Circulating adhesion molecules in apoE-deficient mouse strains with different atherosclerosis susceptibility

Uric acid promotes myocardial infarction injury via activating pyrin domain-containing 3 inflammasome and reactive oxygen species/transient receptor potential melastatin 2/Ca2+pathway

Cardiomyocytes injury has been considered as a key contributor for myocardial infarction (MI). Uric acid (UA) can induce cardiomyocytes injury, which is closely related to NLRP3 activation and inflammatory factor generation. However, the mechanism how UA modulates cardiomyocytes remains elusive. Western blotting and qRT-PCR were applied for measuring protein and mRNA expression, respectively. ROS production and Ca²⁺ influx were measured by flow cytometry. Patch clamp technique was used for measuring transient receptor potential melastatin 2 (TRPM2) channel. Ligation of left anterior descending for 2 h was performed to induce MI animal model. The rats were treated by different concentration of uric acid. The artery tissues were stained by HE and collected for measurement of NLRP3 and inflammatory factors. Supplementation of UA significantly promoted apoptosis, and augmented the expression of intercellular adhesion molecule-1, chemoattractant protein-1, vascular cell adhesion molecule-1, and NLRP3 inflammasome. Knockdown of NLRP3 reversed the influence of UA on MI by decreasing collagen deposition, fibrotic area, apoptosis. The expression of NLRP3 inflammasome increased markedly after treatment of UA. UA activated ROS/TRPM2/Ca²⁺ pathway through targeting NLRP3. UA activated NLRP3 inflammasome and augments inflammatory factor production, which in turn exacerbates cardiomyocytes injury. Knockdown of NLRP3 reversed the influence of UA on apoptosis and cell cycle. UA may promote cardiomyocytes injury through activating NLRP3 inflammasome and ROS/TRPM2 channel/Ca²⁺ pathway.

Phenotypic and Genetic Evidence for a More Prominent Role of Blood Glucose than Cholesterol in Atherosclerosis of Hyperlipidemic Mice

Hyperlipidemia and type 2 diabetes (T2D) are major risk factors for atherosclerosis. Apoe-deficient (Apoe−/−) mice on certain genetic backgrounds develop hyperlipidemia, atherosclerosis, and T2D when fed a Western diet. Here, we sought to dissect phenotypic and genetic relationships of blood lipids and glucose with atherosclerotic plaque formation when the vasculature is exposed to high levels of cholesterol and glucose. Male F2 mice were generated from LP/J and BALB/cJ Apoe−/− mice and fed a Western diet for 12 weeks. Three significant QTL Ath51, Ath52 and Ath53 on chromosomes (Chr) 3 and 15 were mapped for atherosclerotic lesions. Ath52 on proximal Chr15 overlapped with QTL for plasma glucose, non-HDL cholesterol, and triglyceride. Atherosclerotic lesion sizes showed significant correlations with fasting, non-fasting glucose, non-fasting triglyceride, and body weight but no correlation with HDL, non-HDL cholesterol, and fasting triglyceride levels. Ath52 for atherosclerosis was down-graded from significant to suggestive level after adjustment for fasting, non-fasting glucose, and non-fasting triglyceride but minimally affected by HDL, non-HDL cholesterol, and fasting triglyceride. Adjustment for body weight suppressed Ath52 but elevated Ath53 on distal Chr15. These results demonstrate phenotypic and genetic connections of blood glucose and triglyceride with atherosclerosis, and suggest a more prominent role for blood glucose than cholesterol in atherosclerotic plaque formation of hyperlipidemic mice.

Genetic Evidence for a Causal Relationship between Hyperlipidemia and Type 2 Diabetes in Mice

Dyslipidemia is considered a risk factor for type 2 diabetes (T2D), yet studies with statins and candidate genes suggest that circulating lipids may protect against T2D development. Apoe-null (Apoe^-/-) mouse strains develop spontaneous dyslipidemia and exhibit a wide variation in susceptibility to diet-induced T2D. We thus used Apoe^-/- mice to elucidate phenotypic and genetic relationships of circulating lipids with T2D. A male F2 cohort was generated from an intercross between LP/J and BALB/cJ Apoe^-/- mice and fed 12 weeks of a Western diet. Fasting, non-fasting plasma glucose, and lipid levels were measured and genotyping was performed using miniMUGA arrays. We uncovered a major QTL near 60 Mb on chromosome 15, Nhdlq18, which affected non-HDL cholesterol and triglyceride levels under both fasting and non-fasting states. This QTL was coincident with Bglu20, a QTL that modulates fasting and non-fasting glucose levels. The plasma levels of non-HDL cholesterol and triglycerides were closely correlated with the plasma glucose levels in F2 mice. Bglu20 disappeared after adjustment for non-HDL cholesterol or triglycerides. These results demonstrate a causative role for dyslipidemia in T2D development in mice.

Genetic Connection between Hyperglycemia and Carotid Atherosclerosis in Hyperlipidemic Mice

Type 2 diabetes (T2D) is a major risk for atherosclerosis and its complications. Apoe-null (Apoe^−/−) mouse strains exhibit a wide range of variations in susceptibility to T2D and carotid atherosclerosis, with the latter being a major cause of ischemic stroke. To identify genetic connections between T2D and carotid atherosclerosis, 145 male F2 mice were generated from LP/J and BALB/cJ Apoe^−/− mice and fed 12 weeks of a Western diet. Atherosclerotic lesions in the carotid arteries, fasting, and non-fasting plasma glucose levels were measured, and genotyping was performed using miniMUGA arrays. Two significant QTL (quantitative trait loci) on chromosomes (Chr) 6 and 15 were identified for carotid lesions. The Chr15 QTL coincided precisely with QTL Bglu20 for fasting and non-fasting glucose levels. Carotid lesion sizes showed a trend toward correlation with fasting and non-fasting glucose levels in F2 mice. The Chr15 QTL for carotid lesions was suppressed after excluding the influence from fasting or non-fasting glucose. Likely candidate genes for the causal association were Tnfrsf11b, Deptor, and Gsdmc2. These results demonstrate a causative role for hyperglycemia in the development of carotid atherosclerosis in hyperlipidemic mice.

Identification of Mep1a as a susceptibility gene for atherosclerosis in mice

Atherosclerosis is the underlying cause of heart attack, ischemic stroke and peripheral arterial disease, and genetic factors involved remain mostly unidentified. We previously identified a significant locus on mouse chromosome 17 for atherosclerosis, Ath49, in an intercross between BALB/c and SM strains. Ath49 partially overlaps in the confidence interval with Ath22 mapped in an AKR × DBA/2 intercross. Bioinformatics analysis prioritized Mep1a, encoding meprin 1α metalloendopeptidase, as a likely candidate gene for Ath49. To prove causality, Mep1a-/-Apoe-/- mice were generated and compared with Mep1a+/+Apoe-/- mice for atherosclerosis development. Mep1a was found abundantly expressed in atherosclerotic lesions but not in healthy aorta and liver of mice. Mep1a-/- Apoe-/- mice exhibited significant reductions in both early and advanced lesion sizes. Loss of Mep1a led to decreased necrosis but increased macrophage and neutrophil contents in advanced lesions, reduced plasma levels of CXCL5 and an oxidative stress biomarker. In addition, Mep1a-/- mice had significantly reduced triglyceride levels on a chow diet. Thus, Mep1a is a susceptibility gene for atherosclerosis and aggravates atherosclerosis partially through action on oxidative stress and inflammation.

Hyperlipidemia Influences the Accuracy of Glucometer-Measured Blood Glucose Concentrations in Genetically Diverse Mice

BACKGROUND

Glucometers are widely used in animal research due to simplicity and ease of utilization, but their accuracy in blood glucose assessment for hyperlipidemic mice is unknown.

METHODS

Here, we compared blood glucose levels measured by a glucometer with plasma glucose levels measured by a standard enzymatic assay for 325 genetically diverse F2 mice derived from LP and BALB/c (BALB) Apoe^-/- mice. Non-fasting glucose levels were measured before initiation of a Western diet and after 11 weeks on the diet.

RESULTS

On chow diet, lab-measured plasma glucose levels were 279.5 ± 42.6 mg/dl (mean ± SD), while blood glucose values measured by glucometer were 138.7 ± 16.6 mg/dl. The two measures had no correlation (R² = 0.006, p = 0.167). On the Western diet, plasma glucose levels rose to 351.1 ± 121.6 mg/dl, while glucometer-measured blood glucose fell to 128.7 ± 27.9 mg/dl. The two measures showed a moderate correlation (R² = 0.111, p = 3.1E-9). Lab-measured plasma glucose showed strong positive correlations with plasma triglyceride and non-high-density lipoprotein cholesterol levels, while glucometer-measured blood glucose showed an inverse correlation with non-high-density lipoprotein levels on the chow diet.

CONCLUSIONS

Our results indicate that hyperlipidemia affects the accuracy of glucometers in measuring blood glucose levels of mice.

