Atherosclerosis quantitative trait loci are sex- and lineage-dependent in an intercross of C57BL/6 and FVB/N low-density lipoprotein receptor-/- mice

Metyrapone Treatment Protects Low-Density Lipoprotein Receptor Knockout Mice against Hypercorticosteronemia Development without Changing Atherosclerosis Susceptibility

The steroid 11beta-hydroxylase inhibitor metyrapone is able to effectively reverse the hypercortisolemia detected in human Cushing's Syndrome patients. In this current preclinical study, we investigated whether metyrapone monotherapy can also reverse the hypercortisolemia-associated increase in atherosclerotic cardiovascular disease risk. In this instance, female low-density lipoprotein receptor knockout mice fed a cholic acid-containing high cholesterol/high fat diet to induce the development of hypercorticosteronemia and atherosclerotic lesions were treated twice daily with 100 mg/kg metyrapone for 4 weeks. Metyrapone effectively protected against hypercorticosteronemia development with endpoint plasma corticosterone levels remaining 43% lower than in controls (p < 0.01). Gene expression analysis in livers and adrenals validated that glucocorticoid receptor signaling was also reduced. Importantly, metyrapone treatment did not impact plasma cholesterol levels or alter atherosclerotic plaque areas or lesional collagen contents. However, metyrapone induced significant systemic lymphocytopenia as evident from marked decreases in splenic white pulp contents and thymus weights (-48% and -41%, respectively; p < 0.001). In conclusion, we have shown that treatment with metyrapone diminishes hypercorticosteronemia without affecting atherosclerosis susceptibility in cholic acid-containing high cholesterol/high fat diet-fed low-density lipoprotein receptor knockout mice. These preclinical findings highlight that restoring plasma glucocorticoid levels to normal is not necessarily sufficient to overcome the cardiovascular co-morbidities associated with human Cushing's disease.

Integrative analysis of hepatic transcriptional profiles reveals genetic regulation of atherosclerosis in hyperlipidemic Diversity Outbred-F1 mice

Atherogenesis is an insipidus but precipitating process leading to serious consequences of many cardiovascular diseases (CVD). Numerous genetic loci contributing to atherosclerosis have been identified in human genome-wide association studies, but these studies have limitations in the ability to control environmental factors and to decipher cause/effect relationships. To assess the power of hyperlipidemic Diversity Outbred (DO) mice in facilitating quantitative trait loci (QTL) analysis of complex traits, we generated a high-resolution genetic panel of atherosclerosis susceptible (DO-F1) mouse cohort by crossing 200 DO females with C57BL/6J males carrying two human genes: encoding apolipoprotein E3-Leiden and cholesterol ester transfer protein. We examined atherosclerotic traits including plasma lipids and glucose in the 235 female and 226 male progeny before and after 16 weeks of a high-fat/cholesterol diet, and aortic plaque size at 24 weeks. We also assessed the liver transcriptome using RNA-sequencing. Our QTL mapping for atherosclerotic traits identified one previously reported female-specific QTL on Chr10 with a narrower interval of 22.73 to 30.80 Mb, and one novel male-specific QTL at 31.89 to 40.25 Mb on Chr19. Liver transcription levels of several genes within each QTL were highly correlated with the atherogenic traits. A majority of these candidates have already known atherogenic potential in humans and/or mice, but integrative QTL, eQTL, and correlation analyses further pointed Ptprk as a major candidate of the Chr10 QTL, while Pten and Cyp2c67 of the Chr19 QTL in our DO-F1 cohort. Finally, through additional analyses of RNA-seq data we identified genetic regulation of hepatic transcription factors, including Nr1h3, contributes to atherogenesis in this cohort. Thus, an integrative approach using DO-F1 mice effectively validates the influence of genetic factors on atherosclerosis in DO mice and suggests an opportunity to discover therapeutics in the setting of hyperlipidemia.

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.

The zebrafish model system for dyslipidemia and atherosclerosis research: Focus on environmental/exposome factors and genetic mechanisms

Dyslipidemias and atherosclerosis play a pivotal role in cardiovascular risk and disease. Although some pathophysiological mechanisms underlying these conditions have been unveiled, several knowledge gaps still remain. Experimental models, both in vitro and in vivo, have been instrumental to our better understanding of such complex processes. The latter have often been based on rodent species, either wild-type or, in several instances, genetically modified. In this context, the zebrafish may represent an additional very useful in vivo experimental model for dyslipidemia and atherosclerosis. Interestingly, the lipid metabolism of zebrafish shares several features with that present in humans, recapitulating some molecular features and pathophysiological aspects in a better way than that of rodents. The zebrafish model may be of help to address questions related to exposome factors as well as to genetic features, aiming to dissect selected aspects of the more complex scenario observed in humans. Indeed, exposome-related dyslipidemia/atherosclerosis research in zebrafish may target different scientific questions, related to nutrition, microbiota, temperature, light exposure at the larval stage, exposure to chemicals and epigenetic consequences of such external factors. Addressing genetic features related to dyslipidemia/atherosclerosis using the zebrafish model is already a reality and active research is now ongoing in this promising area. Novel technologies (gene and genome editing) may help to identify new candidate genes involved in dyslipidemia and dyslipidemia-related diseases. Based on these considerations, the zebrafish experimental model appears highly suitable for the study of exposome factors, genes and molecules involved in the development of atherosclerosis-related disease as well as for the validation of novel potential treatment options.

Quantitative trait locus mapping in mice identifies phospholipase Pla2g12a as novel atherosclerosis modifier

BACKGROUND AND AIMS

In a previous work, a female-specific atherosclerosis risk locus on chromosome (Chr) 3 was identified in an intercross of atherosclerosis-resistant FVB and atherosclerosis-susceptible C57BL/6 (B6) mice on the LDL-receptor deficient (Ldlr^-/-) background. It was the aim of the current study to identify causative genes at this locus.

