Blocking TNF-alpha attenuates aneurysm formation in a murine model

Pharmacologic Management of Aneurysms

Current management of aortic aneurysms relies exclusively on prophylactic operative repair of larger aneurysms. Great potential exists for successful medical therapy that halts or reduces aneurysm progression and hence alleviates or postpones the need for surgical repair. Preclinical studies in the context of abdominal aortic aneurysm identified hundreds of candidate strategies for stabilization, and data from preoperative clinical intervention studies show that interventions in the pathways of the activated inflammatory and proteolytic cascades in enlarging abdominal aortic aneurysm are feasible. Similarly, the concept of pharmaceutical aorta stabilization in Marfan syndrome is supported by a wealth of promising studies in the murine models of Marfan syndrome-related aortapathy. Although some clinical studies report successful medical stabilization of growing aortic aneurysms and aortic root stabilization in Marfan syndrome, these claims are not consistently confirmed in larger and controlled studies. Consequently, no medical therapy can be recommended for the stabilization of aortic aneurysms. The discrepancy between preclinical successes and clinical trial failures implies shortcomings in the available models of aneurysm disease and perhaps incomplete understanding of the pathological processes involved in later stages of aortic aneurysm progression. Preclinical models more reflective of human pathophysiology, identification of biomarkers to predict severity of disease progression, and improved design of clinical trials may more rapidly advance the opportunities in this important field.

Acute Inflammatory Responses to Exercise in Patients with Abdominal Aortic Aneurysm

PURPOSE

Inflammation and extracellular matrix degeneration contribute to abdominal aortic aneurysm (AAA) development. We aimed to assess the effect of exercise intensity on circulating biomarkers of inflammation and extracellular matrix degeneration in patients with AAA and healthy older adults.

METHODS

Twenty patients with AAA (74 ± 6 yr) and 20 healthy males (72 ± 5 yr) completed moderate-intensity cycling at 40% peak power output, higher-intensity intervals at 70% peak power output, and control (rest) on separate days. Circulating matrix metalloproteinase-9 (MMP-9), transforming growth factor beta 1, interleukin-6 (IL-6), IL-10, and tumor necrosis factor alpha (TNF-α) were analyzed at rest and 0 to 90 min postexercise.

RESULTS

Biomarkers at baseline were similar between groups. IL-6 responses to exercise were similar between groups, with a greater increase in ΔIL-6 after moderate-intensity compared with higher-intensity exercise (P < 0.001). Delta MMP-9 showed a 118-ng·mL (95% confidence interval = 23 to 214, P = 0.02) greater increase immediately after higher-intensity exercise compared with changes in control in both groups. Delta MMP-9 then decreased by 114 ng·mL (18 to 211, P = 0.02) 90 min after higher-intensity exercise compared with the changes in control. Delta TNF-α was not different between protocols in healthy adults. In patients with AAA, delta TNF-α showed a greater decrease after higher-intensity compared with moderate-intensity exercise (-6.1 pg·mL, -8.5 to -3.6, P < 0.001) and control (-4.9 pg·mL, -7.4 to -2.4, P < 0.001). IL-10 and transforming growth factor beta 1 did not change in either group.

CONCLUSIONS

These findings suggest that a bout of higher-intensity exercise elicits a greater anti-inflammatory response compared with moderate-intensity exercise, which may be further augmented in patients with AAA. Exercise-induced reductions in biomarkers associated with AAA progression may represent a protective effect of exercise in patients with AAA.

Characterization of CD4+ T Cell Subsets in Patients with Abdominal Aortic Aneurysms

BACKGROUND

The mediators produced by CD4+ T lymphocytes are involved in the pathogenesis of aneurysmal lesions in abdominal aortic aneurysm (AAA) patients. The aim of this study was to identify and characterize the CD4+ T cell subsets involved in human AAA.

METHODS

The CD4+ T cell subsets in 30 human aneurysmal lesions were determined using flow cytometry (FC) and immunohistochemistry (IHC). The peripheral blood mononuclear cells (PBMCs) from patients with AAA were also analyzed by FC and compared with control subjects.

RESULTS

Human aneurysmal lesions contained IFN-γ, IL-12p35, IL-4, IL-23p19, IL-17R, and IL-22 positive cells. PBMCs from AAA patients had higher expression levels of IFN-γ, TNF-α, IL-4, and IL-22 when compared to controls.

CONCLUSIONS

Our results show the presence of TH1, TH2, TH17, and TH22 subsets in aneurysmal lesions of AAA patients and suggest that these cells may be mainly activated in situ, where they can induce tissue degradation and contribute to the pathogenesis of AAA.

Pathophisiology of abdominal aortic aneurysm: biomarkers and novel therapeutic targets

Abdominal aortic aneurysm (AAA) is a vascular pathology with a high rate of morbidity and mortality and a prevalence that, in men over 65 years, can reach around 8%. In this disease, usually asymptomatic, there is a progressive dilatation of the vascular wall that can lead to its rupture, a fatal phenomenon in more than 80% of cases. The treatment of patients with asymptomatic aneurysms is limited to periodic monitoring with imaging tests, control of cardiovascular risk factors and treatment with statins and antiplatelet therapy. There is no effective pharmacological treatment capable of limiting AAA progression or avoiding their rupture. At present, the aortic diameter is the only marker of risk of rupture and determines the need for surgical repair when it reaches values greater than 5.5cm. This review addresses the main aspects related to epidemiology, risk factors, diagnosis and clinical management of AAA, exposes the difficulties to have good biomarkers of this pathology and describes the strategies for the identification of new therapeutic targets and biomarkers in AAA.

Tamsulosin attenuates abdominal aortic aneurysm growth

BACKGROUND

Tamsulosin, an α_1A-adrenergic receptor inhibitor, is prescribed to treat benign prostatic hyperplasia in men >60 years of age, the same demographic most susceptible to abdominal aortic aneurysm. The goal of this study was to investigate the effect of tamsulosin on abdominal aortic aneurysm pathogenesis.

METHODS

Abdominal aortic aneurysms were induced in WT C57BL/6 male mice (n = 9-18/group), using an established topical elastase abdominal aortic aneurysm model. Osmotic pumps were implanted in mice 5 days before operation to create the model, administering either low dose (0.125 µg/day tamsulosin), high dose (0.250µg/day tamsulosin), or vehicle treatments with and without topical application of elastase. Blood pressures were measured preoperatively and on postoperative days 0, 3, 7, and 14. On postoperative day 14, aortic diameter was measured before harvest. Sample aortas were prepared for histology and cytokine analysis.

RESULTS

Measurements of systolic blood pressure did not differ between groups. Mice treated with the low dose of tamsulosin and with the high dose of tamsulosin showed decreased aortic diameter compared with vehicle-treated control (93% ± 24 versus 94% ± 30 versus 132% ± 24, respectively; P = .0003, P = .0003). Cytokine analysis demonstrated downregulation of pro-inflammatory cytokines in both treatment groups compared with the control (P < .05). Histology exhibited preservation of elastin in both low- and high-dose tamsulosin-treated groups (P = .0041 and P = .0018, respectively).

CONCLUSION

Tamsulosin attenuates abdominal aortic aneurysm formation with increased preservation of elastin and decreased production of pro-inflammatory cytokines. Further studies are necessary to elucidate the mechanism by which tamsulosin attenuates abdominal aortic aneurysm pathogenesis.

PPARγ agonist rosiglitazone alters the temporal and spatial distribution of inflammation during abdominal aortic aneurysm formation

Research into inflammation during abdominal aortic aneurysm (AAA) formation remains inconclusive. The present study aimed to demonstrate the temporal and spatial distribution of inflammatory cytokines, and to confirm the effect of peroxisome proliferator‑activated receptor γ (PPARγ) on the incidence of AAA formation and the distribution of inflammation in the disease process. Male apolipoprotein E‑/‑ mice were randomly divided into eight groups: Angiotensin II (Ang‑II)‑only 7, 14, 21, 28 and 42 days groups, Ang‑II with rosiglitazone (RGZ) 28 and 42 days groups, and the saline control 42 days group. The early stage was defined as between 7 and 21 days, and the late stage as between 28 and 42 days. Incidences of early rupture and late rupture, aneurysm formation and the maximum diameters of the aorta were recorded. Suprarenal abdominal aortic tissues were collected for histological analysis, and western blotting was performed to reveal the distribution of inflammation. Treatment with Ang‑II caused a significant dilation of the aorta in the late stage; however, this was not observed in the early stage. RGZ reduced the maximum diameters in the late stage. With the pathological process alterations, the inflammatory type shifted. Regarding temporal distribution, the tumor necrosis factor (TNF)‑α expression level was increased over time, and the interleukin (IL)‑10 expression level significantly decreased. When considering the spatial distribution, TNF‑α was expressed dominantly in the aneurysmal body and IL‑10 was dominant in the aneurysmal neck in the late stage. The PPARγ agonist RGZ may reduce the expression of TNF‑α in the late stage and increase the expression level of IL‑10, maintaining the TNF‑α or IL‑10 expression levels at the same levels as in the early stage. Aortic inflammation during AAA formation is dynamic. Protective anti‑inflammatory cytokines are upregulated in the early 'compensatory stage'; however, pro‑inflammatory cytokines are dominant in the late 'decompensatory stage'. PPARγ is likely to continue to upregulate the expression of anti‑inflammatory cytokines, extend the 'compensatory stage', and decelerate the process of AAA development and rupture.

