Ischemic damage to the brain results in substantial morbidity during the perinatal period as well as mortality in the later decades of life. Studies in the intact animal as well as in vitro have established that the extreme physiologic perturbations which occur during CNS ischemia trigger a delayed form of neuronal death which is dependent on new gene transcription and that hypoxia triggered gene responses precede activation of delayed apoptotic cell death. One approach to the identification of novel therapeutic strategies which would protect against this form of neuronal cell death is through examination of the mechanisms which direct hypoxia responsive gene expression in the CNS. The phylogenetically conserved hypoxia response is manifest in the mammalian systems through transcriptional activation and post- transcriptional mRNA stabilization. In the periphery, transcriptional events are known to be mediated through the hypoxia inducible transcription factor, HIF-1alpha, which binds cognate cis elements in the promoter region of a restricted set of genes thereby simulating the rate of gene transcription. Information regarding the utilization of this hypoxia responsive mechanism within the various cellular compartments of the CNS (neuronal, astrocytic and microglial) and their relationship to apoptotic neuronal loss is lacking, however. Broadly, we hypothesize that early in the post-ischemic CNS hypoxic-regulated gene expression exhibits heterogeneity within the cellular compartments in the CNS and that this response triggers a sequence which either directly or indirectly elicits delayed neuronal death. We plan to exploit hypoxia responsive HSV viral vectors to map the regional and temporal evolution of hypoxic signaling within the compartments of the ischemic murine CNS. Subsequent studies will utilize HIF neuronal isoform specific antibodies to characterize HIF isoform induction, cellular localization and confirm DNA binding reactivity through EMSA supershift assays all under hypoxic conditions. We hypothesize that these experiments will characterize heterogeneous hypoxic response and will define discrete factors in ischemia induced CNS transcriptional activation. Our long-term goals are to identify early responses in the ischemic brain and subsequently identify regulatory nodes in the hypoxic signal cascade which can selectively modulate hypoxia gene activation. Such findings will highlight novel therapeutic strategies directed against hypoxia induced delayed neuronal death.
| Halterman, M W; Miller, C C; Federoff, H J (1999) Hypoxia-inducible factor-1alpha mediates hypoxia-induced delayed neuronal death that involves p53. J Neurosci 19:6818-24 |
