Biomedical subjects

E M Rubin

Publications and source records attributed to E M Rubin.

At least 91 records · Page 5Linked to original sources

PubMed1994

Expression of human apolipoprotein B and assembly of lipoprotein(a) in transgenic mice.

The atherogenic macromolecule lipoprotein(a) [Lp(a)] has resisted in vivo analyses partly because it is found in a limited number of experimental animals. Although transgenic mice expressing human apolipoprotein (a) [apo(a)] have previously been described, they failed to assemble Lp(a) particles because of the inability of human apo(a) to associate with mouse apolipoprotein B (apoB). We isolated a 90-kilobase P1 phagemid containing the human apoB gene and with this DNA generated 13 lines of transgenic mice of which 11 expressed human apoB. The human apoB transcript was expressed and edited in the liver of the transgenic mice. Plasma concentrations of human apoB, as well as low density lipoprotein (LDL), were related to transgene copy number; the transgenic line with the most copies of human apoB had a > 4-fold increase in LDL cholesterol compared with nontransgenics and a lipoprotein profile similar to that of humans. When human apoB and apo(a) transgenic mice were bred together, plasma apo(a) in mice expressing both human proteins was tightly associated with lipoproteins in the LDL density region. These studies demonstrate the successful expression of human apoB and the efficient assembly of Lp(a) in mice.

Animals↗

PubMed1994

Studies of lipoprotein (a) and high density lipoproteins in transgenic mice.

The many genetic components contributing to atherosclerosis in humans have been difficult to untangle, due in part to the lack of genetically defined model systems. To investigate the in vivo properties of two particularly puzzling human lipoproteins, lipoprotein (a) (Lp(a)) and high-density lipoprotein (HDL), we have engineered mice to produce human-like analogues in their plasma. In these studies, we have examined the effect that protein composition has on the antiatherogenic properties of HDL and the interaction of human apolipoprotein(a) (apo(a)) and human apolipoprotein B (apo B) in forming Lp(a).

Animals↗

PubMed1994

Atherosclerosis in mice: getting to the heart of a polygenic disorder.

The mouse is being increasingly used as a model system for understanding the common and complex polygenic condition of atherosclerosis. Mice have been created in which genes involved in this condition have been overexpressed or have been altered by gene targeting. Here, we concentrate on recent experiments that use transgenic and gene knockout mice as an in vivo assay system to unravel the interactions between various genes involved in atherogenesis. We focus in particular on examples in which unique insights into the human condition have been derived from studies in mice.

Animals↗

PubMed1994

The properties of HDL in genetically engineered mice.

Genes involved in HDL structure and metabolism have been overexpressed through the introduction of transgenes or inactivated by gene targeting in mice. These new experimental substrates make it possible to address hypotheses relevant to the biology of HDL that were previously inaccessible through human studies. The in-vivo studies performed to date with these engineered mice have provided insight into structural determinants of HDL, uncovered interactions between proteins that act on HDL and clarified the role that HDL-associated proteins play in atherosclerosis. Further use of these animals, coupled with the development of new engineered lines of mice, should help unravel many questions associated with the in-vivo biological properties and metabolism of HDL.

Animals↗

PubMed1994

The mouse as a model for human cardiovascular disease and hyperlipidemia.

The mouse has been used as an experimental model for atherosclerosis research for only a short time; however, the sophisticated genetics of this species has resulted in a number of innovative approaches that are not possible with other models. The availability of inbred, congenic, recombinant inbred, and mutant strains has resulted in the discovery of a number of genes affecting atherosclerosis susceptibility. More importantly, the newer genetic technologies such as quantitative trait-loci mapping, transgenic mice, and gene-targeted mice are producing important insights into atherosclerosis. This review, focusing on murine models of cardiovascular disease and hyperlipidemia, will be divided into two parts: naturally occurring models and genetically engineered models.

Animals↗

PubMed1994

Effect of human apoE4 on the clearance of chylomicron-like lipid emulsions and atherogenesis in transgenic mice.

