The 5-lipoxygenase pathway promotes pathogenesis of hyperlipidemia-dependent aortic aneurysm.

Activation of the 5-lipoxygenase (5-LO) pathway leads to the biosynthesis of proinflammatory leukotriene lipid mediators. Genetic studies have associated 5-LO and its accessory protein, 5-LO-activating protein, with cardiovascular disease, myocardial infarction and stroke. Here we show that 5-LO-positive macrophages localize to the adventitia of diseased mouse and human arteries in areas of neoangiogenesis and that these cells constitute a main component of aortic aneurysms induced by an atherogenic diet containing cholate in mice deficient in apolipoprotein E. 5-LO deficiency markedly attenuates the formation of these aneurysms and is associated with reduced matrix metalloproteinase-2 activity and diminished plasma macrophage inflammatory protein-1alpha (MIP-1alpha; also called CCL3), but only minimally affects the formation of lipid-rich lesions. The leukotriene LTD(4) strongly stimulates expression of MIP-1alpha in macrophages and MIP-2 (also called CXCL2) in endothelial cells. These data link the 5-LO pathway to hyperlipidemia-dependent inflammation of the arterial wall and to pathogenesis of aortic aneurysms through a potential chemokine intermediary route.

Cysteinyl leukotriene 2 receptor-mediated vascular permeability via transendothelial vesicle transport.

Cysteinyl leukotrienes (CysLTs) are potent mediators of inflammation synthesized by the concerted actions of 5-lipoxygenase (5-LO), 5-LO-activating protein (FLAP), leukotriene C(4) synthase, and additional downstream enzymes, starting with arachidonic acid substrate. CysLTs produced by macrophages, eosinophils, mast cells, and other inflammatory cells activate 3 different high-affinity CysLT receptors: CysLT(1)R, CysLT(2)R, and GPR 17. We sought to investigate vascular sites of CysLT(2)R expression and the role and mechanism of this receptor in mediating vascular permeability events. Vascular expression of CysLT(2)R was investigated by reporter gene expression in a novel CysLT(2)R deficient-LacZ mouse model. CysLT(2)R was expressed in small, but not large, vessels in mouse brain, bladder, skin, and cremaster muscle. Intravital, in addition to confocal and electron, microscopy investigations using FITC-labeled albumin in cremaster postcapillary venule preparations indicated rapid CysLT-mediated permeability, which was blocked by application of BAY-u9773, a dual CysLT(1)R/CysLT(2)R antagonist or by CysLT(2)R deficiency. Endothelial human CysLT(2)R overexpression in mice exacerbated vascular leakage even in the absence of exogenous ligand. The enhanced vascular permeability mediated by CysLT(2)R takes place via a transendothelial vesicle transport mechanism as opposed to a paracellular route and is controlled via Ca(2+) signaling. Our results reveal that CysLT(2)R can mediate inflammatory reactions in a vascular bed-specific manner by altering transendothelial vesicle transport-based vascular permeability.

The lamina adventitia is the major site of immune cell accumulation in standard chow-fed apolipoprotein E-deficient mice.

OBJECTIVE: Cells of adaptive immunity have been implicated in atherogenesis. Though substantial information is available on immune cells in atherosclerotic lesions of the lamina intima, cells in the lamina adventitia have received less attention. METHODS AND RESULTS: The composition of immune cells in the innominate artery and abdominal aorta was examined in young, adult, and old apolipoprotein (apo) E(-/-) and wild-type mice on standard mouse chow. In the innominate artery of apoE(-/-) mice, adventitial T cells increased at 32, 52, and 78 weeks exceeding those of the intima by 6-, 24-, and 85-fold. Single T cells dominated in young mice, later T/B cell clusters emerged, and lymphoid-like structures reminiscent of inflammatory follicles formed preferentially in the abdominal aorta of old mice. Follicles contained organized sets of immune response-regulating cells: Interdigitating dendritic cells, T cell effectors, proliferating B cells, and plasma cells. Adventitial T cell inflammation was associated with a marked increase in transcripts of the chemokine MIP-1alpha in the aorta but not in spleen or liver. CONCLUSIONS: Adventitial lymphocyte infiltration and formation of inflammatory follicle-like structures in the abdominal aorta of old apoE(-/-) mice point to the adventitia as a site of local adaptive immune reactions during atherogenesis in hyperlipidemic mice.