Inflammation and enhanced atherogenesis in the carotid artery with altered blood flow in an atherosclerosis-resistant mouse strain

Ligation of the common carotid artery near its bifurcation in apolipoprotein E-deficient (Apoe^-/- ) mice leads to rapid atherosclerosis development, which is affected by genetic backgrounds. BALB/cJ (BALB) mice are resistant to atherosclerosis, developing much smaller aortic lesions than C57BL/6 (B6) mice. In this study, we examined cellular events leading to lesion formation in carotid arteries with or without blood flow restriction of B6 and BALB Apoe^-/- mice. Blood flow was obstructed by ligating the left common carotid artery near its bifurcation in one group of mice, and other group received no surgical intervention. Without blood flow interruption, BALB-Apoe^-/- mice formed much smaller atherosclerotic lesions than B6-Apoe^-/- mice after 12 weeks of Western diet (3,325 ± 1,086 vs. 81,549 ± 9,983 µm² /section; p = 2.1E-7). Lesions occurred at arterial bifurcations in both strains. When blood flow was obstructed, ligated carotid artery of both strains showed notable lipid deposition, inflammatory cell infiltration, and rapid plaque formation. Neutrophils and macrophages were observed in the arterial wall of BALB mice 3 days after ligation and 1 week after ligation in B6 mice. CD4 T cells were observed in intimal lesions of BALB but not B6 mice. By 4 weeks, both strains developed similar sizes of advanced lesions containing foam cells, smooth muscle cells, and neovessels. Atherosclerosis also occurred in straight regions of the contralateral common carotid artery where MCP-1 was abundantly expressed in the intima of BALB mice. These findings indicate that the disturbed blood flow is more prominent than high fat diet in promoting inflammation and atherosclerosis in hyperlipidemic BALB mice.

Regional Variation in Genetic Control of Atherosclerosis in Hyperlipidemic Mice

Atherosclerosis is a polygenic disorder that often affects multiple arteries. Carotid arteries are common sites for evaluating subclinical atherosclerosis, and aortic root is the standard site for quantifying atherosclerosis in mice. We compared genetic control of atherosclerosis between the two sites in the same cohort derived from two phenotypically divergent Apoe-null (Apoe ^-/-) mouse strains. Female F2 mice were generated from C57BL/6 (B6) and C3H/He (C3H) Apoe ^-/- mice and fed 12 weeks of Western diet. Atherosclerotic lesions in carotid bifurcation and aortic root and plasma levels of fasting lipids and glucose were measured. 153 genetic markers across the genome were typed. All F2 mice developed aortic atherosclerosis, while 1/5 formed no or little carotid lesions. Genome-wide scans revealed 3 significant loci on chromosome (Chr) 1, Chr15, 6 suggestive loci for aortic atherosclerosis, 2 significant loci on Chr6, Chr12, and 6 suggestive loci for carotid atherosclerosis. Only 2 loci for aortic lesions showed colocalization with loci for carotid lesions. Carotid lesion sizes were moderately correlated with aortic lesion sizes (r = 0.303; P = 4.6E-6), but they showed slight or no association with plasma HDL, non-HDL cholesterol, triglyceride, or glucose levels among F2 mice. Bioinformatics analyses prioritized Cryge as a likely causal gene for Ath30, Cdh6 and Dnah5 as causal genes for Ath22 Our data demonstrate vascular site-specific effects of genetic factors on atherosclerosis in the same animals and highlight the need to extend studies of atherosclerosis to sites beyond aortas of mice.

Genetic linkage of oxidative stress with cardiometabolic traits in an intercross derived from hyperlipidemic mouse strains

BACKGROUND AND AIMS

Oxidative stress is associated with cardiometabolic traits in observational studies, yet the underlying causal relationship remains unclear. Apolipoprotein E-deficient (Apoe^-/-) mice develop significant hyperlipidemia and hyperglycemia on a Western diet. Here we conducted linkage analysis to investigate genetic connections between cardiometabolic traits and oxidative stress.

METHODS

266 female F2 mice were generated from an intercross between C57BL/6 (B6) and BALB/c (BALB) Apoe^-/- mice and fed 12 weeks of Western diet. Plasma levels of HDL, LDL cholesterol, triglycerides, glucose and malondialdehyde (MDA) and atherosclerosis in aortic root and left carotid artery were measured. 127 microsatellite markers across the genome were genotyped.

RESULTS

One significant locus at 78.3 cM on chromosome (Chr) 1 (LOD score: 3.85), named Mda1, and two suggestive loci near 60.3 cM on Chr1 (LOD score: 2.32, named Mda2 due to replication in a separate cross) and 19.6 cM on Chr4 (LOD score: 2.34) were identified for MDA levels. Mda1 coincided precisely with loci for LDL, triglyceride, glucose, and body weight and overlapped with a locus for atherosclerosis in the aortic root. Plasma LDL, triglyceride, and glucose explained 25.5, 19.2, and 24.2% of the variation in MDA levels of F2 mice, respectively. After correction for triglyceride or LDL, QTLs for MDA on Chr1 and Chr4 disappeared. QTLs on Chr1 disappeared, remained on Chr4, and additional QTLs on Chr12 and Chr13 were detected after correction for glucose. The QTL on Chr12, named Mda3, had a significant LOD score of 8.034 and peaked 62.22 at cM.

CONCLUSIONS

We demonstrated a causative role for cardiometabolic traits in oxidative stress and identified hyperlipidemia and hyperglycemia as a major driver of oxidative stress.

Atherogenesis in the Carotid Artery with and without Interrupted Blood Flow of Two Hyperlipidemic Mouse Strains

PURPOSE

Atherosclerosis in the carotid arteries is a common cause of ischemic stroke. We examined atherogenesis in the left carotid artery with and without interrupted blood flow of C57BL/6 (B6) and C3H-Apoe-deficient (Apoe-/-) mouse strains.

METHODS

Blood flow was interrupted by ligating the common carotid artery near its bifurcation in one group of mice and another group was not interrupted.

RESULTS

Without interference with blood flow, C3H-Apoe-/- mice developed no atherosclerosis in the carotid artery, while B6-Apoe-/- mice formed advanced atherosclerotic lesions (98,019 ± 10,594 μm2/section) after 12 weeks of a Western diet. When blood flow was interrupted by ligating the common carotid artery near its bifurcation, C3H-Apoe-/- mice showed fatty streak lesions 2 weeks after ligation, and by 4 weeks fibrous lesions had formed, although they were smaller than in B6-Apoe-/- mice. Neutrophil adhesion to endothelium and infiltration in lesions was observed in ligated arteries of both strains. Treatment of B6-Apoe-/- mice with antibody against neutrophils had little effect on lesion size.

CONCLUSIONS

These findings demonstrate the dramatic influences of genetic backgrounds and blood flow on atherogenesis in the carotid artery of hyperlipidemic mice.

Mouse Models for Atherosclerosis Research-Which Is My Line?

Atherosclerosis is one of the primary causes of cardiovascular disease and mortality. This chronic immunometabolic disease evolves during decades in humans and encompasses different organs and immune cell types, as well as local and systemic processes that promote the progression of the disease. The most frequently used animal model to study these atherogenic processes and inter-organ crosstalk in a short time frame are genetically modified mouse models. Some models have been used throughout the last decades, and some others been developed recently. These models have important differences in cholesterol and lipoprotein metabolism, reverse cholesterol transport pathway, obesity and diabetes as well as inflammatory processes. Therefore, the disease develops and progresses differently in the various mouse models. Since atherosclerosis is a multifaceted disease and many processes contribute to its progression, the choice of the right mouse model is important to study specific aspects of the disease. We will describe the different mouse models and provide a roadmap to facilitate current and future atherosclerosis researchers to choose the right model depending on their scientific question.

Accelerated atherogenesis in completely ligated common carotid artery of apolipoprotein E-deficient mice

Complete ligation of the common carotid artery near its bifurcation induces neointimal formation due to smooth muscle cell proliferation in normolipidemic wild-type mice, but it was unknown what would happen to hyperlipidemic apolipoprotein E-deficient (Apoe-/-) mice. Examination of these mice revealed rapid development of atherosclerotic lesions in completely ligated carotid arteries within 4 weeks. Mice were fed a Western diet, starting 1 week before ligation, or a chow diet. Foam cell lesions formed as early as 1 week after ligation in mice fed the Western diet and 2 weeks in mice fed the chow diet. Fibrous lesions comprised of foam cells and smooth muscle cells and more advance lesions containing neovessels occurred at 2 and 4 weeks after ligation, respectively, in the Western diet group. Lesions were larger and more advanced in the Western diet group than the chow group. Neutrophil infiltration was observed in growing intimal lesions in both diet groups, while CD8+ T cells were found in lesions of chow-fed mice. This study demonstrates that Apoe-/- mice develop the entire spectrum of atherosclerosis in ligated carotid arteries in an accelerated manner and this model could be a valuable tool for investigating the development and therapy of atherosclerosis.

