Many types of insults or injury lead to seizures and neuronal loss, which ultimately can lead to devastating and intractable long-term consequences, including cognitive impairment, chronic epilepsy and disability. Our labs have identified a central role of neurotrophins, particularly proNGF in mediating neuronal apoptosis following severe seizures (status epilepticus;SE). Neurotrophins, initially characterized for their survival and differentiative actions on neurons, are initially synthesized as precursors that are cleaved to release C-terminal mature forms that bind to Trk receptors to promote neuronal survival, and synaptic actions. Recent studies suggest that the precursor form of NGF (proNGF) acts as a distinct ligand by binding to a receptor complex of p75 and sortilin to initiate neuronal death. Our labs have demonstrated that SE rapidly induces p75 and proNGF in the hippocampus, in rodent models. Importantly, infusion of function blocking anti-proNGF antibodies, or genetic deletion of p75, rescues neuronal death following SE, providing a mechanism and target for therapy to prevent neuronal loss after SE, and its consequence, epileptogenesis. Here we extend these collaborative studies to utilize novel knock-in mouse lines that expressed HA-epitope tagged NGF, or proNGF under its endogenous promoter elements. These animals circumvent the current limitations in sensitivity of reagents, and markedly enhance our ability to detect endogenous NGF. Thus we will be able to identify cell specific and temporal patterns of NGF/proNGF synthesis in neurons and glia under basal conditions and after SE. Using the proNGF mouse, we will quantitatively evaluate the effects of augmented proNGF following SE induction, to assess whether excess proNGF leads to exacerbated neuronal cell death. We will also use video-EEG to assess the consequence of excess proNGF on the development of epilepsy. Finally, and most important, we will investigate whether antagonists of proNGF, identified in a high through-put drug screen, can prevent or attenuate neuronal death following SE and prevent the onset of epilepsy. These antagonists consist of FDA-approved drugs that have minimal toxicity and efficiently block proNGF-induced apoptosis in cultured neurons. The possibility of identifying approved drugs that have the capacity to prevent neuronal death from severe seizures has significant potential for clinical application, both for epileptic patient populations, and for those suffering seizures as a consequence of brain trauma or stroke.
Insults or injury that cause severe seizures can lead to neuronal loss and the development of epilepsy, but the underlying mechanisms that lead to these outcomes are not clear, and there are few strategies to prevent them. ProNGF is produced in the brain after experimental status epilepticus (SE), and leads to neuronal death. We will use a proNGF knock-in mouse model to investigate which cells secrete proNGF under basal conditions and after SE and whether neuronal loss and the development of recurrent seizures (epilepsy) are exacerbated by excess proNGF. We will also determine whether antagonists of proNGF binding to p75 neurotrophin receptor protect neurons from apoptosis after SE and prevent epileptogenesis. The possibility of identifying approved drugs that have the capacity to prevent neuronal death after insults or injury associated with severe seizures has significant potential for clinical application.
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