A Study Of The Thoracic Aortic Dissection And Thoracic Aortic Aneurysm Development Via BRM Mediated SMC Phenotypic Transition

Background and Objective: Thoracic aortic aneurysm(TAA) and thoracic aorticdissection(TAD), are serious diseases threatening patient’s life. Relevant studies haveshown that the frail aorta caused by the change of sturcture of aortic media is thepathologic basic of TAA and TAD. Studies in recent years shown that the phenotypicswitching of smooth muscular cell (SMC) is a vital factor of the occurrence of TAA andRAD. There are two phenotypes of arterial SMC. One is contractile SMC, which is highlydifferentiated and has weak capability of migration and proliferation. Another one issynthetic SMC, which is lowly differentiated and has the ability of migration andproliferation. In normal aorta, contractile SMC is in the majority. However, in TAA andTAD, the amount and proportion of synthetic SMC rise significantly, which means that thephenotypic swithching from contractile SMC to synthetic SMC may participates in thedevelopment of TAA and TAD.BRM gene code the unwinding enzyme with the ability of ATPase is a core catalyticsubunit of SWI/SNF. BRM can change the connection between histone and target gene tomodulate the expression of gene. Many studies have shown that BRM play a importantrole in the modulation of the proliferation, differentiation and apoptosis of many kinds ofcells. However, there has been few studies about the fuction of BRM to modulate thephenotypic switching of vascular smooth muscular cell（VSMC）and its relationship withthe occurrence of TAA and TAD.The aim of our research is to identify the relationship between BRM and theoccurrence of the TAA and TAD. Further more, we will study the mechanism of thephenotypic switching of VSMC modulated by BRM in the TAA and TAD in order toprovide new target and theory evidence for the prevention, diagnosis and treatment of theTAD and TAA.Methods: The present study was divided into two sections.1. Collect aortic tissueform patients who suffered from thoracic aortic dissection(31cases) or TAA(11cases) andunderwent surgery in Changhai Hospital from January2011to December2012. Excludehereditary disease sucha as Marfan syndrome, and TAA or TAD caused by Syphilis.Normal aorta samples of control group (8cases) were obtained from the autopsy cases atdeath within24hours and cases undergoing heart transplant during the same period inChanghai Hospital. The location of BRM in impaired aorta and normal aorta were detectedby Immunohistochemical staining. Total RNA was extracted from the fresh samples using Trizol method. The expression level of mRNA of BRM was examined by quantitativeRT-PCR(qRT-PCR) analysis. The expression level of mRNA of seven genes wereexamined by quantitative RT-PCR analysis as well,which include MMP2and MMP9inMatrix metalloproteinase family, caspase-3in cysteinyl aspartate specific proteinase family,Smooth muscle-specific gene α-SMA and SM22α and two components of the extracellularmatrix, Fibulin4and Elastin. BRM protein in three kinds of aortic tissue was detected byWestern Blot.2.Eukaryotic expression plasmid of BRM open reading frame wasconstructed and then primary human aortic smooth muscle cells was transfected. Identifytransfection efficiency after48hours. Total RNA was extracted from the cells using Trizolmethod. The expression level of mRNA of MMP2, MMP9, caspase-3, α-SMA, SM22α,Fibulin4and Elastin were examined by quantitative RT-PCR.Result:1.the expression of BRM in aorta. Immunohistochemical staining shownthat BRM mainly exist in the VSMC in the media. The content of BRM in TAA, TAD andnormal aorta exist significant difference(P<0.05). The content of BRM in TAA wassignificantly higher than that in the orther two groups.qRT-PCR analysis shown thatmRNA of BRM in TAA and TAD were higher than that in the normal aortic tissue(P<0.05)and mRNA of BRM in TAA is higher than that in TAD(P<0.05). Western Blot shown thatthe amounts of BRM protein in TAD, TAA and control group exist significantdifference(P<0.05). TAA contained the highest amount of BRM protein, which wasfollowed by TAD.2.the expression of mRNA of MMP2, MMP9, caspase-3, α-SMA,SM22α, Fibulin4and Elastin. qRT-PCR analysis shown that the amounts of mRNA ofMMP2and MMP9within TAA and TAD were higher than that in control group(allP<0.05), the amounts of mRNA of α-SMA, SM22α and Elastin were lower than that incontrol group(all P<0.05) and the mRNA of Fibulin4and caspase-3in TAA, TAD andcontrol group do not exist significant difference(all P>0.05).3. the expression of mRNAof MMP2, MMP9, caspase-3, α-SMA, SM22α, Fibulin4and Elastin in primaryhuman aortic smooth muscle cells transfected by BRM:Total RNA was extracted fromthe cells using Trizol method after primary human aortic smooth muscle cells weretransfected by BRM. qRT-PCR analysis shown that the amounts of mRNA of MMP2andMMP9of the cells transfected by BRM were higher than that in control group(P<0.05), theamounts of mRNAof α-SMA, SM22α and Elastin were lower than that in control group(allP<0.05) and the mRNA of Fibulin4and caspase-3in both kinds of cells do not existsignificant difference(all P>0.05). Conclusion:1.The expression of BRM in the TAA and TAD elevated than normalaortic tissue, suggesting that BRM play a role in the morbidity and progression of TAA andTAD.2. It can be confirmed histologically and cytologically that high expression of BRMin aorta can lead to higher expression of mRNA of MMP2and MMP9and lowerexpression of mRNAof α-SMA, SM22α and Elastin, suggesting that BRM may play a rolein the morbidity of TAA and TAD by promoting the phenotypic swithching fromcontractile SMC to synthetic SMC in the aorta.