Role of parnaparin in atherosclerosis

Atherosclerosis is characterized by a proliferation of vascular smooth muscle cells (VSMCs) and their migration to the intima, which induces thickening of the intima itself, but the mechanism remains poorly understood. Low molecular weight heparin (LMWH) inhibits the proliferation of VSMCs. Previous studies have shown that a LMWH, parnaparin (PNP), acts on the processes of atherogenesis and atheroprogression in experimental animal models. The aim of this study was to investigate the involvement of oxidative stress, inflammation and VSMCs in the regulation of vascular wall homeostasis. We also considered the possibility of restoring vascular pathological changes using PNP treatment. In order to evaluate vascular remodelling in this study we have analysed the morphological changes in aortas of an animal model of atherosclerosis, apolipoprotein E-deficient mice (ApoE-/-) fed with a normal or a western diet without treatment or treated with PNP. We also analysed, by immunohistochemistry, the expression of proteins linked to atherogenesis and atheroprogression - an enzyme involved in oxidative stress, iNOS, examples of inflammatory mediators, such as tumour necrosis factor alpha (TNF-α), interleukins 1 and 6 (IL-1 and IL-6), and markers of VSMC changes, in particular plasminogen activator inhibitor-1 and thrombospondin-1 (PAI-1 and TSP-1). Our results could suggest that PNP downregulates VSMC proliferation and migration, mediated by PAI-1 and TSP-1, and reduces inflammation and oxidative stress in vessels. These data suggested that LMWH, in particular PNP, could be a theoretically practical tool in the prevention of atherosclerotic vascular modification.

Polygenic Control of Carotid Atherosclerosis in a BALB/cJ × SM/J Intercross and a Combined Cross Involving Multiple Mouse Strains

Atherosclerosis in the carotid arteries is a major cause of ischemic stroke, which accounts for 85% of all stroke cases. Genetic factors contributing to carotid atherosclerosis remain poorly understood. The aim of this study was to identify chromosomal regions harboring genes contributing to carotid atherosclerosis in mice. From an intercross between BALB/cJ (BALB) and SM/J (SM) apolipoprotein E-deficient (Apoe^-/-) mice, 228 female F2 mice were generated and fed a "Western" diet for 12 wk. Atherosclerotic lesion sizes in the left carotid artery were quantified. Across the entire genome, 149 genetic markers were genotyped. Quantitative trait locus (QTL) analysis revealed eight loci for carotid lesion sizes, located on chromosomes 1, 5, 12, 13, 15, 16, and 18. Combined cross-linkage analysis using data from this cross, and two previous F2 crosses derived from BALB, C57BL/6J and C3H/HeJ strains, identified five significant QTL on chromosomes 5, 9, 12, and 13, and nine suggestive QTL for carotid atherosclerosis. Of them, the QTL on chromosome 12 had a high LOD score of 9.95. Bioinformatic analysis prioritized Arhgap5, Akap6, Mipol1, Clec14a, Fancm, Nin, Dact1, Rtn1, and Slc38a6 as probable candidate genes for this QTL. Atherosclerotic lesion sizes were significantly correlated with non-HDL cholesterol levels (r = 0.254; p = 0.00016) but inversely correlated with HDL cholesterol levels (r = -0.134; p = 0.049) in the current cross. Thus, we demonstrated the polygenic control of carotid atherosclerosis in mice. The correlations of carotid lesion sizes with non-HDL and HDL suggest that genetic factors exert effects on carotid atherosclerosis partially through modulation of lipoprotein homeostasis.

Mapping and Congenic Dissection of Genetic Loci Contributing to Hyperglycemia and Dyslipidemia in Mice

Background

Patients with dyslipidemia have an increased risk of developing type 2 diabetes, and diabetic patients often have dyslipidemia. Potential genetic connections of fasting plasma glucose with plasma lipid profile were evaluated using hyperlipidemic mice.

Methods

225 male F₂ mice were generated from BALB/cJ (BALB) and SM/J(SM) Apoe-deficient (Apoe^−/−) mice and fed a Western diet for 5 weeks. Fasting plasma glucose and lipid levels of F₂ mice were measured before and after 5 weeks of Western diet and quantitative trait locus (QTL) analysis was performed using data collected from these two time points. 144 SNP(single nucleotide polymorphism) markers across the entire genome were typed.

Results

One major QTL (logarithm of odds ratio (LOD): 6.46) peaked at 12.7 cM on chromosome 9,Bglu16, and 3 suggestive QTLs on chromosomes 15, 18 and X were identified for fasting glucose, and over 10 loci identified for lipid traits. Bglu16 was adjacent to a major QTL, Hdlq17, for high-density lipoprotein (HDL) cholesterol (LOD: 6.31, peak: 19.1 cM). A congenic strain with a donor chromosomal region harboring Bglu16 and Hdlq17 on the Apoe^−/− background showed elevations in plasma glucose and HDL levels. Fasting glucose levels were significantly correlated with non-HDL cholesterol and triglyceride levels, especially on the Western diet, but only marginally correlated with HDL levels in F₂ mice.

Conclusions

We have demonstrated a correlative relationship between fasting glucose and plasma lipids in a segregating F₂ population under hyperlipidemic conditions, and this correlation is partially due to genetic linkage between the two disorders.

Genetic linkage of hyperglycemia and dyslipidemia in an intercross between BALB/cJ and SM/J Apoe-deficient mouse strains

BACKGROUND

Individuals with dyslipidemia often develop type 2 diabetes, and diabetic patients often have dyslipidemia. It remains to be determined whether there are genetic connections between the 2 disorders.

METHODS

A female F2 cohort, generated from BALB/cJ (BALB) and SM/J (SM) Apoe-deficient (Apoe(-/-)) strains, was started on a Western diet at 6 weeks of age and maintained on the diet for 12 weeks. Fasting plasma glucose and lipid levels were measured before and after 12 weeks of Western diet. 144 genetic markers across the entire genome were used for quantitative trait locus (QTL) analysis.

RESULTS

One significant QTL on chromosome 9, named Bglu17 [26.4 cM, logarithm of odds ratio (LOD): 5.4], and 3 suggestive QTLs were identified for fasting glucose levels. The suggestive QTL near the proximal end of chromosome 9 (2.4 cM, LOD: 3.12) was replicated at both time points and named Bglu16. Bglu17 coincided with a significant QTL for HDL (high-density lipoprotein) and a suggestive QTL for non-HDL cholesterol levels. Plasma glucose levels were inversely correlated with HDL but positively correlated with non-HDL cholesterol levels in F2 mice on either chow or Western diet. A significant correlation between fasting glucose and triglyceride levels was also observed on the Western diet. Haplotype analysis revealed that "lipid genes" Sik3, Apoa1, and Apoc3 were probable candidates for Bglu17.

CONCLUSIONS

We have identified multiple QTLs for fasting glucose and lipid levels. The colocalization of QTLs for both phenotypes and the sharing of potential candidate genes demonstrate genetic connections between dyslipidemia and type 2 diabetes.

Variation in Type 2 Diabetes-Related Phenotypes among Apolipoprotein E-Deficient Mouse Strains

We recently have found that apolipoprotein E-deficient (Apoe(-/-)) mice with the C57BL/6 background develop type 2 diabetes when fed a Western diet for 12 weeks. In the present study we constructed multiple Apoe(-/-) mouse strains to find diabetes-related phenotyptic variations that might be linked to atherosclerosis development. Evaluation of both early and advanced lesion formation in aortic root revealed that C57BL/6, SWR/J, and SM/J Apoe(-/-) mice were susceptible to atherosclerosis and that C3H/HeJ and BALB/cJ Apoe(-/-) mice were relatively resistant. On a chow diet, fasting plasma glucose varied among strains with C3H/HeJ having the highest (171.1 ± 9.7 mg/dl) and BALB/cJ the lowest level (104.0 ± 6.6 mg/dl). On a Western diet, fasting plasma glucose rose significantly in all strains, with C57BL/6, C3H/HeJ and SWR/J exceeding 250 mg/dl. BALB/cJ and C3H/HeJ were more tolerant to glucose loading than the other 3 strains. C57BL/6 was sensitive to insulin while other strains were not. Non-fasting blood glucose was significantly lower in C3H/HeJ and BALB/cJ than C57BL/6, SM/J, and SWR/J. Glucose loading induced the 1st and the 2nd phase of insulin secretion in BALB/cJ, but the 2nd phase was not observed in other strains. Morphological analysis showed that BALB/cJ had the largest islet area (1,421,493 ± 61,244 μm(2)) and C57BL/6 had the smallest one (747,635 ± 41,798 μm(2)). This study has demonstrated strain-specific variations in the metabolic and atherosclerotic phenotypes, thus laying the basis for future genetic characterization.

Influence of phthalates on glucose homeostasis and atherosclerosis in hyperlipidemic mice

BACKGROUND

Phthalates are widely used as plasticizer and are considered as a typical endocrine-disrupting chemical. Epidemiological studies have associated serum or urinary phthalate metabolites with the prevalence of type 2 diabetes or related phenotypes. However, direct evidence supporting a causal role for exposure to phthalates in type 2 diabetes is lacking.

