The potential involvement of glycocalyx disruption in abdominal aortic aneurysm pathogenesis.

BACKGROUND: Abdominal aortic aneurysm is a weakening and expansion of the abdominal aorta. Currently, there is no drug treatment to limit abdominal aortic aneurysm growth. The glycocalyx is the outermost layer of the cell surface, mainly composed of glycosaminoglycans and proteoglycans. OBJECTIVE: The aim of this review was to identify a potential relationship between glycocalyx disruption and abdominal aortic aneurysm pathogenesis. METHODS: A narrative review of relevant published research was conducted. RESULTS: Glycocalyx disruption has been reported to enhance vascular permeability, impair immune responses, dysregulate endothelial function, promote extracellular matrix remodeling and modulate mechanotransduction. All these effects are implicated in abdominal aortic aneurysm pathogenesis. Glycocalyx disruption promotes inflammation through exposure of adhesion molecules and release of proinflammatory mediators. Glycocalyx disruption affects how the endothelium responds to shear stress by reducing nitric oxide availabilty and adversely affecting the storage and release of several antioxidants, growth factors, and antithromotic proteins. These changes exacerbate oxidative stress, stimulate vascular smooth muscle cell dysfunction, and promote thrombosis, all effects implicated in abdominal aortic aneurysm pathogenesis. Deficiency of key component of the glycocalyx, such as syndecan-4, were reported to promote aneurysm formation and rupture in the angiotensin-II and calcium chloride induced mouse models of abdominal aortic aneurysm. CONCLUSION: This review provides a summary of past research which suggests that glycocalyx disruption may play a role in abdominal aortic aneurysm pathogenesis. Further research is needed to establish a causal link between glycocalyx disruption and abdominal aortic aneurysm development.

SIRT6-mediated vascular smooth muscle cells senescence participates in the pathogenesis of abdominal aortic aneurysm.

BACKGROUND AND AIMS: In this study, we carried out a clinical sample study, and in vivo and in vitro studies to evaluate the effect of SIRT6 and SIRT6-mediated vascular smooth muscle senescence on the development of abdominal aortic aneurysm (AAA). METHOD AND RESULTS: AAA specimen showed an increased P16, P21 level and a decreased SIRT6 level compared with control aorta. Time curve study of Ang II infusion AAA model showed similar P16, P21 and SIRT6 changes at the early phase of AAA induction. The in vivo overexpression of SIRT6 significantly prevented AAA formation in Ang II infusion model. The expression of P16 and P21 was significantly reduced after SIRT6 overexpression. SIRT6 overexpression also attenuated chronic inflammation and neo-angiogenesis in Ang II infusion model. The overexpression of SIRT6 could attenuate premature senescence, inflammatory response and neo-angiogenesis in human aortic smooth muscle cells (HASMC) under Ang II stimulation. CONCLUSIONS: SIRT6 overexpression could limit AAA formation via attenuation of vascular smooth muscle senescence, chronic inflammation and neovascularity.

Pathogenesis-Guided Rational Engineering of Nanotherapies for the Targeted Treatment of Abdominal Aortic Aneurysm by Inhibiting Neutrophilic Inflammation.

Abdominal aortic aneurysm (AAA) remains a fatal disease in the elderly. Currently, no drugs can be clinically used for AAA therapy. Considering the pivotal role of neutrophils in the pathogenesis of AAA, herein we propose the targeted therapy of AAA by site-specifically regulating neutrophilic inflammation. Based on a luminol-conjugated α-cyclodextrin material (LaCD), intrinsically anti-inflammatory nanoparticles (NPs) were engineered by simple nanoprecipitation, which were examined as a nanotherapy (defined as LaCD NP). After efficient accumulation in the aneurysmal aorta and localization in pathologically relevant inflammatory cells in rats with CaCl2-induced AAA, LaCD NP significantly alleviated AAA progression, as implicated by the decreased aortic expansion, suppressed elastin degradation, inhibited calcification, and improved structural integrity of the abdominal aorta. By functionalizing LaCD NP with alendronate, a calcification-targeting moiety, the in vivo aneurysmal targeting capability of LaCD NP was considerably enhanced, thereby affording significantly potentiated therapeutic outcomes in AAA rats. Mechanistically, LaCD NP can effectively inhibit neutrophil-mediated inflammatory responses in the aneurysmal aorta. Particularly, LaCD NP potently attenuated the formation of neutrophil extracellular traps (NETs), thereby suppressing NETs-mediated pro-inflammatory events and NETosis-associated negative effects responsible for AAA progression. Consequently, we demonstrated the effectiveness and underlying mechanisms of anti-NETosis nanotherapies for the targeted treatment of AAA. Our findings provide promising insights into discovering precision therapies for AAA and other inflammatory vascular diseases.

