Despite the success of antiretroviral therapy in improving mortality, HIV-infected persons remain at increased risk of death and have increased burden of non-infectious diseases including chronic kidney disease (CKD). HIV-associated nephropathy (HIVAN) occurs almost exclusively in persons of African ancestry and polymorphisms in Apolipoprotein L1 (APOL1) account for the majority of this excess risk. Persons who are homozygous for the G1 or G2 renal risk alleles (or G1/G2 compound heterozygotes) have markedly increased risk of non-diabetic ESRD and a 30-fold increased risk of HIVAN. Little is known regarding the mechanisms by which these variants confer increased risk of progressive CKD. As the great majority of persons harboring two renal risk alleles do not develop kidney disease, a second hit, such as HIV infection, is required to unmask the predisposition to APOL1-mediated kidney injury. Our long-term goal is to delineate the mechanisms by which APOL1 renal risk alleles predispose individuals to kidney failure to devise new strategies to prevent and kidney disease this vulnerable population. The objective of this proposal is to identify novel mechanisms by which APOL1 renal risk alleles promote HIV-induced injury in human kidney cells. Our central hypothesis is that APOL1 renal risk alleles alter the ability of cellular proteins to bind to APOL1, thereby promoting HIV- induced injury via dysregulation of cellular pathways that ultimately promote cell death. Our hypothesis is supported by data from our lab and others demonstrating that: 1) APOL1 genotype of a transplanted kidney (and not the recipient) confers increased risk of kidney failure after transplantation, suggesting that local APOL1 expression in kidney cells promotes kidney injury; 2) overexpression of APOL1 risk alleles in kidney cells is more toxic than wild type alleles in vitro; 3) preliminary data from our laboratory demonstrating differences in cellular proteins (including those with roles in cell cycle and innate immunity) that bind APOL1 in the context of HIV infection. We will test our hypothesis and address critically important questions in two specific aims. In our first specific aim, we will use novel isogenic human podocyte, tubular, and endothelial cell lines to delineate the cellular processes that are dysregulated by APOL1 risk alleles in the context of HIV infection. In our second specific aim, we use biopsies previously collected from HIV-positive patients with focal segmental glomerulosclerosis (FSGS) and data from the Nephrotic Syndrome Study Network (NEPTUNE) to determine genes that are differentially expressed in kidney biopsy specimens from HIV-positive versus HIV- negative patients with FSGS and we will use innovative proteomic and RNA expression analyses to identify RNA and proteins that are differentially regulated by APOL1 risk alleles in the context of HIV infection and to identify proteins that display altered binding to APOL1 risk variants after HIV infection. These results will have a positive impact because they will provide new insights that will improve our ability to prevent and treat kidney disease in persons living with HIV/AIDS and in HIV-negative persons of African ancestry.