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

Characterizing the immune response to myocardial infarction in pigs

Though myocardial infarction (MI) in pigs is a well-established translational large animal model, it has not yet been widely used for immunotherapy studies, and a comprehensive description of the immune response to MI in this species is lacking. We induced MI in Landrace pigs by balloon occlusion of the left anterior descending artery over 90 min. Within 14 days, the necrotic myocardium was progressively replaced by scar tissue with involvement of myofibroblasts. We characterized the immune response in the heart ex vivo by (immuno)histology, flow cytometry, and RNA sequencing of myocardial tissue on days 3, 7, and 14 after MI. Besides a clear predominance of myeloid cells among heart-infiltrating leukocytes, we detected activated T cells and an increasing proportion of CD4+ Foxp3+ regulatory T cells (Treg), especially in the infarct core-findings that closely mirror what has been observed in mice and humans after MI. Transcriptome data indicated inflammatory activity that was persistent but markedly changing in character over time and linked to extracellular matrix biology. Analysis of lymphocytes in heart-draining lymph nodes revealed significantly higher proliferation rates of T helper cell subsets, including Treg on day 7 after MI, compared to sham controls. Elevated frequencies of myeloid progenitors in the spleen suggest that it might be a site of emergency myelopoiesis after MI in pigs, as previously shown in mice. We thus provide a first description of the immune response to MI in pigs, and our results can aid future research using the species for preclinical immunotherapy studies.

Distinct properties of putative trophoblast stem cells established from somatic cell nuclear-transferred pig blastocysts

BACKGROUND

Genetically modified pigs are considered ideal models for studying human diseases and potential sources for xenotransplantation research. However, the somatic cell nuclear transfer (SCNT) technique utilized to generate these cloned pig models has low efficiency, and fetal development is limited due to placental abnormalities.

RESULTS

In this study, we unprecedentedly established putative porcine trophoblast stem cells (TSCs) using SCNT and in vitro-fertilized (IVF) blastocysts through the activation of Wing-less/Integrated (Wnt) and epidermal growth factor (EGF) pathways, inhibition of transforming growth factor-β (TGFβ) and Rho-associated protein kinase (ROCK) pathways, and supplementation with ascorbic acid. We also compared the transcripts of putative TSCs originating from SCNT and IVF embryos and their differentiated lineages. A total of 19 porcine TSCs exhibiting typical characteristics were established from SCNT and IVF blastocysts (TSCsNT and TSCsIVF). Compared with the TSCsIVF, TSCsNT showed distinct expression patterns suggesting unique TSCsNT characteristics, including decreased mRNA expression of genes related to apposition, steroid hormone biosynthesis, angiopoiesis, and RNA stability.

CONCLUSION

This study provides valuable information and a powerful model for studying the abnormal development and dysfunction of trophoblasts and placentas in cloned pigs.

Pseudorabies virus upregulates low-density lipoprotein receptors to facilitate viral entry

Pseudorabies virus (PRV) is the causative agent of Aujeszky's disease in pigs. The low-density lipoprotein receptor (LDLR) is a transcriptional target of the sterol-regulatory element-binding proteins (SREBPs) and participates in the uptake of LDL-derived cholesterol. However, the involvement of LDLR in PRV infection has not been well characterized. We observed an increased expression level of LDLR mRNA in PRV-infected 3D4/21, PK-15, HeLa, RAW264.7, and L929 cells. The LDLR protein level was also upregulated by PRV infection in PK-15 cells and in murine lung and brain. The treatment of cells with the SREBP inhibitor, fatostatin, or with SREBP2-specific small interfering RNA prevented the PRV-induced upregulation of LDLR expression as well as viral protein expression and progeny virus production. This suggested that PRV activated SREBPs to induce LDLR expression. Furthermore, interference in LDLR expression affected PRV proliferation, while LDLR overexpression promoted it. This indicated that LDLR was involved in PRV infection. The study also demonstrated that LDLR participated in PRV invasions. The overexpression of LDLR or inhibition of proprotein convertase subtilisin/kexin type 9 (PCSK9), which binds to LDLR and targets it for lysosomal degradation, significantly enhanced PRV attachment and entry. Mechanistically, LDLR interacted with PRV on the plasma membrane, and pretreatment of cells with LDLR antibodies was able to neutralize viral entry. An in vivo study indicated that the treatment of mice with the PCSK9 inhibitor SBC-115076 promoted PRV proliferation. The data from the study indicate that PRV hijacks LDLR for viral entry through the activation of SREBPs.IMPORTANCEPseudorabies virus (PRV) is a herpesvirus that primarily manifests as fever, pruritus, and encephalomyelitis in various domestic and wild animals. Owing to its lifelong latent infection characteristics, PRV outbreaks have led to significant financial setbacks in the global pig industry. There is evidence that PRV variant strains can infect humans, thereby crossing the species barrier. Therefore, gaining deeper insights into PRV pathogenesis and developing updated strategies to contain its spread are critical. This study posits that the low-density lipoprotein receptor (LDLR) could be a co-receptor for PRV infection. Hence, strategies targeting LDLR may provide a promising avenue for the development of effective PRV vaccines and therapeutic interventions.

Targeting proprotein convertase subtilisin/kexin type 9 (PCSK9): from bench to bedside

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has evolved as a pivotal enzyme in lipid metabolism and a revolutionary therapeutic target for hypercholesterolemia and its related cardiovascular diseases (CVD). This comprehensive review delineates the intricate roles and wide-ranging implications of PCSK9, extending beyond CVD to emphasize its significance in diverse physiological and pathological states, including liver diseases, infectious diseases, autoimmune disorders, and notably, cancer. Our exploration offers insights into the interaction between PCSK9 and low-density lipoprotein receptors (LDLRs), elucidating its substantial impact on cholesterol homeostasis and cardiovascular health. It also details the evolution of PCSK9-targeted therapies, translating foundational bench discoveries into bedside applications for optimized patient care. The advent and clinical approval of innovative PCSK9 inhibitory therapies (PCSK9-iTs), including three monoclonal antibodies (Evolocumab, Alirocumab, and Tafolecimab) and one small interfering RNA (siRNA, Inclisiran), have marked a significant breakthrough in cardiovascular medicine. These therapies have demonstrated unparalleled efficacy in mitigating hypercholesterolemia, reducing cardiovascular risks, and have showcased profound value in clinical applications, offering novel therapeutic avenues and a promising future in personalized medicine for cardiovascular disorders. Furthermore, emerging research, inclusive of our findings, unveils PCSK9's potential role as a pivotal indicator for cancer prognosis and its prospective application as a transformative target for cancer treatment. This review also highlights PCSK9's aberrant expression in various cancer forms, its association with cancer prognosis, and its crucial roles in carcinogenesis and cancer immunity. In conclusion, this synthesized review integrates existing knowledge and novel insights on PCSK9, providing a holistic perspective on its transformative impact in reshaping therapeutic paradigms across various disorders. It emphasizes the clinical value and effect of PCSK9-iT, underscoring its potential in advancing the landscape of biomedical research and its capabilities in heralding new eras in personalized medicine.

Current status and future of gene engineering in livestock

The application of gene engineering in livestock is necessary for various reasons, such as increasing productivity and producing disease resistance and biomedicine models. Overall, gene engineering provides benefits to the agricultural and research aspects, and humans. In particular, productivity can be increased by producing livestock with enhanced growth and improved feed conversion efficiency. In addition, the application of the disease resistance models prevents the spread of infectious diseases, which reduces the need for treatment, such as the use of antibiotics; consequently, it promotes the overall health of the herd and reduces unexpected economic losses. The application of biomedicine could be a valuable tool for understanding specific livestock diseases and improving human welfare through the development and testing of new vaccines, research on human physiology, such as human metabolism or immune response, and research and development of xenotransplantation models. Gene engineering technology has been evolving, from random, time-consuming, and laborious methods to specific, time-saving, convenient, and stable methods. This paper reviews the overall trend of genetic engineering technologies development and their application for efficient production of genetically engineered livestock, and provides examples of technologies approved by the United States (US) Food and Drug Administration (FDA) for application in humans. [BMB Reports 2024; 57(1): 50-59].

