The Effect And Mechanism Of Angiotensin-(1-7) In The Pathogenesis Of Abdominal Aortic Aneurysm

ObjectiveAbdominal aortic aneurysm(AAA)is defined as a segmental fusiform or cystiform dilatation of the abdominal aorta exceeding the normal vessel diameter by 50%.As most patients with AAA are asymptomatic until rupture develops,leading to a high mortality rate of 80%,an effective approach to preventing AAA formation and progression is highly warranted.Although the pathological features of AAA have been elucidated as degraded matrix of the vascular media,decrease of vascular smooth muscle cells and infiltration of inflammatory cells such as macrophages and lymphocytes,the pathogenesis driving these pathological changes remains poorly understood,resulting in the status quo of "still no pills" for AAA.In the past few years,with the rapid progress in molecular biology and pharmacology,the essential role of the renin-angiotensin system(RAS)in the pathogenesis of AAA has received renewed attention.Recently,the newly found members of RAS,angiotensin-converting enzyme-2(ACE2)and angiotensin-(1-7)[Ang-(1-7)],have gained an increased attraction in the field of cardiovascular research.Recent studies in our and other laboratories showed that Ang-(1-7)inhibited atherosclerotic lesion formation and enhanced plaque stability in apolipoprotein E-knockout(ApoE-/-)mice,thus acting as a counteractive factor of angiotensin ?(Ang ?).Our group further demonstrated that ACE2 gene transfer significantly prevented AAA formation in ApoE-/-mice by inhibiting inflammatory response and matrix metalloprotease(MMP)activation.However,the direct effect of Ang-(1-7)treatment on the incidence and severity of AAA remains elusive.To test the hypothesis that Ang-(1-7)treatment may attenuate AAA via inhibiting vascular inflammation,extracellular matrix degradation and smooth muscle cells(SMCs)apoptosis,an animal model of AAA was established by Ang ? infusion to ApoE-/-mice.MethodsIn the in vivo study,one hundred mice were randomly divided into five groups(n=20,each group):control,Ang ?-treated;Ang ? + Ang-(1-7)-treated,Ang ? +Ang-(1-7)+ A779-treated and Ang ?+ Ang-(1-7)+ PD123319-treated groups.After four weeks high-fat feeding and all mice were treated with continuous subcutaneous infusion of different drugs by an osmotic pump for another four weeks.After drug treatment for four weeks,all mice underwent euthanasia for further pathological studies.In the in vitro study,we used RAW264.7 mouse macrophage cell line and human primary aortic smooth muscle cells(HSMCs).These cells were divided into control,Ang ?-treated,Ang ? + Ang-(1-7)-treated,Ang ? + Ang-(1-7)+ A779-treated and Ang ? + Ang-(1-7)+ PD123319-treated groups.Then these samples were detected by Western blot,Real-time PCR,Histology and Immunohistochemical staining,TUNEL assay,etc.All data were expressed as mean± SEM and the statistical analyses involved with the use of SPSS 18.0.One-way ANOVA test with Tukey post-hoc analysis and chi-square tests were used to compare data among multiple groups.P<0.05 was considered statistically significant.ResultsIn the in vivo experiment,Ang-(1-7)treatment reduced the incidence and severity of AAA induced by Ang II infusion,and the mechanisms involved inhibited macrophage infiltration,attenuated expression of interleukin 6(IL-6),tumor necrosis factor-a(TNF-a),monocyte chemoattractant protein 1(MCP-1)and matrix metalloprotease 2(MMP2),as well as abated SMCs apoptosis in the abdominal aortic tissues.However,the addition of A779 or PD123319 treatment in these mice reversed Ang-(1-7)-mediated beneficial effects on AAA.In the in vitro experiment,Ang-(1-7)treatment mitigated the mRNA expression of IL-6,TNF-? and MCP-1 induced by Ang II stimulation in macrophages.In addition,Ang-(1-7)treatment significantly suppressed apoptosis and MMP2 expression and activity in Ang II-treated SMCs.The molecular mechanism may involve inhibition of extracellular signal-regulated kinasel/2(ERK1/2)signaling pathways via Ang-(1-7)stimulation of Mas receptor(MasR)and angiotensin ?ype 2 receptor(AT2R).ConclusionsIn conclusion,our study demonstrated that in a mouse model of AAA induced by Ang ? infusion,Ang-(1-7)treatment remarkably attenuated the formation and severity of AAA as well as aortic wall remodeling via alleviating inflammatory response,expression of MMPs and the apoptosis of SMCs.The molecular mechanisms may involve inhibited ERK1/2 signaling pathways via Ang-(1-7)stimulation of MasR and AT2R.