Endothelial cysteinyl leukotriene 2 receptor expression and myocardial ischemia/reperfusion injury.

Myocardial infarction with associated reperfusion injury results most commonly from complications of atherothrombosis combined with leukocyte-mediated oxidative damage and inflammatory events. The consequences can be devastating owing to the high risk for mortality or loss of quality of life from ensuing heart failure. Therefore, understanding and controlling the inflammatory response that leads to myocardial injury are of paramount importance for better therapies. Cysteinyl leukotrienes are well known lipid mediators of inflammation. They exert their cellular actions via several distinct G-protein-coupled receptors. The detection of the cysteinyl leukotriene 2 receptor (CysLT(2)R) within the heart and vasculature has led to studies to investigate its role in myocardial ischemia/reperfusion injury. Recent experiments with induced mutant mouse models have revealed that excessive CysLT(2)R activation in vascular endothelium controls vascular permeability and determines the extent of myocardial injury. Development of specific CysLT(2)R antagonists should be encouraged to study this in greater detail in preclinical animal models.

Endothelial cysteinyl leukotriene 2 receptor expression mediates myocardial ischemia-reperfusion injury.

Cysteinyl leukotrienes (CysLTs) have been implicated as inflammatory mediators of cardiovascular disease. Three distinct CysLT receptor subtypes transduce the actions of CysLTs but the role of the endothelial CysLT2 receptor (CysLT2R) in cardiac function is unknown. Here, we investigated the role of CysLT2R in myocardial ischemia-reperfusion (I/R) injury using transgenic (tg) mice overexpressing human CysLT2R in vascular endothelium and nontransgenic (ntg) littermates. Infarction size in tg mice increased 114% compared with ntg mice 48 hours after I/R; this increase was blocked by the CysLT receptor antagonist BAY-u9773. Injection of 125 I-albumin into the systemic circulation revealed significantly enhanced extravasation of the label in tg mice, indicating increased leakage of the coronary endothelium, combined with increased incidence of hemorrhage and cardiomyocyte apoptosis. Expression of proinflammatory genes such as Egr-1, VCAM-1, and ICAM was significantly increased in tg mice relative to ntg controls. Echocardiographic assessment 2 weeks after I/R revealed decreased anterior wall thickness in tg mice. Furthermore, the postreperfusion time constant tau of isovolumic relaxation was significantly increased in tg animals, indicating diastolic dysfunction. These results reveal that endothelium-targeted overexpression of CysLT2R aggravates myocardial I/R injury by increasing endothelial permeability and exacerbating inflammatory gene expression, leading to accelerated left ventricular remodeling, induction of peri-infarct zone cellular apoptosis, and impaired cardiac performance.

Expanding expression of the 5-lipoxygenase pathway within the arterial wall during human atherogenesis.

Oxidation products of low-density lipoproteins have been suggested to promote inflammation during atherogenesis, and reticulocyte-type 15-lipoxygenase has been implicated to mediate this oxidation. In addition, the 5-lipoxygenase cascade leads to formation of leukotrienes, which exhibit strong proinflammatory activities in cardiovascular tissues. Here, we studied both lipoxygenase pathways in human atherosclerosis. The 5-lipoxygenase pathway was abundantly expressed in arterial walls of patients afflicted with various lesion stages of atherosclerosis of the aorta and of coronary and carotid arteries. 5-lipoxygenase localized to macrophages, dendritic cells, foam cells, mast cells, and neutrophilic granulocytes, and the number of 5-lipoxygenase expressing cells markedly increased in advanced lesions. By contrast, reticulocyte-type 15-lipoxygenase was expressed at levels that were several orders of magnitude lower than 5-lipoxygenase in both normal and diseased arteries, and its expression could not be related to lesion pathology. Our data support a model of atherogenesis in which 5-lipoxygenase cascade-dependent inflammatory circuits consisting of several leukocyte lineages and arterial wall cells evolve within the blood vessel wall during critical stages of lesion development. They raise the possibility that antileukotriene drugs may be an effective treatment regimen in late-stage disease.