Familial hypercholesterolemia and atherosclerosis in cloned minipigs created by DNA transposition of a human PCSK9 gain-of-function mutant

Porcine oocyte mtDNA copy number is high or low depending on the donor

Oocyte capacity is relevant in understanding decreasing female fertility and in the use of assisted reproductive technologies in human and farm animals. Mitochondria are important to the development of a functionally good oocyte and the oocyte mtDNA copy number has been introduced as a useful parameter for prediction of oocyte competence. The aim of this study was to investigate: (i) if the oocyte donor has an influence on its oocyte's mtDNA copy number; and (ii) the relation between oocyte size and mtDNA copy number using pre- and postpubertal pig oocytes. Cumulus-oocyte complexes were collected from individual donor pigs. The oocytes were allocated into different size-groups, snap-frozen and single-oocyte mtDNA copy number was estimated by quantitative real-time PCR using the genes ND1 and COX1. Results showed that mean mtDNA copy number in oocytes from any individual donor could be categorized as either 'high' (≥100,000) or 'low' (<100,000) with no difference in threshold between pre- and postpubertal oocytes. No linear correlation was detected between oocyte size and mtDNA copy number within pre- and postpubertal oocytes. This study demonstrates the importance of the oocyte donor in relation to oocyte mtDNA copy number, irrespectively of the donor's puberty status and the oocyte's growth stage. Observations from this study facilitate both further investigations of the importance of mtDNA copy number and the unravelling of relations between different mitochondrial parameters and oocyte competence.

Myocardial and Peripheral Ischemia Causes an Increase in Circulating Pregnancy-Associated Plasma Protein-A in Non-atherosclerotic, Non-heparinized Pigs

The usefulness of circulating pregnancy-associated plasma protein-A (PAPP-A) as a biomarker for acute coronary syndrome (ACS) is widely debated. We used the pig as a model to assess PAPP-A dynamics in the setting of myocardial ischemia. Induction of myocardial ischemia by ligation of the left anterior descending (LAD) coronary artery caused a systemic rise in PAPP-A. However, the ischemic myocardium was excluded as the source of PAPP-A. Interestingly, induction of ischemia in peripheral tissues by ligation of the left femoral artery caused a systemic rise in PAPP-A originating from the left hind limb. This is the first study to demonstrate PAPP-A elevations in the absence of atherosclerosis or heparin during myocardial ischemia. Our findings thus add to the current discussion of the usefulness of PAPP-A as a biomarker for ACS.

Postmortem findings in cloned and transgenic piglets dead before weaning

Important factors contributing to the well-known high mortality of piglets produced by SCNT are gross malformations of vital organs. The aim of the present retrospective study was to describe malformations found in cloned piglets, transgenic or not, dying or culled before weaning on Day 28. Large White (LW) embryos were transferred to 78 LW recipients, while 72 recipients received Göttingen embryos (67 transgenic and five not transgenic) and 56 received Yucatan embryos (43 transgenic and 13 not transgenic). Overall pregnancy rate was 76%, and there were more abortions in recipients with minipig embryos than in those with LW embryos (26% and 24% vs. 6%). Piglets (n = 815) were born from 128 sows with 6.5 ± 0.4 full-born piglets per litter. The overall rate of stillborn piglets was 21% of all born with the number of stillborn piglets ranging from one to nine in a litter. The mortality of the surviving piglets during the first month was 48%. Thus, altogether 58% of the full-born piglets died before weaning. In 87 of the 128 litters (68%), one to 12 of the piglets showed major or minor malformations. Malformations were found in 232 piglets (29.5% of all born). A single malformation was registered in 152 piglets, but several piglets showed two (n = 58) or more (n = 23) malformations (7.4% and 2.8% of all born, respectively). A significantly higher malformation rate was found in transgenic Göttingen and Yucatan piglets (32% and 46% of all born, respectively) than in nontransgenic LW (17%). There was a gender difference in the transgenic minipigs because male piglets had a higher rate of malformations (49.1%) than females (29.7%). The most common defects in the cloned piglets were in the digestive (12.2%), circulatory (9.4%), reproductive (11.3%), and musculoskeletal (9.1%) systems. Malformations of the musculoskeletal system were most frequent in Göttingen (16.3% vs. approximately 5.5% in the two other breeds), whereas abnormal cardiopulmonary systems were most frequent in Yucatan piglets (26.9% vs. 2.1% in LW and 5.3% in Göttingen). In conclusion, these results show that pig cloning results in a considerable loss of piglets and that many of these can be related to various malformations that all are also seen in noncloned piglets. Because approximately half of the cloned piglets still survive, even with eventual unknown minor malformations, use of pigs as models for human diseases is still realistic. However, continued efforts are needed to further reduce the level of malformations.

Göttingen minipig model of diet-induced atherosclerosis: influence of mild streptozotocin-induced diabetes on lesion severity and markers of inflammation evaluated in obese, obese and diabetic, and lean control animals

Background

From a pharmacological perspective, readily-available, well-characterized animal models of cardiovascular disease, including relevant in vivo markers of atherosclerosis are important for evaluation of novel drug candidates. Furthermore, considering the impact of diabetes mellitus on atherosclerosis in human patients, inclusion of this disease aspect in the characterization of a such model, is highly relevant. The objective of this study was to evaluate the effect of mild streptozotocin-induced diabetes on ex- and in vivo end-points in a diet-induced atherosclerotic minipig model.