Crosstalk of platelets with macrophages and fibroblasts aggravates inflammation, aortic wall stiffening, and osteopontin release in abdominal aortic aneurysm.

AIMS: Abdominal aortic aneurysm (AAA) is a highly lethal disease with progressive dilatation of the abdominal aorta accompanied by degradation and remodelling of the vessel wall due to chronic inflammation. Platelets play an important role in cardiovascular diseases, but their role in AAA is poorly understood. METHODS AND RESULTS: The present study revealed that platelets play a crucial role in promoting AAA through modulation of inflammation and degradation of the extracellular matrix (ECM). They are responsible for the up-regulation of SPP1 (osteopontin, OPN) gene expression in macrophages and aortic tissue, which triggers inflammation and remodelling and also platelet adhesion and migration into the abdominal aortic wall and the intraluminal thrombus (ILT). Further, enhanced platelet activation and pro-coagulant activity result in elevated gene expression of various cytokines, Mmp9 and Col1a1 in macrophages and Il-6 and Mmp9 in fibroblasts. Enhanced platelet activation and pro-coagulant activity were also detected in AAA patients. Further, we detected platelets and OPN in the vessel wall and in the ILT of patients who underwent open repair of AAA. Platelet depletion in experimental murine AAA reduced inflammation and ECM remodelling, with reduced elastin fragmentation and aortic diameter expansion. Of note, OPN co-localized with platelets, suggesting a potential role of OPN for the recruitment of platelets into the ILT and the aortic wall. CONCLUSION: In conclusion, our data strongly support the potential relevance of anti-platelet therapy to reduce AAA progression and rupture in AAA patients.

Neutrophil Elastase Inhibition by Sivelestat (ONO-5046) Attenuates AngII-Induced Abdominal Aortic Aneurysms in Apolipoprotein E-Deficient Mice.

BACKGROUND: Abdominal aortic aneurysm (AAA) is an arterial disease characterized by dilatation of the aortic wall. It has been suggested that neutrophil counts and neutrophil elastase activity are associated with AAA. We investigated whether a neutrophil elastase (NE) inhibitor, sivelestat (Siv), had a protective effect against angiotensin II (AngII)-induced AAAs. METHODS: Male apolipoprotein E-deficient mice were assigned into three groups: Vehicle + saline, AngII + saline, and AngII + Siv. All mice were administered intraperitoneally with either Siv or vehicle twice daily after AngII infusion. RESULTS: In the 4-week AngII infusion study, plasma NE concentration (P = 0.041) and its activity (P = 0.011) were elevated by AngII. These increases were attenuated by Siv (concentration:P = 0.010, activity:P = 0.027). Further, plasma elastase activity was closely correlated with aortic width (R = 0.6976, P < 0.001). In the 1-week AngII infusion study, plasma and tissue elastase activity increased by AngII (plasma:P = 0.034, tissue:P < 0.001), but were reduced by Siv (plasma:P = 0.014, tissue:P = 0.024). AngII increased aortic width (P = 0.011) but was attenuated by co-administration of Siv (P = 0.022). Moreover, Siv decreased the incidence of AAAs (P = 0.009). Elastin fragmentation induced by AngII was reduced by Siv. Many inflammatory cells that were either CD68 or Gr-1 positive were observed in the AngII + saline group, whereas few inflammatory cells were accumulated in the AngII + Siv group. MMP-2 and MMP-9 were enhanced by AngII, but were reduced by Siv. In vitro, MMP-2 activity was induced by human NE (medium:P < 0.001, cells:P = 0.001), which was attenuated by co-incubation of Siv in medium (P < 0.001) and protein of human aortic smooth muscle cells (P = 0.001). CONCLUSIONS: Siv attenuated AngII-induced AAA through the inhibition of NE.

Macrophage-mediated downregulation of lncRNA Carmn in mouse abdominal aortic aneurysm.

