Genetic analysis of murine strains C57BL/6J and C3H/HeJ to confirm the map position of Ath-1, a gene determining atherosclerosis susceptibility

Inflammasome Activation Aggravates Cutaneous Xanthomatosis and Atherosclerosis in ACAT1 (Acyl-CoA Cholesterol Acyltransferase 1) Deficiency in Bone Marrow

Objective- ACAT1 (Acyl-CoA cholesterol acyltransferase 1) esterifies cellular free cholesterol, thereby converting macrophages to cholesteryl ester-laden foam cells in atherosclerotic lesions and cutaneous xanthoma. Paradoxically, however, loss of ACAT1 in bone marrow causes the aggravation of atherosclerosis and the development of severe cutaneous xanthoma in hyperlipidemic mice. Recently, it has been reported that cholesterol crystals activate NLRP3 (NACHT, LRR [leucine-rich repeats], and PYD [pyrin domain] domain-containing protein 3) inflammasomes, thereby contributing to the development of atherosclerosis. The present study aimed to clarify the role of NLRP3 inflammasomes in the worsening of atherosclerosis and cutaneous xanthoma induced by ACAT1 deficiency. Approach and Results- Ldlr-null mice were transplanted with bone marrow from WT (wild type) mice and mice lacking ACAT1, NLRP3, or both. After the 4 types of mice were fed high-cholesterol diets, we compared their atherosclerosis and skin lesions. The mice transplanted with Acat1-null bone marrow developed severe cutaneous xanthoma, which was filled with numerous macrophages and cholesterol clefts and had markedly increased expression of inflammatory cytokines, and increased atherosclerosis. Loss of NLRP3 completely reversed the cutaneous xanthoma, whereas it improved the atherosclerosis only partially. Acat1-null peritoneal macrophages showed enhanced expression of CHOP (C/EBP [CCAAT/enhancer binding protein] homologous protein) and TNF-α (tumor necrosis factor-α) but no evidence of inflammasome activation, after treatment with acetylated LDL (low-density lipoprotein). Conclusions- Elimination of ACAT1 in bone marrow-derived cells aggravates cutaneous xanthoma and atherosclerosis. The development of cutaneous xanthoma is induced mainly via the NLRP3 inflammasome activation.

Mouse models of ageing and their relevance to disease

Ageing is a process that gradually increases the organism's vulnerability to death. It affects different biological pathways, and the underlying cellular mechanisms are complex. In view of the growing disease burden of ageing populations, increasing efforts are being invested in understanding the pathways and mechanisms of ageing. We review some mouse models commonly used in studies on ageing, highlight the advantages and disadvantages of the different strategies, and discuss their relevance to disease susceptibility. In addition to addressing the genetics and phenotypic analysis of mice, we discuss examples of models of delayed or accelerated ageing and their modulation by caloric restriction.

Mining the genome for lipid genes

Mining of the genome for lipid genes has since the early 1970s helped to shape our understanding of how triglycerides are packaged (in chylomicrons), repackaged (in very low density lipoproteins; VLDL), and hydrolyzed, and also how remnant and low-density lipoproteins (LDL) are cleared from the circulation. Gene discoveries have also provided insights into high-density lipoprotein (HDL) biogenesis and remodeling. Interestingly, at least half of these key molecular genetic studies were initiated with the benefit of prior knowledge of relevant proteins. In addition, multiple important findings originated from studies in mouse, and from other types of non-genetic approaches. Although it appears by now that the main lipid pathways have been uncovered, and that only modulators or adaptor proteins such as those encoded by LDLRAP1, APOA5, ANGPLT3/4, and PCSK9 are currently being discovered, genome wide association studies (GWAS) in particular have implicated many new loci based on statistical analyses; these may prove to have equally large impacts on lipoprotein traits as gene products that are already known. On the other hand, since 2004 - and particularly since 2010 when massively parallel sequencing has become de rigeur - no major new insights into genes governing lipid metabolism have been reported. This is probably because the etiologies of true Mendelian lipid disorders with overt clinical complications have been largely resolved. In the meantime, it has become clear that proving the importance of new candidate genes is challenging. This could be due to very low frequencies of large impact variants in the population. It must further be emphasized that functional genetic studies, while necessary, are often difficult to accomplish, making it hazardous to upgrade a variant that is simply associated to being definitively causative. Also, it is clear that applying a monogenic approach to dissect complex lipid traits that are mostly of polygenic origin is the wrong way to proceed. The hope is that large-scale data acquisition combined with sophisticated computerized analyses will help to prioritize and select the most promising candidate genes for future research. We suggest that at this point in time, investment in sequence technology driven candidate gene discovery could be recalibrated by refocusing efforts on direct functional analysis of the genes that have already been discovered. This article is part of a Special Issue entitled: From Genome to Function.

