Blocking TNF-alpha attenuates aneurysm formation in a murine model

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.

Inactivation of PI3Kδ induces vascular injury and promotes aneurysm development by upregulating the AP-1/MMP-12 pathway in macrophages

OBJECTIVE

An aneurysm is an inflammatory vascular condition. Phosphatidylinositol 3-kinases δ is highly expressed in leukocytes, and play a key role in innate immunity. However, the link between phosphatidylinositol 3-kinases δ and aneurysm development has not yet been elucidated.

APPROACH AND RESULTS

Carotid ligation unexpectedly induced characteristic aneurysm formation beneath the ligation point in p110δ(D910A/D910A) mice (n=25; P<0.001 versus wild-type). Besides, p110δ inactivation exacerbated CaCl2-induced abdominal aortic aneurysms development. A reverse transcription polymerase chain reaction microarray revealed significant extracellular matrix components degradation and matrix metalloproteinases (MMPs) upregulation in the abdominal aorta of p110δ(D910A/D910A) mice. Similarly, the expression of both collagen I and IV was significantly decreased (n=10; P<0.05 versus wild-type) in carotid artery. Western blot assay confirmed that MMP-12 was significantly upregulated in arteries of p110δ(D910A/D910A) mice (n=10; P<0.01 versus wild-type). In vitro, p110δ inactivation marked increase peritoneal macrophages recruitment and synergistically enhance tumor necrosis factor-α-induced recruitment. A specific phosphatidylinositol 3-kinases δ inhibitor (IC87114) or genetic p110δ inactivation upregulated MMP-12 expression and c-Jun phosphorylation (n=6; P<0.05 versus wild-type macrophages). IC87114 also increased activator protein-1 DNA-binding activity (n=6; P<0.001 versus control) and enhanced the effect of tumor necrosis factor-α on activator protein-1-binding activity (n=5; P<0.01 versus tumor necrosis factor-α treatment groups). Knockdown of c-Jun suppressed the effect of the IC87114 and tumor necrosis factor-α on MMP-12 mRNA expression (n=5 in each group; P<0.01 versus scrRNA treatment groups).

CONCLUSIONS

Our findings demonstrate that p110δ inactivation leads to extracellular matrix degradation in vessels and promotes aneurysm development by inducing macrophages migration and upregulating the activator protein-1/MMP-12 pathway in macrophages.

Human sLZIP promotes atherosclerosis via MMP-9 transcription and vascular smooth muscle cell migration

Atherosclerosis is a chronic inflammatory response of the vascular wall, and immune responses are involved in every phase of atherosclerosis, from initiation, to progression, and finally to plaque rupture. Cytokines are the major atherogenic mediators that promote plaque formation and progression by activation of inflammatory cells. They induce expressions of matrix metalloproteinases (MMPs), leading to vascular smooth muscle cell (VSMC) migration in atherosclerotic lesions. Although chronic inflammatory mediators, including tumor necrosis factor α (TNF-α) and MMPs, exacerbate atherosclerosis, the molecular mechanism of atherogenesis remains unclear. In this study we investigated the role of a novel transcription factor the human small leucine zipper protein (sLZIP) in TNF-α-induced MMP expression, VSMC migration, and atherosclerosis progression. The proinflammatory cytokine TNF-α enhanced sLZIP expression by 3-fold via activation of NF-κB signaling. sLZIP induced MMP-9 transcription and the proteolytic activity of MMP-9 by 2.8- and 3.2-fold (P< 0.05), respectively, in macrophages, leading to enhancement of VSMC migration by 2.7-fold (P<0.005). sLZIP(OE/+) (sLZIP transgenic); LDLR(-/-) mice fed a high-cholesterol diet exhibited enhanced arterial plaque formation and increased VSMC migration from the media into the intima by 2.8- and 2.6-fold (P<0.01), respectively, compared with atherosclerosis-prone LDLR(-/-) mice. These results indicate that human sLZIP plays a critical role in development of atherosclerosis and can be used as a therapeutic target molecule for treatment of atherosclerosis.

Chemokine (C-X-C motif) receptor 4 blockade by AMD3100 inhibits experimental abdominal aortic aneurysm expansion through anti-inflammatory effects

OBJECTIVE

Inflammation plays a critical role in the development of abdominal aortic aneurysms (AAAs). Because stromal cell-derived factor 1 (SDF-1) is known for its ability to attract inflammatory cells, we investigated whether SDF-1/chemokine (C-X-C motif) receptor 4 (CXCR4) axis is expressed in aneurysmal aortic wall and plays a role in AAA physiopathology and asked whether its blockade modulates AAA formation and expansion.

APPROACH AND RESULTS

Quantitative real-time polymerase chain reaction analysis showed that SDF-1α and CXCR4 mRNA levels are increased in both human and CaCl2-induced mouse AAA wall and are positively correlated to the aortic diameter in mice. ELISA quantification and immunostaining demonstrated that, in mice, aortic SDF-1α is rapidly induced during AAA formation, first by apoptotic vascular smooth muscle cells in the injured media and then by adventitial macrophages once AAA is fully established. Using green fluorescent protein-positive (GFP(+/-)) bone marrow transplantation experiments, we demonstrated that aortic SDF-1 overexpression is implicated in the recruitment of bone marrow-derived macrophages within the AAA wall. Furthermore, in mice, blockade of CXCR4 by AMD3100 decreases the infiltration of adventitial macrophages, inhibits AAA formation, and prevents aortic wall destruction. AMD3100 reduces the mRNA levels of MMP-12 and MMP-14 as well as that of inflammatory effectors MCP-1, MIP-1β, MIP-2α, RANTES, IL-1β, IL-6, TNF-α, and E-selectin. Finally, AMD3100 stabilizes the diameter of formed, expanding AAAs in 2 experimental models.

CONCLUSIONS

SDF-1/CXCR4 axis is upregulated in human and mouse AAAs. Blockade of CXCR4 with AMD3100 suppresses AAA formation and progression in two rodent models. Blockade of SDF-1/CXCR4 axis may represent a new strategy to limit progression of small human AAAs.

Adiponectin attenuates abdominal aortic aneurysm formation in hyperlipidemic mice

OBJECTIVE

Abdominal aortic aneurysms (AAA) are age-associated, life-threatening inflammatory dilations of the abdominal aorta. Human population studies have shown an association between obesity and AAA formation, but the molecular mechanisms underlying this connection remain largely unexplored. Adiponectin is an anti-inflammatory adipokine that is downregulated in obesity. In this study we evaluated the role of adiponectin in a model of AAA using apolipoprotein E/adiponectin double-knockout (Apoe(-/-)Apn(-/-)) mice.

APPROACH AND RESULTS

Angiotensin II (Ang II)-infusion in male Apoe(-/-)Apn(-/-) mice led to a higher incidence of AAA and a significant increase of maximal aortic diameter compared with that of Apoe(-/-) mice (2.12 ± 0.07 mm vs. 1.67 ± 0.09 mm, respectively at 28 days). Adiponectin deficiency augmented the early infiltration of macrophages and increased the expression of pro-inflammatory factors in the dilated aortic wall. MMP-2 and MMP-9 activation was also augmented in the aorta of Apoe(-/-)Apn(-/-) mice compared to Apoe(-/-) mice. These data suggest that the downregulation of adiponectin could directly contribute to the elevated incidence of AAA observed in obese individuals.

