Determinants of atherosclerosis susceptibility in the C3H and C57BL/6 mouse model: evidence for involvement of endothelial cells but not blood cells or cholesterol metabolism

Metabolomics and mitochondrial dysfunction in cardiometabolic disease

Circulating metabolites are indicators of systemic metabolic dysfunction and can be detected through contemporary techniques in metabolomics. These metabolites are involved in numerous mitochondrial metabolic processes including glycolysis, fatty acid β-oxidation, and amino acid catabolism, and changes in the abundance of these metabolites is implicated in the pathogenesis of cardiometabolic diseases (CMDs). Epigenetic regulation and direct metabolite-protein interactions modulate metabolism, both within cells and in the circulation. Dysfunction of multiple mitochondrial components stemming from mitochondrial DNA mutations are implicated in disease pathogenesis. This review will summarize the current state of knowledge regarding: i) the interactions between metabolites found within the mitochondrial environment during CMDs, ii) various metabolites' effects on cellular and systemic function, iii) how harnessing the power of metabolomic analyses represents the next frontier of precision medicine, and iv) how these concepts integrate to expand the clinical potential for translational cardiometabolic medicine.

Ovarian inflammation mediated by Toll-like receptor 4 increased transcripts of maternal effect genes and decreased embryo development†

Obese women are subfertile and have reduced assisted reproduction success, which may be due to reduced oocyte competence. We hypothesize that consumption of a high-fat/high-sugar diet induces ovarian inflammation, which is a primary contributor to decreased oocyte quality and pre-implantation embryo development. To test this hypothesis, C57BL/6 (B6) mice with a normal inflammatory response and C3H/HeJ (C3H) mice with a dampened inflammatory response due to dysfunctional Toll-like receptor 4 were fed either normal chow or high-fat/high-sugar diet. In both B6 and C3H females, high-fat/high-sugar diet induced excessive adiposity and hyperglycemia compared to normal chow-fed counterparts. Conversely, ovarian CD68 levels and oocyte expression of oxidative stress markers were increased when collected from B6 high-fat/high-sugar but not C3H high-fat/high-sugar mice. Following in vitro fertilization of in vivo matured oocytes, blastocyst development was decreased in B6-high-fat/high-sugar but not C3H high-fat/high-sugar mice. Expression of cumulus cell markers of oocyte quality were altered in both B6 high-fat/high-sugar and C3H high-fat/high-sugar. However, there were no diet-dependent differences in spindle abnormalities in either B6 or C3H mice, suggesting potential defects in cytoplasmic maturation. Indeed, there were significant increases in the abundance of maternal effect gene mRNAs in oocytes from only B6 high-fat/high-sugar mice. These differentially expressed genes encode proteins of the subcortical maternal complex and associated with mRNA metabolism and epigenetic modifications. These genes regulate maternal mRNA degradation at oocyte maturation, mRNA clearance at the zygotic genome activation, and methylation of imprinted genes suggesting a mechanism by which inflammation induced oxidative stress impairs embryo development.

Ldlr-Deficient Mice with an Atherosclerosis-Resistant Background Develop Severe Hyperglycemia and Type 2 Diabetes on a Western-Type Diet

Apoe^-/- and Ldlr^-/- mice are two animal models extensively used for atherosclerosis research. We previously reported that Apoe^-/- mice on certain genetic backgrounds, including C3H/HeJ (C3H), develop type 2 diabetes when fed a Western diet. We sought to characterize diabetes-related traits in C3H-Ldlr^-/- mice through comparing with C3H-Apoe^-/- mice. On a chow diet, Ldlr^-/- mice had lower plasma total and non-HDL cholesterol levels but higher HDL levels than Apoe^-/- mice. Fasting plasma glucose was much lower in Ldlr^-/- than Apoe^-/- mice (male: 122.5 ± 5.9 vs. 229.4 ± 17.5 mg/dL; female: 144.1 ± 12.4 vs. 232.7 ± 6.4 mg/dL). When fed a Western diet, Ldlr^-/- and Apoe^-/- mice developed severe hypercholesterolemia and also hyperglycemia with fasting plasma glucose levels exceeding 250 mg/dL. Both knockouts had similar non-HDL cholesterol and triglyceride levels, and their fasting glucose levels were also similar. Male Ldlr^-/- mice exhibited greater glucose tolerance and insulin sensitivity compared to their Apoe^-/- counterpart. Female mice showed similar glucose tolerance and insulin sensitivity though Ldlr^-/- mice had higher non-fasting glucose levels. Male Ldlr^-/- and Apoe^-/- mice developed moderate obesity on the Western diet, but female mice did not. These results indicate that the Western diet and ensuing hyperlipidemia lead to the development of type 2 diabetes, irrespective of underlying genetic causes.

