Tissue Sampling Guides for Porcine Biomedical Models

Effects of volume management on free flap perfusion and metabolism in a large animal model study

Free flap failure represents a substantial clinical burden. The role of intraoperative volume management remains controversial, with valid studies lacking. Here, using a large animal model, we investigated the influence of volume management on free flap perfusion and metabolism. Autotransfer of a musculocutaneous gracilis flap was performed on 31 German domestic pigs, with arterial anastomosis and catheterization of the pedicle vein for sequential blood sampling. Flap reperfusion was followed by induction of a hemorrhagic shock with maintenance for 30 min and subsequent circulation stabilization with crystalloid solution, crystalloid solution and catecholamine, autotransfusion or colloidal solution. Flap perfusion and oxygenation were periodically assessed using hyperspectral imaging. Flap metabolism was assessed via periodic blood gas analyses. Hyperspectral imaging revealed no difference in either superficial or deep tissue oxygen saturation, tissue hemoglobin or tissue water content between the test groups at any time point. Blood gas analyses showed that lactate levels were significantly increased in the group that received crystalloid solution and catecholamine, after circulatory stabilization and up to 2 h after. We conclude that, in hemorrhagic shock, volume management impacts acid-base balance in free flaps. Crystalloid solutions with norepinephrine increase lactate levels, yet short-term effects on flap perfusion seem minimal, suggesting that vasopressors are not detrimental.

Decreased β-cell volume and insulin secretion but preserved glucose tolerance in a growth hormone insensitive pig model

PURPOSE

Growth hormone (GH) is a central regulator of β-cell proliferation, insulin secretion and sensitivity. Aim of this study was to investigate the effect of GH insensitivity on pancreatic β-cell histomorphology and consequences for metabolism in vivo.

METHODS

Pancreata from pigs with growth hormone receptor deficiency (GHR-KO, n = 12) were analyzed by unbiased quantitative stereology in comparison to wild-type controls (WT, n = 12) at 3 and 7-8.5 months of age. In vivo secretion capacity for insulin and glucose tolerance were assessed by intravenous glucose tolerance tests (ivGTTs) in GHR-KO (n = 3) and WT (n = 3) pigs of the respective age groups.

RESULTS

Unbiased quantitative stereological analyses revealed a significant reduction in total β-cell volume (83% and 73% reduction in young and adult GHR-KO vs. age-matched WT pigs; p < 0.0001) and volume density of β-cells in the pancreas of GHR-KO pigs (42% and 39% reduction in young and adult GHR-KO pigs; p = 0.0018). GHR-KO pigs displayed a significant, age-dependent increase in the proportion of isolated β-cells in the pancreas (28% in young and 97% in adult GHR-KO vs. age-matched WT pigs; p = 0.0009). Despite reduced insulin secretion in ivGTTs, GHR-KO pigs maintained normal glucose tolerance.

CONCLUSION

GH insensitivity in GHR-KO pigs leads to decreased β-cell volume and volume proportion of β-cells in the pancreas, causing a reduced insulin secretion capacity. The increased proportion of isolated β-cells in the pancreas of GHR-KO pigs highlights the dependency on GH stimulation for proper β-cell maturation. Preserved glucose tolerance accomplished with decreased insulin secretion indicates enhanced sensitivity for insulin in GH insensitivity.

Multi-omics analysis of diabetic pig lungs reveals molecular derangements underlying pulmonary complications of diabetes mellitus

Growing evidence shows that the lung is an organ prone to injury by diabetes mellitus. However, the molecular mechanisms of these pulmonary complications have not yet been characterized comprehensively. To systematically study the effects of insulin deficiency and hyperglycaemia on the lung, we combined proteomics and lipidomics with quantitative histomorphological analyses to compare lung tissue samples from a clinically relevant pig model for mutant INS gene-induced diabetes of youth (MIDY) with samples from wild-type littermate controls. Among others, the level of pulmonary surfactant-associated protein A (SFTPA1), a biomarker of lung injury, was moderately elevated. Furthermore, key proteins related to humoral immune response and extracellular matrix organization were significantly altered in abundance. Importantly, a lipoxygenase pathway was dysregulated as indicated by 2.5-fold reduction of polyunsaturated fatty acid lipoxygenase ALOX15 levels, associated with corresponding changes in the levels of lipids influenced by this enzyme. Our multi-omics study points to an involvement of reduced ALOX15 levels and an associated lack of eicosanoid switching as mechanisms contributing to a proinflammatory milieu in the lungs of subjects with diabetes mellitus.

Structural and proteomic repercussions of growth hormone receptor deficiency on the pituitary gland: Lessons from a translational pig model

Growth hormone receptor deficiency (GHRD) results in low serum insulin-like growth factor 1 (IGF1) and high, but non-functional serum growth hormone (GH) levels in human Laron syndrome (LS) patients and animal models. This study investigated the quantitative histomorphological and molecular alterations associated with GHRD. Pituitary glands from 6 months old growth hormone receptor deficient (GHR-KO) and control pigs were analyzed using a quantitative histomorphological approach in paraffin (9 GHR-KO [5 males, 4 females] vs. 11 controls [5 males, 6 females]), ultrathin sections tissue sections (3 male GHR-KO vs. 3 male controls) and label-free proteomics (4 GHR-KO vs. 4 control pigs [2 per sex]). GHR-KO pigs displayed reduced body weights (60% reduction in comparison to controls; p < .0001) and decreased pituitary volumes (54% reduction in comparison to controls; p < .0001). The volume proportion of the adenohypophysis did not differ in GHR-KO and control pituitaries (65% vs. 71%; p = .0506) and GHR-KO adenohypophyses displayed a reduced absolute volume but an unaltered volume density of somatotrophs in comparison to controls (21% vs. 18%; p = .3164). In GHR-KO pigs, somatotroph cells displayed a significantly reduced volume density of granules (23.5%) as compared to controls (67.7%; p < .0001). Holistic proteome analysis of adenohypophysis samples identified 4660 proteins, of which 592 were differentially abundant between the GHR-KO and control groups. In GHR-KO samples, the abundance of somatotropin precursor was decreased, whereas increased abundances of proteins involved in protein production, transport and endoplasmic reticulum (ER) stress were revealed. Increased protein production and secretion as well as significantly reduced proportion of GH-storing granules in somatotroph cells of the adenohypophysis without an increase in volume density of somatotroph cells in the adenohypophysis could explain elevated serum GH levels in GHR-KO pigs.