Glucagon-Like peptide-1: A new therapeutic target to treat abdominal aortic aneurysm?

Recent antidiabetic drugs including GLP-1 receptor agonists and DPP-IV inhibitors have demonstrated protective effects in several cardiovascular diseases but their effect in abdominal aortic aneurysm (AAA) is far less known. AAA can be associated with extremely high rates of mortality and pharmacological treatments are still lacking underlining the real need to identify new therapeutic targets. The aim of this review was to summarize current knowledge on the role of GLP-1 pathway in AAA. A systematic literature review was performed and 6 relevant studies (2 clinical and 4 experimental) were included. Experimental studies demonstrated a protective effect of both GLP-1 receptor agonists and DPP-IV inhibitors through targeting the main pathophysiological mechanisms underlying AAA formation. The effects of these drugs in human AAA are still poorly known. In the limelight of clinical and experimental studies, we discuss current limits and future directions.

Cell-Specific Functions of ADAM17 Regulate the Progression of Thoracic Aortic Aneurysm

RATIONALE

ADAM17 (a disintegrin and metalloproteinase-17) is a membrane-bound enzyme that regulates bioavailability of multiple transmembrane proteins by proteolytic processing. ADAM17 has been linked to several pathologies, but its role in thoracic aortic aneurysm (TAA) has not been determined.

OBJECTIVE

The objective of this study was to explore the cell-specific functions of vascular ADAM17 in the pathogenesis and progression of TAA.

METHODS AND RESULTS

In aneurysmal thoracic aorta from patients, ADAM17 was increased in tunica media and intima. To determine the function of ADAM17 in the major cells types within these regions, we generated mice lacking ADAM17 in smooth muscle cells (SMC; Adam17^f/f/Sm22^Cre/+ ) or endothelial cells (Adam17^f/f/Tie2^Cre/+ ). ADAM17 deficiency in either cell type was sufficient to suppress TAA dilation markedly and adverse remodeling in males and females (in vivo) although through different mechanisms. ADAM17 deficiency in SMCs prevented the contractile-to-synthetic phenotypic switching in these cells after TAA induction, preventing perivascular fibrosis, inflammation, and adverse aortic remodeling. Loss of ADAM17 in endothelial cells protected the integrity of the intimal barrier by preserving the adherens junction (vascular endothelial-cadherin) and tight junctions (junctional adhesion molecule-A and claudin). In vitro studies on primary mouse thoracic SMCs and human primary aortic SMCs and endothelial cells (±ADAM17 small interfering RNA) confirmed the cell-specific functions of ADAM17 and demonstrated the cross-species validity of these findings. To determine the impact of ADAM17 inhibition in treating TAA, we used an ADAM17-selective inhibitor (PF-548) before or 3 days after TAA induction. In both cases, ADAM17 inhibition prevented progression of aneurysmal growth.

CONCLUSIONS

We have identified distinct cell-specific functions of ADAM17 in TAA progression, promoting pathological remodeling of SMC and impairing integrity of the intimal endothelial cell barrier. The dual impact of ADAM17 deficiency (or inhibition) in protecting 2 major cell types in the aortic wall highlights the unique position of this proteinase as a critical treatment target for TAA.

CD40L Deficiency Protects Against Aneurysm Formation

OBJECTIVE

The mechanisms underlying formation of arterial aneurysms remain incompletely understood. Because inflammation is a common feature during the progressive degeneration of the aortic wall, we studied the role of the costimulatory molecule CD40L, a major driver of inflammation, in aneurysm formation.

APPROACH AND RESULTS

Transcriptomics data obtained from human abdominal aortic aneurysms and normal aortas revealed increased abundance of both CD40L and CD40 in media of thrombus-free and thrombus-covered human abdominal aortic aneurysms samples. To further unravel the role of CD40L in aneurysm formation, apolipoprotein E-deficient (Apoe^-/-) and Cd40l^-/-Apoe^-/- mice were infused with angiotensin II for 7 and 28 days. Only a minority of Cd40l^-/-Apoe^-/- mice (33% and 17%) developed (dissecting) aneurysms compared with 75% and 67% of Apoe^-/- littermates after 7 and 28 days of infusion, respectively. Total vessel area of the aorta at the suprarenal level was 52% smaller in angiotensin II-infused Cd40l^-/-Apoe^-/- mice compared with that in angiotensin II-infused Apoe^-/- mice. Chimeric Apoe^-/- mice repopulated with Cd40l^-/-Apoe^-/- bone marrow afforded a similar protection against dissecting aneurysm formation. Moreover, lack of CD40L protected mice from fatal aneurysm rupture. T helper cell and macrophage accumulation in aneurysmal tissue was reduced in Cd40l^-/-Apoe^-/- mice with a concomitant decrease in expression of proinflammatory chemo- and cytokines. In addition, aneurysms of Cd40l^-/-Apoe^-/- mice displayed reduced abundance of matrix metalloproteinase-13 and an increase in tissue inhibitor of metalloproteinase-3 while activity of matrix metalloproteinase-2 and matrix metalloproteinase-9 was diminished.

CONCLUSIONS

Deficiency of (hematopoietic) CD40L protects against dissecting aneurysm formation and reduces the incidence of fatal rupture. This is associated with a decreased accumulation and activation of inflammatory cells and a dampened protease activity in the arterial wall.

Necroptosis in cardiovascular disease - a new therapeutic target

Contrary to the apoptosis-necrosis binary view of cell death, recent experimental evidence demonstrates that several forms of necrosis, represented by necroptosis, are regulated or programmed in nature. Multiple death stimuli known to be associated with cardiovascular disease are capable of causing either apoptosis or necroptosis. Whether a cell dies from apoptosis or necroptosis has distinct consequences on inflammation. It is known that apoptosis, a non-lytic form of death mediated by the caspase family of proteases, does not generally evoke an immune response. Necroptosis, on the other hand, is a lytic form of cell death. Due to the rapid loss of plasma membrane integrity, cells dying from necroptosis release proinflammatory intracellular contents and subsequently cause inflammation. Our review delineates various genetic and biochemical evidence that demonstrates a compelling role of necroptosis in the pathogenesis and/or progression of cardiovascular disease including myocardial infarction, atherosclerosis, and aortic aneurysm. Through recent studies of necroptosis in cardiovascular diseases, we attempt to discuss the role of necroptosis in vascular inflammation as well as the potential of necroptosis inhibitors in future clinical management of cardiovascular events. Inhibiting necroptosis in the vasculature has an overall protective role and necroptosis may represent a new therapeutic target to prevent the development and progression of cardiovascular diseases.

CD1d deficiency inhibits the development of abdominal aortic aneurysms in LDL receptor deficient mice

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta leading to serious complications and mostly to death. AAA development is associated with an accumulation of inflammatory cells in the aorta including NKT cells. An important factor in promoting the recruitment of these inflammatory cells into tissues and thereby contributing to the development of AAA is angiotensin II (Ang II). We demonstrate that a deficiency in CD1d dependent NKT cells under hyperlipidemic conditions (LDLr^-/-CD1d^-/- mice) results in a strong decline in the severity of angiotensin II induced aneurysm formation when compared with LDLr^-/- mice. In addition, we show that Ang II amplifies the activation of NKT cells both in vivo and in vitro. We also provide evidence that type I NKT cells contribute to AAA development by inducing the expression of matrix degrading enzymes in vSMCs and macrophages, and by cytokine dependently decreasing vSMC viability. Altogether, these data prove that CD1d-dependent NKT cells contribute to AAA development in the Ang II-mediated aneurysm model by enhancing aortic degradation, establishing that therapeutic applications which target NKT cells can be a successful way to prevent AAA development.