Reticulocalbin 2 as a Potential Biomarker and Therapeutic Target for Atherosclerosis

Vascular inflammation initiated by oxidized lipoproteins drives initiation, progression, and even rupture of atherosclerotic plaques. Yet, to date, no biomarker is directly linked to oxidized lipid-induced vascular inflammation. Reticulocalbin 2 (RCN2) is a key regulator of basal and oxidized lipid-induced cytokine production in arterial wall cells. We evaluated the potential of circulating RCN2 to identify subjects with or at risk of developing atherosclerosis. Immunohistochemical analysis revealed abundant RCN2 expression in the endothelium and adventitia of normal arteries and in atherosclerotic lesions of both humans and mice. Atherosclerosis-susceptible C57BL/6 (B6) mice had higher plasma Rcn2 levels than resistant C3H mice. High-fat diet feeding raised plasma Rcn2 levels of both strains. In humans, patients with coronary artery disease (CAD) or peripheral artery disease (PAD) showed elevated serum RCN2 levels compared to healthy controls. In a cohort of 92 CAD patients, serum RCN2 exhibited a significant inverse correlation with HDL cholesterol and K+ levels and a trend toward association with white blood cell account, Na+, statin treatment, and diastolic blood pressure. HDL treatment suppressed Rcn2 expression in endothelial cells. This study suggests that circulating RCN2 is a potential non-invasive biomarker for identifying individuals with atherosclerosis and HDL protects against atherosclerosis by downregulation of RCN2 expression in endothelial cells.

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.

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.

Reactive Oxygen Species (ROS), Intimal Thickening, and Subclinical Atherosclerotic Disease

Arteriosclerosis causes significant morbidity and mortality worldwide. Central to this process is the development of subclinical non-atherosclerotic intimal lesions before the appearance of pathologic intimal thickening and advanced atherosclerotic plaques. Intimal thickening is associated with several risk factors, including oxidative stress due to reactive oxygen species (ROS), inflammatory cytokines and lipid. The main ROS producing systems in-vivo are reduced nicotinamide dinucleotide phosphate (NADPH) oxidase (NOX). ROS effects are context specific. Exogenous ROS induces apoptosis and senescence, whereas intracellular ROS promotes stem cell differentiation, proliferation, and migration. Lineage tracing studies using murine models of subclinical atherosclerosis have revealed the contributory role of medial smooth muscle cells (SMCs), resident vascular stem cells, circulating bone-marrow progenitors and endothelial cells that undergo endothelial-mesenchymal-transition (EndMT). This review will address the putative physiological and patho-physiological roles of ROS in controlling vascular cell fate and ROS contribution to vascular regeneration and disease progression.

Recommendation on Design, Execution, and Reporting of Animal Atherosclerosis Studies: A Scientific Statement From the American Heart Association

Animal studies are a foundation for defining mechanisms of atherosclerosis and potential targets of drugs to prevent lesion development or reverse the disease. In the current literature, it is common to see contradictions of outcomes in animal studies from different research groups, leading to the paucity of extrapolations of experimental findings into understanding the human disease. The purpose of this statement is to provide guidelines for development and execution of experimental design and interpretation in animal studies. Recommendations include the following: (1) animal model selection, with commentary on the fidelity of mimicking facets of the human disease; (2) experimental design and its impact on the interpretation of data; and (3) standard methods to enhance accuracy of measurements and characterization of atherosclerotic lesions.

Recommendation on Design, Execution, and Reporting of Animal Atherosclerosis Studies: A Scientific Statement From the American Heart Association

Animal studies are a foundation for defining mechanisms of atherosclerosis and potential targets of drugs to prevent lesion development or reverse the disease. In the current literature, it is common to see contradictions of outcomes in animal studies from different research groups, leading to the paucity of extrapolations of experimental findings into understanding the human disease. The purpose of this statement is to provide guidelines for development and execution of experimental design and interpretation in animal studies. Recommendations include the following: (1) animal model selection, with commentary on the fidelity of mimicking facets of the human disease; (2) experimental design and its impact on the interpretation of data; and (3) standard methods to enhance accuracy of measurements and characterization of atherosclerotic lesions.