Variations in DNA elucidate molecular networks that cause disease

Identifying variations in DNA that increase susceptibility to disease is one of the primary aims of genetic studies using a forward genetics approach. However, identification of disease-susceptibility genes by means of such studies provides limited functional information on how genes lead to disease. In fact, in most cases there is an absence of functional information altogether, preventing a definitive identification of the susceptibility gene or genes. Here we develop an alternative to the classic forward genetics approach for dissecting complex disease traits where, instead of identifying susceptibility genes directly affected by variations in DNA, we identify gene networks that are perturbed by susceptibility loci and that in turn lead to disease. Application of this method to liver and adipose gene expression data generated from a segregating mouse population results in the identification of a macrophage-enriched network supported as having a causal relationship with disease traits associated with metabolic syndrome. Three genes in this network, lipoprotein lipase (Lpl), lactamase beta (Lactb) and protein phosphatase 1-like (Ppm1l), are validated as previously unknown obesity genes, strengthening the association between this network and metabolic disease traits. Our analysis provides direct experimental support that complex traits such as obesity are emergent properties of molecular networks that are modulated by complex genetic loci and environmental factors.

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.

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.

Toll-like receptors and atherosclerosis: key contributors in disease and health?

The identification of Toll-like receptors (TLRs) as key patternrecognition receptors of innate immunity has opened inquiries into previously unknown disease mechanisms. The ability of TLRs to detect a spectrum of pathogen-derived molecules defines their importance in innate immunity and provides a mechanistic link between infection and disease. Atherosclerosis is a chronic inflammatory disease where immune and metabolic factors interact to initiate and propagate arterial lesions. An understanding of TLRs in atherosclerosis could clarify the etiology of this complex process. Furthermore, the existence of host-derived endogenous TLR ligands may implicate TLR involvement in disease mechanisms beyond innate immunity, such as a role in homeostatic mechanisms to resolve injury. Our current knowledge of TLRs in atherosclerosis is discussed in this review with emphasis on experimental studies in atherosclerosis-susceptible mouse models. Highlights from studies of TLR involvement in other disease processes have demonstrated that TLR-dependent mechanisms probably parallel those found in atherosclerosis, some of which could be important in mitigating atherosclerotic injury. Finally, an appreciation of the pro- and anti-atherosclerotic mechanisms of TLR activation over the entire lifetime of an organism will provide clues to the role of TLRs in both health and disease.

Human genetic evidence that OX40 is implicated in myocardial infarction

We recently showed that genetic variants in OX40L are associated with myocardial infarction (MI) and severity of coronary artery disease in human. A number of studies also suggest a possible role for OX40 (the OX40L receptor) as a factor contributing to atherosclerosis. In the present study, the OX40 gene was screened for variants associated with precocious MI, using individuals with MI before the age of 60 and controls. Despite the fact that the OX40 gene is highly conserved between species and that relatively few common genetic variants were encountered, an association with MI was seen for a polymorphism in intron 5 (rs2298212). In silico investigation suggested that genetic variation (rs2298211), linked to this intronic variant, is possibly affecting spliceosome function. Our results provide evidence that variants in human OX40 might influence susceptibility to MI. The relevance of these findings is supported by the vital functions fulfilled by OX40 in mammals as reflected by the high level of evolutionary conservation.

