Abstract: FR-OR061

A New Mouse Model of Chronic Proteinuria Due to a Glomerular Basement Membrane Laminin-521 Polymerization Defect

Session Information

Category: Glomerular

  • 1002 Glomerular: Basic/Experimental Pathology

Authors

  • Funk, Steven Daniel, Washington University School of Medicine, St. Louis, Missouri, United States
  • Bayer, Raymond H, Washington University School of Medicine, St. Louis, Missouri, United States
  • Miner, Jeffrey H., Washington University School of Medicine, St. Louis, Missouri, United States
Background

The glomerular basement membrane (GBM) is a dense extracellular matrix that separates endothelium from podocytes. The GBM is thought to stabilize foot processes and slit diaphragms and, together with podocytes and endothelium, forms the glomerular filtration barrier. GBM integrity is maintained by: 1) polymerization of laminin α5β2γ1 (LM-521) via tripartite α-β-γ chain NH2-terminal LN domain interactions; 2) attachment of the LMα5 C-terminal LG domain to podocyte & endothelial cell integrins; and 3) linkage of the laminin network to the type IV collagen network by nidogen. Null and missense mutations in the LMβ2 chain of LM-521 cause nephrotic syndrome. In previous studies of Lamb2-/- mice proteinuria preceded both foot process effacement and loss of slit diaphragms. Thus, LAMB2 LN domain missense mutations found in nephrotic patients may cause disease by impairing laminin polymerization.

Methods

In vivo CRISPR gene editing was used to generate a point mutation in the LN domain of mouse LAMB2, but DNA analysis of 1 founder showed an unexpected in-frame, 44 amino acid deletion within the LN domain. Homozygous LAMB2-d44 mice were observed for up to 8 months. Urine, blood, and tissues were taken at select time points to evaluate albuminuria, BUN, histopathology, and GBM composition and ultrastructure.

Results

The unexpected LAMB2-d44 mutation is analogous to the dy-2J mutation in mouse LMα2 that causes severe muscular dystrophy due to defective LM-211 polymerization. The GBM of LAMB2-d44 mice contained a normal level of LAMB2, but the mice exhibited modest proteinuria between 4-6 wks of age and nephrotic range by 8 wks. Foot process swelling was observed at 6 wks of age, with effacement at 8 wks. LAMB2-d44 mice died spontaneously from 4 months onward, but some lived over 8 months. Moderate glomerulosclerosis, tubular dilations, protein casts, and occasional immune infiltrates were commonly observed features.

Conclusion

LAMB2-d44 mice exhibit modest proteinuria early but have intact foot processes. Chronic nephrotic range proteinuria is accompanied by effacement. This mutant will serve as a tool to test innovative protein-based methods for strengthening the GBM’s laminin network and reducing proteinuria. More generally, this new genetic model of nephrotic syndrome will useful for investigating disease progression.

Funding

  • NIDDK Support