IL-1β (Interleukin-1β) and TNF-α (Tumor Necrosis Factor-α) Impact Abdominal Aortic Aneurysm Formation by Differential Effects on Macrophage Polarization

OBJECTIVE

Abdominal aortic aneurysms are inflammatory in nature and are associated with some risk factors that also lead to atherosclerotic occlusive disease, most notably smoking. The purpose of our study was to identify differential cytokine expression in patients with abdominal aortic aneurysm and those with atherosclerotic occlusive disease. Based on this analysis, we further explored and compared the mechanism of action of IL (interleukin)-1β versus TNF-α (tumor necrosis factor-α) in abdominal aortic aneurysm formation.

APPROACH AND RESULTS

IL-1β was differentially expressed in human plasma with lower levels detected in patients with abdominal aortic aneurysm compared with matched atherosclerotic controls. We further explored its mechanism of action using a murine model and cell culture. Genetic deletion of IL-1β and IL-1R did not inhibit aneurysm formation or decrease MMP (matrix metalloproteinase) expression. The effects of IL-1β deletion on M1 macrophage polarization were compared with another proinflammatory cytokine, TNF-α. Bone marrow-derived macrophages from IL-1β^-/- and TNF-α^-/- mice were polarized to an M1 phenotype. TNF-α deletion, but not IL-1β deletion, inhibited M1 macrophage polarization. Infusion of M1 polarized TNF-α^-/- macrophages inhibited aortic diameter growth; no inhibitory effect was seen in mice infused with M1 polarized IL-1β^-/- macrophages.

CONCLUSIONS

Although IL-1β is a proinflammatory cytokine, its effects on aneurysm formation and macrophage polarization differ from TNF-α. The differential effects of IL-1β and TNF-α inhibition are related to M1/M2 macrophage polarization and this may account for the differences in clinical efficacy of IL-1β and TNF-α antibody therapies in management of inflammatory diseases.

Premature aortic smooth muscle cell differentiation contributes to matrix dysregulation in Marfan Syndrome

Thoracic aortic aneurysm and dissection are life-threatening complications of Marfan syndrome (MFS). Studies of human and mouse aortic samples from late stage MFS demonstrate increased TGF-β activation/signaling and diffuse matrix changes. However, the role of the aortic smooth muscle cell (SMC) phenotype in early aneurysm formation in MFS has yet to be fully elucidated. As our objective, we investigated whether an altered aortic SMC phenotype plays a role in aneurysm formation in MFS. We describe previously unrecognized concordant findings in the aortas of a murine model of MFS, mgR, during a critical and dynamic phase of early development. Using Western blot, gelatin zymography, and histological analysis, we demonstrated that at postnatal day (PD) 7, before aortic TGF-β levels are increased, there is elastic fiber fragmentation/disorganization and increased levels of MMP-2 and MMP-9. Compared to wild type (WT) littermates, aortic SMCs in mgR mice express higher levels of contractile proteins suggesting a switch to a more mature contractile phenotype. In addition, tropoelastin levels are decreased in mgR mice, a finding consistent with a premature switch to a contractile phenotype. Proliferation assays indicate a decrease in the proliferation rate of mgR cultured SMCs compared to WT SMCs. KLF4, a regulator of smooth muscle cell phenotype, was decreased in aortic tissue of mgR mice. Finally, overexpression of KLF4 partially reversed this phenotypic change in the Marfan SMCs. This study indicates that an early phenotypic switch appears to be associated with initiation of important metabolic changes in SMCs that contribute to subsequent pathology in MFS.

Association of TNF-α-3959T/C Gene Polymorphisms in the Chinese Population with Intracranial Aneurysms

Recent studies have demonstrated that cytokines play an important role in the pathogenesis of intracranial aneurysm (IA). Tumor necrosis factor-α (TNF-α) is an important proinflammatory cytokine, which was shown to influence the development of IA, but there is no research data from China. Hence, the purpose of this study was to explore the relationship between TNF-α polymorphisms and IA in China. The association of genetic variants of TNF-α gene expression was investigated in a Chinese population with IA. The TNF-α-3959T>C(rs1799964), 4127C>A(rs1800630), 4133C>T(rs1799724), 4184C>T(rs4248158), and 4752G>A(rs361525) gene polymorphisms in 192 IA cases and 112 controls were analyzed using polymerase chain reaction (PCR). Differences in genotype and allele frequencies between patients and controls were tested. There were no significant differences in 4127C>A (p = 0.072), 4133C>T (p = 0.373), 4184C>T (p = 0.749), and 4752G>A (p = 0.184) genotype frequencies between the IA group and the control group. But this case-control association study revealed that TNF-α-3959T>C (p < 0.001) was significantly associated with increased risk of IA. These results suggested that a novel TNF-α locus was found to be closely correlated with the occurrence of IA in Chinese.

The role of IL-6 in pathogenesis of abdominal aortic aneurysm in mice

Although the pathogenesis of abdominal aortic aneurysm (AAA) remains unclear, evidence is accumulating to support a central role for inflammation. Inflammatory responses are coordinated by various soluble cytokines of which IL-6 is one of the major proinflammatory cytokines. In this study we examined the role of IL-6 in the pathogenesis of experimental AAA induced by a periaortic exposure to CaCl2 in mice. We now report that the administration of MR16-1, a neutralizing monoclonal antibody specific for the mouse IL-6 receptor, mildly suppressed the development of AAA. The inhibition of IL-6 signaling provoked by MR16-1 also resulted in a suppression of Stat3 activity. Conversely, no significant changes in either NFκB activity, Jnk activity or the expression of matrix metalloproteinases (Mmp) -2 and -9 were identified. Transcriptome analyses revealed that MR16-1-sensitive genes encode chemokines and their receptors, as well as factors that regulate vascular permeability and cell migration. Imaging cytometric analyses then consistently demonstrated reduced cellular infiltration for MR16-1-treated AAA. These results suggest that IL-6 plays an important but limited role in AAA pathogenesis, and primarily regulates cell migration and infiltration. These data would also suggest that IL-6 activity may play an important role in scenarios of continuous cellular infiltration, possibly including human AAA.

Vascular ADAM17 (a Disintegrin and Metalloproteinase Domain 17) Is Required for Angiotensin II/β-Aminopropionitrile-Induced Abdominal Aortic Aneurysm

Angiotensin II (AngII)-activated epidermal growth factor receptor has been implicated in abdominal aortic aneurysm (AAA) development. In vascular smooth muscle cells (VSMCs), AngII activates epidermal growth factor receptor via a metalloproteinase, ADAM17 (a disintegrin and metalloproteinase domain 17). We hypothesized that AngII-dependent AAA development would be prevented in mice lacking ADAM17 in VSMCs. To test this concept, control and VSMC ADAM17-deficient mice were cotreated with AngII and a lysyl oxidase inhibitor, β-aminopropionitrile, to induce AAA. We found that 52.4% of control mice did not survive because of aortic rupture. All other surviving control mice developed AAA and demonstrated enhanced expression of ADAM17 in the AAA lesions. In contrast, all AngII and β-aminopropionitrile-treated VSMC ADAM17-deficient mice survived and showed reduction in external/internal diameters (51%/28%, respectively). VSMC ADAM17 deficiency was associated with lack of epidermal growth factor receptor activation, interleukin-6 induction, endoplasmic reticulum/oxidative stress, and matrix deposition in the abdominal aorta of treated mice. However, both VSMC ADAM17-deficient and control mice treated with AngII and β-aminopropionitrile developed comparable levels of hypertension. Treatment of C57Bl/6 mice with an ADAM17 inhibitory antibody but not with control IgG also prevented AAA development. In conclusion, VSMC ADAM17 silencing or systemic ADAM17 inhibition seems to protect mice from AAA formation. The mechanism seems to involve suppression of epidermal growth factor receptor activation.