METHODS

To determine the potential influence of phthalates on glucose homeostasis and atherosclerosis, female apolipoprotein E-deficient (Apoe(-/-)) mice were started at 6 weeks of age on a Western diet together with or without Bis-(2-ethylhexyl) phthalate. Phthalate was administered in drinking water at a daily dosage of 100 mg/kg. We examined glucose and insulin tolerance, plasma glucose and triglyceride levels, body weight, and atherosclerotic lesions in the aortic root.

RESULTS

Two weeks after treatment, phthalate-exposed mice had significantly higher fasting blood glucose level (97.9 ± 2.1 vs. 84.3 ± 5.3 mg/dl, P = 0.034) and exhibited a trend of increased glucose intolerance compared to control mice. Insulin tolerance test on non-fasted mice 3 weeks after treatment revealed that phthalate had little influence on insulin sensitivity though phthalate-treated mice had a higher glucose concentration (159.2 ± 6.0 vs. 145.2 ± 3.6 mg/dl; P = 0.086). On the Western diet, Apoe(-/-) mice showed a time-dependent rise in fasting plasma glucose and triglyceride levels. However, no significant differences were observed between phthalate-treated and control mice in either phenotype after 4, 8, and 12 weeks of phthalate exposure. Neither body weight nor atherosclerotic lesions of Apoe(-/-) mice was affected.

CONCLUSION

This study indicates that exposure to phthalates gives rise to a brief interference of glucose homeostasis but has little impact on the development of type 2 diabetes and atherosclerosis in Apoe(-/-) mice.

PET imaging detection of macrophages with a formyl peptide receptor antagonist

Macrophages are a major inflammatory cell type involved in the development and progression of many important chronic inflammatory diseases. We previously found that apolipoprotein E-deficient (Apoe(-/-)) mice with the C57BL/6 (B6) background develop type 2 diabetes mellitus (T2DM) and accelerated atherosclerosis when fed a Western diet and that there are increased macrophage infiltrations in pancreatic islets and aorta. The formyl peptide receptor 1 (FPR1) is abundantly expressed on the surface of macrophages. The purpose of this study was to evaluate the applicability of cinnamoyl-F-(D)L-F-(D)L-F (cFLFLF), a natural FPR1 antagonist, to detection of macrophages in the pancreatic islets and aorta. (64)Cu labeled cFLFLF and (18)F-fluorodeoxyglucose (FDG) were administered to mice with or without T2DM. Diabetic mice showed an increased (18)FDG uptake in the subcutaneous fat compared with control mice, but pancreatic uptake was minimal for either group. In contrast, diabetic mice exhibited visually noticeable more cFLFLF-(64)Cu retention in pancreas and liver than control mice. The heart and pancreas isolated from diabetic mice contained more macrophages and showed stronger PET signals than those of control mice. Flow cytometry analysis revealed the presence of macrophages but not neutrophils in pancreatic islets. Real-time PCR analysis revealed much higher FPR1 expression in pancreatic islets of diabetic over control mice. Autoradiography and immunohistochemical analysis confirmed abundant FPR1 expression in atherosclerotic lesions. Thus, (64)Cu-labeled cFLFLF peptide is a more effective PET agent for detecting macrophages compared to FDG.

[Immunological disorders of diabetes mellitus in experimental rat models]

A comprehensive understanding of the pathogenic mechanism is the prerequisite for proper disease management. However, the mechanisms of diabetes mellitus and diabetic complication remain extremely complicated and unresolved. While immune reactions are involved in the pathogenesis of diabetes and diabetic complication, the diabetic condition itself can influence immune responses. Furthermore, both diabetes and immune reactions are regulated by genetic and environmental factors. As a result, animal models have evolved to be powerful research tools to elucidate the complicated mechanisms for the pathogenesis of diabetes. Recently, various animal models of diabetes have been developed in rats, which provide advantages over mouse models in the scale of tissue samples and variation in type 2 diabetes models. In this review, we introduced rat models of diabetes and summarized the immune reactions in diabetic rats to propose the relationship between immune reactions and diabetes. Type 1 diabetes is induced by self-reactive cellular immune reactions. On the other hand, type 2 diabetes in rat models is associated with augmentation of innate immune reactions and increased humoral immunity. For example, helper T (Th) 1/Th17 cells are prevalent in non-obese type 1 diabetes rats (diabetes-prone BioBreeding rats), while non-obese type 2 diabetes rats (Goto-Kakizaki rat) show higher levels of natural IgM and T cell ratios with elevated Th2 cells compared with Wister rats. The investigation of immunological disorders in various diabetic rat models is useful to elucidate complicated mechanisms for the pathophysiology of diabetes. In future studies, immunological experimentations altering Th1/Th17 or Th2 cell levels and natural immune reactions may lend support to understanding the causes of diabetes and predicting the pathological conditions in diabetes.

Synergistic effects of high blood cholesterol and hypertension on leukocyte and platelet recruitment in the cerebral microcirculation

Hypertension or hypercholesterolemia can induce a proinflammatory and prothrombogenic phenotype in the microcirculation of the brain; however, less is known about how the combination of these risk factors affects the vasculature. We recently reported that a moderate (60%) increase in plasma cholesterol blunts the recruitment of leukocytes and platelets in the cerebral microvessels elicited by hypertension. In this study, we examined whether larger increments in blood cholesterol (4-fold) exerts a similar modulating influence on the vasculature in the presence of hypertension. Apolipoprotein E-knockout mice with deoxycorticosterone acetate salt-induced hypertension were placed on a high-cholesterol diet and exhibited exaggerated leukocyte and platelet adhesion responses in cerebral microvessels. Intermittent feeding (every fourth day) with high-cholesterol diet yielded similar phenotypic changes in the vasculature. Once the mice were placed on high-cholesterol diet, 4 days on normal diet (ND) were needed to revert to a normal vascular phenotype. Angiotensin II type 1 receptors and reactive oxygen species seem to contribute to the vascular responses induced by hypercholesterolemia and hypertension. Our findings indicate that the combination of hypertension and large increases in plasma cholesterol concentration results in a severe, but reversible, inflammatory and thrombogenic phenotype in the cerebral microvasculature.

Atherosclerosis susceptibility Loci identified in an extremely atherosclerosis-resistant mouse strain

Background

C3H/HeJ (C3H) mice are extremely resistant to atherosclerosis, especially males. To understand the underlying genetic basis, we performed quantitative trait locus (QTL) analysis on a male F₂ (the second generation from an intercross between 2 inbred strains) cohort derived from an intercross between C3H and C57BL/6 (B6) apolipoprotein E–deficient (Apoe^−/−) mice.

Methods and Results

Two hundred forty‐six male F₂ mice were started on a Western diet at 8 weeks of age and kept on the diet for 5 weeks. Atherosclerotic lesions in the aortic root and fasting plasma lipid levels were measured. One hundred thirty‐four microsatellite markers across the entire genome were genotyped. Four significant QTLs on chromosomes (Chr) 2, 4, 9, and 15 and 4 suggestive loci on Chr1, Chr4, and Chr7 were identified for atherosclerotic lesions. Unexpectedly, the C3H allele was associated with increased lesion formation for 2 of the 4 significant QTLs. Six loci for high‐density lipoprotein (HDL), 6 for non‐HDL cholesterol, and 3 for triglycerides were also identified. The QTL for atherosclerosis on Chr9 replicated Ath29, originally mapped in a female F₂ cohort derived from B6 and C3H Apoe^−/− mice. This locus coincided with a QTL for HDL, and there was a moderate, but statistically significant, correlation between atherosclerotic lesion sizes and plasma HDL cholesterol levels in F₂ mice.

Conclusions

These data indicate that most atherosclerosis susceptibility loci are distinct from those for plasma lipids except for the Chr9 locus, which exerts effect through interactions with HDL.

New quantitative trait loci for carotid atherosclerosis identified in an intercross derived from apolipoprotein E-deficient mouse strains

Carotid atherosclerosis is the primary cause of ischemic stroke. To identify genetic factors contributing to carotid atherosclerosis, we performed quantitative trait locus (QTL) analysis using female mice derived from an intercross between C57BL/6J (B6) and BALB/cJ (BALB) apolipoprotein E (Apoe^−/−) mice. We started 266 F₂ mice on a Western diet at 6 wk of age and fed them the diet for 12 wk. Atherosclerotic lesions in the left carotid bifurcation and plasma lipid levels were measured. We genotyped 130 microsatellite markers across the entire genome. Three significant QTLs, Cath1 on chromosome (Chr) 12, Cath2 on Chr5, and Cath3 on Chr13, and four suggestive QTLs on Chr6, Chr9, Chr17, and Chr18 were identified for carotid lesions. The Chr6 locus replicated a suggestive QTL and was named Cath4. Six QTLs for HDL, three QTLs for non-HDL cholesterol, and three QTLs for triglyceride were found. Of these, a significant QTL for non-HDL on Chr1 at 60.3 cM, named Nhdl13, and a suggestive QTL for HDL on ChrX were new. A significant locus for HDL (Hdlq5) was overlapping with a suggestive locus for carotid lesions on Chr9. A significant correlation between carotid lesion sizes and HDL cholesterol levels was observed in the F₂ population (R = −0.153, P = 0.0133). Thus, we have identified several new QTLs for carotid atherosclerosis and the locus on Chr9 may exert effect through interactions with HDL.

