Progressive hippocampal atrophy has been demonstrated in humans with epilepsy. Such SEIZURE-induced neurodegeneration may be under the control of the CASPASE family of cell death regulating enzymes, as our recent studies in brains of patients with intractable epilepsy showed the presence and activation of the programmed cell death/apoptosis pathway. INITIATOR caspases begin the cell death process: following activation of surface- expressed death receptors - the EXTRINSIC pathway, or following mitochondrion-based events within the cell - the INTRINSIC pathway. Subsequently these caspases activate downstream EFFECTOR caspases, which carry out the execution and disassembly of the cell. Intervention in this cell death cascade has considerable implications for the therapeutic treatment of neurodegenerative diseases to which epilepsy may now be added. Therefore the broad, long-term goals of this proposal are to characterize the contribution of the caspase family of cell death-controlling enzymes in mediating seizure-induced brain injury. They hypotheses to be tested are (A) Neuronal death occurs following seizures and is initiated by caspases 2, 8 and/or 10 of the extrinsic death receptor pathway. (B) Caspase 2, 8 and/or 10 activation requires recruitment to death receptors by adaptor proteins in response to death ligands. (C) Activation of the intrinsic, mitochondrion-dependent caspase-9 pathway is co- dependent on the death receptor pathway via the cytochrome c releasing factor Bid. (D) Novel effector caspases 6 and 7 are activated by seizures via these extrinsic and intrinsic pathways and contribute to neuronal death.
The specific aims are: 1) Characterize the expression, processing and consequences of activation of the extrinsic death-signaling pathway caspases 2, 8 and 10 using an in vivo rat model of brief limbic seizures. 2) Characterize the expression and functional interaction of death receptors with their adaptor protein(s) in the signal transduction and recruitment of caspases 2, 8 and 10 following seizures. 3) Characterize the expression, processing and consequences of activation of the intrinsic caspase-9-dependent pathway in seizure-induced brain injury. 4) Characterize the activation of the novel death effector caspases 6 and 7 in response to the extrinsic and/or intrinsic initiator pathways following seizures. 5) Characterize the involvement of extrinsic, intrinsic and death effector caspases mediating apoptosis induced by seizure-like activity in neuronal cultures in vitro. Elucidation of the molecular control of seizure-induced cell death will further our understanding of brain injury processes and take a significant step toward therapeutic approaches to reduce brain injury in epilepsy.
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