HIV-1 Nef acts in synergy with APOL1-G1 to induce nephrocyte cell death in a new Drosophila model of HIV-related kidney diseases
BackgroundPeople carrying two APOL1 risk alleles (RA) G1 or G2 are at greater risk of developing HIV-associated nephropathy (HIVAN). Studies in transgenic mice showed that the expression of HIV-1 genes in podocytes, and nef in particular, led to HIVAN. However, it remains unclear whether APOL1-RA and HIV-1 Nef interact to induce podocyte cell death. MethodWe generated transgenic (Tg) flies that express APOL1-G1 (derived from a child with HIVAN) and HIV-1 nef specifically in the nephrocytes, the fly equivalent of mammalian podocytes, and assessed their individual and combined effects on the nephrocyte filtration structure and function. ResultsWe found that HIV-1 Nef acts in synergy with APOL1-G1 resulting in nephrocyte structural and functional defects. Specifically, HIV-1 Nef itself can induce endoplasmic reticulum (ER) stress without affecting autophagy. Furthermore, Nef exacerbates the organelle acidification defects and autophagy reduction induced by APOL1-G1. The synergy between HIV-1 Nef and APOL1-G1 is built on their joint effects on elevating ER stress, triggering nephrocyte dysfunction and ultimately cell death. ConclusionsUsing a new Drosophila model of HIV-1-related kidney diseases, we identified ER stress as the converging point for the synergy between HIV-1 Nef and APOL1-G1 in inducing nephrocyte cell death. Given the high relevance between Drosophila nephrocytes and human podocytes, this finding suggests ER stress as a new therapeutic target for HIV-1 and APOL1-associated nephropathies. HIGHLIGHTSO_LIA new transgenic Drosophila model to study the pathogenesis of HIV-1-related kidney diseases with nephrocyte-specific expression of HIV-1 nef and an APOL1-G1 risk allele derived from a patient with HIVAN. C_LIO_LIAPOL1-G1 caused organelle acidification defects, reduced formation of autophagolysosomes, and reduced autophagy and protein aggregation, which culminated in ER stress. C_LIO_LIHIV-1 Nef induced ER stress through an autophagy-independent pathway. Furthermore, Nef and APOL1-G1 acted synergistically to heighten ER stress, which resulted in nephrocyte dysfunction and cell death. C_LI SIGNIFICANCE STATEMENTAPOL1 risk alleles are strongly linked to HIV-associated nephropathy (HIVAN) in people of African descent, but how HIV-1 and APOL1 interact and which pathways they might converge upon is unclear. A new Drosophila model to study HIV-1 Nef and APOL1-G1 (a risk allele) showed that Nef can induce ER stress in nephrocytes by itself, as well as exacerbate the organelle acidification defects and reduced autophagy induced by APOL1-G1, which further stimulates ER stress to a level that could cause nephrocyte cell death. Thus, we identified ER stress as the converging point for the synergy between APOL1-G1 and HIV-1 Nef in kidney cells, providing a potential therapeutic target for HIV-1 and APOL1-associated nephropathies.