IL-1ß Inhibition Partially Negates the Beneficial Effects of Diet-Induced Atherosclerosis Regression in Mice.

BACKGROUND: Thromboembolic events secondary to rupture or erosion of advanced atherosclerotic lesions is the global leading cause of death. The most common and effective means to reduce these major adverse cardiovascular events, including myocardial infarction and stroke, is aggressive lipid lowering via a combination of drugs and dietary modifications. However, we know little regarding the effects of reducing dietary lipids on the composition and stability of advanced atherosclerotic lesions, the mechanisms that regulate these processes, and what therapeutic approaches might augment the benefits of lipid lowering. METHODS: Smooth muscle cell lineage-tracing Apoe-/- mice were fed a high-cholesterol Western diet for 18 weeks and then a zero-cholesterol standard laboratory diet for 12 weeks before treating them with an IL (interleukin)-1ß or control antibody for 8 weeks. We assessed lesion size and remodeling indices, as well as the cellular composition of aortic and brachiocephalic artery lesions, indices of plaque stability, overall plaque burden, and phenotypic transitions of smooth muscle cell and other lesion cells by smooth muscle cell lineage tracing combined with single-cell RNA sequencing, cytometry by time-of-flight, and immunostaining plus high-resolution confocal microscopic z-stack analysis. RESULTS: Lipid lowering by switching Apoe-/- mice from a Western diet to a standard laboratory diet reduced LDL cholesterol levels by 70% and resulted in multiple beneficial effects including reduced overall aortic plaque burden, as well as reduced intraplaque hemorrhage and necrotic core area. However, contrary to expectations, IL-1ß antibody treatment after diet-induced reductions in lipids resulted in multiple detrimental changes including increased plaque burden and brachiocephalic artery lesion size, as well as increasedintraplaque hemorrhage, necrotic core area, and senescence as compared with IgG control antibody-treated mice. Furthermore, IL-1ß antibody treatment upregulated neutrophil degranulation pathways but downregulated smooth muscle cell extracellular matrix pathways likely important for the protective fibrous cap. CONCLUSIONS: Taken together, IL-1ß appears to be required for the maintenance of standard laboratory diet-induced reductions in plaque burden and increases in multiple indices of plaque stability.

Sustained Focal Vascular Inflammation Accelerates Atherosclerosis in Remote Arteries.

OBJECTIVE: Evidence from preclinical and clinical studies has demonstrated that myocardial infarction promotes atherosclerosis progression. The impact of focal vascular inflammation on the progression and phenotype of remote atherosclerosis remains unknown. Approach and Results: We used a novel ApoE-/- knockout mouse model of sustained arterial inflammation, initiated by mechanical injury in the abdominal aorta. Using serial in vivo molecular MRI and ex vivo histology and flow cytometry, we demonstrate that focal arterial inflammation triggered by aortic injury, accelerates atherosclerosis in the remote brachiocephalic artery. The brachiocephalic artery atheroma had distinct histological features including increased plaque size, plaque permeability, necrotic core to collagen ratio, infiltration of more inflammatory monocyte subsets, and reduced collagen content. We also found that arterial inflammation following focal vascular injury evoked a prolonged systemic inflammatory response manifested as a persistent increase in serum IL-6 (interleukin 6). Finally, we demonstrate that 2 therapeutic interventions-pravastatin and minocycline-had distinct anti-inflammatory effects at the plaque and systemic level. CONCLUSIONS: We show for the first time that focal arterial inflammation in response to vascular injury enhances systemic vascular inflammation, accelerates remote atheroma progression and induces plaques more inflamed, lipid-rich, and collagen-poor in the absence of ischemic myocardial injury. This inflammatory cascade is modulated by pravastatin and minocycline treatments, which have anti-inflammatory effects at both plaque and systemic levels that mitigate atheroma progression.

Ultrasound Molecular Imaging of Atherosclerosis With Nanobodies: Translatable Microbubble Targeting Murine and Human VCAM (Vascular Cell Adhesion Molecule) 1.