Identifying novel genes for atherosclerosis through mouse-human comparative genetics

Susceptibility to atherosclerosis is determined by both environmental and genetic factors. Its genetic determinants have been studied by use of quantitative-trait-locus (QTL) analysis. So far, 21 atherosclerosis QTLs have been identified in the mouse: 7 in a high-fat-diet model only, 9 in a sensitized model (apolipoprotein E- or LDL [low-density lipoprotein] receptor-deficient mice) only, and 5 in both models, suggesting that different gene sets operate in each model and that a subset operates in both. Among the 27 human atherosclerosis QTLs reported, 17 (63%) are located in regions homologous (concordant) to mouse QTLs, suggesting that these mouse and human atherosclerosis QTLs have the same underlying genes. Therefore, genes regulating human atherosclerosis will be found most efficiently by first finding their orthologs in concordant mouse QTLs. Novel mouse QTL genes will be found most efficiently by using a combination of the following strategies: identifying QTLs in new crosses performed with previously unused parental strains; inducing mutations in large-scale, high-throughput mutagenesis screens; and using new genomic and bioinformatics tools. Once QTL genes are identified in mice, they can be tested in human association studies for their relevance in human atherosclerotic disease.

Peroxiredoxin 6 deficiency and atherosclerosis susceptibility in mice: significance of genetic background for assessing atherosclerosis

Peroxiredoxin 6 (Prdx6; also called antioxidant protein 2, or Aop2) is a candidate gene for Ath1, a locus responsible for the respective susceptibility and resistance of mouse strains C57BL/6J (B6) and C3H/HeJ (C3H) to diet-induced atherosclerosis. To evaluate if Prdx6 underlies Ath1, we compared the diet-induced atherosclerotic lesions in Prdx6 targeted mutant (Prdx6-/-) mice of different genetic backgrounds: B6, 129, and B6;129. PRDX6 protein and mRNA were expressed in normal and atherosclerotic aortas. B6;129 Prdx6-/- macrophages oxidized LDL significantly more than did controls. Plasma lipid hydroperoxide levels were higher in atherogenic diet-fed Prdx6-/- mice with B6;129 and B6 backgrounds than in controls. Prdx6-/- and controls in a 129 genetic background were equally lesion-resistant, and Prdx6-/- and controls in a B6 background were equally lesion-susceptible. In contrast, Prdx6-/- mice in a B6;129 background had significantly larger aortic root lesions than did littermate wild type controls. Therefore, although PRDX6 protein did not affect atherosclerosis susceptibility in either the resistant 129 background or the susceptible B6 background, it may inhibit atherosclerosis in backgrounds with mixed pro- and anti-atherogenic genes. Thus, genetic background plays an important role in modulating atherogenesis in targeted mutant mice. However, we think it is unlikely that Prdx6 underlies Ath1.

Positional identification of TNFSF4, encoding OX40 ligand, as a gene that influences atherosclerosis susceptibility

Ath1 is a quantitative trait locus on mouse chromosome 1 that renders C57BL/6 mice susceptible and C3H/He mice resistant to diet-induced atherosclerosis. The quantitative trait locus region encompasses 11 known genes, including Tnfsf4 (also called Ox40l or Cd134l), which encodes OX40 ligand. Here we report that mice with targeted mutations of Tnfsf4 had significantly (P <or= 0.05) smaller atherosclerotic lesions than did control mice. In addition, mice overexpressing Tnfsf4 had significantly (P <or= 0.05) larger atherosclerotic lesions than did control mice. In two independent human populations, the less common allele of SNP rs3850641 in TNFSF4 was significantly more frequent (P <or= 0.05) in individuals with myocardial infarction than in controls. We therefore conclude that Tnfsf4 underlies Ath1 in mice and that polymorphisms in its human homolog TNFSF4 increase the risk of myocardial infarction in humans.

A torrid zone on mouse chromosome 1 containing a cluster of recombinational hotspots

Within the 2.38-Mb Ath1 region of mouse chromosome 1, 42 of 45 genetic crossovers from crosses between C57BL/6J (B6) and either C3H/HeJ (H) or Mus spretus (SPRET) occurred in four zones (A-D); zone A, 100 kb long, contained a cluster of at least four recombination hotspots. F1 sperm assays indicate that within this "torrid zone" the most active hotspot (A3) can initiate recombination on H and SPRET but not B6 chromosomes. The A3 DNA sequence contains a (G/C)TTT repeat, long stretches of A or T, and a cyclic variation in AT content. Recombination was drastically reduced in a cross between B6 and a B6.SPRET Ath1 congenic strain, but was unaffected in a B6 x B6.H Ath1 congenic cross. Similar nonrandom clustering of hotspots has been observed in yeast and the major histocompatibility complexes of human and mouse. To the extent that torrid zones are a general feature of mammalian genomes, they have considerable implications for genetic mapping strategies in both human populations and mouse crosses.