Apolipoprotein (apo) E is a ligand for lipoprotein receptors and mediates the cellular uptake of several different lipoproteins. Human apoE occurs in three allelic forms designated E2, E3, and E4. The E2 isoform is associated with changes in lipoprotein metabolism, and the E4 isoform is associated with Alzheimer's disease and an increased risk of coronary heart disease. In this study transgenic mice were generated to assess the effect of a sustained increase in plasma apoE4 concentration. The transgenic animals had three- to sixfold increases in total plasma apoE, associated primarily with the non-high-density lipoprotein (HDL) fractions of plasma lipoproteins. In response to an atherogenic diet the transgenic mice developed hypercholesterolemia similar to that in nontransgenic mice but did not experience the decrease in HDL cholesterol normally observed in this strain of C57BL/6 mice. The rate of plasma clearance of a lipid emulsion mimicking lymph chylomicrons was measured in transgenic mice expressing the human apoE4 gene and compared with the clearance rate in nontransgenic control animals. In animals fed a low-fat diet the emulsion lipids were cleared significantly more rapidly from the plasma of transgenic than control mice. In animals adapted to a high-fat diet, the clearance of chylomicron remnants was slowed markedly in both transgenic and control mice and was not significantly accelerated in transgenic compared with control animals. We also investigated the effect of increasing the plasma concentration of apoE4 on the progression of atherosclerotic heart disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

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.

Animals↗

PubMed1994

Fatal massive hemoptysis secondary to intralobar sequestration.

We report the case of a 29-year-old woman who died of massive hemoptysis due to hemorrhage from an intralobar pulmonary sequestration into the tracheobronchial tree. The sequestration had been diagnosed in childhood but had been managed nonoperatively. This case emphasizes the need for early surgical treatment of pulmonary sequestration.

Acute Disease↗

PubMed1994

Human apolipoprotein A-I prevents atherosclerosis associated with apolipoprotein[a] in transgenic mice.

Elevated levels of apolipoprotein[a] (apo[a]) and apolipoprotein A-I (apoA-I) are associated, respectively, with increased and decreased atherosclerosis risk, in both humans and transgenic mice. To investigate the interactions of these two important lipid-associated proteins, we assessed the effect of expression of human apoA-I and apo[a] transgenes, both singularly and together, on murine atherogenesis. Mice expressing the apo[a] transgene have a lipoprotein profile similar to nontransgenic controls, yet have significantly increased susceptibility to diet-induced atherosclerosis. Compared to mice expressing only the apo[a] transgene, mice expressing both apo[a] and apoA-I transgenes have twofold greater high density lipoprotein (HDL) concentrations and approximately a 20-fold decrease in development of early atherosclerotic lesions. The finding of decreased atherosclerosis in the setting of elevated apo[a] and apoA-I suggests that elevations of apoA-I and HDL have a dominant effect in reducing atherosclerosis susceptibility in various settings, including those not associated with alterations of plasma lipids.

Animals↗

PubMed1994

Comparative image cytometric DNA ploidy of liver cell dysplasia and hepatocellular carcinoma.

Large-cell liver cell dysplasia (LCD), suggested to be a preneoplastic change that progresses to hepatocellular carcinoma (HCC), has a reported frequency of DNA aneuploidy by flow cytometry intermediate between that of nonneoplastic liver (0%) and HCC (80%). We assessed DNA ploidy by image cytometry of Feulgen-stained 5-microns sections of 30 livers with LCD and of 60 HCCs (29 with LCD in adjacent nonmalignant liver). All 30 LCDs were aneuploid, 27 (90%) of which were multiploid--11 (41%) with hyperdiploid and hypertetraploid peaks. Forty-eight (80%) HCCs were aneuploid; in nine of 20 (42%) with a hyperdiploid peak, a hyperdiploid peak was also present in the LCDs, but in none was there less than 0.24 between DNA indices. Besides the 12 (20%) diploid HCCs, a diploid peak was present in four heterogenous, three multiploid, and six HCCs with two phenotypes and two genotypes, one of which was diploid. One aneuploid/hyperdiploid peak in each of 22 nonneoplastic and 24 cirrhotic livers did not have a corresponding LCD or HCC aneuploid peak. These data do not suggest that dysplastic hepatocytes form a single mutant clone that progresses to HCC.

Aneuploidy↗

PubMed1993

Selective erythroid replacement in murine beta-thalassemia using fetal hematopoietic stem cells.

