Recessive, gain-of-function toxicity in an APOL1 BAC transgenic mouse model mirrors human APOL1 kidney disease

Abstract

People of recent sub-Saharan African ancestry develop kidney failure much more frequently than other groups. A large fraction of this disparity is due to two coding sequence variants in the APOL1 gene. Inheriting two copies of these APOL1 risk variants, known as G1 and G2, causes high rates of focal segmental glomerulosclerosis (FSGS), HIV-associated nephropathy and hypertension-associated end-stage kidney disease. Disease risk follows a recessive mode of inheritance, which is puzzling given the considerable data that G1 and G2 are toxic gain-of-function variants. We developed coisogenic bacterial artificial chromosome (BAC) transgenic mice harboring either the wild-type (G0), G1 or G2 forms of human APOL1. Expression of interferon gamma (IFN-γ) via plasmid tail vein injection results in upregulation of APOL1 protein levels together with robust induction of heavy proteinuria and glomerulosclerosis in G1/G1 and G2/G2 but not G0/G0 mice. The disease phenotype was greater in G2/G2 mice. Neither heterozygous (G1/G0 or G2/G0) risk variant mice nor hemizygous (G1/−, G2/−) mice had significant kidney injury in response to IFN-γ, although the heterozygous mice had a greater proteinuric response than the hemizygous mice, suggesting that the lack of significant disease in humans heterozygous for G1 or G2 is not due to G0 rescue of G1 or G2 toxicity. Studies using additional mice (multicopy G2 and a non-isogenic G0 mouse) supported the notion that disease is largely a function of the level of risk variant APOL1 expression. Together, these findings shed light on the recessive nature of APOL1-nephropathy and present an important model for future studies.

JAK inhibitor blocks COVID-19 cytokine–induced JAK/STAT/APOL1 signaling in glomerular cells and podocytopathy in human kidney organoids

“…This hypothesis was supported by recent reports that transgenic overexpression of APOL1 risk alleles in mouse podocytes or GECs caused podocytopathy, endotheliopathy, glomerulopathy, and clinical manifestations of kidney failure (10)(11)(12)(13)(14). These murine disease models suggest that the mechanism that underlies COVID-19-induced APOL1 expression would be a potential therapeutic target for COVAN.…”

“…Dose-dependent APOL1 cytotoxicity was also reported in similar cell-based systems (34). Moreover, APOL1 transgenic mouse models have not only validated the causal link between APOL1 risk alleles and podocyte injury but have demonstrated that the degree of podocytopathy correlated with APOL1 expression levels (10,(12)(13)(14)35). Our discovery that 8 of 9 patients with COVAN demonstrated robust glomerular APOL1 expression relative to control individuals and the evidence that expression of endogenous APOL1 risk alleles causes podocytopathy in human kidney micro-organoids support the causal link between APOL1 and podocytopathy.…”

Lessons From APOL1 Animal Models

“…They also showed that the heterozygous mice (G0/G1 or G0/G2) had greater proteinuria response than hemizygous mice (G1/-or G2/-), suggesting that APOL1-G0 does not rescue -G1 or -G2 allele toxicity. Further, mice with a multicopy G2 transgene (G2 multi /G2 multi ) showed the greatest proteinuria response with worst prognosis, supporting the recessive nature of APOL1nephropathy and the notion that disease is a function of the expression level of APOL1 risk variant (21).…”

Endoplasmic reticulum-translocation is essential for APOL1 cellular toxicity

“…We did not explore the therapeutic potential of ΔMSALFL in a bacterial artificial chromosome (BAC) transgenic murine model harboring either the wild-type (G0), G1 or G2 forms of human APOL1 ( McCarthy et al., 2021 ).…”