OBJECTIVE: Contrast-enhanced ultrasound molecular imaging (CEUMI) of endothelial expression of VCAM (vascular cell adhesion molecule)-1 could improve risk stratification for atherosclerosis. The microbubble contrast agents developed for preclinical studies are not suitable for clinical translation. Our aim was to characterize and validate a microbubble contrast agent using a clinically translatable single-variable domain immunoglobulin (nanobody) ligand. Approach and Results: Microbubble with a nanobody targeting VCAM-1 (MBcAbVcam1-5) and microbubble with a control nanobody (MBVHH2E7) were prepared and characterized in vitro. Attachment efficiency to VCAM-1 under continuous and pulsatile flow was investigated using activated murine endothelial cells. In vivo CEUMI of the aorta was performed in atherosclerotic double knockout and wild-type mice after injection of MBcAbVcam1-5 and MBVHH2E7. Ex vivo CEUMI of human endarterectomy specimens was performed in a closed-loop circulation model. The surface density of the nanobody ligand was 3.5×105 per microbubble. Compared with MBVHH2E7, MBcAbVcam1-5 showed increased attachment under continuous flow with increasing shear stress of 1-8 dynes/cm2 while under pulsatile flow attachment occurred at higher shear stress. CEUMI in double knockout mice showed signal enhancement for MBcAbVcam1-5 in early (P=0.0003 versus MBVHH2E7) and late atherosclerosis (P=0.007 versus MBVHH2E7); in wild-type mice, there were no differences between MBcAbVcam1-5 and MBVHH2E7. CEUMI in human endarterectomy specimens showed a 100% increase in signal for MBcAbVcam1-5versus MBVHH2E7 (20.6±27.7 versus 9.6±14.7, P=0.0156). CONCLUSIONS: CEUMI of the expression of VCAM-1 is feasible in murine models of atherosclerosis and on human tissue using a clinically translatable microbubble bearing a VCAM-1 targeted nanobody.

Degradation of Glycocalyx and Multiple Manifestations of Endothelial Dysfunction Coincide in the Early Phase of Endothelial Dysfunction Before Atherosclerotic Plaque Development in Apolipoprotein E/Low-Density Lipoprotein Receptor-Deficient Mice.

Background The impairment of endothelium-dependent vasodilation, increased endothelial permeability, and glycocalyx degradation are all important pathophysiological components of endothelial dysfunction. However, it is still not clear whether in atherosclerosis, glycocalyx injury precedes other features of endothelial dysfunction or these events coincide. Methods and Results Herein, we demonstrate that in 4- to 8-week-old apolipoprotein E/low-density lipoprotein receptor-deficient mice, at the stage before development of atherosclerotic plaques, impaired acetylcholine-induced vasodilation, reduced NO production in aorta, and increased endothelial permeability were all observed; however, flow-mediated dilation in the femoral artery was fully preserved. In 4-week-old mice, glycocalyx coverage was reduced and endothelial stiffness was increased, whereas glycocalyx length was significantly decreased at 8 weeks of age. Early changes in endothelial function were also featured by increased plasma concentration of biomarkers of glycocalyx disruption (endocan), biomarkers of endothelial inflammation (soluble vascular cell adhesion molecule 1), increased vascular permeability (angiopoietin 2), and alterations in hemostasis (tissue plasminogen activator and plasminogen activator inhibitor 1). In 28-week-old mice, at the stage of advanced atherosclerotic plaque development, impaired NO production and nearly all other features of endothelial dysfunction were changed to a similar extent, compared with the preatherosclerotic plaque phase. The exceptions were the occurrence of acetylcholine-induced vasoconstriction in the aorta and brachiocephalic artery, impaired flow-mediated vasodilation in the femoral artery, and further reduction of glycocalyx length and coverage with a concomitant further increase in endothelial permeability. Conclusions In conclusion, even at the early stage before the development of atherosclerotic plaques, endothelial dysfunction is a complex multifactorial response that has not been previously appreciated.

A diet enriched with tree nuts reduces severity of atherosclerosis but not abdominal aneurysm in angiotensin II-infused apolipoprotein E deficient mice.

BACKGROUND AND AIMS: Diets enriched with tree nuts have been demonstrated to reduce the risk of atherosclerosis-related cardiovascular events. Abdominal aortic aneurysm (AAA) shares common risk factors with atherosclerosis and AAA patients commonly have atherosclerosis related cardiovascular events. AAA has some distinct pathological and clinical characteristics to those of atherosclerosis. No previous study has examined the effect of a diet enriched with tree nuts on experimental or clinical AAA. This study investigated the effect of a diet enriched with tree nuts on the development and severity of AAA within an experimental rodent model. METHODS: Male apolipoprotein E deficient mice were allocated to a diet enriched with tree nuts or control diet for 56 days (n = 17 per group). After 28 days, all mice were infused with angiotensin II whilst being maintained on their respective diets. The primary outcome was AAA severity assessed by the supra-renal aortic diameter, measured by ultrasound and ex vivo morphometric analysis. The severity of atherosclerosis was assessed by computer-aided analysis of Sudan IV stained aortic arches and sections of brachiocephalic arteries prepared with Van Gieson's stain. RESULTS: The diet enriched with tree nuts did not influence aortic diameter or aortic rupture incidence. Mice receiving the diet enriched with tree nuts had significantly less atherosclerosis within the brachiocephalic artery (p = 0.033) but not in the aortic arch. CONCLUSIONS: This experimental study suggests that a diet enriched with tree nuts does not reduce the severity of AAA, but does reduce the severity of atherosclerosis within the brachiocephalic artery. The study was not powered to identify a moderate effect of the diet on the primary outcome and therefore this cannot be excluded.