CONCLUSIONS

Adiponectin attenuates Ang II-induced vascular inflammation and AAA formation in mice.

The ω-3 polyunsaturated fatty acid, eicosapentaenoic acid, attenuates abdominal aortic aneurysm development via suppression of tissue remodeling

Abdominal aortic aneurysm (AAA) is a prevalent vascular disease that can progressively enlarge and rupture with a high rate of mortality. Inflammation and active remodeling of the aortic wall have been suggested to be critical in its pathogenesis. Meanwhile, ω-3 polyunsaturated fatty acids such as eicosapentaenoic acid (EPA) are known to reduce cardiovascular events, but its role in AAA management remains unclear. Here, we show that EPA can attenuate murine CaCl₂-induced AAA formation. Aortas from BALB/c mice fed an EPA-diet appeared less inflamed, were significantly smaller in diameter compared to those from control-diet-fed mice, and had relative preservation of aortic elastic lamina. Interestingly, CT imaging also revealed markedly reduced calcification of the aortas after EPA treatment. Mechanistically, MMP2, MMP9, and TNFSF11 levels in the aortas were reduced after EPA treatment. Consistent with this finding, RAW264.7 macrophages treated with EPA showed attenuated Mmp9 levels after TNF-α simulation. These results demonstrate a novel role of EPA in attenuating AAA formation via the suppression of critical remodeling pathways in the pathogenesis of AAAs, and raise the possibility of using EPA for AAA prevention in the clinical setting.

Molecular and physiological events in respiratory muscles and blood of rats exposed to inspiratory threshold loading

High-intensity exercise induces oxidative stress and inflammatory events in muscles. Tumor necrosis factor (TNF)-α may alter muscle protein metabolism or promote muscle regeneration. We hypothesized that a program of noninvasive chronic inspiratory loading of different intensities induces a differential pattern of physiological, molecular, and cellular events within rat diaphragms. Antioxidants and TNF-α blockade may influence those events. In the diaphragm, gastrocnemius, and blood of rats exposed to high-intensity inspiratory threshold loads (2 hour every 24 hours for 14 days), with and without treatment with N-acetyl cysteine or infliximab (anti-TNF-α antibody), inflammatory cells and cytokines, superoxide anion production, myogenesis markers, and muscle structure were explored. In all animals, maximum inspiratory pressure (MIP) and body weight were determined. High-intensity inspiratory loading for 2 weeks caused a decline in MIP and body weight, and in the diaphragm induced a reduction in fast-twitch fiber proportions and sizes, whereas inflammatory cells and cytokine levels, including TNF-α immunohistochemical expression, superoxide anion, internal nuclei counts, and markers of myogenesis were increased. Blockade of TNF-α improved respiratory muscle function and structure, and animal weight, and, in the diaphragm, reduced inflammatory cell numbers and superoxide anion production drastically while inducing larger increases in protein and messenger RNA levels and immunohistochemical expression of TNF-α, internal nuclei, and markers of muscle regeneration. Blunting of TNF-α also induced a reduction in blood inflammatory cytokines and superoxide anion production. We conclude that TNF-α synthesized by inflammatory cells or myofibers could have differential effects on muscle structure and function in response to chronic, noninvasive, high-intensity inspiratory threshold loading.

Caveolin 1 is critical for abdominal aortic aneurysm formation induced by angiotensin II and inhibition of lysyl oxidase

Although AngII (angiotensin II) and its receptor AT1R (AngII type 1 receptor) have been implicated in AAA (abdominal aortic aneurysm) formation, the proximal signalling events primarily responsible for AAA formation remain uncertain. Caveolae are cholesterol-rich membrane microdomains that serve as a signalling platform to facilitate the temporal and spatial localization of signal transduction events, including those stimulated by AngII. Cav1 (caveolin 1)-enriched caveolae in vascular smooth muscle cells mediate ADAM17 (a disintegrin and metalloproteinase 17)-dependent EGFR (epidermal growth factor receptor) transactivation, which is linked to vascular remodelling induced by AngII. In the present study, we have tested our hypothesis that Cav1 plays a critical role for the development of AAA at least in part via its specific alteration of AngII signalling within caveolae. Cav1-/- mice and the control wild-type mice were co-infused with AngII and β-aminopropionitrile to induce AAA. We found that Cav1-/- mice with the co-infusion did not develop AAA compared with control mice in spite of hypertension. We found an increased expression of ADAM17 and enhanced phosphorylation of EGFR in AAA. These events were markedly attenuated in Cav1-/- aortas with the co-infusion. Furthermore, aortas from Cav1-/- mice with the co-infusion showed less endoplasmic reticulum stress, oxidative stress and inflammatory responses compared with aortas from control mice. Cav1 silencing in cultured vascular smooth muscle cells prevented AngII-induced ADAM17 induction and activation. In conclusion, Cav1 appears to play a critical role in the formation of AAA and associated endoplasmic reticulum/oxidative stress, presumably through the regulation of caveolae compartmentalized signals induced by AngII.

Rapamycin limits the growth of established experimental abdominal aortic aneurysms

OBJECTIVES

Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease affecting 4-8% of men older than 60 years. No pharmacologic strategies limit disease progression, aneurysm rupture, or aneurysm-related death. We examined the ability of rapamycin to limit the progression of established experimental AAAs.

METHODS

AAAs were created in 10-12-week-old male C57BL/6J mice via the porcine pancreatic elastase (PPE) infusion method. Beginning 4 days after PPE infusion, mice were treated with rapamycin (5 mg/kg/day) or an equal volume of vehicle for 10 days. AAA progression was monitored by serial ultrasound examination. Aortae were harvested for histological analyses at sacrifice.

RESULTS

Three days after PPE infusion, prior to vehicle or rapamycin treatment, aneurysms were enlarging at an equal rate between groups. In the rapamycin group, treatment reduced aortic enlargement by 38%, and 53% at 3 and 10 days, respectively. On histological analysis, medial elastin and smooth muscle cell populations were relatively preserved in the rapamycin group. Rapamycin treatment also reduced mural macrophage density and neoangiogenesis.

CONCLUSION

Rapamycin limits the progression of established experimental aneurysms, increasing the translational potential of mechanistic target of rapamycin-related AAA inhibition strategies.

Recombinant human thrombomodulin suppresses experimental abdominal aortic aneurysms induced by calcium chloride in mice

OBJECTIVE

To investigate whether recombinant thrombomodulin containing all the extracellular domains (rTMD123) has therapeutic potential against aneurysm development.

SUMMARY BACKGROUND DATA

The pathogenesis of abdominal aortic aneurysm (AAA) is characterized by chronic inflammation and proteolytic degradation of extracellular matrix. Thrombomodulin, a transmembrane glycoprotein, exerts anti-inflammatory activities such as inhibition of cytokine production and sequestration of proinflammatory high-mobility group box 1 (HMGB1) to prevent it from engaging the receptor for advanced glycation end product (RAGE) that may sustain inflammation and tissue damage.

