High level expression of human apolipoprotein A-I in transgenic rats raises total serum high density lipoprotein cholesterol and lowers rat apolipoprotein A-I

Ectopic expression of tethered human follicle-stimulating hormone (hFSH) gene in transgenic mice

To determine whether the mammary gland can be used to secrete large quantities of a bioactive heterodimeric protein into milk, we used a bovine beta-casein promoter to target and express human follicle-stimulating hormone (hFSH) in the mammary gland into the milk of transgenic mice. We also identified the effects of hFSH leaked into the bloodstream. Transgenic mice produced a high level (up to 300 mIU/ml) of recombinant hFSH in the mammary gland. Human FSH was expressed in the mammary gland and brain, as determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. In vitro bioactivity was also identified by cyclic AMP (cAMP) assay. The highest activity was showed in the transgenic mice line 11. However, hFSH leaked into the bloodstream was a powerful factor in the generation of breast and ovarian tumors from the transgenic mice line 11. These results suggest that change of endogenous hormones (FSH and progesterone) may affect the morphology and blood cell counts of peripheral blood and, especially, provoke breast and ovarian tumors.

Advances in transgenic rat production

Predictable and reproducible production of transgenic rats from a standardized input of egg donors and egg recipients is essential for routine rat model production. In the course of establishing a transgenic rat service, transgenic founders were produced from three transgenes in outbred Sprague-Dawley (SD) rats and four transgenes in inbred Fischer 344 (F344) rats. Key parameters that affect transgenesis efficiency were assessed, including superovulation treatments, methods to prepare pseudopregnant recipients, and microinjection technique. Five superovulation regimens were compared and treatment with 20 IU PMSG and 30 IU HCG was selected for routine use. Four methods to prepare pseudopregnant egg recipients were compared and estrus synchronization with LHRHa and mating to vasectomized males was selected as most effective. More than 80% of eggs survived microinjection when modified pronuclear microinjection needles and DNA buffers were used. The efficiencies of transgenic production in rats and C57BL/6J (B6J) mice were compared to provide a context for assessing the difficulty of transgenic rat production. Compared to B6J mice, SD rat transgenesis required fewer egg donors per founder, fewer pseudopregnant egg recipients per founder, and produced more founders per eggs microinjected. Similar numbers of injection days were required to produce founders. These results suggest that SD rat transgenesis can be more efficient than B6J mouse transgenesis with the appropriate technical refinements. Advances in transgenic rat production have the potential to increase access to rat models.

Human apoA-I expression in CETP transgenic rats leads to lower levels of apoC-I in HDL and to magnification of CETP-mediated lipoprotein changes

Plasma cholesteryl ester transfer protein (CETP) has a profound effect on neutral lipid transfers between HDLs and apolipoprotein B (apoB)-containing lipoproteins when it is expressed in combination with human apoA-I in HuAI/CETP transgenic (Tg) rodents. In the present study, human apoA-I-mediated lipoprotein changes in HuAI/CETPTg rats are characterized by 3- to 5-fold increments in the apoB-containing lipoprotein-to-HDL cholesterol ratio, and in the cholesteryl ester-to-triglyceride ratio in apoB-containing lipoproteins. These changes occur despite no change in plasma CETP concentration in HuAI/CETPTg rats, as compared with CETPTg rats. A number of HDL apolipoproteins, including rat apoA-I and rat apoC-I are removed from the HDL surface as a result of human apoA-I overexpression. Rat apoC-I, which is known to constitute a potent inhibitor of CETP, accounts for approximately two-thirds of CETP inhibitory activity in HDL from wild-type rats, and the remainder is carried by other HDL-bound apolipoprotein inhibitors. It is concluded that human apoA-I overexpression modifies HDL particles in a way that suppresses their ability to inhibit CETP. An apoC-I decrease in HDL of HuAI/CETPTg rats contributes chiefly to the loss of the CETP-inhibitory potential that is normally associated with wild-type HDL.