In vivo inhibition of nuclear factor of activated T-cells leads to atherosclerotic plaque regression in IGF-II/LDLR-/-ApoB100/100 mice.

AIMS: Despite vast clinical experience linking diabetes and atherosclerosis, the molecular mechanisms leading to accelerated vascular damage are still unclear. Here, we investigated the effects of nuclear factor of activated T-cells inhibition on plaque burden in a novel mouse model of type 2 diabetes that better replicates human disease. METHODS & RESULTS: IGF-II/LDLR-/-ApoB100/100 mice were generated by crossbreeding low-density lipoprotein receptor-deficient mice that synthesize only apolipoprotein B100 (LDLR-/-ApoB100/100) with transgenic mice overexpressing insulin-like growth factor-II in pancreatic ß cells. Mice have mild hyperglycaemia and hyperinsulinaemia and develop complex atherosclerotic lesions. In vivo treatment with the nuclear factor of activated T-cells blocker A-285222 for 4 weeks reduced atherosclerotic plaque area and degree of stenosis in the brachiocephalic artery of IGF-II/LDLR-/-ApoB100/100 mice, as assessed non-invasively using ultrasound biomicroscopy prior and after treatment, and histologically after termination. Treatment had no impact on plaque composition (i.e. muscle, collagen, macrophages). The reduced plaque area could not be explained by effects of A-285222 on plasma glucose, insulin or lipids. Inhibition of nuclear factor of activated T-cells was associated with increased expression of atheroprotective NOX4 and of the anti-oxidant enzyme catalase in aortic vascular smooth muscle cells. CONCLUSION: Targeting the nuclear factor of activated T-cells signalling pathway may be an attractive approach for the treatment of diabetic macrovascular complications.

Fibronectin Containing Extra Domain A Induces Plaque Destabilization in the Innominate Artery of Aged Apolipoprotein E-Deficient Mice.

OBJECTIVE: Fibronectin containing extra domain A (Fn-EDA) is an endogenous ligand of TLR4 (toll-like receptor 4) and is abundant in the extracellular matrix of advanced atherosclerotic lesions in human and mice. Irrespective of sex, deletion of Fn-EDA reduces early atherosclerosis in apolipoprotein E-deficient (Apoe-/-) mice. However, the contribution of Fn-EDA in advanced atherosclerosis remains poorly characterized. We determined the contribution of Fn-EDA in advanced atherosclerotic lesions of aged (1-year-old) Apoe-/- mice. APPROACH AND RESULTS: Plaque composition was determined in the innominate artery, a plaque instability site that is known to mimic several histological features of vulnerable human plaques. Female Apoe-/-, Fn-EDA-/-Apoe-/-, TLR4-/-Apoe-/-, and Fn-EDA-/-TLR4-/-Apoe-/- mice were fed a high-fat Western diet for 44 weeks. Fn-EDA-/-Apoe-/- mice exhibited reduced plaque size characterized by smaller necrotic cores, thick fibrous caps containing abundant vascular smooth muscle cells and collagen, reduced CD68/MMP9 (matrix metalloproteinase 9)-positive content, less accumulation of MMP-cleaved extracellular matrix aggrecan, and decreased vascular smooth muscle cell and macrophage apoptosis (P<0.05 versus Apoe-/- mice). Together these findings suggest that Fn-EDA induces plaque destabilization. Deletion of TLR4 reduced histological features of plaque instability in Apoe-/- mice but did not further reduce features of plaque destabilization in Fn-EDA-/-Apoe-/- mice, suggesting that TLR4 may contribute to Fn-EDA-induced plaque destabilization. Fn-EDA potentiated TLR4-dependent MMP9 expression in bone marrow-derived macrophages, suggesting that macrophage TLR4 may contribute to Fn-EDA-mediated plaque instability. CONCLUSIONS: Fn-EDA induces histological features of plaque instability in established lesions of aged Apoe-/- mice. The abundance of Fn-EDA in advanced atherosclerotic lesions may increase the risk of plaque destabilization.

