PROJECT SUMMARY/ ABSTRACT A dire consequence of acute kidney injury (AKI) is a dramatically increased risk to develop chronic kidney disease (CKD). CKD accounts for 6.7% of Medicare expenses. Understanding the mechanisms by which AKI progresses to CKD is essential for developing therapies, for which none currently exist. Renal microvasculature, including pericytes and endothelial cells, are damaged in AKI, leading to recruitment of inflammatory cells which contributes to progression to CKD. However, cellular, and molecular mechanisms that drive this process are largely unknown. Pericytes are a heterogeneous mesenchymal population and have been identified as a major source of myofibroblasts that drives CKD. Understanding the molecular mechanisms that mediates maladaptive endothelial-pericyte crosstalk leading to exacerbated and prolonged inflammation could drive therapeutic exploitation of this phenomenon. Previously, it has been shown that the systemic blockade of Vascular endothelial growth factor receptor 2 (VEGF-R2) blocks CKD progression. My preliminary data, knocking out VegfR2 in renal stromally derived cells (RSC) (termed VegfR2RSC-/-) that includes pericytes, confirms the protective nature of this loss-of-function. I found that, in CKD models by renal ischemia/ reperfusion injury (IRI) as well as by cisplatin, VegfR2RSC-/- mice have attenuated CKD progression, along with having mitigated inflammation and preserved vascular function. My bulk RNA-sequencing analysis with isolated RSCs demonstrates that inflammatory pathways are activated while short-chain fatty acid metabolism pathways are suppressed during AKI-to-CKD transition. Mechanistically, VegfR2RSC-/- kidneys (1) have reduced expression of a pro-inflammatory signaling axis of Thrombospondin-1 (TSP1)/ CD148, and (2) have increased expression of fatty acid metabolism associated genes contributing to the enhanced protection. To home in on the timing of the protection, I have generated a tamoxifen-inducible RSC-specific VegfR2 knockout (iVegfR2RSC-/-) mouse. I found that, after pre-treatment of tamoxifen, iVegfR2RSC-/- mice are significantly protected against AKI. Together, these data informed my overarching hypothesis that renal pericyte-specific VEGF-R2 signaling dysregulates pericyte- endothelial crosstalk stimulating inflammation to exacerbate CKD. I propose the following aims to test this: Aim 1 will test the hypothesis that pericyte-specific VEGF-R2 signaling exacerbates AKI-to-CKD transition. Aim 2 will test the hypothesis that pericyte VEGF-R2 signaling mediates maladaptive pericyte-endothelial crosstalk to exacerbate inflammation, promoting AKI-to-CKD. Aim 3 will test the hypothesis that inhibiting VegfR2 signaling in renal pericytes enhances vascular repair, mitigates inflammation, and blocks progression to CKD after AKI. For the K01 Award, I enlisted innovative mentors. The University of Pittsburgh has an extraordinary number of faculty with research programs focused on AKI, ...