PROJECT SUMMARY Sepsis is a serious clinical condition with life-threatening organ dysfunction caused by a dysregulated host response to infection. Up to 70% of septic patients and more than 50% sepsis survivors develop neurocognitive dysfunction, a debilitating condition termed sepsis-associated encephalopathy (SAE). While both clinical and experimental data suggest the role of inflammation in the pathogenesis of SAE, the exact causes and the molecular mechanisms leading to cerebral inflammation and neurocognitive dysfunction are not well understood. We have recently shown that host cellular RNAs including microRNAs are released into the blood circulation during sepsis and that circulating host RNA levels are closely associated with sepsis severity in animals. Moreover, extracellular (ex) RNA of different species (human and rodents) and organs (spleen and heart) and certain uridine-rich miRNAs can function as damage-associated molecular patterns (DAMPs) and drive proinflammatory responses through a TLR7-dependent mechanism in peripheral immune cells, in microglial cells, and in intact animals. Based on these information and other published literatures, we hypothesize that innate immune activation driven by ex-miRNA-TLR7 signaling functions as a key mechanism in cerebral inflammation and neurocognitive dysfunction following sepsis. To test the hypothesis, we propose the following specific aims: Aim 1: To demonstrate the role of circulating ex-miRNAs in brain inflammation in sepsis; Aim 2: To evaluate the role of plasma exosomes, as ex-miRNA carriers, in brain inflammation; Aim 3: To test the contribution of ex-miRNAs®TLR7 signaling to brain inflammation in sepsis; Aim 4: To demonstrate that targeting ex-miRNA®TLR7 signaling pathways improves the long-term neurocognitive function in sepsis survivors. The overall goal of this proposal is to investigate the function and mechanisms of ex-miRNA®TLR7 signaling in brain inflammation and neurocognitive dysfunction following sepsis. The anticipated results will provide mechanistic insights into the pathogenesis of sepsis-associated encephalopathy and potential novel therapeutic targets.