| Background: Aortic dissection(AD)is an event of sudden onset in which blood leaves the normal aortic channel through a usually discrete point of exit(intimal tear)and rapidly dissects inner from outer layers of the media to produce a false channel.The characteristics of AD is rapid progression,high mortality,lacking of effective drugs.Surgery is the only way to cure.Hypertension is the most common basis of AD.Control of blood pressure is very important for AD prevention and treatment.Blood pressure elevation increases the mechanical strain of the vessel wall and eventually leads to AD,although its detail mechanism is not clear.It has been confirmed that matrix metalloproteinase-9(MMP-9)is very important in AD development,and mechanical strain induced MMP-9 expression in vascular smooth muscle cells,however,it has not been clear how the mechanical signals become biological signals and lead to MMP-9 expression in vessels.The purpose of the study is to clarify the molecular mechanism of mechanical strain induced expression of matrix metalloproteinase-9 in aortic dissection.The first part: The influence of varying mechanical strain and different mechanical stretch time on the expression of matrix metalloproteinase-9 in aortic dissection vessels Objective: The present study evaluated the changes in the expression of MMP-9 induced by varying degrees of mechanical strain and different mechanical stretch time in rat abdominal aortic vessels and human aortic dissection vessels in vitro.Methods: The abdominal aortic dissection model was implemented by injection of porcine pancreatic elastase to tunicae media vasorum of the abdominal aorta.After 48 h of establishing of abdominal aortic dissection model,aortic dissection rings isolated from male Sprague Dawley rats(n=30)were divided into 6 experimental groups.In a temperature controlled,constant flow chamber,the aortic rings in the groups(group1 to group4)were stretched by a mechanical stress of 0g,1g,3g,and 5g for 30 minutes.The aortic dissection rings in the groups(group5 to group6)were stretched by a mechanical stress of 3g for 1h or 2h.The protein expression levels of MMP-9 in all 6 groups were analyzed by Western blotting.The aortic rings from 10 patients with stanford A aortic dissection were stretched by a mechanical strain of 0g,3g,4g,5g,6g,7g,8g,9g for 30 min.The expression of MMP-9 was analyzed by Western blotting.Results: After 24 h of establishing of abdominal aortic dissection model,the Doppler ultrasound confirmed the formation of abdominal aortic dissection.Stretching by mechanical strain in the order of 1g,3g,or 5g induced the expression of MMP-9 in the aortic dissection rings.The expression of MMP-9 increased with increasing mechanical strain until 3g,then further increases strain leading to down-regulating of the expression of MMP-9.The expression of MMP-9 and the stretch time was not a positive correlation.In the human aortic dissection,the expression of MMP-9 was increased after stretched by a mechanical strain of 4g,5g,6g,and fall after stretched by a mechanical strain of 8g,9g.Conclusions: Injection of porcine pancreatic elastase to tunicae media vasorum of the abdominal aorta is a good way to establish of abdominal aortic dissection model.Varying mechanical strain induce differential expression of MMP-9 in rat aortic vessels in vitro.The maximum level of expression was seen at a strength of 3g.The expression of MMP-9 and the stretch time was not a positive correlation.The expression of MMP-9 in human aortic dissection was up-regulated with mechanical strains of 4 to 6g,but down-regulated with mechanical strains of 8g,9g.The second part:Mechanical strain induced expression of matrix metalloproteinase-9 via the stretchactive channel in rat abdominal aortic dissectionObjective: The aim of the study was to investigate the expression of matrix metalloproteinase-9(MMP-9)in rat's abdominal aortic dissection via mechanical strain so as to offer a better understanding of the possible mechanisms of aortic dissection.Methods: The abdominal aortic dissection model was implemented by injection of porcine pancreatic elastase to tunicae media vasorum of the abdominal aorta.80 SD rats were divided into two groups:aortic dissection group(8 groups,n=40),sham group(8 groups,n=40),at day 0,1,3,5,7,14,21,30 after establishment of aortic dissection model,the serum MMP-9 levels were measured by ELISA.The abdomianal aortic dissection rings isolated from male Sprague Dawley rats(n=40)were divided into 8 experimental groups.The rat's aortic dissection vessels in the groups(group1 to group4)were stretched in vitro with a mechanical strength of 0,1,3,or 5 g for 30 mins.The vascular rings in the groups(group5 to group8)were pretreated with gadolinium ? chloride hexahydrate(Gd Cl3),streptomycin,SN50 and SN50 M,followed by stretching with a mechanical strain of 3g for 30 minutes.The messenger RNA of MMP-9 and the protein of MMP-9 were analyzed by real-time reverse transcription polymerase chain reaction(RT-PCR)and Western blotting,and the nuclear factor ?B(NF-?B)was detected by enzyme-linked immunosorbent assay(ELISA).Results: After the rat abdominal aortic dissection model was established,the expression of MMP-9 in the serum increased with time extended.The results showed that large amount of expression of MMP-9 in rat aortic dissection vessels stretched with mechanical strains of 1,3,5g,and small amount of expression with 0g,but this effect was most blocked by two stretch-activated ion channel(SAC)blockers: gadolinium ? chloride hexahydrated(Gd Cl3)and streptomycin.The NF-?B activity in aortic rings were activated by stretched with a mechanical strain of 3g,and were blocked by Gd Cl3,streptomycin and the NF-?B peptide inhibitor SN50,but not by the inactive SN50 analogue SN50 M.Conculsion: The expression of MMP-9 in the serum increased with time extended in rat abdominal aortic dissection.Mechanical strain induces MMP-9 expression in aortic dissection vessels,and this process is by activating the stretch-activated channel(SAC)-induced NF-?B pathway. |
PDF Full Text Request