Mechanisms and intervention of cGAS signaling in brain trauma-induced neuroinflammation and neurodegeneration - Project Summary Traumatic brain injury (TBI) leads to long-term neurological issues, including an increased risk of Alzheimer's disease and related dementias, but effective therapies are lacking due to its complex secondary injury mechanisms. Leakage of genomic and mitochondrial (mt) DNA into the cytosol and extracellular microenvironment is key to TBI pathogenesis. Brain injury triggers the release of extracellular vesicles (EVs) as a response to cellular stress, inflammation, and damage. In TBI, EVs may carry both nuclear DNA and mtDNA released from damaged cells. These DNA fragments are typically packaged inside the EVs or associated with their surface. Cyclic GMP-AMP synthase (cGAS) is a major cytosolic DNA sensor that catalyzes cyclic GMP- AMP formation, which, in turn, activates stimulator of interferon (IFN) genes (STING) and promotes type 1 IFN signaling. A critical question is what underlying mechanisms drive cGAS dysfunction after TBI. Our preliminary data suggests that DNA accumulation in EVs after TBI may activate cGAS signaling in microglia and macrophages, driving neuroinflammation and neurodegeneration. Cellular senescence, triggered by DNA damage in glial cells, further contributes to TBI-related dysfunction. The recent discovery of senescence in neurons, a cell type that is postmitotic from birth, has been surprising, given that proliferation arrest was long considered central to the senescent state. Mounting evidence suggests that the cGAS pathway plays an essential role in cellular senescence due to its regulation of downstream signaling after DNA damage. Yet, the role of cGAS-mediated cellular senescence in TBI pathogenesis remains unexplored. The scientific premise of this proposal is further strengthened by our new preliminary discoveries: 1) A marked increase in cGAS-STING expression levels was detected 1d after injury, which persisted for up to 4 weeks following TBI; 2) DNA analysis showed increased DNA in EVs from injured tissues, triggering cGAS upregulation in microglia and macrophages; 3) Genetic ablation of cGAS showed significantly reduced tissue damage and improved recovery along with reduced senescence markers; 4) Early cGAS inhibition with TDI-6570 improved recovery, reducing inflammation and senescence; 5) Research diet pellets containing TDI-6570 protected against cognitive deficits in an AD mouse model with tauopathy. Accordingly, we hypothesized that brain injury activates cGAS signaling in microglia and macrophages through DNA containing extracellular vesicles, promoting brain neuroinflammation and neurodegeneration by inducing cellular senescence, ultimately resulting in neurological dysfunction. We will tackle three Specific Aims. Aim 1: Investigate the mechanism by which TBI activates cGAS signaling. Aim 2: Determine cGAS- mediated molecular mechanisms in TBI pathogenesis. Aim 3: Evaluate the therapeutic potential of targeting cGAS in the treatment of TBI. We expect that our data will demonstrate a new avenue for understanding of cGAS-mediated cellular senescence after TBI and the beneficial effect of cGAS inhibition in TBI recovery.
