RESUMO
Hypoxia-inducible factor 1 alpha (HIF-1alpha) is a transcription factor that was suggested in vitro to promote cell death by modulation of proapoptotic genes. In this report, we tested the hypothesis of an in vivo proapoptotic role of HIF-1alpha after an ischemic insult. For this purpose, HIF-1alpha and procaspase-3 mRNA and protein expressions were examined in rat brain subjected to 12- and 24-h permanent focal ischemia and the presence of an HIF-1 binding activity to the caspase-3 gene promoter was explored. The results showed that HIF-1alpha and procaspase-3 expressions increased with a similar pattern in response to ischemia. In addition, caspase-3 activation was observed in cells that express HIF-1alpha. Moreover, electrophoretic mobility assay revealed a specific HIF-1 binding activity to the caspase-3 gene promoter. Altogether the present data provide strong arguments for a causative relationship between HIF-1alpha and caspase-3 inductions through a functional binding activity to the caspase-3 gene promoter.
Assuntos
Caspase 3/metabolismo , Subunidade alfa do Fator 1 Induzível por Hipóxia/metabolismo , Hipóxia-Isquemia Encefálica/metabolismo , Trombose Intracraniana/metabolismo , Regiões Promotoras Genéticas/genética , Telencéfalo/metabolismo , Animais , Sítios de Ligação/genética , Caspase 3/genética , Modelos Animais de Doenças , Ativação Enzimática/genética , Regulação Enzimológica da Expressão Gênica/genética , Subunidade alfa do Fator 1 Induzível por Hipóxia/genética , Hipóxia-Isquemia Encefálica/genética , Hipóxia-Isquemia Encefálica/fisiopatologia , Trombose Intracraniana/genética , Trombose Intracraniana/fisiopatologia , Masculino , Oxigênio/metabolismo , Ligação Proteica/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Telencéfalo/fisiopatologiaRESUMO
To evaluate the effect of body iron stores on the vulnerability of the brain to ischemia, a focal permanent brain ischemia was induced by photothrombotic occlusion of cortical vessels in rats with or without chronic treatment with iron dextran (25 mg iron/kg, every other day for 20 days, intraperitoneally). Iron dextran induced systemic iron overload as evidenced by high ferritin (Ft) ( x 5) and total iron levels ( x 3) in serum as well as increased Ft expression in the liver and heart. Conversely, neither serum free iron levels nor Ft expression in the brain were changed by iron dextran. Finally, infarct volume was not modified by iron dextran. In addition, induction of ischemia in rats treated with FeCl(3) (560 microg iron/kg, intravenously) as a means of increasing serum free iron levels during the ischemic period did not enlarge infarct volume. We then explored the effect of brain ischemia itself on serum Ft by measuring serum Ft before and after induction of brain ischemic insults with different neurologic outcomes in rats (brain embolization with microspheres, photothrombotic occlusion of cortical vessels, four-vessel occlusion). Serum Ft levels were found higher at day 1 after ischemia than before ischemia only in rats subjected to the most severe insult (brain embolization). In conclusion, our study showed that increased body iron stores do not increase the vulnerability of the brain to ischemia and that brain ischemia, if severe, results in the elevation of serum Ft levels.