Genetic diversity, growth and heart function of Auckland Island pigs, a potential source for organ xenotransplantation

One of the prerequisites for successful organ xenotransplantation is a reasonable size match between the porcine organ and the recipient's organ to be replaced. Therefore, the selection of a suitable genetic background of source pigs is important. In this study, we investigated body and organ growth, cardiac function, and genetic diversity of a colony of Auckland Island pigs established at the Center for Innovative Medical Models (CiMM), LMU Munich. Male and female Auckland Island pig kidney cells (selected to be free of porcine endogenous retrovirus C) were imported from New Zealand, and founder animals were established by somatic cell nuclear transfer (SCNT). Morphologically, Auckland Island pigs have smaller body stature compared to many domestic pig breeds, rendering their organ dimensions well-suited for human transplantation. Furthermore, echocardiography assessments of Auckland Island pig hearts indicated normal structure and functioning across various age groups throughout the study. Single nucleotide polymorphism (SNP) analysis revealed higher runs of homozygosity (ROH) in Auckland Island pigs compared to other domestic pig breeds and demonstrated that the entire locus coding the swine leukocyte antigens (SLAs) was homozygous. Based on these findings, Auckland Island pigs represent a promising genetic background for organ xenotransplantation.

Growth hormone insensitivity and adipose tissue: tissue morphology and transcriptome analyses in pigs and humans

PURPOSE

Growth hormone receptor knockout (GHR-KO) pigs have recently been developed, which serve as a large animal model of Laron syndrome (LS). GHR-KO pigs, like individuals with LS, are obese but lack some comorbidities of obesity. The purpose of this study was to examine the histological and transcriptomic phenotype of adipose tissue (AT) in GHR-KO pigs and humans with LS.

METHODS

Intraabdominal (IA) and subcutaneous (SubQ) AT was collected from GHR-KO pigs and examined histologically for adipocyte size and collagen content. RNA was isolated and cDNA sequenced, and the results were analyzed to determine differentially expressed genes that were used for enrichment and pathway analysis in pig samples. For comparison, we also performed limited analyses on human AT collected from a single individual with and without LS.

RESULTS

GHR-KO pigs have increased adipocyte size, while the LS AT had a trend towards an increase. Transcriptome analysis revealed 55 differentially expressed genes present in both depots of pig GHR-KO AT. Many significant terms in the enrichment analysis of the SubQ depot were associated with metabolism, while in the IA depot, IGF and longevity pathways were negatively enriched. In pathway analysis, multiple expected and novel pathways were significantly affected by genotype, i.e. KO vs. controls. When GH related gene expression was analyzed, SOCS3 and CISH showed species-specific changes.

CONCLUSION

AT of GHR-KO pigs has several similarities to that of humans with LS in terms of adipocyte size and gene expression profile that help describe the depot-specific adipose phenotype of both groups.

Systemic deletion of DMD exon 51 rescues clinically severe Duchenne muscular dystrophy in a pig model lacking DMD exon 52

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease caused by mutations in the DMD gene, leading to complete absence of dystrophin and progressive degeneration of skeletal musculature and myocardium. In DMD patients and in a corresponding pig model with a deletion of DMD exon 52 (DMDΔ52), expression of an internally shortened dystrophin can be achieved by skipping of DMD exon 51 to reframe the transcript. To predict the best possible outcome of this strategy, we generated DMDΔ51-52 pigs, additionally representing a model for Becker muscular dystrophy (BMD). DMDΔ51-52 skeletal muscle and myocardium samples stained positive for dystrophin and did not show the characteristic dystrophic alterations observed in DMDΔ52 pigs. Western blot analysis confirmed the presence of dystrophin in the skeletal muscle and myocardium of DMDΔ51-52 pigs and its absence in DMDΔ52 pigs. The proteome profile of skeletal muscle, which showed a large number of abundance alterations in DMDΔ52 vs. wild-type (WT) samples, was normalized in DMDΔ51-52 samples. Cardiac function at age 3.5 mo was significantly reduced in DMDΔ52 pigs (mean left ventricular ejection fraction 58.8% vs. 70.3% in WT) but completely rescued in DMDΔ51-52 pigs (72.3%), in line with normalization of the myocardial proteome profile. Our findings indicate that ubiquitous deletion of DMD exon 51 in DMDΔ52 pigs largely rescues the rapidly progressing, severe muscular dystrophy and the reduced cardiac function of this model. Long-term follow-up studies of DMDΔ51-52 pigs will show if they develop symptoms of the milder BMD.

Standardized tissue sampling guidelines for histopathological and molecular analyses of rainbow trout (Oncorhynchus mykiss) in ecotoxicological studies

In ecotoxicology, evaluation of toxicities and no observed effect concentrations (NOEC) of test compounds in experimental fish is commonly based on molecular-, biochemical- and analytical chemistry analyses of organ/tissue samples and the assessment of (histo-) pathological lesions. Standardization of organ/tissue sampling locations, sample numbers, and sample processing contributes to warrant the reproducibility and inter- and intra-study comparability of analysis results. The present article provides the first comprehensive tissue sampling guidelines specifically adapted to rainbow trout (Oncorhynchus mykiss) as a frequently used fish species in ecotoxicological studies. A broad spectrum of ~40 different organs and tissues is covered. Appropriate sampling locations, sample sizes and sample numbers for subsequent routine histopathological evaluation (all organs/tissue) and for molecular analyses (~30 organs/tissues) are described in detail and illustrated with schematic drawings and representative macroscopic and histological images. These field-proven sampling guidelines were developed based on the pertinent literature and practical experience in ecotoxicological fish studies. They are intended to serve as a standard reference for any routine ecotoxicological study using rainbow trout as a test system. A broad application of the featured tissue sampling procedures will help to improve the reproducibility of analyses and to reduce inter- and intra-study variability induced by sampling bias and (normal) inter-sample morphological variation, and will therefore provide a robust basis for reliable characterization of toxicity and NOEC identification of diverse test substances and aquatic pollutants.