METHODS

We established a congenic mouse model, where FVB.Chr3^B6/B6 mice carried an 80 Mb interval of distal Chr3 on an otherwise FVB.Ldlr^-/- background, to validate the Chr3 locus. Candidate genes were identified using genome-wide expression analyses. Differentially expressed genes were validated using quantitative PCRs in F0 and F2 mice and their functions were investigated in pathophysiologically relevant cells.

RESULTS

Fine-mapping of the Chr3 locus revealed two overlapping, yet independent subloci for female atherosclerosis susceptibility: when transmitted by grandfathers to granddaughters, the B6 risk allele increased atherosclerosis and downregulated the expression of the secreted phospholipase Pla2g12a (2.6 and 2.2 fold, respectively); when inherited by grandmothers, the B6 risk allele induced vascular cell adhesion molecule 1 (Vcam1). Down-regulation of Pla2g12a and up-regulation of Vcam1 were validated in female FVB.Chr3^B6/B6 congenic mice, which developed 2.5 greater atherosclerotic lesions compared to littermate controls (p=0.039). Pla2g12a was highly expressed in aortic endothelial cells in vivo, and knocking-down Pla2g12a expression by RNAi in cultured vascular endothelial cells or macrophages increased their adhesion to ECs in vitro.

CONCLUSIONS

Our data establish Pla2g12a as an atheroprotective candidate gene in mice, where high expression levels in ECs and macrophages may limit the recruitment and accumulation of these cells in nascent atherosclerotic lesions.

Genetic architecture of atherosclerosis dissected by QTL analyses in three F2 intercrosses of apolipoprotein E-null mice on C57BL6/J, DBA/2J and 129S6/SvEvTac backgrounds

Quantitative trait locus (QTL) analyses of intercross populations between widely used mouse inbred strains provide a powerful approach for uncovering genetic factors that influence susceptibility to atherosclerosis. Epistatic interactions are common in complex phenotypes and depend on genetic backgrounds. To dissect genetic architecture of atherosclerosis, we analyzed F2 progeny from a cross between apolipoprotein E-null mice on DBA/2J (DBA-apoE) and C57BL/6J (B6-apoE) genetic backgrounds and compared the results with those from two previous F2 crosses of apolipoprotein E-null mice on 129S6/SvEvTac (129-apoE) and DBA-apoE backgrounds, and B6-apoE and 129-apoE backgrounds. In these round-robin crosses, in which each parental strain was crossed with two others, large-effect QTLs are expected to be detectable at least in two crosses. On the other hand, observation of QTLs in one cross only may indicate epistasis and/or absence of statistical power. For atherosclerosis at the aortic arch, Aath4 on chromosome (Chr)2:66 cM follows the first pattern, with significant QTL peaks in (DBAx129)F2 and (B6xDBA)F2 mice but not in (B6x129)F2 mice. We conclude that genetic variants unique to DBA/2J at Aath4 confer susceptibility to atherosclerosis at the aortic arch. A similar pattern was observed for Aath5 on chr10:35 cM, verifying that the variants unique to DBA/2J at this locus protect against arch plaque development. However, multiple loci, including Aath1 (Chr1:49 cM), and Aath2 (Chr1:70 cM) follow the second type of pattern, showing significant peaks in only one of the three crosses (B6-apoE x 129-apoE). As for atherosclerosis at aortic root, the majority of QTLs, including Ath29 (Chr9:33 cM), Ath44 (Chr1:68 cM) and Ath45 (Chr2:83 cM), was also inconsistent, being significant in only one of the three crosses. Only the QTL on Chr7:37 cM was consistently suggestive in two of the three crosses. Thus QTL analysis of round-robin crosses revealed the genetic architecture of atherosclerosis.

Adam17 Deficiency Promotes Atherosclerosis by Enhanced TNFR2 Signaling in Mice

OBJECTIVE

ADAM17 (a disintegrin and metalloproteinase 17) is a sheddase releasing different types of membrane-bound proteins, including adhesion molecules, cytokines, and their receptors as well as inflammatory mediators. Because these substrates modulate important mechanisms of atherosclerosis, we hypothesized that ADAM17 might be involved in the pathogenesis of this frequent disease.

APPROACH AND RESULTS

Because Adam17-knockout mice are not viable, we studied the effect of Adam17 deficiency on atherosclerosis in Adam17 hypomorphic mice (Adam17^ex/ex), which have low residual Adam17 expression. To induce atherosclerosis, mice were crossed onto the low-density lipoprotein receptor (Ldlr)-deficient background. We found that Adam17^ex/ex.Ldlr^-/- mice developed ≈1.5-fold larger atherosclerotic lesions, which contained more macrophages and vascular smooth muscle cells than wild-type littermate controls (Adam17^wt/wt.Ldlr^-/-). Reduced Adam17-mediated shedding led to significantly increased protein levels of membrane-resident TNFα (tumor necrosis factor) and TNFR2 (tumor necrosis factor receptor 2), resulting in a constitutive activation of TNFR2 signaling. At the same time, Adam17 deficiency promoted proatherosclerotic cellular functions, such as increased proliferation and reduced apoptosis in cultured macrophages and vascular smooth muscle cells and increased adhesion of macrophages to vascular endothelial cells. Because siRNA (small interfering RNA)-mediated knockdown of Tnfr2 rescued from aberrant proliferation and from misregulation of apoptosis in Adam17-depleted cells, our data indicate that TNFR2 is an important effector of ADAM17 in our mouse model.

CONCLUSIONS

Our results provide evidence for an atheroprotective role of ADAM17, which might be mediated by cleaving membrane-bound TNFα and TNFR2, thereby preventing overactivation of endogenous TNFR2 signaling in cells of the vasculature.

