AimsInnate immune and inflammatory responses are involved in myocardial ischaemia/reperfusion (I/R) injury. The interleukin-1 receptor (IL-1R)-mediated, MyD88-dependent nuclear factor kappa B (NF-κB) activation pathway plays an important role in the induction of innate immunity and inflammation. However, the role of the IL-1R-MyD88 pathway in myocardial I/R injury has not been thoroughly investigated. We hypothesized that inhibition of the interaction of IL-1R with MyD88 will attenuate myocardial ischaemic injury through reducing inflammatory responses.Methods and resultsMale C57BL/6 mice were subjected to myocardial ischaemia (45 min) followed by reperfusion (4 h). In the treatment group, after mice were subjected to ischaemia (45 min), the TIR/BB-loop mimetic (AS-1), which inhibits the interaction of IL-1R with MyD88, was administered immediately before reperfusion. Hearts were harvested and cellular proteins were isolated for immunoprecipitation and immunoblotting. AS-1 administration significantly decreased infarct size by 32.92 compared with the untreated I/R group. Ejection fraction and fractional shortening in AS-1-treated mice were also significantly increased by 18.0 and 25.6, respectively, compared with the untreated I/R group. AS-1 administration significantly decreased the I/R-increased interaction between IL-1R and MyD88, attenuated the I/R-increased NF-κB binding activity, and reduced levels of inflammatory cytokines and adhesion molecules in the myocardium compared with the untreated I/R group. In addition, AS-1 administration significantly decreased myocardial myeloperoxidase activity by 23.6 and neutrophil infiltration in the myocardium compared with the untreated I/R group.ConclusionThe results demonstrated an important role for the IL-1R-mediated MyD88-dependent signalling pathway in myocardial I/R injury. The data suggest that modulation of the IL-1R/MyD88 interaction could be a strategy for reducing myocardial ischaemic injury.

The macrophage scavenger receptor class A (SR-A) participates in the innate immune and inflammatory responses. This study examined the role of macrophage SR-A in myocardial ischemia/reperfusion (I/R) injury and hypoxia/reoxygenation (H/R)-induced cell damage. SR-A-/- and WT mice were subjected to ischemia (45min) followed by reperfusion for up to 7days. SR-A-/- mice showed smaller myocardial infarct size and better cardiac function than did WT I/R mice. SR-A deficiency attenuated I/R-induced myocardial apoptosis by preventing p53-mediated Bak-1 apoptotic signaling. The levels of microRNA-125b in SR-A-/- heart were significantly greater than in WT myocardium. SR-A is predominantly expressed on macrophages. To investigate the role of SR-A macrophages in H/R-induced injury, we isolated peritoneal macrophages from SR-A deficient (SR-A-/-) and wild type (WT) mice. Macrophages were subjected to hypoxia followed by reoxygenation. H/R markedly increased NF-κB binding activity as well as KC and MCP-1 production in WT macrophages but not in SR-A-/- macrophages. H/R induced caspase-3/7 and -8 activities and cell death in WT macrophages, but not in SR-A-/- macrophages. The levels of miR-125b in SR-A-/- macrophages were significantly higher than in WT macrophages. Transfection of WT macrophages with miR-125b mimics attenuated H/R-induced caspase-3/7 and -8 activities and H/R-decreased viability, and prevented H/R-increased p-53, Bak-1 and Bax expression. The data suggest that SR-A deficiency attenuates myocardial I/R injury by targeting p53-mediated apoptotic signaling. SR-A-/- macrophages contain high levels of miR-125b which may play a role in the protective effect of SR-A deficiency on myocardial I/R injury and H/R-induced cell damage.

The macrophage scavenger receptor class A (SR-A) participates in the innate immune and inflammatory responses. This study examined the role of macrophage SR-A in myocardial ischemia/reperfusion (I/R) injury and hypoxia/reoxygenation (H/R)-induced cell damage. SR-A-/- and WT mice were subjected to ischemia (45min) followed by reperfusion for up to 7days. SR-A-/- mice showed smaller myocardial infarct size and better cardiac function than did WT I/R mice. SR-A deficiency attenuated I/R-induced myocardial apoptosis by preventing p53-mediated Bak-1 apoptotic signaling. The levels of microRNA-125b in SR-A-/- heart were significantly greater than in WT myocardium. SR-A is predominantly expressed on macrophages. To investigate the role of SR-A macrophages in H/R-induced injury, we isolated peritoneal macrophages from SR-A deficient (SR-A-/-) and wild type (WT) mice. Macrophages were subjected to hypoxia followed by reoxygenation. H/R markedly increased NF-κB binding activity as well as KC and MCP-1 production in WT macrophages but not in SR-A-/- macrophages. H/R induced caspase-3/7 and -8 activities and cell death in WT macrophages, but not in SR-A-/- macrophages. The levels of miR-125b in SR-A-/- macrophages were significantly higher than in WT macrophages. Transfection of WT macrophages with miR-125b mimics attenuated H/R-induced caspase-3/7 and -8 activities and H/R-decreased viability, and prevented H/R-increased p-53, Bak-1 and Bax expression. The data suggest that SR-A deficiency attenuates myocardial I/R injury by targeting p53-mediated apoptotic signaling. SR-A-/- macrophages contain high levels of miR-125b which may play a role in the protective effect of SR-A deficiency on myocardial I/R injury and H/R-induced cell damage.