Leucocyte expression of complement C5a receptors exacerbates infarct size after myocardial reperfusion injury.

Early reperfusion is mandatory for the treatment of acute myocardial infarction. This process, however, also induces additional loss of viable myocardium, called ischaemia-reperfusion (IR) injury. Complement activation plays an important role in IR injury, partly through binding of C5a to its major receptor (C5aR). We investigated the role of C5aR on infarct size and cardiac function in a model for myocardial IR injury. BALB/c (WT) mice and C5aR(-/-) mice underwent coronary occlusion for 30 min, followed by reperfusion. Infarct size, determined 24 h after IR, was reduced in C5aR(-/-) mice compared with WT mice (28.5 ± 2.1 vs. 35.7 ± 2.5%, P = 0.017). Bone marrow (BM) chimaera experiments showed that this effect was due to the absence of C5aR on circulating leucocytes, since a similar reduction in infarct size was observed in WT mice with C5aR-deficient BM cells (25.3 ± 2.2 vs. 34.6 ± 2.8%, P < 0.05), but not in C5aR(-/-) mice with WT BM cells. Reduced infarct size was associated with fewer neutrophils, T cells, and macrophages in the infarcted area 24 h after IR in C5aR(-/-) mice, and also with lower levels of Caspase-3/7 indicating less inflammation and apoptosis. Echocardiography 4 weeks after IR showed an improved ejection fraction in C5aR(-/-) mice (25.8 ± 5.5 vs. 19.2 ± 5.4%, P < 0.001). The absence of C5aR on circulating leucocytes reduces infarct size, is associated with reduced leucocyte infiltration and with less apoptosis in the infarcted myocardium, and improves cardiac function in a mouse model of myocardial IR injury. Selective blocking of C5aR might be a promising strategy to prevent myocardial IR injury.

De Hoog VC ，Timmers L ，Van Duijvenvoorde A ，De Jager SC ，Van Middelaar BJ ，Smeets MB ，Woodruff TM ，Doevendans PA ，Pasterkamp G ，Hack CE ，De Kleijn DP ... -  《-》

The receptor for activated complement factor 5 (C5aR) conveys myocardial ischemic damage by mediating neutrophil transmigration.

Tissue loss after myocardial ischemia with reperfusion (MI/R) is in part conveyed by neutrophil recruitment to post-ischemic myocardium. Strategies to prevent reperfusion injury would help to limit myocardial damage. The receptor for activated complement factor 5 (C5aR) plays a prominent role in inflammation. We examine the effects of C5aR-deficiency on reperfusion injury after MI/R. C5aR(-/-)-mice and their C57BL/6- (WT) littermates underwent transient myocardial ischemia followed by different time points of reperfusion. Infarct size and leukocyte infiltration were determined. Expression of C5aR, inflammatory cytokines and adhesion molecules were analyzed by real-time RT-PCR. Leukocyte-endothelial interactions were assessed by low-shear adhesion- and transmigration-assays in vitro. Myocardial C5aR mRNA expression was 2.8-fold increased by ischemia. Infarct size per area-at-risk and leukocyte recruitment into infarctions were reduced in C5aR(-/-)-compared to WT-mice as well as in WT mice treated with the C5aR-antagonist JPE1375. IL-6, IL-1β, ICAM-1 and VCAM-1 expression were not different, while TNFα expression was reduced in C5aR(-/-)-mice after MI/R. In vitro, C5aR on leukocytes is required for effective transendothelial migration but not adhesion. Expression of MMP9 and JAM-A, molecules that are involved in leukocyte transmigration, were reduced in C5aR(-/-) mice in vivo. Genetic C5aR deficiency blunts the inflammatory response in murine MI/R resulting in reduced inflammatory cell recruitment, which is due to a C5aR-dependent effect on leukocyte transmigration across inflamed endothelium into the ischemic myocardium. This effect could be related to MMP9- and JAM-A expression in response to ischemia and reperfusion.