Genetic analysis of ligation-induced neointima formation in an F2 intercross of C57BL/6 and FVB/N inbred mouse strains

Objective

Proliferation and migration of vascular smooth muscle cells (SMCs) are central for arterial diseases including atherosclerosis and restenosis. We hypothesized that the underlying mechanisms may be modeled by carotid ligation in mice. In FVB/N inbred mice, ligation leads to abundant neointima formation with proliferating media-derived SMCs, whereas in C57BL/6 mice hardly any neointima is formed. In the present study, we aimed to identify the chromosomal location of the causative gene variants in an F2 intercross between these two mouse strains.

Methods and Results

The neointimal cross-sectional area was significantly different between FVB/N, C57BL/6 and F1 female mice 4 weeks after ligation. Carotid artery ligation and a genome scan using 800 informative SNP markers were then performed in 157 female F2 mice. Using quantitative trait loci (QTL) analysis, we identified suggestive, but no genome-wide significant, QTLs on chromosomes 7 and 12 for neointimal cross-sectional area and on chromosome 14 for media area. Further analysis of the cross revealed 4 QTLs for plasma cholesterol, which combined explained 69% of the variation among F2 mice.

Conclusions

We identified suggestive QTLs for neointima and media area after carotid ligation in an intercross of FVB/N and C57BL/6 mice, but none that reached genome-wide significance indicating a complex genetic architecture of the traits. Genome-wide significant QTLs for total cholesterol levels were identified on chromosomes 1, 3, 9, and 12.

Genetic determinants of atherosclerosis, obesity, and energy balance in consomic mice

Metabolic diseases such as obesity and atherosclerosis result from complex interactions between environmental factors and genetic variants. A panel of chromosome substitution strains (CSSs) was developed to characterize genetic and dietary factors contributing to metabolic diseases and other biological traits and biomedical conditions. Our goal here was to identify quantitative trait loci (QTLs) contributing to obesity, energy expenditure, and atherosclerosis. Parental strains C57BL/6 and A/J together with a panel of 21 CSSs derived from these progenitors were subjected to chronic feeding of rodent chow and atherosclerotic (females) or diabetogenic (males) test diets, and evaluated for a variety of metabolic phenotypes including several traits unique to this report, namely fat pad weights, energy balance, and atherosclerosis. A total of 297 QTLs across 35 traits were discovered, two of which provided significant protection from atherosclerosis, and several dozen QTLs modulated body weight, body composition, and circulating lipid levels in females and males. While several QTLs confirmed previous reports, most QTLs were novel. Finally, we applied the CSS quantitative genetic approach to energy balance, and identified three novel QTLs controlling energy expenditure and one QTL modulating food intake. Overall, we identified many new QTLs and phenotyped several novel traits in this mouse model of diet-induced metabolic diseases.

Quantitative trait loci affecting atherosclerosis at the aortic root identified in an intercross between DBA2J and 129S6 apolipoprotein E-null mice

Apolipoprotein E-null mice on a DBA/2J genetic background (DBA-apoE) are highly susceptible to atherosclerosis in the aortic root area compared with those on a 129S6 background (129-apoE). To explore atherosclerosis-responsible genetic regions, we performed a quantitative trait locus (QTL) analysis using 172 male and 137 female F2 derived from an intercross between DBA-apoE and 129-apoE mice. A genome-wide scan identified two significant QTL for the size of lesions at the root: one is Ath44 on Chromosome (Chr) 1 at 158 Mb, and the other Ath45 on Chr 2 at 162 Mb. Ath44 co-localizes with but appears to be independent of a previously reported QTL, Ath1, while Ath45 is a novel QTL. DBA alleles of both Ath44 and Ath45 confer atherosclerosis-susceptibility. In addition, a QTL on Chr 14 at 73 Mb was found significant only in males, and 129 allele conferring susceptibility. Further analysis detected female-specific interactions between a second QTL on Chr 1 at 73 Mb and a QTL on Chr 3 at 21 Mb, and between Chr 7 at 84 Mb and Chr 12 at 77 Mb. These loci for the root atherosclerosis were independent of QTLs for plasma total cholesterol and QTLs for triglycerides, but a QTL for HDL (Chr 1 at 126 Mb) overlapped with the Ath44. Notably, haplotype analysis among 129S6, DBA/2J and C57BL/6 genomes and their gene expression data narrowed the candidate regions for Ath44 and Ath45 to less than 5 Mb intervals where multiple genome wide associations with cardiovascular phenotypes have also been reported in humans. SNPs in or near Fmo3, Sele and Selp for Ath44, and Lbp and Pkig for Ath45 were suggested for further investigation as potential candidates underlying the atherosclerosis susceptibility.

Altered expression of Raet1e, a major histocompatibility complex class 1-like molecule, underlies the atherosclerosis modifier locus Ath11 10b

RATIONALE

Quantitative trait locus mapping of an intercross between C57.Apoe⁻/⁻ and FVB.Apoe⁻/⁻ mice revealed an atherosclerosis locus controlling aortic root lesion area on proximal chromosome 10, Ath11. In a previous work, subcongenic analysis showed Ath11 to be complex with proximal (10a) and distal (10b) regions.

OBJECTIVE

To identify the causative genetic variation underlying the atherosclerosis modifier locus Ath11 10b.

METHODS AND RESULTS

We now report subcongenic J, which narrows the 10b region to 5 genes, Myb, Hbs1L, Aldh8a1, Sgk1, and Raet1e. Sequence analysis of these genes revealed no amino acid coding differences between the parental strains. However, comparing aortic expression of these genes between F1.Apoe⁻/⁻ Chr10SubJ((B/F)) and F1.Apoe⁻/⁻ Chr10SubJ((F/F)) uncovered a consistent difference only for Raet1e, with decreased, virtually background, expression associated with increased atherosclerosis in the latter. The key role of Raet1e was confirmed by showing that transgene-induced aortic overexpression of Raet1e in F1.Apoe⁻/⁻ Chr10SubJ((F/F)) mice decreased atherosclerosis. Promoter reporter constructs comparing C57 and FVB sequences identified an FVB mutation in the core of the major aortic transcription start site abrogating activity.