METHODS

The in vivo effects of treatment and posttreatment with rTMD123 on aortic dilatation were measured using the CaCl2-induced AAA model in mice.

RESULTS

Characterization of the CaCl2-induced model revealed that HMGB1 and RAGE, both localized mainly to macrophages, were persistently upregulated during a 28-day period of AAA development. In vitro, rTMD123-HMGB1 interaction prevented HMGB1 binding to macrophages, thereby prohibiting activation of HMGB1-RAGE signaling in macrophages. In vivo, short-term treatment with rTMD123 upon AAA induction suppressed the levels of proinflammatory cytokines, HMGB1, and RAGE in the aortic tissue; reduced the infiltrating macrophage number; and finally attenuated matrix metalloproteinase production, extracellular matrix destruction, and AAA formation without disturbing vascular calcification. Consistently, posttreatment with rTMD123 seven days after AAA induction alleviated vascular inflammation and retarded AAA progression.

CONCLUSIONS

These data suggest that rTMD123 confers protection against AAA development. The mechanism of action may be associated with reduction of proinflammatory mediators, blockade of macrophage recruitment, and suppression of HMGB1-RAGE signaling involved in aneurysm formation and downstream macrophage activation.

Tumor necrosis factor-α modulates cerebral aneurysm formation and rupture

Inflammation is a critical process behind cerebral aneurysm formation and rupture. Tumor necrosis factor alpha (TNF-α) is a key immune modulator that has been implicated in cerebral aneurysm pathophysiology. This may occur through TNF-α-mediated endothelial injury, smooth muscle cell phenotypic modulation, recruitment of macrophages, activation of chemotactic cytokines, upregulation of matrix remodeling genes, production of free radicals leading to oxidative stress, and ultimately cellular apoptosis. Recent studies have indicated that TNF-α may be a potential target for the development of novel medical therapies, but additional experimental data is needed to clarify the intricacies of TNF-α activation and its critical downstream targets in cerebral aneurysms. This review provides an update on the mechanisms underlying TNF-α-induced molecular modulation in cerebral aneurysms.

Micromanaging abdominal aortic aneurysms

The contribution of abdominal aortic aneurysm (AAA) disease to human morbidity and mortality has increased in the aging, industrialized world. In response, extraordinary efforts have been launched to determine the molecular and pathophysiological characteristics of the diseased aorta. This work aims to develop novel diagnostic and therapeutic strategies to limit AAA expansion and, ultimately, rupture. Contributions from multiple research groups have uncovered a complex transcriptional and post-transcriptional regulatory milieu, which is believed to be essential for maintaining aortic vascular homeostasis. Recently, novel small noncoding RNAs, called microRNAs, have been identified as important transcriptional and post-transcriptional inhibitors of gene expression. MicroRNAs are thought to "fine tune" the translational output of their target messenger RNAs (mRNAs) by promoting mRNA degradation or inhibiting translation. With the discovery that microRNAs act as powerful regulators in the context of a wide variety of diseases, it is only logical that microRNAs be thoroughly explored as potential therapeutic entities. This current review summarizes interesting findings regarding the intriguing roles and benefits of microRNA expression modulation during AAA initiation and propagation. These studies utilize disease-relevant murine models, as well as human tissue from patients undergoing surgical aortic aneurysm repair. Furthermore, we critically examine future therapeutic strategies with regard to their clinical and translational feasibility.

Molecular imaging of experimental abdominal aortic aneurysms

Current laboratory research in the field of abdominal aortic aneurysm (AAA) disease often utilizes small animal experimental models induced by genetic manipulation or chemical application. This has led to the use and development of multiple high-resolution molecular imaging modalities capable of tracking disease progression, quantifying the role of inflammation, and evaluating the effects of potential therapeutics. In vivo imaging reduces the number of research animals used, provides molecular and cellular information, and allows for longitudinal studies, a necessity when tracking vessel expansion in a single animal. This review outlines developments of both established and emerging molecular imaging techniques used to study AAA disease. Beyond the typical modalities used for anatomical imaging, which include ultrasound (US) and computed tomography (CT), previous molecular imaging efforts have used magnetic resonance (MR), near-infrared fluorescence (NIRF), bioluminescence, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). Mouse and rat AAA models will hopefully provide insight into potential disease mechanisms, and the development of advanced molecular imaging techniques, if clinically useful, may have translational potential. These efforts could help improve the management of aneurysms and better evaluate the therapeutic potential of new treatments for human AAA disease.

Novel mechanisms of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are a common but asymptomatic disease that has high susceptibility to rupture. Current therapeutic options are limited to surgical procedures because no pharmacological approaches have been proven to decrease either expansion or rupture of human AAAs. The current dearth of effective medical treatment is attributed to insufficient understanding of the mechanisms underlying the initiation, propagation and rupture of AAAs. This review will emphasize recent advances in mechanistic studies that may provide insights into potential pharmacological treatments for this disease. While we primarily focus on recent salient findings, we also discuss mechanisms that continue to be controversial depending on models under study. Despite the progress on exploring mechanisms of experimental AAAs, ultimate validation of mechanisms will require completion of prospective double-blinded clinical trials. In addition, we advocate increased emphasis of collaborative studies using animal models and human tissues for determination of mechanisms that explore expansion and rupture of existing AAAs.

Cardiovascular disease in autoimmune rheumatic diseases

Various autoimmune rheumatic diseases (ARDs), including rheumatoid arthritis, spondyloarthritis, vasculitis and systemic lupus erythematosus, are associated with premature atherosclerosis. However, premature atherosclerosis has not been uniformly observed in systemic sclerosis. Furthermore, although experimental models of atherosclerosis support the role of antiphospholipid antibodies in atherosclerosis, there is no clear evidence of premature atherosclerosis in antiphospholipid syndrome (APA). Ischemic events in APA are more likely to be caused by pro-thrombotic state than by enhanced atherosclerosis. Cardiovascular disease (CVD) in ARDs is caused by traditional and non-traditional risk factors. Besides other factors, inflammation and immunologic abnormalities, the quantity and quality of lipoproteins, hypertension, insulin resistance/hyperglycemia, obesity and underweight, presence of platelets bearing complement protein C4d, reduced number and function of endothelial progenitor cells, apoptosis of endothelial cells, epigenetic mechanisms, renal disease, periodontal disease, depression, hyperuricemia, hypothyroidism, sleep apnea and vitamin D deficiency may contribute to the premature CVD. Although most research has focused on systemic inflammation, vascular inflammation may play a crucial role in the premature CVD in ARDs. It may be involved in the development and destabilization of both atherosclerotic lesions and of aortic aneurysms (a known complication of ARDs). Inflammation in subintimal vascular and perivascular layers appears to frequently occur in CVD, with a higher frequency in ARD than in non-ARD patients. It is possible that this inflammation is caused by infections and/or autoimmunity, which might have consequences for treatment. Importantly, drugs targeting immunologic factors participating in the subintimal inflammation (e.g., T- and B-cells) might have a protective effect on CVD. Interestingly, vasa vasorum and cardiovascular adipose tissue may play an important role in atherogenesis. Inflammation and complement depositions in the vessel wall are likely to contribute to vascular stiffness. Based on biopsy findings, also inflammation in the myocardium and small vessels may contribute to premature CVD in ARDs (cardiac ischemia and heart failure). There is an enormous need for an improved CVD prevention in ARDs. Studies examining the effect of DMARDs/biologics on vascular inflammation and CV risk are warranted.

