RESUMO
Here we studied the role of signaling through ErbB-family receptors in interactions between unmyelinated axons and non-myelinating Schwann cells in adult nerves. We generated transgenic mice that postnatally express a dominant-negative ErbB receptor in non-myelinating but not in myelinating Schwann cells. These mutant mice present a progressive peripheral neuropathy characterized by extensive Schwann cell proliferation and death, loss of unmyelinated axons and marked heat and cold pain insensitivity. At later stages, C-fiber sensory neurons die by apoptosis, a process that may result from reduced GDNF (glial cell line-derived neurotrophic factor) expression in the sciatic nerve. Neuregulin 1 (NRG1)-ErbB signaling mediates, therefore, reciprocal interactions between non-myelinating Schwann cells and unmyelinated sensory neuron axons that are critical for Schwann cell and C-fiber sensory neuron survival. This study provides new insights into ErbB signaling in adult Schwann cells, the contribution of non-myelinating Schwann cells in maintaining trophic support of sensory neurons, and the possible role of disrupted ErbB signaling in peripheral sensory neuropathies.
Assuntos
Acetiltransferases , Morte Celular/fisiologia , Receptores ErbB/fisiologia , Regulação da Expressão Gênica no Desenvolvimento , Glicoproteínas , Neurônios Aferentes/fisiologia , Receptor trkA , Células de Schwann/fisiologia , Transdução de Sinais/fisiologia , Proteínas Adaptadoras de Transdução de Sinal , Envelhecimento , Animais , Animais Recém-Nascidos , Axônios/metabolismo , Axônios/ultraestrutura , Comportamento Animal , Western Blotting , Bromodesoxiuridina/metabolismo , Proteínas de Transporte/metabolismo , Contagem de Células , Morte Celular/genética , Receptores ErbB/genética , Gânglios Espinais/citologia , Gânglios Espinais/metabolismo , Fator Neurotrófico Derivado de Linhagem de Célula Glial , Homozigoto , Hiperalgesia/metabolismo , Imuno-Histoquímica , Marcação In Situ das Extremidades Cortadas , Lectinas/metabolismo , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Transgênicos , Microscopia Eletrônica , Bainha de Mielina/ultraestrutura , Fatores de Crescimento Neural/metabolismo , Neuregulina-1/metabolismo , Proteínas de Neurofilamentos/metabolismo , Proteínas Oncogênicas v-fos/metabolismo , Medição da Dor , Tempo de Reação , Receptor ErbB-4 , Receptores Purinérgicos P2/metabolismo , Receptores Purinérgicos P2X3 , Nervo Isquiático/metabolismo , Nervo Isquiático/ultraestrutura , Transdução de Sinais/genética , Medula Espinal/metabolismo , Medula Espinal/ultraestrutura , Transativadores/metabolismo , Fatores de Transcrição/metabolismoRESUMO
Growth factor suppression of apoptosis correlates with the phosphorylation and inactivation of multiple proapoptotic proteins, including the BCL-2 family member BAD. However, the physiological events required for growth factors to block cell death are not well characterized. To assess the contribution of BAD inactivation to cell survival, we generated mice with point mutations in the BAD gene that abolish BAD phosphorylation at specific sites. We show that BAD phosphorylation protects cells from the deleterious effects of apoptotic stimuli and attenuates death pathway signaling by raising the threshold at which mitochondria release cytochrome c to induce cell death. These findings establish a function for endogenous BAD phosphorylation, and elucidate a mechanism by which survival kinases block apoptosis in vivo.
Assuntos
Apoptose , Proteínas de Transporte/metabolismo , Fator de Crescimento Insulin-Like I/farmacologia , Mitocôndrias/metabolismo , Fator de Crescimento Derivado de Plaquetas/farmacologia , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Transdução de Sinais , Animais , Linfócitos B/citologia , Proteínas de Transporte/genética , Diferenciação Celular , Sobrevivência Celular , Células Cultivadas , Grupo dos Citocromos c/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Fibroblastos/citologia , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Células-Tronco Hematopoéticas/citologia , Células-Tronco Hematopoéticas/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Neurônios/citologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Fosforilação , Proteínas Proto-Oncogênicas c-bcl-2/genética , Linfócitos T/citologia , Timo/citologia , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteína de Morte Celular Associada a bclRESUMO
Angelman syndrome (AS), characterized by motor dysfunction, mental retardation, and seizures, is caused by several genetic etiologies involving chromosome 15q11-q13, including mutations of the UBE3A gene. UBE3A encodes UBE3A/E6-AP, a ubiquitin-protein ligase, and shows brain-specific imprinting, with brain expression predominantly from the maternal allele. Lack of a functional maternal allele of UBE3A causes AS. In order to understand the causal relationship between maternal UBE3A mutations and AS, we have constructed a mouse model with targeted inactivation of Ube3a. The inactive allele contains a lacZ reporter gene for analysis of brain-specific imprinting. Maternal, but not paternal, transmission of the targeted allele leads to beta-galactosidase activity in hippocampal and cerebellar neurons. Maternal inheritance of the Ube3a mutant allele also causes impaired performance in tests of motor function and spatial learning, as well as abnormal hippocampal EEG recordings. As predicted from the dependence of UBE3A-mediated ubiquitination of p53 on HPV E6 protein, our maternal-deficient mice show normal brain p53 levels.