Inhibition of the mTOR pathway in abdominal aortic aneurysm: implications of smooth muscle cell contractile phenotype, inflammation, and aneurysm expansion

The development of effective pharmacological treatment of abdominal aortic aneurysm (AAA) potentially offers great benefit to patients with preaneurysmal aortic dilation by slowing the expansion of aneurysms and reducing the need for surgery. To date, therapeutic targets for slowing aortic dilation have had low efficacy. Thus, in this study, we aim to elucidate possible mechanisms driving aneurysm progression to identify potential targets for pharmacological intervention. We demonstrate that mechanistic target of rapamycin (mTOR) signaling is overactivated in aortic smooth muscle cells (SMCs), which contributes to murine AAA. Rapamycin, a typical mTOR pathway inhibitor, dramatically limits the expansion of the abdominal aorta following intraluminal elastase perfusion. Furthermore, reduction of aortic diameter is achieved by inhibition of the mTOR pathway, which preserves and/or restores the contractile phenotype of SMCs and downregulates macrophage infiltration, matrix metalloproteinase expression, and inflammatory cytokine production. Taken together, these results highlight the important role of the mTOR cascade in aneurysm progression and the potential application of rapamycin as a therapeutic candidate for AAA.

NEW & NOTEWORTHY This study provides novel observations that mechanistic target of rapamycin (mTOR) signaling is overactivated in aortic smooth muscle cells and contributes to mouse abdominal aortic aneurysm (AAA) and that rapamycin protects against aneurysm development. Our data highlight the importance of preservation and/or restoration of the smooth muscle cell contractile phenotype and reduction of inflammation by mTOR inhibition in AAA.

Monocytes and macrophages in abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is a life-threatening disease associated with high morbidity, and high mortality in the event of aortic rupture. Major advances in open surgical and endovascular repair of AAA have been achieved during the past 2 decades. However, drug-based therapies are still lacking, highlighting a real need for better understanding of the molecular and cellular mechanisms involved in AAA formation and progression. The main pathological features of AAA include extracellular matrix remodelling associated with degeneration and loss of vascular smooth muscle cells and accumulation and activation of inflammatory cells. The inflammatory process has a crucial role in AAA and substantially influences many determinants of aortic wall remodelling. In this Review, we focus specifically on the involvement of monocytes and macrophages, summarizing current knowledge on the roles, origin, and functions of these cells in AAA development and its complications. Furthermore, we show and propose that distinct monocyte and macrophage subsets have critical and differential roles in initiation, progression, and healing of the aneurysmal process. On the basis of experimental and clinical studies, we review potential translational applications to detect, assess, and image macrophage subsets in AAA, and discuss the relevance of these applications for clinical practice.

Abnormal kynurenine pathway of tryptophan catabolism in cardiovascular diseases

Kynurenine pathway (KP) is the primary path of tryptophan (Trp) catabolism in most mammalian cells. The KP generates several bioactive catabolites, such as kynurenine (Kyn), kynurenic acid (KA), 3-hydroxykynurenine (3-HK), xanthurenic acid (XA), and 3-hydroxyanthranilic acid (3-HAA). Increased catabolite concentrations in serum are associated with several cardiovascular diseases (CVD), including heart disease, atherosclerosis, and endothelial dysfunction, as well as their risk factors, including hypertension, diabetes, obesity, and aging. The first catabolic step in KP is primarily controlled by indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO). Following this first step, the KP has two major branches, one branch is mediated by kynurenine 3-monooxygenase (KMO) and kynureninase (KYNU) and is responsible for the formation of 3-HK, 3-HAA, and quinolinic acid (QA); and another branch is controlled by kynurenine amino-transferase (KAT), which generates KA. Uncontrolled Trp catabolism has been demonstrated in distinct CVD, thus, understanding the underlying mechanisms by which regulates KP enzyme expression and activity is paramount. This review highlights the recent advances on the effect of KP enzyme expression and activity in different tissues on the pathological mechanisms of specific CVD, KP is an inflammatory sensor and modulator in the cardiovascular system, and KP catabolites act as the potential biomarkers for CVD initiation and progression. Moreover, the biochemical features of critical KP enzymes and principles of enzyme inhibitor development are briefly summarized, as well as the therapeutic potential of KP enzyme inhibitors against CVD is briefly discussed.

Translational Relevance and Recent Advances of Animal Models of Abdominal Aortic Aneurysm

Human abdominal aortic aneurysm (AAA) pathophysiology is not yet completely understood. In conductance arteries, the insoluble extracellular matrix, synthesized by vascular smooth muscle cells, assumes the function of withstanding the intraluminal arterial blood pressure. Progressive loss of this function through extracellular matrix proteolysis is a main feature of AAAs. As most patients are now treated via endovascular approaches, surgical AAA specimens have become rare. Animal models provide valuable complementary insights into AAA pathophysiology. Current experimental AAA models involve induction of intraluminal dilation (nondissecting AAAs) or a contained intramural rupture (dissecting models). Although the ideal model should reproduce the histological characteristics and natural history of the human disease, none of the currently available animal models perfectly do so. Experimental models try to represent the main pathophysiological determinants of AAAs: genetic or acquired defects in extracellular matrix, loss of vascular smooth muscle cells, and innate or adaptive immune response. Nevertheless, most models are characterized by aneurysmal stabilization and healing after a few weeks because of cessation of the initial stimulus. Recent studies have focused on ways to optimize existing models to allow continuous aneurysmal growth. This review aims to discuss the relevance and recent advances of current animal AAA models.

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A mathematical model of aortic aneurysm formation

Abdominal aortic aneurysm (AAA) is a localized enlargement of the abdominal aorta, such that the diameter exceeds 3 cm. The natural history of AAA is progressive growth leading to rupture, an event that carries up to 90% risk of mortality. Hence there is a need to predict the growth of the diameter of the aorta based on the diameter of a patient’s aneurysm at initial screening and aided by non-invasive biomarkers. IL-6 is overexpressed in AAA and was suggested as a prognostic marker for the risk in AAA. The present paper develops a mathematical model which relates the growth of the abdominal aorta to the serum concentration of IL-6. Given the initial diameter of the aorta and the serum concentration of IL-6, the model predicts the growth of the diameter at subsequent times. Such a prediction can provide guidance to how closely the patient’s abdominal aorta should be monitored. The mathematical model is represented by a system of partial differential equations taking place in the aortic wall, where the media is assumed to have the constituency of an hyperelastic material.

Cyanidin-3-O-glucoside Induces Apoptosis and Inhibits Migration of Tumor Necrosis Factor-α-Treated Rat Aortic Smooth Muscle Cells

Blueberries are rich in anthocyanins (ACNs), which have recently been noted to protect against atherosclerosis development in mice. Cyanidin-3-O-glucoside (C3G), a member of blueberry ACN family, can inhibit the tumor necrosis factor-α (TNF-α)-induced proliferation of vascular smooth muscle cells (VSMCs). However, the effects of C3G on VSMC apoptosis and migration remain unclear. This study was thus conducted to examine whether and how C3G affected the apoptosis and migration of rat aortic smooth muscle cells (RASMCs) challenged by TNF-α. Primary cultured RASMCs were pretreated with C3G (25, 50 or 100 μM) for 2 h and then stimulated with TNF-α (10 ng/ml) for additional 24 h. Our results illustrated that C3G pretreatment induced significant apoptosis in TNF-α-stimulated RASMCs in a dose-dependent way, which was accompanied with increased cleaved caspase-3, caspase-9 and Bax and decreased Bcl-2. Moreover, RASMC migration was enhanced by TNF-α, but markedly suppressed by C3G pretreatment. The expressions and activities of matrix metalloproteinase-2 (MMP-2) and MMP-9 were inhibited by C3G. In addition, TNF-α-enhanced nuclear translocation of nuclear factor kappa B (NF-κB) subunit p65 and phosphorylation of NF-κB inhibitor α (IκBα) in RASMCs were attenuated by C3G. In summary, our study reveals that C3G can induce significant apoptosis in TNF-α-treated RASMCs and markedly inhibit their migration.

