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Abstract: SA-PO633

Kidney C5aR Is Expressed in Resident Macrophages, Tubular Epithelial Cells, and in Association With Fibrosis

Session Information

Category: Glomerular Diseases

  • 1302 Glomerular Diseases: Immunology and Inflammation

Authors

  • Sullivan, Kathleen M., ChemoCentryx, San Carlos, California, United States
  • Dunlap, Carolyn, ChemoCentryx, San Carlos, California, United States
  • Ertl, Linda, ChemoCentryx, San Carlos, California, United States
  • Miao, Zhenhua, ChemoCentryx, San Carlos, California, United States
  • Schall, Thomas J., ChemoCentryx, San Carlos, California, United States
Background

TAVNEOS® (avacopan) is a potent inhibitor of C5aR, the pro-inflammatory receptor for complement fragment C5a. Identifying the cellular targets of avacopan is critical for understanding the mechanism of action in kidney disease; however, published reports on C5aR expression in the kidney vary widely (Abe et al., 2001; Yuan et al., 2012). To address this issue, we investigated the mRNA and protein expression of C5aR in human and mouse kidneys.

Methods

We performed in situ hybridization (ISH) on formalin-fixed, paraffin embedded (FFPE) tissue blocks using mRNA probes for C5aR and C5L2, the alternative C5a receptor that plays a role in dampening C5aR activity (Bamberg et al., 2010). We tested commercial C5aR and C5L2 antibodies for immunohistochemistry (IHC) with control FFPE cell pellets and tissues. Macrophage (CD68) and tubule subpopulation (CALB1, SLC13A3) antibodies were validated for IHC and a dual IHC-ISH method. Kidney FFPE tissues were from normal human subjects and lupus nephritis patients, or from mouse models, including surgical nephrectomy and the bm12 inducible lupus model, in a human C5aR knock-in (hC5aR KI) strain.

Results

Two commercial antibodies specific for human C5aR by IHC had overlapping but distinct expression patterns in interstitial and tubular cells. We confirmed this result by using ISH, and identified the cells expressing C5aR as macrophages and a discrete subpopulation of distal tubule epithelial cells. C5L2 was observed in the same kidney cell types, but at a lower expression level than C5aR. The hC5aR KI mouse kidney had a similar expression pattern for C5aR compared to human. C5aR expressing cells localized to areas of fibrosis in kidney disease models and lupus nephritis biopsies.

Conclusion

In both mouse and human kidneys, we observed C5aR expression on macrophages, on a subpopulation of tubular epithelial cells, and in association with fibrosis. The antibody-specific differences in C5aR detection may be due to cell-dependent post-translational modification, since expression of C5aR detected by both antibodies was confirmed by ISH. C5aR expression in the kidney is consistent with its role in inflammation and tissue remodeling, and suggests the hypothesis that treatment with avacopan may reduce inflammation-driven fibrosis in disease.

Funding

  • Commercial Support