The long noncoding RNA (lncRNA) CARMN (cardiac mesoderm enhancer associated noncoding RNA) is a highly conserved lncRNA that expresses primarily by smooth muscle cells (SMCs). Recent literature demonstrates that CARMN plays a critical role in the differentiation and maintaining of the contractile state of vascular SMCs. Because aortic SMCs show diminished contractile proteins in abdominal aortic aneurysms (AAAs), we hypothesize that the expression of CARMN is downregulated in the aortic wall affected by aneurysm. In this study, we analyzed publicly available single-cell or bulk RNA sequencing data comparing healthy and aneurysmal mouse aortic tissues. In both healthy and diseased aortas, Carmn expression was enriched in SMCs characterized by the high expression of SMC-specific contractile proteins including Myh11 and Acta2. Carmn expression levels varied among the sub-clusters of SMCs and consequently along the aortic tree. Comparing to the corresponding sham aorta, aortas from 3 distinct AAA models contained less Carmn. To validate the Carmn downregulation, we induced AAA using the Angiotensin II and CaCl2 models. In situ hybridization showed that Carmn mRNA located in the nuclei of SMCs and became downregulated within a few days following the aneurysm induction. Mechanistically, we tested whether Carmn expression is regulated by infiltrating macrophages --- the predominant inflammatory cells found in aneurysmal tissues --- by treating healthy mouse aortic SMCs with media conditioned by macrophages primed with pro-inflammatory or anti-inflammatory cytokines. PCR analysis showed that inflammatory macrophages reduced the expression of Carmn and contractile genes including Myh11 and Acta2. Taken together, our results from bioinformatic and experimental analyses demonstrate that Carmn is downregulated in different AAA models, likely by inflammatory macrophages. The negative regulation of Carmn in AAA tissues may explain at least in part the loss of SMC contractile state during the pathogenesis of this progressive degenerative disease.

A Novel Method for the Rat Model of Abdominal Aortic Aneurysm Induced by Retroperitoneal Implantation of an Osmotic Pump System With Lipopolysaccharide.

BACKGROUND: Few methods can cocurrently mimic the pathological characteristics and nature history of human abdominal aortic aneurysms (AAAs), especially for the exist of the self-healing tendency of rodents. This study tested a novel method for the AAA rat model induced by retroperitoneal implantation of an osmotic pump system with lipopolysaccharide (LPS) based on the hypothesis that chronic inflammation of perivascular adipose tissue directly influenced the development and progression of AAAs. METHODS: 20 male Sprague-Dawley rats (10-month-old) fed with the Paigen diet were randomly divided into 4 groups: the blank group ×2, the sham group ×4, the empty capsule group ×4, and the LPS capsule group ×10. The LPS capsule group received implantations of the ALZET® osmotic pump capsule with LPS (3.6 µg/day) parallel to the abdominal aorta through a retroperitoneal approach. Two weeks later, 6 rats were randomly selected from the LPS capsule group to form the anti-inflammatory group and received implantations of another osmotic pump capsule with interleukin (IL)-10 (75 ng/day) through the same approach. The changes in abdominal aortic diameter were observed by ultrasound every 2 weeks, and samples were harvested for histopathologic and immunohistochemical analysis 6 weeks later. RESULTS: Within the 6 weeks after modeling, the LPS capsule group showed sustained and significant aortic dilatation (P < 0.01), while the anti-inflammatory group showed a rapid and obvious shrinkage 2 weeks after the IL-10 osmotic pump capsule implantation (P < 0.01). The LPS capsule group presented excellent pathological mimicking of human AAAs and showed severe medial degeneration with the least elastic content among the 5 groups at the end of the sixth week (P < 0.05). Notably, the anti-inflammatory group showed perfect medial preservation with the most elastic content (P < 0.05) and the highest elastin/collagen ratio (P < 0.01) at the end of the study. Matrix metalloproteinases (MMP) 2 and 9 and toll-like receptor 2 showed strong expression in the LPS capsule group at the end of the sixth week, which was significantly higher than that in the blank group and sham group. Interestingly, the anti-inflammatory group showed a slightly higher MMP9 expression than the LPS capsule group though there was no statistical difference between them. CONCLUSIONS: This novel method for the rat AAA model induced by retroperitoneal implantation of an osmotic pump capsule with LPS can concurrently mimic the histological characteristics and natural history of human AAAs. Further studies were needed to improve the osmotic pump system.

Higher matrix stiffness promotes VSMC senescence by affecting mitochondria-ER contact sites and mitochondria/ER dysfunction.