Anti-atherosclerotic effects of pravastatin in brachiocephalic artery in comparison with en face aorta and aortic roots in ApoE/LDLR-/- mice.

BACKGROUND: Cholesterol-dependent and independent mechanisms were proposed to explain anti-atherosclerotic action of statins in humans. However, their effects in murine models of atherosclerosis have not been consistently demonstrated. Here, we studied the effects of pravastatin on atherosclerosis in ApoE/LDLR-/- mice fed a control and atherogenic diet. METHODS: ApoE/LDLR-/- mice were fed a control (CHOW) or an atherogenic (Low Carbohydrate High Protein, LCHP) diet. Two doses of pravastatin (40mg/kg and 100mg/kg) were used. The anti-atherosclerotic effects of pravastatin in en face aorta, cross-sections of aortic roots and brachiocephalic artery (BCA) were analysed. The lipid profile was determined. Fourier Transform Infrared Spectroscopy followed by Fuzzy C-Means (FCM) clustering was used for the quantitative assessment of plaque composition. RESULTS: Treatment with pravastatin (100mg/kg) decreased total and LDL cholesterol only in the LCHP group, but displayed a pronounced anti-atherosclerotic effect in BCA and abdominal aorta. The anti-atherosclerotic effect of pravastatin (100mg/kg) in BCA was associated with significant alterations of the chemical plaque composition, including a fall in cholesterol and cholesterol esters contents independently on total cholesterol and LDL concentration in plasma. CONCLUSIONS: Pravastatin at high (100mg/kg), but not low dose displayed a pronounced anti-atherosclerotic effect in ApoE/LDLR-/- mice fed a CHOW or LCHP diet that was remarkable in BCA, visible in en face aorta, whereas it was not observed in aortic roots, suggesting that previous inconsistencies might have been due to the various sites of atherosclerotic plaque analysis.

Pioglitazone-Incorporated Nanoparticles Prevent Plaque Destabilization and Rupture by Regulating Monocyte/Macrophage Differentiation in ApoE-/- Mice.

OBJECTIVE: Inflammatory monocytes/macrophages produce various proteinases, including matrix metalloproteinases, and degradation of the extracellular matrix by these activated proteinases weakens the mechanical strength of atherosclerotic plaques, which results in a rupture of the plaque. Peroxisome proliferator-activated receptor-γ induces a polarity shift of monocytes/macrophages toward less inflammatory phenotypes and has the potential to prevent atherosclerotic plaque ruptures. Therefore, we hypothesized that nanoparticle-mediated targeted delivery of the peroxisome proliferator-activated receptor-γ agonist pioglitazone into circulating monocytes could effectively inhibit plaque ruptures in a mouse model. APPROACH AND RESULTS: We prepared bioabsorbable poly(lactic-co-glycolic-acid) nanoparticles containing pioglitazone (pioglitazone-NPs). Intravenously administered poly(lactic-co-glycolic-acid) nanoparticles incorporated with fluorescein isothiocyanate were found in circulating monocytes and aortic macrophages by flow cytometric analysis. Weekly intravenous administration of pioglitazone-NPs (7 mg/kg per week) for 4 weeks decreased buried fibrous caps, a surrogate marker of plaque rupture, in the brachiocephalic arteries of ApoE(-/-) mice fed a high-fat diet and infused with angiotensin II. In contrast, administration of control-NPs or an equivalent dose of oral pioglitazone treatment produced no effects. Pioglitazone-NPs inhibited the activity of matrix metalloproteinases and cathepsins in the brachiocephalic arteries. Pioglitazone-NPs regulated inflammatory cytokine expression and also suppressed the expression of extracellular matrix metalloproteinase inducer in bone marrow-derived macrophages. CONCLUSIONS: Nanoparticle-mediated delivery of pioglitazone inhibited macrophage activation and atherosclerotic plaque ruptures in hyperlipidemic ApoE(-/-) mice. These results demonstrate a promising strategy with a favorable safety profile to prevent atherosclerotic plaque ruptures.

Effects of the factor Xa inhibitor, fondaparinux, on the stability of atherosclerotic lesions in apolipoprotein E-deficient mice.

