Transglutaminase type 2 in human abdominal aortic aneurysm is a potential factor in the stabilization of extracellular matrix.

The aim of this study was to evaluate transglutaminase type 2 (TG2) expression in human abdominal aortic aneurysm (AAA) tissue and to elucidate a potential role of TG2 in AAA formation. TG2, which is a Ca(2+)-dependent cross-linking enzyme, has been proven important for stabilizing the extracellular matrix. However, there is no evidence of the effect of TG2 on AAA formation in a human model. Aortic wall tissues were obtained during surgery in AAA patients (n = 38) and in patients with aortoiliac occlusive disease (Control; n = 4) in the Asan Medical Center from March 2011 to February 2012. In each AAA patient, the aortic neck (Neck) and maximally dilated portion (Max) of the aneurysm were sampled for analysis. TG2 expression was evaluated using immunohistochemistry and Western blotting. In addition, ex vivo experiments of isolated AAA tissue culture with the TG2 inhibitor cystamine and recombinant human TG2 were performed. Among 38 AAA patients, 11 had ruptured (contained or free) AAAs. The mean maximal diameter of AAAs was 6.09 ± 1.46 cm. TG2 expressions of Max were significantly increased compared with those of Control (1.7-fold increase of Control; P = .00). Compared with Control, the intensities of tissue necrosis factor-α, matrix metalloproteinase (MMP)-2, MMP-9, and tissue inhibitors of metalloproteinase-2 were significantly upregulated in Max (1.7-fold, 1.5-fold, 1.3-fold, and 1.6-fold increases of Control; P = .00, P = .004, P = .046, and P = .007, respectively). Furthermore, double immunofluorescent staining showed that colocalization of TG2/transforming growth factor-β or TG2/fibronectin was prominent in Max compared with those of Neck or Control. In addition, MMP-2 intensity was upregulated in ruptured AAAs compared with unruptured AAAs, with marginal significance (P = .078). Ex vivo experiments showed that protein expressions of tissue necrosis factor-α, MMP-2, and MMP-9 in cultured AAA tissue were decreased by recombinant human TG2 but were increased by exogenous cystamine. The TG2 expression in the maximally dilated portion of AAAs was enhanced compared with that of nondilated aorta. It is suggested that TG2 has a potential effect in stabilization of extracellular matrix by inhibition of proinflammatory cytokines and MMPs or by interaction with fibronectin and transforming growth factor-β.

Shin S ，Cho YP ，Jun H ，Park H ，Hong HN ，Kwon TW ... -  《-》

Activation of transglutaminase type 2 for aortic wall protection in a rat abdominal aortic aneurysm formation.

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. 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. 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-1β, 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). 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.

Munezane T ，Hasegawa T ，Suritala ，Tanaka A ，Okada K ，Okita Y ... -  《-》

Suppression of abdominal aortic aneurysm formation by inhibition of prolyl hydroxylase domain protein through attenuation of inflammation and extracellular matrix disruption.

Watanabe A ，Ichiki T ，Sankoda C ，Takahara Y ，Ikeda J ，Inoue E ，Tokunou T ，Kitamoto S ，Sunagawa K ... -  《-》

Intraluminal abdominal aortic aneurysm thrombus is associated with disruption of wall integrity.