Inhibition of Receptor-Interacting Protein Kinase 1 with Necrostatin-1s ameliorates disease progression in elastase-induced mouse abdominal aortic aneurysm model

Abdominal aortic aneurysm (AAA) is a common aortic disease with a progressive nature. There is no approved pharmacological treatment to effectively slow aneurysm growth or prevent rupture. Necroptosis is a form of programmed necrosis that is regulated by receptor-interacting protein kinases (RIPs). We have recently demonstrated that the lack of RIP3 in mice prevented aneurysm formation. The goal of the current study is to test whether perturbing necroptosis affects progression of existing aneurysm using the RIP1 inhibitors Necrostatin-1 (Nec-1) and an optimized form of Nec-1, 7-Cl-O-Nec-1 (Nec-1s). Seven days after aneurysm induction by elastase perfusion, mice were randomly administered DMSO, Nec-1 (3.2 mg/kg/day) and Nec-1s (1.6 mg/kg/day) via intraperitoneal injection. Upon sacrifice on day 14 postaneurysm induction, the aortic expansion in the Nec-1s group (64.12 ± 4.80%) was significantly smaller than that of the DMSO group (172.80 ± 13.68%) (P < 0.05). The mean aortic diameter of Nec-1 treated mice appeared to be smaller (121.60 ± 10.40%) than the DMSO group, though the difference was not statistically significant (P = 0.1). Histologically, the aortic structure of Nec-1s-treated mice appeared normal, with continuous and organized elastin laminae and abundant αActin-expressing SMCs. Moreover, Nect-1s treatment diminished macrophage infiltration and MMP9 accumulation and increased aortic levels of tropoelastin and lysyl oxidase. Together, our data suggest that pharmacological inhibition of necroptosis with Nec-1s stabilizes pre-existing aneurysms by diminishing inflammation and promoting connective tissue repair.

Inhibition of KLF5-Myo9b-RhoA Pathway-Mediated Podosome Formation in Macrophages Ameliorates Abdominal Aortic Aneurysm

RATIONALE

Abdominal aortic aneurysms (AAAs) are characterized by pathological remodeling of the aortic wall. Although both increased Krüppel-like factor 5 (KLF5) expression and macrophage infiltration have been implicated in vascular remodeling, the role of KLF5 in macrophage infiltration and AAA formation remains unclear.

OBJECTIVE

To determine the role of KLF5 in AAA formation and macrophage infiltration into AAAs.

METHODS AND RESULTS

KLF5 expression was significantly increased in human AAA tissues and in 2 mouse models of experimental AAA. Moreover, in myeloid-specific Klf5 knockout mice (myeKlf5^-/- mice), macrophage infiltration, medial smooth muscle cell loss, elastin degradation, and AAA formation were markedly decreased. In cell migration and time-lapse imaging analyses, the migration of murine myeKlf5^-/- macrophages was impaired, and in luciferase reporter assays, KLF5 activated Myo9b (myosin IXB) transcription by direct binding to the Myo9b promoter. In subsequent coimmunostaining studies, Myo9b was colocalized with filamentous actin, cortactin, vinculin, and Tks5 in the podosomes of phorbol 12,13-dibutyrate-treated macrophages, indicating that Myo9b participates in podosome formation. Gain- and loss-of-function experiments showed that KLF5 promoted podosome formation in macrophages by upregulating Myo9b expression. Furthermore, RhoA-GTP levels increased after KLF5 knockdown in macrophages, suggesting that KLF5 lies upstream of RhoA signaling. Finally, Myo9b expression was increased in human AAA tissues, located in macrophages, and positively correlated with AAA size.

CONCLUSIONS

These data are the first to indicate that KLF5-dependent regulation of Myo9b/RhoA is required for podosome formation and macrophage migration during AAA formation, warranting consideration of the KLF5-Myo9b-RhoA pathway as a therapeutic target for AAA treatment.

Deficiency of γδT cells protects against abdominal aortic aneurysms by regulating phosphoinositide 3-kinase/AKT signaling

OBJECTIVE

It is known that T lymphocytes are activated in human abdominal aortic aneurysms (AAAs). γδT cells, as a subset of T cells, play a role in many inflammation-related diseases. However, whether γδT cells participate in the formation of AAA remains unknown. In this study, we explored the role of γδT cells in AAA lesions.

METHODS AND RESULTS

Using the porcine pancreatic elastase-induced AAA model, we found that knock out of γδT cells significantly attenuated AAA formation. To elucidate how γδT cells contribute to AAA, microarray analysis was performed, which found that the phosphoinositide 3-kinase/AKT signaling pathway was activated in elastase-perfused γδT knockout (γδT KO) mice. By studying differentially expressed genes involved in phosphoinositide 3-kinase signaling, we found that proliferation-related genes (Sos1, Mtor, Myc) were upregulated whereas apoptosis-related genes (Pten, Bcl1, Bad) were downregulated in elastase-perfused γδT KO mice. Furthermore, histopathologic analysis showed increased PCNA⁺ and decreased TUNEL⁺ cells in elastase-perfused γδT KO mice compared with wild-type mice. In addition, inflammatory cytokines including interleukin-1β, Mcp-1, and tumor necrosis factor-α were downregulated in the aneurysm tissues of elastase-perfused γδT KO mice.

CONCLUSIONS

These data reveal a pathogenic role of γδT cells in the experimental AAA model, likely through mechanisms regulating cell proliferation and mediating inflammatory response. Thus, targeting of γδT cells may offer a potential therapeutic method for aortic aneurysms.

2-Methoxycinnamaldehyde inhibits the TNF-α-induced proliferation and migration of human aortic smooth muscle cells

The abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) is a crucial event in the development of atherosclerosis, and tumor necrosis factor-α (TNF-α) is actively involved in this process by enhancing the proliferation and migration of VSMCs. 2-Methoxycinnamaldehyde (MCA) is a natural compound of Cinnamomum cassia. Although 2-hydroxycinnamaldehyde (HCA), another compound from Cinnamomum cassia, has been widely studied with regard to its antitumor activity, MCA has not attracted researchers' interest due to its mild toxic effects on cancer cells and its mechanisms of action remain unknown. In this study, we examined the effects of MCA on the TNF-α-induced proliferation and migration of human aortic smooth muscle cells (HASMCs). As shown by our results, MCA inhibited TNF-α-induced cell proliferation by reducing the levels of cyclin D1, cyclin D3, CDK4 and CDK6, and increasing the levels of the cyclin-dependent kinase inhibitors, p21 and p27, without resulting in cellular cytotoxicity. Furthermore, MCA decreased the level of secreted matrix metalloproteinase (MMP)-9 by inhibiting MMP-9 transcription. Unexpectedly, MCA did not affect the TNF-α-induced levels of mitogen-activated protein kinases (MAPKs). However, by showing that MCA potently inhibited the degradation of IκBα and the subsequent nuclear translocation of nuclear factor-κB (NF-κB), we demonstrated that MCA exerts its effects through the NF-κB signaling pathway. MCA also effectively inhibited platelet-derived growth factor (PDGF)-induced HASMC migration. Taken together, these observations suggest that MCA has the potential for use as an anti-atherosclerotic agent.

Focal Adhesion Kinase Promotes the Progression of Aortic Aneurysm by Modulating Macrophage Behavior

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a life-threatening vascular disease that is associated with persistent inflammation and extracellular matrix degradation. The molecular mechanisms underlying the macrophage-mediated progression of AAA remain largely unclear.

APPROACH AND RESULTS

We show that focal adhesion kinase (FAK) expression and activity are enhanced in macrophages that are recruited to AAA tissue. FAK potentiates tumor necrosis factor-α-induced secretion of matrix-degrading enzymes and chemokines by cultured macrophages. FAK also promotes macrophage chemotaxis. In mice, the administration of a FAK inhibitor that tempers local macrophage accumulation markedly suppresses the development and progression of chemically induced AAA.

CONCLUSIONS

FAK plays a key role in macrophage behavior, which underlies the chronic progression of AAA. These findings provide insights into AAA progression and identify FAK as a novel therapeutic target.