Quantitative trait locus mapping for atherosclerosis susceptibility

PURPOSE OF REVIEW

Atherosclerosis is a complex trait with both environmental and genetic aspects. Although some progress has been made in defining genes associated with atherosclerosis in humans, animal models have been useful in learning about pathways and genes involved in atherogenesis. This review describes an unbiased genetic mapping method called quantitative trait locus mapping and progress in using this method to identify genes that alter atherosclerosis susceptibility in mice.

RECENT FINDINGS

Approximately 10 well defined genetic loci have been described that are associated with lesion severity in diet-induced or gene knockout mouse models of atherosclerosis. Recently, two of these genetic loci were narrowed considerably by analysis of genetic recombinants within these loci. In addition, a computational method to discover quantitative trait loci has been applied to atherosclerosis. However, none of the genes responsible for these atherosclerosis quantitative trait loci has been definitively identified. The recent completion of the mouse draft genome should facilitate the task of identifying these genes.

SUMMARY

Quantitative trait locus mapping studies in mouse models of atherosclerosis have defined genetic regions that alter lesion severity. The identification of the responsible genes may lead to insights into the pathogenesis of atherosclerosis as well as to candidates for human genetic association studies.

A phenotype-sensitizing Apoe-deficient genetic background reveals novel atherosclerosis predisposition loci in the mouse

Therapeutic intervention for atherosclerosis has predominantly concentrated on regulating cholesterol levels; however, these therapeutics are not efficacious for all patients, suggesting that other factors are involved. This study was initiated to identify mechanisms that regulate atherosclerosis predisposition in mice other than cholesterol level regulation. To do so we performed quantitative trait locus analysis using two inbred strains that each carry the atherosclerosis phenotype-sensitizing Apoe deficiency and that have been shown to have widely disparate predilection to atherosclerotic lesion formation. One highly significant locus on chromosome 10 (LOD = 7.8) accounted for 19% of the variance in lesion area independent of cholesterol. Two additional suggestive loci were identified on chromosomes 14 (LOD = 3.2) and 19 (LOD = 3.2), each accounting for 7-8% of the lesion variance. In all, five statistically significant and suggestive loci affecting lesion size but not lipoprotein levels were identified. Many of these were recapitulated in an independent confirmatory cross. In summary, two independently performed crosses between C57BL/6 and FVB/N Apoe-deficient mice have revealed several previously unreported atherosclerosis susceptibility loci that are distinct from loci linked to lipoprotein levels.

Transgenic expression of cholesterol-7-alpha-hydroxylase prevents atherosclerosis in C57BL/6J mice

C57BL/6J mice are susceptible to atherosclerosis when fed a diet consisting of fat, cholesterol, and taurocholate. The susceptibility to diet-induced atherosclerosis is linked to a reduction in plasma high density lipoprotein (HDL). Diet-induced reduction of plasma HDL shows a physiological and a genetic correlation with repression of cholesterol-7-alpha-hydroxylase, the liver-specific enzyme that regulates the conversion of cholesterol into bile acids. To examine the hypothesis that the repression of cholesterol-7-alpha-hydroxylase is responsible for initiating the metabolic alterations leading to the formation of atherosclerosis and gallstones, we determined whether constitutive transgenic expression of cholesterol-7-alpha-hydroxylase in C57BL/6J mice would confer resistance to these 2 common human diseases. When fed the atherogenic diet, nontransgenic littermates, but not cholesterol-7-alpha-hydroxylase transgenic mice, accumulated cholesterol and cholesterol esters in their livers and plasma. Although the atherogenic diet caused a marked decrease in plasma HDL cholesterol in nontransgenic mice, HDL levels in transgenic mice remained relatively unchanged. Moreover, the ability of cholesterol-7-alpha-hydroxylase transgenic mice to maintain cholesterol and lipoprotein homeostasis completely prevented the formation of atherosclerosis and gallstones. These data establish the integral role that cholesterol-7-alpha-hydroxylase has in maintaining hepatic cholesterol homeostasis and, thus, in the susceptibility to the formation of gallstones and atherosclerosis.