An inhibitory effect of tumor necrosis factor-alpha antagonist to gene expression in monocrotaline-induced pulmonary hypertensive rats model

Purpose

Tumor necrosis factor (TNF)-α is thought to contribute to pulmonary hypertension. We aimed to investigate the effect of infliximab (TNF-α antagonist) treatment on pathologic findings and gene expression in a monocrotaline-induced pulmonary hypertension rat model.

Methods

Six-week-old male Sprague-Dawley rats were allocated to 3 groups: control (C), single subcutaneous injection of normal saline (0.1 mL/kg); monocrotaline (M), single subcutaneous injection of monocrotaline (60 mg/kg); and monocrotaline + infliximab (M+I), single subcutaneous injection of monocrotaline plus single subcutaneous injection of infliximab (5 mg/kg). The rats were sacrificed after 1, 5, 7, 14, or 28 days. We examined changes in pathology and gene expression levels of TNF-α, endothelin-1 (ET-1), endothelin receptor A (ERA), endothelial nitric oxide synthase (eNOS), matrix metalloproteinase (MMP)2, and tissue inhibitor of matrix metalloproteinase (TIMP).

Results

The increase in medial wall thickness of the pulmonary arteriole in the M+I group was significantly lower than that in the M group on day 7 after infliximab treatment (P<0.05). The number of intra-acinar muscular arteries in the M+I group was lower than that in the M group on days 14 and 28 (P<0.05). Expression levels of TNF-α, ET-1, ERA, and MMP2 were significantly lower in the M+I group than in the M group on day 5, whereas eNOS and TIMP expressions were late in the M group (day 28).

Conclusion

Infliximab administration induced early changes in pathological findings and expression levels of TNF-α, and MMP2 in a monocrotaline-induced pulmonary hypertension rat model.

A cytokine axis regulates elastin formation and degradation

Underlying the dynamic regulation of tropoelastin expression and elastin formation in development and disease are transcriptional and post-transcriptional mechanisms that have been the focus of much research. Of particular importance is the cytokine-governed elastin regulatory axis in which the pro-elastogenic activities of transforming growth factor β-1 (TGFβ1) and insulin-like growth factor-I (IGF-I) are opposed by anti-elastogenic activities of basic fibroblast growth factor (bFGF/FGF-2), heparin-binding epidermal growth factor-like growth factor (HB-EGF), EGF, PDGF-BB, TGFα, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-1β and noncanonical TGFβ1 signaling. A key mechanistic feature of the regulatory axis is that cytokines influence elastin formation through effects on the cell cycle involving control of cyclin-cyclin dependent kinase complexes and activation of the Ras/MEK/ERK signaling pathway. In this article we provide an overview of the major cytokines/growth factors that modulate elastogenesis and describe the underlying molecular mechanisms for their action on elastin production.

Adenosine 2A receptor modulates inflammation and phenotype in experimental abdominal aortic aneurysms

Activation of the adenosine 2A receptor (A2AR) reduces inflammation in models of acute injury but contribution in development of chronic abdominal aortic aneurysms (AAAs) is unknown. Elastase perfusion to induce AAA formation in A2AR-knockout (A2ARKO) and C57BL6/J wild-type (WT) mice resulted in nearly 100% larger aneurysms in A2ARKO compared to WT at d 14 (P<0.05), with evidence of greater elastin fragmentation, more immune cell infiltration, and increased matrix metallatoproteinase (MMP) 9 expression (P<0.05). Separately, exogenous A2AR antagonism in elastase-perfused WT mice also resulted in larger aneurysms (P<0.05), while A2AR agonism limited aortic dilatation (P<0.05). Activated Thy-1.2(+) T lymphocytes from WT mice treated in vitro with A2AR antagonist increased cytokine production, and treatment with A2AR agonist decreased cytokine production (P<0.05 for all). Primary activated CD4(+) T lymphocytes from A2ARKO mice exhibited greater chemotaxis (P<0.05). A2AR antagonist increased chemotaxis of activated CD4(+) cells from WT mice in vitro, and A2AR agonist reduced this effect (P<0.05). A2AR activation attenuates AAA formation partly by inhibiting immune cell recruitment and reducing elastin fragmentation. These findings support augmenting A2AR signaling as a putative target for limiting aneurysm formation.

Peptide inhibitor of CXCL4-CCL5 heterodimer formation, MKEY, inhibits experimental aortic aneurysm initiation and progression

OBJECTIVE

Macrophages are critical contributors to abdominal aortic aneurysm (AAA) disease. We examined the ability of MKEY, a peptide inhibitor of CXCL4-CCL5 interaction, to influence AAA progression in murine models.

APPROACH AND RESULTS

AAAs were created in 10-week-old male C57BL/6J mice by transient infrarenal aortic porcine pancreatic elastase infusion. Mice were treated with MKEY via intravenous injection either (1) before porcine pancreatic elastase infusion or (2) after aneurysm initiation. Immunostaining demonstrated CCL5 and CCR5 expression on aneurysmal aortae and mural monocytes/macrophages, respectively. MKEY treatment partially inhibited migration of adaptively transferred leukocytes into aneurysmal aortae in recipient mice. Although all vehicle-pretreated mice developed AAAs, aneurysms formed in only 60% (3/5) and 14% (1/7) of mice pretreated with MKEY at 10 and 20 mg/kg, respectively. MKEY pretreatment reduced aortic diameter enlargement, preserved medial elastin fibers and smooth muscle cells, and attenuated mural macrophage infiltration, angiogenesis, and aortic metalloproteinase 2 and 9 expression after porcine pancreatic elastase infusion. MKEY initiated after porcine pancreatic elastase infusion also stabilized or reduced enlargement of existing AAAs. Finally, MKEY treatment was effective in limiting AAA formation after angiotensin II infusion in apolipoprotein E-deficient mice.

CONCLUSIONS

MKEY suppresses AAA formation and progression in 2 complementary experimental models. Peptide inhibition of CXCL4-CCL5 interactions may represent a viable translational strategy to limit progression of human AAA disease.

AKT2 confers protection against aortic aneurysms and dissections

RATIONALE

Aortic aneurysm and dissection (AAD) are major diseases of the adult aorta caused by progressive medial degeneration of the aortic wall. Although the overproduction of destructive factors promotes tissue damage and disease progression, the role of protective pathways is unknown.

OBJECTIVE

In this study, we examined the role of AKT2 in protecting the aorta from developing AAD.

