Severe hypercholesterolemia and atherosclerosis in apolipoprotein E-deficient mice created by homologous recombination in ES cells

apoE-deficient mice have been created by homologous recombination in ES cells. On a low fat, low cholesterol chow diet these animals have plasma cholesterol levels of 494 mg/dl compared with 60 mg/dl in control animals, and when challenged with a high fat Western-type diet, these animals have plasma cholesterol levels of 1821 mg/dl compared with 132 mg/dl in controls. This marked hypercholesterolemia is primarily due to elevated levels of very low and intermediate density lipoproteins. At 10 weeks of age, apoE-deficient mice have already developed atherosclerotic lesions in the aorta and coronary and pulmonary arteries. apoE-deficient mice are a promising small animal model to help understand the role of apoE in vivo and the genetic and environmental determinants of atherosclerosis.

Inhibition of early atherogenesis in transgenic mice by human apolipoprotein AI

Epidemiological surveys have identified a strong inverse relationship between the amount in the plasma of high density lipoproteins (HDL), apolipoprotein AI (ApoA-I), the major protein component of HDL, and the risk for atherosclerosis in humans. It is not known if this relationship arises from a direct antiatherogenic effect of these plasma components or if it is the result of other factors also associated with increases in ApoA-I and HDL levels. Because some strains of mice are susceptible to diet-induced formation of preatherosclerotic fatty streak lesions, and because of available techniques for the genetic manipulation of this organism, the murine system offers a unique setting in which to investigate the process of early atherogenesis. To test the hypothesis that induction of a high plasma concentration of ApoA-I and HDL would inhibit this process, we studied the effects of atherogenic diets on transgenic mice expressing high amounts of human ApoA-I. We report that transgenic mice with high plasma ApoA-I and HDL levels were significantly protected from the development of fatty streak lesions.

VISTA : visualizing global DNA sequence alignments of arbitrary length

SUMMARY

VISTA is a program for visualizing global DNA sequence alignments of arbitrary length. It has a clean output, allowing for easy identification of similarity, and is easily configurable, enabling the visualization of alignments of various lengths at different levels of resolution. It is currently available on the web, thus allowing for easy access by all researchers.

AVAILABILITY

VISTA server is available on the web at http://www-gsd.lbl.gov/vista. The source code is available upon request.

CONTACT

vista@lbl.gov

An apolipoprotein influencing triglycerides in humans and mice revealed by comparative sequencing

Comparison of genomic DNA sequences from human and mouse revealed a new apolipoprotein (APO) gene (APOAV) located proximal to the well-characterized APOAI/CIII/AIV gene cluster on human 11q23. Mice expressing a human APOAV transgene showed a decrease in plasma triglyceride concentrations to one-third of those in control mice; conversely, knockout mice lacking Apoav had four times as much plasma triglycerides as controls. In humans, single nucleotide polymorphisms (SNPs) across the APOAV locus were found to be significantly associated with plasma triglyceride levels in two independent studies. These findings indicate that APOAV is an important determinant of plasma triglyceride levels, a major risk factor for coronary artery disease.

A YAC mouse model for Huntington's disease with full-length mutant huntingtin, cytoplasmic toxicity, and selective striatal neurodegeneration

We have produced yeast artificial chromosome (YAC) transgenic mice expressing normal (YAC18) and mutant (YAC46 and YAC72) huntingtin (htt) in a developmental and tissue-specific manner identical to that observed in Huntington's disease (HD). YAC46 and YAC72 mice show early electrophysiological abnormalities, indicating cytoplasmic dysfunction prior to observed nuclear inclusions or neurodegeneration. By 12 months of age, YAC72 mice have a selective degeneration of medium spiny neurons in the lateral striatum associated with the translocation of N-terminal htt fragments to the nucleus. Neurodegeneration can be present in the absence of macro- or microaggregates, clearly showing that aggregates are not essential to initiation of neuronal death. These mice demonstrate that initial neuronal cytoplasmic toxicity is followed by cleavage of htt, nuclear translocation of htt N-terminal fragments, and selective neurodegeneration.