CONCLUSIONS

This nonbiased approach has revealed Raet1e, a major histocompatibility complex class 1-like molecule expressed in lesional aortic endothelial cells and macrophage-rich regions, as a novel atherosclerosis gene and represents one of the few successes of the quantitative trait locus strategy in complex diseases.

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.

Quantitative trait loci mapping of the mouse plasma proteome (pQTL)

A current challenge in the era of genome-wide studies is to determine the responsible genes and mechanisms underlying newly identified loci. Screening of the plasma proteome by high-throughput mass spectrometry (MALDI-TOF MS) is considered a promising approach for identification of metabolic and disease processes. Therefore, plasma proteome screening might be particularly useful for identifying responsible genes when combined with analysis of variation in the genome. Here, we describe a proteomic quantitative trait locus (pQTL) study of plasma proteome screens in an F(2) intercross of 455 mice mapped with 177 genetic markers across the genome. A total of 69 of 176 peptides revealed significant LOD scores (≥5.35) demonstrating strong genetic regulation of distinct components of the plasma proteome. Analyses were confirmed by mechanistic studies and MALDI-TOF/TOF, liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses of the two strongest pQTLs: A pQTL for mass-to-charge ratio (m/z) 3494 (LOD 24.9, D11Mit151) was identified as the N-terminal 35 amino acids of hemoglobin subunit A (Hba) and caused by genetic variation in Hba. Another pQTL for m/z 8713 (LOD 36.4; D1Mit111) was caused by variation in apolipoprotein A2 (Apoa2) and cosegregated with HDL cholesterol. Taken together, we show that genome-wide plasma proteome profiling in combination with genome-wide genetic screening aids in the identification of causal genetic variants affecting abundance of plasma proteins.

Sequencing and characterization of the FVB/NJ mouse genome

Background

The FVB/NJ mouse strain has its origins in a colony of outbred Swiss mice established in 1935 at the National Institutes of Health. Mice derived from this source were selectively bred for sensitivity to histamine diphosphate and the B strain of Friend leukemia virus. This led to the establishment of the FVB/N inbred strain, which was subsequently imported to the Jackson Laboratory and designated FVB/NJ. The FVB/NJ mouse has several distinct characteristics, such as large pronuclear morphology, vigorous reproductive performance, and consistently large litters that make it highly desirable for transgenic strain production and general purpose use.

Results

Using next-generation sequencing technology, we have sequenced the genome of FVB/NJ to approximately 50-fold coverage, and have generated a comprehensive catalog of single nucleotide polymorphisms, small insertion/deletion polymorphisms, and structural variants, relative to the reference C57BL/6J genome. We have examined a previously identified quantitative trait locus for atherosclerosis susceptibility on chromosome 10 and identify several previously unknown candidate causal variants.

Conclusion

The sequencing of the FVB/NJ genome and generation of this catalog has increased the number of known variant sites in FVB/NJ by a factor of four, and will help accelerate the identification of the precise molecular variants that are responsible for phenotypes observed in this widely used strain.

Differences in health status affect susceptibility and mapping of genetic loci for atherosclerosis (fatty streak) in inbred mice

OBJECTIVE

We observed differences in atherosclerosis susceptibility in mouse inbred strains over the years as the health status of our animal rooms increased. Therefore, we investigated the effect of animal room health status on atherosclerosis susceptibility in different strains. As these data can also be used for genome-wide association mapping, we performed a mapping study and compared our results with previously found quantitative trait loci for atherosclerosis in mouse and humans.

METHODS AND RESULTS

Males and females from 48 inbred strains were housed in 2 animal rooms with different health status and given an atherogenic diet. We compared atherosclerosis susceptibility between animal rooms and between sexes and found that susceptibility is dependent on both health status and sex. Subsequently, the data were used for associations with loci on the mouse genome using 63 222 single nucleotide polymorphism. Three loci in males and 4 loci in females were identified using the data from the low-health status room. No significant associations were identified using the data from the high-health status room.

CONCLUSIONS

Health status influences susceptibility to atherosclerosis and suggests that microbiological pressure plays an important role in the development of atherosclerosis in many strains. As we were only able to map susceptibility loci using the data from the lower health status room, we argue that susceptibility under these conditions is determined by a few key loci, whereas in the higher health status room different mechanisms might play a role in the differences in atherosclerosis susceptibility between strains and we did not have enough power to map the loci that are involved.

High-resolution association mapping of atherosclerosis loci in mice

OBJECTIVE

The purpose of this study was to fine map previously identified quantitative trait loci affecting atherosclerosis in mice using association analysis.

METHODS AND RESULTS

We recently showed that high-resolution association analysis using common inbred strains of mice is feasible if corrected for population structure. To use this approach for atherosclerosis, which requires a sensitizing mutation, we bred human apolipoprotein B-100 transgenic mice with 22 different inbred strains to produce F1 heterozygotes. Mice carrying the dominant transgene were tested for association with high-density single nucleotide polymorphism maps. Here, we focus on high-resolution mapping of the previously described atherosclerosis 30 locus on chromosome 1. Compared with the previous linkage analysis, association improved the resolution of the atherosclerosis 30 locus by more than an order of magnitude. Using expression quantitative trait locus analysis, we identified one of the genes in the region, desmin, as a strong candidate.

CONCLUSIONS

Our high-resolution mapping approach accurately identifies and fine maps known atherosclerosis quantitative trait loci. These results suggest that high-resolution genome-wide association analysis for atherosclerosis is feasible in mice.

Genetics of atherosclerosis

Genome-wide association studies (GWAS) from the past several years have provided the first unbiased evidence of the genes contributing to common cardiovascular disease traits in European and some Asian populations. The results not only confirmed the importance of prior knowledge, such as the central role of lipoproteins, but also revealed that there is still much to learn about the underlying mechanisms of this disease, as most of the associated genes do not appear to be involved in pathways previously connected to atherosclerosis. In this review, I focus on the common forms of the disease and look at both human and animal model studies. I summarize what was known before GWAS, highlight how the field has been changed by GWAS, and discuss future considerations, such as the limitations of GWAS and strategies that may lead to a more complete, mechanistic understanding of atherosclerosis.

