Complicated abdominal aortic aneurysm (AAA) is a major cause of mortality in elderly men. Ang II-dependent TGF-β activity promotes aortic aneurysm progression in experimental Marfan syndrome. However, the role of TGF-β in experimental models of AAA has not been comprehensively assessed. Here, we show that systemic neutralization of TGF-β activity breaks the resistance of normocholesterolemic C57BL/6 mice to Ang II-induced AAA formation and markedly increases their susceptibility to the disease. These aneurysms displayed a large spectrum of complications on echography, including fissuration, double channel formation, and rupture, leading to death from aneurysm complications. The disease was refractory to inhibition of IFN-γ, IL-4, IL-6, or TNF-α signaling. Genetic deletion of T and B cells or inhibition of the CX3CR1 pathway resulted in partial protection. Interestingly, neutralization of TGF-β activity enhanced monocyte invasiveness, and monocyte depletion markedly inhibited aneurysm progression and complications. Finally, TGF-β neutralization increased MMP-12 activity, and MMP-12 deficiency prevented aneurysm rupture. These results clearly identify a critical role for TGF-β in the taming of the innate immune response and the preservation of vessel integrity in C57BL/6 mice, which contrasts with its reported pathogenic role in Marfan syndrome.

Matrix metalloproteinases (MMPs) are thought to be involved in the growth, destabilization, and eventual rupture of atherosclerotic lesions. Using the mouse brachiocephalic artery model of plaque instability, we compared apolipoprotein E (apoE)͞MMP-3, apoE͞MMP-7, apoE͞MMP-9, and apoE͞MMP-12 double knockouts with their age-, strain-, and sex-matched apoE single knockout controls. Brachiocephalic artery plaques were significantly larger in apoE͞MMP-3 and apoE͞MMP-9 double knockouts than in controls. The number of buried fibrous layers was also significantly higher in the double knockouts, and both knockouts exhibited cellular compositional changes indicative of an unstable plaque phenotype. Conversely, lesion size and buried fibrous layers were reduced in apoE͞MMP-12 double knockouts compared with controls, and double knockouts had increased smooth muscle cell and reduced macrophage content in the plaque, indicative of a stable plaque phenotype. ApoE͞MMP-7 double knockout plaques contained significantly more smooth muscle cells than controls, but neither lesion size nor features of stability were altered in these animals. Hence, MMP-3 and MMP-9 appear normally to play protective roles, limiting plaque growth and promoting a stable plaque phenotype. MMP-12 supports lesion expansion and destabilization. MMP-7 has no effect on plaque growth or stability, although it is associated with reduced smooth muscle cell content in plaques. These data demonstrate that MMPs are directly involved in atherosclerotic plaque destabilization and clearly show that members of the MMP family have widely differing effects on atherogenesis.animal models ͉ atherosclerosis M atrix metalloproteinases (MMPs) are a group of Ͼ20 zinccontaining endopeptidases that are either secreted or expressed at the cell surface of all of the main vascular cell types. MMPs have overlapping specificities, but each can process at least one extracellular matrix component, and many nonmatrix substrates have also been described. Given this complexity it is not surprising that multiple roles for MMPs have been proposed, including regulation of cell migration, proliferation, and death. As a result, roles for MMPs in atherosclerotic plaque growth and fibrous cap formation have been suggested (1). On the other hand, the presence of elevated mRNA, protein, and activity levels of MMPs within atherosclerotic lesions, particularly at the shoulder regions of the fibrous cap (2-5), has led to the suggestion that they degrade strength-giving extracellular matrix components, including fibrillar collagens. By this mechanism MMPs could promote atherosclerotic plaque destabilization, the main cause of myocardial infarction in humans.Intervention studies in animal models have been used to investigate the potential roles of MMPs in cardiovascular disease. For example, inhibition of MMP activity by adenovirusmediated delivery of the gene for human tissue inhibitor of metalloproteinases (TIMP)-1 reduced lesion size in the aortic root of apolipoprotein E (apoE) knockout mice (6). H...