Abdominal aortic aneurysm (AAA) is a prevalent condition characterized by the weakening and bulging of the abdominal aorta. This study aimed to investigate the impact of a stiff matrix on vascular smooth muscle cells (VSMCs) in AAA development. Bioinformatics analysis revealed that differentially expressed genes (DEGs) in VSMCs of an AAA mouse model were enriched in cellular senescence and related pathways. To simulate aging-related changes, VSMCs were cultured on stiff matrices, and compared to those on soft matrices, the VSMCs cultured on stiff matrices exhibited cellular senescence. Furthermore, the mutual distance between mitochondria and endoplasmic reticulum (ER) in VSMCs was increased, indicating altered mitochondria-endoplasmic reticulum contacts (MERCs). The observed upregulation of reactive oxygen species (ROS) levels, antioxidant gene expression, and decreased mitochondrial membrane potential suggested the presence of mitochondrial dysfunction in VSMCs cultured on a stiff matrix. Additionally, the induction of ER stress-related genes indicated ER dysfunction. These findings collectively indicated impaired functionality of both mitochondria and ER in VSMCs cultured on a stiff matrix. Moreover, our data revealed that high lipid levels exacerbated the effects of high matrix stiffness on VSMCs senescence, MERC sites, and mitochondria/ER dysfunction. Importantly, treatment with the antilipemic agent CI-981 effectively reversed these detrimental effects. These findings provide insights into the role of matrix stiffness, mitochondrial dysfunction, ER stress, and lipid metabolism in AAA development, suggesting potential therapeutic targets for intervention.

Effect of Hydralazine on Angiotensin II-Induced Abdominal Aortic Aneurysm in Apolipoprotein E-Deficient Mice.

The rupture of an abdominal aortic aneurysm (AAA) causes about 200,000 deaths worldwide each year. However, there are currently no effective drug therapies to prevent AAA formation or, when present, to decrease progression and rupture, highlighting an urgent need for more research in this field. Increased vascular inflammation and enhanced apoptosis of vascular smooth muscle cells (VSMCs) are implicated in AAA formation. Here, we investigated whether hydralazine, which has anti-inflammatory and anti-apoptotic properties, inhibited AAA formation and pathological hallmarks. In cultured VSMCs, hydralazine (100 µM) inhibited the increase in inflammatory gene expression and apoptosis induced by acrolein and hydrogen peroxide, two oxidants that may play a role in AAA pathogenesis. The anti-apoptotic effect of hydralazine was associated with a decrease in caspase 8 gene expression. In a mouse model of AAA induced by subcutaneous angiotensin II infusion (1 µg/kg body weight/min) for 28 days in apolipoprotein E-deficient mice, hydralazine treatment (24 mg/kg/day) significantly decreased AAA incidence from 80% to 20% and suprarenal aortic diameter by 32% from 2.26 mm to 1.53 mm. Hydralazine treatment also significantly increased the survival rate from 60% to 100%. In conclusion, hydralazine inhibited AAA formation and rupture in a mouse model, which was associated with its anti-inflammatory and anti-apoptotic properties.

Inhibition of smooth muscle cell death by Angiotensin 1-7 protects against abdominal aortic aneurysm.

Abdominal aortic aneurysm (AAA) represents a debilitating vascular disease characterized by aortic dilatation and wall rupture if it remains untreated. We aimed to determine the effects of Ang 1-7 in a murine model of AAA and to investigate the molecular mechanisms involved. Eight- to 10-week-old apolipoprotein E-deficient mice (ApoEKO) were infused with Ang II (1.44 mg/kg/day, s.c.) and treated with Ang 1-7 (0.576 mg/kg/day, i.p.). Echocardiographic and histological analyses showed abdominal aortic dilatation and extracellular matrix remodeling in Ang II-infused mice. Treatment with Ang 1-7 led to suppression of Ang II-induced aortic dilatation in the abdominal aorta. The immunofluorescence imaging exhibited reduced smooth muscle cell (SMC) density in the abdominal aorta. The abdominal aortic SMCs from ApoEKO mice exhibited markedly increased apoptosis in response to Ang II. Ang 1-7 attenuated cell death, as evident by increased SMC density in the aorta and reduced annexin V/propidium iodide-positive cells in flow cytometric analysis. Gene expression analysis for contractile and synthetic phenotypes of abdominal SMCs showed preservation of contractile phenotype by Ang 1-7 treatment. Molecular analyses identified increased mitochondrial fission, elevated cellular and mitochondrial reactive oxygen species (ROS) levels, and apoptosis-associated proteins, including cytochrome c, in Ang II-treated aortic SMCs. Ang 1-7 mitigated Ang II-induced mitochondrial fission, ROS generation, and levels of pro-apoptotic proteins, resulting in decreased cell death of aortic SMCs. These results highlight a critical vasculo-protective role of Ang 1-7 in a degenerative aortic disease; increased Ang 1-7 activity may provide a promising therapeutic strategy against the progression of AAA.

