PROJECT SUMMARY Post-sepsis neurocognitive impairment is a devastating sequela of severe sepsis causing long-term disability in up to ~50% of sepsis survivors and accelerating the onset of dementia and the need for institutionalization in the elderly. The cellular and molecular mechanisms leading to neurocognitive dysfunction in sepsis survivors are not well understood making the cause of this devastating complication difficult to predict, prevent, or treat. While there is evidence that blood brain barrier (BBB) dysfunction during sepsis associates with neurocognitive impairment, the endothelial signaling pathways governing BBB permeability and their impact on cognitive dysfunction are not well understood. The sphingosine-1-phosphate (S1P) pathway regulates endothelial function via G-protein coupled receptors (S1PR). Under the parent R01, we have found that S1PR2 is potently induced in cerebral microvessels during stroke leading to BBB leakage and brain injury. However, we do not know how endothelial S1PR2 affects the BBB and cognitive dysfunction during sepsis, which is restricting the investigation of its potential value as a therapeutic target to prevent this devastating complication. The objective of this administrative supplement is to determine the role of endothelial-specific S1PR2 signaling in sepsis-induced BBB permeability and cognitive dysfunction. Our central hypothesis is that during sepsis, upregulation of S1PR2 in cerebral microvessels induces BBB dysfunction and it can be targeted as novel vasoprotective therapy to ameliorate cognitive impairment. This hypothesis is supported by our data using mouse models of sepsis and unique reagents and resources validated in our investigative team under the parent R01, such as tissue specific genetically engineered mice, novel methods to conduct molecular assays in cerebral microvessels, first-in-class S1PR2 antagonists and behavior tests to assess cognitive function in mice. In this request for supplemental funding, we aim to pursue two important extensions of the existing grant. The first goal is to determine the role of endothelial S1PR2 in cerebral microvascular (BBB) dysfunction and post-sepsis cognitive impairment. This work extends aim 1 of the original R01 in which we have found that lack of S1PR2 specifically in the endothelium mitigates brain injury in stroke. The second goal is to determine the efficacy of a novel S1PR2 antagonist to mitigate sepsis-induced BBB and cognitive dysfunction. This work extends aim 3 of the parent R01, in which, we have validated the efficacy of a novel S1PR2 antagonist in stroke. The proposed pilot studies are highly relevant to the understanding of the vascular contributions to dementia because they are expected to provide initial proof of the role of endothelial S1PR2 in BBB leakage and post-sepsis cognitive dysfunction and the therapeutic potential of this pathway. This initial evidence will be critical for a future R01 submission aiming at investigat...