Hydrogen sensors from Pd‐functionalized multi‐layer graphene nanoribbon networks are fabricated. The fabrication method of these networks is simple, low cost, and scalable, and their high specific surface area facilitates efficient functionalization and gas adsorption. These networks show high sensitivity to hydrogen at parts‐per‐million concentration levels at room temperature with a fast response and recovery time.

Background-These studies examined the early time course of plaque development and destabilization in the brachiocephalic artery of the apolipoprotein E-knockout mouse, the effects of pravastatin thereon, and the effects of pravastatin on established unstable plaques. Methods and Results-Male apolipoprotein E-knockout mice were fed a high-fat, cholesterol-enriched diet from the age of 8 weeks. Animals were euthanized at 1-week intervals between 4 and 9 weeks of fat feeding. Acutely ruptured plaques were observed in the brachiocephalic arteries of 3% of animals up to and including 7 weeks of fat feeding but in 62% of animals after 8 weeks, which suggests that there is a sharp increase in the number of plaque ruptures at 8 weeks. These acute plaque ruptures then appear to heal and form buried fibrous caps; after 9 weeks of fat feeding, mice had 1.05Ϯ0.15 buried fibrous caps at a single site in the brachiocephalic artery. Pravastatin (40 mg/kg of body weight per day for 9 weeks; resultant plasma concentration 16Ϯ4 nmol/L) had no effect on plasma cholesterol concentration in fat-fed apolipoprotein E-knockout mice but reduced the number of buried fibrous caps by 43% (PϽ0.0001). In longer-term experiments, the delay of pravastatin treatment until unstable plaques had developed reduced the incidence of acute plaque rupture by 36% (PϽ0.0001). Conclusions-Plaque rupture occurs at high frequency in the brachiocephalic arteries of male apolipoprotein E-knockout mice after 8 weeks of fat feeding. Pravastatin treatment inhibits early plaque rupture and is also effective when begun after unstable plaques have developed.

Abstract-The brachiocephalic arteries of fat-fed apolipoprotein E knockout mice develop plaques that frequently rupture and form luminal thromboses. The morphological characteristics of plaques without evidence of instability or with healed previous ruptures (intact) and vessels with acutely ruptured plaques (ruptured) have now been defined, to understand the process of plaque destabilization in more detail. Ninety-eight apolipoprotein E knockout mice were fed a diet supplemented with 21% lard and 0.15% cholesterol, for 5 to 59 weeks. Of these 98 mice, 51 had an acutely ruptured plaque in the brachiocephalic artery. See cover and page 713The apolipoprotein E (apoE) knockout mouse has become established as a model of hypercholesterolemia and atherosclerotic lesion development. 2-5 After 6 months on a high-fat diet, advanced fibrous plaques are observed with thin luminal elastin and collagen fibers capping small lipid-rich globular lesions. 5 Four studies have now reported that the lesions of apoE knockout mice can spontaneously become unstable. 6 -9 The brachiocephalic (also known as the innominate) artery, which is the first branch from the aortic arch, bifurcating to form the right common carotid artery and the right subclavian artery, is a site of predilection for the development of such vulnerable lesions. It provides a small and well-defined area in which to study the progressive loss of plaque stability and, eventually, rupture.In a previous study, 7 a small number of apoE knockout mice were examined. All of these had died suddenly, which meant that it was not possible to perfusion fix their arteries. In the current study, the development and morphology of brachiocephalic artery plaques have been characterized in a cohort of 98 apoE knockout mice. Ruptured and intact lesions have been compared both in animals dying suddenly and in those that were perfusion fixed after scheduled termination. Methods AnimalsHomozygous apoE knockout mice 10 were obtained from Charles River Laboratories (Manston, Kent, UK). The strain background of these animals was 50% C57BL/6, 50% 129SvJ, as determined by fingerprinting of tail-tip DNA. The housing and care of the animals and all the procedures used in these studies were performed in accordance with the guidelines and regulations of the University of Bristol and the United Kingdom Home Office. HusbandryStarting at 6 to 8 weeks of age, 98 apoE knockout mice (51 male) were fed a high-fat rodent diet containing 21% fat from lard and supplemented with 0.15% (wt/wt) cholesterol (Special Diets Services) for a period of 5 to 59 weeks. Cages were checked daily, and any animals that had suffered sudden death were immediately removed and processed for histological examination. TerminationAnimals were anesthetized by intraperitoneal injection of sodium pentobarbitone before exsanguination by arterial perfusion via the