Role of CB1 Cannabinoid Receptors in Vascular Responses and Vascular Remodeling of the Aorta in Female Mice.

Both the endocannabinoid system (ECS) and estrogens have significant roles in cardiovascular control processes. Cannabinoid type 1 receptors (CB1Rs) mediate acute vasodilator and hypotensive effects, although their role in cardiovascular pathological conditions is still controversial. Estrogens exert cardiovascular protection in females. We aimed to study the impact of ECS on vascular functions. Experiments were performed on CB1R knockout (CB1R KO) and wild-type (WT) female mice. Plasma estrogen metabolite levels were determined. Abdominal aortas were isolated for myography and histology. Vascular effects of phenylephrine (Phe), angiotensin II, acetylcholine (Ach) and estradiol (E2) were obtained and repeated with inhibitors of nitric oxide synthase (NOS, Nω-nitro-L-arginine) and of cyclooxygenase (COX, indomethacin). Histological stainings (hematoxylin-eosin, resorcin-fuchsin) and immunostainings for endothelial NOS (eNOS), COX-2, estrogen receptors (ER-α, ER-ß) were performed. Conjugated E2 levels were higher in CB1R KO compared to WT mice. Vasorelaxation responses to Ach and E2 were increased in CB1R KO mice, attenuated by NOS-inhibition. COX-inhibition decreased Phe-contractions, while it increased Ach-relaxation in the WT group but not in the CB1R KO. Effects of indomethacin on E2-relaxation in CB1R KO became opposite to that observed in WT. Histology revealed lower intima/media thickness and COX-2 density, higher eNOS and lower ER-ß density in CB1R KO than in WT mice. CB1R KO female mice are characterized by increased vasorelaxation associated with increased utilization of endothelial NO and a decreased impact of constrictor prostanoids. Our results indicate that the absence or inhibition of CB1Rs may have beneficial vascular effects.

Association of NOTCH3 With Elastic Fiber Dispersion in the Infrarenal Abdominal Aorta of Cynomolgus Monkeys.

BACKGROUND: The regional heterogeneity of vascular components and transcriptomes is an important determinant of aortic biology. This notion has been explored in multiple mouse studies. In the present study, we examined the regional heterogeneity of aortas in nonhuman primates. METHODS: Aortic samples were harvested from the ascending, descending thoracic, suprarenal, and infrarenal regions of young control monkeys and adult monkeys with high fructose consumption for 3 years. The regional heterogeneity of aortic structure and transcriptomes was examined by histological and bulk RNA sequencing analyses, respectively. RESULTS: Immunostaining of CD31 and αSMA (alpha-smooth muscle actin) revealed that endothelial and smooth muscle cells were distributed homogeneously across the aortic regions. In contrast, elastic fibers were less abundant and dispersed in the infrarenal aorta compared with other regions and associated with collagen deposition. Bulk RNA sequencing identified a distinct transcriptome related to the Notch signaling pathway in the infrarenal aorta with significantly increased NOTCH3 mRNA compared with other regions. Immunostaining revealed that NOTCH3 protein was increased in the media of the infrarenal aorta. The abundance of medial NOTCH3 was positively correlated with the dispersion of elastic fibers. Adult cynomolgus monkeys with high fructose consumption displayed vascular wall remodeling, such as smooth muscle cell loss and elastic fiber disruption, predominantly in the infrarenal region. The correlation between NOTCH3 and elastic fiber dispersion was enhanced in these monkeys. CONCLUSIONS: Aortas of young cynomolgus monkeys display regional heterogeneity of their transcriptome and the structure of elastin and collagens. Elastic fibers in the infrarenal aorta are dispersed along with upregulation of medial NOTCH3.

Dysregulations of Key Regulators of Angiogenesis and Inflammation in Abdominal Aortic Aneurysm.