Transgenic modifications of the rat genome

The laboratory rat (R. norvegicus) is a very important experimental animal in several fields of biomedical research. This review describes the various techniques that have been used to generate transgenic rats: classical DNA microinjection and more recently described techniques such as lentiviral vector-mediated DNA transfer into early embryos, sperm-mediated transgenesis, embryo cloning by nuclear transfer and germline mutagenesis. It will also cover techniques associated to transgenesis such as sperm cryopreservation, embryo freezing and determination of zygosity. The availability of several technologies allowing genetic manipulation in the rat coupled to genomic data will allow biomedical research to fully benefit from the rat as an experimental animal.

Factors affecting production of transgenic rats by ICSI-mediated DNA transfer: effects of sonication and freeze-thawing of spermatozoa, rat strains for sperm and oocyte donors, and different constructs of exogenous DNA

Factors affecting the efficiency of producing transgenic rats by intracytoplasmic sperm injection (ICSI)-mediated DNA transfer were investigated. Epididymal spermatozoa from Sprague-Dawley (SD) rats were sonicated and/or frozen-thawed for cutting the tail and membrane disruption. The sperm heads were exposed for 1 min to different concentrations (0.02-2.5 microg/ml) of 3.0 kb enhanced green fluorescent protein (EGFP) DNA solution, and then microinjected into the denuded F1 hybrid (Donryu x LEW) rat oocytes. The optimal concentration of EGFP DNA solution was 0.1 microg/ml, as determined by the in vitro developmental competence into morulae/blastocysts of the ICSI oocytes and the EGFP expression of the resultant embryos. The efficiency of producing transgenic rat offspring (per transferred zygote) was 2.8%, 1.6%, and 3.3% in the oocytes injected with sonicated, frozen-thawed, and sonicated + frozen-thawed sperm heads, respectively. The founder transgenic rats carrying the EGFP gene transmitted their transgenes to their progeny according to the Mendelian fashion, suggesting the stable incorporation of the transgenes into the rat genomes. Four rat strains (F344, LEW, Donryu, and SD) were compared for their suitability as sperm/oocyte donors for the production of transgenic rats by ICSI with sonicated, frozen-thawed and solution of EGFP DNA-exposed sperm heads. The efficiency of producing transgenic rats in the SD strain (8.2%) was higher than that in the LEW strain (0.9%), while those in the F344 and Donryu strains (4.3%-4.4%) were intermediate. One plasmid DNA (Fyn, 5.0 kb) and two BAC DNA (BAC/Fyn, 208 kb; Svet1/IRES-Cre, 186 kb) were successfully introduced into the SD rat genomes via ICSI, with the producing efficiencies of 2.8%, 0.9%, and 2.4%, respectively.

Expression of simian CETP in normolipidemic Fisher rats has a profound effect on large sized apoE-containing HDL

In order to investigate the direct effect of cholesteryl ester transfer protein (CETP) on the structure and composition of HDL in vivo, simian CETP was expressed in Fisher rat that spontaneously displays high plasma levels of HDL1. In the new CETPTg rat line, the production of active CETP by the liver induced a significant 48% decrease in plasma HDL cholesterol, resulting in a 34% decrease in total cholesterol level (P < 0.01 in both cases). Among the various plasma HDL subpopulations, the largest HDL were those mostly affected by CETP, with a 74% decrease in HDL1 versus a significantly weaker 38% decrease in smaller HDL2 (P < 0.0001). Apolipoprotein E (apoE)-containing HDL1 were selectively affected by CETP expression, whereas apoA content of HDL remained unmodified. The reduction in the apoE content of serum HDL observed in CETPTg rats compared to controls (53%, P < 0.02) suggests that apoE in HDL may constitute in vivo a major determinant of their ability to interact with CETP. These results bring new insight into the lack of HDL1 in plasma from CETP-deficient heterozygotes despite their substantial 50% decrease in CETP activity. In addition, they indicate that HDL1 constitute reliable and practicable sensors of very low plasma CETP activity in vivo.

