Modeling of ACTN4-Based Podocytopathy Using Drosophila Nephrocytes

Johanna Odenthal; Sebastian Dittrich; Vivian Ludwig; Tim Merz; Katrin Reitmeier; Björn Reusch; Martin Höhne; Zülfü C Cosgun; Maximilian Hohenadel; Jovana Putnik; Heike Göbel; Markus M Rinschen; Janine Altmüller; Sybille Koehler; Bernhard Schermer; Thomas Benzing; Bodo B Beck; Paul T Brinkkötter; Sandra Habbig; Malte P Bartram

doi:10.1016/j.ekir.2022.10.024

Modeling of ACTN4-Based Podocytopathy Using Drosophila Nephrocytes

Kidney Int Rep. 2022 Oct 31;8(2):317-329. doi: 10.1016/j.ekir.2022.10.024. eCollection 2023 Feb.

Authors

Johanna Odenthal¹, Sebastian Dittrich¹, Vivian Ludwig¹, Tim Merz¹, Katrin Reitmeier¹, Björn Reusch^{2

3}, Martin Höhne¹, Zülfü C Cosgun⁴, Maximilian Hohenadel⁵, Jovana Putnik⁶, Heike Göbel⁷, Markus M Rinschen^{8

9

10}, Janine Altmüller^{11

12}, Sybille Koehler¹, Bernhard Schermer^{1

13}, Thomas Benzing^{1

13}, Bodo B Beck^{2

3}, Paul T Brinkkötter¹, Sandra Habbig⁴, Malte P Bartram¹

Affiliations

¹ Department II of Internal Medicine and Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne, University Hospital Cologne, Cologne, Germany.
² Center for Molecular Medicine Cologne, Faculty of Medicine, University of Cologne, University Hospital Cologne, Cologne, Germany.
³ Institute of Human Genetics, Faculty of Medicine, University of Cologne, University Hospital Cologne, Cologne, Germany.
⁴ Department of Pediatrics, Faculty of Medicine, University of Cologne, University Hospital Cologne, Cologne, Germany.
⁵ Department of Pediatrics, Division of Pediatric Nephrology, University of Bonn, Bonn, Germany.
⁶ Mother and Child Health Care Institute of Serbia "Dr Vukan Čupić," Department of Nephrology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia.
⁷ Institute of Pathology, University Hospital of Cologne, Cologne, Germany.
⁸ Department of Biomedicine, Aarhus University, Aarhus, Denmark.
⁹ Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark.
¹⁰ III Medical Clinic, University Hospital Hamburg Eppendorf, Hamburg, Germany.
¹¹ Berlin Institute of Health at Charité-Universitätsmedizin Berlin, Max Delbrück Center for Molecular Medicine, Berlin, Germany.
¹² Cologne Center for Genomics, University of Cologne, Cologne, Germany.
¹³ Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases, Faculty of Medicine, University of Cologne, University Hospital Cologne, Cologne, Germany.

Abstract

Introduction: Genetic disorders are among the most prevalent causes leading to progressive glomerular disease and, ultimately, end-stage renal disease (ESRD) in children and adolescents. Identification of underlying genetic causes is indispensable for targeted treatment strategies and counseling of affected patients and their families.

Methods: Here, we report on a boy who presented at 4 years of age with proteinuria and biopsy-proven focal segmental glomerulosclerosis (FSGS) that was temporarily responsive to treatment with ciclosporin A. Molecular genetic testing identified a novel mutation in alpha-actinin-4 (p.M240T). We describe a feasible and efficient experimental approach to test its pathogenicity by combining in silico, in vitro, and in vivo analyses.

Results: The de novo p.M240T mutation led to decreased alpha-actinin-4 stability as well as protein mislocalization and actin cytoskeleton rearrangements. Transgenic expression of wild-type human alpha-actinin-4 in Drosophila melanogaster nephrocytes was able to ameliorate phenotypes associated with the knockdown of endogenous actinin. In contrast, p.M240T, as well as other established disease variants p.W59R and p.K255E, failed to rescue these phenotypes, underlining the pathogenicity of the novel alpha-actinin-4 variant.

Conclusion: Our data highlight that the newly identified alpha-actinin-4 mutation indeed encodes for a disease-causing variant of the protein and promote the Drosophila model as a simple and convenient tool to study monogenic kidney disease in vivo.

Keywords: ACTN4; Drosophila; FSGS; nephrocyte; nephrotic syndrome; podocyte.