Effects of dietary lipid level and environmental temperature on lipid metabolism in the intestine and liver, and choline requirement in Atlantic salmon (Salmo salar L) parr

Choline was recently established as an essential nutrient for Atlantic salmon at all life stages. Choline deficiency is manifested as an excessive accumulation of dietary fat within the intestinal enterocytes, a condition known as steatosis. Most of today's plant-based salmon feeds will be choline-deficient unless choline is supplemented. Choline's role in lipid transport suggests that choline requirement may depend on factors such as dietary lipid level and environmental temperature. The present study was therefore conducted to investigate whether lipid level and water temperature can affect steatosis symptoms, and thereby choline requirement in Atlantic salmon. Four choline-deficient plant-based diets were formulated differing in lipid level of 16, 20, 25 and 28 % and fed to salmon of 25 g initial weight in duplicate tanks per diet at two different environmental temperatures: 8 and 15 °C. After 8 weeks of feeding, samples of blood, tissue and gut content from six fish per tank were collected, for analyses of histomorphological, biochemical and molecular biomarkers of steatosis and choline requirement. Increasing lipid level did not affect growth rate but increased relative weight and lipid content of the pyloric caeca and histological symptoms of intestinal steatosis and decreased fish yield. Elevation of the water temperature from 8 to 15 °C, increased growth rate, relative weight of the pyloric caeca, and the histological symptoms of steatosis seemed to become more severe. We conclude that dietary lipid level, as well as environmental temperature, affect choline requirement to a magnitude of importance for fish biology and health, and for fish yield.

Detection of Diclofenac-Induced Alterations in Rainbow Trout (Oncorhynchus mykiss) Using Quantitative Stereological Methods

In 2013, the nonsteroidal anti-inflammatory drug diclofenac (DCF) was included in the watch list for emerging pollutants under the European Union Water Framework Directive. Frequently, monitoring data revealed DCF concentrations in surface waters exceeding the proposed environmental quality standards of 0.04 µg L^-1 and 0.126 µg L^-1 . In recent literature, the possible effects of DCF on fish are discussed controversially. To contribute to a realistic risk assessment of DCF, a 28-day exposure experiment was carried on rainbow trout (Oncorhynchus mykiss). To warrant reliability of data, experiments were conducted considering the Criteria for Reporting and Evaluating Ecotoxicity Data. The test concentrations of DCF used (0.1, 0.5, 1, 5, 25, and 100 µg L^-1 ) also included environmentally relevant concentrations. The lowest-observed-effect concentration (LOEC) for a significant decrease in the plasma concentrations of the DCF biomarker prostaglandin E2 was 0.5 µg L^-1 (male fish). For objective evaluation of relevant histomorphological parameters of gills and trunk kidneys, unbiased quantitative stereological methods were applied. In the gills, significant increases in the thickness of the secondary lamella and in the true harmonic mean of barrier thickness in secondary lamellae were present at DCF concentrations of 25 µg L^-1 and 100 µg L^-1 . In the trunk kidneys, the absolute and relative volumes of nephrons were significantly decreased, paralleled by a significant increase of the volume of the interstitial renal tissue. With regard to quantitative histomorphological alterations in the trunk kidney, the observed LOEC was 0.5 µg L^-1 . The quantitative histomorphological analyses that were conducted allow identification and objective quantification of even subtle but significant morphological effects and thus provide an important contribution for the comparability of study results for the determination of no-observed-effect concentrations (NOEC). Environ Toxicol Chem 2023;42:859-872. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessment of hemodynamics, blood gases, and lung histopathology of healthy Pig model on two different mechanical ventilators

In response to COVID-19 global crisis and arising from social responsibility, efforts have been exerted to promptly research, develop and manufacture ICU ventilators locally to meet the spike in demand. This study aimed at: Evaluating the safety and performance of a newly developed mechanical ventilator; EZVent compared to a commercial ventilator regarding hemodynamics, arterial blood gases (ABG), lung inflammatory markers, and histopathology in a healthy pig model using three different ventilation modes. Methods: Eight adult male pigs were anesthetized and randomly assigned into two equal groups: Commercial vent and EZVent group, the animals of which were ventilated using a standard commercial ventilator and EZVent, respectively. On every animal, three ventilation modes were tested, each mode for 30 min: CMV-VC, CMV-PC, and CPAP-PS modes. Vital signs, ECG, Lung Mechanics (LM), and ABG were measured before ventilation and after 30 min of ventilation of each mode. After animals’ euthanasia, histological examinations of lung samples including morphometric assessment of alveolar edema, alveolar wall thickening, and the mean number of inflammatory cellular infiltrate/cm² of lung tissue were analyzed. TNF-α and Il-6 expression and localization in lung tissue were assessed by western blot and immunohistochemistry. Results: The vital signs, LM, ABG, morphometric analysis, and histopathological score during the different ventilation modes showed non-significant differences between the study groups. TNF-α and IL-6 were minimally expressed in the bronchiolar epithelium and the alveolar septa. Their increased expression level was insignificant. Conclusion: EZVent is equivalent to the commercial ventilator regarding its safety and efficacy.

Scientific and Regulatory Policy Committee Points to Consider for Medical Device Implant Site Evaluation in Nonclinical Studies

Nonclinical implantation studies are a common and often critical step for medical device safety assessment in the bench-to-market pathway. Nonclinical implanted medical devices or drug-device combination products require complex macroscopic and microscopic pathology evaluations due to the physical presence of the device itself and unique tissue responses to device materials. The Medical Device Implant Site Evaluation working group of the Society of Toxicologic Pathology's (STP) Scientific and Regulatory Policy Committee (SRPC) was tasked with reviewing scientific, technical, and regulatory considerations for these studies. Implant site evaluations require highly specialized methods and analytical schemes that should be designed on a case-by-case basis to address specific study objectives. Existing STP best practice recommendations can serve as a framework when performing nonclinical studies under Good Laboratory Practices and help mitigate limitations in standards and guidances for implant evaluations (e.g., those from the International Organization for Standardization [ISO], ASTM International). This article integrates standards referenced by sponsors and regulatory bodies with practical pathology evaluation methods for implantable medical devices and combination products. The goal is to ensure the maximum accuracy and scientific relevance of pathology data acquired during a medical device or combination drug-device implantation study.

