Abstract: TH-PO0293
A Drosophila Nephrocyte Platform for Functional Interpretation of COL4A3/4/5 Variants
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
- Duan, Jianli, University of Maryland Baltimore School of Medicine, Baltimore, Maryland, United States
- Zhao, Yunpo, University of Maryland Baltimore School of Medicine, Baltimore, Maryland, United States
- Ng, Derek K., Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, United States
- Sampson, Matt G., Boston Children's Hospital, Boston, Massachusetts, United States
- Han, Zhe, University of Maryland Baltimore School of Medicine, Baltimore, Maryland, United States
Background
Variants in COL4A3, COL4A4, and COL4A5 are classically linked to Alport syndrome, but are increasingly identified in patients with nephrotic syndrome, steroid-resistant nephrotic syndrome, and FSGS. Many remain difficult to interpret clinically, creating a need for rapid in vivo functional assays. Drosophila nephrocytes share key filtration-barrier features with mammalian podocytes, including slit diaphragm-like structures and a surrounding basement membrane.
Methods
We analyzed the two Drosophila type IV collagen genes expressed in nephrocytes, Col4a1 and Viking (Vkg). Nephrocyte-specific RNAi was used to knock down Col4a1 or Vkg, followed by fluorescent tracer uptake assays. Transgenic flies expressing human COL4A3, COL4A4, COL4A5, or patient-derived COL4A5 variants were tested for rescue of collagen-deficient nephrocyte phenotypes.
Results
Col4a1 and Vkg were both expressed in nephrocytes, with an approximately 2:1 Col4a1:Vkg ratio, supporting a defined nephrocyte collagen IV system. Knockdown of either gene impaired nephrocyte filtration function. Human collagen IV chains showed selective rescue: COL4A4 and COL4A5 rescued Col4a1-RNAi phenotypes, whereas COL4A3 preferentially rescued Vkg-RNAi phenotypes. Using the Col4a1-RNAi/COL4A5 rescue platform, wild-type COL4A5 restored nephrocyte function, while multiple known pathogenic or likely pathogenic COL4A5 variants failed to rescue. Additional COL4A5 variants of uncertain significance showed distinct rescue profiles, separating functionally impaired variants from variants with preserved activity.
Conclusion
Drosophila nephrocytes contain a simplified type IV collagen system that models key aspects of the human COL4A3/COL4A4/COL4A5 network. This platform provides rapid in vivo functional evidence for interpreting collagen IV variants identified in Alport-spectrum disease, nephrotic syndrome, SRNS, and FSGS.
Funding
- NIDDK Support