Genetic analysis of atherosclerosis and glucose homeostasis in an intercross between C57BL/6 and BALB/cJ apolipoprotein E-deficient mice

BACKGROUND

Diabetic patients have an increased risk of developing atherosclerosis and related complications compared with nondiabetic individuals. The increased cardiovascular risk associated with diabetes is due in part to genetic variations that influence both glucose homeostasis and atherosclerotic lesion growth. Mouse strains C57BL/6J (B6) and BALB/cJ (BALB) exhibit distinct differences in fasting plasma glucose and atherosclerotic lesion size when deficient in apolipoprotein E (Apoe(-/-)). Quantitative trait locus (QTL) analysis was performed to determine genetic factors influencing the 2 phenotypes.

METHODS AND RESULTS

Female F(2) mice (n=266) were generated from an intercross between B6.Apoe(-/-) and BALB.Apoe(-/-) mice and fed a Western diet for 12 weeks. Atherosclerotic lesions in the aortic root, fasting plasma glucose, and body weight were measured. 130 microsatellite markers across the entire genome were genotyped. Four significant QTLs, Ath1 on chromosome (Chr) 1, Ath41 on Chr2, Ath42 on Chr5, and Ath29 on Chr9, and 1 suggestive QTL on Chr4, were identified for atherosclerotic lesion size. Four significant QTLs, Bglu3 and Bglu12 on Chr1, Bglu13 on Chr5, Bglu15 on Chr12, and 2 suggestive QTLs on Chr9 and Chr15 were identified for fasting glucose levels on the chow diet. Two significant QTLs, Bglu3 and Bglu13, and 1 suggestive locus on Chr8 were identified for fasting glucose on the Western diet. One significant locus on Chr1 and 2 suggestive loci on Chr9 and Chr19 were identified for body weight. Ath1 and Ath42 coincided with Bglu3 and Bglu13, respectively, in the confidence interval.

CONCLUSIONS

We have identified novel QTLs that have major influences on atherosclerotic lesion size and glucose homeostasis. The colocalization of QTLs for atherosclerosis and diabetes suggests possible genetic connections between the 2 diseases.

Characterization of Bglu3, a mouse fasting glucose locus, and identification of Apcs as an underlying candidate gene

Bglu3 is a quantitative trait locus for fasting glucose on distal chromosome 1 identified in an intercross between C57BL/6 (B6) and C3H/HeJ (C3H) apolipoprotein E-deficient (apoE(-/-)) mice. This locus was subsequently replicated in two separate mouse intercrosses. The objective of this study was to characterize Bglu3 through construction and analysis of a congenic strain and identify underlying candidate genes. Congenic mice were constructed by introgressing a genomic region harboring Bglu3 from C3H.apoE(-/-) into B6.apoE(-/-) mice. Mice were started with a Western diet at 6 wk of age and maintained on the diet for 12 wk. Gene expression in the liver was analyzed by microarrays. Congenic mice had significantly higher fasting glucose levels and developed more significant glucose intolerance compared with B6.apoE(-/-) mice on the Western diet. Microarray analysis revealed 336 genes to be differentially expressed in the liver of congenic mice. Further pathway analysis suggested a role for acute phase response signaling in regulating glucose intolerance. Apcs, encoding an acute phase response protein serum amyloid P (SAP), is located underneath the linkage peak of Bglu3. Multiple single nucleotide polymorphisms between B6 and C3H mice were detected within and surrounding Apcs. Apcs expression in the liver was significantly higher in congenic and C3H mice compared with B6 mice. The Western diet consumption led to a gradual rise in plasma SAP levels, which was accompanied by rising fasting glucose in both B6 and C3H apoE(-/-) mice. Expression of C3H Apcs in B6.apoE(-/-) mice aggravated glucose intolerance. Bglu3 is confirmed to be a locus affecting diabetes susceptibility, and Apcs is a probable candidate gene.

Hyperglycemia in apolipoprotein E-deficient mouse strains with different atherosclerosis susceptibility

Background

Type 2 diabetes mellitus (T2DM) is associated with an increased risk of atherosclerotic vascular disease, but it is unknown whether the other way around is true too. C57BL/6 (B6) and BALB/cJ (BALB) are two mouse strains that differ markedly in their susceptibility to atherosclerosis. In this study we investigated the development of diet-induced T2DM in these two strains.

Methods and Results

When deficient in apolipoprotein E (apoE^-/-) and fed a Western diet for 12 weeks, atherosclerosis-susceptible B6 mice developed significant hyperglycemia. In contrast, atherosclerosis-resistant BALB apoE^-/- mice had much lower plasma glucose levels than B6.apoE^-/- mice on either chow or Western diet and during an intraperitoneal glucose tolerance test. In response to glucose BALB.apoE^-/- mice displayed both the first and second phases of insulin secretion but the second phase of insulin secretion was absent in B6.apoE^-/- mice. In response to insulin B6.apoE^-/- mice showed a deeper and longer-lasting fall in blood glucose levels while BALB.apoE^-/- mice showed little reduction in glucose levels. Pancreatic islet area of BALB.apoE^-/- mice on light microscopy nearly doubled the area of B6.apoE^-/- mice. Most circulating proinflammatory cytokines were lower in BALB.apoE^-/- than in B6.apoE^-/- mice on the Western diet, as determined by protein arrays. Increased macrophage infiltration in islets was observed in B6.apoE^-/- mice by immunostaining for Mac2 and also by flow cytometry.

Conclusion

This study demonstrates that defects in insulin secretion rather than defects in insulin resistance explain the marketed difference in susceptibility to T2DM in the B6.apoE^-/- and BALB.apoE^-/- mouse model. A smaller islet mass and more prominent islet inflammation may explain the vulnerability of B6.apoE^-/- mice to diet-induced diabetes.

Identification of Soat1 as a quantitative trait locus gene on mouse chromosome 1 contributing to hyperlipidemia

We previously identified two closely linked quantitative trait loci (QTL) on distal chromosome 1 contributing to major variations in plasma cholesterol and triglyceride levels in an intercross derived from C57BL/6 (B6) and C3H/HeJ (C3H) apolipoprotein E-deficient (apoE^−/−) mice. Soat1, encoding sterol o-acyltransferase 1, is a functional candidate gene located underneath the proximal linkage peak. We sequenced the coding region of Soat1 and identified four single nucleotide polymorphisms (SNPs) between B6 and C3H mice. Two of the SNPs resulted in amino-acid substitutions (Ile147Val and His205Tyr). Functional assay revealed an increased enzyme activity of Soat1 in peritoneal macrophages of C3H mice relative to those of B6 mice despite comparable protein expression levels. Allelic variants of Soat1 were associated with variations in plasma cholesterol and triglyceride levels in an intercross between B6.apoE^−/− and C3H.apoE^−/− mice. Inheritance of the C3H allele resulted in significantly higher plasma lipid levels than inheritance of the B6 allele. Soat1 variants were also significantly linked to major variations in plasma esterified cholesterol levels but not with free cholesterol levels. Trangenic expression of C3H Soat1 in B6.apoE^−/− mice resulted in elevations of plasma cholesterol and triglyceride levels. These results indicate that Soat1 is a QTL gene contributing to hyperlipidemia.

Resident intimal dendritic cells and the initiation of atherosclerosis

PURPOSE OF REVIEW

To highlight the fact that regional differences in the normal arterial intima are critical to atherosclerotic lesion formation driven by systemic risk factors.

RECENT FINDINGS

At arterial curvatures, bifurcations and branches unique hemodynamics influence endothelial cell signaling and gene expression patterns, which create a proinflammatory environment, with low-grade recruitment of monocytes and accumulation of cells with dendritic features in the intima. Upon induction of hypercholesterolemia, these resident intimal dendritic cells initiate atherosclerosis by rapidly engulfing lipid and becoming the first foam cells in nascent lesions. This step precedes endothelial cell activation and increased monocyte recruitment.

SUMMARY

The unique features of the arterial intima at atherosclerosis-susceptible sites do not lead to disease under normal physiological conditions, but this intimal environment promotes the initiation of atherogenesis upon induction of systemic risk factors such as hypercholesterolemia.

