Project Summary Chronic kidney disease (CKD) is a common condition that significantly increases risks for end stage kidney disease (ESKD) and premature death. Because CKD is generally progressive and irreversible, molecular research to better understand its etiology and identify novel therapeutic targets is critically needed. Recent studies identified two common variants in the gene encoding apolipoprotein L1 (APOL1) that cause rapid kidney function decline and ESKD in Black patients with CKD. However, the mechanisms underlying the higher risk conferred by the APOL1 variants are still unknown. In addition, not all individuals with the high risk APOL1 genotype experience rapid CKD progression. As the molecular endpoint of endogenous and exogenous processes, examination of the human metabolome provides an opportunity to discover biological pathways linking APOL1 to CKD progression and identify factors that modify the effects of APOL1 on this complex phenotype. Despite the promise of metabolomics study, work in this area remains sparse. The overall objective of this application is to elucidate molecular mechanisms that mediate and/or modify the association between APOL1 risk alleles and CKD progression. We hypothesize that a comprehensive study of metabolites in urinary samples of CKD patients will discern biological pathways underlying APOL1-associated CKD progression. Our study will leverage baseline 24-hour urine samples, annually measured kidney function, and stringently adjudicated CKD events in up to 17 years follow-up among all 1,224 Black participants of the ongoing Chronic Renal Insufficiency Cohort (CRIC) Study. Untargeted metabolomics profiling using baseline 24-hour urine samples will be conducted among these participants and used to identify metabolites altered by APOL1 risk alleles (Aim 1). We will then examine the prospective associations of baseline metabolites with CKD progression among the Black CRIC participants (Aim 2). To articulate the molecular mechanisms underlying APOL1-associated CKD progression, we will assess the mediating and modifying effects of metabolites on this association (Aim 3). As exploratory work, we will generate a catalogue of urinary-plasma metabolite correlations by leveraging metabolomics data from simultaneously collected urine and plasma samples among 346 CRIC study participants (Aim 4a). Urinary metabolites identified in Aims 1-3 that have a moderate-to-high correlation (in Aim 4a) will be evaluated for replication using plasma metabolomics data among 558 participants of the African American Study of Kidney Disease and Hypertension (Aim 4b). The proposed work represents the first urinary metabolomics study focusing on APOL1 risk alleles and CKD progression among Black patients with CKD. This innovative metabolomics study among a high-risk group is likely to reveal novel mechanisms of CKD progression. Our findings may also provide evidence-based targets for the development of...