Early disruption of photoreceptor cell architecture and loss of vision in a humanized pig model of usher syndromes

Usher syndrome (USH) is the most common form of monogenic deaf-blindness. Loss of vision is untreatable and there are no suitable animal models for testing therapeutic strategies of the ocular constituent of USH, so far. By introducing a human mutation into the harmonin-encoding USH1C gene in pigs, we generated the first translational animal model for USH type 1 with characteristic hearing defect, vestibular dysfunction, and visual impairment. Changes in photoreceptor architecture, quantitative motion analysis, and electroretinography were characteristics of the reduced retinal virtue in USH1C pigs. Fibroblasts from USH1C pigs or USH1C patients showed significantly elongated primary cilia, confirming USH as a true and general ciliopathy. Primary cells also proved their capacity for assessing the therapeutic potential of CRISPR/Cas-mediated gene repair or gene therapy in vitro. AAV-based delivery of harmonin into the eye of USH1C pigs indicated therapeutic efficacy in vivo.

Developmental Effects of (Pre-)Gestational Diabetes on Offspring: Systematic Screening Using Omics Approaches

Worldwide, gestational diabetes affects 2-25% of pregnancies. Due to related disturbances of the maternal metabolism during the periconceptional period and pregnancy, children bear an increased risk for future diseases. It is well known that an aberrant intrauterine environment caused by elevated maternal glucose levels is related to elevated risks for increased birth weights and metabolic disorders in later life, such as obesity or type 2 diabetes. The complexity of disturbances induced by maternal diabetes, with multiple underlying mechanisms, makes early diagnosis or prevention a challenging task. Omics technologies allowing holistic quantification of several classes of molecules from biological fluids, cells, or tissues are powerful tools to systematically investigate the effects of maternal diabetes on the offspring in an unbiased manner. Differentially abundant molecules or distinct molecular profiles may serve as diagnostic biomarkers, which may also support the development of preventive and therapeutic strategies. In this review, we summarize key findings from state-of-the-art Omics studies addressing the impact of maternal diabetes on offspring health.

Differential Effects of Insulin-Deficient Diabetes Mellitus on Visceral vs. Subcutaneous Adipose Tissue-Multi-omics Insights From the Munich MIDY Pig Model

Adipose tissue (AT) is no longer considered to be responsible for energy storage only but is now recognized as a major endocrine organ that is distributed across different parts of the body and is actively involved in regulatory processes controlling energy homeostasis. Moreover, AT plays a crucial role in the development of metabolic disease such as diabetes. Recent evidence has shown that adipokines have the ability to regulate blood glucose levels and improve metabolic homeostasis. While AT has been studied extensively in the context of type 2 diabetes, less is known about how different AT types are affected by absolute insulin deficiency in type 1 or permanent neonatal diabetes mellitus. Here, we analyzed visceral and subcutaneous AT in a diabetic, insulin-deficient pig model (MIDY) and wild-type (WT) littermate controls by RNA sequencing and quantitative proteomics. Multi-omics analysis indicates a depot-specific dysregulation of crucial metabolic pathways in MIDY AT samples. We identified key proteins involved in glucose uptake and downstream signaling, lipogenesis, lipolysis and β-oxidation to be differentially regulated between visceral and subcutaneous AT in response to insulin deficiency. Proteins related to glycogenolysis, pyruvate metabolism, TCA cycle and lipogenesis were increased in subcutaneous AT, whereas β-oxidation-related proteins were increased in visceral AT from MIDY pigs, pointing at a regionally different metabolic adaptation to master energy stress arising from diminished glucose utilization in MIDY AT. Chronic, absolute insulin deficiency and hyperglycemia revealed fat depot-specific signatures using multi-omics analysis. The generated datasets are a valuable resource for further comparative and translational studies in clinical diabetes research.

A scalable, clinically severe pig model for Duchenne muscular dystrophy

Large animal models for Duchenne muscular dystrophy (DMD) are crucial for evaluation of diagnostic procedures and treatment strategies. Pigs cloned from male cells lacking DMD exon 52 (DMDΔ52) resemble molecular, clinical and pathological hallmarks of DMD, but die before sexual maturity and cannot be propagated by breeding. Therefore, we generated female DMD+/- carriers. A single founder animal had 11 litters with 29 DMDY/-, 34 DMD+/- as well as 36 male and 29 female wild-type offspring. Breeding with F1 and F2 DMD+/- carriers resulted in additional 114 DMDY/- piglets. With intensive neonatal management, the majority survived for 3-4 months, providing statistically relevant cohorts for experimental studies. Pathological investigations and proteome studies of skeletal muscles and myocardium confirmed the resemblance of human disease mechanisms. Importantly, DMDY/- pigs reveal progressive myocardial fibrosis and increased expression of connexin-43, associated with significantly reduced left ventricular ejection fraction already at age 3 months. Furthermore, behavioral tests provided evidence for impaired cognitive ability. Our breeding cohort of DMDΔ52 pigs and standardized tissue repositories provide important resources for studying DMD disease mechanisms and for testing novel treatment strategies.

