The C5a/C5aR2 axis promotes renal inflammation and tissue damage
Ting Zhang, Kun-yi Wu, Ning Ma, Ling-lin Wei, Malgorzata Garstka, Wuding Zhou, Ke Li
Ting Zhang, Kun-yi Wu, Ning Ma, Ling-lin Wei, Malgorzata Garstka, Wuding Zhou, Ke Li
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Research Article Inflammation Nephrology

The C5a/C5aR2 axis promotes renal inflammation and tissue damage

Abstract

C5a is a potent inflammatory mediator that binds C5aR1 and C5aR2. Although pathogenic roles of the C5a/C5aR1 axis in inflammatory disorders are well documented, the roles for the C5a/C5aR2 axis in inflammatory disorders and underlying mechanisms remain unclear. Here, we show that the C5a/C5aR2 axis contributes to renal inflammation and tissue damage in a mouse model of acute pyelonephritis. Compared with WT littermates, C5ar2–/– mice had significantly reduced renal inflammation, tubular damage, and renal bacterial load following bladder inoculation with uropathogenic E. coli. The decrease in inflammatory responses in the kidney of C5ar2–/– mice was correlated with reduced intrarenal levels of high mobility group box-1 protein (HMGB1), NLRP3 inflammasome components, cleaved caspase-1, and IL-1β. In vitro, C5a stimulation of macrophages from C5ar1–/– mice (lacking C5aR1 but expressing C5aR2) led to significant upregulation of HMGB1 release, NLRP3/cleaved caspase-1 inflammasome activation, and IL-1β secretion. Furthermore, blockade of HMGB1 significantly reduced C5a-mediated upregulation of NLRP3/cleaved caspase-1 inflammasome activation and IL-1β secretion in the macrophages, implying a HMGB1-dependent upregulation of NLRP3/cleaved caspase-1 inflammasome activation in macrophages. Our findings demonstrate a pathogenic role for the C5a/C5aR2 axis in renal injury following renal infection and suggest that the C5a/C5aR2 axis contributes to renal inflammation and tissue damage through upregulation of HMGB1 and NLRP3/cleaved caspase-1 inflammasome.

Authors

Ting Zhang, Kun-yi Wu, Ning Ma, Ling-lin Wei, Malgorzata Garstka, Wuding Zhou, Ke Li

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Figure 5

Expression and distribution of C5aR2 in murine kidney.

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Expression and distribution of C5aR2 in murine kidney. (A and B) RT-PCR ...
(A and B) RT-PCR were performed in normal and infected kidney tissues of WT mice. (A) The agarose gel of conventional PCR showing the PCR products for C5aR2 and internal control GAPDH. The 100-bp DNA markers are shown alongside the gel. (B) Results of quantitative PCR. Data are expressed as analyzed by 1-way ANOVA with multiple comparisons test (n = 6 mice/group). Data are shown as mean ± SD. (C) Immunochemical staining for C5aR2 in (WT) normal and infected mouse kidney sections (24 hpi). Images were taken from cortex, corticomedullary junction, and medulla of the kidney sections, stained with anti-C5aR2 (red), LCA (green; used for identifying renal structure), and DAPI (blue). Boxed regions correspond to the images at the bottom panel. Arrows indicate cells stained positive for C5aR2. Scale bars: 100 μm (top 2 panels), 50 μm (bottom panel). (D) Immunochemical staining for CD11b and C5aR2 in (WT) infected kidney sections (24 hpi). Images were taken from corticomedullary junction. CD11b (green), C5aR2 (red), and DAPI (blue). Arrows indicate cells stained positive for both CD11b and C5aR2. Scale bars: 50 μm. A representative of 3 experiments is shown.