METHODS AND RESULTS

AKT2 and phospho-AKT levels were significantly downregulated in human thoracic AAD tissues, especially within the degenerative medial layer. Akt2-deficient mice showed abnormal elastic fibers and reduced medial thickness in the aortic wall. When challenged with angiotensin II, these mice developed aortic aneurysm, dissection, and rupture with features similar to those in humans, in both thoracic and abdominal segments. Aortas from Akt2-deficient mice displayed profound tissue destruction, apoptotic cell death, and inflammatory cell infiltration that were not observed in aortas from wild-type mice. In addition, angiotensin II-infused Akt2-deficient mice showed significantly elevated expression of matrix metalloproteinase-9 (MMP-9) and reduced expression of tissue inhibitor of metalloproteinase-1 (TIMP-1). In cultured human aortic vascular smooth muscle cells, AKT2 inhibited the expression of MMP-9 and stimulated the expression of TIMP-1 by preventing the binding of transcription factor forkhead box protein O1 to the MMP-9 and TIMP-1 promoters.

CONCLUSIONS

Impaired AKT2 signaling may contribute to increased susceptibility to the development of AAD. Our findings provide evidence of a mechanism that underlies the protective effects of AKT2 on the aortic wall and that may serve as a therapeutic target in the prevention of AAD.

Locally applied leptin induces regional aortic wall degeneration preceding aneurysm formation in apolipoprotein E-deficient mice

OBJECTIVE

Leptin promotes atherosclerosis and vessel wall remodeling. As abdominal aortic aneurysm (AAA) formation involves tissue remodeling, we hypothesized that local leptin synthesis initiates and promotes this process.

METHODS AND RESULTS

Human surgical AAA walls were analyzed for antigen and mRNA levels of leptin and leptin receptor, as well as mRNA for matrix metalloproteinases (MMP)-9 and MMP-12. Leptin and leptin receptor antigen were evident in all AAAs, and leptin, MMP-9, and MMP-12 mRNA was increased relative to age-matched nondilated controls. To simulate in vivo local leptin synthesis, ApoE(-/-) mice were subjected to a paravisceral periaortic application of low-dose leptin. Leptin-treated aortas exhibited decreased transforming growth factor-β and increased MMP-9 mRNA levels 5 days after surgery, and leptin receptor mRNA was upregulated by day 28. Serial ultrasonography demonstrated accelerated regional aortic diameter growth after 28 days, correlating with local medial degeneration, increased MMP-9, MMP-12, and periadventitial macrophage clustering. Furthermore, the combination of local periaortic leptin and systemic angiotensin II administration augmented medial MMP-9 synthesis and aortic aneurysm size.

CONCLUSIONS

Leptin is locally synthesized in human AAA wall. Paravisceral aortic leptin in ApoE(-/-) mice induces local medial degeneration and augments angiotensin II-induced AAA, thus suggesting novel mechanistic links between leptin and AAA formation.

Efficacy and mechanism of angiotensin II receptor blocker treatment in experimental abdominal aortic aneurysms

Background

Despite the importance of the renin-angiotensin (Ang) system in abdominal aortic aneurysm (AAA) pathogenesis, strategies targeting this system to prevent clinical aneurysm progression remain controversial and unproven. We compared the relative efficacy of two Ang II type 1 receptor blockers, telmisartan and irbesartan, in limiting experimental AAAs in distinct mouse models of aneurysm disease.

Methodology/Principal Findings

AAAs were induced using either 1) Ang II subcutaneous infusion (1000 ng/kg/min) for 28 days in male ApoE^−/− mice, or 2) transient intra-aortic porcine pancreatic elastase infusion in male C57BL/6 mice. One week prior to AAA creation, mice started to daily receive irbesartan (50 mg/kg), telmisartan (10 mg/kg), fluvastatin (40 mg/kg), bosentan (100 mg/kg), doxycycline (100 mg/kg) or vehicle alone. Efficacy was determined via serial in vivo aortic diameter measurements, histopathology and gene expression analysis at sacrifice. Aortic aneurysms developed in 67% of Ang II-infused ApoE^−/− mice fed with standard chow and water alone (n = 15), and 40% died of rupture. Strikingly, no telmisartan-treated mouse developed an AAA (n = 14). Both telmisartan and irbesartan limited aneurysm enlargement, medial elastolysis, smooth muscle attenuation, macrophage infiltration, adventitial neocapillary formation, and the expression of proteinases and proinflammatory mediators. Doxycycline, fluvastatin and bosentan did not influence aneurysm progression. Telmisartan was also highly effective in intra-aortic porcine pancreatic elastase infusion-induced AAAs, a second AAA model that did not require exogenous Ang II infusion.

Conclusion/Significance

Telmisartan suppresses experimental aneurysms in a model-independent manner and may prove valuable in limiting clinical disease progression.

Experimental abdominal aortic aneurysm formation is mediated by IL-17 and attenuated by mesenchymal stem cell treatment

BACKGROUND

Abdominal aortic aneurysm (AAA) formation is characterized by inflammation, smooth muscle activation and matrix degradation. This study tests the hypothesis that CD4+ T-cell-produced IL-17 modulates inflammation and smooth muscle cell activation, leading to the pathogenesis of AAA and that human mesenchymal stem cell (MSC) treatment can attenuate IL-17 production and AAA formation.

METHODS AND RESULTS

Human aortic tissue demonstrated a significant increase in IL-17 and IL-23 expression in AAA patients compared with control subjects as analyzed by RT-PCR and ELISA. AAA formation was assessed in C57BL/6 (wild-type; WT), IL-23(-/-) or IL-17(-/-) mice using an elastase-perfusion model. Heat-inactivated elastase was used as control. On days 3, 7, and 14 after perfusion, abdominal aorta diameter was measured by video micrometry, and aortic tissue was analyzed for cytokines, cell counts, and IL-17-producing CD4+ T cells. Aortic diameter and cytokine production (MCP-1, RANTES, KC, TNF-α, MIP-1α, and IFN-γ) was significantly attenuated in elastase-perfused IL-17(-/-) and IL-23(-/-) mice compared with WT mice on day 14. Cellular infiltration (especially IL-17-producing CD4+ T cells) was significantly attenuated in elastase-perfused IL-17(-/-) mice compared with WT mice on day 14. Primary aortic smooth muscle cells were significantly activated by elastase or IL-17 treatment. Furthermore, MSC treatment significantly attenuated AAA formation and IL-17 production in elastase-perfused WT mice.

CONCLUSIONS

These results demonstrate that CD4+ T-cell-produced IL-17 plays a critical role in promoting inflammation during AAA formation and that immunomodulation of IL-17 by MSCs can offer protection against AAA formation.

Development of a novel murine model of aortic aneurysms using peri-adventitial elastase

BACKGROUND

Our aim was to establish a novel model of abdominal aortic aneurysms (AAA) in mice using application of peri-adventitial elastase.

METHODS

C57BL/6J male mice underwent infrarenal peri-adventitial application of either (1) sodium chloride (control; n = 7), (2) porcine pancreatic elastase (PPE; n = 14), or (3) PPE and doxycycline (PPE + doxycycline 200 mg/kg; n = 11) for 14 days. Aortas were analyzed by video micrometry, immunohistochemistry, qualitative polymerase chain reaction, and zymography. Groups underwent Mann-Whitney U comparisons.