BACKGROUND: Atherosclerosis is a progressive inflammatory disease that can lead to sudden cardiac events by plaque rupture and subsequent thrombosis. Factor Xa (FXa) not only occupies a crucial position in the coagulation cascade responsible for thrombin generation, but also has pro-inflammatory effects. The hypothesis that Fondaparinux, the selective FXa inhibitor, attenuates plaque progression and promotes stability of atherosclerotic lesions was assessed. METHODS AND RESULTS: Fondaparinux (5 mg/kg body weight/day) or 0.9% saline was intraperitoneally administered for 4 weeks to apolipoprotein E-deficient mice (n=12 per group) with established atherosclerotic lesions in the innominate arteries. Fondaparinux did not remarkably decrease the progression of atherosclerosis development in apolipoprotein E-deficient mice, but increased the thickness of fibrous cap (P=0.049) and decreased the ratio of necrotic core (P=0.001) significantly. Moreover, Fondaparinux reduced the staining against Mac-2 (P=0.017), α-SMA (P=0.002), protease-activated receptor (PAR)-1 (P=0.001), PAR-2 (P=0.003), CD-31 (P=0.024), MMP-9 (P=0.000), MMP-13(P=0.011), VCAM-1 (P=0.041) and the mRNA expression of inflammatory mediators (P<0.05) significantly, such as interleukin (IL)-6, MCP-1, IFN-γ, TNF-α, IL-10 and Egr-1. CONCLUSIONS: Fondaparinux, the selective FXa inhibitor, can promote the stability of atherosclerotic lesions in apolipoprotein E-deficient mice, possibly through inhibiting expression of the inflammatory mediators in plaque and reduced synthesis of MMP-9 and MMP-13.

Angiopoietin-2 blocking antibodies reduce early atherosclerotic plaque development in mice.

OBJECTIVE: Angiopoietin-2 (Ang-2) blocking agents are currently undergoing clinical trials for use in cancer treatment. Ang-2 has also been associated with rupture-prone atherosclerotic plaques in humans, suggesting a role for Ang-2 in plaque stability. Despite the availability of Ang-2 blocking agents, their clinical use is still lacking. Our aim was to establish if Ang-2 has a role in atheroma development and in the transition of subclinical to clinically relevant atherosclerosis. We investigated the effect of antibody-mediated Ang-2 blockage on atherogenesis after in a mouse model of atherosclerosis. METHODS: Hypercholesterolemic (low-density lipoprotein receptor(-/-) apolipoprotein B(100/100)) mice were subjected to high-cholesterol diet for eight weeks, one group with and one group without Ang-2 blocking antibody treatment during weeks 4-8.To enhance plaque development, a peri-adventitial collar was placed around the carotid arteries at the start of antibody treatment. Aortic root, carotid arteries and brachiocephalic arteries were analyzed to evaluate the effect of Ang-2 blockage on atherosclerotic plaque size and stable plaque characteristics. RESULTS: Anti-Ang-2 treatment reduced the size of fatty streaks in the brachiocephalic artery (-72%, p < 0.05). In addition, antibody-mediated Ang-2 blockage reduced plasma triglycerides (-27%, p < 0.05). In contrast, Ang-2 blockage did not have any effect on the size or composition (collagen content, macrophage percentage, adventitial microvessel density) of pre-existing plaques in the aortic root or collar-induced plaques in the carotid artery. CONCLUSIONS: Ang-2 blockage was beneficial as it decreased fatty streak formation and plasma triglyceride levels, but had no adverse effect on pre-existing atherosclerosis in hypercholesterolemic mice.

Endothelial glucocorticoid receptor suppresses atherogenesis--brief report.

OBJECTIVE: The purpose of this study was to determine the role of the endothelial glucocorticoid receptor in the pathogenesis of atherosclerosis. APPROACH AND RESULTS: Control mice and mice lacking the endothelial glucocorticoid receptor were bred onto an Apoe knockout background and subjected to high-fat diet feeding for 12 weeks. Assessment of body weight and total cholesterol and triglycerides before and after the diet revealed no differences between the 2 groups of mice. However, mice lacking the endothelial glucocorticoid receptor developed more severe atherosclerotic lesions in the aorta, brachiocephalic artery, and aortic sinus, as well as a heightened inflammatory milieu as evidenced by increased macrophage recruitment in the lesions. CONCLUSIONS: These data suggest that the endothelial glucocorticoid receptor is important for tonic inhibition of inflammation and limitation of atherosclerosis progression in this model.

Genetic network identifies novel pathways contributing to atherosclerosis susceptibility in the innominate artery.