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.

Circulating anti-β2-glycoprotein I antibodies of peripheral arterial disease patients trigger a genomic overexpression of Toll-like receptor 4 in endothelial cells

OBJECTIVE

Circulating anti-β2-glycoprotein I (ABGPI) antibodies are associated with peripheral arterial disease (PAD) and induce the expression of leukocyte adhesion molecules and proinflammatory cytokines by endothelial cells. Our aim is to study a transcriptional activation pathway of the innate immune system through the cellular signalling cascade triggered by receptors Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4) of endothelial cells after the exposure of these cells to seropositive ABGPI human serum obtained from PAD patients.

METHODS

We obtained serum samples from PAD patients and controls without PAD. ABGPI serum titer was detected using indirect immunofluorescence. Our sample was stratified into three groups: group I (PAD and ABGPI titer ≥1:100; n = 15), group II (PAD and ABGPI titer <1:100; n = 15), and control participants (no PAD; n = 15). All serum samples were incubated with human aortic endothelial cell (HAEC) culture. Genomic expression of TLR2 and TLR4 receptors and their shared intracellular signalling molecules, myeloid differentiation primary response gene 88 (MyD88), and interleukin (IL)-1 receptor-associated kinase (1IRAK1), were measured after the exposure of HAECs to each serum.

RESULTS

HAEC genomic expression of TLR4 was higher after the exposure to group I serum than after the exposure to group II serum (log10×10-relative quantification [RQ]: 1.80 ± 0.42 vs 1.37 ± 0.39; P = .01) or control serum (log10×10-RQ: 1.80 ± 0.42 vs 1.09 ± 0.26; P < .01). TLR4 expression was higher in group II than in the control group (log10×10-RQ: 1.37 ± 0.39 vs 1.09 ± 0.26; P = .04). TLR4 expression correlated with MyD88 (r = 0.54; P < .01) and IRAK1 (r = 0.55; P < .01) expression. We recorded a positive correlation between MyD88 and IRAK1 genomic expression (r = 0.58; P < .01).

CONCLUSIONS

Our results suggest that serum from PAD patients with elevated ABGPI antibodies induces a genomic overexpression of TLR4 and its cellular signalling molecules in endothelial cells.

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.

Mitochondrial genetic background modulates bioenergetics and susceptibility to acute cardiac volume overload

Dysfunctional bioenergetics has emerged as a key feature in many chronic pathologies such as diabetes and cardiovascular disease. This has led to the mitochondrial paradigm in which it has been proposed that mtDNA sequence variation contributes to disease susceptibility. In the present study we show a novel animal model of mtDNA polymorphisms, the MNX (mitochondrial-nuclear exchange) mouse, in which the mtDNA from the C3H/HeN mouse has been inserted on to the C57/BL6 nuclear background and vice versa to test this concept. Our data show a major contribution of the C57/BL6 mtDNA to the susceptibility to the pathological stress of cardiac volume overload which is independent of the nuclear background. Mitochondria harbouring the C57/BL6J mtDNA generate more ROS (reactive oxygen species) and have a higher mitochondrial membrane potential relative to those with C3H/HeN mtDNA, independent of nuclear background. We propose this is the primary mechanism associated with increased bioenergetic dysfunction in response to volume overload. In summary, these studies support the 'mitochondrial paradigm' for the development of disease susceptibility, and show that the mtDNA modulates cellular bioenergetics, mitochondrial ROS generation and susceptibility to cardiac stress.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

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.

