APOL1 Variant-Expressing Endothelial Cells Exhibit Autophagic Dysfunction and Mitochondrial Stress
Apolipoprotein L1 (APOL1) gene risk variants (RV) associate with renal and cardiovascular disease particularly in SLE. We hypothesized that in RV-carrying human umbilical vein endothelial cells (HUVECs) cytokine-induced APOL1 expression compromises mitochondrial respiration, lysosome integrity, and autophagic flux. HUVEC cultures of each APOL1 genotype were generated. APOL1 was expressed using IFN{gamma}; HUVEC mitochondrial function, lysosome integrity, and autophagic flux were measured. IFN{gamma} increased APOL1 expression across all genotypes 20-fold (p=0.001). Compared to the homozygous G0 (ancestral) allele (0RV), high risk (2RV) HUVECs 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 lysosome compartment (p<0.001), and an accumulation of autophagosomes suggesting a defect in autophagic flux. Treatment of 0RV HUVECs with a non-selective lysosome inhibitor, hydroxychloroquine, produced autophagosome accumulations similar to the 2RV cells, thus implicating lysosome dysfunction in blocking autophagy. Compared to 0RV and 2RV HUVECs, 1 RV cells demonstrated an intermediate autophagy defect which was exacerbated by IFN{gamma}. Our findings implicate dysfunction of mitochondrial respiration, lysosome, and autophagy in APOL1 RV-mediated endothelial cytotoxicity. IFN{gamma} amplified this phenotype even in variant heterozygous cells-a potential underpin of the APOL1/inflammation interaction. This is the first description of APOL1 pathobiology in variant heterozygous cell cultures.