Methods

Castrated male Göttingen minipigs were fed standard chow (CD), atherogenic diet alone (HFD) or with superimposed mild streptozotocin-induced diabetes (HFD-D). Circulating markers of inflammation (C-reactive protein (CRP), oxidized low-density lipoprotein (oxLDL), plasminogen activator inhibitor-1, lipid and glucose metabolism were evaluated together with coronary and aortic atherosclerosis after 22 or 43 diet-weeks. Group differences were evaluated by analysis of variance for parametric data and Kruskal–Wallis test for non-parametric data. For qualitative assessments, Fisher’s exact test was applied. For all analyses, p < 0.05 was considered statistically significant.

Results

Overall, HFD and HFD-D displayed increased CRP, oxLDL and lipid parameters compared to CD at both time points. HFD-D displayed impaired glucose metabolism as compared to HFD and CD. Advanced atherosclerotic lesions were observed in both coronary arteries and aorta of HFD and HFD-D, with more advanced plaque findings in the aorta but without differences in lesion severity or distribution between HFD and HFD-D. Statistically, triglyceride was positively (p = 0.0039), and high-density lipoprotein negatively (p = 0.0461) associated with aortic plaque area.

Conclusions

In this model, advanced coronary and aortic atherosclerosis was observed, with increased levels of inflammatory markers, clinically relevant to atherosclerosis. No effect of mild streptozotocin-induced diabetes was observed on plaque area, lesion severity or inflammatory markers.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0670-2) contains supplementary material, which is available to authorized users.

Highly efficient CRISPR/Cas9-mediated transgene knockin at the H11 locus in pigs

Transgenic pigs play an important role in producing higher quality food in agriculture and improving human health when used as animal models for various human diseases in biomedicine. Production of transgenic pigs, however, is a lengthy and inefficient process that hinders research using pig models. Recent applications of the CRISPR/Cas9 system for generating site-specific gene knockout/knockin models, including a knockout pig model, have significantly accelerated the animal model field. However, a knockin pig model containing a site-specific transgene insertion that can be passed on to its offspring remains lacking. Here, we describe for the first time the generation of a site-specific knockin pig model using a combination of CRISPR/Cas9 and somatic cell nuclear transfer. We also report a new genomic “safe harbor” locus, named pH11, which enables stable and robust transgene expression. Our results indicate that our CRISPR/Cas9 knockin system allows highly efficient gene insertion at the pH11 locus of up to 54% using drug selection and 6% without drug selection. We successfully inserted a gene fragment larger than 9 kb at the pH11 locus using the CRISPR/Cas9 system. Our data also confirm that the gene inserted into the pH11 locus is highly expressed in cells, embryos and animals.

Prospect and progress of gene therapy in treating atherosclerosis

INTRODUCTION

Despite considerable improvements in therapies, atherosclerotic cardiovascular diseases remain the leading cause of death worldwide. Therefore, in addition to current treatment options, new therapeutic approaches are still needed.

AREAS COVERED

In this review, novel gene and RNA interference-based therapy approaches and promising target genes for treating atherosclerosis are addressed. In addition, relevant animal models for the demonstration of the efficacy of different gene therapy applications, and current progress toward more efficient, targeted and safer gene transfer vectors are reviewed.

EXPERT OPINION

Atherosclerosis represents a complex multifactorial disease that is dependent on the interplay between lipoprotein metabolism, cellular reactions and inflammation. Recent advances and novel targets, especially in the field of RNA interference-based therapies, are very promising. However, it should be noted that the modulation of a particular gene is not as clearly associated with a complex polygenic disease as it is in the case of monogenic diseases. A deeper understanding of molecular mechanisms of atherosclerosis, further progress in vector development and the demonstration of treatment efficacy in relevant animal models will be required before gene therapy of atherosclerosis meets its clinical reality.

Animal models of coronary heart disease

Cardiovascular disease, predominantly coronary heart disease and stroke, leads to high morbidity and mortality not only in developed worlds but also in underdeveloped regions. The dominant pathologic foundation for cardiovascular disease is atherosclerosis and as to coronary heart disease, coronary atherosclerosis and resulting lumen stenosis, even total occlusions. In translational research, several animals, such as mice, rabbits and pigs, have been used as disease models of human atherosclerosis and related cardiovascular disorders. However, coronary lesions are either naturally rare or hard to be fast induced in these models, hence, coronary heart disease induction mostly relies on surgical or pharmaceutical interventions with no or limited primary coronary lesions, thus unrepresentative of human coronary heart disease progression and pathology. In this review, we will describe the progress of animal models of coronary heart disease following either spontaneous or diet-accelerated coronary lesions.

Diabetes with poor glycaemic control does not promote atherosclerosis in genetically modified hypercholesterolaemic minipigs

AIMS/HYPOTHESIS

Diabetes is associated with an increased risk of atherosclerotic cardiovascular disease, but whether there is a direct and independent role for impaired glucose control in atherogenesis remains uncertain. We investigated whether diabetes with poor glycaemic control would accelerate atherogenesis in a novel pig model of atherosclerosis, the D374Y-PCSK9(+) transgenic minipig.

METHODS

Nineteen minipigs were fed a cholesterol-enriched, high-fat diet; ten of these pigs were injected with streptozotocin to generate a model of diabetes. Restricted feeding was implemented to control the pigs' weight gain and cholesterol intake. After 49 weeks of high-fat feeding, the major arteries were harvested for a detailed analysis of the plaque burden and histological plaque type.

