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

Single-cell transcriptome in silico analysis reveals conserved regulatory programs in macrophages/monocytes of abdominal aortic aneurysm from multiple mouse models and human

Abdominal aortic aneurysm (AAA) is a life-threatening disease and there is currently a lack of effective treatment to prevent it rupturing. ScRNA-seq studies of AAA are still lacking. In the study, we analyzed the published AAA scRNA-seq datasets from the mouse elastase-induced model, CaCl₂ treatment model, Ang II-induced model and human by using bioinformatic approaches and in silico analysis. A total of 26 cell clusters were obtained and 11 cell types were identified from multiple mouse AAA models. Also, the proportion of Mφ/Mo increased in the AAA group and Mφ/Mo was divided into seven subtypes. There were significant differences in transcriptional regulation patterns of Mφ/Mo in different AAA models. The enrichment pathways of upregulated or downregulated genes from Mφ/Mo in the three mouse datasets were different. The actived regulons of Mφ/Mo had strong specificity and the repressed regulons showed high consistency. The co-upregulated genes as well as actived regulons and co-downregulated genes as well as repressed regulons were closely correlated and formed regulatory networks. Mφ/Mo from human AAA dataset was divided into five subtypes. The proportion of three macrophage subpopulations increased but the proportion of two monocyte subpopulations decreased. In the AAA group, the upregulated or downregulated genes of Mφ/Mo were enriched in different pathways. After further analyzing the genes in Mφ/Mo of both mouse and human scRNA-seq datasets, two genes were upregulated in the four datasets, IL-1B and THBS1. In conclusion, in silico analysis of scRNA-seq revealed that Mφ/Mo and their regulatory related genes as well as interaction networks played an important role in the pathogenesis of AAA.

A novel abdominal aortic aneurysm model produced by periarterial application of hydrochloric acid

Previous abdominal aortic aneurysm (AAA) animal modeling methodologies were either expensive or complicated. Here, we developed a novel AAA model which was simple to set up and generated minimal calcification. Twenty-four rats were divided randomly into four groups. Groups 1, 2 and 3 underwent surgery in which 15% hydrochloric acid (HCl) was applied periarterially to the abdominal aorta for 5 min, followed by sacrifice 1 week (group 1), 2 weeks (group 2), and 4 weeks (group 3) after surgery. The maximum aortic diameter (MAD) was measured at surgery and before animal sacrifice. Rats in group 4 were sham-treated. The MADs in group 1, 2 and 3 showed significant dilation compared with group 4, with a mean dilation rate of 33.8% in the first week after surgery. Histopathological examination revealed infiltration of macrophages into the adventitia, obvious apoptosis of smooth muscle cells, and rupture and collapse of the elastic fibers. Furthermore, no calcification was observed in the dilated aorta. The mRNA expression levels of inflammatory factors were at least two-fold higher in group 1 than in group 4, indicating significant inflammatory response in the progression of AAA information. In conclusion, periarterial application of 15% HCl is a convenient and reliable model to create an abdominal aortic aneurysm in rats, and the potential development mechanism may be related to the proinflammatory effects of HCl.

Transglutaminase 2 moderates the expansion of mouse abdominal aortic aneurysms

Objective

Previously published work has indicated that transcripts encoding transglutaminase 2 (TG2) increase markedly in a rat model of abdominal aortic aneurysm. This study determines whether TG2 and the related TG, factor XIII-A (FXIII-A), protect against aortic aneurysm development in mice.

Methods

C57BL/6J wild-type, Tgm2 ^-/- knockout, F13a1 ^-/- knockout, and Tgm2 ^-/- /F13a1 ^-/- double knockout mice were subjected to laparotomy and periaortic application of CaCl₂.

Results

Tgm2 ^-/- mice showed slightly greater aortic dilatation at 6 weeks after treatment when compared with wild type. However, vessels from Tgm2 ^-/- mice, but not wild-type mice, continued to dilate up to 6 months after injury and by 24 weeks, a greater number of Tgm2 ^-/- mice had developed aneurysms (16/17 vs 10/19; P = .008). Laparotomy resulted in a high death rate in F13a1 ^-/- knockout mice, more frequently from cardiac complications than from hemorrhage, but among F13a1 ^-/- mice that survived for 6 weeks after CaCl₂ treatment, abdominal aortic aneurysm diameter was unaltered relative to wild-type mice. Laparotomy resulted in a higher death rate among Tgm2 ^-/- /F13a1 ^-/- double knockout mice, owing to an increased frequency of delayed bleeding. Surprisingly, Tgm2 ^-/- /F13a1 ^-/- double knockout mice showed a trend toward decreased dilatation of the aorta 6 weeks after injury, and this finding was replicated in Tgm2 ^-/- /F13a1 ^-/- mice subjected to carotid artery injury. Levels of transcripts encoding TG2 were not increased in the aortas of injured wild-type or F13a1 ^-/- knockout mice relative to uninjured mice, although changes in the levels of other transcripts accorded with previous descriptions of the CaCl₂ aneurysm model in mice.

