The Effect Of N-terminal Amino Acid Change Of AngⅡ On Abdominal Aortic Aneurysm Formation

Background:The renin-angiotensin system(RAS)plays a key role in the regulation of cardiovascular pathophysiological process,and intervention of components of this system is also a common tool in most cardiovascular target protection strategies.However,the biological effects of current clinical treatment of cardiovascular diseases cannot be fully explained by our knowledge of the system,indicating that our understanding of RAS is not sufficient.RAS has been recognized as the major vasoconstrictive system in the human body for a long time since it was found.The physiological effects mediated by the interaction of angiotensin II with angiotensin I(AT1)receptor are the classical pathway components in the RAS system.As the heptapeptide Ang(1-7)was found which came from AngⅡ through the enzymatic reaction of ACE2,we have a new understanding of the RAS family components,because it produced antagonistic biological effects on AngⅡ.As far as we know now,RAS is a two-way adjustment system which can be precisely regulated according to the environmental changes of the body.On the one hand,it contains peptides of the classical pathway of RAS which induce vasoconstriction,promote cell or tissue proliferation and aggregation of inflammatory factors;on the other hand,it also contains some protective peptides which exert opposite effect compared to the above,but our knowledge about these peptides remains not clear enough.The novel peptide AngiotensinA(AngA)we know recently came from AngⅡ through decarboxlylation of the N-terminal amino acid.It can be metabolized to Alamandine through the enzymatic activity of renin-angiotensin converting enzyme 2(ACE2),and then interact with the receptor MrgD to exert vasodilation and and anti-proliferative effect;However,AngA can also act on AT1 to produce a vasoconstriction effect similar to AngⅡ.This new octapeptide is in the intersection of RAS regulation just as AngⅡ,which way to go depends on its metabolic methods and the results are opposite.There are certain limitations regarding the studies of AngA which promotes vasoconstriction,the experiments focus on cell culture or monitoring blood pressure change using catheter then transfer the amplified signal to the computer.These conditions are not consistent with real physiology.To further clarify the physiological function of AngA and improve our understanding of RAS,we used the classical mouse model of AngⅡ-induced aortic aneurysm formation to explore the effect of AngA and also analyze reason of the high mortality rate of aneurysm disease according to the research results.Methods:This study is mainly divided into three parts to gradually explore the pathophysiological function of AngA using a classical mouse model of AngⅡ-mediated aortic aneurysm formation.First,based on the previous studies of AngA and the computer affinity simulation test of this study,we compared aortic aneurysm formation,blood pressure,cholesterol and other related factors change between AngⅡ(1000 ng/kg/min)and AngA(1000 ng/kg/min)at the background of low density lipoprotein receptor(LDLR-/-)and apolipoprotein E(ApoE-/-)knockout mice for 4 weeks.Second,in order to further explore whether AngA will affect the ability of AngⅡ-mediated aortic aneurysm formation and systolic blood pressure,we coinfused AngA(1000 ng/kg/min)with AngⅡ(1000 ng/kg/min)the compared to AngⅡ(1000 ng/kg/min)for 4 weeks.Last,we increased the concentration of AngA to 10-fold(10000 ng/kg/min)and compared to AngⅡ(1000 ng/kg/min)to see the incidence of aortic aneurysm formation and blood pressure change.Results:In the first part,we gave the Western diet to LDLR-/-mice for 4 weeks,the incidence of aortic aneurysm formation of AngⅡ(1000 ng/kg/min)group(N=10)was 60%and one of them developed aortic aneurysm rupture;while AngA(1000 ng/kg/min)group(N=10)did not occur aortic aneurysm formation.To verify the reproducibility of above results,we compared the effect of these two peptides at the background of ApoE-/-mice given normal diet for 4 weeks.The results showed that the incidence of aortic aneurysm formation in AngⅡ(1000 ng/kg/min)group(N=10)was 90%,with four of them occurred aneurysm rupture;Similar AngA(1000 ng/kg/min)group(N=10)had no aortic aneurysm formation.The systolic blood pressure of AngⅡ group increased significantly at the last week compared to the baseline in both of hypercholesterolemia mouse model,but there was no significant change in AngA group at the last week.In the second part,we did it at the background of ApoE-/-mice given normal diet for 4 weeks.The first group is Saline group(N=5)as a negative control;the second group is AngA(1000 ng/kg/min)group(N=5)in order to verify the reproducibility of the above results;the third group is AngⅡ group(1000 ng/kg/min)(N=10)as a positive control and the last group is AngⅡ(1000 ng/kg/min)plus AngA(1000 ng/kg/min)group(N=10)as an observation group in this section.After 4 weeks,the incidence of aortic aneurysm formation in AngⅡ group was 70%and two of them developed aortic aneurysm rupture.The incidence of aortic aneurysm formation in AngⅡ plus AngA group was 78%,with one of them occurred aneurysm rupture.While both Saline group and AngA group had no aortic aneurysm formation.In the third part,ApoE-/-mice were given normal diet for 4 weeks.AngⅡ(1000 ng/kg/min)group(N=10)was regarded as a positive control group,and AngA(10000 ng/kg/min)group(N=10)with the 10-fold concentration compared to AngⅡ was the observation group.After 4 weeks,the incidence of aortic aneurysm in AngⅡ group was 80%,and two of them had aneurysm rupture;while the incidence of aortic aneurysm in AngA group was 30%,with no aneurysm rupture.Conclusion:The effect of AngA which came from decarboxylation of the N-terminal amino acid of AngⅡ decreased significantly on the abdominal aortic aneurysm formation.