C5aR Expression in Kidney Tubules, Macrophages and Fibrosis
The anaphylatoxin C5a and its receptor C5aR (CD88) are complement pathway effectors implicated in renal diseases, including ANCA-associated vasculitis. We investigated the kidney expression of C5aR and a second C5a receptor C5L2 by using immunohistochemistry and in situ hybridization on formalin-fixed, paraffin-embedded human and mouse kidney. C5aR was detected on interstitial macrophages and in multiple tubular regions, both distal and proximal; C5L2 had a similar expression pattern. The 5/6 nephrectomy model of chronic kidney injury exhibited increased C5aR expression by infiltrating cells within the fibrotic regions. Functional assessment of myeloid C5aR in vitro revealed that C5a induced the expression of chemokines and remodeling factors by macrophages, including CCL-3/-4/-7,-20, MMP-1/-3/-8/-12, and F3, and promoted survival by blocking neutrophil apoptosis. C5a activity was C5aR dependent, as demonstrated by reversal with the C5aR inhibitor avacopan. Collectively, these results suggest that myeloid C5aR may induce excessive inflammation in the kidney via immune cell recruitment, extracellular matrix destruction, and remodeling, resulting in fibrotic tissue deposition.