Nervous System Sampling for General Toxicity and Neurotoxicity Studies in the Laboratory Minipig With Emphasis on the Göttingen Minipig

The use of minipigs as an alternative nonclinical species has increased in the last 20 years. The Society of Toxicologic Pathology (STP) has produced generic "best practice" recommendations for nervous system sampling in nonrodents during general toxicity studies (Toxicol Pathol 41[7]: 1028-1048, 2013), but their adaptation to the minipig has not been attempted. Here, we describe 2 trimming schemes suitable for evaluating the unique neuroanatomic features of the minipig brain in nonclinical toxicity studies. The first scheme is intended for general toxicity studies (Tier 1) to screen agents with unknown or no anticipated neurotoxic potential; this approach using 7 coronal hemisections accords with the published STP "best practice" recommendations. The second trimming scheme for neurotoxicity studies (Tier 2) uses 14 coronal hemisections and 2 full coronal sections to investigate toxicants where the nervous system is a suspected or known target organ. Collection of spinal cord, ganglia (somatic and autonomic), and nerves from minipigs during nonclinical studies should follow published STP "best practice" recommendations for sampling the central (CNS, Toxicol Pathol 41[7]: 1028-1048, 2013) and peripheral (PNS, Toxicol Pathol 46[4]: 372-402, 2018) nervous systems.

International Harmonization of Nomenclature and Diagnostic Criteria (INHAND): Nonproliferative and Proliferative Lesions of the Minipig

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions) Project (www.toxpath.org/inhand.asp) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying microscopic lesions observed in most tissues and organs from the minipig used in nonclinical safety studies. Some of the lesions are illustrated by color photomicrographs. The standardized nomenclature presented in this document is also available electronically on the internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous lesions as well as lesions induced by exposure to test materials. Relevant infectious and parasitic lesions are included as well. A widely accepted and utilized international harmonization of nomenclature for lesions in laboratory animals will provide a common language among regulatory and scientific research organizations in different countries and increase and enrich international exchanges of information among toxicologists and pathologists.

CD8+ T Cells Involved in Metabolic Inflammation in Visceral Adipose Tissue and Liver of Transgenic Pigs

Anti-inflammatory therapies have the potential to become an effective treatment for obesity-related diseases. However, the huge gap of immune system between human and rodent leads to limitations of drug discovery. This work aims at constructing a transgenic pig model with higher risk of metabolic diseases and outlining the immune responses at the early stage of metaflammation by transcriptomic strategy. We used CRISPR/Cas9 techniques to targeted knock-in three humanized disease risk genes, GIPR^dn , hIAPP and PNPLA3^I148M . Transgenic effect increased the risk of metabolic disorders. Triple-transgenic pigs with short-term diet intervention showed early symptoms of type 2 diabetes, including glucose intolerance, pancreatic lipid infiltration, islet hypertrophy, hepatic lobular inflammation and adipose tissue inflammation. Molecular pathways related to CD8⁺ T cell function were significantly activated in the liver and visceral adipose samples from triple-transgenic pigs, including antigen processing and presentation, T-cell receptor signaling, co-stimulation, cytotoxicity, and cytokine and chemokine secretion. The similar pro-inflammatory signaling in liver and visceral adipose tissue indicated that there might be a potential immune crosstalk between the two tissues. Moreover, genes that functionally related to liver antioxidant activity, mitochondrial function and extracellular matrix showed distinct expression between the two groups, indicating metabolic stress in transgenic pigs' liver samples. We confirmed that triple-transgenic pigs had high coincidence with human metabolic diseases, especially in the scope of inflammatory signaling at early stage metaflammation. Taken together, this study provides a valuable large animal model for the clinical study of metaflammation and metabolic diseases.

A new method for physical disector analyses of numbers and mean volumes of immunohistochemically labeled cells in paraffin sections

BACKGROUND

In the neurosciences, the physical disector method represents an established quantitative stereological method for unbiased sampling and counting of cells in histological tissue sections of known thickness. Physical disector analyses are conventionally performed using plastic-embedded tissue samples, because plastic-embedding causes a comparably low and definable shrinkage of the embedded tissue, and the thickness of thin plastic sections can be determined adequately. However, immunohistochemistry protocols often don't work satisfactorily in sections of plastic-embedded tissue.

NEW METHOD

Here, a new methodological approach is presented, allowing for physical disector analyses of immunohistochemically labeled cells in paraffin sections. The embedding-related tissue shrinkage is standardized by using defined tissue sample volumes and paraffin volumes, and the extent of tissue shrinkage can be determined accurately from the sample volumes prior to and after embedding. Co-embedding of polyethylene section thickness standards together with the tissue samples allows the precise determination of individual paraffin section thicknesses by spectral reflectance measurements.

RESULTS AND COMPARISON WITH EXISTING METHOD(S)

The applicability of the new method is demonstrated by physical disector analysis of immunohistochemically identified somatotroph cells in paraffin sections of porcine pituitary gland tissue. With consideration of individual shrinkage factors and section thicknesses, the cell numbers and mean volumes estimated in paraffin disector sections do not significantly differ from the results obtained by analyses of plastic-embedded pituitary tissue samples of the identical animals (2.4% average difference).

CONCLUSIONS

The featured method enables combination of paraffin section immunohistochemistry and physical disector analyses for unbiased quantitative stereological analyses of different cell types.

Unbiased analysis of obesity related, fat depot specific changes of adipocyte volumes and numbers using light sheet fluorescence microscopy

In translational obesity research, objective assessment of adipocyte sizes and numbers is essential to characterize histomorphological alterations linked to obesity, and to evaluate the efficacies of experimental medicinal or dietetic interventions. Design-based quantitative stereological techniques based on the analysis of 2D-histological sections provide unbiased estimates of relevant 3D-parameters of adipocyte morphology, but often involve complex and time-consuming tissue processing and analysis steps. Here we report the application of direct 3D light sheet fluorescence microscopy (LSFM) for effective and accurate analysis of adipocyte volumes and numbers in optically cleared adipose tissue samples from a porcine model of diet-induced obesity (DIO). Subcutaneous and visceral adipose tissue samples from DIO-minipigs and lean controls were systematically randomly sampled, optically cleared with 3DISCO (3-dimensional imaging of solvent cleared organs), stained with eosin, and subjected to LSFM for detection of adipocyte cell membrane autofluorescence. Individual adipocytes were unbiasedly sampled in digital 3D reconstructions of the adipose tissue samples, and their individual cell volumes were directly measured by automated digital image analysis. Adipocyte numbers and mean volumes obtained by LSFM analysis did not significantly differ from the corresponding values obtained by unbiased quantitative stereological analysis techniques performed on the same samples, thus proving the applicability of LSFM for efficient analysis of relevant morphological adipocyte parameters. The results of the present study demonstrate an adipose tissue depot specific plasticity of adipocyte growth responses to nutrient oversupply. This was characterized by an exclusively hypertrophic growth of visceral adipocytes, whereas adipocytes in subcutaneous fat tissue depots also displayed a marked (hyperplastic) increase in cell number. LSFM allows for accurate and efficient determination of relevant quantitative morphological adipocyte parameters. The applied stereological methods and LSFM protocols are described in detail and can serve as a guideline for unbiased quantitative morphological analyses of adipocytes in other studies and species.

