The Role Of Macrophage MST1 In Inflammation Response After AMI

Acute myocardial infarction（AMI）is one of the most frequent causes of death in the developed countries and is rising in developing countries.As immune system components of the microenvironment of infarcted heart,monocytes/macrophages play critical roles in regulating the resolution of inflammation after AMI which are recruited to the infarct in two phases.The first phase was dominated by Ly6C^high monocytes at1-3 days and Ly6C^low monocytes are predominant at 4-10 days in the second phase.Ly6C^high monocytes can give rise to Ly6C^low monocytes,M1-macrophages in the early stage switch to M2-macrophages in healing stages.Disrupted transition of monocytes/macrophages attenuates wound repair after AMI.However,the mechanism under this transition is largely unknown.The acute inflammation can permit elimination of the invading microorganisms and facilitate tissue repairment.Initiation and resolution of inflammation are closely arranged by different clusters of lipid mediators（LM）,which due to chronic inflammation or self-resolving inflammation.Macrophages are an important source of LM that balance inflammation and its resolution.The polarization of macrophages is associated with differential regulation of LM.In particularly,distinct gene regulation of arachidonic acid metabolism related enzymes has been reported in M1-and M2-polarized human macrophages.Moreover,macrophages biosynthesized phenotype-specific lipid mediators during infections.Whether the same mechanism is performed after MI has not yet been elucidated.The mammalian sterile20-like kinase 1/2（MST1/2）mediates cell apoptosis or tumor development.Loss-of-function mutation for MST1 is identified to be a common variable immunodeficiency and cause a series of disorders in human.Although MST1/2has been widely studied as one of the key components in classic Hippo pathway kinases cascade for a long time,for example,it can mediate LATS1/2 to activate the downstream effectors.However,in recent years,more studies have demonstrated critical functions of MST1 independent of Hippo pathway in innate immune responses against pathogens and autoimmune diseases.Therefore,this study aims to identify the role of MST1/2 in resolution of acute inflammatory diseases,such as AMI in mice.Furthermore,to study the underlying mechanism of macrophage MST1/2 in inflammation through metabolomics and molecular biological methods.In the present study,we found MST1 is significantly elevated in macrophages after AMI,while MST2 has no change,suggesting that MST1 may be involved in the resolution of AMI.Through bone marrow transplantation and MST1/2 transgenic mice,results found that loss of MST1/2 in macrophages exacerbated post-AMI heart failure,increased M1-macrophages infiltration and promoted pro-inflammatory gene expression.Next,we used another acute inflammation model to verify our finding in AMI,and found MST1 depletion promoted recruitment of Ly6C^high monocytes/macrophages in peritonitis.To investigate the mechanism the role of macrophage MST1 in the resolution of acute inflammation,LC-MS analysis was performed after AMI in mice.Results discovered that in MST1 depleted macrophages,metabolites of5-lipoxygenases（5-LOX）related pathway increased,especially the content of leukotriene B4（LTB4）.These results suggest that the proinflammatory effect of MST1is related to 5-LOX.In addition,we found MST1 interacted with 5-LOX by binding PLAT domain,and phosphorylated threonine 218 site（T218）of 5-LOX in HEK293T cells.Phosphorylation at T218 site blocked the interaction of 5-LOX anchoring on nuclear membrane with arachidonate 5-lipoxygenase-activating protein（FLAP）,thereby inhibiting LTB4 Synthesis.In this paper,LTB4 receptor antagonist CP105696was used and found that CP105696 can specifically inhibit the pro-inflammatory response caused by MST1 deletion in macrophages.Finally,CP105696 was orally administrated to the mice undertaken AMI,and found it could effectively restore heart failure,reduce tissue apoptosis,inhibit proinflammatory factors expression and promote angiogenesis caused by losing macrophage MST1.In conclusion,this study reveals the key role of macrophage MST1 and underlying mechanism in resolution of acute inflammation after AMI.It showed a key target of macrophage MST1 and suggested the pathway MST1-5LOX^Thr218-FLAP-LTB4 in inflammatory response.Furthermore,LTB4 receptor antagonists specifically blocked the effect of MST1 deletion in macrophages after AMI which provides new strategy and a potential therapeutic target of acute inflammatory disease,especially AMI.