Glomerular Elasticity and Gene Expression Patterns Define Two Phases of Alport Nephropathy

Abstract

Rationale: Mutations in COL4A3,4, or 5 cause Alport syndrome and contribute to other glomerular diseases. Potential mechanisms include abnormal GBM structure, chemistry, elasticity, or ER stress. The causes of initial podocyte injury are not fully defined in collagen IV nephropathies. Objectives: We characterized renal function, structural and biophysical properties of glomerular capillaries and podocytes, and renal gene expression patterns in Col4a3 KO mice (BL6) over the 8-month course of disease. To test for a role for ER stress, we treated Col4a3 KO mice with TUDCA. Findings: Col4a3 KO mice develop proteinuria and reduced renal function at 4 to 5 months, but their glomerular capillaries become abnormally deformable, and podocytes are dislodged into the urine with volume loading at 3 months. Glomeruli become maximally deformable at 4 months with loss of 40% of their podocytes, and then stiffen progressively with progression of renal disease. In parallel, kidneys become increasingly fibrotic with proteinuria and inflammatory infiltrates as renal failure progresses. Bulk renal gene expression changes from 2 and 4 months where it shows increased expression of genes related to matrix organization, cytokine signaling, and cell injury to reduction in genes coding for differentiated renal tubular and metabolic proteins. Treatment of mice with TUDCA minimized glomerular injury, loss of renal function, and increased expression of genes that inhibit MAP, tyrosine kinase, and TGF Beta. Conclusion: Renal disease in Col4a3 KO mice progresses in two phases, before overt proteinuria with early podocyte injury and loss, and later with overt proteinuria and progressive fibrosis. Suppression of renal injury by TUDCA implicates ER stress and MAP, tyrosine kinase, and TGF-B signaling as a disease mechanism.