The Neonatal and Juvenile Pig in Pediatric Drug Discovery and Development

Pharmacotherapy in pediatric patients is challenging in view of the maturation of organ systems and processes that affect pharmacokinetics and pharmacodynamics. Especially for the youngest age groups and for pediatric-only indications, neonatal and juvenile animal models can be useful to assess drug safety and to better understand the mechanisms of diseases or conditions. In this respect, the use of neonatal and juvenile pigs in the field of pediatric drug discovery and development is promising, although still limited at this point. This review summarizes the comparative postnatal development of pigs and humans and discusses the advantages of the juvenile pig in view of developmental pharmacology, pediatric diseases, drug discovery and drug safety testing. Furthermore, limitations and unexplored aspects of this large animal model are covered. At this point in time, the potential of the neonatal and juvenile pig as nonclinical safety models for pediatric drug development is underexplored.

Transcriptomic and Morphological Analysis of Cells Derived from Porcine Buccal Mucosa-Studies on an In Vitro Model

Simple Summary

Domestic pigs express high phylogenetic similarity to humans and are often used as a compatible model in biomedical research. Porcine tissues are used as an accessible biomaterial in human skin transplants and tissue architecture reconstruction. We used transcriptional analysis to investigate the dynamics of complex biological system of the mucosa. Additionally, we performed computer analysis of microscopic images of cultured cells in vitro. Computer analysis of images identified epithelial cells and connective tissue cells in in vitro culture.

Abstract

Transcriptional analysis and live-cell imaging are a powerful tool to investigate the dynamics of complex biological systems. In vitro expanded porcine oral mucosal cells, consisting of populations of epithelial and connective lineages, are interesting and complex systems for study via microarray transcriptomic assays to analyze gene expression profile. The transcriptomic analysis included 56 ontological groups with particular focus on 7 gene ontology groups that are related to the processes of differentiation and development. Most analyzed genes were upregulated after 7 days and downregulated after 15 and 30 days of in vitro culture. The performed transcriptomic analysis was then extended to include automated analysis of differential interference contrast microscopy (DIC) images obtained during in vitro culture. The analysis of DIC imaging allowed to identify the different populations of keratinocytes and fibroblasts during seven days of in vitro culture, and it was possible to evaluate the proportion of these two populations of cells. Porcine mucosa may be a suitable model for reference research on human tissues. In addition, it can provide a reference point for research on the use of cells, scaffolds, or tissues derived from transgenic animals for applications in human tissues reconstruction.

A practical guide to unbiased quantitative morphological analyses of the gills of rainbow trout (Oncorhynchus mykiss) in ecotoxicological studies

Rainbow trout (Oncorhynchus mykiss) are frequently used as experimental animals in ecotoxicological studies, in which they are experimentally exposed to defined concentrations of test substances, such as heavy metals, pesticides, or pharmaceuticals. Following exposure to a broad variety of aquatic pollutants, early morphologically detectable toxic effects often manifest in alterations of the gills. Suitable methods for an accurate and unbiased quantitative characterization of the type and the extent of morphological gill alterations are therefore essential prerequisites for recognition, objective evaluation and comparison of the severity of gill lesions. The aim of the present guidelines is to provide practicable, standardized and detailed protocols for the application of unbiased quantitative stereological analyses of relevant morphological parameters of the gills of rainbow trout. These gill parameters inter alia include the total volume of the primary and secondary gill lamellae, the surface area of the secondary gill lamellae epithelium (i.e., the respiratory surface) and the thickness of the diffusion barrier. The featured protocols are adapted to fish of frequently used body size classes (300-2000 g). They include well-established, conventional sampling methods, probes and test systems for unbiased quantitative stereological analyses of light- and electron microscopic 2-D gill sections, as well as the application of modern 3-D light sheet fluorescence microscopy (LSFM) of optically cleared gill samples as an innovative, fast and efficient quantitative morphological analysis approach. The methods shown here provide a basis for standardized and representative state-of-the-art quantitative morphological analyses of trout gills, ensuring the unbiasedness and reproducibility, as well as the intra- and inter-study comparability of analyses results. Their broad implementation will therefore significantly contribute to the reliable identification of no observed effect concentration (NOEC) limits in ecotoxicological studies and, moreover, to limit the number of experimental animals by reduction of unnecessary repetition of experiments.

Growth hormone receptor knockout to reduce the size of donor pigs for preclinical xenotransplantation studies

BACKGROUND

Many genetically multi-modified donor lines for xenotransplantation have a background of domestic pigs with rapid body and organ growth. The intrinsic growth potential of porcine xeno-organs may impair their long-term function after orthotopic transplantation in non-human primate models. Since growth hormone is a major stimulator of postnatal growth, we deleted its receptor (GHR-KO) to reduce the size of donor pigs in one step.

METHODS

Heart weight and proteome profile of myocardium were investigated in GHR-KO and control pigs. GHR-KO mutations were introduced using CRISPR/Cas9 in an α1,3-galactosyltransferase (GGTA1)-deficient background expressing the human cluster of differentiation (hCD46) and human thrombomodulin (hTHBD) to generate quadruple-modified (4GM) pigs.