RESULTS

Stable hyperglycaemia was achieved in the diabetic minipigs, while the plasma total and LDL-cholesterol and creatinine levels were unaffected. Diabetes failed to increase atherosclerosis in any of the vessels examined. The plaque burden in the aorta and right coronary artery was comparable between the groups, and was even reduced in the left anterior descending (LAD) coronary and iliofemoral arteries in the diabetic pigs compared with the controls. The distribution of plaque types and the collagen and macrophage contents were similar between the groups, except for a reduced infiltration of macrophages in the LAD arteries of the diabetic pigs.

CONCLUSIONS/INTERPRETATION

Poorly controlled diabetes with no alterations in plasma cholesterol or creatinine concentrations did not augment the plaque burden or promote the development of more advanced lesions in this large-animal model of human-like atherosclerosis. This is consistent with clinical studies in patients with type 1 diabetes, indicating that hyperglycaemia per se is not an independent promoter of atherosclerotic disease, but that other diabetes-associated risk factors are important.

Inducing Persistent Flow Disturbances Accelerates Atherogenesis and Promotes Thin Cap Fibroatheroma Development in D374Y-PCSK9 Hypercholesterolemic Minipigs

BACKGROUND

Although disturbed flow is thought to play a central role in the development of advanced coronary atherosclerotic plaques, no causal relationship has been established. We evaluated whether inducing disturbed flow would cause the development of advanced coronary plaques, including thin cap fibroatheroma.

METHODS AND RESULTS

D374Y-PCSK9 hypercholesterolemic minipigs (n=5) were instrumented with an intracoronary shear-modifying stent (SMS). Frequency-domain optical coherence tomography was obtained at baseline, immediately poststent, 19 weeks, and 34 weeks, and used to compute shear stress metrics of disturbed flow. At 34 weeks, plaque type was assessed within serially collected histological sections and coregistered to the distribution of each shear metric. The SMS caused a flow-limiting stenosis, and blood flow exiting the SMS caused regions of increased shear stress on the outer curvature and large regions of low and multidirectional shear stress on the inner curvature of the vessel. As a result, plaque burden was ≈3-fold higher downstream of the SMS than both upstream of the SMS and in the control artery (P<0.001). Advanced plaques were also primarily observed downstream of the SMS, in locations initially exposed to both low (P<0.002) and multidirectional (P<0.002) shear stress. Thin cap fibroatheroma regions demonstrated significantly lower shear stress that persisted over the duration of the study in comparison with other plaque types (P<0.005).

CONCLUSIONS

These data support a causal role for lowered and multidirectional shear stress in the initiation of advanced coronary atherosclerotic plaques. Persistently lowered shear stress appears to be the principal flow disturbance needed for the formation of thin cap fibroatheroma.

Production of Cloned Miniature Pigs Expressing High Levels of Human Apolipoprotein(a) in Plasma

High lipoprotein(a) [Lp(a)] levels are a major risk factor for the development of atherosclerosis. However, because apolipoprotein(a) [apo(a)], the unique component of Lp(a), is found only in primates and humans, the study of human Lp(a) has been hampered due to the lack of appropriate animal models. Using somatic cell nuclear transfer (SCNT) techniques, we produced transgenic miniature pigs expressing human apo(a) in the plasma. First, we placed the hemagglutinin (HA)-tagged cDNA of human apo(a) under the control of the β-actin promoter and cytomegalovirus enhancer, and then introduced this construct into kidney epithelial cells. Immunostaining of cells with anti-HA antibody allowed identification of cells stably expressing apo(a); one of the positive clones was used to provide donor cells for SCNT, yielding blastocysts that expressed apo(a). Immunohistochemical analysis of tissue sections and RT-PCR analysis of total RNA from organs of cloned piglet revealed that apo(a) is expressed in various tissues/organs including heart, liver, kidney, and intestine. More importantly, a transgenic line exhibited a high level (>400 mg/dL) of Lp(a) in plasma, and the transgenic apo(a) gene was transmitted to the offspring. Thus, we generated a human apo(a)–transgenic miniature pig that can be used as a model system to study advanced atherosclerosis related to human disease. The anatomical and physiological similarities between the swine and human cardiovascular systems will make this pig model a valuable source of information on the role of apo(a) in the formation of atherosclerosis, as well as the mechanisms underlying vascular health and disease.

Genetically modified pigs to model human diseases

Genetically modified mice are powerful tools to investigate the molecular basis of many human diseases. Mice are, however, of limited value for preclinical studies, because they differ significantly from humans in size, general physiology, anatomy and lifespan. Considerable efforts are, thus, being made to develop alternative animal models for a range of human diseases. These promise powerful new resources that will aid the development of new diagnostics, medicines and medical procedures. Here, we provide a comprehensive review of genetically modified porcine models described in the scientific literature: various cancers, cystic fibrosis, Duchenne muscular dystrophy, autosomal polycystic kidney disease, Huntington’s disease, spinal muscular atrophy, haemophilia A, X-linked severe combined immunodeficiency, retinitis pigmentosa, Stargardt disease, Alzheimer’s disease, various forms of diabetes mellitus and cardiovascular diseases.