A comparative study on the integration of exogenous DNA into mouse, rat, rabbit, and pig genomes

Transgenic mammals, from small laboratory rodents to domestic animals, have been successfully produced to date, but their production efficiency within or across species has been variable. This is probably due to the differences in the type of injected DNA and/or technical procedures employed in each laboratory, as well as the reproductive characteristics of the species. Here we report the direct comparison of the efficiencies of producing transgenic mice, rats, rabbits and pigs by one technician using a fusion gene composed of the bovine alpha S1-casein promoter and human growth hormone (hGH) gene. Before the fusion gene was injected into the zygotes, high magnitude centrifugation to visualize the pronuclei was necessary for all of the pig zygotes and one-third of the rabbit zygotes, but not for mouse and rat zygotes. Post-injection survival of the mouse zygotes (67.1%) was lower than those of the rat, rabbit and pig zygotes (89.6 to 100%). The volume change of the pronucleus following DNA injection was the lowest in mice (50% increase), moderate in rabbits (148% increase), and the most prominent in rats (238% increase). The data from only 1 pig zygote indicated a 22% increase in the pronucleus volume by DNA injection. The PCR analyses of the tail DNA of new born offspring indicated that 0.8% (4/493), 4.8% (22/463), 0.8% (3/367) and 0.9% (2/221) of the injected eggs in mice, rats, rabbits and pigs, respectively, developed into transgenic offspring. Some of the founder animals in all four species expressed the transgene in the mammary gland which was confirmed in hGH mRNA by RT-PCR and/or hGH peptide in Witch's milk with ELISA. These results suggest that the maximum volume of DNA solution injectable into the pronucleus is a possible factor explaining the species differences in the production of transgenic animals.

Accumulation of cholestatic lipoproteins in ANIT-treated human apolipoprotein A-I transgenic rats is diminished through dose-dependent apolipoprotein A-I activation of LCAT

Administration of alpha-naphthylisothiocyanate (ANIT) to rats induces changes to plasma lipids consistent with cholestasis. We have previously shown (J. Lipid Res. 37 (1996) 1086) that animals treated with ANIT accumulate large amounts of free cholesterol (FC) and phospholipid (PL)-rich cholestatic lipoproteins in the LDL density range by 48 h. This lipid was cleared by 120 h through apparent movement into HDL with concomitant cholesteryl ester (CE) production. It was hypothesised that the clearance was mediated through the movement of the PL and FC into apolipoprotein A-I (apo A-I) containing lipoproteins followed by LCAT esterification to form CE. To test this hypothesis, rats overexpressing various amounts of human apo A-I (TgR[HuAI] rats) were treated with ANIT (100 mg/kg) and the effect of plasma apo A-I concentration on plasma lipids and lipoprotein distribution was examined. In untreated TgR[HuAI] rats, human apo A-I levels were strongly correlated to plasma PL (r(2)=0. 94), FC (r(2)=0.93) and CE (r(2)=0.90), whereas in ANIT-treated TgR[HuAI] rats, human apo A-I levels were most strongly correlated to CE levels (r(2)=0.80) and an increased CE/FC ratio (r(2)=0.62) and the movement of cholestatic lipid in the LDL to HDL. Since LCAT activity was not affected by ANIT treatment, these results demonstrate that the ability of LCAT to esterify the plasma FC present in cholestatic liver disease is limited by in vivo apo A-I activation of the cholestatic lipid and not by the catalytic capacity of LCAT.