Identification of a coordinate regulator of interleukins 4, 13, and 5 by cross-species sequence comparisons

Long-range regulatory elements are difficult to discover experimentally; however, they tend to be conserved among mammals, suggesting that cross-species sequence comparisons should identify them. To search for regulatory sequences, we examined about 1 megabase of orthologous human and mouse sequences for conserved noncoding elements with greater than or equal to 70% identity over at least 100 base pairs. Ninety noncoding sequences meeting these criteria were discovered, and the analysis of 15 of these elements found that about 70% were conserved across mammals. Characterization of the largest element in yeast artificial chromosome transgenic mice revealed it to be a coordinate regulator of three genes, interleukin-4, interleukin-13, and interleukin-5, spread over 120 kilobases.

The effects of alcoholism on skeletal and cardiac muscle

To determine the prevalence of alcoholic myopathy and cardiomyopathy, we studied a group of 50 asymptomatic alcoholic men (mean age, 38.5 years) entering an outpatient treatment program. Studies performed included an assessment of muscle strength by electronic myometer, muscle biopsy, echocardiography, and radionuclide cardiac scanning, with comparison to healthy control subjects of similar age. The patients' mean (+/- SEM) daily alcohol consumption was 243 +/- 13 g over an average of 16 years. These patients had no clinical or laboratory signs of malnutrition or electrolyte imbalance. Forty-two percent of the patients, as compared with none of the controls, had strength of less than 20 kg as measured in the deltoid muscle. Muscle-biopsy specimens from 23 patients (46 percent) had histologic evidence of myopathy. In the cardiac studies, when the alcoholic patients were compared with 20 healthy controls, the patients had a significantly lower mean ejection fraction (59 vs. 67 percent), a lower mean shortening fraction (33 vs. 38 percent), a greater mean end-diastolic diameter (51 vs. 49 mm), and a greater mean left ventricular mass (123 vs. 106 g per square meter of body-surface area). One third of the alcoholics had an ejection fraction of 55 percent or less, as compared with none of the controls. Endomyocardial biopsy specimens from six patients with ejection fractions below 50 percent showed histologic changes of cardiomyopathy. The estimated total lifetime dose of ethanol correlated inversely with muscular strength (r = -0.65; P less than 0.001). In an analysis that also included six patients with symptomatic alcoholic cardiomyopathy, the estimated total lifetime dose of ethanol correlated inversely with the ejection fraction (r = -0.58; P less than 0.001) and directly with the left ventricular mass (r = 0.59; P less than 0.001). We conclude that myopathy of skeletal muscle and cardiomyopathy are common among persons with chronic alcoholism and that alcohol is toxic to striated muscle in a dose-dependent manner.

Transgenic knockout mice with exclusively human sickle hemoglobin and sickle cell disease

To create mice expressing exclusively human sickle hemoglobin (HbS), transgenic mice expressing human alpha-, gamma-, and betaS-globin were generated and bred with knockout mice that had deletions of the murine alpha- and beta-globin genes. These sickle cell mice have the major features (irreversibly sickled red cells, anemia, multiorgan pathology) found in humans with sickle cell disease and, as such, represent a useful in vivo system to accelerate the development of improved therapies for this common genetic disease.

Apolipoprotein AI transgene corrects apolipoprotein E deficiency-induced atherosclerosis in mice

Apolipoprotein E (apo E)-deficient mice are severely hypercholesterolemic and develop advanced atheromas independent of diet. The C57BL/6 strain differs from most inbred strains by having lower HDL concentrations and a high risk of developing early atherosclerotic lesions when fed an atherogenic diet. The relative HDL deficiency and atherosclerosis susceptibility of the C57BL/6 strain are corrected with the expression of a human apolipoprotein AI (apo AI) transgene in this genetic background. To examine if increases in apo AI and HDL are also effective in minimizing apo E deficiency--induced atherosclerosis, we introduced the human apo AI transgene into the hypercholesterolemic apo E knockout background. Similar elevations of total plasma cholesterol occurred in both the apo E knockout and apo E knockout mice also expressing the human apo AI transgene. The latter animals, however, also showed a two- to threefold increase in HDL and a sixfold decrease in susceptibility to atherosclerosis. This study demonstrates that elevating the concentration of apo AI reduces atherosclerosis in apo E deficient-mice and suggests that elevation of apo AI and HDL may prove to be a useful approach for treating unrelated causes of heightened atherosclerosis susceptibility.