New drugs for treating dyslipidemia: beyond statins

Statins have been shown to be very effective and safe in numerous randomized clinical trials, and became the implacable first-line treatment against atherogenic dyslipidemia. However, even with optimal statin treatment, 60% to 80% of residual cardiovascular risk still exists. The patients with familial hypercholesterolemia which results in extremely high level of low density lipoprotein cholesterol (LDL-C) level and the patients who are intolerant or unresponsive to statins are the other hurdles of statin treatment. Recently, new classes of lipid-lowering drugs have been developed and some of them are available for the clinical practice. The pro-protein convertase subtilisin/kexintype 9 (PCSK9) inhibitor increases the expression of low density lipoprotein (LDL) receptor in hepatocytes by enhancing LDL receptor recycling. The microsomal triglyceride transport protein (MTP) inhibitor and antisense oligonucleotide against apolipoprotein B (ApoB) reduce the ApoB containing lipoprotein by blocking the hepatic very low density lipoprotein synthesis pathway. The apolipoprotein A1 (ApoA1) mimetics pursuing the beneficial effect of high density lipoprotein cholesterol and can reverse the course of atherosclerosis. ApoA1 mimetics had many controversial clinical data and need more validation in humans. The PCSK9 inhibitor recently showed promising results of significant LDL-C lowering in familial hypercholesterolemia (FH) patients from the long-term phase III trials. The MTP inhibitor and antisesnse oligonucleotide against ApoB were approved for the treatment of homozygous FH but still needs more consolidated evidences about hepatic safety such as hepatosteatosis. We would discuss the benefits and concerns of these new lipid-lowering drugs anticipating additional benefits beyond statin treatment.

Effect of testosterone deficiency on cholesterol metabolism in pigs fed a high-fat and high-cholesterol diet

Background

Testosterone deficiency is associated with increased serum cholesterol levels. However, how testosterone deficiency precisely affects cholesterol metabolism remains unclear. Therefore, in the current study, we examined the effect of testosterone deficiency on cholesterol metabolism and liver gene expression in pigs fed a high-fat and high-cholesterol (HFC) diet.

Methods

Sexually mature male miniature pigs (6–7 months old) were randomly divided into 3 groups as follows: intact male pigs fed an HFC diet (IM + HFC), castrated male pigs fed an HFC diet (CM + HFC), and castrated pigs with testosterone replacement fed an HFC diet (CM + HFC + T). Serum testosterone levels and lipid profiles were measured, and gene expression levels associated with hepatic cholesterol metabolism were determined. Furthermore, total hepatic cholesterol contents and the activities of enzymes mediating hepatic cholesterol metabolism were measured.

Results

Serum testosterone levels were significantly decreased in CM + HFC pigs, and testosterone replacement attenuated castration-induced testosterone deficiency. Castration significantly increased the serum levels of total cholesterol, low-density lipoprotein cholesterol and triglycerides, as well as hepatic lipid contents in pigs fed an HFC diet. Compared with IM + HFC and CM + HFC + T pigs, low-density lipoprotein receptor (LDLR) mRNA expression and protein levels were significantly decreased in the livers of CM + HFC pigs. In contrast, we found that compared with IM + HFC pigs, hepatic proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA and serum PCSK9 protein levels were significantly increased in CM + HFC pigs. Moreover, testosterone treatment reversed the increase in PCSK9 expression in CM + HFC pigs. However, neither castration nor testosterone replacement affected the expression of the other hepatic genes that were tested.

Conclusions

This study demonstrated that castration-induced testosterone deficiency caused severe hypercholesterolemia in pigs fed an HFC diet; furthermore, these effects could be reversed by testosterone replacement therapy. Altered hepatic PCSK9 and LDLR expression, resulting in reduced LDL-cholesterol clearance, may contribute to the increased serum cholesterol levels induced by testosterone deficiency and an HFC diet. These results deepen our understanding of the underlying molecular mechanisms that mediate the effects of testosterone deficiency on cholesterol metabolism.

Molecular and cellular function of the proprotein convertase subtilisin/kexin type 9 (PCSK9)

The proprotein convertase subtilisin/kexin type 9 (PCSK9) has emerged as a promising treatment target to lower serum cholesterol, a major risk factor of cardiovascular diseases. Gain-of-function mutations of PCSK9 are associated with hypercholesterolemia and increased risk of cardiovascular events. Conversely, loss-of-function mutations cause low-plasma LDL-C levels and a reduction of cardiovascular risk without known unwanted effects on individual health. Experimental studies have revealed that PCSK9 reduces the hepatic uptake of LDL-C by increasing the endosomal and lysosomal degradation of LDL receptors (LDLR). A number of clinical studies have demonstrated that inhibition of PCSK9 alone and in addition to statins potently reduces serum LDL-C concentrations. This review summarizes the current data on the regulation of PCSK9, its molecular function in lipid homeostasis and the emerging evidence on the extra-hepatic effects of PCSK9.

Selection of pre- versus postpubertal pig oocytes for parthenogenetic activation and somatic cell nuclear transfer

Pig oocytes have been used increasingly for in vitro production techniques in recent years. The slaughterhouse-derived oocytes that are often used are mostly of prepubertal origin. The aims of the present study were to compare the developmental competence between pre- and postpubertal pig oocytes, and to develop a simple and practical method for the selection of prepubertal pig oocytes for parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT) based on oocyte morphology after IVM and oocyte inside zona pellucida (ZP) diameter (‘small’ ≤110 µm; ‘medium’ >110 µm; ‘large’ ≥120 µm). Meiotic competence and blastocyst rates after PA and SCNT of prepubertal oocytes increased with oocyte size, with the large prepubertal oocytes reaching a level similar to postpubertal oocytes after SCNT. Blastocyst cell number was not related to oocyte inside ZP diameter and oocyte donor to the same extent as blastocyst rate. Very low blastocyst rates were obtained after PA of morphologically bad pre- and postpubertal oocytes. In conclusion, measurement of inside ZP diameter combined with morphological selection is useful to remove incompetent oocytes. Further studies are needed to clarify the relative importance of cytoplasmic volume and stage in oocyte growth phase.

In vitro manipulation techniques of porcine embryos: a meta-analysis related to transfers, pregnancies and piglets

During the last 17 years, considerable advancements have been achieved in the production of pigs, transgenic and non-transgenic, by methods of somatic cell nuclear transfer, in vitro fertilisation, intracytoplasmic sperm injection, microinjection and sperm-mediated gene transfer by artificial insemination. Therefore, a review of the overall efficiency for the developmental competence of embryos produced by these in vitro methods would be useful in order to obtain a more thorough overview of this growing area with respect to its development and present status. In this review a meta-analysis was used to analyse data collected from all published articles with a focus on zygotes and embryos for transfer, pregnancy, full-term development and piglets born. It was generally concluded that an increasing level of in vitro manipulation of porcine embryos decreased the overall efficiency for production of piglets. The techniques of nuclear transfer have been developed markedly through the increasing number of studies performed, and the results have become more stable. Prolonged in vitro culture period did not lead to any negative effect on nuclear transfer embryos after their transfer and it resulted in a similar or even higher litter size. More complete information is needed in future scientific articles about these in vitro manipulation techniques to establish a more solid basis for the evaluation of their status and to reveal and further investigate any eventual problems.

Current progress of genetically engineered pig models for biomedical research

The first transgenic pigs were generated for agricultural purposes about three decades ago. Since then, the micromanipulation techniques of pig oocytes and embryos expanded from pronuclear injection of foreign DNA to somatic cell nuclear transfer, intracytoplasmic sperm injection-mediated gene transfer, lentiviral transduction, and cytoplasmic injection. Mechanistically, the passive transgenesis approach based on random integration of foreign DNA was developed to active genetic engineering techniques based on the transient activity of ectopic enzymes, such as transposases, recombinases, and programmable nucleases. Whole-genome sequencing and annotation of advanced genome maps of the pig complemented these developments. The full implementation of these tools promises to immensely increase the efficiency and, in parallel, to reduce the costs for the generation of genetically engineered pigs. Today, the major application of genetically engineered pigs is found in the field of biomedical disease modeling. It is anticipated that genetically engineered pigs will increasingly be used in biomedical research, since this model shows several similarities to humans with regard to physiology, metabolism, genome organization, pathology, and aging.

Increasing efficiency in production of cloned piglets

The low efficiency in obtaining piglets after production of cloned embryos was challenged in two steps-first by performing in vitro culture for 5-6 days after cloning to obtain later-stage embryos for more precise selection for transfer, and second by reducing the number of embryos transferred per recipient sow. The data set consisted of combined results from a 4-year period where cloning was performed to produce piglets that were transgenic for important human diseases. For this, different transgenes and cell types were used, and the cloning work was performed by several persons using oocytes from different pig breeds, but following a standardized and optimized protocol. Results showed that in vitro culture is possible with a relatively stable rate of transferable embryos around 41% and a pregnancy rate around 90%. Furthermore, a reduction from around 80 embryos to 40 embryos transferred per recipient was possible without changing the efficiency of around 14% (piglets born out of embryos transferred). It was concluded that this approach can increase the efficiency in obtaining piglets by means of in vitro culture and selection of high-quality embryos with subsequent transfer into more recipients. Such changes can also reduce the need for personnel, time, and material when working with this technology.

Driving DNA transposition by lentiviral protein transduction

Gene vectors derived from DNA transposable elements have become powerful molecular tools in biomedical research and are slowly moving into the clinic as carriers of therapeutic genes. Conventional uses of DNA transposon-based gene vehicles rely on the intracellular production of the transposase protein from transfected nucleic acids. The transposase mediates mobilization of the DNA transposon, which is typically provided in the context of plasmid DNA. In recent work, we established lentiviral protein transduction from Gag precursors as a new strategy for direct delivery of the transposase protein. Inspired by the natural properties of infecting viruses to carry their own enzymes, we loaded lentivirus-derived particles not only with vector genomes carrying the DNA transposon vector but also with hundreds of transposase subunits. Such particles were found to drive efficient transposition of the piggyBac transposable element in a range of different cell types, including primary cells, and offer a new transposase delivery approach that guarantees short-term activity and limits potential cytotoxicity. DNA transposon vectors, originally developed and launched as a non-viral alternative to viral integrating vectors, have truly become viral. Here, we briefly review our findings and speculate on the perspectives and potential advantages of transposase delivery by lentiviral protein transduction.