Genetic basis of atherosclerosis: insights from mice and humans

Atherosclerosis is a complex and heritable disease involving multiple cell types and the interactions of many different molecular pathways. The genetic and molecular mechanisms of atherosclerosis have, in part, been elucidated by mouse models; at least 100 different genes have been shown to influence atherosclerosis in mice. Importantly, unbiased genome-wide association studies have recently identified a number of novel loci robustly associated with atherosclerotic coronary artery disease. Here, we review the genetic data elucidated from mouse models of atherosclerosis, as well as significant associations for human coronary artery disease. Furthermore, we discuss in greater detail some of these novel human coronary artery disease loci. The combination of mouse and human genetics has the potential to identify and validate novel genes that influence atherosclerosis, some of which may be candidates for new therapeutic approaches.

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.

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.

Cosegregation of aortic root atherosclerosis and intermediate lipid phenotypes on chromosomes 2 and 8 in an intercross of C57BL/6 and BALBc/ByJ low-density lipoprotein receptor-/- mice

OBJECTIVE

We sought to identify novel atherosclerosis-modifying loci and their potential functional links in a genome-wide approach using cosegregation analysis of atherosclerosis and related intermediate phenotypes in mice.

METHODS AND RESULTS

We carried out an F2 intercross between atherosclerosis-susceptible C57BL/6 mice and atherosclerosis-resistant BALB/cByJ mice on the low-density lipoprotein receptor(-/-) background to examine the genetic basis for their differences in atherosclerosis susceptibility. Atherosclerotic lesion size and a comprehensive panel of 61 atherosclerosis-related phenotypes, including plasma levels of lipids, cytokines, and chemokines were measured in 376 F2 mice. Quantitative trait locus mapping revealed a novel significant locus (logarithm of odds, 6.18) for atherosclerosis on proximal mouse chromosome (Chr) 2 (Ath39), which was associated with major variations in lesion size (14%). Plasma very-low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol, lanosterol, and phytosterol levels cosegregated with atherosclerosis at this locus. Moreover, these lipid traits showed significant correlations with lesion size, suggesting that they share the same underlying genetic factor. We also describe a second male-specific locus on Chr 8 (Ath40) where atherosclerosis and lipids cosegregated.

CONCLUSIONS

Our study revealed new loci for atherosclerosis susceptibility on mouse Chr 2 and 8, which might exert their effects on lesion size via plasma lipid levels.

Features of the metabolic syndrome in the Berlin Fat Mouse as a model for human obesity

BACKGROUND

The Berlin Fat Mouse BFMI860 is a polygenic obesity mouse model which harbors a natural major gene defect resulting in early onset of obesity. To elucidate adult bodily responses in BFMI860 mice that develop juvenile obesity, we studied features of the metabolic syndrome at 20 weeks.

METHODS

We examined fat deposition patterns, adipokines, lipid profiles in serum, glucose homeostasis, and insulin sensitivity in mice that were fed either a standard maintenance (SMD) or a high-fat diet (HFD).

RESULTS

Like many obese humans, BFMI860 mice showed hyperleptinemia accompanied by hypoadiponectinemia already at SMD that was further unbalanced as a result of HFD. Furthermore, BFMI860 mice had high triglyceride concentrations. However, triglyceride clearance after an oral oil gavage was impaired on SMD but improved on HFD. The oral and intraperitoneal glucose as well as the insulin tolerance tests provided evidence for reduced insulin sensitivity under SMD and insulin resistance on HFD. BFMI860 mice can maintain normal glucose clearance over a wide range of feeding conditions according to an adaptation via increasing the insulin concentrations.

CONCLUSIONS

BFMI860 mice show obesity, dyslipidemia, and insulin resistance as three major components of the metabolic syndrome. As these mice develop the described phenotype as a result of a major gene defect, they are a unique model for the investigation of genetic and pathophysiological mechanisms underlying the observed features of the metabolic syndrome and to search for potential strategies to revert the adverse effects under controlled conditions.

The mouse atherosclerosis locus at chromosome 10 (Ath11) acts early in lesion formation with subcongenic strains delineating 2 narrowed regions

OBJECTIVE

Ath11, an atherosclerosis susceptibility locus on proximal chromosome 10 (0 to 21 cM) revealed in a cross between apolipoprotein E deficient C57BL/6 (B6) and FVB mice, was recently confirmed in congenic mice. The objectives of this study were to assess how Ath11 affects lesion development and morphology, to determine aortic gene expression in congenics, and to narrow the congenic interval.

METHODS AND RESULTS

Assessing lesion area over time in congenic mice showed that homozygosity for the FVB allele increased lesion area at 6 weeks persisting through to 24 weeks of age. Staining of aortic root sections at 16 weeks did not reveal obvious differences between congenics. Aortic expression-array analysis at 6 weeks revealed 97 genes that were >2-fold regulated, including 1 gene in the quantitative trait locus interval, Aldh8a1, and 2 gene clusters regulated by Hnf4alpha and Esr1. Analysis of lesion area in 11 subcongenic strains revealed 2 narrowed regions, 10a (21 genes), acting in females, and 10b (7 genes), acting in both genders.

CONCLUSIONS

Ath11 appears to act early in lesion formation, with significant effects on aortic gene expression. This quantitative trait locus is genetically complex, containing a female-specific region 10a from 0 to 7.3 megabases (21 genes) and a gender-independent region 10b from 20.1 to 21.9 megabases (7 genes).

