The Role And Mechanism Of CXCR7 And PGE₂ In Ischemic Heart Disease

BackgroundGenome-wide association studies revealed that the CXCL12 genetic locus(which en-codes the chemokine CXCL12)is associated with the risk of coronary artery disease and myocardial infarction.CXCL12 has two receptors,CXCR4 and CXCR7.The role of CXCR4 in cardiovascular diseases,including myocardial infarction and atherosclerosis,has been relatively clear.Unlike CXCR4,the function of CXCR7 in cardiovascular dis-eases is largely unknown.Our previous research found that CXCR7 was expressed in in-jured arterial endothelium of human and mouse,and endothelial cell(EC)CXCR7 medi-ated mechanical injury-induced vascular remodeling and cardiac remodeling after myocar-dial infarction.The aim of this study is to determine the role of the EC CXCR7 in athero-sclerosis.MethodsEC Cxcr7 conditional knockout(Cxcr7f/f Cdh5CreERT2+:Cxcr7f/f and EC specific promoter Cdh5 driven CreERT2,abbreviated as cKO)mice were crossed with low density lipoprotein receptor(Ldlr)knockout mice to obtain Cxcr7f/f Cdh5CreERT2+ Ldlr-/-(abbre-viated as cKO Ldlr-/-)mice and littermate control Cxcr7f/f Cdh5CreERT2-Ldlr-/-(abbrevi-ated as Ctl Ldlr-/-)mice.After treatment with tamoxifen,EC-specific Cxcr7 knock out mice with defects in lipid metabolism were obtained and fed with high-fat diet for 8 or 16 weeks to induce atherosclerosis.Mechanistically,the effect of endothelial Cxcr7 knockout on lipid metabolism was studied through lipid uptake experiment and detection of blood lipid levels.The number of white blood cells in the peripheral blood was counted using hemo-cytometer.The infiltration of inflammatory cells in atherosclerotic plaques was detected by immunofluorescence.Leukocytes rolling and adhesion in blood vessels after high-fat feeding were monitored in vivo under fluorescence microscope.The CXCR7 antagonist CCX771 was administered to wild-type mice and circulating CXCL12 level and leukocyte rolling and adhesion in vivo were detected.In addition,partial carotid artery ligation was used to restrict flow,and a high-fat diet was given for 4 weeks to induce rapid atheroscle-rosis.ResultsWe found that loss of endothelial Cxcr7 reduced atherosclerotic plaque formation induced by high-fat diet,reduced the infiltration of macrophages in the plaque,increased the number of leukocytes in the blood,and increased CXCL12 level in circulation.Deletion of EC Cxcr7 had no effect on blood lipids and uptake of cholesterol by adipose tissue.In vivo imaging showed that deletion of EC Cxcr7 reduced the number of leuko-cytes rolling or adhesion to the vascular endothelium.Furthermore,carotid artery blood flow was restricted for 4 weeks to induce atherosclerosis.Consistently,we found that loss of EC Cxcr7 significantly reduced the formation of plaque of common carotid artery.ConclusionDeletion EC Cxcr7 has no effect on lipid metabolism,while elevated the level of circulating CXCL12,reduced the interaction of inflammatory cells with vascular endothe-lium,inhibited vascular inflammation,thus inhibiting atherosclerosis.Targeting EC CXCR7 has potential clinical application value in preventing and curing atherosclerosis.BackgroundCardiovascular diseases have high morbidity and mortality worldwide.Among vari-ous cardiovascular diseases,myocardial infarction is a major cause of heart failure.Reper-fusion through antithrombotic or mechanical methods to restore blood flow of blocked blood vessels is an effective treatment to rescue ischemic myocardium.However,reperfu-sion itself can cause damage to ischemic region,namely myocardial ischemia reperfusion(MI/R)injury.MI/R injury inhibits the effectiveness of reperfusion therapy in patients with myocardial infarction and is a determinant of heart failure.Traditional nonsteroidal anti-inflammatory drugs(NSAIDs)that inhibit both cycloox-ygenase(COX)-1 and COX-2,or those selective for COX-2 inhibition,inhibit the biosyn-thesis of prostaglandins(PG),and have a wide clinical application.However,some clinical studies have shown that their use is associated with an increased risk of heart failure.As an alternative target of COX-2,mPGES-1 inhibitors have superiority in cardiovascular adverse events such as thrombosis and vascular restenosis,but the role of mPGES-1 in myocardial ischemia-reperfusion injury remains unknown.MethodsMice deficient in Cox-1,or-2,or mPges-1,or endothelial PGE receptor(Ep)-4,to-gether with pharmacological interventions,were utilized in a 30-minute ischemia and 24-hour reperfusion mouse model of MI/R.Prostaglandin metabolites in plasma and urine after MI/R were detected by mass spectrometry-liquid chromatography.Myocardial m i-crovascular perfusion was assessed before and after myocardial ischemia and reperfusion using laser Doppler flow technique in vivo.Dilatation of arterioles downstream of femoral artery after I/R was detected in vivo by fluorescence microscope.Vasodilation function was detected by vascular tension test in vitro.Leukocytes rolling and adhesion in the fem-oral artery after I/R were monitored in vivo.Immunofluorescence staining and flow cy-tometry were used to detect the infiltration of inflammatory cells in the heart after MI/R.ResultsCox-1 deficiency reduced biosynthesis of PGE2 and increased infarct size in the heart after MI/R,while Cox-2 deletion had no effect on MI/R injury.Deletion of mPges-1 also depressed PGE2,increased the infiltration of inflammatory cells in the injured myocardium,and exacerbated MI/R injury.Cardiac perfusion was impaired by mPges-1 deletion following reperfusion detected by laser Doppler,without change in baseline flow.Consist-ently,mPges-1 deletion abolished arteriolar dilation response induced by I/R in vivo and acetylcholine ex vivo,which is mediated via EP4 receptor.Moreover,mPGES-1-derived PGE2 acting on EP4 receptor restrained myeloid cell adhesion to endothelial cells in vitro and limited leukocytes adhesion to vasculature during I/R in vivo.Endothelium-restricted deletion of Ep4 receptor impaired microcirculatory perfusion and exacerbated cardiac in-jury after MI/R.In contrast,treatment with misoprostol,a clinically available PGE ana-logue,reduced infiltration of inflammatory cells in the heart,improved cardiac microcir-culation,protected heart function and protected against MI/R injury.ConclusionCOX-1/mPGES-1 derived PGE2 acting on endothelial EP4 receptor,promotes arteri-olar dilation,inhibits leukocyte-endothelial cell interaction,improves microcirculation,and thus protects against MI/R injury.mPGES-1 is a key protective molecule in microcir-culation.Endothelial EP4 agonists and PGE analogs such as misoprostol may be effective therapeutic agents to inhibit MI/R injury.