Oleoylethanolamide Stabilizes Atherosclerotic Plaque Through Regulating Macrophage Polarization Via AMPK-PPARα Pathway

Background:Atherosclerotic plaque rupture is the major trigger of acute cardiocerebral vascular events worldwide with high rates of disability and mortality,such as myocardial infarction,stroke and heart failure.Monocytes-derived macrophages,as a vital constituent of plaque,participate in all the stages(initiation,progression and regression)of atherosclerosis,and closely linked with the plaque destabilization.The total amount of macrophages in plaque was considered directly responsible for vulnerable plaques,while recent study indicates that the macrophage subtype ratio(M1/M2)rather than the number plays the decisive role in plaque fate.Under the influence of various immune microenvironment,macrophages can be induced to heterogeneous phenotypes,and currently exist in two antagonistic subsets:pro-inflammatory M1 and anti-inflammatory M2,accelerating the vulnerability or stability of atherosclerotic plaques,respectively;importantly,macrophage plasticity indicates that subtypes(M1,M2)can change from one another.Hence,the novel insight of regulating macrophage polarization,suppressing M1 and promoting M2,can be an effective approach to stabilize atherosclerotic plaques,lowering the occurrence of acute cardio-cerebral vascular events.OEA,a natural fatty acid ethanolamine compound,produced and secreted by the small intestinal enterocytes or adipocytes after fat intake and the cells in ischemic lesion area,it’s one of the peroxisome proliferator-activated receptor α’s(PPARα)activity regulator.The benefits(anti-inflammation,antioxidant,antidyslipidemia and neuroprotection)of OEA via activating PPARa signaling pathway have been reported,but whether OEA owned the ability to regulate macrophage polarization,improve atherosclerotic plaque stability and the possible mechanism still remained unknown.To address this question,the present study was designed in both vivo and vitro.Objective:The effect of OEA on atherosclerotic plaque stability and its mechanism.Methods:Macrophages derived from THP-1 were treated with OEA followed by LPS/IFN-y,and the markers of M1,M2 macrophages were monitored by western blot,real-time PCR and immunofluorescence staining.The effect of OEA on macrophage polarization in the arch of aortic arteries was tested by immunofluorescence staining and western blot,and the plaque stability was completed by Masson’s trichrome and hematoxylin and eosin(HE)in apolipoprotein E(ApoE)-/-mice.Results:OEA treatment enhanced the expression of two classic M2 macrophage markers,macrophage mannose receptor(CD206)and transforming growth factor(TGF-β),while the expression of inducible nitric oxide synthase(iNOS)and tumor necrosis factor(TNF-α)(M1 macrophages)were decreased in THP-1-derived macrophages.Blocking of PPARa using siRNA and inhibition of AMP-activated protein kinase(AMPK)by its inhibitor compound C almost abolished the OEAinduced expression of macrophage subtype markers.In addition,OEA significantly suppressed Mland promoted M2 macrophage polarization,increased collagen content and decreased necrotic core size in atherosclerotic plaques of ApoE-/-mice,which were linked with the high expression of PPARa and p-AMPK.Conclusion:OEA improved atherosclerotic plaque stability through regulating macrophage polarization via AMPK-PPARa pathway.