The STAT3 Response of Excitatory Neurons to Epileptogenic Brain Injury

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Abstract Temporal lobe epilepsy (TLE) is a progressive disorder mediated by pathological changes in molecular cascades and neural circuit remodeling in the hippocampus resulting in increased susceptibility to spontaneous seizures and cognitive dysfunction. Targeting these cascades could prevent or reverse symptom progression and has the potential to provide viable disease-modifying treatments that could reduce the portion of TLE patients (>30%) not responsive to current medical therapies. The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway has recently been implicated in the pathogenesis of TLE. This pathway is known to be involved in inflammation and immunity, and to be critical for neuronal functions such as synaptic plasticity and synaptogenesis. Our laboratories previously showed that a STAT3 inhibitor, WP1066, could greatly reduce the number of spontaneous recurrent seizures (SRS) in an animal model of pilocarpine-induced status epilepticus (SE). While this suggests promise for JAK/STAT inhibitors as disease-modifying therapies, the potential adverse effects of systemic or global CNS pathway inhibition limits their use. Development of more targeted therapeutics will require a detailed understanding of JAK/STAT-induced epileptogenic responses in different cell types. To this end, we have developed a new transgenic line where dimer-dependent STAT3 signaling is functionally knocked out (fKO) by tamoxifen-induced Cre expression specifically in forebrain excitatory neurons (eNs) via the Calcium/Calmodulin Dependent Protein Kinase II alpha (CamK2a) promoter. We now report that STAT3 KO in excitatory neurons (eNSTAT3fKO) markedly reduces the progression of epilepsy (SRS frequency) in the intrahippocampal kainate (IHKA) TLE model and protects mice from kainic acid (KA)-induced memory deficits as assessed by Contextual Fear Conditioning. Using data from bulk hippocampal tissue RNA-sequencing, we further discovered a transcriptomic signature for the IHKA model that contains a substantial number of genes, particularly in synaptic plasticity and inflammatory gene networks, that are down-regulated after KA-induced SE in wild-type but not eNSTAT3fKO mice. In this application, we will test the hypothesis that STAT3 signaling in excitatory neurons is a key driver of epilepsy progression via the selective silencing of genes that regulate synaptic plasticity and neuroinflammation. With an integration of open discovery using multiomics and quantitative molecular imaging (Aims 1 and 3), in combination with electrophysiology and neuropharmacology (Aim 2), we will elucidate the genome’s response to injury (24 h and 4 wks after IHKA) within different cell types and determine why STAT3 KO in eNs inhibits disease progression after KA injection by identifying direct and indirect effects of loss of eNSTAT3 expression on both excitatory and inhibitory neurons. We will also determine the relationship between eNSTAT3 signaling and glial activation by examining effects of eNSTAT3KO on the glial transcriptome and inflammatory markers of microglia and astrocytes. Our results will ascertain if cell-type specific modulation of STAT3 signaling or its downstream targets are promising strategies for therapeutic intervention.