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Kidney Week

Abstract: PO1306

Inhibition of Endoplasmic Reticulum Stress Signaling Rescues Cytotoxicity of Human APOL1 Risk Variants in Drosophila

Session Information

Category: Genetic Diseases of the Kidneys

  • 1002 Genetic Diseases of the Kidneys: Non-Cystic

Authors

  • Gerstner, Lea, Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany
  • Chen, Mengmeng, Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany
  • Kampf, Lina Luise, Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany
  • Milosavljevic, Julian, Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany
  • Lang, Konrad, Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany
  • Helmstädter, Martin, Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany
  • Hermle, Tobias F., Division of Nephrology, University Medical Center Freiburg, Freiburg, Baden-Württemberg, Germany

Group or Team Name

  • Hermle lab
Background

Renal risk variants of the APOL1 gene are associated with severe kidney disease, putting homozygous carriers at risk. APOL1 G1- and G2-alleles likely represent gain-of-function (GOF) mutations as human subjects with APOL1 null alleles have been found to be without renal anomalies. A wide range of mechanisms that are frequently in conflict have been described for APOL1-associated nephropathies.

Methods

The genetic tool-kit in Drosophila allows unique in vivo insights into disrupted cellular homeostasis. To perform a mechanistic analysis in this model, we expressed APOL1 control and the GOF renal risk variants in the podocyte-like Drosophila nephrocytes and a wing precursor tissue.

Results

APOL1 risk variant expression entailed elevated endocytic function of garland cell nephrocytes while processing of endocytic cargo and slit diaphragm morphology remained unimpaired. All APOL1 variants located to the endoplasmic reticulum (ER) and electron microscopy revealed significantly elevated ER swelling upon expression of risk variant G2-APOL1, indicating stimulation of ER stress. We employed Drosophila wing precursor tissue since this epithelial model enables unique recording of relative changes side by side within the same animal to study ER stress. Overexpression of the renal risk variants G1 and G2 caused a markedly stronger upregulation of PDI and apoptosis, while expression of wildtype APOL1 resulted in milder upregulation. As a control, ER stress was absent upon deletion of 9 aa in the BH3 domain in the G2-APOL1 construct. We further confirmed APOL1-dependent ER stress by detection of chaperone induction and an Xbp1-reporter in the wing precursor. Both, genetic and pharmacological inhibition of ER stress abrogated apoptosis identifying ER stress as the essential factor of APOL1-induced cytotoxicity. This represents the first rescue of APOL1-associated cytotoxicity in vivo. Direct ER stress induction in nephrocytes phenocopied APOL1 risk variant expression, supporting that ER stress underlies the gain-of-function in nephrocytes.

Conclusion

Our data reveal ER stress as the essential consequence of APOL1 risk variant expression in vivo, indicating this pathway’s central role in the pathogenesis of APOL1-associated nephropathies.

Funding

  • Government Support – Non-U.S.