Conclusions

Knockout of Tgm2, but not F13a1 exacerbates aortic dilatation, suggesting that TG2 confers protection. However, levels of TG2 messenger RNA are not acutely elevated after injury. FXIII-A plays a role in preventing postoperative damage after laparotomy, confirming previous reports that it prevents distal organ damage after trauma. TG2 promotes wound healing after surgery and, in its absence, the bleeding diathesis associated with FXIII-A deficiency is further exposed.

Fast-degrading TEVGs Lead to Increased ECM Cross-linking Enzymes Expression

Tissue-engineered vascular grafts (TEVGs) require adequate extracellular matrix (ECM) to withstand arterial pressure. Tissue transglutaminase (TG2) and lysyl oxidase (LOX) are enzymes that cross-link ECM proteins and play a pivotal role in the development of vascular stiffness associated with aging. The purpose of this study is to investigate the expression of ECM cross-linking enzymes and mechanisms of scaffold degeneration leading to vascular stiffness in TEVG remodeling. Fast- and slow-degrading electrospun TEVGs were fabricated using polydioxanone (PDO) and poly(L-lactide-co-caprolactone) (PLCL) copolymer, with a PDO/PLCL ratio of 9:1 for fast-degrading and 1:1 for slow-degrading graft. These grafts were implanted in rats (n=5/group) as abdominal aortic interposition conduits. The grafts were harvested at one month to evaluate patency, mechanical properties, vascular neotissue formation and the expression of ECM cross-linking enzymes. All TEVGs were patent without any aneurysmal formation at one month. ECM area, TG2 positive area and LOX positive area were significantly greater in fast-degrading TEVGs compared to slow-degrading TEVGs, with significantly less remaining scaffold. The mechanical properties of fast-degrading TEVGs were similar to that of native aorta, as demonstrated by strain-stress curve. In conclusion, at one month, fast-degrading TEVGs had rapid and well-organized ECM with greater TG2 and LOX expression and native-like mechanical properties, compared to slow-degrading TEVGs.

Transglutaminase 2 as a novel target in chronic kidney disease - Methods, mechanisms and pharmacological inhibition

Chronic kidney disease (CKD) is a global health problem with a prevalence of 10-15%. Progressive fibrosis of the renal tissue is a main feature of CKD, but current treatment strategies are relatively unspecific and delay, but do not prevent, CKD. Exploration of novel pharmacological targets to inhibit fibrosis development are therefore important. Transglutaminase 2 (TG2) is known to be central for extracellular collagenous matrix formation, but TG2 is a multifunctional enzyme and novel research has broadened our view on its extra- and intracellular actions. TG2 exists in two conformational states with different catalytic properties as determined by substrate availability and local calcium concentrations. The open conformation of TG2 depends on calcium and has transamidase activity, central for protein modification and cross-linking of extracellular protein components, while the closed conformation is a GTPase involved in transmembrane signaling processes. We first describe different methodologies to assess TG2 activity in renal tissue and cell cultures such as biotin cadaverine incorporation. Then we systematically review animal CKD models and preliminary studies in humans (with diabetic, IgA- and chronic allograft nephropathy) to reveal the role of TG2 in renal fibrosis. Mechanisms behind TG2 activation, TG2 externalization dependent on Syndecan-4 and interactions between TG and profibrotic molecules including transforming growth factor β and the angiotensin II receptor are discussed. Pharmacological TG2 inhibition shows antifibrotic effects in CKD. However, the translation of TG2 inhibition to treat CKD in patients is a challenge as clinical information is limited, and further studies on pharmacokinetics and efficacy of the individual compounds are required.

