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 Brinkkötter, Sandra Habbig, Malte P. Bartram
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 .