Tumor suppressor APC protein is essential in mucosal repair from colonic inflammation through angiogenesis. Am J Pathol. 2013;182:1263-1274. [PMID: 23395091 DOI: 10.1016/j.ajpath.2012.12.005]

Mucosal repair after acute colonic inflammation is central to maintaining mucosal homeostasis. Failure of mucosal repair often leads to chronic inflammation, sometimes associated with inflammatory bowel disease (IBD). The adenomatous polyposis coli (APC) tumor suppressor gene regulates the Wnt signaling pathway, which is essential for epithelial development, and inactivation of APC facilitates colorectal cancer. Our previous study suggested that APC is involved in pathogenesis of colonic inflammation; however, its role in mucosal repair remains unknown. In this article, we report that colitis induced by dextran sodium sulfate persisted with delayed mucosal repair in Kyoto Apc Delta (KAD) rats lacking the APC C terminus. Defects in the repair process were accompanied by an absence of a fibrin layer covering damaged mucosa and reduced microvessel angiogenesis. APC was up-regulated in vascular endothelial cells (VECs) in inflamed mucosa in KAD and F344 (control) rats. The VECs of KAD rats revealed elevated cell adhesion and low-branched and short-length tube formation. We also found that DLG5, which is associated with IBD pathogenesis, was up-regulated in VECs in inflamed mucosa and interacted with the C terminus of APC. This finding suggests that loss of interaction between the APC C terminus and DLG5 affects VEC morphology and function and leads to persistence of colitis. Therefore, APC is essential for maintenance of intestinal mucosal homeostasis and can consequently contribute to IBD pathogenesis.

Genetic-genomic replication to identify candidate mouse atherosclerosis modifier genes

Objective

Genetics plays a large role in atherosclerosis susceptibility in humans and mice. We attempted to confirm previously determined mouse atherosclerosis‐associated loci and use bioinformatics and transcriptomics to create a catalog of candidate atherosclerosis modifier genes at these loci.

Methods and Results

A strain intercross was performed between AKR and DBA/2 mice on the apoE^−/− background generating 166 F₂ progeny. Using the phenotype log10 of the aortic root lesion area, we identified 3 suggestive atherosclerosis quantitative trait loci (Ath QTLs). When combined with our prior strain intercross, we confirmed 3 significant Ath QTLs on chromosomes 2, 15, and 17, with combined logarithm of odds scores of 5.9, 5.3, and 5.6, respectively, which each met the genome‐wide 5% false discovery rate threshold. We identified all of the protein coding differences between these 2 mouse strains within the Ath QTL intervals. Microarray gene expression profiling was performed on macrophages and endothelial cells from this intercross to identify expression QTLs (eQTLs), the loci that are associated with variation in the expression levels of specific transcripts. Cross tissue eQTLs and macrophage eQTLs that replicated from a prior strain intercross were identified. These bioinformatic and eQTL analyses produced a comprehensive list of candidate genes that may be responsible for the Ath QTLs.

Conclusions

Replication studies for clinical traits as well as gene expression traits are worthwhile in identifying true versus false genetic associations. We have replicated 3 loci on mouse chromosomes 2, 15, and 17 that are associated with atherosclerosis. We have also identified protein coding differences and multiple replicated eQTLs, which may be useful in the identification of atherosclerosis modifier genes.

Ribosomal protein L17, RpL17, is an inhibitor of vascular smooth muscle growth and carotid intima formation

BACKGROUND

Carotid intima-media thickening is associated with increased cardiovascular risk in humans. We discovered that intima formation and cell proliferation in response to carotid injury is greater in SJL/J (SJL) in comparison with C3HeB/FeJ (C3H/F) mice. The purpose of this study was to identify candidate genes contributing to intima formation.

METHODS AND RESULTS

We performed microarray and bioinformatic analyses of carotid arteries from C3H/F and SJL mice. Kyoto Encyclopedia of Genes and Genomes analysis showed that the ribosome pathway was significantly up-regulated in C3H/F in comparison with SJL mice. Expression of a ribosomal protein, RpL17, was >40-fold higher in C3H/F carotids in comparison with SJL. Aortic vascular smooth muscle cells from C3H/F grew slower in comparison to SJL. To determine the role of RpL17 in vascular smooth muscle cell growth regulation, we analyzed the relationship between RpL17 expression and cell cycle progression. Cultured vascular smooth muscle cells from mice, rats, and humans showed that RpL17 expression inversely correlated with growth as shown by decreased cells in S phase and increased cells in G(0)/G(1). To prove that RpL17 acted as a growth inhibitor in vivo, we used pluronic gel delivery of RpL17 small interfering RNA to C3H/F carotid arteries. This resulted in an 8-fold increase in the number of proliferating cells. Furthermore, following partial carotid ligation in SJL mice, RpL17 expression in the intima and media decreased, but the number of proliferating cells increased.