Genes within the MHC region have a dramatic influence on radiation-enhanced atherosclerosis in mice

BACKGROUND

C3H/HeJ (C3H) mice develop much smaller atherosclerotic lesions than C57BL/6 (B6) mice when deficient in apolipoprotein E (apoE⁻(/)⁻) or fed an atherogenic diet. The 2 strains differ in H2 haplotypes, with B6 having H2(b) and C3H having H2(k). C3.SW-H2(b)/SnJ (C3.SW) is a congenic strain of C3H/HeJ in which H2(k) is replaced with H2(b).

METHODS AND RESULTS

We performed bone marrow transplantation and found that atherosclerosis-resistant C3.SW.apoE⁻(/)⁻ mice reconstituted with bone marrow from either C3.SW.apoE⁻(/)⁻ or B6.apoE⁻(/)⁻ mice after lethal irradiation had significantly larger atherosclerotic lesions than B6.apoE⁻(/)⁻ mice receiving identical treatments and much larger lesions than C3H.apoE⁻(/)⁻ mice reconstituted with syngeneic bone marrow. For syngeneic transplantation, C3.SW.apoE⁻(/)⁻ mice exhibited a 21-fold increase in lesion size over C3H.apoE⁻(/)⁻ mice (152 800±21 937 versus 7060±2290 μm²/section) and a near 4-fold increase over B6.apoE⁻(/)⁻ mice (40 529±4675 μm²/section). C3.SW.apoE⁻(/)⁻ mice reconstituted with syngeneic marrow exhibited enhanced lesion formation relative to those reconstituted with B6 marrow (152 800±21 937 versus 107 000±9374 μm²/section; P=0.067). Sublethal irradiation led to a 6-fold increase of lesion size in C3.SW.apoE⁻(/)⁻ mice (9795±2804 versus 1550±607 μm²/section; P=0.008). Wild-type C3.SW mice reconstituted with apoE(+/+) or apoE⁻(/)⁻ bone marrow had significantly larger atherosclerotic lesions than C3H mice receiving identical treatments on an atherogenic diet.

CONCLUSIONS

These results indicate that gene(s) within the H2 region have a dramatic impact on radiation-enhanced atherosclerosis, and their effect is conveyed partially through bone marrow-derived cells.

Reduction of monocyte chemoattractant protein-1 and interleukin-8 levels by ticlopidine in TNF-alpha stimulated human umbilical vein endothelial cells

Atherosclerosis and its associated complications represent major causes of morbidity and mortality in the industrialized or Western countries. Monocyte chemoattractant protein-1 (MCP-1) is critical for the initiating and developing of atherosclerotic lesions. Interleukin-8 (IL-8), a CXC chemokine, stimulates neutrophil chemotaxis. Ticlopidine is one of the antiplatelet drugs used to prevent thrombus formation relevant to the pathophysiology of atherothrombosis. In this study, we found that ticlopidine dose-dependently decreased the mRNA and protein levels of TNF-α-stimulated MCP-1, IL-8, and vascular cell adhesion molecule-1 (VCAM-1) in human umbilical vein endothelial cells (HUVECs). Ticlopidine declined U937 cells adhesion and chemotaxis as compared to TNF-α stimulated alone. Furthermore, the inhibitory effects were neither due to decreased HUVEC viability, nor through NF-kB inhibition. These results suggest that ticlopidine decreased TNF-α induced MCP-1, IL-8, and VCAM-1 levels in HUVECs, and monocyte adhesion. Therefore, the data provide additional therapeutic machinery of ticlopidine in treatment and prevention of atherosclerosis.

Quantitative trait locus analysis of circulating adhesion molecules in hyperlipidemic apolipoprotein E-deficient mice

Circulating soluble adhesion molecules have been suggested as useful markers to predict several clinical conditions such as atherosclerosis, type 2 diabetes, obesity, and hypertension. To determine genetic factors influencing plasma levels of soluble vascular cell adhesion molecule-1 (VCAM-1) and P-selectin, quantitative trait locus (QTL) analysis was performed on an intercross between C57BL/6J (B6) and C3H/HeJ (C3H) mouse strains deficient in apolipoprotein E-deficient (apoE-/-). Female F2 mice were fed a western diet for 12 weeks. One significant QTL, named sVcam1 (71 cM, LOD 3.9), on chromosome 9 and three suggestive QTLs on chromosomes 5, 13 and 15 were identified to affect soluble VCAM-1 levels. Soluble P-selectin levels were controlled by one significant QTL, named sSelp1 (8.5 cM, LOD 3.4), on chromosome 16 and two suggestive QTLs on chromosomes 10 and 13. Both adhesion molecules showed significant or an apparent trend of correlations with body weight, total cholesterol, and LDL/VLDL cholesterol levels in the F2 population. These results indicate that plasma VCAM-1 and P-selectin levels are complex traits regulated by multiple genes, and this regulation is conferred, at least partially, by acting on body weight and lipid metabolism in hyperlipidemic apoE-/- mice.

Genetically programmed biases in Th1 and Th2 immune responses modulate atherogenesis

Atherosclerotic lesions contain T lymphocytes, which orchestrate adaptive immunity and regulate many innate immune pathways. This study examined the influence of Th1 and Th2 helper cell subsets on atherogenesis in two ApoE(-/-) mouse strains, C57BL/6 and BALB/c, which display opposite T-cell subset polarizations. ApoE(-/-) BL/6 mice showed predominant Th1-like immune responses on polyclonal stimulation of splenic CD4(+) T cells and had IgG2a antibodies to oxidized low-density lipoprotein (a disease-related antigen) whereas ApoE(-/-) BALB/c mice displayed predominant Th2 responses by CD4(+) T cells and an IgG1 isotype response toward oxidized low-density lipoprotein. ApoE(-/-) BL/6 and BALB/c mice consumed a high-cholesterol diet for 10, 16, and 24 weeks with equivalent cholesterolemic responses. The Th1-slanted BL/6 mice developed significantly more atherosclerosis in the aortic root and abdominal aorta at all time points compared with BALB/c mice, supporting a proatherogenic role for Th1 response. Progression of atherosclerosis was associated with increased levels of interleukin (IL)-6 in mouse serum and CD4(+) T-cell culture supernatants and increased levels of the acute-phase protein, serum amyloid A (SAA). Both IL-6 and SAA levels rose significantly in ApoE(-/-) BL/6 mice compared with BALB/c mice. The circulating cytokine milieu (IL-6) and acute phase reactants such as SAA may reflect alterations in the Th1/Th2 balance. The results presented here illustrate how genetically determined modifiers of both immune and inflammatory responses can modulate atherogenesis independently of lipid levels.

Relative reduction of endothelial nitric-oxide synthase expression and transcription in atherosclerosis-prone regions of the mouse aorta and in an in vitro model of disturbed flow

Atherosclerosis develops in distinct regions of the arterial tree. Defining patterns and mechanisms of endothelial cell gene expression in different regions of normal arteries is key to understanding the initial molecular events in atherogenesis. In this study, we demonstrated that the expression of endothelial nitric-oxide synthase (eNOS), an atheroprotective gene, and its phosphorylation on Ser(1177), a marker of activity, were lower in regions of the normal mouse aorta that are predisposed to atherosclerosis. The same expression pattern was observed in mouse strains that are both susceptible and resistant to atherosclerosis, and the topography of eNOS expression was inverse to p65, the main nuclear factor-kappaB subunit. Modeling of disturbed and uniform laminar flow in vitro reproduced the expression patterns of eNOS and p65 that were found in vivo. Heterogeneous nuclear RNA expression and RNA polymerase II chromosome immunoprecipitation studies demonstrated that regulation of transcription contributed to increased eNOS expression in response to shear stress. In vivo, the transcription of eNOS was reduced in regions of the mouse aorta predisposed to atherosclerosis, as defined by reporter gene expression in eNOS promoter-beta-galactosidase reporter transgenic mice. These data suggest that disturbed hemodynamic patterns found at arterial branches and curvatures uniquely modulate endothelial cell gene expression by regulating transcription, potentially explaining why these regions preferentially develop atherosclerosis when risk factors such as hypercholesterolemia are introduced.

Quantitative trait locus analysis of carotid atherosclerosis in an intercross between C57BL/6 and C3H apolipoprotein E-deficient mice

BACKGROUND AND PURPOSE

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit marked differences in atherosclerotic lesion formation in the carotid arteries on the apolipoprotein E-deficient (apoE(-/-)) background when fed a Western diet. Quantitative trait locus analysis was performed on an intercross between B6.apoE(-/-) and C3H.apoE(-/-) mice to determine genetic factors contributing to variation in the phenotype.

METHODS

Female B6.apoE(-/-) mice were crossed with male C3H.apoE(-/-) mice to generate F(1) hybrids, which were intercrossed to generate 241 female F(2) progeny. At 6 weeks of age, F(2) mice were started on a Western diet. After being fed the diet for 12 weeks, F(2) mice were analyzed for phenotypes such as lesion size in the left carotid arteries and plasma lipid levels and typed for 154 genetic markers spanning the mouse genome.