RESULTS

At day 14 compared with baseline, control animals had minimal aortic dilation, whereas fusiform aneurysms were seen in PPE (control, 20 ± 3%; PPE, 82 ± 15%; P ≤ .003). Doxycycline abrogated aneurysm formation (PPE, 82 ± 15%; PPE + doxycycline, 37 ± 10%; P ≤ .03). Compared with control and PPE + doxycycline, immunohistochemistry demonstrated greater elastin fiber degradation, macrophage infiltration, and matrix metalloproteinase-9 expression in PPE. Ki-67 and cleaved caspase-3 were lower in control versus PPE. The loss of smooth muscle marker expression seen with PPE was preserved in PPE + doxycycline. Zymography confirmed that both MMP-2 and -9 were more active in PPE than PPE + doxycycline.

CONCLUSION

Peri-adventitial application of elastase is a simple, reproducible in vivo model of aneurysm formation leading to consistent infrarenal aortic aneurysm development by day 14, with inflammatory cell infiltration and MMP upregulation. Doxycycline inhibits AAA progression in this model via limiting matrix degradation and preserving differentiated smooth muscle cells.

Quercetin, a flavonoid with anti-inflammatory activity, suppresses the development of abdominal aortic aneurysms in mice

Inflammation has been implicated as a contributing factor in the development of abdominal aortic aneurysms (AAA). Quercetin, a natural flavonoid with anti-inflammatory properties, is known for its beneficial effects on vascular disease. In this study, we examined the effects of quercetin to inflammatory cell infiltration, subsequent expression of cytokines and activation of proteases on the expansion of experimental AAA. Aneurysms were induced by abluminal application of calcium chloride in C57/BL6 mice. Quercetin (60 mg/kg) was administered once daily by gavage beginning 2 weeks before AAA induction and continuing for 8 weeks. Mice treated with quercetin exhibited a 32.7% reduction in aortic size compared with vehicle-treated controls. Prevention of AAA was associated with preservation of medial structure, as well as a relative reduction in macrophage and CD3(+) T cell infiltration in aortic tissue, inflammatory cytokines release and nuclear factor κB activation. Quercetin also reduced the expression of matrix metalloproteinase (MMP)-2, MMP-9, cathepsin B, and cathepsin K in aortic tissue. In addition, quercetin treatment increased tissue inhibitors of metalloproteinases (TIMP)-1 gene expression. These data indicate that quercetin may be useful for the prevention and treatment of AAA via blocking the inflammatory response and inhibiting the proteases involved in the pathogenesis of this disease.

MMP-2 regulates Erk1/2 phosphorylation and aortic dilatation in Marfan syndrome

RATIONALE

Aneurysm and dissection of the ascending thoracic aorta are the main cardiovascular complications of Marfan syndrome (MFS) resulting in premature death. Studies using mouse models of MFS have shown that activation of transforming growth factor-beta (TGF-β) and the concomitant upregulation of matrix metalloproteinases (MMPs) contribute to aneurysm development. Our previous study showed that doxycycline delayed aneurysm rupture in a mouse model of MFS, Fbn1(mgR/mgR). Losartan has been shown to prevent aneurysms in another mouse model of MFS, Fbn1(C1039G/+), through inhibition of the Erk1/2 pathway. However, the role of MMP-2 in MFS and effect of losartan on the lifespan of MFS mice remain unknown.

OBJECTIVE

We investigated the role of MMP-2 in MFS and compared the effects of losartan and doxycycline on aortic dilatation and survival in Fbn1(mgR/mgR) mice.

METHODS AND RESULTS

By life table analysis, we found that losartan and doxycycline improved the survival of Fbn1(mgR/mgR) mice. Gelatin zymography and Western blot data showed that only doxycycline inhibited MMP-2 expression, whereas both drugs decreased Erk1/2 phosphorylation. When combined, only one of nine mice died within the 30-week study; aortic histology and diameter were normalized and the effects on Smad2 phosphorylation was additive. To further explore the role of MMP-2 in MFS, we created MMP-2-deficient Fbn1(mgR/mgR) mice. MMP-2 deletion inhibited activation of TGF-β and phosphorylation of Erk1/2 and Smad2 and prolonged the lifespan of the mice.

CONCLUSIONS

These studies demonstrated that inhibition of MMP-2 by doxycycline delayed the manifestations of MFS, in part, through its ability to decrease active TGF-β and the noncanonical signaling cascade downstream of TGF-β. This study further suggested that targeting TGF-β signaling at different points might be a more effective strategy for inhibiting disease progression.

Emerging role of mast cells and macrophages in cardiovascular and metabolic diseases

Mast cells are essential in allergic immune responses. Recent discoveries have revealed their direct participation in cardiovascular diseases and metabolic disorders. Although more sophisticated mechanisms are still unknown, data from animal studies suggest that mast cells act similarly to macrophages and other inflammatory cells and contribute to human diseases through cell-cell interactions and the release of proinflammatory cytokines, chemokines, and proteases to induce inflammatory cell recruitment, cell apoptosis, angiogenesis, and matrix protein remodeling. Reduced cardiovascular complications and improved metabolic symptoms in animals receiving over-the-counter antiallergy medications that stabilize mast cells open another era of mast cell biology and bring new hope to human patients suffering from these conditions.

Resveratrol counteracts systemic and local inflammation involved in early abdominal aortic aneurysm development

BACKGROUND

Monocyte activation, macrophage infiltration, vascular oxidative stress and matrix proteolysis are inflammatory key steps contributing to abdominal aortic aneurysm (AAA) development. A phenotypical and functional heterogeneity is recognizable in monocytes by the differential expression of surface molecules: CD62L- subset corresponds to activated monocytes, while CD143/ACE surface expression increases during their differentiation into macrophages. In this work, Resveratrol, which is an antioxidant polyphenol with vasoprotective properties, has been evaluated for its potential to limit aneurysm development and monocyte-dependent inflammatory response in a model of elastase-induced AAA.

METHODS

Male Sprague-Dawley rats received Resveratrol (10 mg/kg/die) (Rsv group, n=15) or vehicle (ethanol) alone (Et-OH group, n=15) continuously from 7 d before until 14 d after the AAA induction with elastase; five littermates were used as untreated control group (Ctr group, n=5). At the end of treatment, CD143 and CD62L monocyte expression was analyzed by flow cytometry, serum antioxidant capacity was evaluated using the TRAP method and circulating TNFα, and MMP-9 were measured with ELISA and gel zymography, respectively. Aortas were subjected to histology and immunohistochemistry for morphological analysis, macrophage infiltration, and MMP-9, TNFα, and VEGF expression.

RESULTS

Resveratrol counteracted the CD62L-monocyte subset expansion, CD143 monocyte expression, and circulating levels of MMP-9 activity and TNFα associated to AAA induction. Similarly, treatment with Resveratrol significantly attenuated AAA expansion, vessel wall macrophage infiltration and MMP-9, VEGF, and TNFα expression, compared with AAA from Et-OH group.

CONCLUSIONS

Resveratrol limited the monocyte-dependent inflammatory response, macrophage differentiation and aortic lumen enlargement in elastase-induced AAA. These data suggest that Resveratrol might be tested in selected patients with small AAA to modulate the early systemic and local inflammatory response associated to AAA progression.

