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Transgenic expression of human APOL1 risk variants in podocytes induces kidney disease in mice

Abstract

African Americans have a heightened risk of developing chronic and end-stage kidney disease, an association that is largely attributed to two common genetic variants, termed G1 and G2, in the APOL1 gene. Direct evidence demonstrating that these APOL1 risk alleles are pathogenic is still lacking because the APOL1 gene is present in only some primates and humans; thus it has been challenging to demonstrate experimental proof of causality of these risk alleles for renal disease. Here we generated mice with podocyte-specific inducible expression of the APOL1 reference allele (termed G0) or each of the risk-conferring alleles (G1 or G2). We show that mice with podocyte-specific expression of either APOL1 risk allele, but not of the G0 allele, develop functional (albuminuria and azotemia), structural (foot-process effacement and glomerulosclerosis) and molecular (gene-expression) changes that closely resemble human kidney disease. Disease development was cell-type specific and likely reversible, and the severity correlated with the level of expression of the risk allele. We further found that expression of the risk-variant APOL1 alleles interferes with endosomal trafficking and blocks autophagic flux, which ultimately leads to inflammatory-mediated podocyte death and glomerular scarring. In summary, this is the first demonstration that the expression of APOL1 risk alleles is causal for altered podocyte function and glomerular disease in vivo.

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Figure 1: Generation of a mouse model with cell-type-specific inducible expression of APOL1 variants.
Figure 2: APOL1-risk-variant-induced phenotype is cell-type- and dose-dependent and likely reversible.
Figure 3: APOL1-risk-allele cells show increased accumulation of intracellular vesicles, mainly late endosomes/autophagosomes.
Figure 4: Risk variants of APOL1 obstruct autophagy flux.
Figure 5: APOL1 risk variants induce inflammatory cell death (pyroptosis) in cells.
Figure 6: Mice with podocyte-specific APOL1 risk-allele expression show increased podocyte loss, autophagy block and increased inflammatory cell death.

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Acknowledgements

Work performed in the Susztak lab is supported by US National Institutes of Health (NIH) grants DK105821, DK087635, DK076077 and DP3 DK108220. The human kidney RNA-sequencing project was performed in collaboration with Boehringer Ingelheim. J. Bi-Karchin was supported by 2T32DK007006. J.B. Kopp. and P.D.D. were supported by the Intramural Research Program, NIDDK, NIH. J.H.M. was supported by R01DK078314 and R01DK058366; T.R. by GM093290 and NS055159; and A.M.C. by AG054108 (NIH). M.A.S. was supported by Kids Kidney Research, and the Bristol Nutrition NIHR-BRU. We would also like to thank the Electron Microscopy Resource Laboratory (EMRL) core facility at the University of Pennsylvania for technical support.

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Authors and Affiliations

Authors

Contributions

P.B. and J.B.-K. designed and performed the experiments, and wrote and revised the manuscript. A.S.D.P. performed initial animal characterization and in vitro studies (TEM and IF). C.Q. analyzed RNA-sequencing data. P.D.D. and J.B.K. helped with the discussion and generated mCherry-APOL1-G0/G1/G2 stable cell lines (not used in the paper). I.S. generated TRE-GFP/APOL1-G1 stable HEK293 cell line. C.M.B.-K. and S.S.P. contributed to the human data presented in the paper. J.H.M. provided the Nphs1-transgenic mice. C.-A.A.H. provided the original APOL1 constructs. T.R. made the bicistronic plasmids containing TRE-GFP/APOL1-G0/G1/G2. K.I. and S.I. provided help with spinning disk confocal microscopy. M.A.S. provided human podocytes. M.B.P. performed the pathological characterization. A.M.C. helped with autophagy studies. K.S. designed and supervised the study and wrote and revised the manuscript.

Corresponding author

Correspondence to Katalin Susztak.

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Competing interests

The Susztak lab is supported in part by Boehringer Ingelheim for a study related to the human data presented in the paper.

Supplementary information

Supplementary Figures and Tables

Supplementary Figures 1–9 and Supplementary Tables 1–4 (PDF 11328 kb)

41591_2017_BFnm4287_MOESM2_ESM.avi

APOL1 is colocalized to the late endosome. Spinning disc confocal microscopy movie of GFP-APOL1(green) and RFPRab7 (late endosome, red). Scale bar: 5μm. (AVI 3516 kb)

41591_2017_BFnm4287_MOESM3_ESM.avi

Risk allele APOL1 shows increased accumulation of recycling endosome. Spinning disc confocal microscopy movies of GFP-APOL1-G0 (AVI 3516 kb)

41591_2017_BFnm4287_MOESM4_ESM.avi

Risk allele APOL1 shows increased accumulation of recycling endosome. Spinning disc confocal microscopy movies of GFP-APOL1-G2 (green) and RFPRab11 (recycling endosome, red), Scale bar: 5μm. (AVI 3341 kb)

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Beckerman, P., Bi-Karchin, J., Park, A. et al. Transgenic expression of human APOL1 risk variants in podocytes induces kidney disease in mice. Nat Med 23, 429–438 (2017). https://doi.org/10.1038/nm.4287

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