RESULTS

One significant quantitative trait locus, named CAth1 (25 cM, log of the odds score: 4.5), on chromosome 12 and 4 suggestive quantitative trait loci, on chromosomes 1, 5, 6, and 11, respectively, were identified to influence carotid lesion size. One significant quantitative trait locus on distal chromosome 1 accounted for major variations in plasma low-density lipoprotein/very-low-density lipoprotein, high-density lipoprotein cholesterol, and triglyceride levels. Carotid lesion size was not significantly correlated with plasma low-density lipoprotein/very-low-density lipoprotein or high-density lipoprotein cholesterol levels.

CONCLUSIONS

These data indicate that the loci for carotid lesions do not overlap with those for aortic lesions as identified in a previous cross derived from the same parental strains, and carotid atherosclerosis and plasma lipids are controlled by separate genetic factors in the B6 and C3H mouse model.

Effect of aging on fatty streak formation in a diet-induced mouse model of atherosclerosis

Age is considered to be a major risk factor for atherosclerosis, but it is unclear whether age has a direct effect on susceptibility to atherosclerosis. Wild-type mice develop fatty streak lesions in the aortic root only when fed a cholate-containing high fat/cholesterol diet. To investigate the influence of age on fatty streak formation, young (10 weeks) and old (53 weeks) female C57BL/6 mice were fed an atherogenic diet containing 15% fat, 1.25% cholesterol and 0.5% sodium cholate for 12 weeks. Atherosclerotic lesions at the aortic root were measured after cryosections were stained with oil red O. Results showed that old mice developed a comparable size of aortic lesions with young counterparts (5,600 +/- 2,480 vs. 6,457 +/- 1,537 microm2/section; p = 0.77), although old mice had significantly higher plasma cholesterol levels than young mice on the atherogenic diet (p < 0.05). Plasma levels of soluble vascular cell adhesion molecule 1 were significantly higher in old mice than in young mice on both chow and Western diets (p < 0.005). These data indicate that age has no direct effect on atherosclerosis susceptibility although it is accompanied by elevations in plasma cholesterol and vascular cell adhesion molecule 1 levels in C57BL/6 mice. Thus, increased cardiovascular events with age are probably related to a progressive increase in plaque size rather than to an increase in atherosclerosis susceptibility.

siRNA silencing reveals role of vascular cell adhesion molecule-1 in vascular smooth muscle cell migration

Vascular cell adhesion molecule-1 (VCAM-1) is an adhesion molecule expressed by endothelial cells for recruitment of leukocytes during inflammation. It is also abundantly expressed by smooth muscle cells in atherosclerotic lesions and in injured arteries. In this study, we examined the role of VCAM-1 in smooth muscle cell migration. Smooth muscle cells were isolated from the aorta of C57BL/6 mice and transfected with short interfering RNAs (siRNAs) targeting VCAM-1. Inhibition on VCAM-1 expression by siRNAs was assessed by Western blot analysis, RT-PCR and by measuring soluble VCAM-1 concentrations in the incubation medium. One siRNA that showed greater suppression on VCAM-1 expression was used for migration assay. A single scratch wound was made on 70% confluent cells and cells migrated from wounded monolayer were counted 24 and 48h after injury. Treatment with VCAM-1 siRNA resulted in a significant reduction in the number of migrated cells. This siRNA also exhibited a minor effect on smooth muscle cell proliferation. Thus, our findings indicate that VCAM-1 is necessary for the migration of smooth muscle cells and interfering VCAM-1 expression could be an effective approach to prevention and treatment of atherosclerosis and restenosis.

Association of a Vcam1 mutation with atherosclerosis susceptibility in diet-induced models of atherosclerosis

We previously identified a G>A single nucleotide polymorphism (SNP) between C57BL/6J (B6) and C3H/HeJ (C3H) mouse strains at position 2077 in the coding region of Vcam1 that leads to substitution of an amino acid from aspartic acid (D) to asparagine (N) in the protein product. In the present study, we investigated the association of this SNP with atherosclerosis susceptibility using a panel of inbred mouse strains, a set of recombinant inbred (RI) strains derived from B6 and C3H mice, and a cohort of F2 mice derived from B6 and C3H apolipoprotein E-deficient (apoE(-/-)) mice. Inbred strain analysis revealed that mouse strains with the B6 Vcam1 genotype developed significantly larger atherosclerotic lesions than strains with the C3H genotype (4622+/-2816 microm(2)/section versus 362+/-697 microm(2)/section; P=0.029). BXH RI strains with the B6 Vcam1 genotype also developed larger atherosclerotic lesions than those with the C3H genotype (8305+/-9031 microm(2)/section versus 2139+/-2931 microm(2)/section) although the difference was not statistically significant (P=0.13). In contrast, no association was detected between Vcam1 and atherosclerotic lesion size in F2 mice. The present data indicate that the G>A mutation of Vcam1 is associated with atherosclerotic lesion formation in the dietary but not apoE(-/-) models of atherosclerosis and this association suggests a role for the Vcam1 gene in influencing atherosclerosis susceptibility.

Paradoxical increase in LDL oxidation by endothelial cells from an atherosclerosis-resistant mouse strain

Oxidative modification of LDL accumulated in the subendothelial space is a critical step in atherogenesis. Mouse strains C57BL/6 (B6) and BALB/c differ markedly in atherosclerosis susceptibility. We sought to determine whether variation of endothelial cells in the capacity to oxidize LDL or in response to minimally modified LDL (MM-LDL) constitutes a genetic component in atherosclerosis. LDL oxidation was assessed by measuring thiobarbituric acid-reactive substance (TBARS) production. Responses to MM-LDL were evaluated by examining induction of monocyte chemotactic protein-1, macrophage-colony stimulating factor, and vascular cell adhesion molecule-1. Both strains exhibited comparable endothelial responses to MM-LDL, whereas BALB/c mice had an increased rate of oxidizing LDL compared with B6 mice. To examine whether endothelial nitric oxide synthase (eNOS) contributed to the difference in LDL oxidation, cells were incubated with native LDL in the presence or absence of N(Omega)-nitro-l-arginine methyl ester (l-NAME), a specific NOS inhibitor. Although l-NAME significantly inhibited endothelial cell-mediated LDL oxidation, it failed to abolish the difference between the strains. In contrast, Baicalein, a specific 12/15 lipoxygenase inhibitor, abolished the difference in LDL oxidation. Thus, the paradoxical increase in LDL oxidation by endothelial cells is attributable to higher oxidant activity of 12/15-lipoxygenase in BALB/c mice and endothelial cells appear unlikely to be a source of the resistance to atherosclerosis.

Endothelial and leukocyte adhesion molecules in primary hypertriglyceridemia

Hypertriglyceridemia is known to be associated to functional impairment of the endothelium and, consequently, to higher risk of atherosclerosis. Nevertheless, some crucial steps in the development of the atherosclerotic plaque are still unknown in primary hypertriglyceridemia. The aim of the present study was to explore the expression of soluble and leukocyte-associated cell adhesion molecules in a group of patients with primary hypertriglyceridemia, both including (n=50) and excluding (n=24) subjects with metabolic syndrome, in comparison with control normotriglyceridemic individuals (n=30). Lipid profile, CETP activity, HDL and VLDL chemical composition were evaluated. Soluble (VCAM-1, ICAM-1 and E-selectin) and leukocyte cell adhesion molecules (CD18, CD49d and CD54) were measured by enzyme-linked immunosorbent assay and flow cytometry, respectively. Patients with primary hypertriglyceridemia as compared with control subjects showed significantly higher VCAM-1 (15.6+/-4.5 ng/ml versus 13.9+/-3.8 ng/ml, respectively; p<0.05) and ICAM-1 (16.9+/-3.1 ng/ml versus 15.2+/-3.2 ng/ml, respectively; p<0.05). Regarding leukocyte cell adhesion molecules, significant increases were also detected in monocyte CD18 (398+/-180 versus 332+/-136 arbitrary units, respectively; p<0.05) and CD54 (49+/-14 versus 42+/-12 arbitrary units, respectively; p<0.05), and lymphocyte CD18 (122+/-53 versus 101+/-33 arbitrary units, respectively; p<0.05). ICAM-1 plasma levels, as well as monocyte CD18 and CD54, and lymphocyte CD18 persisted elevated even if patients with metabolic syndrome were discarded among those with hypertriglyceridemia. The increase in circulating and leukocyte cell adhesion molecules in primary hypertriglyceridemic patients would highlight the inflammatory process which is a key event in atherogenesis.

Increased atherosclerosis following treatment with a dual PPAR agonist in the ApoE knockout mouse

OBJECTIVE

Recent reports have suggested that dual peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonists are associated with adverse cardiovascular events. This study aimed to investigate the actions of the non-thiazolidinedione PPARalpha/gamma agonist, compound 3q, on plaque development in the apolipoprotein E knockout (apoE KO) mouse, a recognised model of accelerated plaque development.