Abdominal aortic aneurysm (AAA) is a chronic vascular disease caused by localized weakening and broadening of the abdominal aorta. AAA is a clearly underdiagnosed disease and is burdened with a high mortality rate (65-85%) from AAA rupture. Studies indicate that abnormal regulation of angiogenesis and inflammation contributes to progression and onset of this disease; however, dysregulations in the molecular pathways associated with this disease are not yet fully explained. Therefore, in our study, we aimed to identify dysregulations in the key regulators of angiogenesis and inflammation in patients with AAA in peripheral blood mononuclear cells (using qPCR) and plasma samples (using ELISA). Expression levels of ANGPT1, CXCL8, PDGFA, TGFB1, VEGFB, and VEGFC and plasma levels of TGF-alpha, TGF-beta 1, VEGF-A, and VEGF-C were found to be significantly altered in the AAA group compared to the control subjects without AAA. Associations between analyzed factors and risk factors or biochemical parameters were also explored. Any of the analyzed factors was associated with the size of the aneurysm. The presented study identified dysregulations in key angiogenesis- and inflammation-related factors potentially involved in AAA formation, giving new insight into the molecular pathways involved in the development of this disease and providing candidates for biomarkers that could serve as diagnostic or therapeutic targets.

MYD88 and Proinflammatory Chemokines in Aortic Atheromatosis: Exploring Novel Statin Effects.

Atherosclerosis is driven by a diverse range of cellular and molecular processes. In the present study, we sought to better understand how statins mitigate proatherogenic inflammation. 48 male New Zealand rabbits were divided into eight groups, each including 6 animals. The control groups received normal chow for 90 and 120 days. Three groups underwent a hypercholesterolemic diet (HCD) for 30, 60, and 90 days. Another three groups underwent HCD for 3 months, followed by normal chow for one month, with or without rosuvastatin or fluvastatin. The cytokine and chemokine expressions were assessed in the samples of thoracic and abdominal aorta. Rosuvastatin significantly reduced MYD88, CCL4, CCL20, CCR2, TNF-α, IFN-ß, IL-1b, IL-2, IL-4, IL-8, and IL-10, both in the thoracic and abdominal aorta. Fluvastatin also downregulated MYD88, CCR2, IFN-ß, IFN-γ, IL-1b, IL-2, IL-4, and IL-10 in both aortic segments. Rosuvastatin curtailed the expression of CCL4, IFN-ß, IL-2, IL-4, and IL-10 more effectively than fluvastatin in both types of tissue. MYD88, TNF-α, IL-1b, and IL-8 showed a stronger downregulation with rosuvastatin compared to fluvastatin only in the thoracic aorta. The CCL20 and CCR2 levels reduced more extensively with rosuvastatin treatment only in abdominal aortic tissue. In conclusion, statin therapy can halt proatherogenic inflammation in hyperlipidemic animals. Rosuvastatin may be more effective in downregulating MYD88 in atherosclerotic thoracic aortas.

Macrophage scavenger receptor A1 antagonizes abdominal aortic aneurysm via upregulating IRG1.

AIMS: Abdominal aortic aneurysm (AAA) is a common, usually asymptomatic disease with high mortality and limited therapeutic options. Extensive extracellular matrix (ECM) fragmentation and transmural inflammation act as major pathological processes of AAA. However, the underlying regulatory mechanisms remain incompletely understood. Herein, we aimed to investigate the role of scavenger receptor A1 (SR-A1), a key pattern recognition receptor modulating macrophage activity, in pathogenesis of AAA. METHODS AND RESULTS: The AAA model was generated by administration of angiotensin II (Ang II) into apolipoprotein E knockout mice or peri-arterial application of calcium phosphate in C57BJ/6L mice. We found that SR-A1 was markedly down-regulated in the macrophages isolated from murine AAA aortas. Global or myeloid-specific ablation of SR-A1 aggravated vascular inflammation, loss of vascular smooth muscle cells and degradation of the extracellular matrix. These effects of SR-A1 deficiency on AAA development were mediated by suppressed immunoresponsive gene 1 (IRG1) and increased inflammatory response in macrophages. Mechanically, binding of SR-A1 with Lyn led to STAT3 phosphorylation and translocation into the nucleus, in which STAT3 promoted IRG1 transcription through directly binding to its promoter. Restoration of macrophage SR-A1 in SR-A1-deficient mice by bone marrow transplantation or administration of 4-octyl itaconate, the derivate of IRG1 product itaconate, could relieve murine AAA. CONCLUSION: Our study reveals a protective effect of macrophage SR-A1-STAT3-IRG1 axis against aortic aneurysm formation via inhibiting inflammation.

Celastrol Supplementation Ablates Sexual Dimorphism of Abdominal Aortic Aneurysm Formation in Mice.