Adenoviral vector-mediated expression of physiologic levels of human factor VIII in nonhuman primates

An E1-, E2a-, E3-deleted adenoviral vector (Av3H82) encoding an epitope-tagged B domain-deleted human factor VIII cDNA (flagged FVIII) was evaluated in nonhuman primates. Twelve cynomolgus monkeys received intravenous administration of Av3H82; 6 monkeys received 6 x 10(11) particles/kg and another 6 received 3 x 10(12) particles/kg. Adenoviral vector transduction of the liver was efficient, reproducible, and linearly dose dependent. Physiologic levels of flagged FVIII were readily detected in plasma samples obtained from monkeys that received the higher dose of vector and human FVIII mRNA was detected in their livers. Expression of transgene mRNA was restricted to the liver by the albumin promoter. Although vector DNA was readily detected in the liver of monkeys that received the lower dose, neither human FVIII mRNA nor flagged FVIII protein could be detected. Vector distribution was widespread, with the highest levels observed in liver and spleen. Histopathology, hematology, and serum chemistry analysis identified the liver and blood as major sites of toxicity. Transient mild serum elevations of liver enzymes were observed, along with a dose-dependent inflammatory response in the liver. In addition, mild lymphoid hyperplasia was observed in the spleen. Mild anemia and a transient decrease in platelet count were observed, as was marrow hyperplasia and extramedullary hematopoiesis.

High-density lipoprotein subclasses and apolipoprotein A-I

Epidemiological and clinical studies showing an association between decreased concentrations of high-density lipoprotein (HDL) cholesterol and increased risk of premature coronary artery disease have generated interest in the mechanism through which HDL prevents atherosclerosis. Recognition of the importance of apolipoproteins (apo(s)) has led to the separation of HDL into subpopulations according to their apolipoprotein composition. It is now recognised that HDL comprises at least two types of apo A-I-containing lipoproteins: LpA-I:A-II containing both apo A-I and apo A-II and LpA-I containing apo A-I but not apo A-II. A majority of studies support the fact that LpA-I is more effective than LpA-I:A-II in promoting cellular cholesterol efflux, the first step in reverse cholesterol transport. Studies in transgenic animals have revealed that the gene transfer of human apo A-I in mice and rabbits increases plasma apo A-I and HDL cholesterol levels and particularly apo A-I-rich HDL particle concentrations, leading to inhibition of the development of dietary or genetically induced atherosclerosis. On the other hand, gene transfer of apo A-II in mice gives conflicting results. The conclusions of some experiments indicate either an atherogenic, or a poorly anti-atherogenic, or even a strongly anti-atherogenic role for apo A-II and for apo A-II-rich HDL lipoproteins. Although these experimental results have been obtained in animals, they confirm previous studies obtained in human clinical studies, indicating that apo A-I-rich HDL (tested as LpA-I in clinical studies) are generally strong plasma markers of atherosclerosis protection while the clinical significance of apo A-I + apo A-II HDL (tested as LpA-I:A-II in clinical studies) is more controversial. The introduction of immunological methods to measure LpA-I and LpA-I:A-II levels in blood make large-scale studies feasible to confirm the clinical significance of these HDL particles.

Haemophilia A gene therapy

Gene therapy for haemophilia A would represent a significant improvement over the current treatment by providing prophylactic expression of FVIII and correction of the coagulation defect. Furthermore, a gene therapy protocol allowing simple, infrequent vector administration may extend haemophilia treatment to remote locations world-wide that currently lack access to FVIII replacement therapy. Within the last half decade, significant progress has been made on the development of gene therapy for the treatment of haemophilia A. Recent achievements include high level clotting factor expression in mice, dogs, and monkeys as well as phenotypic correction in haemophiliac mice and dogs. With the efforts that are currently directed toward the improvement of gene transfer vectors and the development of technologies to enable sustained clotting factor expression, gene therapy for haemophilia A will ultimately become a reality.