Transcriptional profiling and network analysis of the murine angiotensin II-induced abdominal aortic aneurysm

We sought to characterize temporal gene expression changes in the murine angiotensin II (ANG II)-ApoE-/- model of abdominal aortic aneurysm (AAA). Aortic ultrasound measurements were obtained over the 28-day time-course. Harvested suprarenal aortic segments were evaluated with whole genome expression profiling at 7, 14, and 28 days using the Agilent Whole Mouse Genome microarray platform and Statistical Analysis of Microarrays at a false discovery rate of <1%. A group of angiotensin-treated mice experienced contained rupture (CR) within 7 days and were analyzed separately. Progressive aortic dilatation occurred throughout the treatment period. However, the numerous early expression differences between ANG II-treated and control were not sustained over time. Ontologic analysis revealed widespread upregulation of inflammatory, immune, and matrix remodeling genes with ANG II treatment, among other pathways such as apoptosis, cell cycling, angiogenesis, and p53 signaling. CR aneurysms displayed significant decreases in TGF-β/BMP-pathway signaling, MAPK signaling, and ErbB signaling genes vs. non-CR/ANG II-treated samples. We also performed literature-based network analysis, extracting numerous highly interconnected genes associated with aneurysm development such as Spp1, Myd88, Adam17 and Lox. 1) ANG II treatment induces extensive early differential expression changes involving abundant signaling pathways in the suprarenal abdominal aorta, particularly wide-ranging increases in inflammatory genes with aneurysm development. 2) These gene expression changes appear to dissipate with time despite continued growth, suggesting that early changes in gene expression influence disease progression in this AAA model, and that the aortic tissue adapts to prolonged ANG II infusion. 3) Network analysis identified nexus genes that may constitute aneurysm biomarkers or therapeutic targets.

Tumor necrosis factor-α converting enzyme is a key mediator of abdominal aortic aneurysm development

OBJECTIVE

Tumor necrosis factor (TNF)-α is known to be elevated in plasma and the aorta in abdominal aortic aneurysm (AAA) patients. We sought to clarify the role of TNF-α converting enzyme (Tace), which cleaves the transmembrane precursor of TNF-α, in AAA development.

METHODS

We obtained aortic sample of AAA during surgical operation to assess the histological features and protein expression of human AAA. AAA was induced in mice with temporal systemic deletion of Tace by the inducible Mx-1 Cre transgene (TaceMx1) and in wild-type littermates (CON) by periaortic application of CaCl(2) (AAA/TaceMx1, AAA/CON).

RESULTS

Tace expression was increased in human AAA samples as compared with normal aorta. Six weeks postoperatively, aortic diameter in AAA/TaceMx1 was decreased than in AAA/CON in association with attenuated TNF-α expression and extracellular matrix disruption. Increased activities of matrix metalloproteinase (MMP)-9 and MMP-2, numbers of Mac-2-positive macrophages, CD3-positive T lymphocytes and CD31-positive vessels in periaortic tissues, mRNA expression of CD68, monocyte chemotactic protein-1, TNF-α, vascular endothelial growth factor-A, p47 and glutathione peroxidases, and protein expression of phospho-c-Jun N-terminal kinase in AAA were all attenuated by Tace deletion. Protein expression of transforming growth factor (TGF)-β1 was upregulated by Tace deletion in sham-operated mice. TGF-β1 expression was further increased in AAA/TaceMx1.

CONCLUSIONS

Tace was overexpressed in the aortic wall in human and experimental AAA. Temporal systemic deletion of Tace prevented AAA development in association with attenuating inflammation, oxidative stress, neoangiogenesis and extracellular matrix disruption, suggesting a crucial role of Tace in AAA development.

Resveratrol prevents the development of abdominal aortic aneurysm through attenuation of inflammation, oxidative stress, and neovascularization

OBJECTIVE

We sought to examine the effect of resveratrol (3,4',5-trihydroxy-trans-stilbene), a plant-derived polyphenolic compound, on the development of abdominal aortic aneurysm (AAA).

METHODS

AAA was induced in mice by periaortic application of CaCl(2). NaCl (0.9%)-applied mice were used as a sham group. Mice were treated with intraperitoneal injection of PBS (Sham/CON, AAA/CON, n=30 for each) or resveratrol (100 mg/kg/day) (AAA/RSVT, n=30). Six weeks after the operation, aortic tissue was excised for further examinations.

RESULTS

Aortic diameter was enlarged in AAA/CON compared with Sham/CON. Resveratrol treatment reduced the aneurysm size and inflammatory cell infiltration in the aortic wall compared with AAA/CON. Elastica Van Gieson staining showed destruction of the wavy morphology of the elastic lamellae in AAA/CON, while it was preserved in AAA/RSVT. The increased mRNA expression of monocyte chemotactic protein-1, tumor necrosis factor-α, intercellular adhesion molecule-1, CD68, vascular endothelial growth factor-A, p47, glutathione peroxidase (GPX)1 and GPX3 were attenuated by resveratrol treatment (all p<0.05). Administration of resveratrol decreased protein expression of phospho-p65 in AAA. The increased 8-hydroxy-2'-deoxyguanosine-positive cell count and 4-hydroxy-2-nonenal-positive cell count in AAA were also reduced by resveratrol treatment. Zymographic activity of matrix metalloproteinase (MMP)-9 and MMP-2 was lower in AAA/RSVT compared with AAA/CON (both p<0.05). Compared with AAA/CON, Mac-2(+) macrophages and CD31(+) vessels in the aortic wall were decreased in AAA/RSVT (both p<0.05).

CONCLUSION

Treatment with resveratrol in mice prevented the development of CaCl(2)-induced AAA, in association with reduced inflammation, oxidative stress, neoangiogenesis, and extracellular matrix disruption. These findings suggest therapeutic potential of resveratrol for AAA.

Regulation of MMP-9 expression by the A2b adenosine receptor and its dependency on TNF-α signaling

OBJECTIVE

Macrophage- and vascular-derived matrix metalloproteinase (MMP)-9 plays an important role in neointima formation after vascular injury. The A2b adenosine receptor (A2bAR) elevates cyclic adenosine monophosphate and suppresses tumor necrosis factor-α (TNF-α) levels at baseline and after vascular injury. Considering the influences of TNF-α on MMP-9 expression and activity, here we examined the effect of the A2bAR on the expression of MMP-9 and its potential dependency on TNF-α.

MATERIALS AND METHODS

We applied protein activity and mRNA analyses of MMP-9 in macrophages derived from A2bAR knockout (KO) and TNF-α receptor KO mice. We employed guidewire-induced femoral artery injuries on A2bAR KO and control mice and analyzed by immunohistochemistry MMP-9 expression in the neointima area.

RESULTS

MMP-9 activity is somewhat less in resident A2bAR KO macrophages compared with wild-type cells. However, MMP-9 is increased in activated macrophages from A2bAR KO when TNF-α is further elevated, or in wild-type cells after TNF-α treatment. In accordance, A2bAR activation downregulates MMP-9 expression in wild-type macrophages, which is ablated in TNF-α receptor KO cells. A greater vascular lesion after femoral artery injury in A2bAR KO mice is associated with elevated TNF-α levels and augmented MMP-9, compared to control mice.

