RESUMO
Although DNA damaging topoisomerase inhibitors induce apoptosis in developing neurons, their effects on adult neurons have not yet been characterized. We report a blockage of RNA-Polymerase-1-driven transcription and nucleolar stress in neocortical neurons of adult rats after intracarotid injection of the DNA-topoisomerase-2 inhibitor, etoposide. Intracerebroventricular injection of etoposide induced a similar response in neonatal rats. In contrast, etoposide triggered neuronal apoptosis in the neonates, but not the adults. Nucleolar disruption and apoptosis were also observed in etoposide-challenged cultured cortical neurons from newborn rats. In that system, activation of the DNA double strand break signaling kinase ataxia telangiectasia-mutated protein kinase, p53 and p53-dependent apoptosis required lower etoposide concentrations than did the p53-independent induction of nucleolar stress. These distinct responses may be coupled to different forms of etoposide-induced DNA damage. Indeed, double strand breaks by the over-expressed endonuclease I-Ppo1 were sufficient to induce p53-dependent apoptosis. Moreover, nucleolar transcription was insensitive to such damage implying single strand breaks and/or topoisomerase-2-DNA adducts as triggers of nucleolar stress. Because nucleolar stress is not age-restricted, it may underlie non-apoptotic neurotoxicity of chemotherapy- or neurodegeneration-associated DNA damage by reducing ribosomal biogenesis in adult brain. Conversely, nucleolar insensitivity to double strand breaks likely contributes to mature neuron tolerance of such lesions.
Assuntos
Antineoplásicos/toxicidade , Nucléolo Celular/efeitos dos fármacos , Dano ao DNA , Etoposídeo/toxicidade , Neurônios/efeitos dos fármacos , Inibidores da Topoisomerase II/toxicidade , Fatores Etários , Animais , Animais Recém-Nascidos , Antineoplásicos/administração & dosagem , Proteínas Mutadas de Ataxia Telangiectasia , Artérias Carótidas , Proteínas de Ciclo Celular/metabolismo , Nucléolo Celular/ultraestrutura , Células Cultivadas , Córtex Cerebral/citologia , Cromossomos de Mamíferos/genética , Quebras de DNA de Cadeia Dupla , Proteínas de Ligação a DNA/metabolismo , Ativação Enzimática , Etoposídeo/administração & dosagem , Injeções Intra-Arteriais , Injeções Intraventriculares , Masculino , Camundongos , Neurônios/ultraestrutura , Proteínas Serina-Treonina Quinases/metabolismo , RNA Polimerase I/fisiologia , Ratos , Ratos Sprague-Dawley , Transcrição Gênica , Proteína Supressora de Tumor p53/metabolismo , Proteínas Supressoras de Tumor/metabolismoRESUMO
Blood vessel loss and inflammation cause secondary degeneration following spinal cord injury. Angiopoietin-1 through the Tie2 receptor, and other ligands through alphavbeta3 integrin, promote endothelial cell survival during developmental or tumour angiogenesis. Here, daily intravenous injections with an alphavbeta3-binding peptide named C16 or an angiopoietin-1 mimetic following a spinal cord contusion at thoracic level 9 in mice rescued epicentre blood vessels, white matter and locomotor function, and reduced detrimental inflammation. Preserved vascularity and reduced inflammation correlated with improved outcomes. C16 and angiopoietin-1 reduced leukocyte transmigration in vitro. Growth factor receptors and integrins facilitate each others' function. Therefore, angiopoietin-1 and C16 were combined and the effects were additive, resulting in almost complete functional recovery. The treatment had lasting effects when started 4 h following injury and terminated after one week. These results identify alphavbeta3 integrin and the endothelial-selective angiopoietin-1 as vascular and inflammatory regulators that can be targeted in a clinically relevant manner for neuroprotection after central nervous system trauma.