RESULTS

At age 6 months, GHR-KO pigs had a 61% reduced body weight and a 63% reduced heart weight compared with controls. The mean minimal diameter of cardiomyocytes was 28% reduced. A holistic proteome study of myocardium samples from the two groups did not reveal prominent differences. Two 4GM founder sows had low serum insulin-like growth factor 1 (IGF1) levels (24 ± 1 ng/mL) and reached body weights of 70.3 and 73.4 kg at 9 months. Control pigs with IGF1 levels of 228 ± 24 ng/mL reached this weight range three months earlier. The 4GM sows showed normal sexual development and were mated with genetically multi-modified boars. Offspring revealed the expected Mendelian transmission of the genetic modifications and consistent expression of the transgenes.

CONCLUSION

GHR-KO donor pigs can be used at an age beyond the steepest phase of their growth curve, potentially reducing the problem of xeno-organ overgrowth in preclinical studies.

Light sheet fluorescence microscopy guided MALDI-imaging mass spectrometry of cleared tissue samples

Light sheet fluorescence microscopy (LSFM) of optically cleared biological samples represents a powerful tool to analyze the 3-dimensional morphology of tissues and organs. Multimodal combinations of LSFM with additional analyses of the identical sample help to limit the consumption of restricted specimen and reduce inter-sample variation. Here, we demonstrate the proof-of-concept that LSFM of cleared brain tissue samples can be combined with Matrix Assisted Laser Desorption/Ionization-Mass Spectrometry Imaging (MALDI-MSI) for detection and quantification of proteins. Samples of freshly dissected murine brain and of archived formalin-fixed paraffin-embedded (FFPE) human brain tissue were cleared (3DISCO). Tissue regions of interest were defined by LSFM and excised, (re)-embedded in paraffin, and sectioned. Mouse sections were coated with sinapinic acid matrix. Human brain sections were pre-digested with trypsin and coated with α-cyano-4-hydroxycinnamic acid matrix. Subsequently, sections were subjected to MALDI-time-of-flight (TOF)-MSI in mass ranges between 0.8 to 4 kDa (human tissue sections), or 2.5–25 kDa (mouse tissue sections) with a lateral resolution of 50 µm. Protein- and peptide-identities corresponding to acquired MALDI-MSI spectra were confirmed by parallel liquid chromatography tandem mass spectrometry (LC–MS/MS) analysis. The spatial abundance- and intensity-patterns of established marker proteins detected by MALDI-MSI were also confirmed by immunohistochemistry.

A decade of experience with genetically tailored pig models for diabetes and metabolic research

The global prevalence of diabetes mellitus and other metabolic diseases is rapidly increasing. Animal models play pivotal roles in unravelling disease mechanisms and developing and testing therapeutic strategies. Rodents are the most widely used animal models but may have limitations in their resemblance to human disease mechanisms and phenotypes. Findings in rodent models are consequently often difficult to extrapolate to human clinical trials. To overcome this ‘translational gap’, we and other groups are developing porcine disease models. Pigs share many anatomical and physiological traits with humans and thus hold great promise as translational animal models. Importantly, the toolbox for genetic engineering of pigs is rapidly expanding. Human disease mechanisms and targets can therefore be reproduced in pigs on a molecular level, resulting in precise and predictive porcine (PPP) models. In this short review, we summarize our work on the development of genetically (pre)diabetic pig models and how they have been used to study disease mechanisms and test therapeutic strategies. This includes the generation of reporter pigs for studying beta-cell maturation and physiology. Furthermore, genetically engineered pigs are promising donors of pancreatic islets for xenotransplantation. In summary, genetically tailored pig models have become an important link in the chain of translational diabetes and metabolic research.

A Detailed Study of Rainbow Trout (Onchorhynchus mykiss) Intestine Revealed That Digestive and Absorptive Functions Are Not Linearly Distributed along Its Length

Simple Summary

Aquaculture is the fastest growing food-producing sector due to the increase of fish intended for human consumption. However, aquaculture growth generates concerns, since carnivorous fish are extensively fed using fish-meal and fish-oil. This constitutes a severe limit to the aquaculture industry, questioning its sustainability. Consequently, alternative feeds are continuously searched through extensive in vivo feeding trials. Undoubtedly, to evaluate their impact on the gastrointestinal tract health, detailed knowledge of the intestine morphology and physiology is required. To date, extensive studies have been performed in several livestock species; however, available information on fish is limited nowadays, most importantly because their alimentary canal is able to easily adapt to external stimuli, and their intestinal morphology is affected by external factors. Therefore, it is essential to establish accurate reference values, especially along the productive cycle of animals raised in standardized conditions. Here, we performed a detailed characterization of the epithelial cells lining the intestinal mucosa in rainbow trout along the first year of development. We studied the absorptive and secretory activity as well as its ability to self-renewal. Our results indicate that, in this species, both digestive and absorptive functions are not linearly distributed along the intestinal length.

Abstract

To increase the sustainability of trout farming, the industry requires alternatives to fish-based meals that do not compromise animal health and growth performances. To develop new feeds, detailed knowledge of intestinal morphology and physiology is required. We performed histological, histochemical, immunohistochemical and morphometric analysis at typical time points of in vivo feeding trials (50, 150 and 500 g). Only minor changes occurred during growth whereas differences characterized two compartments, not linearly distributed along the intestine. The first included the pyloric caeca, the basal part of the complex folds and the villi of the distal intestine. This was characterized by a significantly smaller number of goblet cells with smaller mucus vacuoles, higher proliferation and higher apoptotic rate but a smaller extension of fully differentiated epithelial cells and by the presence of numerous pinocytotic vacuolization. The second compartment was formed by the proximal intestine and the apical part of the posterior intestine complex folds. Here we observed more abundant goblet cells with bigger vacuoles, low proliferation rate, few round apoptotic cells, a more extended area of fully differentiated cells and no pinocytotic vacuoles. Our results suggest that rainbow trout intestine is physiologically arranged to mingle digestive and absorptive functions along its length.