BACKGROUND: Abdominal aortic aneurysms (AAAs) are permanent dilations of the abdominal aorta with 4-5 times greater prevalence in males than in females. The aim of this study is to define whether Celastrol, a pentacyclic triterpene from the root extracts of Tripterygium wilfordii, supplementation influences angiotensin II (AngII)-induced AAAs in hypercholesterolemic mice. METHODS: Age-matched (8-12 weeks old) male and female low-density lipoprotein (Ldl) receptor-deficient mice were fed a fat-enriched diet supplemented with or without Celastrol (10 mg/kg/day) for five weeks. After one week of diet feeding, mice were infused with either saline (n = 5 per group) or AngII (500 or 1000 ng/kg/min, n = 12-15 per group) for 28 days. RESULTS: Dietary supplementation of Celastrol profoundly increased AngII-induced abdominal aortic luminal dilation and external aortic width in male mice as measured by ultrasonography and ex vivo measurement, with a significant increase in incidence compared to the control group. Celastrol supplementation in female mice resulted in significantly increased AngII-induced AAA formation and incidence. In addition, Celastrol supplementation significantly increased AngII-induced aortic medial elastin degradation accompanied by significant aortic MMP9 activation in both male and female mice compared to saline and AngII controls. CONCLUSIONS: Celastrol supplementation to Ldl receptor-deficient mice ablates sexual dimorphism and promotes AngII-induced AAA formation, which is associated with increased MMP9 activation and aortic medial destruction.

Tributyrin Intake Attenuates Angiotensin II-Induced Abdominal Aortic Aneurysm in LDLR-/- Mice.

Abdominal aortic aneurysm (AAA) is a multifactorial cardiovascular disease with a high risk of death, and it occurs in the infrarenal aorta with vascular dilatation. High blood pressure acts on the aortic wall, resulting in rupture and causing life-threatening intra-abdominal hemorrhage. Vascular smooth muscle cell (VSMC) dysregulation and extracellular matrix (ECM) degradation, especially elastin breaks, contribute to structural changes in the aortic wall. The pathogenesis of AAA includes the occurrence of oxidative stress, inflammatory cell infiltration, elastic fiber fragmentation, VSMC apoptosis, and phenotypic transformation. Tributyrin (TB) is decomposed by intestinal lipase and has a function similar to that of butyrate. Whether TB has a protective effect against AAA remains uncertain. In the present study, we established an AAA murine model by angiotensin II (AngII) induction in low-density lipoprotein receptor knockout (LDLR-/-) mice and investigated the effects of orally administered TB on the AAA size, ratio of macrophage infiltration, levels of matrix metalloproteinase (MMP) expression, and epigenetic regulation. TB attenuates AngII-induced AAA size and decreases elastin fragmentation, macrophage infiltration, and MMP expression in the medial layer of the aorta and reduces the levels of SBP (systolic blood pressure, p < 0.001) and MMP-2 (p < 0.02) in the serum. TB reduces the AngII-stimulated expression levels of MMP2 (p < 0.05), MMP9 (p < 0.05), MMP12, and MMP14 in human aortic smooth muscle cells (HASMCs). Moreover, TB and valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, suppress AngII receptor type 1 (AT1R, p < 0.05) activation and increase the expression of acetyl histone H3 by HDAC activity inhibition (p < 0.05). Our findings suggest that TB exerts its protective effect by suppressing the activation of HDAC to attenuate the AngII-induced AT1R signaling cascade.

DOCK2 Deficiency Attenuates Abdominal Aortic Aneurysm Formation-Brief Report.

BACKGROUND: Abdominal aortic aneurysm (AAA) is a potentially lethal disease that lacks pharmacological treatment. Degradation of extracellular matrix proteins, especially elastin laminae, is the hallmark for AAA development. DOCK2 (dedicator of cytokinesis 2) has shown proinflammatory effects in several inflammatory diseases and acts as a novel mediator for vascular remodeling. However, the role of DOCK2 in AAA formation remains unknown. METHODS: Ang II (angiotensin II) infusion of ApoE-/- (apolipoprotein E deficient) mouse and topical elastase-induced AAA combined with DOCK2-/- (DOCK2 knockout) mouse models were used to study DOCK2 function in AAA formation/dissection. The relevance of DOCK2 to human AAA was examined using human aneurysm specimens. Elastin fragmentation in AAA lesion was observed by elastin staining. Elastin-degrading enzyme MMP (matrix metalloproteinase) activity was measured by in situ zymography. RESULTS: DOCK2 was robustly upregulated in AAA lesion of Ang II-infused ApoE-/- mice, elastase-treated mice, as well as human AAA lesions. DOCK2-/- significantly attenuated the Ang II-induced AAA formation/dissection or rupture in mice along with reduction of MCP-1 (monocyte chemoattractant protein-1) and MMP expression and activity. Accordingly, the elastin fragmentation observed in ApoE-/- mouse aorta infused with Ang II and elastase-treated aorta was significantly attenuated by DOCK2 deficiency. Moreover, DOCK2-/- decreased the prevalence and severity of aneurysm formation, as well as the elastin degradation observed in the topical elastase model. CONCLUSIONS: Our results indicate that DOCK2 is a novel regulator for AAA formation. DOCK2 regulates AAA development by promoting MCP-1 and MMP2 expression to incite vascular inflammation and elastin degradation.

