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Abstract: FR-PO704

Using Drosophila melanogaster to Characterize Potentially Pathogenic Patient Mutations Associated With Nephrotic Syndrome and Focal Segmental Glomerulosclerosis

Session Information

Category: Glomerular Diseases

  • 1304 Glomerular Diseases: Podocyte Biology


  • Odenthal, Johanna, Uniklinik Koln, Koln, Nordrhein-Westfalen, Germany
  • Beck, Bodo B., Uniklinik Koln, Koln, Nordrhein-Westfalen, Germany
  • Schermer, Bernhard, Uniklinik Koln, Koln, Nordrhein-Westfalen, Germany
  • Benzing, Thomas, Uniklinik Koln, Koln, Nordrhein-Westfalen, Germany
  • Brinkkoetter, Paul T., Uniklinik Koln, Koln, Nordrhein-Westfalen, Germany
  • Bartram, Malte P., Uniklinik Koln, Koln, Nordrhein-Westfalen, Germany

Regulation of actin cytoskeleton organization is at the center of podocyte morphology and homeostasis during health and disease. The actin-binding and -crosslinking protein Alpha-actinin 4 (ACTN4) has been shown to play an essential role in this context, as mutations in the ACTN4 gene are leading to an autosomal-dominant form of focal segmental glomerulosclerosis (FSGS). Here, performing gene panel sequencing in a pediatric patient presenting with steroid resistant nephrotic syndrome and FSGS, a de novo, potentially disease causing variant of ACTN4 was identified, which was previously undescribed and not found in available genome or exome databases. Our aim is to elucidate the pathogenic potential of this variant for podocytes and FSGS progression.


To investigate the pathogenic potential of the newly identified ACTN4 variant (ACTN4-M240T), we employed the genetic toolbox of Drosophila. The fly holds podocyte-equivalent cells called nephrocytes, which are responsible for filtration and detoxification of the hemolymph. Cell-specific genetic manipulation enabled us to analyze RNAi-mediated knockdown of Actinin, the single fly homolog, in nephrocytes and its impact on cell morphology and function. Rescue experiments with the novel human ACTN4 variant will now give indication about possible pathogenic consequences of the mutation when compared to wildtype as well as previously described disease-associated variants of ACTN4.


Knockdown of Drosophila Actinin in nephrocytes leads to severe functional and morphological defects, as seen by impacted filtration capacity and reduced nephrocyte diaphragm length. Transgenic expression of wildtypic human ACTN4 resulted in partial rescue of the Actinin-knockdown associated phenotypes. In contrast, expression of ACTN4-M240T as well as other FSGS-associated ACTN4-mutant proteins neither ameliorated functional nor morphological defects.


Our results underline the importance of Actinin and actin cytoskeleton regulation for nephrocyte/podocyte biology. As ACTN4-M240T was not able to rescue Actinin-knockdown associated phenotypes, but in contrast, showed similar results to other pathogenic variants of ACTN4, we conclude that also ACTN4-M240T is a pathogenic variant of ACTN4.