Transient forebrain or global ischemia arising during cardiac arrest affects 150,000 Americans each year and in many cases results in delayed death of hippocampal neurons and severe cognitive deficits. To date, treatment of the neurodegeneration and cognitive deficits associated with global ischemia is an unmet need. Our recent discovery that a single, acute injection of the ovarian hormone estradiol administered after an ischemic attack ameliorates neuronal injury and cognitive loss in an animal model of global ischemia is a novel finding with important clinical implications. The clinical relevance of this discovery is heightened by our observation that acute estradiol is effective when administered icv or subcutaneously and affords robust protection in young adult and middle-aged female animals. The overall objective is to identify molecular mechanisms underlying acute estradiol neuroprotection and identify novel therapeutic targets for intervention in the neurodegeneration associated with global ischemia. The central hypothesis driving the research is that estradiol acts by coordinate activation of the nuclear receptor transcription factor ER1 and the G-protein coupled receptor GPR30, JAK/ STAT signaling, epigenetic remodeling and transcription of pro-survival genes to rescue CA1 neurons from ischemia-induced neuronal death.
Specific Aims are: 1. Determine whether estradiol acts via ER1 and GPR30 to engage JAK/STAT signaling and protect hippocampal neurons. Experiments will examine 1) ability of estradiol and GPR30 agonists administered after an ischemic episode to rescue impaired synaptic plasticity, cognitive deficits and neuronal death;2) ability of GPR30 antagonists and RNAi-mediated silencing of GPR30 to block acute estradiol protection;3) ability of estradiol to blunt CTMP, an endogenous inhibitor of Akt;and 4) ability of estradiol to activate JAK/STAT signaling and ability of STAT3 inhibitors and RNAi-mediated silencing of STAT3 to block estradiol protection. 2. Examine whether STAT3-dependent transcription is critical for estradiol protection. Experiments will examine 1) ability of estradiol to promote transcription of STAT3 target genes;2) ability of STAT3 decoy DNA, dnSTAT3 and STAT3 peptide inhibitor to block transcription and estradiol neuroprotection;3) ability of estradiol to promote transcription of CREB target genes;and 4) ability of caCREB to mimic estradiol protection and of dnCREB to block estradiol protection. 3. Determine whether estradiol acts via epigenetic remodeling to promote transcription of genes implicated in neuronal survival. Experiments will examine 1) ability of estradiol to promote epigenetic remodeling of STAT3 and CREB target genes implicated in neuronal survival (enhanced association with marks of "active" transcription, decreased association with marks of "silent" transcription and altered clipping of histone N-terminal tails);2) ability of epigenetic modifications to alter expression of pro-survival genes;3) causal relation between genes altered by ischemia and neuronal death. These studies will accelerate development of therapeutic strategies to ameliorate neuronal death and cognitive deficits not only in ischemia, but other neurodegenerative disorders.
Global ischemia arising as a consequence of cardiac arrest affects ~200,000 Americans per year and in many cases results in neurological deficits. To date, treatment of the neurodegeneration and cognitive deficits associated with global ischemia is an unmet need. It is thus critical that new molecular mechanistic information be revealed and brought into the translational arena with the goal of developing novel treatment strategies for neuroprotection, rescue and repair in order to ameliorate the deleterious consequences of brain ischemia. Our preliminary findings show that a single dose of the ovarian hormone, estradiol, administered after the ischemic event ameliorates neuronal death and cognitive deficits in an animal model. Identification of genes with altered epigenetic regulation in ischemia will accelerate development of therapeutic strategies not only for global ischemia, but in other neurologic disorders such as stroke.
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