Genetic background determines the extent of atherosclerosis in ApoE-deficient mice

Two strains of ApoE-deficient mice were found to have markedly different plasma lipoprotein profiles and susceptibility to atherosclerosis when fed either a low-fat chow or a high-fat Western-type diet. FVB/NJ ApoE-deficient (FVB E0) mice had higher total cholesterol, HDL cholesterol, ApoA1, and ApoA2 levels when compared with C57BL/6J ApoE-deficient (C57 E0) mice. At 16 weeks of age, mean aortic root atherosclerotic lesion area was 7- to 9-fold higher in chow diet-fed C57 E0 mice and 3.5-fold higher in Western diet-fed C57 E0 mice compared with FVB E0 mice fed similar diets. Lesion area in chow diet-fed first-generation mice from a strain intercross was intermediate in size compared with parental values. The distribution of the lesion area in 150 chow diet-fed second-generation progeny spanned the range of the lesion area in both parental strains. There were no correlations between total cholesterol, non-HDL cholesterol, HDL cholesterol, ApoA1, ApoA2, ApoJ, or anti-cardiolipin antibodies and lesion area in the second-generation progeny. Thus, a genomic approach may succeed in identifying the genes responsible for the variation in atherosclerosis susceptibility in these 2 strains of ApoE-deficient mice, which could not be explained by measured plasma parameters.

MCP-1 deficiency reduces susceptibility to atherosclerosis in mice that overexpress human apolipoprotein B

The earliest recognizable atherosclerotic lesions are fatty streaks composed of lipid-laden macrophages (foam cells). Circulating monocytes are the precursors of these foam cells, but the molecular mechanisms that govern macrophage trafficking through the vessel wall are poorly understood. Monocyte chemoattractant protein-1 (MCP-1), a member of the chemokine (chemotactic cytokine) family, is a potent monocyte agonist that is upregulated by oxidized lipids. Recent studies in hypercholesterolemic mice lacking apo E or the low-density lipoprotein receptor have suggested a role for MCP-1 in monocyte recruitment to early atherosclerotic lesions. To determine if MCP-1 is critically involved in atherogenesis in the setting of elevated physiological plasma cholesterol levels, we deleted the MCP-1 gene in transgenic mice expressing human apo B. Here we report that the absence of MCP-1 provides dramatic protection from macrophage recruitment and atherosclerotic lesion formation in apo B transgenic mice, without altering lipoprotein metabolism. Taken together with the results of earlier studies, these data provide compelling evidence that MCP-1 plays a critical role in the initiation of atherosclerosis.

Regulation of the metabolism of plasma lipoproteins by apolipoprotein A-II

Mouse apolipoprotein (apo) A-II has three variants (type A, B, and C) among inbred strains. To clarify the role of ApoA-II in the metabolism of high density lipoproteins (HDL), we constructed a new congenic mouse strain (P1.R1-Apoa2b) with type B ApoA-II of the SAMR1 strain on the genetic background of the SAMP1 strain, and examined it together with another ApoA-II congenic strain (R1.P1-Apoa2c) containing type C ApoA-II of the SAMPI strain on the SAMR1 strain and the parental SAMP1 and SAMR1 strains. Genetic characterization of the congenic strains indicated that only small regions surrounding the ApoA-II gene of the parental strains had been transferred. The strains with Apoa2c had lower plasma concentrations of HDL and ApoA-II, and a smaller HDL particle size than strains with Apoa2b. We detected no significant differences in the mRNA levels of ApoA-II or in the in vitro translational efficiency of the ApoA-II mRNA among the four strains. These findings suggested that the differences in the post-translational modification or efficiency of secretion between the Apoa2b and Apoa2c protein regulates the ApoA-II concentration which in turn determines the concentration and size of HDL in mice.

Tissue-specific expression and cholesterol regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) in mice. Molecular cloning of mouse ACAT cDNA, chromosomal localization, and regulation of ACAT in vivo and in vitro

