ABSTRACT
OBJECTIVE: The altered structure and composition of the vascular extracellular matrix (ECM) influences the formation of abdominal aortic aneurysms (AAA). Transglutaminase type 2 (TG2), which is a Ca(2+)-dependent cross-linking enzyme, has been proven the importance for ECM homeostasis, but there is no evidence of TG2 in AAA formation. The hypothesis was investigated that TG2 contributes to protect aortic walls during remodeling of the AAAs. METHODS: In a rat abdominal aortic aneurysm model using a combination of intraluminal elastase infusion and extraluminal calcium chloride, TG2 expression and activity were evaluated at 1 and 8 weeks after the AAA preparation (n = 6 at each endpoint), compared with those of the non-prepared aorta (n = 6). Additionally, ex vivo experiments of isolated AAA tissue culture with recombinant human TG2, TG2 inhibitor cystamine, or tissue necrosis factor (TNF)-α were performed. RESULTS: TG2 mRNA expression in the AAAs was significantly upregulated at both 1 and 8 weeks (22.4-fold and 5.4-fold increases of the non-prepared aorta, P = .0022 and P = .0048, respectively). TG2 protein expression and activity were also enhanced by fluorescent staining of the AAAs. Similar mRNA upregulation of TNF-α, interleukin-1ß, matrix metalloproteinases (MMP)-2, MMP-9, and tissue inhibitors of metalloproteinases (TIMP)-1 and TIMP-2 was observed in the AAAs, and TG2 and TNF-α were colocalized in the aortic walls at 1 week. Ex vivo experiments showed that mRNA expressions of TNF-α, MMP-2, and MMP-9 in the cultured AAA tissue were decreased by exogenous TG2, whereas were increased by cystamine. TNF-α exposure to the AAA tissues was significantly upregulated TG2 mRNA expression (P = .0333). CONCLUSION: TG2 expression and activity in AAA formation were enhanced, possibly due to compensatory reaction. TG2 has a potential role of ECM protector in aortic walls during remodeling of the AAAs.
Subject(s)
Aorta, Abdominal/enzymology , Aortic Aneurysm, Abdominal/prevention & control , GTP-Binding Proteins/metabolism , Transglutaminases/metabolism , Animals , Aorta, Abdominal/drug effects , Aortic Aneurysm, Abdominal/chemically induced , Aortic Aneurysm, Abdominal/enzymology , Aortic Aneurysm, Abdominal/genetics , Calcium Chloride , Cystamine/pharmacology , Disease Models, Animal , Enzyme Activation , Enzyme Inhibitors/pharmacology , GTP-Binding Proteins/antagonists & inhibitors , GTP-Binding Proteins/genetics , Gene Expression Regulation, Enzymologic , Humans , Inflammation Mediators/metabolism , Interleukin-1beta/genetics , Male , Matrix Metalloproteinase 2/genetics , Matrix Metalloproteinase 9/genetics , Pancreatic Elastase , Protein Glutamine gamma Glutamyltransferase 2 , RNA, Messenger/metabolism , Rats , Rats, Sprague-Dawley , Recombinant Proteins/metabolism , Time Factors , Tissue Culture Techniques , Tissue Inhibitor of Metalloproteinase-1/genetics , Tissue Inhibitor of Metalloproteinase-2/genetics , Transglutaminases/antagonists & inhibitors , Transglutaminases/genetics , Tumor Necrosis Factor-alpha/genetics , Tumor Necrosis Factor-alpha/metabolismABSTRACT
OBJECTIVE: The pathogenesis of thoracic aortic aneurysms (TAA) is still unclear. A recent investigation indicated that angiotensin II, a potent activator of NADH/NADPH oxidase, plays an important role in aneurysmal formation. We investigated the potential role of p22phox-based NADH/NADPH oxidase in the pathogenesis of TAA. METHODS: Human thoracic aneurysmal (n=40) and non-aneurysmal (control, n=39) aortic sections were examined, and the localization of p22phox, an essential component of the oxidase, and its expressional differences were investigated by immunohistochemistry and Western blot. In situ reactive oxygen species (ROS) generation was examined by the dihydroethidium method, and the impact of medical treatment on p22phox expression was investigated by multiple regression analysis. RESULTS: In situ production of ROS and the expression of p22phox increased markedly in TAA throughout the wall, and Western blot confirmed the enhanced expression of p22phox. The expression was more intense in the regions where monocytes/macrophages accumulated. In these inflammatory regions, numerous chymase-positive mast cells and angiotensin converting enzyme-positive macrophages were present. Their localization closely overlapped the in situ activity of matrix metalloproteinase and the expression of p22phox. Multiple regression analysis revealed that medical treatment with statin and angiotensin II type 1 receptor blocker (ARB) suppressed p22phox expression in TAA. CONCLUSION: Our findings indicate the role of p22phox-based NADH/NADPH oxidase and the local renin-angiotensin system in the pathogenesis of TAA. Statin and ARB might have inhibitory effects on the formation of aneurysms via the suppression of NADH/NADPH oxidase.