Aortic arch curvature and atherosclerosis have overlapping quantitative trait loci in a cross between 129S6/SvEvTac and C57BL/6J apolipoprotein E-null mice

RATIONALE

Apolipoprotein E-null mice with a 129S6/SvEvTac strain background (129-apoE) develop atherosclerotic plaques faster in the aortic arch but slower in the aortic root than those with a C57BL/6J background (B6-apoE). The shape of the aortic arch also differs in the 2 strains.

OBJECTIVE

Because circulating plasma factors are the same at both locations, we tested the hypothesis that genetic factors affecting vascular geometry also affect the location and extent of atherosclerotic plaque development.

METHODS AND RESULTS

Tests on the F2 progeny from a cross between 129-apoE-null and B6-apoE-null mice showed that the extent of atherosclerosis in the aortic arch is significantly correlated in males, but not in females, with the shape of arch curvature (r=0.34, P<0.0001) and weakly with the arch diameter (r=0.20, P=0.02). Quantitative trait locus (QTL) analysis identified 2 significant peaks for aortic arch lesion size on chromosome 1 (105 Mb, LOD=5.0, and 163 Mb, LOD=6.8), and a suggestive QTL on chromosome 15 (96 Mb, LOD=4.7). A significant QTL for aortic root lesion size was on chromosome 9 (61 Mb, LOD=6.9), but it was distinct from the QTLs for arch lesion size. Remarkably, the QTLs for susceptibility to atherosclerosis in the arch overlapped with a significant QTL that affects curvature of the arch on chromosome 1 (121 Mb, LOD=5.6) and a suggestive QTL on chromosome 15 (76 Mb, LOD=3.5).

CONCLUSIONS

The overlapping QTLs for curvature of the aortic arch and atherosclerosis support that the ontogeny of the aortic arch formation is a potential risk factor for atherosclerosis.

Novel cerebrovascular pathology in mice fed a high cholesterol diet

Background

Hypercholesterolemia causes atherosclerosis in medium to large sized arteries. Cholesterol is less known for affecting the microvasculature and has not been previously reported to induce microvascular pathology in the central nervous system (CNS).

Results

Mice with a null mutation in the low-density lipoprotein receptor (LDLR) gene as well as C57BL/6J mice fed a high cholesterol diet developed a distinct microvascular pathology in the CNS that differs from cholesterol-induced atherosclerotic disease. Microvessel diameter was increased but microvascular density and length were not consistently affected. Degenerative changes and thickened vascular basement membranes were present ultrastructurally. The observed pathology shares features with the microvascular pathology of Alzheimer's disease (AD), including the presence of string-like vessels. Brain apolipoprotein E levels which have been previously found to be elevated in LDLR-/- mice were also increased in C57BL/6J mice fed a high cholesterol diet.

Conclusion

In addition to its effects as an inducer of atherosclerosis in medium to large sized arteries, hypercholesterolemia also induces a microvascular pathology in the CNS that shares features of the vascular pathology found in AD. These observations suggest that high cholesterol may induce microvascular disease in a range of CNS disorders including AD.

The ubiquitin-editing enzyme A20 (TNFAIP3) is a central regulator of immunopathology

Nuclear factor (NF)-kappaB has an important role in immunity and inappropriate NF-kappaB activity has been linked with many autoimmune and inflammatory diseases. Multiple mechanisms normally ensure the proper termination of NF-kappaB activation. In this context, the intracellular ubiquitin-editing protein A20 (also known as Tumor Necrosis Factor Alpha-Induced Protein 3 or TNFAIP3) is a key player in the negative feedback regulation of NF-kappaB signaling in response to multiple stimuli. Moreover, A20 also regulates tumor necrosis factor (TNF)-induced apoptosis. Recent genetic studies demonstrate a clear association between several mutations in the human A20 locus and immunopathologies such as Crohn's disease, rheumatoid arthritis, systemic lupus erythematosus, psoriasis and type 1 diabetes. These findings further illustrate the importance of A20 in the resolution of inflammation and the prevention of human disease.

Novel strategy using F1-congenic mice for validation of QTLs: studies at the proximal chromosome 10 atherosclerosis susceptibility locus

OBJECTIVE

We have previously identified a quantitative trait locus (QTL) for atherosclerosis susceptibility on proximal chromosome 10 (Chr10) (Ath11) in independent crosses of FVB and C57BL/6 (B6) mice on the apolipoprotein E (ApoE-/-) and LDL receptor (LDLR-/-) deficient backgrounds. The aims of the current study were to (1) test a novel strategy for validating QTLs using interval-specific congenic strains that were heterozygous (F1) across the genome, (2) validate the Chr10 QTL, and (3) to assess whether the phenotype is transferable by bone marrow transplantation.

METHODS AND RESULTS

We generated Chr10 (0 to 21 cM) interval-specific mice on the F1.ApoE-/- background by crossing congenic FVB.ApoE-/-Chr10(B6/FVB) with B6.ApoE-/-, and B6.ApoE-/-Chr10(B6/FVB) with FVB.ApoE-/- mice. Lesion size was significantly larger in the resultant F1.ApoE-/-Chr10(FVB/FVB) mice compared to F1.ApoE-/-Chr10(B6/FVB) and F1.ApoE-/-Chr10(B6/B6) mice, validating the Chr10 QTL. The effect of the congenic interval was more robust on the F1.ApoE-/- than on the FVB.ApoE-/- and B6.ApoE-/- backgrounds. Bone marrow transplantation in congenic mice showed that the effect of the proximal Chr10 interval was not transferable by bone marrow-derived cells.

CONCLUSIONS

A novel strategy of congenic strains on an F1 background proved useful to validate an atherosclerosis susceptibility QTL on mouse proximal Chr10.

PECAM-independent thioglycollate peritonitis is associated with a locus on murine chromosome 2

Background

Previous studies have demonstrated that knockout or inhibition of Platelet/Endothelial Cell Adhesion Molecule (PECAM, CD31) in a number of murine strains results in impaired inflammatory responses, but that no such phenotype is seen in the C57BL/6 (B6) murine background.

