APOL1 variant-expressing endothelial cells exhibit autophagic dysfunction and mitochondrial stress

Abstract

Polymorphisms in the Apolipoprotein L1 (<i>APOL1</i>) gene are common in ancestrally African populations, and associate with kidney injury and cardiovascular disease. These risk variants (RV) provide an advantage in resisting <i>Trypanosoma brucei</i>, the causal agent of African trypanosomiasis, and are largely absent from non-African genomes. Clinical associations between the <i>APOL1</i> high risk genotype (HRG) and disease are stronger in those with comorbid infectious or immune disease. To understand the interaction between cytokine exposure and <i>APOL1</i> cytotoxicity, we established human umbilical vein endothelial cell (HUVEC) cultures representing each <i>APOL1</i> genotype. Untreated HUVECs were compared to IFNɣ-exposed; and <i>APOL1</i> expression, mitochondrial function, lysosome integrity, and autophagic flux were measured. IFNɣ increased median <i>APOL1</i> expression across all genotypes 22.1 (8.3 to 29.8) fold (p=0.02). Compared to zero risk variant-carrying HUVECs (0RV), HUVECs carrying 2 risk variant copies (2RV) showed both depressed baseline and maximum mitochondrial oxygen consumption (p<0.01), and impaired mitochondrial networking on MitoTracker assays. These cells also demonstrated a contracted lysosomal compartment, and an accumulation of autophagosomes suggesting a defect in autophagic flux. Upon blocking autophagy with non-selective lysosome inhibitor, hydroxychloroquine, autophagosome accumulation between 0RV HUVECs and untreated 2RV HUVECs was similar, implicating lysosomal dysfunction in the HRG-associated autophagy defect. Compared to 0RV and 2RV HUVECs, HUVECs carrying 1 risk variant copy (1RV) demonstrated intermediate mitochondrial respiration and autophagic flux phenotypes, which were exacerbated with IFNɣ exposure. Taken together, our data reveal that IFNɣ induces <i>APOL1</i> expression, and that each additional RV associates with mitochondrial dysfunction and autophagy inhibition. IFNɣ amplifies this phenotype even in 1RV HUVECs, representing the first description of <i>APOL1</i> pathobiology in variant heterozygous cell cultures.