HIV-1 Nef acts in synergy with APOL1-G1 to induce nephrocyte cell death in a new Drosophila model of HIV-related kidney diseases.

BACKGROUND: People 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.

METHOD: We 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.

RESULTS: We 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). Through a different pathway, Nef exacerbates the organelle acidification defects and reduced autophagy 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.

CONCLUSIONS: A new Drosophila model of HIV-1-related kidney diseases 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.

HIGHLIGHTS: Developed a 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. APOL1-G1 caused organelle acidification defects, reduced formation of autophagolysosomes, and reduced autophagy and protein aggregation, which culminated in ER stress.HIV-1 Nef induced ER stress through an autophagy-independent pathway. In addition, Nef acted through an autophagy-dependent pathway that heightened the ER stress. It did so through APOL1-G1-mediated autophagy pathway disruption, which resulted in nephrocyte dysfunction and cell death.

SIGNIFICANCE STATEMENT: APOL1 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.