Mechanism Of Reversal Of Cardiac Hypertrophy By Angiotensin-(1-7) Via P38MAPK Pathway

Objective:The pathogenesis of cardiac hypertrophy requires a variety of biochemical reactions in vivo,and its pathological changes include ventricular hypertrophy,cardiac interstitial fibrosis,and collagen deposition between cardiomyocytes.Abnormal expression of the target gene and signal transduction between cells are the important factors in the occurrence of nuclear target gene.The mitogen-activated protein kinase(MAPK)pathway plays an important role in the current signal transduction pathways.Activation of renin-angiotensin system(RAS)in vivo is an important cause of myocardial hypertrophy,and its bioactive product Ang II can lead to myocardial hypertrophy,myocardial interstitial fibrosis and myocardial cell apoptosis by activating the p38 MAPK signal transduction pathway.Ang(1-7),on the other hand,can bind to Mas receptor to produce vasodilator smooth muscle,reduce angiogenesis,reduce cell proliferation and interstitial fibrosis,and can reduce or reverse ventricular hypertrophy and remodeling.However,the intracellular signal transduction mechanism of Ang(1-7)is still unclear.The purpose of this study was to establish a mouse model of cardiac hypertrophy induced by Ang II,to investigate whether Ang(1-7)can inhibit the formation of hypertrophy factors and reverse the occurrence of cardiac hypertrophy by participating in the regulation of p38 MAPK signal transduction pathway.Methods:1.C57BL/6J male mice(8-10 weeks old)were selected and divided into 5groups :Ang II group,Ang(1-7)group,Ang II+KD group,Ang II+(1-7)group and sham operation group,with 6 mice in each group.In advance,Ang II,Ang(1-7)and Ang II+(1-7)were injected into the osmotic pump respectively(Ang II dose was1.0ug/kg/min,Ang(1-7)dose was 0.5g /kg/min),and then the filled osmotic pump was placed into the sterile normal saline centrifugal tube and incubated in an incubator at 37℃ for 24 hours.The skin of the neck and back of the mice was cut and scraped out into a 1cm×3cm transverse area.After iodine disinfection,the skin was cut and dissociated.Then the head end of the osmotic pump containing the reagent was embedded inwardly.Mice in the Ang II + KD group were given candesartan(2.1mg/kg/day)daily after the Ang II osmotic pump was installed,and the volume of gastric juice was about 0.1-0.2 ml each time.2.The mice were weighed and underwent color doppler echocardiography before surgery and before execution,and the data of left ventricular end-systolic volume,left ventricular end-diastolic volume,left ventricular posterior wall and ventricular septum thickness,ejection fraction and left ventricular shortening fraction were measured.After the mice were sacrificed,the hearts were extracted to calculate the heart/weight mass ratio,and the right lower limb tibia was intercepted to calculate the heart mass/tibial length ratio.The expressions of ERK,p38 and their phosphorylated proteins in ventricular myocardial tissue were detected by Western blot.Results:1.Heart/weight mass ratio(heart-body ratio): The Ang II group was higher than the other four groups,and the difference was statistically significant.Ang II+(1-7)group and Ang II+KD group were slightly higher than Ang(1-7)group and sham operation group,with no statistical difference.2.Heart weight/tibial length ratio(tibial heart ratio): The ratio of Ang II group was greater than that of the other four groups,with statistical difference.There was no significant difference in the ratio between Ang II+(1-7)group and Ang II+KD group.3.Color doppler echocardiography: The left ventricular posterior wall and ventricular septum thickness and cardiac ejection fraction in Ang II group were higher than the other four groups,while the left ventricular end-diastolic volume and left ventricular shortening fraction were lower than the other four groups.There was no statistical difference between the Ang II+(1-7)group and the Ang II+KD group,which was slightly higher than the Ang(1-7)group and the sham operation group.4.Western blot results:Bax protein expression level: The Ang II group was significantly higher than the other four groups,with a statistical difference(P<0.05).There was no significant difference among the Ang II+(1-7)group,the Ang II+KD group and the sham operation group(P>0.05).Bcl-2 protein expression level: The Ang II group was significantly lower than the other four groups,with a statistical difference(P<0.05).There was no significantdifference among the Ang(1-7),Ang II+(1-7)group,Ang II+KD group and any two groups of the sham operation group(P>0.05).Mas1 protein expression level:The lowest value was found in the Ang II group,which was statistically different from the Ang II+(1-7)group and the Ang(1-7)group(P<0.05),and no statistically different from the Ang II+KD group and the sham operation group(P>0.05).β-MHC protein expression level:The Ang II group was the highest,which was significantly higher than the other four groups,with a statistical difference(P<0.05).Ang-(1-7)group was the lowest,and there was a statistical difference compared with the sham group(P<0.05).There was no significant difference between the Ang-(1-7)group,Ang II+(1-7)group and Ang II+KD group(P>0.05). P38 protein expression: There was no statistical difference in the total P38 protein expression among the groups,and the phosphorylated P38 protein Ang II group was higher than the other four groups,with statistical difference(P<0.05).Conclusion:4.1 A mouse model of cardiac hypertrophy was established by continuous subcutaneous injection of Ang II with a micro osmotic pump.The mechanism may be that Ang II continuously stimulates the phosphorylation of p38 pathway protein,activates the p38 MAPK signal transduction pathway,and leads to the occurrence of cardiac hypertrophy and myocardial cell apoptosis.4.2 Western blot results show that Ang-(1-7)intervention and candesartan in mice to a certain extent,reversal of myocardial hypertrophy and myocardial apoptosis and protect the role of myocardial hypertrophy reconstruction,its mechanism may be Ang-(1-7)inhibition of p38 lightning channel protein phosphorylation,Ang-(1-7)inhibit p38 MAPK signaling pathways activated reverse myocardial hypertrophy and myocardial apoptosis.