CONCLUSIONS

Ablation of the A2bAR in activated macrophages increases MMP-9. A2bAR activation reduces MMP-9 expression, which depends on TNF-α and could contribute to the protective role of A2bAR in a vascular injury model.

Mast cells: important players in the orchestrated pathogenesis of abdominal aortic aneurysms

Mast cells (MCs) regulate inflammation and immunity. Their granular content includes heparin, histamine, and several enzymes (tryptase, chymase, carboxypeptidase, and cathepsin G). In addition, activated MCs synthesize and release eicosanoids and a large number of cytokines and chemokines. Recent findings suggest a role of MCs in abdominal aortic aneurysms (AAAs) in humans, where they are found in the media and adventitia. Experimentally induced AAA in MC-deficient animals and animals treated with MC inhibitors demonstrate that MCs are involved in the pathogenesis of AAA via several different mechanisms. MC-dependent activation of metalloproteinases and the renin-angiotensin system, contribution to smooth muscle cell apoptosis, and release of proteolytic enzymes are some key examples. Human studies indicate that MCs are the main source of cathepsin G in AAAs and contribute to activation of the renin-angiotensin system via chymase and cathepsin G. Activated MCs also contribute to neovascularization, inflammation, and atherosclerosis, all hallmarks of AAA. Thus, we may envision that MC stabilizing agents, as well as leukotriene receptor antagonists and histamine receptor blockers already in clinical use for treatment of other diseases, could also be tested for their efficacy in preventing development and growth of AAA.

Vascular smooth muscle cell peroxisome proliferator-activated receptor-γ deletion promotes abdominal aortic aneurysms

OBJECTIVE

Peroxisome proliferator-activated receptor-γ (PPARγ) plays an important role in the vasculature; however, the role of PPARγ in abdominal aortic aneurysms (AAA) is not well understood. We hypothesized that PPARγ in smooth muscle cells (SMCs) attenuates the development of AAA. We also investigated PPARγ-mediated signaling pathways that may prevent the development of AAA.

METHODS

We determined whether periaortic application of CaCl(2) renders vascular SMC-selective PPARγ knockout (SMPG KO) mice more susceptible to destruction of normal aortic wall architecture.

RESULTS

There is evidence of increased vessel dilatation in the abdominal aorta 6 weeks after 0.25M periaortic CaCl(2) application in SMPG KO mice compared with littermate controls (1.4 ± 0.3 mm [n = 8] vs 1.1 ± 0.2 mm [n = 7]; P = .000119). Results from SMPG KO mice indicate medial layer elastin degradation was greater 6 weeks after abluminal application of CaCl(2) to the abdominal aorta (P < .01). Activated cathepsin S, a potent elastin-degrading enzyme, was increased in SMPG KO mice vs wild-type controls. To further identify a role of PPARγ signaling in reducing the development of AAA, we demonstrated that adenoviral-mediated PPARγ overexpression in cultured rat aortic SMCs decreases (P = .022) the messenger RNA levels of cathepsin S. In addition, a chromatin immunoprecipitation assay detected PPARγ bound to a peroxisome proliferator-activated receptor response element (PPRE) -141 to -159 bp upstream of the cathepsin S gene sequence in mouse aortic SMCs. Also, adenoviral-mediated PPARγ overexpression and knockdown in cultured rat aortic SMCs decreases (P = .013) and increases (P = .018) expression of activated cathepsin S. Finally, immunohistochemistry demonstrated a greater inflammatory infiltrate in SMPG KO mouse aortas, as evidenced by elevations in F4/80 and tumor necrosis factor-α expression.

CONCLUSION

In this study, we identify PPARγ as an important contributor in attenuating the development of aortic aneurysms by demonstrating that loss of PPARγ in vascular SMCs promotes aortic dilatation and elastin degradation. Thus, PPARγ activation may be potentially promising medical therapy in reducing the risk of AAA progression and rupture.

Molecular imaging of matrix metalloproteinase activation to predict murine aneurysm expansion in vivo

Rupture and dissection are major causes of morbidity and mortality in arterial aneurysm and occur more frequently in rapidly expanding aneurysms. Current imaging modalities provide little information on aneurysm beyond size. Matrix metalloproteinase (MMP) activation plays a key role in the pathogenesis of aneurysm. We investigated whether imaging MMP activation in aneurysm helps predict its propensity to expansion.

METHODS

We used a model of carotid aneurysm in apolipoprotein E-deficient (apoE(-/-)) mice. Radiotracers with specificity for activated MMPs were used to detect and quantify MMP activation by micro-SPECT/CT in vivo. Tracer uptake was confirmed by autoradiography and gamma-well counting, and specificity was demonstrated using an excess of unlabeled precursor and a specific MMP inhibitor.

RESULTS

We demonstrated that several MMPs are expressed with distinct temporal patterns in aneurysm. Significant focal uptake was observed in aneurysmal carotid arteries, peaking at 4 wk after aneurysm induction. In a group of animals imaged serially at 2 and 4 wk after aneurysm induction, MMP tracer uptake at 2 wk correlated well with the vessel area assessed by histology at 4 wk.

CONCLUSION

Molecular imaging of MMP activation is a useful experimental, and potentially clinical, tool to noninvasively predict the propensity of an aneurysm to expansion in vivo.

Gastroprotective activity of atractylenolide III from Atractylodes ovata on ethanol-induced gastric ulcer in vitro and in vivo

Objectives

The rhizome of Atractylodes ovata De Candolle is popularly used in traditional Chinese medicine to treat gastrointestinal diseases. However, the major gastroprotective compounds of A. ovata have not been identified. This study reports on the principal gastro- protective component of A. ovata.

Methods

Five sesquiterpenoids (atractylon, atractylenolides I, II, III and biatractylolide) were isolated from the extracts of A. ovata rhizome via silica gel column chromatography. The gastroprotective effects of these five sesquiterpenoids were measured in in-vitro ethanol-induced primary culture rat gastric mucosal (PRGM) cell damage and in-vivo ethanol-induced acute rat gastric ulcer models.

Key findings

Atractylon, atractylenolide I and biatractylolide were strongly toxic in PRGM cells, whilst atractylenolides II and III were not. Atractylenolide II did not show cytoprotective effects, but oral administration of atractylenolide III dose-dependently prevented ethanol-induced PRGM cell death and cell membrane damage. The EC50 values were 0.27 and 0.34 mm, respectively. In the in-vivo assay, atractylenolide III 10 mg/kg significantly reduced 70% ethanol-induced Wistar rat gastric ulcer. Atractylenolide III could inhibit matrix metalloproteinase (MMP)-2 and MMP-9 expression through upregulation of tissue inhibitors of metalloproteinase from the gastric ulcerated tissues.

Conclusions

Atractylenolide III was the major gastroprotective component of A. ovata in ethanol-induced acute gastric ulcer. It is suggested that the gastroprotective mechanism of atractylenolide III was via inhibition of the MMP-2 and MMP-9 pathway.