CONCLUSIONS

RpL17 acts as a vascular smooth muscle cell growth inhibitor (akin to a tumor suppressor) and represents a potential therapeutic target to limit carotid intima-media thickening.

Genetic susceptibility to atherosclerosis

Atherosclerosis is a complex multifocal arterial disease involving interactions of multiple genetic and environmental factors. Advances in techniques of molecular genetics have revealed that genetic ground significantly influences susceptibility to atherosclerotic vascular diseases. Besides further investigations of monogenetic diseases, candidate genes, genetic polymorphisms, and susceptibility loci associated with atherosclerotic diseases have been identified in recent years, and their number is rapidly increasing. This paper discusses main genetic investigations fields associated with human atherosclerotic vascular diseases. The paper concludes with a discussion of the directions and implications of future genetic research in arteriosclerosis with an emphasis on prospective prediction from an early age of individuals who are predisposed to develop premature atherosclerosis as well as to facilitate the discovery of novel drug targets.

Animal models of atherosclerosis

Atherosclerosis is a chronic inflammatory disorder that is the underlying cause of most cardiovascular disease. Both cells of the vessel wall and cells of the immune system participate in atherogenesis. This process is heavily influenced by plasma lipoproteins, genetics, and the hemodynamics of the blood flow in the artery. A variety of small and large animal models have been used to study the atherogenic process. No model is ideal as each has its own advantages and limitations with respect to manipulation of the atherogenic process and modeling human atherosclerosis or lipoprotein profile. Useful large animal models include pigs, rabbits, and nonhuman primates. Due in large part to the relative ease of genetic manipulation and the relatively short time frame for the development of atherosclerosis, murine models are currently the most extensively used. Although not all aspects of murine atherosclerosis are identical to humans, studies using murine models have suggested potential biological processes and interactions that underlie this process. As it becomes clear that different factors may influence different stages of lesion development, the use of mouse models with the ability to turn on or delete proteins or cells in tissue specific and temporal manner will be very valuable.

Genome scans for transmission ratio distortion regions in mice

Transmission ratio distortion (TRD) is the departure from the expected genotypic frequencies under Mendelian inheritance. This departure can be due to multiple physiological mechanisms during gametogenesis, fertilization, fetal and embryonic development, and early neonatal life. Although a few TRD loci have been reported in mouse, inheritance patterns have never been evaluated for TRD. In this article, we developed a Bayesian binomial model accounting for additive and dominant deviation TRD mechanisms. Moreover, this model was used to perform genome-wide scans for TRD quantitative trait loci (QTL) on six F2 mouse crosses involving between 296 and 541 mice and between 72 and 1854 genetic markers. Statistical significance of each model was checked at each genetic marker with Bayes factors. Genome scans revealed overdominance TRD QTL located in mouse chromosomes 1, 2, 12, 13, and 14 and additive TRD QTL in mouse chromosomes 2, 3, and 15, although these results did not replicate across mouse crosses. This research contributes new statistical tools for the analysis of specific genetic patterns involved in TRD in F2 populations, our results suggesting a relevant incidence of TRD phenomena in mouse with important implications for both statistical analyses and biological research.

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.

Animal models of calcific aortic valve disease

Calcific aortic valve disease (CAVD), once thought to be a degenerative disease, is now recognized to be an active pathobiological process, with chronic inflammation emerging as a predominant, and possibly driving, factor. However, many details of the pathobiological mechanisms of CAVD remain to be described, and new approaches to treat CAVD need to be identified. Animal models are emerging as vital tools to this end, facilitated by the advent of new models and improved understanding of the utility of existing models. In this paper, we summarize and critically appraise current small and large animal models of CAVD, discuss the utility of animal models for priority CAVD research areas, and provide recommendations for future animal model studies of CAVD.