Human Adipose-Derived Stem Cells Suppress Elastase-Induced Murine Abdominal Aortic Inflammation and Aneurysm Expansion Through Paracrine Factors

Abdominal aortic aneurysm (AAA) is a potentially lethal disease associated with immune activation-induced aortic degradation. We hypothesized that xenotransplantation of human adipose-derived stem cells (hADSCs) would reduce aortic inflammation and attenuate expansion in a murine AAA model. Modulatory effects of ADSCs on immune cell subtypes associated with AAA progression were investigated using human peripheral blood mononuclear cells (hPBMNCs) cocultured with ADSCs. Murine AAA was induced through elastase application to the abdominal aorta in C57BL/6 mice. ADSCs were administered intravenously, and aortic changes were determined by ultrasonography and videomicrometry. Circulating monocytes, aortic neutrophils, CD28- T cells, FoxP3+ regulatory T cells (Tregs), and CD206+ M2 macrophages were assessed at multiple terminal time points. In vitro, ADSCs induced M2 macrophage and Treg phenotypes while inhibiting neutrophil transmigration and lymphocyte activation without cellular contact. Intravenous ADSC delivery reduced aneurysmal expansion starting from day 4 [from baseline: 54.8% (saline) vs. 16.9% (ADSCs), n = 10 at baseline, n = 4 at day 4, p < 0.001], and the therapeutic effect persists through day 14 (from baseline: 64.1% saline vs. 24.6% ADSCs, n = 4, p < 0.01). ADSC administration increased aortic Tregs by 20-fold (n = 5, p < 0.01), while decreasing CD4+CD28- (-28%), CD8+CD28- T cells (-61%), and Ly6G/C+ neutrophils (-43%, n = 5, p < 0.05). Circulating CD115+CXCR1-LY6C+-activated monocytes decreased in the ADSC-treated group by day 7 (-60%, n = 10, p < 0.05), paralleled by an increase in aortic CD206+ M2 macrophages by 2.4-fold (n = 5, p < 0.05). Intravenously injected ADSCs transiently engrafted in the lung on day 1 without aortic engraftment at any time point. In conclusion, ADSCs exhibit pleiotropic immunomodulatory effects in vitro as well as in vivo during the development of AAA. The temporal evolution of these effects systemically as well as in aortic tissue suggests that ADSCs induce a sequence of anti-inflammatory cellular events mediated by paracrine factors, which leads to amelioration of AAA progression.

Elastin-Derived Peptides Promote Abdominal Aortic Aneurysm Formation by Modulating M1/M2 Macrophage Polarization

Abdominal aortic aneurysm is a dynamic vascular disease characterized by inflammatory cell invasion and extracellular matrix degradation. Damage to elastin in the extracellular matrix results in release of elastin-derived peptides (EDPs), which are chemotactic for inflammatory cells such as monocytes. Their effect on macrophage polarization is less well known. Proinflammatory M1 macrophages initially are recruited to sites of injury, but, if their effects are prolonged, they can lead to chronic inflammation that prevents normal tissue repair. Conversely, anti-inflammatory M2 macrophages reduce inflammation and aid in wound healing. Thus, a proper M1/M2 ratio is vital for tissue homeostasis. Abdominal aortic aneurysm tissue reveals a high M1/M2 ratio in which proinflammatory cells and their associated markers dominate. In the current study, in vitro treatment of bone marrow-derived macrophages with EDPs induced M1 macrophage polarization. By using C57BL/6 mice, Ab-mediated neutralization of EDPs reduced aortic dilation, matrix metalloproteinase activity, and proinflammatory cytokine expression at early and late time points after aneurysm induction. Furthermore, direct manipulation of the M1/M2 balance altered aortic dilation. Injection of M2-polarized macrophages reduced aortic dilation after aneurysm induction. EDPs promoted a proinflammatory environment in aortic tissue by inducing M1 polarization, and neutralization of EDPs attenuated aortic dilation. The M1/M2 imbalance is vital to aneurysm formation.

Nationwide Study on the Risk of Abdominal Aortic Aneurysms in Patients With Psoriasis

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a complex multifactorial disease associated with a high morbidity and mortality. Increased inflammation including T-helper 17 cell-mediated effects has been implicated in AAA pathogenesis. Psoriasis is considered to be a T-helper 17-driven chronic inflammatory disease and in view of potentially overlapping inflammatory mechanisms, we investigated the risk of AAA in patients with psoriasis in a nationwide cohort.

APPROACH AND RESULTS

The study comprised all Danish residents aged ≥18 years followed up from January 1, 1997, until diagnosis of AAA, December 31, 2011, migration or death. Information on comorbidity, concomitant medication, and socioeconomic status was identified by individual-level linkage of administrative registers. Incidence rates for AAA were calculated and incidence rate ratios adjusted for age, sex, comorbidity, medications, socioeconomic status, and smoking were estimated in Poisson regression models. A total of 5 495  203 subjects were eligible for analysis. During the study period, we identified 59 423 patients with mild psoriasis and 11 566 patients with severe psoriasis. The overall incidence rates of AAA were 3.72, 7.30, and 9.87 per 10 000 person-years for the reference population (23 696 cases), mild psoriasis (240 cases), and severe psoriasis (50 cases), respectively. The corresponding adjusted incidence rate ratios for AAA were increased in patients with psoriasis with incidence rate ratios of 1.20 (95% confidence interval, 1.03-1.39) and 1.67 (confidence interval, 1.21-2.32) for subjects with mild and severe disease, respectively.

CONCLUSIONS

In a nationwide cohort, psoriasis was associated with a disease severity-dependent increased risk of AAA. The mechanisms and consequences of this novel finding require further investigation.

TNFα mediates stress-induced depression by upregulating indoleamine 2,3-dioxygenase in a mouse model of unpredictable chronic mild stress

Depression is often preceded by exposure to stressful life events. Chronic stress causes perturbations in the immune system, and up-regulates production of proinflammatory cytokines, which has been proposed to be associated with the pathogenesis of clinical depression. However, the potential mechanisms by which stress-induced proinflammatory cytokines lead to the development of depression are not well understood. Here, we sought to screen the main proinflammatory cytokines and the potential mechanisms linking inflammation to depression-like behavior during unpredictable, chronic, mild stress (UCMS), in vivo. Mice were allocated into four groups in each separate experiment: saline-control, saline-UCMS, drug-control and drug-UCMS. Development of depression-like behavior was reflected as a reduction in sucrose preference, and increased immobility in both the forced swim and tail suspension tests. The following drugs were administered intraperitoneally: the pan-anti-inflammatory tetracycline derivative, minocycline (30 mg/kg, daily), the tumor necrosis factor (TNF)α monoclonal antibody, infliximab (10 mg/kg, twice weekly), and the indoleamine 2, 3-dioxygenase (IDO) inhibitor, 1-methyltryptophan (1-MT, 10 mg/mouse, daily). Plasma TNFα, IL-1β and IL-18 increased significantly after the four-week UCMS exposure. Pretreatment of mice with minocycline completely blocked any upregulation. Concurrent with development of depression-like behaviors, the concentration of TNFα in plasma and the cerebral cortex increased remarkably. The tryptophan-degrading enzyme IDO was up-regulated in the cortex following UCMS exposure. Treatment of mice with minocycline, infliximab or 1-MT prevented the development of depression-like behaviors. Furthermore, blockade of TNFα inhibited expression of IDO and protected cortical neurons from UCMS-induced damage. These results suggest that TNFα plays a critical role in mediating UCMS-induced depression through up-regulation of IDO and subsequent damage of cortical neurons.

Toll-Like Receptor 4 Is Essential in the Development of Abdominal Aortic Aneurysm

Toll-like receptor (TLR) family plays a key role in innate immunity and various inflammatory responses. TLR4, one of the well-characterized pattern-recognition receptors, can be activated by endogenous damage-associated molecular pattern molecules such as high mobility group box 1 (HMGB1) to sustain sterile inflammation. Evidence suggested that blockade of TLR4 signaling may confer protection against abdominal aortic aneurysm (AAA). Herein we aimed to obtain further insight into the mechanism by which TLR4 might promote aneurysm formation. Characterization of the CaCl₂-induced AAA model in mice revealed that upregulation of TLR4 expression, localized predominantly to vascular smooth muscle cells (VSMCs), was followed by a late decline during a 28-day period of AAA development. In vitro, TLR4 expression was increased in VSMCs treated with HMGB1. Knockdown of TLR4 by siRNA attenuated HMGB1-enhanced production of proinflammatory cytokines, specifically interleukin-6 and monocyte chemoattractant protein-1 (MCP-1), and matrix-degrading matrix metalloproteinase (MMP)-2 from VSMCs. In vivo, two different strains of TLR4-deficient (C57BL/10ScNJ and C3H/HeJ) mice were resistant to CaCl₂-induced AAA formation compared to their respective controls (C57BL/10ScSnJ and C3H/HeN). Knockout of TLR4 reduced interleukin-6 and MCP-1 levels and HMGB1 expression, attenuated macrophage accumulation, and eventually suppressed MMP production, elastin destruction and VSMC loss. Finally, human AAA exhibited higher TLR4 expression that was localized to VSMCs. These data suggest that TLR4 signaling contributes to AAA formation by promoting a proinflammatory status of VSMCs and by inducing proteinase release from VSMCs during aneurysm initiation and development.