Genomic strategies to identify mammalian regulatory sequences

With the continuing accomplishments of the human genome project, high-throughput strategies to identify DNA sequences that are important in mammalian gene regulation are becoming increasingly feasible. In contrast to the historic, labour-intensive, wet-laboratory methods for identifying regulatory sequences, many modern approaches are heavily focused on the computational analysis of large genomic data sets. Data from inter-species genomic sequence comparisons and genome-wide expression profiling, integrated with various computational tools, are poised to contribute to the decoding of genomic sequence and to the identification of those sequences that orchestrate gene regulation. In this review, we highlight several genomic approaches that are being used to identify regulatory sequences in mammalian genomes.

Ts1Cje, a partial trisomy 16 mouse model for Down syndrome, exhibits learning and behavioral abnormalities

A mouse model for Down syndrome, Ts1Cje, has been developed. This model has made possible a step in the genetic dissection of the learning, behavioral, and neurological abnormalities associated with segmental trisomy for the region of mouse chromosome 16 homologous with the so-called "Down syndrome region" of human chromosome segment 21q22. Tests of learning in the Morris water maze and assessment of spontaneous locomotor activity reveal distinct learning and behavioral abnormalities, some of which are indicative of hippocampal dysfunction. The triplicated region in Ts1Cje, from Sod1 to Mx1, is smaller than that in Ts65Dn, another segmental trisomy 16 mouse, and the learning deficits in Ts1Cje are less severe than those in Ts65Dn. In addition, degeneration of basal forebrain cholinergic neurons, which was observed in Ts65Dn, was absent in Ts1Cje.

Hepatic microsomal enzymes in man and rat: induction and inhibition by ethanol

The feeding of ethanol increased significantly the activities of hepatic pentobarbital and benzpyrene hydroxylases in rats, and, in human volunteers, doubled pentobarbital hydroxylase activity. In vitro ethanol inhibited aniline, pentobarbital, and benzpyrene hydroxylases. These data may explain, at least in part, the increased tolerance of alcoholics to sedatives when sober, and the enhanced sensitivity to sedatives when inebriated.

The Behavior Rating Scale for Dementia of the Consortium to Establish a Registry for Alzheimer's Disease. The Behavioral Pathology Committee of the Consortium to Establish a Registry for Alzheimer's Disease

OBJECTIVE

The purpose of the study was to develop a standardized instrument, the Behavior Rating Scale for Dementia, for rating psychopathology in patients with probable Alzheimer's disease and to conduct a multicenter pilot study of this instrument.

METHOD

The rating scale was developed collaboratively on the basis of clinical experience and existing instruments. Items were scaled according to frequency of psychopathology and were administered to an informant who was familiar with the subject. The scale was administered in a standardized manner by trained examiners who had met predetermined certification standards. The study group consisted of 303 subjects with probable Alzheimer's disease who had undergone standardized clinical evaluations by the Consortium to Establish a Registry for Alzheimer's Disease.

RESULTS

Subjects had an average of 15 problems rated as present in the preceding month. Wide variability in the nature of disturbances was found, with a number of items rated as present since the illness began but not in the past month. Interrater agreement was high. Factor analysis suggested eight preliminary factors that mapped onto clinically relevant domains: depressive features, psychotic features, defective self-regulation, irritability/agitation, vegetative features, apathy, aggression, and affective lability.

CONCLUSIONS

The Behavior Rating Scale for Dementia provides a standardized, reliable measure that can be administered to caregivers of demented subjects. On the basis of the present study, the scale has been revised slightly. After additional studies in progress, the Behavior Rating Scale for Dementia will be available for general use in assessing a wide range of psychopathology in dementia.