An association of intraluminal thrombus (ILT) with abdominal aortic aneurysm (AAA) growth has been suggested. Previous in vitro experiments have demonstrated that aneurysm-associated thrombus may secrete proteolytic enzymes and may develop local hypoxia that might lead to the formation of tissue-damaging reactive oxygen species. In this study, we assessed the hypothesis that ventral ILT thickness is associated with markers of proteolysis and with lipid oxidation in the underlying AAA vessel wall. Ventral AAA tissue was collected from asymptomatic patients at the site of maximal diameter during open aneurysm repair. Segments were divided, one part for biochemical measurements and one for histologic analyses. We measured total cathepsin B, cathepsin S levels, and matrix metalloproteinase (MMP)-2 and MMP-9 activity. Myeloperoxidase and thiobarbituric acid reactive substances were determined as measures of lipid oxidation. Histologic segments were analyzed semiquantitatively for the presence of collagen, elastin, vascular smooth muscle cells (VSMCs), and inflammatory cells. Preoperative computed tomography angiography scans of 83 consecutive patients were analyzed. A three-dimensional reconstruction was obtained, and a center lumen line of the aorta was constructed. Ventral ILT thickness was measured in the anteroposterior direction at the level of maximal aneurysm diameter on the orthogonal slices. Ventral ILT thickness was positively correlated with aortic diameter (r=0.25; P=.02) and with MMP-2 levels (r=0.27; P=.02). No biochemical correlations were observed with MMP-9 activity or cathepsin B and S expression. No correlation between ventral ILT thickness and myeloperoxidase or thiobarbituric acid reactive substances was observed. Ventral ILT thickness was negatively correlated with VSMCs (no staining, 18.5 [interquartile range, 12.0-25.5] mm; minor, 17.6 [10.7-22.1] mm; moderate, 14.5 [4.6-21.7] mm; and heavy, 8.0 [0.0-12.3] mm, respectively; P=.01) and the amount of elastin (no staining, 18.6 [12.2-30.0] mm; minor, 16.5 [9.0-22.1] mm; moderate, 11.7 [2.5-15.3] mm; and heavy 7.7 [0.0-7.7] mm, respectively; P=.01) in the medial aortic layer. ILT thickness appeared to be associated with VSMCs apoptosis and elastin degradation and was positively associated with MMP-2 concentrations in the underlying wall. This suggests that ILT thickness affects AAA wall stability and might contribute to AAA growth and rupture. ILT thickness was not correlated with markers of lipid oxidation.

Koole D ，Zandvoort HJ ，Schoneveld A ，Vink A ，Vos JA ，van den Hoogen LL ，de Vries JP ，Pasterkamp G ，Moll FL ，van Herwaarden JA ... -  《-》

Circumferential heterogeneity in the abdominal aortic aneurysm wall composition suggests lateral sides to be more rupture prone.

The purpose of this study was to identify local differences in inflammation and tissue degradation within the circumference of the abdominal aortic aneurysm (AAA). AAAs have the potential to rupture, and it is unknown why this predominantly occurs at the posterolateral wall. Blood flow dynamics likely influence rupture location but do not explain the whole picture, suggesting that other factors inside the AAA wall have a prominent role. As part of the Aneurysm-Express study, full thickness circular biopsy specimens of AAAs from 25 patients were obtained during surgery according to a standardized protocol. Tissue from the dorsal, ventral, and lateral sides was processed for histology and protein extraction. Levels of matrix metalloproteinase (MMP)-2 and MMP-9 and various cytokines were measured. Lateral AAA sites, when compared with the ventral and dorsal segments, showed more microvessels (median [interquartile range] per mm(2), 91.8 [72.6-124.6] vs 73.9 [63.0-108.0] and 73.6 [52.7-109.5]; P = .013 and P = .005, respectively) and more adventitial inflammation (16.1% [13.5%-24.7%] vs 5.8% [2.8%-18.6%] and 6.3% [4.3%-13.5%]; P = .001 and P < .001, respectively). We observed a higher active MMP-9 (0.139 [0.059-0.339] ng/mL vs 0.060 [0.000-0.157] ng/mL and 0.045 [0.000-0.147] ng/mL; P = .001 and P = .014, respectively) and higher interleukin-8 (28.644 [11.921-62.587] pg/mL vs 16.442 [4.300-34.130] pg/mL and 18.258 [8.273-44.989] pg/mL; P < .001 and P = .010, respectively). Biopsy specimens of the ventral AAA wall do not optimally reflect the magnitude of inflammatory processes in the AAA. The lateral sides of the AAA contain more microvessels, more inflammatory cells, more active proteases, and higher cytokine levels. These results suggest that the lateral aortic regions are more rupture-prone and may better reflect the inflammatory status in histopathologic examinations.

Hurks R ，Pasterkamp G ，Vink A ，Hoefer IE ，Bots ML ，van de Pavoordt HD ，de Vries JP ，Moll FL ... -  《-》