Proteolytically active ADAM10 and ADAM17 carried on membrane microvesicles in human abdominal aortic aneurysms

The intraluminal thrombus (ILT) of human abdominal aortic aneurysm (AAA) has been suggested to damage the underlying aortic wall, but previous work found scant activity of soluble proteases in the abluminal layer of the ILT, adjacent to the aneurysm. We hypothesised that transmembrane proteases carried by membrane microvesicles (MV) from dying cells remain active in the abluminal ILT. ILTs and AAA segments collected from 21 patients during surgical repair were assayed for two major transmembrane proteases, ADAM10 (a disintegrin and metalloprotease-10) and ADAM17. We also exposed cultured cells to tobacco smoke and assessed ADAM10 and ADAM17 expression and release on MVs. Immunohistochemistry showed abundant ADAM10 and ADAM17 protein in the ILT and underlying aneurysmal aorta. Domain-specific antibodies indicated both transmembrane and shed ADAM17. Importantly, ADAM10 and ADAM 17 in the abluminal ILT were enzymatically active. Electron microscopy of abluminal ILT and aortic wall showed MVs with ADAM10 and ADAM17. By flow cytometry, ADAM-positive microvesicles from abluminal ILT carried the neutrophil marker CD66, but not the platelet marker CD61. Cultured HL60 neutrophils exposed to tobacco smoke extract showed increased ADAM10 and ADAM17 content, cleavage of these molecules into active forms, and release of MVs carrying mature ADAM10 and detectable ADAM17. In conclusion, our results implicate persistent, enzymatically active ADAMs on MVs in the abluminal ILT, adjacent to the aneurysmal wall. The production of ADAM10- and ADAM17-positive MVs from smoke-exposed neutrophils provides a novel molecular mechanism for the vastly accelerated risk of AAA in smokers.

Membrane-Bound Thrombomodulin Regulates Macrophage Inflammation in Abdominal Aortic Aneurysm

Objective—

Thrombomodulin (TM), a glycoprotein constitutively expressed in the endothelium, is well known for its anticoagulant and anti-inflammatory properties. Paradoxically, we recently found that monocytic membrane-bound TM (ie, endogenous TM expression in monocytes) triggers lipopolysaccharide- and gram-negative bacteria–induced inflammatory responses. However, the significance of membrane-bound TM in chronic sterile vascular inflammation and the development of abdominal aortic aneurysm (AAA) remains undetermined.

Approach and Results—

Implicating a potential role for membrane-bound TM in AAA, we found that TM signals were predominantly localized to macrophages and vascular smooth muscle cells in human aneurysm specimens. Characterization of the CaCl 2 -induced AAA in mice revealed that during aneurysm development, TM expression was mainly localized in infiltrating macrophages and vascular smooth muscle cells. To investigate the function of membrane-bound TM in vivo, transgenic mice with myeloid- (LysMcre/TM flox/flox ) and vascular smooth muscle cell–specific (SM22-cre tg /TM flox/flox ) TM ablation and their respective wild-type controls (TM flox/flox and SM22-cre tg /TM +/+ ) were generated. In the mouse CaCl 2 -induced AAA model, deficiency of myeloid TM, but not vascular smooth muscle cell TM, inhibited macrophage accumulation, attenuated proinflammatory cytokine and matrix metalloproteinase-9 production, and finally mitigated elastin destruction and aortic dilatation. In vitro TM-deficient monocytes/macrophages, versus TM wild-type counterparts, exhibited attenuation of proinflammatory mediator expression, adhesion to endothelial cells, and generation of reactive oxygen species. Consistently, myeloid TM–deficient hyperlipidemic mice (ApoE −/− /LysMcre/TM flox/flox ) were resistant to AAA formation induced by angiotensin II infusion, along with reduced macrophage infiltration, suppressed matrix metalloproteinase activities, and diminished oxidative stress.

Conclusions—

Membrane-bound TM in macrophages plays an essential role in the development of AAA by enhancing proinflammatory mediator elaboration, macrophage recruitment, and oxidative stress.

Background differences in baseline and stimulated MMP levels influence abdominal aortic aneurysm susceptibility

OBJECTIVE

Evidence has demonstrated profound influence of genetic background on cardiovascular phenotypes. Murine models in Marfan syndrome (MFS) have shown that genetic background-related variations affect thoracic aortic aneurysm formation, rupture, and lifespan of mice. MFS mice with C57Bl/6 genetic background are less susceptible to aneurysm formation compared to the 129/SvEv genetic background. In this study, we hypothesize that susceptibility to abdominal aortic aneurysm (AAA) will be increased in 129/SvEv mice versus C57Bl/6 mice. We tested this hypothesis by assessing differences in aneurysm size, tissue properties, immune response, and MMP expression.

METHODS

Mice of C57Bl/6 or 129/SvEv background underwent AAA induction by periaortic application of CaCl2. Baseline aortic diameters, tissue properties and MMP levels were measured. After aneurysm induction, diameters, MMP expression, and immune response (macrophage infiltration and bone marrow transplantation) were measured.

RESULTS

Aneurysms were larger in 129/SvEv mice than C57Bl/6 mice (83.0% ± 13.6 increase compared to 57.8% ± 6.4). The aorta was stiffer in the 129/SvEv mice compared to C57Bl/6 mice (952.5 kPa ± 93.6 versus 621.4 kPa ± 84.2). Baseline MMP-2 and post-aneurysm MMP-2 and -9 levels were higher in 129/SvEv aortas compared to C57Bl/6 aortas. Elastic lamella disruption/fragmentation and macrophage infiltration were increased in 129/SvEv mice. Myelogenous cell reversal by bone marrow transplantation did not affect aneurysm size.

CONCLUSIONS

These data demonstrate that 129/SvEv mice are more susceptible to AAA compared to C57Bl/6 mice. Intrinsic properties of the aorta between the two strains of mice, including baseline expression of MMP-2, influence susceptibility to AAA.

Platelet Inhibitors Reduce Rupture in a Mouse Model of Established Abdominal Aortic Aneurysm

OBJECTIVE

Rupture of abdominal aortic aneurysms causes a high morbidity and mortality in the elderly population. Platelet-rich thrombi form on the surface of aneurysms and may contribute to disease progression. In this study, we used a pharmacological approach to examine a role of platelets in established aneurysms induced by angiotensin II infusion into hypercholesterolemic mice.

APPROACH AND RESULTS

Administration of the platelet inhibitors aspirin or clopidogrel bisulfate to established abdominal aortic aneurysms dramatically reduced rupture. These platelet inhibitors reduced abdominal aortic platelet and macrophage recruitment resulting in decreased active matrix metalloproteinase-2 and matrix metalloproteinase-9. Platelet inhibitors also resulted in reduced plasma concentrations of platelet factor 4, cytokines, and components of the plasminogen activation system in mice. To determine the validity of these findings in human subjects, a cohort of aneurysm patients were retrospectively analyzed using developed and validated algorithms in the electronic medical record database at Vanderbilt University. Similar to mice, administration of aspirin or P2Y12 inhibitors was associated with reduced death among patients with abdominal aortic aneurysm.

CONCLUSIONS

These results suggest that platelets contribute to abdominal aortic aneurysm progression and rupture.

Angiotensin II-induced TLR4 mediated abdominal aortic aneurysm in apolipoprotein E knockout mice is dependent on STAT3

Abdominal Aortic Aneurysm (AAA) is a major cause of mortality and morbidity in men over 65 years of age. Male apolipoprotein E knockout (ApoE(-/-)) mice infused with angiotensin II (AngII) develop AAA. Although AngII stimulates both JAK/STAT and Toll-like receptor 4 (TLR4) signaling pathways, their involvement in AngII mediated AAA formation is unclear. Here we used the small molecule STAT3 inhibitor, S3I-201, the TLR4 inhibitor Eritoran and ApoE(-/-)TLR4(-/-) mice to evaluate the interaction between STAT3 and TLR4 signaling in AngII-induced AAA formation. ApoE(-/-) mice infused for 28 days with AngII developed AAAs and increased STAT3 activation and TLR4 expression. Moreover, AngII increased macrophage infiltration and the ratio of M1 (pro-inflammatory)/M2 (healing) macrophages in aneurysmal tissue as early as 7-10 days after AngII infusion. STAT3 inhibition with S3I-201 decreased the incidence and severity of AngII-induced AAA formation and decreased MMP activity and the ratio of M1/M2 macrophages. Furthermore, AngII-mediated AAA formation, MMP secretion, STAT3 phosphorylation and the ratio of M1/M2 macrophages were markedly decreased in ApoE(-/-)TLR4(-/-) mice, and in Eritoran-treated ApoE(-/-) mice. TLR4 and pSTAT3 levels were also increased in human aneurysmal tissue. These data support a role of pSTAT3 in TLR4 dependent AAA formation and possible therapeutic roles for TLR4 and/or STAT3 inhibition in AAA.