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the esterification of cholesterol with long chain fatty acids and is believed to play an important part in the development of atherosclerotic lesions. To facilitate the study of ACAT's role in this process, we have used the human ACAT K1 clone previously described (Chang, C. C. Y., Huh, H. Y., Cadigan, K. M. and Chang, T. Y. (1993) J. Biol. Chem. 268, 20747-20755) to isolate mouse ACAT cDNA from a liver cDNA library. The 3.7-kilobase cDNA clone isolated contains a 1620-base pair open reading frame which encodes a protein of 540 amino acids. The predicted mouse ACAT protein is 87% identical to the protein product of human ACAT K1 and shares many of the same secondary structural features, including two transmembrane domains, a leucine heptad motif consistent with dimer or multimer formation, and five regions homologous to the "signature sequences" found in other enzymes that catalyze acyl adenylation followed by acyl thioester formation and acyl transfer. Using the cDNA as a hybridization probe, we mapped the gene encoding mouse ACAT to chromosome 1 in a region syntenic to human chromosome 1 where the ACAT gene is located. Northern blot analysis and RNase protection assays of mouse tissues revealed that ACAT mRNA is expressed most highly in the adrenal gland, ovary, and preputial gland and is least abundant in skeletal muscle, adipose tissue, heart, and brain. To study the dietary regulation of ACAT mRNA expression in mouse tissues, we fed C57BL/6J mice a high-fat, high-cholesterol (HF/HC) atherogenic diet for 3 weeks and measured ACAT mRNA levels in various tissues by RNase protection. The HF/HC diet had little effect on ACAT mRNA levels in the small intestine, aorta, adrenal, or peritoneal macrophages, whereas hepatic ACAT mRNA levels were doubled in mice fed the atherogenic diet. ACAT activity in liver microsomes was similarly increased in cholesterol-fed mice, suggesting that mouse ACAT is regulated at least in part at the level of mRNA abundance. Additionally, a significant positive correlation was observed between ACAT activity and microsomal free cholesterol levels in chow- and cholesterol-fed mice, supporting the concept of cholesterol availability as a regulator of ACAT. To further investigate the regulation of ACAT activity under controlled conditions, ACAT-deficient Chinese hamster ovary cells were stably transfected with the mouse ACAT cDNA clone driven by a cytomegalovirus promoter. Two transfected Chinese hamster ovary cell lines that expressed the mouse ACAT transgene regained the ability to esterify cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative trait locus analysis of susceptibility to diet-induced atherosclerosis in recombinant inbred mice

Quantitative trait locus (QTL) analysis is a statistical method that can be applied to identify loci making a significant impact on a phenotype. For the phenotype of susceptibility to diet-induced atherosclerosis in the mouse, we have studied four quantitative traits: area of aortic fatty streaks and serum concentrations of high-density lipoprotein-bound cholesterol (HDL-cholesterol), apolipoprotein A-I, and apolipoprotein A-II (apo A-II). QTL analysis revealed a significant locus on chromosome 1 distal impacting serum apo A-II concentration on a high-fat diet and serum HDL-cholesterol concentration on a chow diet. This locus is presumably Apoa-2, the structural gene for apo A-II. QTL analysis of aortic fatty streaks failed to reveal a significant locus.

The MspI restriction fragment length polymorphism 3' to the apolipoprotein A-II gene: relationships with lipids, apolipoproteins, and premature coronary artery disease

In previous studies, a restriction fragment length polymorphism (RFLP) has been identified using MspI restriction endonuclease in the 3' region of the apo A-II gene. The rare variant site for this MspI (M2) has been reported to be associated with higher levels of HDL cholesterol and apo A-II. We have studied the frequency and lipid associations of this RFLP in a population of 168 coronary artery disease (CAD) male and female patients, who had more than 50% narrowing of one or more arteries prior to age 60 years, as well as 255 aged-matched males and females from the Framingham Offspring Study. We also studied 31 kindreds in which the proband had premature CAD. The frequency of the M2 allele was higher in CAD cases (0.20) than in the controls (0.13) (P less than 0.05). In general, those subjects carrying the M2 allele had lower HDL cholesterol and apo A-I plasma levels; however, this difference was only significant (P less than 0.02 and 0.002, respectively) in females with CAD. No cosegregation of the M2 allele with hypoalphalipoproteinemia was found in 31 kindreds studied. However, in both generations there was a trend for those subjects carrying the M2 allele to have lower HDL cholesterol levels than those carrying the M1 allele. Sequence analysis of the apo A-II gene of subjects homozygous for either the M1 (n = 1) or the M2 allele (n = 2) revealed that this RFLP is due to a T----C single base mutation 528 bp 3' to the apo A-II gene. In the subjects homozygous for the M2 allele no other mutations were found within the coding region of the apo A-II gene that could result in changes in the primary sequence of the protein. These data indicate that the MspI RFLP 3' to the apo A-II gene is somewhat more frequent in the CAD group. However, there was no significant association between this RFLP and any of the parameters examined. In conclusion, this DNA marker lacks the specificity to be clinically useful for CAD risk assessment in the population studied.

