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Kidney Week

Abstract: FR-PO146

The Role of Complement C1r and C1s Serine Proteases in Kidney Fibrosis

Session Information

Category: CKD (Non-Dialysis)

  • 1903 CKD (Non-Dialysis): Mechanisms


  • Xavier, Sandhya, University of Virginia/Department of Medicine, Charlottesville, Virginia, United States
  • Sahu, Ranjit K., University of Virginia, Charlottesville, Virginia, United States
  • Portilla, Didier, University of Virginia Health System, Charlottesville, Virginia, United States

We previously reported increased expression of C1q in kidney cells as a pathophysiologic mechanism leading to kidney fibrosis. The classical pathway of complement activation is initiated by the assembly of the C1 complex which consists of C1q and serine proteases C1r and C1s. We hypothesize that activation of classical pathway in kidney cells contributes to tubulointerstitial fibrosis, and tested this idea in mice with global deletion of C1r.


We performed real time-PCR, immunohistochemistry, in situ hybridization, western blotting and microarray based gene expression analysis in wild type (WT) and in C1r-/- mice subjected to unilateral ureteral obstruction (UUO) or folic acid injury (FA). We overexpressed human C1r in human tubular epithelial cells


Administration of FA or UUO injury in WT mice led to upregulation of C1r and C1s mRNA and protein in whole kidney tissue. In situ hybridization and immunohistochemistry localized increased expression of these proteases to distal tubular epithelial cells. C1r deletion reduced fibrosis in both animal models. While kidney inflammation and complement activation measured by increased expression of C3 fragments were significantly reduced in the FA model, C3 formation and inflammation were not affected in the UUO mice, despite the reduction in fibrosis. While C1r-/- mice had reduced C1s expression, stable transfection of human C1r in renal epithelial cells led to increased expression of both C1r and C1s. Gene expression arrays corroborated downregulation of probe sets representing C1r and C1s in kidney tissue of C1r-/- mice, as well as downregulation of genes associated with connective tissue and collagen. C1r-/- mice treated with FA had reduced expression of genes associated with increased inflammation.


In conclusion our studies support the role of classical complement pathway activation during fibrosis via increased expression of C1r in distal tubular epithelial cells and identify C1r as a novel potential therapeutic target for the treatment of progressive kidney disease.


  • NIDDK Support