We have explored the application of fetal hematopoietic stem cell (HSC) transplants for cellular replacement in a murine model of beta-thalassemia. Liver-derived HSCs from nonthalassemic syngeneic murine fetal donors were transplanted into nonirradiated neonatal beta-thalassemic recipients. Significant erythrocyte chimerism (9-27%) was demonstrated in the majority of recipients at 1 month and remained stable or increased (up to 55%) during long-term follow-up in almost all cases. Chimeras had improved phenotypes, as evidenced by decreased reticulocyte counts, increased mean erythrocyte deformability, and decreased iron deposits in comparison to controls. To investigate whether the high degree of peripheral blood chimerism was predominantly a feature of erythroid elements or was a general feature of all hematopoietic elements, chimeras were created using donor HSCs "tagged" with a DNA transgene. Whereas donor hemoglobin comprised > 30% of total hemoglobin, nucleated tagged nonerythroid donor cells comprised < 1% of peripheral blood elements. Explanations for the observed selective increase in erythroid chimerism include longer survival of normal donor red cells compared to that of thalassemic red cells and the effective maturation of the donor erythroid elements in the bone marrow in chimeric animals. The latter explanation bears consideration because it is consistent with the process of ineffective erythropoiesis, well documented to occur in thalassemia, in which the majority of thalassemic erythroid cells are destroyed during erythropoiesis prior to release from the bone marrow. Overall, these data demonstrate the potential for significant erythroid chimerism and suggest that fetal HSC transplantation may play a significant role in future treatment.

Animals↗

PubMed1993

Analysis of the human zeta-globin gene promoter in transgenic mice.

zeta-Globin is the embryonic form of the alpha chain of hemoglobin. Transgenic mice generated with zeta-globin constructs containing the zeta-globin gene, 557 bp of 5' flanking sequence, and 2-kb of 3' flanking sequence linked to the beta-globin locus control region hypersensitive site 2 (HS2) expressed human zeta-globin only in embryonic yolk sac erythroid tissue, and not in definitive erythroid tissue in the fetal liver or in adult peripheral blood. To determine what sequences in the 5' flanking region of the zeta-globin gene might be important for developmental specificity, a series of 5' deletion constructs of the zeta-globin gene were made and used to generate transgenic mice. The 5' ends of these constructs were located 417, 207, and 128 bp 5' to the zeta-globin transcriptional start site, and HS2 was included to increase the level of erythroid-specific expression. In all lines of mice tested, human zeta-globin was expressed only in embryonic tissue, and not in fetal livers or in adult peripheral blood. Expression was independent of copy number and appeared to be dependent on the site of transgene insertion. These data suggest that the proximal 128 bp of the zeta-globin promoter is sufficient to properly regulate zeta-globin expression during development.

Animals↗

PubMed1993

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.

Animals↗

PubMed1992

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.

Animals↗

PubMed1992

Expression of human apolipoprotein A-II and its effect on high density lipoproteins in transgenic mice.

Apolipoproteins A-I and A-II comprise approximately 70 and 20%, respectively, of the total protein content of HDL. Evidence suggests that apoA-I plays a central role in determining the structure and plasma concentration of HDL, while the role of apoA-II is uncertain. To help define the function of apoA-II and determine what effect increasing its plasma concentration has on HDL, transgenic mice expressing human apoA-II and both human apoA-I and human apoA-II were produced. Human apoA-II mRNA is expressed exclusively in the livers of transgenic animals, and the protein exists as a dimer as it does in humans. High level expression of human apoA-II did not increase HDL concentrations or decrease plasma concentrations of murine apoA-I and apoA-II in contrast to what was observed in mice overexpressing human apoA-I. The primary effect of overexpressing human apoA-II was the appearance of small HDL particles composed exclusively of human apoA-II. HDL from mice transgenic for both human apoA-I and human apoA-II displayed a unique size distribution when compared with either apoA-I or apoA-II transgenic mice and contain particles with both these human apolipoproteins. These results in mice, indicating that human apoA-II participates in determining HDL size, parallel results from human studies.

Animals↗

PubMed1992

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.

Animals↗

PubMed1992

Apolipoprotein AI expression and high density lipoprotein distribution in transgenic mice during development.

The developmental changes in apoAI expression in human apolipoprotein AI (apoAI) transgenic and nontransgenic control mice and the effect of these changes on high density lipoprotein (HDL) sizes were investigated. Results demonstrated that both human and mouse apoAI mRNA levels sharply increased following delivery and then decreased prior to weaning. Unlike the changes in apoAI mRNA, plasma apoAI concentration and HDL mass increased following delivery and remained elevated as the animals matured. In these animals, parallel increases in plasma apoAI and HDL mass with development were accompanied by increases in HDL particle sizes. Control mice demonstrated a monodisperse population of particles that increased in particle size from 7.5 nm (at 2 days prior to birth) to 9.8 nm (at 13 days after birth). The latter is similar to the adult HDL size and distribution. Transgenic mice, unlike controls, exhibited several distinct HDL populations, which also increased in size as animals matured. These results suggest that post-transcriptional factors are important in regulating apoAI plasma levels and that developmental changes in plasma apoAI concentrations are associated with changes in HDL size distribution.

Aging↗

PubMed1991

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.

Animals↗