Abstract: FR-PO0765
β-Arrestin Ortholog krz Regulates Actin and Slit Diaphragm Dynamics in Drosophila Nephrocytes
Session Information
- Glomerular Diseases: Cell Homeostasis and Novel Injury Mechanisms
November 07, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Glomerular Diseases
- 1401 Glomerular Diseases: Mechanisms, including Podocyte Biology
Authors
- Milosavljevic, Julian, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany
- Guillarmain, Charlotte, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany
- Windisch, Sébastien Eric, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany
- Lang, Konrad, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany
- Helmstädter, Martin, Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany
- Hermle, Tobias F., Renal Division, Department of Medicine, Faculty of Medicine and Medical Center - University of Freiburg, Freiburg, Germany
Background
β-Arrestins mediate endocytosis of the slit diaphragm protein nephrin in a phosphorylation dependent manner, a process that is increased under hyperglycemic conditions. While deletion of either β-Arrestin 1 or 2 reduced albuminuria in a diabetic mouse model, the effect of a complete β-Arrestin loss in podocytes remains unknown. Here, we present the first in vivo model of total β-Arrestin deficiency in podocyte-like Drosophila nephrocytes to investigate their role in maintaining slit diaphragm integrity.
Methods
Using RNA interference, we silenced krz, the sole orthologue of mammalian β-Arrestins in podocyte-like nephrocytes in Drosophila. Immunofluorescence and confocal microscopy were used to assess slit diaphragm integrity and endolysosomal compartments. Ex vivo assays using tracer endocytosis were employed to study functional effects of krz-RNAi. Transmission electron microscopy (TEM) provided insights into ultrastructural alterations of the filtration barrier and endosomal system.
Results
Silencing of krz resulted in subcortical mislocalization of the slit diaphragm proteins Sns (Nephrin) and Kirre (NEPH1), suggesting impaired endocytosis of these proteins. TEM images revealed formation of ectopic slit diaphragms within the membrane invaginations of nephrocytes, the labyrinthine channels. Visualizing labyrinthine channels using passive diffusion of a fluorophore-labeled tracer in nephrocytes revealed elongated channels after krz silencing. Investigating potential causes of altered channel morphology, we stained phalloidin to label the actin cytoskeleton. Knockdown of krz resulted in the appearance of dense, ring-like actin structures in close proximity to ectopic slit diaphragm proteins, implicating increased actin polymerization. Ex vivo tracer uptake assays demonstrated reduced endocytic activity and mislocalization of the tracer to a perinuclear compartment. While the early endosomal compartment remained unaffected, Rab7-stainings revealed that late endosomes were also mislocalized to the perinuclear region, overlapping with the tracer signal.
Conclusion
Loss of krz resulted in mislocalization of slit diaphragm proteins, increased actin polymerization and endolysosomal defects, suggesting a pleiotropic role for this key regulator of signaling in nephrocytes.
Funding
- Government Support – Non-U.S.