Genetic heterogeneity of lipoproteins in inbred strains of mice: analysis by gel-permeation chromatography

To assess genetic variation of murine lipoprotein profiles, plasma lipoproteins of 11 inbred strains, AKR/J, BALB/cByJ, C3H/HeJ, C57BL/6J, C57BL/6ByJ, C57L/J, DBA/1LacJ, 129/J, NZB/B1NJ, PL/J, and SWR/J, were analyzed by gel-permeation chromatography (fast peptide liquid chromatography) and nondenaturing gradient gel electrophoresis. Vena caval blood was drawn after 18 to 20 hours of fasting. Plasma triglyceride and cholesterol concentrations ranged from 12.9 mg/dL (C57BL/6ByJ) to 66.9 mg/dL (C3H/HeJ) and from 54.8 mg/dL (AKR/J) to 128.5 mg/dL (NZB/B1NJ), respectively. Mouse strain-related heterogeneities of very low-, low-, and high-density lipoprotein (VLDL, LDL, and HDL, respectively) concentrations were documented; VLDL-triglyceride concentrations ranged from 7.5 mg/dL to 38.8 mg/dL, LDL cholesterol from 12.0 mg/dL to 39.6 mg/dL, and HDL cholesterol from 41.3 mg/dL to 92.4 mg/dL. Hyper-VLDL-triglyceridemia was present in C3H/HeJ and SWR/J strains and hyper-LDL-cholesterolemia in NZB/B1NJ, C3H/HeJ, and DBA/1LacJ. VLDL cholesterol/VLDL triglyceride ratios also ranged widely among strains (0.13 to 0.43), with C57BL/6J, C57BL/6ByJ, and C57L/J, the strains particularly susceptible to diet-induced atherosclerosis, having the highest VLDL-lipid ratio. LDL and HDL size heterogeneities were also observed. LDL and HDL diameters ranged between 24.1 nm and 29.4 nm, and between 9.24 nm and 10.32 nm, respectively. Although LDL sizes showed no segregation, HDL sizes fell into two groups. C57L/J and C57BL/6J possessed low HDL-cholesterol concentrations and small-sized HDL. HDL sizes were positively correlated with HDL-cholesterol concentrations (r = .90, P less than .001) and LDL-cholesterol concentrations (r = .85, P less than .001), but LDL sizes did not correlate with lipoprotein concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic analysis of strains C57BL/6J and BALB/cJ for Ath-1, a gene determining atherosclerosis susceptibility in mice

We previously reported that mice have at least one major gene determining atherosclerosis susceptibility, Ath-1. Susceptible alleles of Ath-1 are found in strain C57BL/6J and are associated with relatively low levels of high-density lipoprotein cholesterol (HDL-C) when these mice are fed an atherogenic diet. Resistant alleles of Ath-1 are found in strains C3H/HeJ and BALB/cJ and are associated with relatively high levels of HDL-C. Data reported earlier from the set of seven recombinant inbred (RI) strains, derived from C57BL/6By and BALB/cBy, showed that these parental strains differed at Ath-1. However, due to the limited number of RI strains, it was not possible to determine with certainty whether Ath-1 was the only major gene determining atherosclerosis susceptibility in these two strains or to determine its map position accurately. In this report, examination of F1, F2, and backcross progeny from a cross between C57BL/6J and BALB/cJ demonstrates that Ath-1 is the major gene determining atherosclerotic lesion formation and HDL-C levels in female mice. The data from male animals suggest that environmental factors or modifying genes also influence male HDL-C levels and thus partly obscure the Ath-1 phenotype. HDL-C levels in F1 progeny resemble the BALB/c parent. The data from the cross provide confirmatory evidence that Ath-1 is linked to Alp-2 on chromosome 1 with a map distance of 4.8 +/- 2.3 (SE). Combining these data with a previous cross between strain C57BL/6 and strain C3H/HeJ gives a map distance between Ath-1 and Alp-2 of 4.9 +/- 1.8 based on 7 crossovers found among 144 tested chromosomes.