GABA(A) Receptor Subunit Regulation in Epileptogenesis

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 DESCRIPTION (provided by applicant): Brain derived neurotrophic factor (BDNF), a critical signaling molecule in the brain, is functionally linked to essential cellular processes, such as those associated with learning and memory. Altered BDNF signaling is thought to play a crucial role in dysregulated neuroplasticity underlying multiple neurological diseases, including epilepsy, yet the complex molecular determinants of these important brain processes are not fully understood. Our laboratories discovered that BDNF modulates inhibition, in part, through activation of the Janus Kinase (JAK)/Signal Transducer and Activator of Transcription (STAT) signaling pathway. Employing primary cultured neurons and rodent models, we have reported that BDNF-induced JAK/STAT signaling represses the expression of synaptic α1 containing GABAA receptors (GABARs) following epileptogenic brain injuries, including status epilepticus (SE) and brain trauma (TBI), and that JAK/STAT inhibition at the time of injury can reduce the severity of subsequent epilepsy. We also have preliminary evidence that BDNF-induced JAK/STAT signaling is mediated by TrKB activation at the cell surface promoting JAK2 autophosphorylation within an intracellular signalsome containing p75 neurotrophin receptors (a complex referred to as (i)p75NTRJ), leading to STAT3 recruitment and activation. Subsequent transport of the (i)p75NTRJ signalsome into the nucleus may alter transcription of multiple target genes, including inducible early cAMP repressor (ICER) that binds to and represses the α1 GABAR gene after SE. To test our hypothesis that BDNF-induced JAK/STAT activation is dysregulated following brain injury causing a systematic change in the transcription of multiple genes that promote epileptogenesis, we will use an unbiased transcriptomic approach, including RNA-seq and ChIP-seq with antibodies to pSTAT3, p75NTR, JAK2, and ICER, in a preclinical epilepsy model utilizing wild-type and transgenic mice with inducible deletion of p75NTR or STAT3 genes. Specifically, we will: 1) Identify the target genes of (i)p75NTRJ that change their expression after epileptogenic brain injury and whether they are specific to neurons or part of a general cellular response using neuron selective or global p75NTR or STAT3 deletion/inhibition; 2) Mechanistically test the relationship of target genes identified in Aim 1 to the genomic response of individual neurons treated with BDNF or kainate; and 3) Determine the functional consequences of neuronal selective or global p75NTR or STAT3 removal on epileptogenesis and cognitive co-morbidities following brain injury. Combining transcriptomic analysis with mouse genetics in an animal model of epilepsy, we will expand our current knowledge of GABAR gene regulation after brain injury to appreciate the complex patterns of genomic changes that underlie epileptogenesis. Such understanding is essential for development of epilepsy modifying therapies targeting intracellular pathways that broadly regulate gene expression & may be more efficacious than those that target the products of single gene candidates in isolation.