Characterization of Ath29, a major mouse atherosclerosis susceptibility locus, and identification of Rcn2 as a novel regulator of cytokine expression

Ath29 is an atherosclerosis susceptibility locus on chromosome 9 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 intercrosses that developed early or advanced atherosclerotic lesions. The objective of this study was to characterize Ath29 through construction and analysis of a congenic strain and identify underlying candidate genes. A congenic line was constructed by introgressing the chromosomal segment harboring Ath29 from C3H.apoE(-/-) into B6.apoE(-/-) mice. Congenic mice developed significantly smaller early and advance atherosclerotic lesions than B6.apoE(-/-) mice. Microarray analysis revealed 317 genes to be differentially expressed in the aorta of congenic mice compared with B6.apoE(-/-) mice. Pathway analysis of these genes suggested the Ca(2+) signaling pathway to be implicated in regulating atherosclerosis susceptibility. Rcn2 is located underneath the linkage peak of Ath29 and involved in Ca(2+) signaling. Multiple single-nucleotide polymorphisms between B6 and C3H mice were detected within and surrounding Rcn2 with one single-nucleotide polymorphism falling within an upstream cAMP response element. Immunostaining demonstrated its expression in atherosclerotic lesions. Knockdown of Rcn2 with small interfering RNAs resulted in significant reductions in both baseline and oxidized phospholipid-induced VCAM-1 and monocyte chemoattractant protein-1 expression by endothelial cells. Ath29 is confirmed to be a major atherosclerosis susceptibility locus affecting both early and advanced lesion formation in mice, and Rcn2 is identified as a novel regulator of cytokine expression.

Genetic susceptibility of the arterial wall is an important determinant of atherosclerosis in C57BL/6 and FVB/N mouse strains

OBJECTIVE

How genetic variations among inbred mouse strains translate into differences in atherosclerosis susceptibility is of significant interest for the development of new therapeutic strategies. The objective of the present study was to examine whether genetically controlled arterial wall properties influence atherosclerosis susceptibility in FVB/N (FVB) and C57BL/6 (B6) apolipoprotein E knockout (apoE(-/-)) mouse strains.

METHODS AND RESULTS

Common carotid artery segments from B6 apoE(-/-), F1 apoE(-/-), and FVB apoE(-/-) mice were transplanted to hybrid F1 apoE(-/-) mice, which can accept grafts from both parental strains without adaptive immune responses. The mice were fed a high-fat diet, and atherosclerosis was induced in the transplanted artery segments by placement of a perivascular constrictive collar. Artery segments from B6 apoE(-/-) mice developed much larger atherosclerotic lesions than artery segments from FVB or F1 apoE(-/-) mice. No differences in aortic arch atherosclerosis of the recipient mice were observed between groups.

CONCLUSIONS

Genetically controlled factors acting at the level of the arterial wall are important determinants of atherosclerosis susceptibility in FVB apoE(-/-) and B6 apoE(-/-) mice.

Innate immunity and monocyte-macrophage activation in atherosclerosis

Innate inflammation is a hallmark of both experimental and human atherosclerosis. The predominant innate immune cell in the atherosclerotic plaque is the monocyte-macrophage. The behaviour of this cell type within the plaque is heterogeneous and depends on the recruitment of diverse monocyte subsets. Furthermore, the plaque microenvironment offers polarisation and activation signals which impact on phenotype. Microenvironmental signals are sensed through pattern recognition receptors, including toll-like and NOD-like receptors - the latter of which are components of the inflammasome - thus dictating macrophage behaviour and outcome in atherosclerosis. Recently cholesterol crystals and modified lipoproteins have been recognised as able to directly engage these pattern recognition receptors. The convergent role of such pathways in terms of macrophage activation is discussed in this review.

Comparative phenotypic assessment of cardiac pathology, physiology, and gene expression in C3H/HeJ, C57BL/6J, and B6C3F1/J mice

Human cardiomyopathies often lead to heart failure, a major cause of morbidity and mortality in industrialized nations. Described here is a phenotypic characterization of cardiac function and genome-wide expression from C3H/HeJ, C57BL/6J, and B6C3F1/J male mice. Histopathologic analysis identified a low-grade background cardiomyopathy (murine progressive cardiomyopathy) in eight of nine male C3H/HeJ mice (age nine to ten weeks), but not in male C57BL/6J and in only of ten male B6C3F1/J mice. The C3H/HeJ mouse had an increased heart rate and a shorter RR interval compared to the B6C3F1/J and C57BL/6J mice. Cardiac genomic studies indicated the B6C3F1/J mice exhibited an intermediate gene expression phenotype relative to the 2 parental strains. Disease-centric enrichment analysis indicated a number of cardiomyopathy-associated genes were induced in B6C3F1/J and C3H/HeJ mice, including Myh7, My14, and Lmna and also indicated differential expression of genes associated with metabolic (e.g., Pdk2) and hypoxic stress (e.g. Hif1a). A novel coexpression and integrated pathway network analysis indicated Prkaa2, Pdk2, Rhoj, and Sgcb are likely to play a central role in the pathophysiology of murine progressive cardiomyopathy in C3H/HeJ mice. Our studies indicate that genetically determined baseline differences in cardiac phenotype have the potential to influence the results of cardiotoxicity studies.