Active conservation of noncoding sequences revealed by three-way species comparisons

Human and mouse genomic sequence comparisons are being increasingly used to search for evolutionarily conserved gene regulatory elements. Large-scale human-mouse DNA comparison studies have discovered numerous conserved noncoding sequences of which only a fraction has been functionally investigated A question therefore remains as to whether most of these noncoding sequences are conserved because of functional constraints or are the result of a lack of divergence time.

Atherogenesis in transgenic mice expressing human apolipoprotein(a)

Elevated plasma levels of the lipoprotein Lp(a) are associated with increased risk for atherosclerosis and its manifestations, myocardial infarction, stroke and restenosis (for reviews, see refs 1-3). Lp(a) differs from low-density lipoprotein by the addition of the glycoprotein apolipoprotein(a), a homologue of plasminogen that contains many tandemly repeated units which resemble the fourth kringle domain of plasminogen, and single homologues of its kringle-5 and protease domain. As plasma Lp(a) concentration is strongly influenced by heritable factors and is refractory to most drug and dietary manipulation, the effects of modulating it are difficult to mimic experimentally. In addition, the absence of apolipoprotein(a) from virtually all species other than primates precludes the use of convenient animal models. Here we show that transgenic mice expressing human apolipoprotein(a) are more susceptible than control mice to the development of lipid-staining lesions in the aorta, and that apolipoprotein(a) co-localizes with lipid deposition in the artery walls.

Functional screening of 2 Mb of human chromosome 21q22.2 in transgenic mice implicates minibrain in learning defects associated with Down syndrome

Using Down syndrome as a model for complex trait analysis, we sought to identify loci from chromosome 21q22.2 which, when present in an extra dose, contribute to learning abnormalities. We generated low-copy-number transgenic mice, containing four different yeast artificial chromosomes (YACs) that together cover approximately 2 megabases (Mb) of contiguous DNA from 21q22.2. We subjected independent lines derived from each of these YAC transgenes to a series of behavioural and learning assays. Two of the four YACs caused defects in learning and memory in the transgenic animals, while the other two YACs had no effect. The most severe defects were caused by a 570-kb YAC; the interval responsible for these defects was narrowed to a 180-kb critical region as a consequence of YAC fragmentation. This region contains the human homologue of a Drosophila gene, minibrain, and strongly implicates it in learning defects associated with Down syndrome.

Expression of human apolipoprotein A-I in transgenic mice results in reduced plasma levels of murine apolipoprotein A-I and the appearance of two new high density lipoprotein size subclasses

In Western societies high density lipoprotein (HDL) levels correlate inversely with the risk for coronary heart disease. The primary protein component of both human and mouse HDL is apolipoprotein A-I (apoAI), which comprises greater than 70% of HDL protein and 30% of HDL mass. Human HDLs include particles of several distinct size subpopulations, whereas HDLs from inbred C57BL/6 mice contain a single population of particles. To study the regulation of apoAI expression and its role in HDL assembly, we created transgenic C57BL/6 mice containing the human apoAI gene. Two independent lines of transgenic mice with approximately twice the normal plasma levels of total apoAI were studied. The level of mouse apoAI is reduced greater than 4-fold in both transgenic lines, comprising only 4% of total plasma apoAI levels in one transgenic line and 13% in the other. We demonstrate that the mechanism responsible for the decrease in mouse apoAI is posttranscriptional. Parallel to the replacement of mouse with human apoAI, the single HDL species normally present in the plasma of C57BL/6 is replaced by two HDL subclasses similar in size to human HDL2b and HDL3a. The changes in murine apolipoprotein levels and HDL subclass size are inherited by all transgenic offspring of the two founder animals. These results suggest a dominant role of apoAI in determining the HDL particle size distribution and a mechanism involving expression of human apoAI transgenes that alters the plasma levels of mouse apoAI.