Celiac disease patient IgA antibodies induce endothelial adhesion and cell polarization defects via extracellular transglutaminase 2

We have recently found that celiac disease patient serum-derived autoantibodies targeted against transglutaminase 2 interfere with several steps of angiogenesis, including endothelial sprouting and migration, though the mechanism involved remained to be fully characterized. This study now investigated the processes underlying the antiangiogenic effects exerted by celiac disease patient antibodies on endothelial cells, with particular regard to the adhesion, migration, and polarization signaling pathway. We observed that celiac IgA reduced endothelial cell numbers by affecting adhesion without increasing apoptosis. Endothelial cells in the presence of celiac IgA showed weak attachment, a high susceptibility to detach from fibronectin, and a disorganized extracellular matrix due to a reduction of protein cross-links. Furthermore, celiac patient IgA led to secretion of active transglutaminase 2 from endothelial cells into the culture supernatants. Additionally, cell surface transglutaminase 2 mediated integrin clustering in the presence of celiac IgA was coupled to augmented expression of β1-integrin. We also observed that celiac patient IgA-treated endothelial cells had migratory defects and a less polarized phenotype when compared to control groups, and this was associated with the RhoA signaling pathway. These biological effects mediated by celiac IgA on endothelial cells were partially influenced but not completely abolished by R281, an irreversible extracellular transglutaminase 2 enzymatic activity inhibitor. Taken together, our results imply that celiac patient IgA antibodies disturb the extracellular protein cross-linking function of transglutaminase 2, thus altering cell-extracellular matrix interactions and thereby affecting endothelial cell adhesion, polarization, and motility.

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Transglutaminase 2 accelerates vascular calcification in chronic kidney disease

BACKGROUND

Transglutaminase 2 (TGM2) is a calcium-dependent enzyme that can cross-link nearly all extracellular matrix (ECM) proteins and can facilitate cell-ECM interaction through integrins. Given the importance of the ECM in vascular calcification we tested the hypothesis that increased TGM2 activity may accelerate vascular calcification in chronic kidney disease (CKD).

METHODS

We utilized thoracic aortas and vascular smooth muscle cells (VSMC) from the Cy/+ rat, a model of progressive CKD that develops arterial calcification on a normal phosphorus diet, compared to normal rats.

RESULTS

VSMC isolated from CKD rats had increased expression and activity of TGM2 compared to cells from normal rats. The increased calcification and expression of alkaline phosphatase activity observed in VSMC from CKD rats compared to normal was inhibited in a dose-dependent manner with the TGM inhibitors cystamine and Z006. Matrix vesicles (MV) from CKD rat VSMC also had increased TGM2 expression and the calcification of MV on type I collagen could be inhibited with cystamine and accelerated by exogenous cross-linking of fibronectin or type I collagen with TGM2. Finally, the calcification of aorta rings from CKD rats in ex vivo cultures was inhibited with TGM2 inhibitor.

CONCLUSION

These data demonstrate a role of TGM2 in the pathogenesis of vascular calcification in CKD through enhancement of MV-ECM calcification.

The calcium chloride-induced rodent model of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) affects ∼5% men aged over 65 years and is an important cause of death in this population. Research into AAA pathogenesis has been fuelled by the need to identify new diagnostic biomarkers and therapeutic targets for this disease. One animal model of AAA involves peri-vascular application of calcium chloride (CaCl(2)) onto the infra-renal aorta of mice and rats to induce extracellular matrix remodelling. Twenty-three studies assessing CaCl(2)-induced AAA and six studies assessing AAA induced by a modified CaCl(2) method were identified. In the current report the preparation and pathological features of this AAA model are discussed. We also compared this animal model to human AAA. CaCl(2)-induced AAA shows the following pathological characteristics typically found in human AAA: calcification, inflammatory cell infiltration, oxidative stress, neovascularisation, elastin degradation and vascular smooth muscle cell apoptosis. A number of mechanisms involved in CaCl(2)-induced AAA have been identified which may be relevant to the pathogenesis of human AAA. Key molecules include c-Jun N-terminal kinase, peroxisome proliferator-activated receptor-γ, chemokine (C-C motif) receptor 2, group x secretory phospholipase A2 and plasminogen. CaCl(2)-induced AAA does not display aortic thrombus, atherosclerosis and rupture which are classical features of human AAA. Advantages of the CaCl(2)-induced AAA technique include (1) it can be applied to wild type mice making assessment of transgenic rodent models more straight forward and rapid; and (2) CaCl(2)-induced AAAs are usually developed in the infra-renal abdominal aorta, which is the most common location of human AAA. Currently findings obtained from the CaCl(2)-induced AAA model or other animal models of AAA have not been translated into the human situation. It is hoped that this deficiency will be corrected over the next decade with a number of clinical trials currently examining novel treatment options for AAA patients.