B lymphocytes in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) is a progressive inflammatory disease of the artery walls. Immune cells, including B lymphocytes, are implicated in the pathogenesis of AAA through interconnected mechanisms. Many studies have shown that compared with normal abdominal aortic tissue, the amount of B lymphocytes that infiltrate the adventitia of AAAs was significantly higher. Activated B lymphocytes promote AAA by producing immunoglobulins, cytokines, and matrix metalloproteinases (MMPs), resulting in the activation of macrophages, mast cells (MCs) and complement pathways. Finally, all of these factors lead to the degradation of collagen and matrix proteins and to aortic wall remodeling, which are hallmarks of AAA. However, few studies focus on the relative function of B cells, and their precise mechanisms in AAA remain unclear. Thus, we summarize the current knowledge on the role of B cells in AAA and offer recommendations for further investigation of preventing the progression of AAA.

Inflammatory cell phenotypes in AAAs: their role and potential as targets for therapy

Abdominal aortic aneurysms (AAAs) are characterized by chronic inflammatory cell infiltration. AAA is typically an asymptomatic disease and caused ≈15 000 deaths annually in the United States. Previous studies have examined both human and murine aortic tissue for the presence of various inflammatory cell types. Studies show that in both human and experimental AAAs, prominent inflammatory cell infiltration, such as CD4(+) T cells and macrophages, occurs in the damaged aortic wall. These cells have the ability to undergo phenotypic modulation based on microenvironmental cues, potentially influencing disease progression. Proinflammatory CD4(+) T cells and classically activated macrophages dominate the landscape of aortic infiltrates. The skew to proinflammatory phenotypes alters disease progression and plays a role in causing chronic inflammation. The local cytokine production and presence of inflammatory mediators, such as extracellular matrix breakdown products, influence the uneven balance of the inflammatory infiltrate phenotypes. Understanding and developing new strategies that target the proinflammatory phenotype could provide useful therapeutic targets for a disease with no current pharmacological intervention.

Clonal expansion of T cells in abdominal aortic aneurysm: a role for doxycycline as drug of choice?

Most reported studies with animal models of abdominal aortic aneurysm (AAA) and several studies with patients have suggested that doxycycline favourably modifies AAA; however, a recent large long-term clinical trial found that doxycycline did not limit aneurysm growth. Thus, there is currently no convincing evidence that doxycycline reduces AAA expansion. Here, we critically review the available experimental and clinical information about the effects of doxycycline when used as a pharmacological treatment for AAA. The view that AAA can be considered an autoimmune disease and the observation that AAA tissue shows clonal expansion of T cells is placed in the light of the well-known inhibition of mitochondrial protein synthesis by doxycycline. In T cell leukaemia animal models, this inhibitory effect of the antibiotic has been shown to impede T cell proliferation, resulting in complete tumour eradication. We suggest that the available evidence of doxycycline action on AAA is erroneously ascribed to its inhibition of matrix metalloproteinases (MMPs) by competitive binding of the zinc ion co-factor. Although competitive binding may explain the inhibition of proteolytic activity, it does not explain the observed decreases of MMP mRNA levels. We propose that the observed effects of doxycycline are secondary to inhibition of mitochondrial protein synthesis. Provided that serum doxycycline levels are kept at adequate levels, the inhibition will result in a proliferation arrest, especially of clonally expanding T cells. This, in turn, leads to the decrease of proinflammatory cytokines that are normally generated by these cells. The drastic change in cell type composition may explain the changes in MMP mRNA and protein levels in the tissue samples.

Immunohistochemical analysis of the natural killer cell cytotoxicity pathway in human abdominal aortic aneurysms

Our previous analysis using genome-wide microarray expression data revealed extreme overrepresentation of immune related genes belonging the Natural Killer (NK) Cell Mediated Cytotoxicity pathway (hsa04650) in human abdominal aortic aneurysm (AAA). We followed up the microarray studies by immunohistochemical analyses using antibodies against nine members of the NK pathway (VAV1, VAV3, PLCG1, PLCG2, HCST, TYROBP, PTK2B, TNFA, and GZMB) and aortic tissue samples from AAA repair operations (n = 6) and control aortae (n = 8) from age-, sex- and ethnicity-matched donors from autopsies. The results confirmed the microarray results. Two different members of the NK pathway, HCST and GRZB, which act at different steps in the NK-pathway, were actively transcribed and translated into proteins in the same cells in the AAA tissue demonstrated by double staining. Furthermore, double staining with antibodies against CD68 or CD8 together with HCST, TYROBP, PTK2B or PLCG2 revealed that CD68 and CD8 positive cells expressed proteins of the NK-pathway but were not the only inflammatory cells involved in the NK-pathway in the AAA tissue. The results provide strong evidence that the NK Cell Mediated Cytotoxicity Pathway is activated in human AAA and valuable insight for future studies to dissect the pathogenesis of human AAA.

Inhibitory effect of statins on inflammation-related pathways in human abdominal aortic aneurysm tissue

HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A) reductase inhibitors (statins) have been suggested to attenuate abdominal aortic aneurysm (AAA) growth. However, the effects of statins in human AAA tissues are not fully elucidated. The aim of this study was to investigate the direct effects of statins on proinflammatory molecules in human AAA walls in ex vivo culture. Simvastatin strongly inhibited the activation of nuclear factor (NF)-κB induced by tumor necrosis factor (TNF)-α in human AAA walls, but showed little effect on c-jun N-terminal kinase (JNK) activation. Simvastatin, as well as pitavastatin significantly reduced the secretion of matrix metalloproteinase (MMP)-9, monocyte chemoattractant protein (MCP)-2 and epithelial neutrophil-activating peptide (CXCL5) under both basal and TNF-α-stimulated conditions. Similar to statins, the Rac1 inhibitor NSC23766 significantly inhibited the activation of NF-κB, accompanied by a decreased secretion of MMP-9, MCP-2 and CXCL5. Moreover, the effect of simvastatin and the JNK inhibitor SP600125 was additive in inhibiting the secretion of MMP-9, MCP-2 and CXCL5. These findings indicate that statins preferentially inhibit the Rac1/NF-κB pathway to suppress MMP-9 and chemokine secretion in human AAA, suggesting a mechanism for the potential effect of statins in attenuating AAA progression.

Receptor-interacting protein kinase 3 contributes to abdominal aortic aneurysms via smooth muscle cell necrosis and inflammation

RATIONALE

Depletion of medial smooth muscle cell (SMC) is a major pathological characteristic of abdominal aortic aneurysm (AAA), although the mechanism by which these cells are eliminated remains incompletely understood. We reasoned that necroptosis, a recently described form of necrosis mediated by receptor-interacting protein kinase 3 (RIP3), may contribute to AAA pathology through the induction of SMC death and the significant production of inflammatory cytokines.

OBJECTIVE

To test the hypothesis that RIP3-mediated necroptosis is actively involved in aneurysm pathogenesis.

METHODS AND RESULTS

RIP3 and RIP1 levels were found to be elevated in human AAAs, most noticeably in SMCs. Elevations of RIP3 and SMC necrosis were also observed in the elastase-induced mouse model of AAAs. Deletion of one or both copies of Rip3 prevented AAA formation. By transplanting Rip3(+/-) aortae to Rip3(+/+) mice, we demonstrated that reduced Rip3 expression in arterial wall was the primary cause of aneurysm resistance. In vitro, adenoviral overexpression of RIP3 was sufficient to trigger SMC necroptosis. Protein kinase C-delta contributed to tumor necrosis factor-α-induced SMC necroptosis by regulating Rip3 expression. Furthermore, Rip3 deficiency impaired tumor necrosis factor-α-induced inflammatory gene expression in aortic SMCs, which was at least in part because of attenuation of p65 Ser536 phosphorylation. In vivo, the lack of RIP3 diminished activation of p65 in SMCs, implicating a necrosis independent function of RIP3 in aneurysms.

CONCLUSIONS

Enhanced RIP3 signaling in aneurysmal tissues contributes to AAA progression by causing SMC necroptosis, as well as stimulating vascular inflammation, and therefore may serve as a novel therapeutic target for AAA treatment.