The C5a/C5aR2 axis promotes renal inflammation and tissue damage

Area of Science:

• Immunology
• Nephrology
• Molecular Biology

Background:

• The C5a complement fragment is a potent inflammatory mediator.
• While the C5a/C5aR1 axis is implicated in inflammation, the role of the C5a/C5aR2 axis remains unclear.
• Understanding C5aR2's function is crucial for inflammatory disease research.

Purpose of the Study:

• To investigate the role of the C5a/C5aR2 axis in renal inflammation and tissue damage.
• To elucidate the underlying mechanisms of C5aR2-mediated inflammation in pyelonephritis.

Main Methods:

• Utilized a mouse model of acute pyelonephritis induced by uropathogenic E. coli.
• Compared wild-type (WT) mice with C5ar2-/- knockout mice.
• Assessed renal inflammation, tubular damage, bacterial load, and inflammatory mediators (HMGB1, NLRP3 inflammasome, IL-1β) in vitro and in vivo.
• Investigated the effect of HMGB1 blockade on C5a-mediated inflammatory responses.

Main Results:

• C5ar2-/- mice exhibited significantly reduced renal inflammation, tubular damage, and bacterial load compared to WT mice.
• Reduced inflammatory responses in C5ar2-/- mice correlated with lower intrarenal levels of HMGB1, NLRP3 inflammasome components, and IL-1β.
• In vitro studies showed C5a stimulation of macrophages (lacking C5aR1) upregulated HMGB1 release and NLRP3 inflammasome activation.
• HMGB1 blockade attenuated C5a-induced NLRP3 inflammasome activation and IL-1β secretion.

Conclusions:

• The C5a/C5aR2 axis plays a pathogenic role in renal injury following infection.
• C5a/C5aR2 signaling contributes to renal inflammation and damage via HMGB1 and NLRP3 inflammasome activation.
• Targeting the C5a/C5aR2 axis may offer a therapeutic strategy for pyelonephritis and related inflammatory conditions.