by the antimitotic fluorodeoxyuridine removed the effects on striatal neurons, suggesting the involvement of astroglial cells in the differentiation induced by BMP-6. The current results confirm the relevance of BMPs in the development of the striatum and emphasize the crucial importance of the trophic interaction between glial and neuronal cells.