Mueller M ，Herzog C ，Larmann J ，Schmitz M ，Hilfiker-Kleiner D ，Gessner JE ，Theilmeier G ... -  《-》

BLT1 antagonist LSN2792613 reduces infarct size in a mouse model of myocardial ischaemia-reperfusion injury.

Restoration of coronary blood flow is crucial in the treatment of acute myocardial infarction. Reperfusion, however, induces ischaemia-reperfusion (IR) injury, which further deteriorates myocardial function. The innate immune system plays an important role in this process, mediating rapid influx of immune cells into the reperfused myocardium. Leukotriene B4 is an important leucocyte chemoattractant, performing its actions through binding to its specific receptor BLT1. We hypothesized that treatment with LSN2792613, a selective BLT1 antagonist, reduces infarct size (IS) in a mouse model of myocardial IR injury. Male C57Bl/6J mice were subjected to myocardial ischaemia for 30 min by surgical coronary artery ligation, followed by reperfusion. Mice received either LSN2792613 or vehicle, three times daily (orally) for up to 72 h after reperfusion. BLT1 inhibition with LSN2792613 reduced IS compared with vehicle treatment (26.9 ± 2.7 vs. 34.9 ± 2.2%, P = 0.030) at 24 h after reperfusion. The levels of IL-6 and keratinocyte chemoattractant were reduced in the infarcted tissue of LSN2792613-treated mice. Reduced apoptosis in LSN2792613-treated mice was suggested by increased levels of phosphorylated JNK and GSK3α/β, and confirmed by flow cytometric analysis showing less apoptotic and necrotic cardiomyocytes in the infarcted myocardium. Echocardiography at 4 weeks after myocardial IR showed a slightly higher ejection fraction and stroke volume in mice treated with LSN2792613 compared with vehicle-treated mice, whereas left ventricular volumes were comparable. Selective BLT1 inhibition with LSN2792613 reduces inflammation and apoptosis following IR, resulting in reduced IS, and therefore might be a promising strategy to prevent myocardial IR injury.

de Hoog VC ，Bovens SM ，de Jager SC ，van Middelaar BJ ，van Duijvenvoorde A ，Doevendans PA ，Pasterkamp G ，de Kleijn DP ，Timmers L ... -  《-》

C5a/C5aR pathway accelerates renal ischemia-reperfusion injury by downregulating PGRN expression.

Recent reports indicate that the complement C5a/C5aR pathway and progranulin (PGRN) deficiency both contribute to ischemia-reperfusion (IR)-induced acute kidney injury. However, the underlying relationship between the C5a/C5aR signaling pathway and PGRN expression during acute kidney injury is poorly understood. In this study, we showed that C5aR expression was significantly upregulated after renal IR, and that C5aR deficiency led to a marked increase in PGRN expression and a significant reduction in tubular damage and production of inflammatory cytokines. In accordance with these results, recombinant C5a caused downregulation of PGRN protein and mRNA levels in renal tubular epithelial cells (HK-2 cells), which could be negated by disruption of C5a/C5aR signaling by the C5aR antagonist, as confirmed by immunofluorescence, western blotting, and quantitative real-time PCR. Moreover, C5aR deficiency resulted in attenuated NF-κB expression 24h after IR, and recombinant C5a potentiated TNFα-induced NF-κB activation in HK-2 cells. Inhibition of NF-κB activation reversed C5a-induced downregulation of PGRN expression. Our results show for the first time that the complement C5a/C5aR pathway aggravates IR-induced acute kidney injury by suppressing PGRN expression and confirm that suppression of PGRN expression is associated with increased NF-κB activation induced by C5a.

Zhang K ，Li GQ ，He QH ，Li Y ，Tang M ，Zheng QY ，Xu GL ，Zhang KQ ... -  《-》

Mesenchymal stem cells alleviate acute kidney injury by down-regulating C5a/C5aR pathway activation.

Tang M ，Zhang K ，Li Y ，He QH ，Li GQ ，Zheng QY ，Zhang KQ ... -  《-》