Abstract: Alzheimer’s disease (AD) is characterized by the accumulation of amyloid-β (Aβ) in plaques and hyperphosphorylated tau in neurofibrillary tangles, as well as neurovascular dysfunctions and neuroinflammation, which together result in neurodegeneration and cognitive impairment. Both clinical and preclinical studies have indicated that neuroinflammation, particularly abnormal and chronic microglia activation, is a major part of AD etiology. Innate immunity is the first line of host defense against invading pathogens and harmful substance. It consists evolutionarily conserved pattern recognition receptors, including Toll-like receptors on the cell surface and intracellular vesicles, and nucleotide sensors such as cyclic GMP-AMP synthase (cGAS) for cytosolic DNA. The activation of these innate signaling pathways triggers the production of inflammatory cytokines and interferons, and further amplifies the immune response by activating a large array of interferon-stimulated genes. Interestingly, the innate immune responses are not always specific, and can often be activated by host molecules in injuries and diseases; however, their contributions to neuroinflammation and AD pathogenesis in aging remain underexplored. Our central hypothesis is that chronic activation of innate immunity in microglia is a fundamental underlying mechanism for neuroinflammation, which can be collectively triggered by amyloid and/or infections, and cGAS- STING mediated innate immunity is a critical biological process in the development and progression of AD. Our preliminary studies showed that cytosolic dsDNA levels were increased in AD post-mortem brain samples and 5xFAD mouse model, which is tightly associated with cGAS-STING pathway activation. More importantly, cGAS knockout mice ameliorated the neuroinflammation and amyloid pathologies in the 5xFAD model, which can be mimicked by a treatment with STING inhibitor H-151. For a better understanding of cGAS-STING pathway in AD, we now propose to study: 1) cGAS-STING dependent modulation of neuroinflammation in vitro using a tri-cellular culture system with iPSC-derived cells, and AD pathogenesis in animal models with cGAS and STING inhibitions; 2) the impact of herpes simplex virus (HSV-1) infection on cGAS-STING pathway and neuroinflammation using iPSC-derived brain organoid models including cerebral and choroid plexus organoids, at signaling and transcriptomic levels; 3) the effect of HSV1 infection on AD-like pathogenesis in EOAD and LOAD mouse models. Through these studies, we hope to achieve an in-depth understanding of the cGAS-STING innate immune pathway in CNS infection, inflammation and AD pathogenesis, and provide new insights into the infectious etiology of AD and related dementia (ADRD).