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Kidney Week

Abstract: SA-PO622

Collagen VI Associates with Basement Membrane Defects in Alport Syndrome

Session Information

Category: Genetic Diseases of the Kidney

  • 803 Genetic Epidemiology and Other Genetic Studies of Common Kidney Diseases

Authors

  • Randles, Michael J., University of Manchester, Manchester, United Kingdom
  • Lausecker, Franziska, University of Manchester, Manchester, United Kingdom
  • Potter, Paul K., Medical Research Council, Harwell, United Kingdom
  • Falcone, Sara, Medical Research Council, Harwell, United Kingdom
  • Suleiman, Hani, Washington University, Saint Louis, Missouri, United States
  • Miner, Jeffrey H., Washington University School of Medicine, St. Louis, Missouri, United States
  • Lennon, Rachel, University of Manchester, Manchester, United Kingdom
Background


Alport Syndrome is caused by genetic defects in COL4A3, COL4A4 or COL4A5, leading to inadequate assembly of the type IV collagen α3, α4, α5 network in basement membranes. In the glomerulus this causes irregularities in glomerular basement membrane (GBM) width and a characteristic basket weave appearance. We aimed to build our basic understanding about the glomerular extracellular matrix (ECM) in Alport syndrome and performed global analysis of composition and ultrastructural imaging in the both the Col4a3-/- and Col4a5-/- Alport mouse models.

Methods


Cellular and ECM fractions from wild type and Alport glomeruli at 6-8 and 16-18 weeks of age were analysed by mass spectrometry (MS)- based proteomics. Imaging included serial block face-scanning electron microscopy (SBF-SEM) and stochastic optical reconstruction microscopy (STORM).

Results


MS analysis revealed moderate changes in the composition of glomerular ECM at 6-8 weeks, even prior to the onset of glomerular barrier dysfunction. These changes included complete absence of type IV collagen α3, α4, α5 in both mouse models and an upregulation of type IV collagen α1, α2, α6 and the interstitial type VI collagen. At 16-18 weeks more dramatic changes were detected including elevated type IV collagen α1, α2, fibronectin, type I collagen, laminin α2 and fibrinogen chains. Global and pathway analysis of cellular fractions indicated changes in actin regulating proteins at 6 weeks and mitochondrial dysfunction at 16 weeks. SBFSEM demonstrated thickened and irregular GBM with evidence of invading podocyte protrusions. Interestingly, STORM localised type VI collagen to GBM defects in Alport mice whereas collagen VI was absent from wild type controls.

Conclusion


Our data demonstrate that Alport syndrome progresses with distinct early changes in ECM followed by more profound ECM accumulation, disruption and a marked increase in type VI collagen in the GBM. Enhanced understanding about the pathways that control matrix deposition in glomerular disease may ultimately inform targeted strategies to correct or repair glomerular barrier dysfunction.