Methodology/Principal Findings

We have undertaken a quantitative trait locus (QTL) mapping effort between FVB/n (FVB) and B6 mice deficient for PECAM to identify the gene or genes responsible for this unique feature of B6 mice. We have identified a locus on murine chromosome 2 at approximately 35.8 Mb that is strongly associated (LOD score = 9.0) with inflammatory responses in the absence of PECAM.

Conclusions/Significance

These data potentiate further study of the diapedesis machinery, as well as potential identification of new components of this machinery. As such, this study is an important step to better understanding the processes of inflammation.

Increased ADAM17 mRNA expression and activity is associated with atherosclerosis resistance in LDL-receptor deficient mice

BACKGROUND

We have previously identified an atherosclerosis quantitative trait locus (QTL) on mouse chromosome (Chr) 12 in an F2-intercross of atherosclerosis-resistant FVB and atherosclerosis-susceptible C57BL/6 (B6) mice on the LDL-receptor deficient (LDL-/-) background. The aim of the present study was to identify potentially causative genes at this locus.

METHODS AND RESULTS

Expression QTL (eQTL) analysis of candidate genes in livers of F2-mice revealed that a disintegrin and metalloproteinase 17 (ADAM17) mRNA expression mapped to the physical position of ADAM17 on proximal Chr12 (21.6 Mb, LOD 3.3) and colocalized with the atherosclerosis QTL. The FVB allele was associated with significantly higher ADAM17 mRNA expression (39%) than the B6 allele. Likewise, ADAM17 mRNA levels in the parental strains were significantly elevated in FVB.LDLR-/- compared to B6.LDLR-/- mice in liver, macrophages, and aorta (68%, 58%, and 32%, respectively). Reporter gene assays revealed a genetic variant that might explain these expression differences. Moreover, FVB.LDLR-/- macrophages showed 5-fold increased PMA-induced shedding of tumor necrosis factor (TNF)-alpha and 32% increased release of TNF-receptor I compared to B6.LDLR-/-. The atherosclerosis locus and expression differences were confirmed in Chr12 interval-specific congenic mice.

CONCLUSIONS

Our data provide functional evidence for ADAM17 as a candidate gene of atherosclerosis susceptibility at the murine Chr12 QTL.

The protective effect of A20 on atherosclerosis in apolipoprotein E-deficient mice is associated with reduced expression of NF-kappaB target genes

Up-regulation of inflammatory responses is considered a driving force of atherosclerotic lesion development. One key regulator of inflammation is the A20 (also called TNF-alpha-induced protein 3 or Tnfaip3) gene, which is responsible for NF-kappaB termination and maps to an atherosclerosis susceptibility locus revealed by quantitative trait locus-mapping studies at mouse proximal chromosome 10. In the current study, we examined the role of A20 in atherosclerotic lesion development. At the aortic root lesion size was found to be increased in C57BL/6 (BG) apolipoprotein E-deficient (ApoE(-/-)) mice haploinsufficient for A20, compared with B6 ApoE(-/-) controls that expressed A20 normally (60% in males and 23% in females; P < 0.001 and P < 0.05, respectively). In contrast, lesion size was found to be decreased in F(1) (B6 x FVB/N) mice overexpressing A20 by virtue of containing an A20 BAC transgene compared with nontransgenic controls (30% in males, P < 0.001, and 17% in females, P = 0.02). The increase in lesions in the A20 haploinsufficient mice correlated with increased expression of proatherosclerotic NF-kappaB target genes, such as vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and macrophage-colony-stimulating factor, and elevated plasma levels of NF-kappaB-driven cytokines. These findings suggest that A20 diminishes atherosclerosis by decreasing NF-kappaB activity, thereby modulating the proinflammatory state associated with lesion development.

Resistance to obesity and resistance to atherosclerosis: is there a metabolic link?

AIM

This review deals with the question whether resistance to obesity affects resistance to atherosclerosis.

DATA SYNTHESIS

Resistance to diet-induced obesity in inbred mouse strains involves an adequate response to Leptin, the main regulator of the energy balance cycle. Leptin, an adipokine with both central and peripheral targets, regulates food intake and energy expenditure. Adequate response to leptin involves repression of stearoyl-CoA desaturase, activation of Amp-activated protein-kinase and uncoupling proteins, resulting in fatty acid oxidation and energy expenditure. Most of the obesity-resistant strains are also resistant to atherosclerosis, but so far no information concerning the response to the leptin cycle is available in these strains when bred onto a LDLR(-/-) or apoE(-/-) background. Recent studies in mouse strains on an atherosclerosis permissive background have identified genetic links between obesity and atherosclerosis. Moreover, information derived from studies on mice was applied in order to learn about the metabolic effectors in humans and is included in this review.

CONCLUSIONS

The data presented in this review provide recent information concerning metabolic pathways that play an important role in the regulation of energy balance, a prerequisite for resistance to obesity. Hopefully they will provide a background for future genetic studies involved in resistance to atherosclerosis.

Genetic and genomic insights into the molecular basis of atherosclerosis

Atherosclerosis is a complex disease involving genetic and environmental risk factors, acting on their own or in synergy. Within the general population, polymorphisms within genes in lipid metabolism, inflammation, and thrombogenesis are probably responsible for the wide range of susceptibility to myocardial infarction, a fatal consequence of atherosclerosis. Genetic linkage studies have been carried out in both humans and mouse models to identify these polymorphisms. Approximately 40 quantitative trait loci for atherosclerotic disease have been found in humans, and approximately 30 in mice. Recently, genome-wide association studies have been used to identify atherosclerosis-susceptibility polymorphisms. Although discovering new atherosclerosis genes through these approaches remains challenging, the pace at which these polymorphisms are being found is accelerating due to rapidly improving bioinformatics resources and biotechnologies. The outcome of these efforts will not only unveil the molecular basis of atherosclerosis but also facilitate the discovery of drug targets and individualized medication against the disease.