BACKGROUND: Atherosclerosis, the underlying cause of cardiovascular disease, results from both genetic and environmental factors. METHODS: In the current study we take a systems-based approach using weighted gene co-expression analysis to identify a candidate pathway of genes related to atherosclerosis. Bioinformatic analyses are performed to identify candidate genes and interactions and several novel genes are characterized using in-vitro studies. RESULTS: We identify 1 coexpression module associated with innominate artery atherosclerosis that is also enriched for inflammatory and macrophage gene signatures. Using a series of bioinformatics analysis, we further prioritize the genes in this pathway and identify Cd44 as a critical mediator of the atherosclerosis. We validate our predictions generated by the network analysis using Cd44 knockout mice. CONCLUSION: These results indicate that alterations in Cd44 expression mediate inflammation through a complex transcriptional network involving a number of previously uncharacterized genes.

Transcriptomics of the fetal hypothalamic response to brachiocephalic occlusion and estradiol treatment.

Estradiol (E2) is a well-known modulator of fetal neuroendocrine activity and has been proposed as a critical endocrine signal readying the fetus for birth and postnatal life. To investigate the modulatory role of E2 on fetal stress responsiveness and the response of the fetal brain to asphyxic stress, we subjected chronically catheterized fetal sheep to a transient (10 min) brachiocephalic artery occlusion (BCO) or sham occlusion. Half of the fetuses received subcutaneous pellets that increased plasma E2 concentrations within the physiological range. Hypothalamic mRNA was analyzed using the Agilent 8x15k ovine array (019921), processed and annotated as previously reported by our laboratory. Analysis of the data by ANOVA revealed that E2 differentially regulated (DR) 561 genes, and BCO DR 894 genes compared with control and E2+BCO DR 1,153 genes compared with BCO alone (all P < 0.05). E2 upregulated epigenetic pathways and downregulated local steroid biosynthesis but did not significantly involve genes known to directly respond to the estrogen receptor. Brachiocephalic occlusion upregulated kinase pathways as well as genes associated with lymphocyte infiltration into the brain and downregulated neuropeptide synthesis. E2 upregulated immune- and apoptosis-related pathways after BCO and reduced kinase and epigenetic pathway responses to the BCO. Responses to BCO are different from responses to hypoxic hypoxia suggesting that mechanisms of responses to these two forms of brain hypoxia are distinct. We conclude that cerebral ischemia caused by BCO might stimulate lymphocyte infiltration into the brain and that this response appears to be modified by estradiol.

Bisphenol A increases atherosclerosis in pregnane X receptor-humanized ApoE deficient mice.

BACKGROUND: Bisphenol A (BPA) is a base chemical used extensively in many consumer products. BPA has recently been associated with increased risk of cardiovascular disease (CVD) in multiple large-scale human population studies, but the underlying mechanisms remain elusive. We previously reported that BPA activates the pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism and has pro-atherogenic effects in animal models upon activation. Interestingly, BPA is a potent agonist of human PXR but does not activate mouse or rat PXR signaling, which confounds the use of rodent models to evaluate mechanisms of BPA-mediated CVD risk. This study aimed to investigate the atherogenic mechanism of BPA using a PXR-humanized mouse model. METHODS AND RESULTS: A PXR-humanized ApoE deficient (huPXR•ApoE(-/-)) mouse line was generated that respond to human PXR ligands and feeding studies were performed to determine the effects of BPA exposure on atherosclerosis development. Exposure to BPA significantly increased atherosclerotic lesion area in the aortic root and brachiocephalic artery of huPXR•ApoE(-/-) mice by 104% (P<0.001) and 120% (P<0.05), respectively. By contrast, BPA did not affect atherosclerosis development in the control littermates without human PXR. BPA exposure did not affect plasma lipid levels but increased CD36 expression and lipid accumulation in macrophages of huPXR•ApoE(-/-) mice. CONCLUSION: These findings identify a molecular mechanism that could link BPA exposure to increased risk of CVD in exposed individuals. PXR is therefore a relevant target for future risk assessment of BPA and related environmental chemicals in humans.

Apolipoprotein A-I protection against atherosclerosis is dependent on genetic background.

