The Role of STING-Mediated Neuroinflammation in Traumatic Brain Injury

Despite its prevalence, there are currently zero treatments available for traumatic brain injuries (TBI). Neuroinflammation is a key aspect of the secondary injury process, but remains poorly understood. Recent work has shown that Type I Interferons, inflammatory cytokines typically produced in response to viral infection, are present in the post-mortem brains of human TBI patients. The cyclic GMP-AMP Synthase- Stimulator of Interferon Genes (cGAS-STING) pathway is one of the primary methods of producing Type I IFNs; therefore, this work sought to evaluate the role of the cGAS-STING pathway in a murine controlled cortical impact (CCI) model of TBI. Using cGAS knockout (KO) or STING KO mice, we show that global loss of either protein results in substantial neuroprotection. One day after injury, animals have reduced lesion size, cell death, and inflammatory cytokine production, as well as reduced motor deficits several days after injury. We also determined that mitochondrial DNA (mtDNA) is present in the cytosol of injured cortical cells, indicating it is available to bind cGAS, a cytosolic pattern recognition receptor. To determine whether brain-resident or peripheral immune cells are responsible for detrimental cGAS-STING signaling after TBI, we utilized bone marrow chimeric animals lacking STING in either the brain or hematopoietic cells and animals lacking STING specifically in microglia. We found that both microglia and peripheral immune cells contribute to STING signaling after neurotrauma, and that loss of STING in either cell population is beneficial. Taken together, this work demonstrates that canonical, cGAS-dependent STING signaling occurs primarily in microglia and peripheral immune cells, resulting in detrimental neuroinflammatory events after TBI.