Identification of pathways for atherosclerosis in mice: integration of quantitative trait locus analysis and global gene expression data

We report a combined genetic and genomic analysis of atherosclerosis in a cross between the strains C3H/HeJ and C57BL/6J on a hyperlipidemic apolipoprotein E-null background. We incorporated sex and sex-by-genotype interactions into our model selection procedure to identify 10 quantitative trait loci for lesion size, revealing a level of complexity greater than previously thought. Of the known risk factors for atherosclerosis, plasma triglyceride levels and plasma glucose to insulin ratios were particularly strongly, but negatively, associated with lesion size. We performed expression array analysis for 23,574 transcripts of the livers and adipose tissues of all 334 F2 mice and identified more than 10,000 expression quantitative trait loci that either mapped to the gene encoding the transcript, implying cis regulation, or to a separate locus, implying trans-regulation. The gene expression data allowed us to identify candidate genes that mapped to the atherosclerosis quantitative trait loci and for which the expression was regulated in cis. Genes highly correlated with lesions were enriched in certain known pathways involved in lesion development, including cholesterol metabolism, mitochondrial oxidative phosphorylation, and inflammation. Thus, global gene expression in peripheral tissues can reflect the systemic perturbations that contribute to atherosclerosis.

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.

Decreased obesity and atherosclerosis in human paraoxonase 3 transgenic mice

Paraoxonase 3 (PON3) is a member of the PON family, which includes PON1, PON2, and PON3. Recently, PON3 was shown to prevent the oxidation of low-density lipoprotein in vitro. To test the role of PON3 in atherosclerosis and related traits, 2 independent lines of human PON3 transgenic (Tg) mice on the C57BL/6J (B6) background were constructed. Human PON3 mRNA was detected in various tissues, including liver, lung, kidney, brain, adipose, and aorta, of both lines of Tg mice. The human PON3 mRNA levels in the livers of PON3 Tg mice were 4- to 7-fold higher as compared with the endogenous mouse Pon3 mRNA levels. Human PON3 protein and activity were detected in the livers of Tg mice as well. No significant differences in plasma total, high-density lipoprotein, and very-low-density lipoprotein/low-density lipoprotein cholesterol and triglyceride and glucose levels were observed between the PON3 Tg and non-Tg mice. Interestingly, atherosclerotic lesion areas were significantly smaller in both lines of male PON3 Tg mice as compared with the male non-Tg littermates on B6 background fed an atherogenic diet. When bred onto the low-density lipoprotein receptor knockout mouse background, the male PON3 Tg mice also exhibited decreased atherosclerotic lesion areas and decreased expression of monocyte chemoattractant protein-1 in the aorta as compared with the male non-Tg littermates. In addition, decreased adiposity and lower circulating leptin levels were observed in both lines of male PON3 Tg mice as compared with the male non-Tg mice. In an F2 cross, adipose Pon3 mRNA levels inversely correlated with adiposity and related traits. Our study demonstrates that elevated PON3 expression significantly decreases atherosclerotic lesion formation and adiposity in male mice. PON3 may play an important role in protection against obesity and atherosclerosis.

Identification of atherosclerosis-modifying genes: pathogenic insights and therapeutic potential

Atherosclerosis is a common, complex trait, with genetic variation in many genes and the environment contributing to risk for this condition, which has multiple and highly variable phenotypic manifestations. Progress has been made in the identification of atherosclerosis-modifying genes in both human studies and through the use of animal models. In the future, it may be possible to administer a genetic test for variation in a handful of the most common atherosclerosis-modifier genes, and thus predict if a patient is likely to develop atherosclerosis and ischemic heart disease. These patients could then be treated aggressively to lower their low-density lipoprotein cholesterol levels and other risk factors, including counseling to make adjustments in their lifestyle. This review will summarize the methods and results thus far in the identification of atherosclerosis-modifier genes.

Chemokines: inflammatory mediators of atherosclerosis

Atherosclerosis as the underlying mechanisms of myocardial infarction, stroke and peripheral artery disease remains the major cause of morbidity and mortality in developed countries. Recent developments in vascular biology have indicated that atherosclerosis can be best characterized as a chronic inflammatory disease of the vessel wall that promotes lesion development and progression. Chemokines regulate and control these processes by orchestrating adhesive interactions of circulating blood cells with the arterial wall and their subsequent extravasation. Exhibiting a high degree of specialization and cooperation, different chemokines mediate distinct steps during the atherogenic recruitment of monocytes and T cells. This diversity of chemokine expression and function might lead to the identification of selective therapeutic targets for the prevention and treatment of atherosclerosis.

Characterization of cardiomyocyte excitation-contraction coupling in the FVB/N-C57BL/6 intercrossed "chocolate" brown mice

Mice are extensively used for gene modification research and isolated cardiomyocytes are essential for evaluation of cardiac function without interference from non-myocyte contribution. This study was designed to characterize cardiomyocyte excitation-contraction coupling in FVB/N-C57BL/6 intercrossed brown mice. Mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix softedge system including peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR(90)), maximal velocity of shortening and relengthening (+/- dL/dt), intracellular Ca(2+) rise and decay rate. Resting cell length was longer in age- and gender-matched C57BL/6 and brown mice compared to FVB strain. PS and +/- dL/dt were significantly lower in brown mice compared to FVB/N and C57BL/6 groups. TPS was shortened in C57BL/6 mice and TR(90) was prolonged in brown mice compared to other groups. Resting intracellular Ca(2+) level and single exponential intracellular Ca(2+) decay constant were comparable among all three mouse lines. Rise in intracellular Ca(2+) in response to electrical stimulus was higher in C57BL/6 mouse myocytes whereas bi-exponential intracellular Ca(2+) decay was faster in brown mice. Myocytes from all three groups exhibited similar fashion of reduction in PS in response to increased stimulus frequency. These data suggest that inherent differences in cardiomyocyte excitation-contraction coupling exist between strains, which may warrant caution when comparing data from these mouse lines.