Mechanisms of Circadian and Synaptic Dysfunction After Repetitive Mild TBI

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Mild traumatic brain injury (mTBI) affects hundreds of millions of young people world-wide each year. Epidemiological studies link repetitive mTBI to dementia and neurodegenerative disease later in life, however causative mechanisms remain undefined. Disruption of circadian rhythms is a prominent manifestation of the post-concussive syndrome and has been associated with Alzheimer’s-like neurodegeneration but the mechanisms linking mTBI, neurodegeneration, and circadian rhythms is unknown, highlighting a key unmet need in mTBI and an unexplored therapeutic opportunity. We previously reported that IL-1 receptor-1 signaling is required for post-injury cognitive deficits in mTBI models, implicating inflammatory pathways as key pathogenic mechanisms. We hypothesized that there would be direct molecular connections between the circadian clock and neuroimmune signaling through the IL-1 receptor pathway. Our preliminary data show that repetitive mTBI induces phosphorylation of the key circadian clock protein BMAL1 in wild type but not IL-1R1-deficient mouse brain. Our ongoing work has identified a critical function for BMAL1 phosphorylation in the organization of presynaptic function and long-term memory. Our results lead to our hypothesis that repetitive mTBI induces synaptic dysfunction and cognitive deficits via IL-1R1-mediated hyperphosphorylation of BMAL1. In Aim 1, we will define how ILR1-mediated pBMAL1 signaling in response to mTBI corrupts the timing of synaptic function and impairs synaptic plasticity. In Aim 2, we will use combinatorial and complementary transgenic approaches including mouse models uniquely available to our groups, to define the cell types responsible for IL-1R-mediated signaling that culminate in cognitive dysfunction after mTBI. Finally, Aim 3 will define a novel signaling pathway by which IL-1-mediated hyperphosphorylation of pBMAL1 after mTBI results in dysfunctional regulation of key synaptic and neuronal kinases such as CaMKIIA with subsequent promulgation of tau-related aggregation and impaired synaptic plasticity. Successful completion of the Aims is expected to provide a cellular and molecular basis for repetitive mTBI-induced cognitive dysfunction and identify new therapeutic targets to alleviate sequelae of concussions and other forms of repetitive mTBI.