Kidney Disease-Associated <i>APOL1</i> Variants Have Dose-Dependent, Dominant Toxic Gain-of-Function.

Abstract

Two coding renal risk variants (RRVs) of the <i>APOL1</i> gene (G1 and G2) are associated with large increases in CKD rates among populations of recent African descent, but the underlying molecular mechanisms are unknown. Mammalian cell culture models are widely used to study cytotoxicity of RRVs, but results have been contradictory. It remains unclear whether cytotoxicity is RRV-dependent or driven solely by variant-independent overexpression. It is also unknown whether expression of the reference <i>APOL1</i> allele, the wild-type G0, could prevent cytotoxicity of RRVs. We generated tetracycline-inducible <i>APOL1</i> expression in human embryonic kidney HEK293 cells and examined the effects of increased expression of <i>APOL1</i> (G0, G1, G2, G0G0, G0G1, or G0G2) on known cytotoxicity phenotypes, including reduced viability, increased swelling, potassium loss, aberrant protein phosphorylation, and dysregulated energy metabolism. Furthermore, whole-genome transcriptome analysis examined deregulated canonical pathways. At moderate expression, RRVs but not G0 caused cytotoxicity in a dose-dependent manner that coexpression of G0 did not reduce. RRVs also have dominant effects on canonical pathways relevant for the cellular stress response. In HEK293 cells, RRVs exhibit a dominant toxic gain-of-function phenotype that worsens with increasing expression. These observations suggest that high steady-state levels of RRVs may underlie cellular injury in <i>APOL1</i> nephropathy, and that interventions that reduce RRV expression in kidney compartments may mitigate <i>APOL1</i> nephropathy.