Expression of Apolipoprotein L1 Risk Variants at the Plasma Membrane and Haplotype-Dependent Cytotoxicity

KEY POINTS: Apolipoprotein L1 variants were transported to the plasma membrane via actin filaments, where they exhibited distinct dynamics. Apolipoprotein L1 was functionally expressed at the plasma membrane and formed a voltage-dependent non-selective cation-permeable pore. Influx of calcium from the extracellular medium was the primary origin of the increased cytosolic calcium crucial for Apolipoprotein L1 cytotoxicity. BACKGROUND: The mechanisms by which apolipoprotein L1 ( APOL1 ) risk variants, G1 and G2, induce kidney disease in individuals of African ancestry remain contentious. METHODS: In this study, we utilized a heterologous expression system of HEK-293 cells and human podocytes to investigate APOL1-mediated cytotoxicity using genetic, electrophysiological, and microscopy-based approaches. RESULTS: APOL1 variants showed dynamic transport in vesicle-like structures toward the plasma membrane via actin filaments. At the plasma membrane, the non-risk APOL1 G0 and risk variants formed non-selective cation-permeable pores for Na + and Ca 2+ , exhibiting functional activity under basal conditions. Extracellular Ca 2+ was identified as the primary source of Ca 2+ influx through APOL1, leading to cytotoxicity. APOL1 risk variants exhibited increased basal channel activity compared to non-risk APOL1 G0, resulting in haplotype-dependent cytotoxicity. Furthermore, we observed that both the M1 (N264K) variant and APOL1 inhibitor, Inaxaplin, exerted protective effects on cell viability by blocking the APOL1-dependent intracellular Ca 2+ influx. CONCLUSIONS: This study demonstrated APOL1 to be a membrane protein involved in the influx of Ca 2+ from the extracellular medium. Increased activity of APOL1 led to markedly increased cytotoxicity, which supports the gain-of-function theory. This effect was prevented by the presence of N264K variant or treatment with the APOL1 inhibitor, Inaxaplin.