Project Summary: Chronic kidney disease (CKD) continues to be a significant factor in global morbidity and mortality. Patients experiencing repetitive acute kidney injury (AKI) are predisposed to CKD. Despite discoveries of novel biomarkers and increasing awareness of kidney health, the prevalence of CKD and end- stage kidney disease (ESKD) continues to rise. To date, the lack of therapeutic options halting progression from AKI to CKD still represents an unmet need. Our preliminary data suggest while activation of complement component 5 receptor 1 (C5aR1) promotes renal tubular epithelial cell (RTEC) damage, C5aR1 signaling on myeloid cells may confer renoprotective effects ameliorating AKI. This project will determine the roles of C5a- C5aR1 axis activation in 1) RTEC cellular senescence and kidney fibrosis (Aim 1), and in 2) myeloid cells responsible for AKI pathogenesis (Aim 2). These aims will test our central hypothesis that C5aR1 activation in kidney resident macrophage (KRM) mitigates the acute phase of AKI, whereas C5a-C5aR1 signaling in RTEC mediates their cellular senescence with subsequent CKD progression and fibrosis. Our findings will lay the fundamental knowledge of the potential clinical use of complement-regulating therapies for kidney diseases. Candidate and Training: The primary objective of this application is to support Dr. Mon-Wei (Sam) Yu's career development into an independent basic scientist in the fields of complement biology and kidney diseases by using novel murine models and immunological approaches. Dr. Yu's proposed training activities are in four areas: 1) Establish innovative scientific questions and design appropriate experiments to answer those questions; 2) Attain the necessary techniques, especially in the immunology field, to perform experiments; 3) Gain training and experiences for big data analysis, and 4) Refine the skills for grantsmanship and manuscript preparation. Environment: Division of Nephrology at Mount Sinai Hospital and the Icahn School of Medicine at Mount Sinai (ISMMS) are fully committed to junior faculty career and scientific development. Dr. Paolo Cravedi and Dr. John Cijiang He (Division Chief) are renowned experts in complement and tubular biology with a strong K Award trainees track record.