Stem cell factor's role in enhancing the quality of fertilized and cloned porcine embryos for improved embryonic stem cell derivation

Stem cell factor (SCF), a cytokine growth factor, is expressed in various tissues of the male and female reproductive organs, including the testis, ovary, and endometrium. Its primary function involves cell survival, differentiation, and proliferation, achieved through its binding to the c-kit receptor. This study aimed to scrutinize the effects of SCF treatment during in vitro culture (IVC) on both the developmental potential and the efficiency of establishing embryonic stem cells (ESCs) from fertilized and cloned porcine embryos. The rates of cleavage and blastocyst formation exhibited no significant differences between fertilized and cloned embryos, even with the addition of SCF. However, it's worth noting that embryos cloned with Cloud eGFP as donor cells demonstrated notably increased rates of hatched blastocysts when treated with SCF, and this increase was statistically significant (p < 0.05). Furthermore, following the complete dissection of the blastocysts, although there was no significant difference in the SCF-treated group, the area of expansion was significantly reduced (p < 0.01) in the group treated with the antagonistic blocker (ACK2) compared to both the control and SCF-treated groups. These outcomes suggest that the SCF/c-kit signaling pathway might play a pivotal role in embryo implantation. As anticipated, the efficiency of deriving ESCs was significantly higher (p < 0.01) in the group subjected to SCF treatment (12.82 ± 1.02%) compared to the control group (5.41 ± 2.25%). In conclusion, this study highlights the crucial role of SCF in enhancing the quality of porcine embryos, a vital step in obtaining high-quality ESCs.

An investigation of the inter and intra post-mortem microstructural change seen in an experimental series of pigs exposed to a marine environment

The identification of marine post-mortem microstructural change in human bone tissue is valuable in forensic casework as evidence of an individual's burial history. This study examined micro-tunneling in pig-bone tissue microstructure that had been submerged in a marine environment. The objective of the experiment was to assess total distribution of post-mortem microstructural change and degree of preservation within and between individual submerged pig skeletons. 14 juvenile pig carcasses were submerged in British Columbia at 92-300 m depths, between four to eight months. Seven pigs were individually submerged within caged platforms, seven were tied to open platforms. Six bones were selected from each carcass: first rib, radius, ulna, middle-rib, tibia, and femur. Two transverse thin sections were sampled at each bone mid-shaft (n = 148) and examined using circularly polarized transmitted light. The distribution of tunnels was assessed by measuring tunnel maximum ingress and diameter at 40 locations of the peripheral cortex. All element types were impacted by peripheral tunneling from the periosteum to the central cortex. Tunnels were observed as radiating, bifurcating with no remineralization boundary, isolated and in clusters. Tunnel diameters ranged between 2.00 μm and 12.8 μm, with a 3.7 μm mean. Ingress measurements ranged between 7.5 μm and 435.8 μm with a 93.0 μm mean. Distribution of post-mortem microstructural change across skeletal elements showed the averaged maximum ingress was deeper in the uncaged (99.6 μm), when compared to caged material (78.5 μm). The averaged tunnel ingress had statistically significant differences between uncaged and caged carcasses overall (p-value=0.02). Results of the study indicate microboring is present in marine submersed mammalian bone microstructure in as little as 134 days. This informs forensic investigators of the rate of skeletal destruction and of the narrow window for forensic recoveries, particularly in an enclosed environment. Furthermore, the presence of marine microboring in bone can assist forensic practitioners to histologically interpret the environmental history of a corpse.

Effect of PCSK9 on atherosclerotic cardiovascular diseases and its mechanisms: Focus on immune regulation

Atherosclerosis is a basic pathological characteristic of many cardiovascular diseases, and if not effectively treated, patients with such disease may progress to atherosclerotic cardiovascular diseases (ASCVDs) and even heart failure. The level of plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) is significantly higher in patients with ASCVDs than in the healthy population, suggesting that it may be a promising new target for the treatment of ASCVDs. PCSK9 produced by the liver and released into circulation inhibits the clearance of plasma low-density lipoprotein-cholesterol (LDL-C), mainly by downregulating the level of LDL-C receptor (LDLR) on the surface of hepatocytes, leading to upregulated LDL-C in plasma. Numerous studies have revealed that PCSK9 may cause poor prognosis of ASCVDs by activating the inflammatory response and promoting the process of thrombosis and cell death independent of its lipid-regulatory function, yet the underlying mechanisms still need to be further clarified. In patients with ASCVDs who are intolerant to statins or whose plasma LDL-C levels fail to descend to the target value after treatment with high-dose statins, PCSK9 inhibitors often improve their clinical outcomes. Here, we summarize the biological characteristics and functional mechanisms of PCSK9, highlighting its immunoregulatory function. We also discuss the effects of PCSK9 on common ASCVDs.

Production of Cloned Pigs by Handmade Cloning

Somatic cell nuclear transfer (SCNT) in pigs is a promising technology in biomedical research by association with transgenesis for xenotransplantation and disease modeling technologies. Handmade cloning (HMC) is a simplified SCNT method that does not require micromanipulators and facilitates the generation of cloned embryos in large quantities. As a result of HMC fine-tuning for porcine-specific requirements of both oocytes and embryos, HMC has become uniquely efficient (>40% blastocyst rate, 80-90% pregnancy rates, 6-7 healthy offspring per farrowing, and with negligible losses and malformations). Therefore, this chapter describes our HMC protocol to obtain cloned pigs.

Application of the transgenic pig model in biomedical research: A review

The large animal model has gradually become an essential part of preclinical research studies, relating to exploring the disease pathological mechanism, genic function, pharmacy, and other subjects. Although the mouse model has already been widely accepted in clinical experiments, the need for finding an animal model with high similarity compared with a human model is urgent due to the different body functions and systems between mice and humans. The pig is an optimal choice for replacement. Therefore, enhancing the production of pigs used for models is an important part of the large animal model as well. Transgenic pigs show superiority in pig model creation because of the progress in genetic engineering. Successful cases of transgenic pig models occur in the clinical field of metabolic diseases, neurodegenerative diseases, and genetic diseases. In addition, the choice of pig breed influences the effort and efficiency of reproduction, and the mini pig has relative obvious advantages in pig model production. Indeed, pig models in these diseases provide great value in studies of their causes and treatments, especially at the genetic level. This review briefly outlines the method used to create transgenic pigs and species of producing transgenic pigs and provides an overview of their applications on different diseases and limitations for present pig model developments.

Recent Update on PCSK9 and Platelet Activation Experimental Research Methods: In Vitro and In Vivo Studies

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a crucial factor in the development and progression of cardiovascular diseases. PCSK9 has been demonstrated to modify LDL plasma levels and increase platelet activation, which promotes atherosclerosis, a defining feature of nearly all cardiovascular diseases. Platelet activation has been shown to promote and maintain the response to atherosclerosis development, from beginning to progression and exacerbation, which can lead to advanced cardiovascular events including myocardial infarction (MI) or death. Research on PCSK9 and platelet activation is currently underway with the main goal of reducing the risk of advanced cardiovascular events by preventing or slowing down atherosclerosis progression. Both in vitro and in vivo studies have been used to explore PCSK9 functions to develop new drugs targeting PCSK9. Finding the most suitable study models that represent the pathological and physiological systems found in humans is very important to achieving the goal. This review aimed to present a current and comprehensive overview of the experimental models that have been used to investigate the role of PCSK9 in platelet activation-induced atherosclerotic cardiovascular diseases.

Expanding Biology of PCSK9: Roles in Atherosclerosis and Beyond

Purpose of Review

Since the discovery of PCSK9 in 2003, this proprotein convertase was shown to target specific receptors for degradation in endosomes/lysosomes, including LDLR and other family members and hence to enhance the levels of circulating LDL-cholesterol (LDLc). Accordingly, inhibitors of PCSK9, including monoclonal antibodies blocking its circulating activity and siRNA silencers of its hepatic expression, are now used in clinics worldwide to treat hypercholesterolemia patients effectively and safely in combination with statins and/or ezetimibe. These powerful treatments reduce the incidence of atherosclerosis by at least 20%. Since 2008, novel targets of PCSK9 began to be defined, thereby expanding its roles beyond LDLc regulation into the realm of inflammation, pathogen infections and cellular proliferation in various cancers and associated metastases.