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.

The expression and functions of toll-like receptors in atherosclerosis. Mediators Inflamm. 2010;2010:393946. [PMID: 20652007 PMCID: PMC2905957 DOI: 10.1155/2010/393946]

Inflammation drives atherosclerosis. Both immune and resident vascular cell types are involved in the development of atherosclerotic lesions. The phenotype and function of these cells are key in determining the development of lesions. Toll-like receptors are the most characterised innate immune receptors and are responsible for the recognition of exogenous conserved motifs on pathogens, and, potentially, some endogenous molecules. Both endogenous and exogenous TLR agonists may be present in atherosclerotic plaques. Engagement of toll-like receptors on immune and resident vascular cells can affect atherogenesis as signalling downstream of these receptors can elicit proinflammatory cytokine release, lipid uptake, and foam cell formation and activate cells of the adaptive immune system. In this paper, we will describe the expression of TLRs on immune and resident vascular cells, highlight the TLR ligands that may act through TLRs on these cells, and discuss the consequences of TLR activation in atherosclerosis.

Increased oxidative stress in atherosclerosis-predisposed regions of the mouse aorta

AIMS

The localization of atherosclerotic lesions to predictable regions in mammalian arteries has been recognized for over a century. We sought to investigate the association between oxidative stress and regional susceptibility of the mouse aorta to atherosclerosis.

MAIN METHODS

En face confocal microscopy was employed to assess oxidative stress in the aortic intima of atherosclerosis-susceptible and protected regions of wild-type C57BL/6 mouse. Expression of reactive oxygen species and antioxidant producing genes were compared in endothelial cells from the susceptible and protected regions.

KEY FINDINGS

In vivo administration of redox-sensitive fluorescent dyes revealed an increase in the production of reactive oxygen species (ROS) in the atherosclerosis-susceptible regions relative to the protected regions. In contrast, Hoechst a redox-insensitive dye distributed evenly in the susceptible and protected regions. Accumulation of superoxide in the susceptible regions of the aorta was significantly blocked by the administration of Diphenyleneiodonium, a flavoprotein inhibitor. mRNA levels of superoxide-producing and scavenging enzymes were significantly increased in the regions predisposed to atherosclerosis. The regional difference in oxidative stress was at a lesser magnitude in BALB/c than the atherosclerosis-susceptible mouse (C57BL/6).

SIGNIFICANCE

Our study for the first time demonstrated an augmented oxidative stress in atherosclerosis-susceptible regions of the normal mouse aorta.

Sex as a profound modifier of atherosclerotic lesion development in apolipoprotein E-deficient mice with different genetic backgrounds

AIM

Research suggests that sex may condition atherosclerosis development against different genetic backgrounds. This study addresses the hypothesis that this effect would be exerted by changes in the different apolipoproteins present in high-density lipoproteins.

METHODS

ApoE-deficient mice of both sexes with Ola 129 and C57BL/6J genetic backgrounds were fed a chow diet for 14 weeks. At the end of the dietary intervention, the development of atherosclerotic lesions, apolipoproteins, lipid metabolism, inflammation and paraoxonase were assessed.

RESULTS

Differences between atherosclerotic lesions in Ola 129 and C57BL/6J strains of apoE-deficient mice were sex-dependent and were only statistically significant in females. Plasma levels of HDL cholesterol and apolipoproteins related to these lipoparticles, such as apoA-I, apoA-II, apoA-IV, apoA-V and apoJ, were significantly different between these two strains and there were sex-related differences in some of these apolipoproteins. Hepatic steatosis was also related to the strain and was independent of sex. In females, changes in HDL cholesterol and apolipoproteins A-I and A-II were important determinants of atherosclerosis, while this was not the case in males.