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Abstract-Recent studies suggest that mast cell-derived neutral proteases can activate matrix-degrading metalloproteinases (MMPs). We have investigated the role of the mast cell proteases tryptase and chymase in the activation of MMPs in human carotid endarterectomy specimens (atherosclerotic, nϭ32) and postmortem carotid arteries (control, nϭ17). In vitro degranulation of mast cells in atherosclerotic carotid arteries by compound 48/80 caused a significant increase in MMP activity. Addition of the nonselective tryptase inhibitor antipain, the specific trypsinlike protease inhibitor 4-amidinophenylmethanesulfonyl fluoride, and the chymase inhibitor chymostatin reduced this increase in MMP activity by 30Ϯ6%, 23Ϯ6%, and 9Ϯ2%, respectively. Immunocytochemistry identified significantly higher numbers of tryptase-containing cells (mast cells) and cells expressing MMP-1 and MMP-3 in the "shoulder" regions of atherosclerotic artery lesions compared with the tunica media of control arteries. Dual immunocytochemistry showed collocation of MMP-1 and MMP-3 with mast cells in the shoulder regions. Degranulation was observed in 78Ϯ5% (meanϮSEM) of mast cells in this area, whereas nonactivated mast cells were observed in all other areas. In situ zymography revealed caseinolytic and gelatinolytic activity in these areas. In conclusion, in vitro mast cell degranulation, which releases mast cell proteases, in carotid arteries increases MMP activity. Furthermore, elevated MMP-1 and MMP-3 expression is collocated with increased numbers of degranulated mast cells and with greater MMP activity in the shoulder regions of atherosclerotic plaques. Activation of MMPs by mast cell-derived proteases may be an important mechanism in atherosclerotic plaque destabilization. (Arterioscler Thromb Vasc Biol. 1998;18:1707-1715.)

Remodelling of the extracellular matrix (ECM) and cell surface by matrix metalloproteinases (MMPs) is an important function of monocytes and macrophages. Recent work has emphasised the diverse roles of classically and alternatively activated macrophages but the consequent regulation of MMPs and their inhibitors has not been studied comprehensively. Classical activation of macrophages derived in vitro from un-fractionated CD16+/− or negatively-selected CD16− macrophages up-regulated MMP-1, -3, -7, -10, -12, -14 and -25 and decreased TIMP-3 steady-state mRNA levels. Bacterial lipopolysaccharide, IL-1 and TNFα were more effective than interferonγ except for the effects on MMP-25, and TIMP-3. By contrast, alternative activation decreased MMP-2, -8 and -19 but increased MMP -11, -12, -25 and TIMP-3 steady-state mRNA levels. Up-regulation of MMPs during classical activation depended on mitogen activated protein kinases, phosphoinositide-3-kinase and inhibitor of κB kinase-2. Effects of interferonγ depended on janus kinase-2. Where investigated, similar effects were seen on protein concentrations and collagenase activity. Moreover, activity of MMP-1 and -10 co-localised with markers of classical activation in human atherosclerotic plaques in vivo. In conclusion, classical macrophage activation selectively up-regulates several MMPs in vitro and in vivo and down-regulates TIMP-3, whereas alternative activation up-regulates a distinct group of MMPs and TIMP-3. The signalling pathways defined here suggest targets for selective modulation of MMP activity.