Recent Findings

Some pathogens such as dengue virus exploit the ability of PCSK9 to target the LDLR for degradation to enhance their ability to infect cells. Aside from increasing the degradation of the LDLR and its family members VLDLR, ApoER2 and LRP1, circulating PCSK9 also reduces the levels of other receptors such as CD36 (implicated in fatty acid uptake), oxidized LDLR receptor (that clears oxidized LDLc) as well as major histocompatibility class-I (MHC-I) receptors (implicated in the immune response to antigens). Thus, these novel targets provided links between PCSK9 and inflammation/atherosclerosis, viral infections and cancer/metastasis. The functional activities of PCSK9, accelerated the development of novel therapies to inhibit PCSK9 functions, including small molecular inhibitors, long-term vaccines, and possibly CRISPR-based silencing of hepatic expression of PCSK9.

Summary

The future of inhibitors/silencers of PCSK9 function or expression looks bright, as these are expected to provide a modern armamentarium to treat various pathologies beyond hypercholesterolemia and its effects on atherosclerosis.

Endothelial cell heterogeneity and microglia regulons revealed by a pig cell landscape at single-cell level

Pigs are valuable large animal models for biomedical and genetic research, but insights into the tissue- and cell-type-specific transcriptome and heterogeneity remain limited. By leveraging single-cell RNA sequencing, we generate a multiple-organ single-cell transcriptomic map containing over 200,000 pig cells from 20 tissues/organs. We comprehensively characterize the heterogeneity of cells in tissues and identify 234 cell clusters, representing 58 major cell types. In-depth integrative analysis of endothelial cells reveals a high degree of heterogeneity. We identify several functionally distinct endothelial cell phenotypes, including an endothelial to mesenchymal transition subtype in adipose tissues. Intercellular communication analysis predicts tissue- and cell type-specific crosstalk between endothelial cells and other cell types through the VEGF, PDGF, TGF-β, and BMP pathways. Regulon analysis of single-cell transcriptome of microglia in pig and 12 other species further identifies MEF2C as an evolutionally conserved regulon in the microglia. Our work describes the landscape of single-cell transcriptomes within diverse pig organs and identifies the heterogeneity of endothelial cells and evolutionally conserved regulon in microglia.

Pigs are important large animal models for biomedical research. Here, the authors construct a single-cell landscape of pig tissues, unravelling the phenotypic heterogeneity of blood endothelial cells in adipose tissues and the evolutionally conserved regulons of microglia in brains.

Animal Models of Atherosclerosis-Supportive Notes and Tricks of the Trade

Atherosclerotic cardiovascular disease is a major cause of death among humans. Animal models have shown that cholesterol and inflammation are causatively involved in the disease process. Apolipoprotein B-containing lipoproteins elicit immune reactions and instigate inflammation in the vessel wall. Still, a treatment that is specific to vascular inflammation is lacking, which motivates continued in vivo investigations of the immune-vascular interactions that drive the disease. In this review, we distill old notions with emerging concepts into a contemporary understanding of vascular disease models. Pros and cons of different models are listed and the complex integrative interplay between cholesterol homeostasis, immune activation, and adaptations of the vascular system is discussed. Key limitations with atherosclerosis models are highlighted, and we suggest improvements that could accelerate progress in the field. However, excessively rigid experimental guidelines or limiting usage to certain animal models can be counterproductive. Continued work in improved models, as well as the development of new models, should be of great value in research and could aid the development of cardiovascular disease diagnostics and therapeutics of the future.

New 3-Dimensional Volumetric Ultrasound Method for Accurate Quantification of Atherosclerotic Plaque Volume

BACKGROUND

Carotid and femoral plaque burden is a recognized biomarker of cardiovascular disease risk. A new electronic-sweep 3-dimensional (3D)-matrix transducer method can improve the functionality and image quality of vascular ultrasound atherosclerosis imaging.

OBJECTIVES

This study aimed to validate this method for plaque volume measurement in early and intermediate-advanced plaques in the carotid and femoral territories.

METHODS

Plaque volumes were measured ex vivo in pig carotid and femoral artery specimens by 3-dimensional vascular ultrasound (3DVUS) using a 3D-matrix (electronic-sweep) transducer and its associated 3D plaque quantification software, and were compared with gold-standard histology. To test the clinical feasibility and accuracy of the 3D-matrix transducer, an experiment was conducted in intermediate-high risk individuals with carotid and femoral atherosclerosis. The results were compared with those obtained using the previously validated mechanical-sweep 3D transducer and established 2-dimensional (2D)-based plaque quantification software.

RESULTS

In the ex vivo study, the authors assessed 19 atherosclerotic plaques (plaque volume, 0.76 µL-56.30 μL), finding strong agreement between measurements with the 3D-matrix transducer and the histological gold-standard (intraclass correlation coefficient [ICC]: 0.992; [95% CI: 0.978-0.997]). In the clinical analysis of 20 patients (mean age 74.6 ± 4.45 years; 40% men), the authors found 64 (36 carotid and 28 femoral) of 80 scanned territories with atherosclerosis (measured atherosclerotic volume, 10 μL-859 μL). There was strong agreement between measurements made from electronic-sweep and mechanical-sweep 3DVUS transducers (ICC: 0.997 [95% CI: 0.995-0.998]). Agreement was also high between plaque volumes estimated by the 2D and 3D plaque quantification software applications (ICC: 0.999 [95% CI: 0.998-0.999]). Analysis time was significantly shorter with the 3D plaque quantification software than with the 2D multislice approach with a mean time reduction of 46%.

CONCLUSIONS

3DVUS using new matrix transducer technology, together with improved 3D plaque quantification software, simplifies the accurate volume measurement of early (small) and intermediate-advanced plaques located in carotid and femoral arteries.

Advances in pig models of human diseases

Animal models of human diseases play a critical role in medical research. Pigs are anatomically and physiologically more like humans than are small rodents such as mice, making pigs an attractive option for modeling human diseases. Advances in recent years in genetic engineering have facilitated the rapid rise of pig models for use in studies of human disease. In the present review, we summarize the current status of pig models for human cardiovascular, metabolic, neurodegenerative, and various genetic diseases. We also discuss areas that need to be improved. Animal models of human diseases play a critical role in medical research. Advances in recent years in genetic engineering have facilitated the rapid rise of pig models for use in studies of human disease. In the present review, we summarize the current status of pig models for human cardiovascular, metabolic, neurodegenerative, various genetic diseases and xenotransplantation.

Immuno-PET Imaging of Atherosclerotic Plaques with [89Zr]Zr-Anti-CD40 mAb—Proof of Concept

Non-invasive imaging of atherosclerosis can help in the identification of vulnerable plaque lesions. CD40 is a co-stimulatory molecule present on various immune and non-immune cells in the plaques and is linked to inflammation and plaque instability. We hypothesize that a 89Zr-labeled anti-CD40 monoclonal antibody (mAb) tracer has the potential to bind to cells present in atherosclerotic lesions and that CD40 Positron Emission Tomography (PET) can contribute to the detection of vulnerable atherosclerotic plaque lesions. To study this, wild-type (WT) and ApoE−/− mice were fed a high cholesterol diet for 14 weeks to develop atherosclerosis. Mice were injected with [89Zr]Zr-anti-CD40 mAb and the aortic uptake was evaluated and quantified using PET/Computed Tomography (CT) imaging. Ex vivo biodistribution was performed post-PET imaging and the uptake in the aorta was assessed with autoradiography and compared with Oil red O staining to determine the tracer potential to detect atherosclerotic plaques. On day 3 and 7 post injection, analysis of [89Zr]Zr-anti-CD40 mAb PET/CT scans showed a more pronounced aortic signal in ApoE−/− compared to WT mice with an increased aorta-to-blood uptake ratio. Autoradiography revealed [89Zr]Zr-anti-CD40 mAb uptake in atherosclerotic plaque areas in ApoE−/− mice, while no signal was found in WT mice. Clear overlap was observed between plaque areas as identified by Oil red O staining and autoradiography signal of [89Zr]Zr-anti-CD40 mAb in ApoE−/− mice. In this proof of concept study, we showed that PET/CT with [89Zr]Zr-anti-CD40 mAb can detect atherosclerotic plaques. As CD40 is associated with plaque vulnerability, [89Zr]Zr-anti-CD40 mAb has the potential to become a tracer to detect vulnerable atherosclerotic plaques.