OBJECTIVE: Inbred mouse strains have different susceptibilities to experimental atherosclerosis. The C57BL/6 strain is among the most sensitive and has, therefore, been the most widely used in atherosclerosis studies, whereas many strains are resistant. The FVB/N strain is highly resistant to atherosclerosis on the apolipoprotein E (apoE)- and low-density lipoprotein (LDL) receptor-deficient backgrounds. High-density lipoprotein and its major apoprotein, apoA-I, have been shown to be protective against atherogenesis on the C57BL/6 background. We here examine the influence of genetic background on the atheroprotective nature of apoA-I. APPROACH AND RESULTS: ApoE-deficient/apoA-I-deficient mice were generated in the C57BL/6 and FVB/N strains from apoE-deficient mice. After 6 to 10 weeks on a Western-type diet, plasma lipids and atherosclerotic lesion size were assessed. Macrophage recruitment, cholesterol regulation, and blood monocyte levels were examined as potential mechanisms driving lesion size differences. FVB/N knockout mice had higher plasma very-LDL/LDL cholesterol than their C57BL/6 counterparts. ApoA-I deficiency decreased very-LDL/LDL cholesterol in C57BL/6 mice but not in FVB/N mice. FVB/N single and double knockout mice had less lesion than C57BL/6 6 to 10 weeks on diet. ApoA-I deficiency augmented lesion development only in C57BL/6 mice. Macrophage recruitment to thioglycollate-treated peritoneum and diet-induced blood monocyte levels reflected the pattern of lesion development among the 4 genotypes. ApoA-I deficiency increased macrophage cholesterol content only in C57BL/6. FVB/N plasma was a better acceptor for macrophage cholesterol efflux than C57BL/6. CONCLUSIONS: ApoA-I is atheroprotective only in certain genetic contexts. In the C57BL/6 context, but not FVB/N, apoA-I decreases inflammatory macrophage recruitment and monocytosis, contributors to lesion formation.

Diesel exhaust particulate increases the size and complexity of lesions in atherosclerotic mice.

OBJECTIVE: Diesel exhaust particulate (DEP), a major component of urban air pollution, has been linked to atherogenesis and precipitation of myocardial infarction. We hypothesized that DEP exposure would increase and destabilise atherosclerotic lesions in apolipoprotein E deficient (ApoE-/-) mice. METHODS: ApoE-/- mice were fed a 'Western diet' (8 weeks) to induce 'complex' atherosclerotic plaques, with parallel experiments in normal chow fed wild-type mice. During the last 4 weeks of feeding, mice received twice weekly instillation (oropharyngeal aspiration) of 35 µL DEP (1 mg/mL, SRM-2975) or vehicle (saline). Atherosclerotic burden was assessed by en-face staining of the thoracic aorta and histological examination of the brachiocephalic artery. RESULTS: Brachiocephalic atherosclerotic plaques were larger in ApoE-/- mice treated with DEP (59 ± 10%) than in controls (32 ± 7%; P = 0.017). In addition, DEP-treated mice had more plaques per section of artery (2.4 ± 0.2 vs 1.8 ± 0.2; P = 0.048) and buried fibrous layers (1.2 ± 0.2 vs 0.4 ± 0.1; P = 0.028). These changes were associated with lung inflammation and increased antioxidant gene expression in the liver, but not with changes in endothelial function, plasma lipids or systemic inflammation. CONCLUSIONS: Increased atherosclerosis is caused by the particulate component of diesel exhaust producing advanced plaques with a potentially more vulnerable phenotype. These results are consistent with the suggestion that removal of the particulate component would reduce the adverse cardiovascular effects of diesel exhaust.

TRAIL-deficiency accelerates vascular calcification in atherosclerosis via modulation of RANKL.

The osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) cytokine system, not only controls bone homeostasis, but has been implicated in regulating vascular calcification. TNF-related apoptosis-inducing ligand (TRAIL) is a second ligand for OPG, and although its effect in vascular calcification in vitro is controversial, its role in vivo is not yet established. This study aimed to investigate the role of TRAIL in vascular calcification in vitro using vascular smooth muscle cells (VSMCs) isolated from TRAIL(-/-) and wild-type mice, as well as in vivo, in advanced atherosclerotic lesions of TRAIL(-/-)ApoE(-/-) mice. The involvement of OPG and RANKL in this process was also examined. TRAIL dose-dependently inhibited calcium-induced calcification of human VSMCs, while TRAIL(-/-) VSMCs demonstrated accelerated calcification induced by multiple concentrations of calcium compared to wild-type cells. Consistent with this, RANKL mRNA was significantly elevated with 24 h calcium treatment, while OPG and TRAIL expression in human VSMCs was inhibited. Brachiocephalic arteries from TRAIL(-/-)ApoE(-/-) and ApoE(-/-) mice fed a high fat diet for 12 w demonstrated increased chondrocyte-like cells in atherosclerotic plaque, as well as increased aortic collagen II mRNA expression in TRAIL(-/-)ApoE(-/-) mice, with significant increases in calcification observed at 20 w. TRAIL(-/-)ApoE(-/-) aortas also had significantly elevated RANKL, BMP-2, IL-1ß, and PPAR-γ expression at 12 w. Our data provides the first evidence that TRAIL deficiency results in accelerated cartilaginous metaplasia and calcification in atherosclerosis, and that TRAIL plays an important role in the regulation of RANKL and inflammatory markers mediating bone turn over in the vasculature.