Decreased early atherosclerotic lesions in hypertriglyceridemic mice expressing cholesteryl ester transfer protein transgene

The human cholesteryl ester transfer protein (CETP) facilitates the transfer of cholesteryl ester from HDL to triglyceride-rich lipoproteins. The activity of CETP results in a reduction in HDL cholesterol levels, but CETP may also promote reverse cholesterol transport. Thus, the net impact of CETP expression on atherogenesis is uncertain. The influence of hypertriglyceridemia and CETP on the development of atherosclerotic lesions in the proximal aorta was assessed by feeding transgenic mice a high cholesterol diet for 16 wk. 13 out of 14 (93%) hypertriglyceridemic human apo CIII (HuCIII) transgenic (Tg) mice developed atherosclerotic lesions, compared to 18 out of 29 (62%) controls. In HuCIII/CETPTg, human apo AI/CIIITg and HuAI/CIII/CETPTg mice, 7 of 13 (54%), 5 of 10 (50%), and 5 of 13 (38%), respectively, developed lesions in the proximal aorta (P < .05 compared to HuCIIITg). The average number of aortic lesions per mouse in HuCIIITg and controls was 3.4 +/- 0.8 and 2.7 +/- 0.6, respectively in HuCIII/CETPTg, HuAI/CIIIg, and HuAI/CIII/CETPTg mice the number of lesions was significantly lower than in HuCIIITg and control mice: 0.9 +/- 0.4, 1.5 +/- 0.5, and 0.9 +/- 0.4, respectively. There were parallel reductions in mean lesion area. In a separate study, we found an increased susceptibility to dietary atherosclerosis in nonhypertriglyceridemic CETP transgenic mice compared to controls. We conclude that CETP expression inhibits the development of early atherosclerotic lesions but only in hypertriglyceridemic mice.

Protein composition determines the anti-atherogenic properties of HDL in transgenic mice

High-density lipoprotein (HDL) contains two major proteins, apolipoprotein A-I (apoA-I) and apolipoprotein A-II (apoA-II), comprising about 70% and 20% of the total HDL protein mass, respectively. HDL exists in human plasma in two main forms, one containing apoA-I with apoA-II (AI/AII-HDL) and another containing apoA-I without apoA-II (AI-HDL). A strong inverse relationship exists between total plasma HDL concentration and atherosclerosis, but the results of studies examining the relationship between AI-HDL and AI/AII-HDL and atherosclerosis have been conflicting. To determine whether these two HDL populations have different effects on atherogenesis, human apoA-I (AI) and human apoA-I and apoA-II (AI/AII) transgenic mice were produced in an atherosclerosis-susceptible strain. Following an atherogenic diet, despite similar total cholesterol and HDL cholesterol concentrations, the area of atherogenic lesions in the AI/AII mice was 15-fold greater than in the AI animals. These studies show that the protein composition of HDL significantly affects its role in atherogenesis and that AI-HDL is more antiatherogenic than AI/AII-HDL.

Effect of alcohol (ethanol) administration on sex-hormone metabolism in normal men

To determine whether ethanol per se affects testosterone metabolism, alcohol was administered to normal male volunteers for periods up to four weeks, resulting in an initial dampening of the episodic bursts of testosterone secretion followed by decreases in both the mean plasma concentration and the production rate of testosterone. The volunteers received adequate nutrition and none lost weight during the study, which tended to exclude a nutritional disturbance as the cause of the decreased testosterone levels. The changes in plasma luteinizing hormone suggested both a central (hypothalamus-pituitary) and gonadal effect of alcohol. In addition, alcohol consumption increased the metabolic clearance rate of testosterone in most subjects studied, probably owing to the combined effects of a decreased plasma binding capacity for the androgen and increased hepatic testosterone A-ring reductase activity. These results indicate that alcohol markedly affects testosterone metabolism independently of cirrhosis or nutritional factors.