CARMA3 Deficiency Aggravates Angiotensin II-Induced Abdominal Aortic Aneurysm Development Interacting Between Endoplasmic Reticulum and Mitochondria.

BACKGROUND: Abdominal aortic aneurysm (AAA) is life threatening and associated with vascular walls' chronic inflammation. However, a detailed understanding of the underlying mechanisms is yet to be elucidated. CARMA3 assembles the CARMA3-BCL10-MALT1 (CBM) complex in inflammatory diseases and is proven to mediate angiotensin II (Ang II) response to inflammatory signals by modulating DNA damage-induced cell pyroptosis. In addition, interaction between endoplasmic reticulum (ER) stress and mitochondrial damage is one of the main causes of cell pyroptosis. METHODS: Male wild type (WT) or CARMA3-/- mice aged 8 to 10 weeks were subcutaneously implanted with osmotic minipumps, delivering saline or Ang II at the rate of 1 µg/kg/min for 1, 2, and 4 weeks. RESULTS: We discovered that CARMA3 knockout promoted formation of AAA and prominently increased diameter and severity of the mice abdominal aorta infused with Ang II. Moreover, a significant increase in the excretion of inflammatory cytokines, expression levels of matrix metalloproteinases (MMPs) and cell death was found in the aneurysmal aortic wall of CARMA3-/- mice infused with Ang II compared with WT mice. Further studies found that the degree of ER stress and mitochondrial damage in the abdominal aorta of CARMA3-/- mice was more severe than that in WT mice. Mechanistically, CARMA3 deficiency exacerbates the interaction between ER stress and mitochondrial damage by activating the p38MAPK pathway, ultimately contributing to the pyroptosis of vascular smooth muscle cells (VSMCs). CONCLUSIONS: CARMA3 appears to play a key role in AAA formation and might be a potential target for therapeutic interventions of AAA.

Mouse Abdominal Aortic Aneurysm Model Induced by Periarterial Incubation of Papain.

For decades, numerous experimental animal models have been developed to examine the pathophysiologic mechanisms and potential treatments for abdominal aortic aneurysms (AAAs) in diverse species with varying chemical or surgical approaches. This study aimed to create an AAA mouse model by the periarterial incubation with papain, which can mimic human AAA with advantages such as simplicity, convenience, and high efficiency. Eighty C57BL/6J male mice were randomly assigned to 1 of the 4 groups: papain (1.0 or 2.0 mg), porcine pancreatic elastase, and phosphate-buffered solution. The aortic segment was wrapped for 20 minutes, and the diameter was measured using ultrasound preoperatively and postoperative days 7 and 14. Then, the mice were killed for histomorphometric and immunohistochemical analyses. According to ultrasound measurements and histomorphometric analyses, on postoperative day 7, 65% of mice in the 1.0-mg papain group and 60% of mice in the 2.0-mg papain group developed AAA. In both papain groups, 100% of mice developed AAA, and 65% of mice in the porcine pancreatic elastase group developed AAA on postoperative day 14. Furthermore, hematoxylin/eosin, elastin van Gieson, and Masson staining of tissues from the papain group revealed thickened media and intimal hyperplasia, collagen sediments, and elastin destruction, indicating that AAA histochemical alteration was similar to that of humans. In addition, the immunohistochemical analysis was conducted to detect infiltrated inflammatory cells, such as macrophages and leukocytes, in the aortic wall and hyperplasic adventitia. The expression of matrix metalloproteinase 2 and 9 was significantly upregulated in papain and human AAA tissues. Periarterial incubation with 1.0 mg of papain for 20 minutes can successfully create an experimental AAA model in mice for 14 days, which can be used to explore the mechanism and treatment of human AAA.