Heterogenic endothelial responses to inflammation: role for differential N-glycosylation and vascular bed of origin.

BACKGROUND: Endothelial cell responses during inflammation are heterogeneous and key for selectivity in how leukocytes hone in on specific sites and why vascular diseases are highly bed specific. However, mechanisms for this specificity remain unclear. METHODS AND RESULTS: Here, we exposed human endothelial cells isolated from 5 systemic arterial beds from 1 donor (to overcome donor-to-donor genetic/epigenetic differences), the umbilical vein, and pulmonary microvasculature to TNF-α, LPS, and IL-1ß and assessed acute (ERK1/2 and p65) and chronic (ICAM-1, VCAM-1 total and surface expression) signaling responses and assessed changes in surface N-glycans and monocyte adhesion. Significant diversity in responses was evident by disparate changes in ERK1/2 and p65 NF-κB phosphorylation, which varied up to 5-fold between different cells and in temporal and magnitude differences in ICAM-1 and VCAM-1 expression (maximal VCAM-1 induction typically being observed by 4 hours, whereas ICAM-1 expression was increased further at 24 hours relative to 4 hours). N-glycan profiles both basally and with stimulation were also bed specific, with hypoglycosylated N-glycans correlating with increased THP-1 monocyte adhesion. Differences in surface N-glycan expression tracked with dynamic up- or downregulation of α-mannosidase activity during inflammation. CONCLUSIONS: These results demonstrate a critical role for the vascular bed of origin in controlling endothelial responses and function to inflammatory stimuli and suggest that bed-specific expression of N-linked sugars may provide a signature for select leukocyte recruitment.

Bone marrow- or vessel wall-derived osteoprotegerin is sufficient to reduce atherosclerotic lesion size and vascular calcification.

OBJECTIVE: Osteoprotegerin (OPG) is a decoy receptor for the osteoclast differentiation factor receptor activator of NF-κB ligand. OPG regulates bone homeostasis, and its inactivation in mice results in severe osteoporosis. OPG deficiency in apolipoprotein E (ApoE)(-/-) mice results in increased atherosclerotic lesion size and calcification. Furthermore, receptor activator of NF-κB ligand enhances macrophage-dependent smooth muscle cell calcification in vitro. Here, we hypothesized that reconstitution of ApoE(-/-)OPG(-/-) mice with ApoE(-/-)OPG(+/+) bone marrow (BM) would be sufficient to rescue lesion progression and vascular calcification. Conversely, reconstitution of ApoE(-/-)OPG(+/+) mice with ApoE(-/-)OPG(-/-) BM may accelerate lesion progression and vascular calcification. APPROACH AND RESULTS: ApoE(-/-)OPG(-/-) mice transplanted with ApoE(-/-)OPG(+/+) BM developed smaller atherosclerotic lesions and deposited less calcium in the innominate artery than that of ApoE(-/-)OPG(-/-) mice transplanted with ApoE(-/-)OPG(-/-) BM. There were no differences in lesion size and calcification in ApoE(-/-)OPG(+/+) mice transplanted with BM from ApoE(-/-)OPG(-/-) or ApoE(-/-)OPG(+/+) mice. The large lesions observed in the ApoE(-/-)OPG(-/-) mice transplanted with OPG(-/-) BM were rich in chondrocyte-like cells, collagen, and proteoglycans. Importantly, the ApoE(-/-)OPG(-/-) mice transplanted with OPG(+/+) BM remained osteoporotic, and the ApoE(-/-)OPG(+/+) mice did not show signs of bone loss regardless of the type of BM received. In coculture experiments, macrophages and mesenchymal stem cells derived from ApoE(-/-)OPG(-/-) BM induced more vascular smooth muscle cell calcification than cells derived from ApoE(-/-)OPG(+/+) mice. CONCLUSIONS: These results indicate that OPG derived either from the BM or from the vessel wall is sufficient to slow down lesion progression and vascular calcification independent of bone turnover.