APOL1–Mediated Cell Injury Involves Disruption of Conserved Trafficking Processes

Abstract

harbors C-terminal sequence variants (G1 and G2), which account for much of the increased risk for kidney disease in sub-Saharan African ancestry populations. Expression of the risk variants has also been shown to cause injury to podocytes and other cell types, but the underlying mechanisms are not understood. We used and to help clarify these mechanisms. Ubiquitous expression of the human APOL1 G1 and G2 disease risk alleles caused near-complete lethality in , with no effect of the G0 nonrisk allele, corresponding to the pattern of human disease risk. We also observed a congruent pattern of cellular damage with tissue-specific expression of APOL1. In particular, expression of APOL1 risk variants in nephrocytes caused cell-autonomous accumulation of the endocytic tracer atrial natriuretic factor-red fluorescent protein at early stages and nephrocyte loss at later stages. We also observed differential toxicity of the risk variants compared with the nonrisk variants in, including impairment of vacuole acidification. Yeast strains defective in endosomal trafficking or organelle acidification but not those defective in autophagy displayed augmented APOL1 toxicity with all isoforms. This pattern of differential injury by the APOL1 risk alleles compared with the nonrisk alleles across evolutionarily divergent species is consistent with an impairment of conserved core intracellular endosomal trafficking processes. This finding should facilitate the identification of cell injury pathways and corresponding therapeutic targets of interest in these amenable experimental platforms.

A tripartite complex of suPAR, APOL1 risk variants and αvβ3 integrin on podocytes mediates chronic kidney disease

“…The formation of such a triple complex results in the activation of multiple α v β 3 -integrin signaling pathways, which leads to the formation of autophagosomes, dysregulation of the actin cytoskeleton and, ultimately, cell detachment. Therefore, our results do not challenge a concurrent mechanism for cell injury emanating from podocyte-generated APOL1 proteins, as was previously suggested 27–30 . Rather, they suggest that, for the podocyte injury to occur, the secreted APOL1 risk-variant protein needs to be internalized by the cell in a urokinase receptor and β 3 -integrin-dependent manner (Supplementary Fig.…”

ApoL1 Overexpression Drives Variant-Independent Cytotoxicity

“…44 Two reports of ectopic expression of variant but not reference APOL1s in the Drosophila nephrocyte, a cell type with some similarities to the podocyte, increased endocytosis and loss of nephrocytes with aging. 45,46 Experiments in Saccharomyces cerevisiae also found a genetic interaction between APOL1 expression and deletion of components in the endocytic pathway. 46 Together, these results suggest that processes such as podocyte adhesion and endocytic trafficking, in addition to cytotoxicity, may also contribute to renal pathology associated with APOL1 risk variants.…”

APOL1 variants change C-terminal conformational dynamics and binding to SNARE protein VAMP8

“…Localization of VAMP8 with its cognate autophagosomal SNARE partner STX17 is diminished in presence of APOL1 variants (24). In addition, mice and Drosophila transgenic for human APOL1 kidney disease risk variants have been shown to have disordered endosomal trafficking and variant-dependent glomerular and nephrocyte injury (24,34,35). Our results suggest a model in which APOL1, in concert with VAMP8 or other SNARE proteins, identifies vesicles containing cargo capable of mediating cellular damage and their functional interaction mediates a cellular response capable of attenuating/mitigating the pathogenic potential of these cargos.…”