Atheroprotective role of C5ar2 deficiency in apolipoprotein E-deficient mice

Abstract

Atherogenic processes and vascular remodelling after arterial injury are controlled and driven by a plethora of factors amongst which the activation of the complement system is pivotal. Recently, we reported a clear correlation between high expressions of the second receptor for complement anaphylatoxin C5a, the C5a receptor-like 2 (C5L2, C5aR2), with high pro-inflammatory cytokine expression in advanced human atherosclerotic plaques. This prompted us to speculate that C5aR2 might have a functional role in atherosclerosis. We, therefore, investigated the role of C5aR2 in atherosclerosis and vascular remodelling. Here, we demonstrate that C5ar2 deletion, in atherosclerosis-prone mice, attenuates atherosclerotic as well as neointimal plaque formation, reduces macrophages and CD3+ T cells and induces features of plaque stability, as analysed by histomorphometry and quantitative immunohistochemistry. As a possible underlying mechanism, C5ar2-deficient plaques showed significantly reduced expression of C5a receptor (C5ar1), Tnf-α as well as Vcam-1, as determined by qPCR and quantitative immunohistochemistry. In addition, in vitro mechanistic studies revealed a reduction of these pro-inflammatory and pro-atherosclerotic mediators in C5ar2-deficient macrophages. Finally, blocking C5ar1 with antagonist JPE1375, in C5ar2(-/-)/Apoe(-/-) mice, led to a further reduction in neointimal plaque formation with reduced inflammation. In conclusion, C5ar2 deficiency attenuates atherosclerosis and neointimal plaque formation after arterial injury. This identifies C5aR2 as a promising target to reduce atherosclerosis and restenosis after vascular interventions.

The Controversial C5a Receptor C5aR2: Its Role in Health and Disease

“…C5aR2 was absent in CD3 + T cells and vascular smooth muscle cells. This proatherogenic role of C5aR2 and its collaboration with C5aR1 were confirmed in vivo mouse models of wire-induced endothelial injury and high-fat diet-induced atherosclerosis [66]. Here, C5aR2 levels were elevated in aortas of wire-injured mice or mice on high-fat diet (12 weeks), both of atherosclerosis-prone ApoE KO.…”

“…But on neutrophils from bone marrow of C5aR2 KO mice, the surface expression of C5aR1 is lower than on those from WT mice [68]. Surface C5aR1 expression on nonstimulated BMDMs from C5aR2 KO mice is lower compared with those from WT littermates, also observed for C5aR2/ApoE double KO [66]. C3aR expression levels in neutrophils were similar between C5aR2 KO and WT mice [68].…”

“…The proinflammation properties of C5aR2 in certain disease models further complicate the matter [7, 65, 66]. In bone marrow-derived mouse macrophages (BMDMs), neutrophils, and transfected HEK293T cells, C5aR2 interacted with C5aR1 and was required for C5a-induced C5aR1 endocytosis and downstream PI3K/ERK signaling in a clathrin adaptor AP2-depedent manner [67].…”

More than complementing Tolls: complement–Toll‐like receptor synergy and crosstalk in innate immunity and inflammation

“…This finding suggests involvement of possible C5aR2–TLR4 crosstalk in the induction of HMGB1 that appears to require mitogen‐activated protein MEK1/2, JNK1/2, and PI3K . Moreover, C5aR2 was shown to mediate C5a‐induced activation of mast cells and to promote atherosclerosis and neointimal plaque formation in apolipoprotein E‐deficient mice . In contrast to these pro‐inflammatory roles by C5aR2, other studies showed that C5aR2 interacts physically with and negatively regulates C5aR1 signaling in neutrophils and macrophages, thereby providing a mechanistic basis for its reported anti‐inflammatory action .…”

“…The underlying signaling mechanism involves induction of PI3K or ERK1/2 signaling, which in turn suppress crucial transcription factors (IRF-1 and IRF-8) that regulate these cytokines mediate C5a-induced activation of mast cells 41 and to promote atherosclerosis and neointimal plaque formation in apolipoprotein E-deficient mice. 42 In contrast to these pro-inflammatory roles by C5aR2, other studies showed that C5aR2 interacts physically with and negatively regulates C5aR1 signaling in neutrophils and macrophages, 39,43 thereby providing a mechanistic basis for its reported anti-inflammatory action. 36 In toto, the activities of C5aR2 appear to be dynamic and contextual depending on cell type, tissue, and disease model.…”