CONCLUSIONS

Our results demonstrate that atherosclerosis-related differences between Ola129 and C57BL/6J genetic backgrounds in apoE-deficient mice are sex-dependent and that this finding is explained by the differences in HDL cholesterol and its apolipoprotein components, mainly apoA-I and A-II. Overall, our findings highlight the importance of taking sex into account in the analysis of atherosclerosis and lipid metabolism in animal models.

Quantitative trait locus analysis of neointimal formation in an intercross between C57BL/6 and C3H/HeJ apolipoprotein E-deficient mice

BACKGROUND

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

METHODS AND RESULTS

Female B6.apoE(-/-) mice were crossed with male C3H.apoE(-/-) mice to generate F(1)s, which were intercrossed to generate 204 male F(2) progeny. At 10 weeks of age, F(2)s underwent endothelium denudation injury to the left common carotid artery. Mice were fed a Western diet for 1 week before and 4 weeks after injury and analyzed for neointimal lesion size, plasma lipid and MCP-1 levels. One significant QTL, named Nih1 (61cM, LOD score: 5.02), on chromosome 12 and a suggestive locus on chromosome 13 (35cM, LOD: 2.67) were identified to influence lesion size. One significant QTL on distal chromosome 1 accounted for major variations in plasma non-HDL cholesterol and triglyceride levels. Four suggestive QTLs on chromosomes 1, 2, and 3 were detected for circulating MCP-1 levels. No correlations were observed between neointimal lesion size and plasma lipid levels or between lesion size and plasma MCP-1 levels.

CONCLUSIONS

Neointimal formation is controlled by genetic factors independent of those affecting plasma lipid levels and circulating MCP-1 levels in the B6 and C3H mouse model.

The adenomatous polyposis coli-associated guanine nucleotide exchange factor Asef is involved in angiogenesis

Mutation of the tumor suppressor adenomatous polyposis coli (APC) is a key early event in the development of most colorectal tumors. APC promotes degradation of beta-catenin and thereby negatively regulates Wnt signaling, whereas mutated APCs present in colorectal tumor cells are defective in this activity. APC also stimulates the activity of the guanine nucleotide exchange factor Asef and regulates cell morphology and migration. Truncated mutant APCs constitutively activate Asef and induce aberrant migration of colorectal tumor cells. Furthermore, we have recently found that Asef and APC function downstream of hepatocyte growth factor and phosphatidylinositol 3-kinase. We show here that Asef is required for basic fibroblast growth factor- and vascular endothelial growth factor-induced endothelial cell migration. We further demonstrate that Asef is required for basic fibroblast growth factor- and vascular endothelial growth factor-induced microvessel formation. Furthermore, we show that the growth as well as vascularity of subcutaneously implanted tumors are markedly impaired in Asef(-/-) mice compared with wild-type mice. Thus, Asef plays a critical role in tumor angiogenesis and may be a promising target for cancer chemotherapy.

Microarray analysis of gene expression in mouse aorta reveals role of the calcium signaling pathway in control of atherosclerosis susceptibility

Inbred mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) exhibit a marked difference in atherosclerotic lesion formation when deficient in apolipoprotein E (apoE(-/-)), and the arterial wall has been identified as a source of the difference in atherosclerosis susceptibility. In the present study, differences in gene expression in aortic walls of the two strains were analyzed by microarrays. Total RNA was extracted from the aorta of 6-wk-old female B6 and C3H apoE(-/-) mice fed a chow or Western diet. There were 1,514 genes in chow fed mice and 590 genes in Western fed mice that were found to be differentially expressed between the two strains. Pathway analysis of differentially expressed genes suggested a role for the calcium signaling pathway in regulating atherosclerosis susceptibility. Oxidized LDL (oxLDL) induced a dose-dependent rise in cytosolic calcium levels in B6 endothelial cells. oxLDL-induced monocyte chemoattractant protein-1 production was inhibited by pretreatment with calcium chelator EGTA or intracellular calcium trapping compound BAPTA, indicating that calcium ions mediate the effect of oxLDL on monocyte chemoattractant protein-1 induction. The present findings demonstrate involvement of the calcium signaling pathway in the inflammatory process of atherogenesis.