PCSK9: a key modulator of cardiovascular health

Since the discovery of proprotein convertase subtilisin kexin 9 (PCSK9) in 2003, this PC has attracted a lot of attention from the scientific community and pharmaceutical companies. Secreted into the plasma by the liver, the proteinase K-like serine protease PCSK9 binds the low-density lipoprotein (LDL) receptor at the surface of hepatocytes, thereby preventing its recycling and enhancing its degradation in endosomes/lysosomes, resulting in reduced LDL-cholesterol clearance. Surprisingly, in a nonenzymatic fashion, PCSK9 enhances the intracellular degradation of all its target proteins. Rare gain-of-function PCSK9 variants lead to higher levels of LDL-cholesterol and increased risk of cardiovascular disease; more common loss-of-function PCSK9 variants are associated with reductions in both LDL-cholesterol and risk of cardiovascular disease. It took 9 years to elaborate powerful new PCSK9-based therapeutic approaches to reduce circulating levels of LDL-cholesterol. Presently, PCSK9 monoclonal antibodies that inhibit its function on the LDL receptor are evaluated in phase III clinical trials. This review will address the biochemical, genetic, and clinical aspects associated with PCSK9's biology and pathophysiology in cells, rodent and human, with emphasis on the clinical benefits of silencing the expression/activity of PCSK9 as a new modality in the treatment of hypercholesterolemia and associated pathologies.

Genetic experimental preparations for studying atherosclerosis

Atherosclerosis is a pathological process with several inputs (biological, chemical, physiological, and others) interacting slowly over a lifetime leading to coronary artery disease, significant morbidity, and a limited lifespan. Over the past two decades, biologists have used experimental preparations from cells, animals, and man to understand the biology of atherosclerosis. Much has been discovered but our use of the standard gene-targeted experimental preparations is now nearing its limit. Better preparations to answer the remaining questions in the field of atherosclerosis biology are needed.

Targeted disruption of LDLR causes hypercholesterolemia and atherosclerosis in Yucatan miniature pigs

Recent progress in engineering the genomes of large animals has spurred increased interest in developing better animal models for diseases where current options are inadequate. Here, we report the creation of Yucatan miniature pigs with targeted disruptions of the low-density lipoprotein receptor (LDLR) gene in an effort to provide an improved large animal model of familial hypercholesterolemia and atherosclerosis. Yucatan miniature pigs are well established as translational research models because of similarities to humans in physiology, anatomy, genetics, and size. Using recombinant adeno-associated virus-mediated gene targeting and somatic cell nuclear transfer, male and female LDLR+/− pigs were generated. Subsequent breeding of heterozygotes produced LDLR−/− pigs. When fed a standard swine diet (low fat, no cholesterol), LDLR+/− pigs exhibited a moderate, but consistent increase in total and LDL cholesterol, while LDLR−/− pigs had considerably elevated levels. This severe hypercholesterolemia in homozygote animals resulted in atherosclerotic lesions in the coronary arteries and abdominal aorta that resemble human atherosclerosis. These phenotypes were more severe and developed over a shorter time when fed a diet containing natural sources of fat and cholesterol. LDLR-targeted Yucatan miniature pigs offer several advantages over existing large animal models including size, consistency, availability, and versatility. This new model of cardiovascular disease could be an important resource for developing and testing novel detection and treatment strategies for coronary and aortic atherosclerosis and its complications.

PCSK9: From discovery to therapeutic applications

The proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates cholesterol metabolism mainly by targeting the low-density lipoprotein receptor (LDLR) for degradation in the liver. Gain-of-function mutations in PCSK9 are one of the genetic causes of autosomal dominant hypercholesterolaemia. Conversely, loss-of-function mutations are associated with lower concentrations of LDL cholesterol (LDL-C) and reduced coronary heart disease. As these loss-of-function mutations are not associated with apparent deleterious effects, PCSK9 inhibition is an attractive new strategy for lowering LDL-C concentration. Among the various approaches to PCSK9 inhibition, human data are only available for inhibition of PCSK9 binding to LDLR by monoclonal antibodies. In phase II studies, the two most advanced monoclonal antibodies in development (alirocumab and evolocumab) decreased atherogenic lipoproteins very effectively and were well tolerated. A dramatic decrease in LDL-C up to 70% can be obtained with the most efficacious doses. Efficacy has been evaluated so far in addition to statins in hypercholesterolaemic patients with or without familial hypercholesterolaemia, in patients with intolerance to statin therapy and in monotherapy. Large phase III programmes are ongoing to evaluate the long-term efficacy and safety of these very promising new agents.

DNA transposition by protein transduction of the piggyBac transposase from lentiviral Gag precursors

DNA transposon-based vectors have emerged as gene vehicles with a wide biomedical and therapeutic potential. So far, genomic insertion of such vectors has relied on the co-delivery of genetic material encoding the gene-inserting transposase protein, raising concerns related to persistent expression, insertional mutagenesis and cytotoxicity. This report describes potent DNA transposition achieved by direct delivery of transposase protein. By adapting integrase-deficient lentiviral particles (LPs) as carriers of the hyperactive piggyBac transposase protein (hyPBase), we demonstrate rates of DNA transposition that are comparable with the efficiency of a conventional plasmid-based strategy. Embedded in the Gag polypeptide, hyPBase is robustly incorporated into LPs and liberated from the viral proteins by the viral protease during particle maturation. We demonstrate lentiviral co-delivery of the transposase protein and vector RNA carrying the transposon sequence, allowing robust DNA transposition in a variety of cell types. Importantly, this novel delivery method facilitates a balanced cellular uptake of hyPBase, as shown by confocal microscopy, and allows high-efficiency production of clones harboring a single transposon insertion. Our findings establish engineered LPs as a new tool for transposase delivery. We believe that protein transduction methods will increase applicability and safety of DNA transposon-based vector technologies.

Developmental potential and kinetics of pig embryos with different cytoplasmic volume

The effects of cytoplasmic volumes on development and developmental kinetics of in vitro produced porcine embryos were investigated. During hand-made cloning (HMC), selected cytoplasts were separated into two groups according to their size in relation to the initial oocyte: ~75% or ~50%. Following two fusion steps and activation (day 0), reconstructed embryos were cultured in vitro for 6 days. Cleavage rates on day 2 as well as blastocyst rates and cell numbers on day 6 were recorded. Results showed that embryo development was no different for ~50% versus ~75% cytoplasm at first fusion. This result was used in the following experiments, where the effect of varying cytoplasm volume in second fusion to obtain a final cytoplasm volume of ~75% to ~200% was tested. The results showed that the lowest quality was obtained when the final cytoplasm volume was ~75% and the highest quality at ~200% of the original oocyte. Similar results were observed in parthenogenetic (PA) embryos activated with different cytoplasmic volumes. A common pattern for the developmental kinetics of HMC and PA embryos was observed: the smaller group tended to have a longer time for the first two cell cycles, but subsequently a shorter time to form morula and blastocyst. In conclusion, the developmental kinetics of in vitro produced embryos was affected by the cytoplasm volume of the initial oocyte, and this further accounted for the developmental ability of the reconstructed embryos.

Molecular cloning and characterization of porcine Na⁺/K⁺-ATPase isoforms α1, α2, α3 and the ATP1A3 promoter

Na⁺/K⁺-ATPase maintains electrochemical gradients of Na⁺ and K⁺ essential for a variety of cellular functions including neuronal activity. The α-subunit of the Na⁺/K⁺-ATPase exists in four different isoforms (α1-α4) encoded by different genes. With a view to future use of pig as an animal model in studies of human diseases caused by Na⁺/K⁺-ATPase mutations, we have determined the porcine coding sequences of the α1-α3 genes, ATP1A1, ATP1A2, and ATP1A3, their chromosomal localization, and expression patterns. Our ATP1A1 sequence accords with the sequences from several species at five positions where the amino acid residue of the previously published porcine ATP1A1 sequence differs. These corrections include replacement of glutamine 841 with arginine. Analysis of the functional consequences of substitution of the arginine revealed its importance for Na⁺ binding, which can be explained by interaction of the arginine with the C-terminus, stabilizing one of the Na⁺ sites. Quantitative real-time PCR expression analyses of porcine ATP1A1, ATP1A2, and ATP1A3 mRNA showed that all three transcripts are expressed in the embryonic brain as early as 60 days of gestation. Expression of α3 is confined to neuronal tissue. Generally, the expression patterns of ATP1A1, ATP1A2, and ATP1A3 transcripts were found similar to their human counterparts, except for lack of α3 expression in porcine heart. These expression patterns were confirmed at the protein level. We also report the sequence of the porcine ATP1A3 promoter, which was found to be closely homologous to its human counterpart. The function and specificity of the porcine ATP1A3 promoter was analyzed in transgenic zebrafish, demonstrating that it is active and drives expression in embryonic brain and spinal cord. The results of the present study provide a sound basis for employing the ATP1A3 promoter in attempts to generate transgenic porcine models of neurological diseases caused by ATP1A3 mutations.

Development of transgenic minipigs with expression of antimorphic human cryptochrome 1

Minipigs have become important biomedical models for human ailments due to similarities in organ anatomy, physiology, and circadian rhythms relative to humans. The homeostasis of circadian rhythms in both central and peripheral tissues is pivotal for numerous biological processes. Hence, biological rhythm disorders may contribute to the onset of cancers and metabolic disorders including obesity and type II diabetes, amongst others. A tight regulation of circadian clock effectors ensures a rhythmic expression profile of output genes which, depending on cell type, constitute about 3-20% of the transcribed mammalian genome. Central to this system is the negative regulator protein Cryptochrome 1 (CRY1) of which the dysfunction or absence has been linked to the pathogenesis of rhythm disorders. In this study, we generated transgenic Bama-minipigs featuring expression of the Cys414-Ala antimorphic human Cryptochrome 1 mutant (hCRY1(AP)). Using transgenic donor fibroblasts as nuclear donors, the method of handmade cloning (HMC) was used to produce reconstructed embryos, subsequently transferred to surrogate sows. A total of 23 viable piglets were delivered. All were transgenic and seemingly healthy. However, two pigs with high transgene expression succumbed during the first two months. Molecular analyzes in epidermal fibroblasts demonstrated disturbances to the expression profile of core circadian clock genes and elevated expression of the proinflammatory cytokines IL-6 and TNF-α, known to be risk factors in cancer and metabolic disorders.

The biology of PCSK9 from the endoplasmic reticulum to lysosomes: new and emerging therapeutics to control low-density lipoprotein cholesterol

Proprotein convertase subtilisin/kexin type 9 (PCSK9) directly binds to the epidermal growth factor-like repeat A domain of low-density lipoprotein receptor and induces its degradation, thereby controlling circulating low-density lipoprotein cholesterol (LDL-C) concentration. Heterozygous loss-of-function mutations in PCSK9 can decrease the incidence of coronary heart disease by up to 88%, owing to lifelong reduction of LDL-C. Moreover, two subjects with PCSK9 loss-of-function mutations on both alleles, resulting in a total absence of functional PCSK9, were found to have extremely low circulating LDL-C levels without other apparent abnormalities. Accordingly, PCSK9 could represent a safe and effective pharmacological target to increase clearance of LDL-C and to reduce the risk of coronary heart disease. Recent clinical trials using anti-PCSK9 monoclonal antibodies that block the PCSK9:low-density lipoprotein receptor interaction were shown to considerably reduce LDL-C levels by up to 65% when given alone and by up to 72% in patients already receiving statin therapy. In this review, we will discuss how major scientific breakthroughs in PCSK9 cell biology have led to the development of new and forthcoming LDL-C-lowering pharmacological agents.

The promises of PCSK9 inhibition

PURPOSE OF REVIEW

In the past 10 years, the LDL receptor inhibitor proprotein convertase subtilisin kexin type 9 (PCSK9) has emerged as a validated target for lowering plasma LDL cholesterol levels. Here we review the most recent reports on PCSK9 out of a total of 500 publications published in print or online before March 2013 and indexed on PubMed.

RECENT FINDINGS

All published in 2012, phase I and II clinical trials demonstrate that fully human monoclonal antibodies targeting PCSK9 dramatically reduce LDL-C and enable patients to reach their target goals, without severe or serious safety issues.

SUMMARY

This review summarizes the discovery of PCSK9, its original mode of action as a secreted inhibitor of the LDL receptor, as well as its genetic regulation by statins. We then focus on the major results from the 2012 phase I and II PCSK9 inhibitor clinical trials. We also review the recent in-vivo studies demonstrating the potential cardiovascular benefits of long-term PCSK9 inhibition and discuss its potential side-effects.

Pig transgenesis by piggyBac transposition in combination with somatic cell nuclear transfer

The production of animals by somatic cell nuclear transfer (SCNT) is inefficient, with approximately 2% of micromanipulated oocytes going to term and resulting in live births. However, it is the most commonly used method for the generation of cloned transgenic livestock as it facilitates the attainment of transgenic animals once the nuclear donor cells are stably transfected and more importantly as alternatives methods of transgenesis in farm animals have proven even less efficient. Here we describe piggyBac-mediated transposition of a transgene into porcine primary cells and use of these genetically modified cells as nuclear donors for the generation of transgenic pigs by SCNT. Gene transfer by piggyBac transposition serves to provide an alternative approach for the transfection of nuclear donor cells used in SCNT.

Mighty minipig in fight against cardiovascular disease

A cloned transgenic minipig model of hypercholesterolemia and accelerated atherosclerosis could accelerate discovery of new therapies for atherosclerotic cardiovascular disease (Al-Mashhadi et al., this issue).

Relaxation of porcine retinal arterioles exposed to hypercholesterolemia in vivo is modified by hepatic LDL-receptor deficiency and diabetes mellitus

Metabolic disturbances in diabetes mellitus include changes in the type and concentration of lipids in the blood plasma which may contribute to the development of diabetic retinopathy. This disease is characterized by changes in retinal blood flow secondary to changes in the tone of retinal arterioles which is regulated by compounds such as adenosine, adenosine triphosphate (ATP), the glutamate agonist N-methyl-d-aspartate (NMDA) and prostaglandin E2 (PGE2). However, the relation between increased plasma low density lipoprotein (LDL) and tone regulation in retinal resistance vessels has not been studied in detail. Twelve male and nine female Yucatan minipigs overexpressing a gain-of-function mutant (D374Y) of the human gene PCSK9 that blocks LDL transport into the liver and twelve wild-type males were studied. The animals were fed a cholesterol rich diet from the age of 60 days, followed by induction of diabetes mellitus in twelve of the transgenic animals. The animals were sacrificed at a mean age of 51 weeks (range 26-60 weeks), followed by inspection and histological examination of retinal vessels, and examination of the changes in vascular tone induced by adenosine, ATP, NMDA and PGE2. In the transgenic pigs without diabetes mellitus ATP-induced relaxation was reduced in isolated arterioles, and a whitish infiltration in an arteriole was observed in 4/8 (50%) of the animals, whereas these changes were not found in the other groups. Histological examination of one of the infiltrations showed staining with Oil Red O representing foamy cells sub-endothelially in the vascular wall indicating atheromatosis. Adenosine, ATP and PGE2 induced a significant concentration-dependent relaxation of retinal arterioles in all groups. The presence of perivascular retinal tissue had no effect on the relaxing effect of adenosine, but increased the relaxing effect of ATP and PGE2 in the two transgenic animal groups, whereas NMDA had no significant effect on vascular tone in any of the groups. Relaxation of porcine retinal arterioles exposed to hypercholesterolemia in vivo is modified by hepatic LDL-receptor deficiency and diabetes mellitus. This suggests that transgenic animal models are suitable for studying the influence of systemic diseases on retinal vascular function.

Porcine models of accelerated coronary atherosclerosis: role of diabetes mellitus and hypercholesterolemia

Animal models of atherosclerosis have proven to be an invaluable asset in understanding the pathogenesis of the disease. However, large animal models may be needed in order to assess novel therapeutic approaches to the treatment of atherosclerosis. Porcine models of coronary and peripheral atherosclerosis offer several advantages over rodent models, including similar anatomical size to humans, as well as genetic expression and development of high-risk atherosclerotic lesions which are similar to humans. Here we review the four models of porcine atherosclerosis, including the diabetic/hypercholesterolemic model, Rapacz-familial hypercholesterolemia pig, the (PCSK9) gain-of-function mutant pig model, and the Ossabaw miniature pig model of metabolic syndrome. All four models reliably represent features of human vascular disease.