SUMMARY HIV-associated nephropathy (HIVAN) is a renal disease caused by the infection of renal epithelial cells (REc) that is seen more frequently in people of African ancestry who carry two APOL1 risk alleles (APOL1-RA) named G1 or G2. The study of HIVAN provides a unique opportunity to define how contacts between HIV+ inflammatory cells and REc may contribute to establish a kidney HIV-1 reservoir, and to determine how APOL1 interact with HIV-1 to precipitate HIVAN in people of African ancestry. In the first cycle of the grant, we have demonstrated that transmembrane TNF-α (tm-TNF-α) facilitates the infection of podocytes and REc cultured from children with HIVAN, and increases the expression of APOL1 in synergy with HIV-1. We also found that tm-TNF-α and APO1 interact to modulate common pathways involved in endocytosis, HIV-1 trafficking, and degradation in REc. Thus, we hypothesize that tm-TNF-α plays a critical role in the pathogenesis of childhood HIVAN by facilitating the infection of REc through cell-to-cell contacts with mononuclear cells, and by increasing the activity of APOL1-RA in these cells. In HIV+ podocytes, these changes tip their homeostatic balance, impairing key endocytic and autophagic pathways that affect their structure, function, and survival. In turn, these events precipitate HIVAN in children and adults. This hypothesis will be tested in three aims. In aim 1, we will determine how tm-TNF-α modulates the transfer of HIV-1 from mononuclear cells to REc cultured from HIV+ children, and elucidate the mechanisms involved. In aim 2 we will define how tm-TNF−α and APOL1-RA interact in vivo to modulate relevant endocytic and autophagy pathways that are essential for the normal function of Drosophila nephrocytes (the fly equivalent of human podocytes) and for the traffic of HIV-1 particles in podocytes. In aim 3, we will determine how APOL1-RA modulate the infection of podocytes cultured from HIV+ children, and define the risk of children carrying two APOL1 RA to develop HIVAN. In summary, these experiments will elucidate how REc are infected with HIV-1, and interact with renal infiltrating inflammatory cells and the APOL1-RA to establish a renal HIV-reservoir and induce chronic kidney diseases.