Project Summary: Sepsis affects more than 19 million people each year. With improved treatment strategies, more and more patients survive sepsis. The majority of these survivors develop cognitive impairment and mental health problems. However, the mechanisms that promote sepsis-associated encephalopathies (SAE) remain largely unknown, and there is a lack of SAE-targeted treatments. The long-term goals of our research program are to understand the mechanisms that lead to cerebrovascular dysfunction and cognitive impairment post sepsis and to develop novel targeted treatments for sepsis-induced cognitive impairment. To reach this goal, we characterized sepsis-induced cognitive impairment using animal models. We observed that mice exhibit hippocampus-dependent memory impairment associated with pathological neuron dysfunction. To understand the mechanisms behind cognitive impairment post sepsis, we focused on specialized cells in the brain called pericytes, which play a major role in regulating cerebral blood flow and maintaining blood brain barrier integrity. Pericytes form part of the neurovascular unit to meet the energy demands of the brain and facilitate neuro- inflammatory responses. However, the role of pericytes in sepsis-induced cognitive impairment remains unknown. Our studies demonstrated that the transcription factor friend leukemia virus integration 1 (Fli-1) regulates pericyte activation and viability. We also observed that brain pericyte numbers decreased after sepsis and that pericytes underwent apoptosis after their initial activation and production of inflammatory mediators. Pericyte loss resulted in vascular leakage and recruitment of inflammatory monocytes. We reported previously that Fli-1 governs pericyte viability through regulating caspase 1/3 expression. In our preliminary studies, we demonstrated that pericyte Fli-1 knockout mice exhibit decreased inflammatory mediator production in response to LPS. More importantly, we demonstrated that Fli-1 levels were higher in the hippocampus regions of post- mortem brain tissue from septic patients compared to controls. In this R35/MIRA application, we propose to use newly developed, unbiased approaches such as single nucleus RNA sequencing and imaging mass cytometry alongside inducible pericyte-specific Fli-1 knockout mice generated in our laboratory and novel antisense oligonucleotide Gapmers targeting Fli-1 recently developed by our group to understand the role of pericytes in vascular dysfunction and cognitive impairment post sepsis. The successful completion of the proposed studies will lead to better understanding of the mechanisms of vascular cognitive impairment post sepsis and the development of novel SAE-targeted treatments.