METHODS

Six-week-old male apoE KO mice were randomised to receive the dual PPARalpha/gamma agonist, compound 3q (3 mg/kg/day), the PPARgamma agonist, rosiglitazone (20 mg/kg/day), the PPARalpha agonist, gemfibrozil (100 mg/kg/day) by gavage or no treatment for 20 weeks (n=12/group).

RESULTS

Gemfibrozil and rosiglitazone significantly reduced lesion area. However, compound 3q was associated with a three-fold increase in total plaque area (versus control p<0.001). This was associated with an upregulation of markers of plaque instability including vascular cell adhesion molecule-1 (3.5-fold, p<0.001), P-selectin (3.4-fold, p<0.001) monocyte chemoattractant protein-1 (3.4-fold; p<0.001) as well as the scavenger receptor, CD36 (2-fold, p<0.01). These disparate effects were observed with the dual PPAR agonist despite lowering LDL cholesterol and improving insulin sensitivity to a similar extent to PPARalpha and gamma agonists used individually.

CONCLUSION

The finding of increased atherogenesis following a dual PPARalpha/gamma agonist is consistent with recent clinical findings. These data provide an important framework for further exploring the potential utility and safety of combinatorial approaches.

Prothrombotic factors enhance heparin-induced thrombocytopenia and thrombosis in vivo in a mouse model

BACKGROUND

Heparin-induced thrombocytopenia/thrombosis (HIT/T) is a common cause of life- and limb-threatening thrombosis. The development of antibodies that react with complexes of heparin and platelet factor 4 (PF4) is fundamental to the development of the disease. However, anti-PF4/heparin antibodies are far more common than is HIT/T and there is less understanding of the factors that contribute to thrombosis in only a subset of patients.

OBJECTIVES

Both qualitative and quantitative differences in multiple factors (e.g. antibodies, heparin and platelets) may influence the clinical course of patients who develop anti-PF4/heparin antibodies. We examined the hypothesis that host-specific factors, such as comorbid prothrombotic conditions, would exacerbate the pathologic effects of anti-PF4/heparin antibodies.

METHODS AND RESULTS

A mouse model transgenic for human Fcgamma RIIa and PF4 and null for mouse PF4 was used to study the influence of prothrombotic conditions on the effects of anti-PF4/heparin antibodies in vivo. To simulate a prothrombotic milieu, mice were fed a hypercholesterolemic diet (HD). HD-fed mice had elevated plasma cholesterol, increased platelet reactivity and increased endothelial activation relative to mice fed a standard diet (SD). Age- and sex-matched mice from each diet group were treated with an anti-PF4/heparin antibody and heparin. HD-fed mice developed more severe thrombocytopenia than similarly treated SD-fed mice. Mice with moderate to severe thrombocytopenia had elevated plasma levels of thrombin-antithrombin complexes, indicative of increased thrombin generation in vivo. Platelet-fibrin thrombi were observed in multiple organs of HD-fed mice that developed severe thrombocytopenia.

CONCLUSIONS

Host-specific factors, such as prothrombotic changes in platelet reactivity and/or endothelial activation, may influence the development of thrombosis in a subset of patients who develop anti-PF4/heparin antibodies.

Direct evidence for a crucial role of the arterial wall in control of atherosclerosis susceptibility

BACKGROUND

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit marked differences in atherosclerosis susceptibility. We sought to determine whether the difference in atherosclerosis susceptibility resides at the level of arterial walls.

METHODS AND RESULTS

Thoracic aortic segments from 8-week-old female B6 and C3H apolipoprotein E-deficient mice were transplanted into the infrarenal aorta of 10-week-old female F1 mice. After transplantation, recipients were maintained on a chow diet for 16 weeks. The donor aortic segments of B6 mice developed significantly larger atherosclerotic lesions than those of C3H (44,983+/-11,702 versus 5600+/-4885 microm2 per section; P=0.011). Expression of vascular cell adhesion molecule (VCAM)-1 by endothelial cells was examined both in vitro and in vivo. B6 mice expressed significantly more VCAM-1 than their C3H counterparts. Sequence analysis of VCAM-1 cDNA revealed a nucleotide difference in the coding region that resulted in substitution of an amino acid in the protein product.

CONCLUSIONS

These data provide direct proof that factors operating in the vessel wall, particularly endothelial cells, can serve as atherosclerosis modifiers and suggest a possibility for the contribution of VCAM-1 to atherosclerosis susceptibility.

Low-grade chronic inflammation in regions of the normal mouse arterial intima predisposed to atherosclerosis

Atherosclerotic lesions develop in regions of arterial curvature and branch points, which are exposed to disturbed blood flow and have unique gene expression patterns. The cellular and molecular basis for atherosclerosis susceptibility in these regions is not completely understood. In the intima of atherosclerosis-predisposed regions of the wild-type C57BL/6 mouse aorta, we quantified increased expression of several proinflammatory genes that have been implicated in atherogenesis, including vascular cell adhesion molecule–1 (VCAM-1) and a relative abundance of dendritic cells, but only occasional T cells. In contrast, very few intimal leukocytes were detected in regions resistant to atherosclerosis; however, abundant macrophages, including T cells, were found throughout the adventitia (Adv). Considerably lower numbers of intimal CD68⁺ leukocytes were found in inbred atherosclerosis-resistant C3H and BALB/c mouse strains relative to C57BL/6 and 129; however, leukocyte distribution throughout the Adv of all strains was similar. The predominant mechanism for the accumulation of intimal CD68⁺ cells was continued recruitment of bone marrow–derived blood monocytes, suggestive of low-grade chronic inflammation. Local proliferation of intimal leukocytes was low. Intimal CD68⁺ leukocytes were reduced in VCAM-1–deficient mice, suggesting that mechanisms of leukocyte accumulation in the intima of normal aorta are analogous to those in atherosclerosis.

Deficiency of inducible NO synthase reduces advanced but not early atherosclerosis in apolipoprotein E-deficient mice

The inducible nitric oxide synthase (iNOS) is abundantly expressed by smooth muscle cells and macrophages in atherosclerotic lesions. Apolipoprotein E-deficient (apoE(-/-)) mice develop early and advanced atherosclerotic lesions. The role of iNOS in both early and advanced atherosclerotic formation was determined in apoE(-/-) mice. Mice were fed chow or a Western diet containing 42% fat, 0.15% cholesterol, and 19.5% casein. At 12 weeks of age on chow diet, iNOS(-/-)/apoE(-/-) mice developed comparable sizes of early atherosclerotic lesions in the aortic root as did iNOS(+/+)/apoE(-/-) mice (30,993+/-4746 vs. 26,648+/-6815 microm(2)/section; P=0.608). After being fed the Western diet for 12 weeks, iNOS(-/-)/apoE(-/-) mice developed significantly smaller advanced lesions than iNOS(+/+)/apoE(-/-) mice (458,734+/-14,942 vs. 519,570+/-22,098 microm(2)/section; P=0.029). This reduction in lesion formation could not be explained by differences in plasma lipid levels. To examine whether iNOS contributed to LDL oxidation, smooth muscle cells were isolated from the aorta, activated with TNF-alpha, and then incubated with native LDL in the absence or presence of N-Omega-nitro-L-arginine methyl ester (L-NAME), a specific NOS inhibitor. L-NAME significantly inhibited LDL oxidation by smooth muscle cells from iNOS(+/+)/apoE(-/-) mice (P=0.048), but it had no effect on LDL oxidation by cells from iNOS(-/-)/apoE(-/-) mice. iNOS(-/-)/apoE(-/-) mice had a significantly lower plasma lipoperoxide level on the Western diet (2.74+/-0.23 vs. 3.89+/-0.41 microM MDA; P=0.021) but not on chow diet (1.02+/-0.07 vs. 1.51+/-0.29 microM MDA; P=0.11). Thus, the absence of iNOS-mediated LDL oxidation may contribute to the reduction in advanced lesion formation of iNOS(-/-)/apoE(-/-) mice.

Hyperlipidemia is a major determinant of neointimal formation in LDL receptor-deficient mice

LDL receptor-deficient (LDLR(-/-)) mice exhibit mild hyperlipidemia on a chow diet but develop severe hyperlipidemia on a high fat diet. In this study, we investigated neointimal formation after removal of the endothelium when LDLR(-/-) mice were fed chow or a Western diet containing 42% fat, 0.15% cholesterol, and 19.5% casein. At 10 weeks of age, female mice underwent endothelial denudation of the left common carotid artery. Two weeks after injury, neointimal formation was barely detectable in the injured vessel when mice developed mild hyperlipidemia on the chow diet. In contrast, neointimal lesions were obvious when mice developed severe hyperlipidemia on the Western diet. Immunohistochemical and histological analyses demonstrated the presence of macrophage foam cells and smooth muscle cells in neointimal lesions. The injured artery also exhibited a significant increase in medial area on the Western diet. Plasma levels of MCP-1 and soluble VCAM-1 were significantly elevated by feeding of the Western diet. These data indicate that hyperlipidemia aggravates neointimal growth in LDLR(-/-) mice by promoting foam cell formation and inflammation.