Opposite regulation of human versus mouse apolipoprotein A-I by fibrates in human apolipoprotein A-I transgenic mice

The regulation of liver apolipoprotein (apo) A-I gene expression by fibrates was studied in human apo A-I transgenic mice containing a human genomic DNA fragment driving apo A-I expression in liver. Treatment with fenofibrate (0.5% wt/wt) for 7 d increased plasma human apo A-I levels up to 750% and HDL-cholesterol levels up to 200% with a shift to larger particles. The increase in human apo A-I plasma levels was time and dose dependent and was already evident after 3 d at the highest dose (0.5% wt/wt) of fenofibrate. In contrast, plasma mouse apo A-I concentration was decreased after fenofibrate in nontransgenic mice. The increase in plasma human apo A-I levels after fenofibrate treatment was associated with a 97% increase in hepatic human apo A-I mRNA, whereas mouse apo A-I mRNA levels decreased to 51%. In nontransgenic mice, a similar down-regulation of hepatic apo A-I mRNA levels was observed. Nuclear run-on experiments demonstrated that the increase in human apo A-I and the decrease in mouse apo A-I gene expression after fenofibrate occurred at the transcriptional level. Since part of the effects of fibrates are mediated through the nuclear receptor PPAR (peroxisome proliferator-activated receptor), the expression of the acyl CoA oxidase (ACO) gene was measured as a control of PPAR activation. Both in transgenic and nontransgenic mice, fenofibrate induced ACO mRNA levels up to sixfold. When transgenic mice were treated with gemfibrozil (0.5% wt/wt) plasma human apo A-I and HDL-cholesterol levels increased 32 and 73%, respectively, above control levels. The weaker effect of this compound on human apo A-I and HDL-cholesterol levels correlated with a less pronounced impact on ACO mRNA levels (a threefold increase) suggesting that the level of induction of human apo A-I gene is related to the PPAR activating potency of the fibrate used. Treatment of human primary hepatocytes with fenofibric acid (500 microM) provoked an 83 and 50% increase in apo A-I secretion and mRNA levels, respectively, supporting that a direct action of fibrates on liver human apo A-I production leads to the observed increase in plasma apo A4 and HDL-cholesterol.

Lower plasma levels and accelerated clearance of high density lipoprotein (HDL) and non-HDL cholesterol in scavenger receptor class B type I transgenic mice

Recent studies have indicated that the scavenger receptor class B type I (SR-BI) may play an important role in the uptake of high density lipoprotein (HDL) cholesteryl ester in liver and steroidogenic tissues. To investigate the in vivo effects of liver-specific SR-BI overexpression on lipid metabolism, we created several lines of SR-BI transgenic mice with an SR-BI genomic construct where the SR-BI promoter region had been replaced by the apolipoprotein (apo)A-I promoter. The effect of constitutively increased SR-BI expression on plasma HDL and non-HDL lipoproteins and apolipoproteins was characterized. There was an inverse correlation between SR-BI expression and apoA-I and HDL cholesterol levels in transgenic mice fed either mouse chow or a diet high in fat and cholesterol. An unexpected finding in the SR-BI transgenic mice was the dramatic impact of the SR-BI transgene on non-HDL cholesterol and apoB whose levels were also inversely correlated with SR-BI expression. Consistent with the decrease in plasma HDL and non-HDL cholesterol was an accelerated clearance of HDL, non-HDL, and their major associated apolipoproteins in the transgenics compared with control animals. These in vivo studies of the effect of SR-BI overexpression on plasma lipoproteins support the previously proposed hypothesis that SR-BI accelerates the metabolism of HDL and also highlight the capacity of this receptor to participate in the metabolism of non-HDL lipoproteins.

Ethanol increases hepatic smooth endoplasmic reticulum and drug-metabolizing enzymes

Rats were fed ethanol for 2 weeks along with diets either adequate or deficient in protein and choline, the latter intake being similar to that of many alcoholics. Hepatic lipids, smooth endoplasmic reticulum, and the activities of drug-metabolizing enzymes (aniline hydroxylase and nitroreductase) were increased with the adequate diet but more so with the deficient one. These results may explain the increased tolerance by alcoholics of drugs such as sedatives.