Pig and Mouse Models of Hyperlipidemia and Atherosclerosis

Atherosclerosis is a chronic inflammatory disorder that is the underlying cause of most cardiovascular disease. Resident cells of the artery wall and cells of the immune system participate in atherogenesis. This process is influenced by plasma lipoproteins, genetics, and the hemodynamics of the blood flow in the artery. A variety of animal models have been used to study the pathophysiology and mechanisms that contribute to atherosclerotic lesion formation. No model is ideal as each has its own advantages and limitations with respect to manipulation of the atherogenic process and modeling human atherosclerosis and lipoprotein profile. In this chapter we will discuss pig and mouse models of experimental atherosclerosis. The similarity of pig lipoprotein metabolism and the pathophysiology of the lesions in these animals with that of humans is a major advantage. While a few genetically engineered pig models have been generated, the ease of genetic manipulation in mice and the relatively short time frame for the development of atherosclerosis has made them the most extensively used model. Newer approaches to induce hypercholesterolemia in mice have been developed that do not require germline modifications. These approaches will facilitate studies on atherogenic mechanisms.

Sex as a Key Determinant of Peripheral Artery Disease – Epidemiology, Differential Outcomes, and Proposed Biological Mechanisms

Atherosclerotic peripheral artery disease (PAD) is associated with functional limitations and an increased risk of poor cardiovascular outcomes. Although men are traditionally viewed at higher risk of PAD than women, the true prevalence and incidence is inconsistent among available reports. Some of this variability is due to differences in PAD-related symptoms among women as well as sex-based differences in diagnostic tests, such as the ankle-brachial index, and it is critical for future epidemiologic studies to account for these differences. Generally, women with PAD experience greater functional impairment and decline then men and are less likely to receive guideline-directed medical therapy. In some settings, women are also more likely to present at later stages of disease and more often undergo lower limb amputation than men. Animal data exploring the biological underpinnings of these sex differences are limited, but several mechanisms have been postulated, including differential plaque morphology, alterations in the immune response, and hormonal variation and protection. Epidemiologic data suggest a link between inflammation and PAD and also reveal sex differences in lipid profiles associated with risk of PAD. In this review, we discuss available data on sex differences in PAD with additional focus on potential biological explanations for these differences. We also emphasize important knowledge gaps in this area, including under-representation of women in PAD clinical trials, to help guide future investigations and eliminate sex disparities in PAD.

Deficiency of ASGR1 in pigs recapitulates reduced risk factor for cardiovascular disease in humans

Genetic variants in the asialoglycoprotein receptor 1 (ASGR1) are associated with a reduced risk of cardiovascular disease (CVD) in humans. However, the underlying molecular mechanism remains elusive. Given the cardiovascular similarities between pigs and humans, we generated ASGR1-deficient pigs using the CRISPR/Cas9 system. These pigs show age-dependent low levels of non-HDL-C under standard diet. When received an atherogenic diet for 6 months, ASGR1-deficient pigs show lower levels of non-HDL-C and less atherosclerotic lesions than that of controls. Furthermore, by analysis of hepatic transcriptome and in vivo cholesterol metabolism, we show that ASGR1 deficiency reduces hepatic de novo cholesterol synthesis by downregulating 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), and increases cholesterol clearance by upregulating the hepatic low-density lipoprotein receptor (LDLR), which together contribute to the low levels of non-HDL-C. Despite the cardioprotective effect, we unexpectedly observed mild to moderate hepatic injury in ASGR1-deficient pigs, which has not been documented in humans with ASGR1 variants. Thus, targeting ASGR1 might be an effective strategy to reduce hypercholesterolemia and atherosclerosis, whereas further clinical evidence is required to assess its hepatic impact.

Previous studies have reported an association between ASGR1 variants and CVD in humans. However, the underlying mechanism is unknown. We used ASGR1-deficient pig to recapitulate the reduced risk features of CVD in humans with ASGR1 variants, indicating that ASGR1 inhibition could be an effective strategy to treat atherosclerotic CVD. Our results highlight the demand for taking advantage of genetically modified large animal models to investigate the pathogenesis and therapeutic development of CVD in humans. Unexpectedly, we demonstrate the first link between ASGR1 deficiency and liver injury, a feature that has not been documented in humans with ASGR1 variants. These results suggest that ASGR1 might be an effective target for reducing CVD, whereas revealing a genetic predisposition to liver disease in humans with ASGR1 variants.

Animal Models of Neointimal Hyperplasia and Restenosis: Species-Specific Differences and Implications for Translational Research

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Neointimal hyperplasia is the major factor contributing to restenosis after angioplasty procedures.

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Multiple animal models exist to study basic and translational aspects of restenosis formation.

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Animal models differ substantially, and species-specific differences have major impact on the pathophysiology of the model.

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Genetic, dietary, and mechanical interventions determine the translational potential of the animal model used and have to be considered when choosing the model.

The process of restenosis is based on the interplay of various mechanical and biological processes triggered by angioplasty-induced vascular trauma. Early arterial recoil, negative vascular remodeling, and neointimal formation therefore limit the long-term patency of interventional recanalization procedures. The most serious of these processes is neointimal hyperplasia, which can be traced back to 4 main mechanisms: endothelial damage and activation; monocyte accumulation in the subintimal space; fibroblast migration; and the transformation of vascular smooth muscle cells. A wide variety of animal models exists to investigate the underlying pathophysiology. Although mouse models, with their ease of genetic manipulation, enable cell- and molecular-focused fundamental research, and rats provide the opportunity to use stent and balloon models with high throughput, both rodents lack a lipid metabolism comparable to humans. Rabbits instead build a bridge to close the gap between basic and clinical research due to their human-like lipid metabolism, as well as their size being accessible for clinical angioplasty procedures. Every different combination of animal, dietary, and injury model has various advantages and disadvantages, and the decision for a proper model requires awareness of species-specific biological properties reaching from vessel morphology to distinct cellular and molecular features.

Epigenetic clock and DNA methylation analysis of porcine models of aging and obesity

DNA-methylation profiles have been used successfully to develop highly accurate biomarkers of age, epigenetic clocks, for many species. Using a custom methylation array, we generated DNA methylation data from n = 238 porcine tissues including blood, bladder, frontal cortex, kidney, liver, and lung, from domestic pigs (Sus scrofa domesticus) and minipigs (Wisconsin Miniature Swine™). Samples used in this study originated from Large White X Landrace crossbred pigs, Large White X Minnesota minipig crossbred pigs, and Wisconsin Miniature Swine™. We present 4 epigenetic clocks for pigs that are distinguished by their compatibility with tissue type (pan-tissue and blood clock) and species (pig and human). Two dual-species human-pig pan-tissue clocks accurately measure chronological age and relative age, respectively. We also characterized CpGs that differ between minipigs and domestic pigs. Strikingly, several genes implicated by our epigenetic studies of minipig status overlap with genes (ADCY3, TFAP2B, SKOR1, and GPR61) implicated by genetic studies of body mass index in humans. In addition, CpGs with different levels of methylation between the two pig breeds were identified proximal to genes involved in blood LDL levels and cholesterol synthesis, of particular interest given the minipig's increased susceptibility to cardiovascular disease compared to domestic pigs. Thus, breed-specific differences of domestic and minipigs may potentially help to identify biological mechanisms underlying weight gain and aging-associated diseases. Our porcine clocks are expected to be useful for elucidating the role of epigenetics in aging and obesity, and the testing of anti-aging interventions.

PCSK9 Gene Participates in the Development of Primary Dyslipidemias

Dyslipidemias are a group of diseases, which are characterized by abnormal blood concentrations of cholesterol, triglycerides and/or low-density lipoprotein-cholesterol (LDL-c). Dyslipidemia is a determinant condition for the progress of an atherosclerotic plaque formation. The resulting atherogenicity is due to at least two mechanisms: first, to the accumulation in the plasma of lipid particles that have the capacity to alter the function of the endothelium and deposit at the atheromatous plaque, and second, at an insufficient concentration of multifactorial type of high density lipoprotein-cholesterol (HDL-c), whose function is to protect against the development of atherosclerosis. Its highest prevalence is encountered among individuals with diabetes, hypertension or overweight. Hyperlipidemia is one of the main predisposing factors for the development of cardiovascular disease. Hyperlipidemia can be the result of a genetic condition, the secondary expression of a primary process or the consequence of exogenous factors (food, cultural, socio-economic, etc.), all of which lead to the elevation of plasma lipid levels. The objective of this study was to carry out an analysis of the genes involved in the development of dyslipidemias that lead to cardiovascular disease with special emphasis on the proprotein convertase subtilin/kexin type 9 (PCSK9) gene. The PCSK9 gene participates in the development of primary dyslipidemias, mainly familial hypercholesterolemia, currently the pharmacological treatment of choice to reduce LDL-c are statins, however, it has been observed that these have been insufficient to eliminate cardiovascular risk, especially in subjects with primary forms of hypercholesterolemia related to genetic mutations, or statin intolerance.

Analysis of 18F-Sodium Fluoride Positron Emission Tomography Signal Sources in Atherosclerotic Minipigs Shows Specific Binding of 18F-Sodium Fluoride to Plaque Calcifications

OBJECTIVE

¹⁸F-sodium fluoride (¹⁸F-NaF) positron emission tomography (PET) imaging is thought to visualize active atherosclerotic plaque calcification. This is supported by the binding of ¹⁸F-NaF to plaque calcification ex vivo, but no prior studies have examined binding of ¹⁸F-NaF to human-like plaque in vivo. Our aim was to validate the specificity of ¹⁸F-NaF PET for plaque calcifications in atherosclerotic minipigs. Approach and Results: Gain-of-function PCSK9^D374Y (proprotein convertase/subtilisin kexin type 9) transgenic Yucatan minipigs (n=4) were fed high-fat diet for 2.5 years to develop atherosclerosis and then subjected to ¹⁸F-NaF PET/computed tomography imaging. The heart, aorta, and iliac arteries were immediately re-scanned ex vivo after surgical extraction. Lesions from the abdominal aorta, iliac arteries, and coronary arteries were cryo-sectioned for autoradiography. Histological plaque characteristics, PET/computed tomography signal, and autoradiography were linked through regression and co-localization analysis. Arterial ¹⁸F-NaF PET signal had intensities comparable to clinical scans and colocalized moderately with calcification detected by computed tomography. Histological analysis showed calcification spanning from microcalcifications near lipid pools and necrotic core to more homogenous macrocalcifications. Comparison with arteries from autopsy cases confirmed the resemblance in localization and appearance with early human plaque calcification. Regression analysis in the abdominal aorta showed correlations with calcified plaque but could not rule out contributions from noncalcified plaque. This was resolved by autoradiography, which showed specific accumulation in plaque calcifications in all examined arteries. In the context of porcine abdominal aorta, ¹⁸F-NaF PET imaging was, however, less accurate than computed tomography for detecting small calcifications.

CONCLUSIONS

¹⁸F-NaF accumulates specifically in calcifications of atherosclerotic plaques in vivo.

A model of atherosclerosis using nicotine with balloon overdilation in a porcine

Pigs are important experimental animals for cardiovascular research. Few porcine coronary atherosclerosis models have been developed; however, their induction requires more than six months. We developed a porcine coronary artery atherosclerosis model using nicotine injection with a balloon overdilation. A coronary balloon was placed in the porcine coronary artery and overdilated to induce a mechanical injury. Nicotine was administrated via intramuscular injection every day, and changes in the coronary artery were observed after four weeks. Coronary angiography revealed nicotine injection with a balloon overdilation group showed narrowing of the coronary artery at the injury site. The combination of balloon and nicotine significantly increased the intimal hyperplasia in optical coherence tomography analysis. Proliferated tunica media were noted in the nicotine injection with balloon overdilation groups and lack of collagen was observed in the tunica media at eight weeks. Quantitative analysis showed increased smooth muscle actin alpha (SMA), cluster of differentiation 68 (CD68), and Krüppel-like factor 4 (KLF4) in the nicotine injection with balloon overdilation groups. Immunohistochemistry results showed CD68-positive cells displayed SMA- and KLF4-positive reactivity in the border zone of the intimal hyperplasia. Our results show that nicotine injection with balloon overdilation can induce atherosclerotic lesions within one month, which can serve as an alternative pig animal model for the development of coronary stents.

Transcriptome and proteome mapping in the sheep atria reveal molecular featurets of atrial fibrillation progression

AIMS

Atrial fibrillation (AF) is a progressive cardiac arrhythmia that increases the risk of hospitalization and adverse cardiovascular events. There is a clear demand for more inclusive and large-scale approaches to understand the molecular drivers responsible for AF, as well as the fundamental mechanisms governing the transition from paroxysmal to persistent and permanent forms. In this study, we aimed to create a molecular map of AF and find the distinct molecular programmes underlying cell type-specific atrial remodelling and AF progression.

METHODS AND RESULTS

We used a sheep model of long-standing, tachypacing-induced AF, sampled right and left atrial tissue, and isolated cardiomyocytes (CMs) from control, intermediate (transition), and late time points during AF progression, and performed transcriptomic and proteome profiling. We have merged all these layers of information into a meaningful three-component space in which we explored the genes and proteins detected and their common patterns of expression. Our data-driven analysis points at extracellular matrix remodelling, inflammation, ion channel, myofibril structure, mitochondrial complexes, chromatin remodelling, and genes related to neural function, as well as critical regulators of cell proliferation as hallmarks of AF progression. Most important, we prove that these changes occur at early transitional stages of the disease, but not at later stages, and that the left atrium undergoes significantly more profound changes than the right atrium in its expression programme. The pattern of dynamic changes in gene and protein expression replicate the electrical and structural remodelling demonstrated previously in the sheep and in humans, and uncover novel mechanisms potentially relevant for disease treatment.

CONCLUSIONS

Transcriptomic and proteomic analysis of AF progression in a large animal model shows that significant changes occur at early stages, and that among others involve previously undescribed increase in mitochondria, changes to the chromatin of atrial CMs, and genes related to neural function and cell proliferation.

Toward the Effective Bioengineering of a Pathological Tissue for Cardiovascular Disease Modeling: Old Strategies and New Frontiers for Prevention, Diagnosis, and Therapy

Cardiovascular diseases (CVDs) still represent the primary cause of mortality worldwide. Preclinical modeling by recapitulating human pathophysiology is fundamental to advance the comprehension of these diseases and propose effective strategies for their prevention, diagnosis, and treatment. In silico, in vivo, and in vitro models have been applied to dissect many cardiovascular pathologies. Computational and bioinformatic simulations allow developing algorithmic disease models considering all known variables and severity degrees of disease. In vivo studies based on small or large animals have a long tradition and largely contribute to the current treatment and management of CVDs. In vitro investigation with two-dimensional cell culture demonstrates its suitability to analyze the behavior of single, diseased cellular types. The introduction of induced pluripotent stem cell technology and the application of bioengineering principles raised the bar toward in vitro three-dimensional modeling by enabling the development of pathological tissue equivalents. This review article intends to describe the advantages and disadvantages of past and present modeling approaches applied to provide insights on some of the most relevant congenital and acquired CVDs, such as rhythm disturbances, bicuspid aortic valve, cardiac infections and autoimmunity, cardiovascular fibrosis, atherosclerosis, and calcific aortic valve stenosis.

Local Pressure Drives Low-Density Lipoprotein Accumulation and Coronary Atherosclerosis in Hypertensive Minipigs

BACKGROUND

The mechanisms by which hypertension accelerates coronary artery disease are poorly understood. Patients with hypertension often have confounding humoral changes, and to date, no experimental models have allowed analysis of the isolated effect of pressure on atherosclerosis in a setting that recapitulates the dimensions and biomechanics of human coronary arteries.

OBJECTIVES

This study sought to analyze the effect of pressure on coronary atherosclerosis and explore the underlying mechanisms.

METHODS

Using inflatable suprarenal aortic cuffs, we increased mean arterial pressure by >30 mm Hg in the cephalad body part of wild-type and hypercholesterolemic proprotein convertase subtilisin kexin type 9 (PCSK9)^D374Y Yucatan minipigs for >1 year. Caudal pressures remained normal.

RESULTS

Under hypercholesterolemic conditions in PCSK9^D374Y transgenic minipigs, cephalad hypertension accelerated coronary atherosclerosis to almost 5-fold with consistent development of fibroatheromas that were sufficiently large to cause stenosis on computed tomography angiography. This was caused by local pressure forces, because vascular beds shielded from hypertension, but exposed to the same humoral factors, showed no changes in lesion formation. The same experiment was conducted under normocholesterolemic conditions in wild-type minipigs to examine the underlying mechanisms. Hypertension produced clear changes in the arterial proteome with increased abundance of mechanical strength proteins and reduced levels of infiltrating plasma macromolecules. This was paralleled by increased smooth muscle cells and increased intimal accumulation of low-density lipoproteins in the coronary arteries.

CONCLUSIONS

Increased pressure per se facilitates coronary atherosclerosis. Our data indicate that restructuring of the artery to match increased tensile forces in hypertension alters the passage of macromolecules and leads to increased intimal accumulation of low-density lipoproteins.

The Digenic Causality in Familial Hypercholesterolemia: Revising the Genotype-Phenotype Correlations of the Disease

Genetically inherited defects in lipoprotein metabolism affect more than 10 million individuals around the globe with preponderance in some parts where consanguinity played a major role in establishing founder mutations. Mutations in four genes have been so far linked to the dominant and recessive form of the disease. Those players encode major proteins implicated in cholesterol regulation, namely, the low-density lipoprotein receptor (LDLR) and its associate protein 1 (LDLRAP1), the proprotein convertase substilin/kexin type 9 (PCSK9), and the apolipoprotein B (APOB). Single mutations or compound mutations in one of these genes are enough to account for a spectrum of mild to severe phenotypes. However, recently several reports have identified digenic mutations in familial cases that do not necessarily reflect a much severe phenotype. Yet, data in the literature supporting this notion are still lacking. Herein, we review all the reported cases of digenic mutations focusing on the biological impact of gene dosage and the potential protective effects of single-nucleotide polymorphisms linked to hypolipidemia. We also highlight the difficulty of establishing phenotype-genotype correlations in digenic familial hypercholesterolemia cases due to the complexity and heterogeneity of the phenotypes and the still faulty in silico pathogenicity scoring system. We finally emphasize the importance of having a whole exome/genome sequencing approach for all familial cases of familial hyperlipidemia to better understand the genetic and clinical course of the disease.

In Vivo Digestion of Egg Products Enriched with DHA: Effect of the Food Matrix on DHA Bioavailability

The aim of the present study was to determine to what extent the food matrix could affect the release of docosahexaenoic acid (DHA) during digestion and its incorporation into systemic circulation. In this aim, three DHA-enriched egg products having the same composition but different structure were developed: omelet, hard-boiled egg, and mousse. Then, nine pigs fitted with T-shape cannulas at duodenal level and a jugular venous catheter were fed with the DHA-enriched egg products, and duodenal effluents and plasma were collected throughout the postprandial period. Results highlighted an undeniable effect of the food matrix on digestion parameters and DHA bioavailability. The transit of DHA and protein through the duodenum was faster after the ingestion of the mousse than after the ingestion of the omelet and hard-boiled egg. While most of the DHA and protein ingested under the form of mousse had already passed through the duodenum 4.5 h after its ingestion, significantly higher quantities were still present in the case of the omelet and hard-boiled egg. In terms of bioavailability, the omelet was the most efficient vector for delivering DHA into systemic circulation. It supplied 56% and 120% more DHA than the hard-boiled egg and the mousse, respectively.

Mouse models of atherosclerosis and their suitability for the study of myocardial infarction

Atherosclerotic plaques impair vascular function and can lead to arterial obstruction and tissue ischaemia. Rupture of an atherosclerotic plaque within a coronary artery can result in an acute myocardial infarction, which is responsible for significant morbidity and mortality worldwide. Prompt reperfusion can salvage some of the ischaemic territory, but ischaemia and reperfusion (IR) still causes substantial injury and is, therefore, a therapeutic target for further infarct limitation. Numerous cardioprotective strategies have been identified that can limit IR injury in animal models, but none have yet been translated effectively to patients. This disconnect prompts an urgent re-examination of the experimental models used to study IR. Since coronary atherosclerosis is the most prevalent morbidity in this patient population, and impairs coronary vessel function, it is potentially a major confounder in cardioprotective studies. Surprisingly, most studies suggest that atherosclerosis does not have a major impact on cardioprotection in mouse models. However, a major limitation of atherosclerotic animal models is that the plaques usually manifest in the aorta and proximal great vessels, and rarely in the coronary vessels. In this review, we examine the commonly used mouse models of atherosclerosis and their effect on coronary artery function and infarct size. We conclude that none of the commonly used strains of mice are ideal for this purpose; however, more recently developed mouse models of atherosclerosis fulfil the requirement for coronary artery lesions, plaque rupture and lipoprotein patterns resembling the human profile, and may enable the identification of therapeutic interventions more applicable in the clinical setting.

A porcine model of phenylketonuria generated by CRISPR/Cas9 genome editing

Phenylalanine hydroxylase-deficient (PAH-deficient) phenylketonuria (PKU) results in systemic hyperphenylalaninemia, leading to neurotoxicity with severe developmental disabilities. Dietary phenylalanine (Phe) restriction prevents the most deleterious effects of hyperphenylalaninemia, but adherence to diet is poor in adult and adolescent patients, resulting in characteristic neurobehavioral phenotypes. Thus, an urgent need exists for new treatments. Additionally, rodent models of PKU do not adequately reflect neurocognitive phenotypes, and thus there is a need for improved animal models. To this end, we have developed PAH-null pigs. After selection of optimal CRISPR/Cas9 genome-editing reagents by using an in vitro cell model, zygote injection of 2 sgRNAs and Cas9 mRNA demonstrated deletions in preimplantation embryos, with embryo transfer to a surrogate leading to 2 founder animals. One pig was heterozygous for a PAH exon 6 deletion allele, while the other was compound heterozygous for deletions of exon 6 and of exons 6-7. The affected pig exhibited hyperphenylalaninemia (2000-5000 μM) that was treatable by dietary Phe restriction, consistent with classical PKU, along with juvenile growth retardation, hypopigmentation, ventriculomegaly, and decreased brain gray matter volume. In conclusion, we have established a large-animal preclinical model of PKU to investigate pathophysiology and to assess new therapeutic interventions.

Dyslipidaemias and Cardiovascular Disease: Focus on the Role of PCSK9 Inhibitors

Genetic, experimental and clinical studies have consistently confirmed that inhibition of Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) can result in significant lowering of LDL-C and two fully human PCSK9 monoclonal antibodies have received regulatory approval for use in highrisk patients. Co-administration of PCSK9 with statins has resulted in extremely low LDL-C levels with excellent short-term safety profiles. While results from Phase III clinical trials provided significant evidence about the role of PCSK9 inhibitors in reducing cardiovascular event rates, their impact on mortality remains less clear. PCSK9 inhibitor therapy can be considered for high-risk patients who are likely to experience significant cardiovascular risk reduction.

Application of Genetically Engineered Pigs in Biomedical Research

Progress in genetic engineering over the past few decades has made it possible to develop methods that have led to the production of transgenic animals. The development of transgenesis has created new directions in research and possibilities for its practical application. Generating transgenic animal species is not only aimed towards accelerating traditional breeding programs and improving animal health and the quality of animal products for consumption but can also be used in biomedicine. Animal studies are conducted to develop models used in gene function and regulation research and the genetic determinants of certain human diseases. Another direction of research, described in this review, focuses on the use of transgenic animals as a source of high-quality biopharmaceuticals, such as recombinant proteins. The further aspect discussed is the use of genetically modified animals as a source of cells, tissues, and organs for transplantation into human recipients, i.e., xenotransplantation. Numerous studies have shown that the pig (Sus scrofa domestica) is the most suitable species both as a research model for human diseases and as an optimal organ donor for xenotransplantation. Short pregnancy, short generation interval, and high litter size make the production of transgenic pigs less time-consuming in comparison with other livestock species This review describes genetically modified pigs used for biomedical research and the future challenges and perspectives for the use of the swine animal models.

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.

Accelerated miniature swine models of advanced atherosclerosis: A review based on morphology

In order to accelerate development of atherosclerosis(AS) in miniature swine models, varieties of strategies and methods have been explored. In addition to traditional methods such as high cholesterol feeding and balloon injury, new methods such as familial hypercholesterolemia induced by gene editing and intramural injection have been applied in recent years. Although it has been claimed that these methods have successfully aggravated lesion areas and stenosis, lesion features induced by different strategies have shown heterogeneity in morphology. In addition, time consumption, high cost, and unavailability are problems that restrict application of these AS models. Here, we summarize strategies and methods to accelerate AS models and further analyze their values, advantages, and shortcomings.

18Fluorodeoxyglucose Accumulation in Arterial Tissues Determined by PET Signal Analysis

BACKGROUND

Arterial ¹⁸fluorodeoxyglucose (FDG) positron emission tomography (PET) is considered a measure of atherosclerotic plaque macrophages and is used for quantification of disease activity in clinical trials, but the distribution profile of FDG across macrophages and other arterial cells has not been fully clarified.

OBJECTIVES

The purpose of this study was to analyze FDG uptake in different arterial tissues and their contribution to PET signal in normal and atherosclerotic arteries.

METHODS

Wild-type and D374Y-PCSK9 transgenic Yucatan minipigs were fed a high-fat, high-cholesterol diet to induce atherosclerosis and subjected to a clinical FDG-PET and computed tomography scan protocol. Volumes of arterial media, intima/lesion, macrophage-rich, and hypoxic tissues were measured in serial histological sections. Distributions of FDG in macrophages and other arterial tissues were quantified using modeling of the in vivo PET signal. In separate transgenic minipigs, the intra-arterial localization of FDG was determined directly by autoradiography.

RESULTS

Arterial FDG-PET signal appearance and intensity were similar to human imaging. The modeling approach showed high accuracy in describing the FDG-PET signal and revealed comparable FDG accumulation in macrophages and other arterial tissues, including medial smooth muscle cells. These findings were verified directly by autoradiography of normal and atherosclerotic arteries.

CONCLUSIONS

FDG is taken up comparably in macrophage-rich and -poor arterial tissues in minipigs. This offers a mechanistic explanation to a growing number of observations in clinical imaging studies that have been difficult to reconcile with macrophage-selective FDG uptake.

Sex as a Biological Variable in Atherosclerosis

Atherosclerosis is a chronic inflammatory vascular disease and the predominant cause of heart attack and ischemic stroke. Despite the well-known sexual dimorphism in the incidence and complications of atherosclerosis, there are relatively limited data in the clinical and preclinical literature to rigorously address mechanisms underlying sex as a biological variable in atherosclerosis. In multiple histological and imaging studies, overall plaque burden and markers of inflammation appear to be greater in men than women and are predictive of cardiovascular events. However, while younger women are relatively protected from cardiovascular disease, by the seventh decade, the incidence of myocardial infarction in women ultimately surpasses that of men, suggesting an interaction between sex and age. Most preclinical studies in animal atherosclerosis models do not examine both sexes, and even in those that do, well-powered direct statistical comparisons for sex as an independent variable remain rare. This article reviews the available data. Overall, male animals appear to have more inflamed yet smaller plaques compared to female animals. Plaque inflammation is often used as a surrogate end point for plaque vulnerability in animals. The available data support the notion that rather than plaque size, plaque inflammation may be more relevant in assessing sex-specific mechanisms since the findings correlate with the sex difference in ischemic events and mortality and thus may be more reflective of the human condition. Overall, the number of preclinical studies directly comparing plaque inflammation between the sexes is extremely limited relative to the vast literature exploring atherosclerosis mechanisms. Failure to include both sexes and to address age in mechanistic atherosclerosis studies are missed opportunities to uncover underlying sex-specific mechanisms. Understanding the mechanisms driving sex as a biological variable in atherosclerotic disease is critical to future precision medicine strategies to mitigate what is still the leading cause of death of men and women worldwide.

Accumulation of Pericardial Fat Is Associated With Alterations in Heart Rate Variability Patterns in Hypercholesterolemic Pigs

BACKGROUND

Heart rate variability (HRV) and pulse rate variability are indices of autonomic cardiac modulation. Increased pericardial fat is associated with worse cardiovascular outcomes. We hypothesized that progressive increases in pericardial fat volume and inflammation prospectively dampen HRV in hypercholesterolemic pigs.

METHODS

WT (wild type) or PCSK9 (proprotein convertase subtilisin-like/kexin type-9) gain-of-function Ossabaw mini-pigs were studied in vivo before and after 3 and 6 months of a normal diet (WT-normal diet, n=4; PCSK9-normal diet, n=6) or high-fat diet (HFD; WT-HFD, n=3; PCSK9-HFD, n=6). The arterial pulse waveform was obtained from an arterial telemetry transmitter to analyze HRV indices, including SD (SD of all pulse-to-pulse intervals over a single 5-minute period), root mean square of successive differences, proportion >50 ms of normal-to-normal R-R intervals, and the calculated ratio of low-to-high frequency distributions (low-frequency power/high-frequency power). Pericardial fat volumes were evaluated using multidetector computed tomography and its inflammation by gene expression of TNF (tumor necrosis factor)-α. Plasma lipid panel and norepinephrine level were also measured.

RESULTS

At diet completion, hypercholesterolemic PCSK9-HFD had significantly (P<0.05 versus baseline) depressed HRV (SD of all pulse-to-pulse intervals over a single 5-minute period, root mean square of successive differences, proportion >50 ms, high-frequency power, low-frequency power), and both HFD groups had higher sympathovagal balance (SD of all pulse-to-pulse intervals over a single 5-minute period/root mean square of successive differences, low-frequency power/high-frequency power) compared with normal diet. Pericardial fat volumes and LDL (low-density lipoprotein) cholesterol concentrations correlated inversely with HRV and directly with sympathovagal balance, while sympathovagal balance correlated directly with plasma norepinephrine. Pericardial fat TNF-α expression was upregulated in PCSK9-HFD, colocalized with nerve fibers, and correlated inversely with root mean square of successive differences and proportion >50 ms.

CONCLUSIONS

Progressive pericardial fat expansion and inflammation are associated with a fall in HRV in Ossabaw mini-pigs, implying aggravated autonomic imbalance. Hence, pericardial fat accumulation is associated with alterations in HRV and the autonomic nervous system. Visual Overview: A visual overview is available for this article.

Swine Disease Models for Optimal Vascular Engineering

Swine disease models are essential for mimicry of human metabolic and vascular pathophysiology, thereby enabling high-fidelity translation to human medicine. The worldwide epidemic of obesity, metabolic disease, and diabetes has prompted the focus on these diseases in this review. We highlight the remarkable similarity between Ossabaw miniature swine and humans with metabolic syndrome and atherosclerosis. Although the evidence is strongest for swine models of coronary artery disease, findings are generally applicable to any vascular bed. We discuss the major strengths and weaknesses of swine models. The development of vascular imaging is an example of optimal vascular engineering in swine. Although challenges regarding infrastructure and training of engineers in the use of swine models exist, opportunities are ripe for gene editing, studies of molecular mechanisms, and use of swine in coronary artery imaging and testing of devices that can move quickly to human clinical studies.

Hyperlipidaemia and cardioprotection: Animal models for translational studies

Hyperlipidaemia is a well-established risk factor for cardiovascular diseases and therefore, many animal model have been developed to mimic the human abnormal elevation of blood lipid levels. In parallel, extensive research for the alleviation of ischaemia/reperfusion injury has revealed that hyperlipidaemia is a major co-morbidity that attenuates the cardioprotective effect of conditioning strategies (preconditioning, postconditioning and remote conditioning) and that of pharmacological interventions by interfering with cardioprotective signalling pathways. In the present review article, we summarize the existing data on animal models of hypercholesterolaemia (total, low density and HDL abnormalities) and hypertriglyceridaemia used in ischaemia/reperfusion injury and protection from it. We also provide recommendations on preclinical animal models to be used for translations of the cardioprotective strategies into clinical practice. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Variation in Coronary Atherosclerosis Severity Related to a Distinct LDL (Low-Density Lipoprotein) Profile: Findings From a Familial Hypercholesterolemia Pig Model

OBJECTIVE

In an adult porcine model of familial hypercholesterolemia (FH), coronary plaque development was characterized. To elucidate the underlying mechanisms of the observed inter-individual variation in disease severity, detailed lipoprotein profiles were determined. Approach and Results: FH pigs (3 years old, homozygous LDLR R84C mutation) received an atherogenic diet for 12 months. Coronary atherosclerosis development was monitored using serial invasive imaging and histology. A pronounced difference was observed between mildly diseased pigs which exclusively developed early lesions (maximal plaque burden, 25% [23%-34%]; n=5) and advanced-diseased pigs (n=5) which developed human-like, lumen intruding plaques (maximal plaque burden, 69% [57%-77%]) with large necrotic cores, intraplaque hemorrhage, and calcifications. Advanced-diseased pigs and mildly diseased pigs displayed no differences in conventional risk factors. Additional plasma lipoprotein profiling by size-exclusion chromatography revealed 2 different LDL (low-density lipoprotein) subtypes: regular and larger LDL. Cholesterol, sphingosine-1-phosphate, ceramide, and sphingomyelin levels were determined in these LDL-subfractions using standard laboratory techniques and high-pressure liquid chromatography mass-spectrometry analyses, respectively. At 3 months of diet, regular LDL of advanced-diseased pigs contained relatively more cholesterol (LDL-C; regular/larger LDL-C ratio 1.7 [1.3-1.9] versus 0.8 [0.6-0.9]; P=0.008) than mildly diseased pigs, while larger LDL contained more sphingosine-1-phosphate, ceramides, and sphingomyelins. Larger and regular LDL was also found in plasma of 3 patients with homozygous FH with varying LDL-C ratios.

CONCLUSIONS

In our adult FH pig model, inter-individual differences in atherosclerotic disease severity were directly related to the distribution of cholesterol and sphingolipids over a distinct LDL profile with regular and larger LDL shortly after the diet start. A similar LDL profile was detected in patients with homozygous FH.

Identification of Glyceraldehyde-3-Phosphate Dehydrogenase Gene as an Alternative Safe Harbor Locus in Pig Genome

The ectopic overexpression of foreign genes in animal genomes is an important strategy for gain-of-function study and establishment of transgenic animal models. Previous studies showed that two loci (Rosa26 and pH11) were identified as safe harbor locus in pig genomes, which means foreign genes can be integrated into this locus for stable expression. Moreover, integration of a transgene may interfere with the endogenous gene expression of the target locus after the foreign fragments are inserted. Here, we provide a new strategy for efficient transgene knock-in in the endogenous GAPDH gene via CRISPR/Cas9 mediated homologous recombination. This strategy has no influence on the expression of the endogenous GAPDH gene. Thus, the GAPDH locus is a new alternative safe harbor locus in the pig genome for foreign gene knock-ins. This strategy is promising for agricultural breeding and biomedical model applications.

Generation of an MC3R knock-out pig by CRSPR/Cas9 combined with somatic cell nuclear transfer (SCNT) technology

BACKGROUND

Melanocortin 3 receptor (MC3R), a rhodopsin-like G protein-coupled receptor, is an important regulator of metabolism. Although MC3R knock-out (KO) mice and rats were generated in earlier studies, the function of MC3R remains elusive. Since pig models have many advantages over rodents in metabolism research, we generated an MC3R-KO pig using a CRSPR/Cas9-based system combined with somatic cell nuclear transfer (SCNT) technology.

METHOD

Four CRSPR/Cas9 target vectors were constructed and then their cleavage efficiency was tested in porcine fetal fibroblasts (PFFs). The pX330-sgRNA1 and pX330-sgRNA4 vectors were used to co-transfect PFFs to obtain positive colonies. PCR screening and sequencing were conducted to identify the genotype of the colonies. The biallelically modified colonies and wild-type control colonies were used simultaneously as donor cells for SCNT. A total of 1203 reconstructed embryos were transferred into 6 surrogates, of which one became pregnant. The genotypes of the resulting piglets were determined by PCR and sequencing, and off-target effects in the MC3R KO piglets were detected by sequencing. Then, offspring were obtained through breeding and six male KO pigs were used for the growth performance analysis.

RESULTS

Four vectors were constructed successfully, and their cleavage efficiencies were 27.96, 44.89, 32.72 and 38.86%, respectively. A total of 21 mutant colonies, including 11 MC3R-/- and 10 MC3R+/- clones, were obtained, corresponding to a gene targeting efficiency of 29.17%, with 15.28% biallelic mutations. A total of 6 piglets were born, and only two MC3R KO piglets were generated, one with malformations and a healthy one. No off-target effects were detected by sequencing in the healthy mutant. Six male MC3R KO pigs were obtained in the F2 generation and their body weight and body fat were both increased compared to wild-type full siblings.

CONCLUSION

A MC3R KO pig strain was generated using the CRSIPR/Cas9-based system, which makes it possible to study the biological function of MC3R in a non-rodent model.

An Animal Model of Human Peripheral Arterial Bending and Deformation

BACKGROUND

Designing peripheral arterial stents has proved challenging, as implanted devices will repetitively and unpredictably deform and fatigue during movement. Preclinical testing is often inadequate, given the lack of relevant animal models. The purpose of this study was to test the hypothesis that deformation of the human peripheral vasculature could be qualitatively and quantitatively modeled using an experimental animal.

METHODS

Anteroposterior contrast angiography was performed in domestic Landrace-Yorkshire farm pigs. Images were obtained with the hind limbs naturally extended then repeated, (1) flexed approximately 90° at the hip and knee, (2) overflexed in a nonphysiological fashion. Quantitative vascular angiographic analysis was utilized to measure arterial diameter, length, and deformation. Percent axial arterial compression and bending were assessed.

RESULTS

Eight iliofemoral arteries in four animals were imaged. Mean luminal diameters of the iliac and femoral segments in the neutral position were 5.4 ± 0.5 mm and 4.6 ± 0.5 mm. Hind limb physiologic flexion induced profound arterial compression, 17 ± 8% and 29 ± 6% and bending, 36°±10° and 76° ± 13° within the iliac and femoral segments, respectively. With extreme flexion, the femoral artery could be reliably bent >90°. The observed findings exceeded the deformation observed historically within the human superficial femoral (∼5% compression and 10° bending) and popliteal artery (∼10% compression and 70° bending).

CONCLUSIONS

Significant nonradial deformation of the porcine iliofemoral arteries was observed during manual hind limb flexion and exceeded that typically observed in humans. This model constitutes a "worst case" scenario for testing deformation and fatigue of intravascular devices indicated for the human peripheral vasculature.

18F-FDG PET/MR-imaging in a Göttingen Minipig model of atherosclerosis: Correlations with histology and quantitative gene expression

BACKGROUND AND AIMS

The advantage of combining molecular and morphological imaging, e.g. positron emission tomography and magnetic resonance imaging (PET/MRI), is reflected in the increased use of these modalities as surrogate end-points in clinical trials. This study aimed at evaluating plaque inflammation using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-PET/MRI, and gene expression in a minipig model of atherosclerosis.

METHODS

Göttingen Minipigs were fed for 60 weeks with fat/fructose/cholesterol-rich diet (FFC), chow (Control) or FFC-diet changed to chow midway (diet normalization group; DNO). In all groups, ¹⁸F-FDG-PET/MRI of the abdominal aorta was assessed midway and at study-end. The aorta was analyzed using histology and gene expression.

RESULTS

At study-end, FFC had significantly higher FDG-uptake compared to Control (target-to-background maximal uptake, TBR_Max (95% confidence interval) CI_TBRMax: 0.092; 7.32) and DNO showed significantly decreased uptake compared to FFC (CI_TBRMax: -5.94;-0.07). No difference was observed between DNO and Control (CI_TBRMax: -2.71; 4.11). FFC displayed increased atherosclerosis and gene expression of inflammatory markers, including vascular cell adhesion molecule 1 (VCAM-1), cluster of differentiation 68 (CD68), matrix metalloproteinase 9 (MMP9), cathepsin K (CTSK) and secreted phosphoprotein 1 (SPP1) compared to Control and DNO (all, p < 0.05). FDG-uptake correlated with gene expression of inflammatory markers, including CD68, ρ_s = 0.58; MMP9, ρ_s = 0.46; SPP1, ρ_s = 0.44 and CTSK, ρ_s = 0.49; (p ≤ 0.01 for all).

CONCLUSIONS

In a model of atherosclerosis, ¹⁸F-FDG-PET/MRI technology allows for detection of inflammation in atherosclerotic plaques, consistent with increased inflammatory gene expression. Our findings corroborate clinical data and are important in pre-clinical drug development targeting plaque inflammation.