Transgenesis in rats: technical aspects and models

The production of transgenic rats by DNA-microinjection into fertilized ova has now become an established procedure, although fewer than 20 lines have been described during the last 5 years. Overall, transgenic rats remain more difficult to produce than transgenic mice, but satisfactory yields have been obtained by several laboratories. A review of the methods used to generate transgenic rats shows considerable variation between different laboratories, particularly in choice of strain, superovulation protocols and the use of embryo culture before reimplantation. In some instances, the production of transgenic rats has provided data that are new and relevant, compared to data obtained in mice bearing the same transgene. Models have been developed for human diseases such as hypertension and autoimmunity, and applications have been found in the study of carcinogenesis and in pharmacological research. Transgenic rat technology also opens up interesting perspectives for transplantation research, in which microsurgery is an essential procedure. Intensive research is in progress in several laboratories to produce rat embryonic stem (ES) cell lines, but existing lines have not participated in germ line formation a prerequisite for their use in gene knock out experiments.

High-level tissue-specific expression of functional human factor VIII in mice

Hemophilia A results from subnormal levels of blood coagulation factor VIII (FVIII) and is an attractive target for gene therapy. However, progress has been impeded by features of FVIII biology such as low mRNA accumulation and the instability of the protein. We have shown previously that a FVIII adenoviral vector, Av1ALH81, allowed high-level expression of human FVIII in mice sustained for several weeks. Here, we have generated a second FVIII adenoviral vector, Av1ALAPH81, in which an intron was introduced into the FVIII expression cassette. Administration of Av1ALAPH81 to mice resulted in significantly increased FVIII plasma levels, 1,046 +/- 163 ng/ml compared to 307 +/- 93 ng/ml of FVIII detected in mice that received Av1ALH81. Normal FVIII levels in humans are 100-200 ng/ml and therapeutic levels are as low as 10 ng/ml. Therapeutic levels are defined as the amount of FVIII necessary to convert severe hemophilia to a moderate or mild hemophiliac condition. The increased potency of the second FVIII adenoviral vector allowed the administration of significantly lower, less toxic vector doses, while retaining the potential for high FVIII expression. Furthermore, we demonstrate that adenoviral-mediated expression of human FVIII can be limited to the liver by inclusion of a liver-specific promoter, thereby achieving the first step in regulated expression of human FVIII in vivo.

Transgenic animals as models for human disease

Since its first description in 1981 (1), transgenic technology has greatly influenced the focus and direction pace of biomedical research. Introduction of foreign DNA into the genome of animals by microinjection into fertilized oocytes is now used in almost every field of research spanning from oncology, immunology and neurology to cardiovascular medicine. The ability to integrate genes in the germline and their successful expression in the host provides an opportunity to study the role of a certain gene in the initiation and propagation of disease. Transgenic methodology serves as the link between molecular biology, introducing in vitro a defined genetic modification and whole animal physiology, with the resulting in vivo alteration of body function. This potential has been exploited to study the pathophysiological role of human genes. Transgenic animals have been used to study aspects of tumor development, immune regulation, cardiovascular development and atherosclerosis. These studies have provided new insights into the genetic origin of certain diseases and have improved our understanding of pathological processes on the cellular level. As a future goal, these studies may also serve the development of new diagnostic tools or novel therapeutic strategies such as gene therapy.

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.

Transgenesis in nonmurine species

Although the mouse remains the species of choice for most transgenic experimentation, it may be preferable or even necessary to use alternative species for certain applications. We review the strategies by which transgenic technology has been applied to other animals, specifically, the rat, rabbit, pig, sheep, goat, and cow. Additionally, we outline the potential applications of alternative transgenic species with reference to the field of hypertension and cardiovascular research.

Transgenic mouse models of lipoprotein metabolism and atherosclerosis

Lipoprotein transport genes have either been added to the germ line of mice by transgenic techniques or knocked out by homologous recombination in embryonic stem cells. The resultant over- or underexpression of these genes has resulted in new insights about how these genes function in the body and their role in lipoprotein metabolism. Either singly or in combination, these genetic modifications can be used to engineer the mouse to make it a better model for human lipoprotein disorders and atherosclerosis.