Linkage between growth retardation and pituitary cell morphology in a dystrophin-deficient pig model of Duchenne muscular dystrophy

OBJECTIVE

Human patients with Duchenne muscular dystrophy (DMD) commonly exhibit a short stature, but the pathogenesis of this growth retardation is not completely understood. Due to the suspected involvement of the growth hormone/insulin-like growth factor 1 (GH/IGF1) system, controversial therapeutic approaches have been developed, including both GH- administration, as well as GH-inhibition. In the present study, we examined relevant histomorphological and ultrastructural features of adenohypophyseal GH-producing somatotroph cells in a porcine DMD model.

METHODS

The numbers and volumes of immunohistochemically labelled somatotroph cells were determined in consecutive semi-thin sections of plastic resin embedded adenohypophyseal tissue samples using unbiased state-of-the-art quantitative stereological analysis methods.

RESULTS

DMD pigs displayed a significant growth retardation, accounting for a 55% reduction of body weight, accompanied by a significant 50% reduction of the number of somatotroph cells, as compared to controls. However, the mean volumes of somatotroph cells and the volume of GH-granules per cell were not altered. Western blot analyses of the adenohypophyseal protein samples showed no differences in the relative adenohypophyseal GH-abundance between DMD pigs and controls.

CONCLUSION

The findings of this study do not provide evidence for involvement of somatotroph cells in the pathogenesis of growth retardation of DMD pigs. These results are in contrast with previous findings in other dystrophin-deficient animal models, such as the golden retriever model of Duchenne muscular dystrophy, where increased mean somatotroph cell volumes and elevated volumes of intracellular GH-granules were reported and associated with DMD-related growth retardation. Possible reasons for the differences of somatotroph morphology observed in different DMD models are discussed.

Functional changes of the liver in the absence of growth hormone (GH) action - Proteomic and metabolomic insights from a GH receptor deficient pig model

OBJECTIVE

The liver is a central target organ of growth hormone (GH), which stimulates the synthesis of insulin-like growth factor 1 (IGF1) and affects multiple biochemical pathways. A systematic multi-omics analysis of GH effects in the liver has not been performed. GH receptor (GHR) deficiency is a unique model for studying the consequences of lacking GH action. In this study, we used molecular profiling techniques to capture a broad spectrum of these effects in the liver of a clinically relevant large animal model for Laron syndrome.

METHODS

We performed holistic proteome and targeted metabolome analyses of liver samples from 6-month-old GHR-deficient (GHR-KO) pigs and GHR-expressing controls (four males, four females per group).

RESULTS

GHR deficiency resulted in an increased abundance of enzymes involved in amino acid degradation, in the urea cycle, and in the tricarboxylic acid cycle. A decreased ratio of long-chain acylcarnitines to free carnitine suggested reduced activity of carnitine palmitoyltransferase 1A and thus reduced mitochondrial import of fatty acids for beta-oxidation. Increased levels of short-chain acylcarnitines in the liver and in the circulation of GHR-KO pigs may result from impaired beta-oxidation of short-chain fatty acids or from increased degradation of specific amino acids. The concentration of mono-unsaturated glycerophosphocholines was significantly increased in the liver of GHR-KO pigs without morphological signs of steatosis, although the abundances of several proteins functionally linked to non-alcoholic fatty liver disease (fetuin B, retinol binding protein 4, several mitochondrial proteins) were increased. Moreover, GHR-deficient liver samples revealed distinct changes in the methionine and glutathione metabolic pathways, in particular, a significantly increased level of glycine N-methyltransferase and increased levels of total and free glutathione. Several proteins revealed a sex-related abundance difference in the control group but not in the GHR-KO group.

CONCLUSIONS

Our integrated proteomics/targeted metabolomics study of GHR-deficient and control liver samples from a clinically relevant large animal model identified a spectrum of biological pathways that are significantly altered in the absence of GH action. Moreover, new insights into the role of GH in the sex-related specification of liver functions were provided.

Porcine models for studying complications and organ crosstalk in diabetes mellitus

The worldwide prevalence of diabetes mellitus and obesity is rapidly increasing not only in adults but also in children and adolescents. Diabetes is associated with macrovascular complications increasing the risk for cardiovascular disease and stroke, as well as microvascular complications leading to diabetic nephropathy, retinopathy and neuropathy. Animal models are essential for studying disease mechanisms and for developing and testing diagnostic procedures and therapeutic strategies. Rodent models are most widely used but have limitations in translational research. Porcine models have the potential to bridge the gap between basic studies and clinical trials in human patients. This article provides an overview of concepts for the development of porcine models for diabetes and obesity research, with a focus on genetically engineered models. Diabetes-associated ocular, cardiovascular and renal alterations observed in diabetic pig models are summarized and their similarities with complications in diabetic patients are discussed. Systematic multi-organ biobanking of porcine models of diabetes and obesity and molecular profiling of representative tissue samples on different levels, e.g., on the transcriptome, proteome, or metabolome level, is proposed as a strategy for discovering tissue-specific pathomechanisms and their molecular key drivers using systems biology tools. This is exemplified by a recent study providing multi-omics insights into functional changes of the liver in a transgenic pig model for insulin-deficient diabetes mellitus. Collectively, these approaches will provide a better understanding of organ crosstalk in diabetes mellitus and eventually reveal new molecular targets for the prevention, early diagnosis and treatment of diabetes mellitus and its associated complications.

Spontaneous Age-Related Histopathological Changes in Microminipigs

Microminipigs have become an attractive animal model for toxicology and pharmacology studies and for human disease models, owing to their manageable size. Although there are numerous reports of spontaneous age-related lesions in mice, rats, dogs, and monkeys, those in minipigs are scarce. In the present study, spontaneous age-related histopathological changes were investigated using 37 microminipigs (20 males and 17 females) that were 6 months to 10 years of age. Abnormal deposits of materials were evident in several animals from 6 years of age, and these deposits included amyloid in the renal medulla, thyroid gland, and adrenal gland, hyaline droplets in glomeruli, and fibrillar inclusions in neurons. Arterial sclerosing changes (intimal thickening, intimal proliferation, and medial mineralization) and proliferative lesions (hyperplasia of hepatocytes, follicular cells, