Mice and minipigs with compromised expression of the Alzheimer's disease gene SORL1 show cerebral metabolic disturbances on hyperpolarized [1-13C]pyruvate and sodium MRI.

The sortilin-related receptor 1 (SORL1) gene, encoding the cellular endosomal sorting-related receptor with A-type repeats (SORLA), is now established as a causal gene for Alzheimer's disease. As the latest addition to the list of causal genes, the pathophysiological effects and biomarker potential of SORL1 variants remain relatively undiscovered. Metabolic dysfunction is, however, well described in patients with Alzheimer's disease and is used as an imaging biomarker in clinical diagnosis settings. To understand the metabolic consequences of loss-of-function SORL1 mutations, we applied two metabolic MRI technologies, sodium (23Na) MRI and MRI with hyperpolarized [1-13C]pyruvate, in minipigs and mice with compromised expression of SORL1. At the age analysed here, both animal models display no conventional imaging evidence of neurodegeneration but show biochemical signs of elevated amyloid production, thus representing the early preclinical disease. With hyperpolarized MRI, the exchange from [1-13C]pyruvate to [1-13C]lactate and 13C-bicarbonate was decreased by 32 and 23%, respectively, in the cerebrum of SORL1-haploinsufficient minipigs. A robust 11% decrease in the sodium content was observed with 23Na-MRI in the same minipigs. Comparably, the brain sodium concentration gradually decreased from control to SORL1 haploinsufficient (-11%) to SORL1 knockout mice (-23%), suggesting a gene dose dependence in the metabolic dysfunction. The present study highlights that metabolic MRI technologies are sensitive to the functional, metabolic consequences of Alzheimer's disease and Alzheimer's disease-linked genotypes. Further, the study suggests a potential avenue of research into the mechanisms of metabolic alterations by SORL1 mutations and their potential role in neurodegeneration.

A genetically modified minipig model for Alzheimer's disease with SORL1 haploinsufficiency.

The established causal genes in Alzheimer's disease (AD), APP, PSEN1, and PSEN2, are functionally characterized using biomarkers, capturing an in vivo profile reflecting the disease's initial preclinical phase. Mutations in SORL1, encoding the endosome recycling receptor SORLA, are found in 2%-3% of individuals with early-onset AD, and SORL1 haploinsufficiency appears to be causal for AD. To test whether SORL1 can function as an AD causal gene, we use CRISPR-Cas9-based gene editing to develop a model of SORL1 haploinsufficiency in Göttingen minipigs, taking advantage of porcine models for biomarker investigations. SORL1 haploinsufficiency in young adult minipigs is found to phenocopy the preclinical in vivo profile of AD observed with APP, PSEN1, and PSEN2, resulting in elevated levels of ß-amyloid (Aß) and tau preceding amyloid plaque formation and neurodegeneration, as observed in humans. Our study provides functional support for the theory that SORL1 haploinsufficiency leads to endosome cytopathology with biofluid hallmarks of autosomal dominant AD.

Effects of castration on atherosclerosis in Yucatan minipigs with genetic hypercholesterolemia.

BACKGROUND: Low plasma testosterone, either spontaneous or as a result of androgen deprivation therapy for prostate cancer, is associated with an increased risk of cardiovascular events. The underlying mechanism in humans is not understood. Experimental studies in mice have shown that castration facilitates atherogenesis and may increase signs of plaque vulnerability. Pigs used for translational atherosclerosis research have frequently been castrated for practical or commercial reasons, but the effect of castration on atherosclerosis has never been systematically evaluated in pigs. OBJECTIVE: To study the effect of castration on atherosclerotic plaque burden and type in genetically modified minipigs with hypercholesterolemia. METHODS: Newborn male Yucatan minipigs with transgenic overexpression of a human gain-of-function mutant of proprotein convertase subtilisin/kexin type 9 were randomized to undergo orchiectomy (n = 8) or serve as controls (n = 6). Minipigs were started on high-fat diet at 3 months of age and the amount and composition of atherosclerotic lesions were analyzed at 12 months of age. Plasma lipid profiles and behavioral parameters were also assessed. RESULTS: Plasma lipids were slightly affected to a more atherogenic profile by orchiectomy, but atherosclerotic lesion size was unaltered in the LAD, thoracic aorta, abdominal aorta, and iliac arteries. The distribution of lesion types (xanthomas, pathological intimal thickening and fibroatheromas) were also not statistically different between groups in any of the examined vascular territories. The abdominal aorta developed the most advanced stages of disease with reproducible fibroatheroma formation, and here it was found that the area of necrotic core was significantly increased in orchiectomized pigs compared with controls. Orchiectomy also reduced aggressive behavior. CONCLUSIONS: Castration does not alter the burden of atherosclerosis in hypercholesterolemic Yucatan minipigs, but may increase necrotic core area in fibroatheromas.

Evaluation of porcine stem cell competence for somatic cell nuclear transfer and production of cloned animals.

Porcine somatic cell nuclear transfer (SCNT) has been used extensively to create genetically modified pigs, but the efficiency of the methodology is still low. It has been hypothesized that pluripotent or multipotent stem cells might result in increased SCNT efficacy as these cells are closer than somatic cells to the epigenetic state found in the blastomeres and therefore need less reprogramming. Our group has worked with porcine SCNT during the last 20 years and here we describe our experience with SCNT of 3 different stem cell lines. The porcine stem cells used were: Induced pluripotent stem cells (iPSCs) created by lentiviral doxycycline-dependent reprogramming and cultered with a GSK3ß- and MEK-inhibitor (2i) and leukemia inhibitor factor (LIF) (2i LIF DOX-iPSCs), iPSCs created by a plasmid-based reprogramming and cultured with 2i and fibroblast growth factor (FGF) (2i FGF Pl-iPSCs) and embryonic germ cells (EGCs), which have earlier been characterized as being multipotent. The SCNT efficiencies of these stem cell lines were compared with that of the two fibroblast cell lines from which the iPSC lines were derived. The blastocyst rates for the 2i LIF DOX-iPSCs were 14.7%, for the 2i FGF Pl-iPSC 10.1%, and for the EGCs 34.5% compared with the fibroblast lines yielding 36.7% and 25.2%. The fibroblast- and EGC-derived embryos were used for embryo transfer and produced live offspring at similar low rates of efficiency (3.2 and 4.0%, respectively) and with several instances of malformations. In conclusion, potentially pluripotent porcine stem cells resulted in lower rates of embryonic development upon SCNT than multipotent stem cells and differentiated somatic cells.

Apolipoprotein E Deficiency Increases Remnant Lipoproteins and Accelerates Progressive Atherosclerosis, But Not Xanthoma Formation, in Gene-Modified Minipigs.

Deficiency of apolipoprotein E (APOE) causes familial dysbetalipoproteinemia in humans resulting in a higher risk of atherosclerotic disease. In mice, APOE deficiency results in a severe atherosclerosis phenotype, but it is unknown to what extent this is unique to mice. In this study, APOE was targeted in Yucatan minipigs. APOE-/- minipigs displayed increased plasma cholesterol and accumulation of apolipoprotein B-48-containing chylomicron remnants on low-fat diet, which was significantly accentuated upon feeding a high-fat, high-cholesterol diet. APOE-/- minipigs displayed accelerated progressive atherosclerosis but not xanthoma formation. This indicates that remnant lipoproteinemia does not induce early lesions but is atherogenic in pre-existing atherosclerosis.

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

Lack of animal models with human-like size and pathology hampers translational research in atherosclerosis. Mouse models are missing central features of human atherosclerosis and are too small for intravascular procedures and imaging. Modeling the disease in minipigs may overcome these limitations, but it has proven difficult to induce rapid atherosclerosis in normal pigs by high-fat feeding alone, and genetically modified models similar to those created in mice are not available. D374Y gain-of-function mutations in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene cause severe autosomal dominant hypercholesterolemia and accelerates atherosclerosis in humans. Using Sleeping Beauty DNA transposition and cloning by somatic cell nuclear transfer, we created Yucatan minipigs with liver-specific expression of human D374Y-PCSK9. D374Y-PCSK9 transgenic pigs displayed reduced hepatic low-density lipoprotein (LDL) receptor levels, impaired LDL clearance, severe hypercholesterolemia, and spontaneous development of progressive atherosclerotic lesions that could be visualized by noninvasive imaging. This model should prove useful for several types of translational research in atherosclerosis.

An improved PCR strategy for fast screening of specific and random integrations in rAAV-mediated gene targeted cell clones.

BACKGROUND: Gene targeting by homologous recombination using recombinant adeno-associated virus (rAAV) is becoming a useful tool for basic research and therapeutic applications due to the remarkably high targeting frequency of rAAV virus vectors. However, the screening for the pure gene-targeted and random-integration-free primary cell clones is difficult since the cells have a limited proliferation capacity and often cannot be grown to produce sufficient DNA for non-PCR based analysis. This hampers the applications of this technology. FINDINGS: In this study, we have developed an improved PCR screening method, which can be used for fast screening of clones with unwanted random integration (RI) of the rAAV genome. This improved screening method includes four PCRs: a PCR for the selection gene (e.g. Neo-PCR), a PCR for targeted gene knockout (e.g. BRCA1-KO-PCR), and two generalized PCRs for random integration of the rAAV genome (5'-AAV-RI-PCR, and 3'-AAV-RI-PCR). We have shown that this screening method greatly facilitates the procedure of screening for BRCA1 (BReast CAncer susceptibility gene 1) targeted cell clones, eliminating cell clones with both BRCA1 knockout and random integration of the rAAV genome. CONCLUSIONS: This screening method has facilitated the screening of correct gene-targeted cells. As the AAV-RI-PCRs are generalized PCRs, this method can also be applied for screening of rAAV-mediated targeting of other genes.

An update on targeted gene repair in mammalian cells: methods and mechanisms.

Transfer of full-length genes including regulatory elements has been the preferred gene therapy strategy for clinical applications. However, with significant drawbacks emerging, targeted gene alteration (TGA) has recently become a promising alternative to this method. By means of TGA, endogenous DNA repair pathways of the cell are activated leading to specific genetic correction of single-base mutations in the genome. This strategy can be implemented using single-stranded oligodeoxyribonucleotides (ssODNs), small DNA fragments (SDFs), triplex-forming oligonucleotides (TFOs), adeno-associated virus vectors (AAVs) and zinc-finger nucleases (ZFNs). Despite difficulties in the use of TGA, including lack of knowledge on the repair mechanisms stimulated by the individual methods, the field holds great promise for the future. The objective of this review is to summarize and evaluate the different methods that exist within this particular area of human gene therapy research.

High hydrostatic pressure treatment of porcine oocytes before handmade cloning improves developmental competence and cryosurvival.

An innovative technique, called the high hydrostatic pressure (HHP) treatment, has been recently reported to improve the cryosurvival of gametes or embryos in certain mammalian species. The aim of the present study was to investigate the in vitro and in vivo developmental competence and cryotolerance of embryos produced by handmade cloning (HMC) after pressure treatment of recipient oocytes. In vitro-matured porcine oocytes were treated with a sublethal hydrostatic pressure of 20 MPa (200 times greater than atmospheric pressure) and recovered for either 1 or 2 h (HHP1 and HHP2 groups, respectively) before they were used for HMC. After 7 days of in vitro culture, blastocyst rates and mean cell numbers were determined. Randomly selected blastocysts were vitrified with the Cryotop method based on minimum volume cooling procedure. The blastocyst rate was higher in the HHP2 group than in the control group (68.2 +/- 4.1% vs. 46.4 +/- 4.2%; p < 0.01), while there was no difference between HHP1 and control group (52.1 +/- 1.2% vs. 49.0 +/- 2.7%; p > 0.05). Similar mean cell numbers of produced blastocysts were obtained in HHP2 and control groups (56 +/- 4 vs. 49 +/- 5; p > 0.05). Subsequent blastocyst vitrification with the Cryotop method resulted in significantly higher survival rate after thawing in the HHP2 group than in the control group (61.6 +/- 4.0% vs. 30.2 +/- 30.9%; p < 0.01). Fifty-six and 57 day 5 to day 7 fresh blastocysts in HHP1 group were transferred into two recipient sows on day 5 of the estrous cycle. One recipient was diagnosed pregnant and gave birth to two healthy piglets by naturally delivery on day 122 of gestation. This pilot study proved that the sublethal HHP treatment of porcine oocytes before HMC results in improved in vitro developmental competence and cryotolerance, and supports embryonic and fetal development as well as pregnancy establishment and maintenance up to the birth of healthy piglets.

Site-specific strand bias in gene correction using single-stranded oligonucleotides.

Targeted gene editing mediated by chimeric RNA-DNA oligonucleotides (RDOs) or single-stranded oligo-deoxyribonucleotides (ssODNs) has been demonstrated in a wide variety of cell types both in vitro and in vivo. In this study we investigated the correlation between the polarity of the used oligonucleotides and the obtained correction frequency in targeted ssODN-mediated correction of two G>A mutations (introduced at positions 659 and 1567, respectively) in an episomal beta-galactosidase gene. At position 659 the highest correction efficiency was observed using an ssODN complementary to the transcribed strand of the target gene. In contrast, at position 1567 the highest correction frequency was observed using an ssODN complementary to the nontranscribed strand of the target gene. It has been reported that site-specific gene editing mediated by ssODNs targeting the nontranscribed strand of the target gene results in a higher gene editing frequency, and it has been suggested that steric hindrance or displacement of ssODNs by traversing transcription complexes prevents efficient targeting of the transcribed strand. However, the results of the present study demonstrate that occupancy by transcriptional complexes alone does not dictate strand bias in ssODN-mediated gene editing, and that the sequences surrounding the targeted nucleotide may profoundly influence strand bias. This finding has important implications for the design of optimal ssODNs for targeted editing of a given nucleotide sequence.

Functional testing of keratin 14 mutant proteins associated with the three major subtypes of epidermolysis bullosa simplex.

Epidermolysis bullosa simplex (EBS) is a group of autosomal dominantly inherited skin disorders characterized by the development of intra-epidermal skin blisters on mild mechanical trauma. The three major clinical subtypes (Weber-Cockayne, Koebner and Dowling-Meara) are all caused by mutations in either the keratin 5 (KRT5) or keratin 14 (KRT14) gene. Previously, we identified three novel KRT14 missense mutations in Danish EBS patients associated with the three different forms of EBS (1). The identified KRT14 mutations represent the full spectrum of the classical EBS subtypes. In the present study we investigated these mutations in a cellular expression system in order to analyse their effects on the keratin cytoskeleton. KRT14 expression vectors were constructed by fusing the nucleotide sequence encoding the FLAG reporter peptide to the 3' end of the KRT14 cDNA sequences. The expression vectors were transiently transfected into normal human primary keratinocytes (NHK), HaCaT or HeLa cells in order to analyze the ability of the mutant K14 proteins to integrate into the existing endogenous keratin filament network (KFN). No effect on the keratin cytoskeleton was observed upon transfection of NHK with the various K14 constructs neither with nor without a subsequently induced heat-stress. In contrast, all constructs, including wild-type K14, caused collapse of the endogenous KFN in a small fraction of the transfected HeLa and HaCaT cells. However, overexpression of the mutation associated with the most severe form of the disease, EBS Dowling-Meara, resulted in a higher number of transfected HaCaT cells with KFN collapse (P < 0.001). Thus, although a background KFN perturbance was observed upon transfection with the wild-type K14 construct, the mutant protein associated with the most severe form of EBS worsened the KFN perturbation significantly compared with the mutant proteins associated with the milder forms of the disease and the normal K14 protein. This shows that the clinical severity of disease-associated mutations identified in patients can be tested using this expression system, although it can not at present be used to discriminate between the milder forms. Assessment of the endogenous K14 protein expression in NHK and HaCaT cells indicated that the higher level of endogenous keratin expression in NHK might make these cells more resistant to perturbation of the keratin cytoskeleton by overexpressed K14 protein than HaCaT cells.

Epidermolysis bullosa simplex keratinocytes with extended lifespan established by ectopic expression of telomerase.

As part of a strategy to develop somatic gene therapy of epidermolysis bullosa simplex (EBS) we have established patient keratinocytes with expanded lifespan by ectopic expression of the human telomerase gene (hTert). The presence of an active telomerase enzyme was demonstrated by the telomerase repeat amplification protocol (TRAP). The hTert(+) cells have a normal karyotype and the cells have, until now, undergone more than 80 population doublings (PDs) after hTert retroviral transduction while control cells exhibited senescence-associated proliferation arrest after 8 PDs. In organotypic culture the hTert(+) cells are capable of forming a stratified epidermis illustrating their preserved ability to differentiate.

Mechanisms underlying targeted gene correction using chimeric RNA/DNA and single-stranded DNA oligonucleotides.

Chimeric RNA/DNA oligonucleotides and modified single-stranded oligonucleotides have been developed for site-specific correction of episomal and chromosomal target genes. The gene repair approach relies on specific hybridization of the oligonucleotides to the target gene generating a mismatch with the targeted point mutation. Restored gene function is anticipated to occur through activation of endogenous repair systems that recognize the created mismatch. We present an overview of the gene correction results obtained in several target genes by employing various oligonucleotide designs and a discussion of the possible mechanisms underlying the gene correction techniques. Experimental data suggest that modified single-stranded oligonucleotides form intermediate three-stranded heteroduplexes involving the human RecA homologue, hRad51, whereas chimeric RNA/DNA oligonucleotides may participate in three or four-stranded intermediate structures. Protein factors such as hRad52, hRad54, hRPA, and p53 may modulate the heteroduplex formation and participate in the activation of the endogenous mismatch repair and/or nucleotide excision repair pathway(s). The efficiency of the gene correction process may furthermore be influenced by the differential recognition of mismatches by repair enzymes and possible sequence context effects.