Kidney Week

Abstract: TH-PO0305

Retromer-Dependent Trafficking Is Essential for Slit Diaphragm Integrity in Drosophila Nephrocytes

Session Information

• Glomerular Diseases: Cell Biology
  October 22, 2026 | Location: Exhibit Hall A, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Glomerular Diseases

• 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology

Authors

• Windisch, Sébastien Eric, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany

Sébastien Eric Windisch, MS

• Milosavljevic, Julian, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany

Julian Milosavljevic, MD

• Selle, Michael, Lighthouse Core Facility, Medical Center - University of Freiburg, Freiburg, Germany

Michael Selle

• Wilhelm, Aaron, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany

Aaron Wilhelm, MS

• Lang, Konrad, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany

Konrad Lang, MD

• Hermle, Tobias F., Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany

Tobias F. Hermle, MD

Background

Endosomal trafficking is required for slit diaphragm integrity in podocytes, yet the recycling of its components to the plasma membrane after endocytosis remains poorly defined. Here, we investigate the role of the retromer complex (Vps26, Vps29, Vps35) in endosomal trafficking of fly nephrin in Drosophila nephrocytes.

Methods

We analyzed the effects of silencing retromer components in podocyte-like nephrocytes using unbiased image segmentation. Transgenic activation or inhibition of specific endosomal regulators allowed to analyze the pathways involved in trafficking of fly nephrin.

Results

We successfully trained the convolutional neural network U-Net for unbiased segmentation of fluorescence microscopy images of the slit diaphragm in podocyte-like nephrocytes. Quantitative analysis of segmented images revealed reduced slit diaphragm density upon silencing of each retromer core component. We validated these results using two hypomorphic alleles of Vps26. Interestingly, knockdown of Snx27, a retromer-associated adaptor that specifically mediates endosome-to–plasma membrane recycling of cargo, phenocopied this effect, suggesting that impaired plasma membrane recycling of fly nephrin underlies the observed phenotype. Consistently, overexpression of the recycling regulator RAB11B partially rescued slit diaphragm density in Vps26- and Vps35-deficient cells. In contrast, activation of fast recycling via Rab4 overexpression or inhibition of endosomal degradation via Rab7 silencing did not restore slit diaphragm integrity. This indicates pathway specificity in nephrin recycling, implying that nephrin is selectively sorted into retromer- and Rab11-dependent recycling pathways, rather than accessing alternative endosomal routes such as Rab4-mediated fast recycling. Retromer depletion also caused pronounced cytoskeletal disruption, with actin mislocalization, and led to shortened labyrinthine channels as assessed by tracer diffusion. These findings indicate that retromer is required for maintaining nephrocyte ultrastructure, likely secondary to its role in slit diaphragm maintenance.

Conclusion

These findings suggest that the retromer complex contributes significantly to the recycling of slit diaphragm components to the plasma membrane in podocyte-like nephrocytes.

Funding

• Government Support – Non-U.S.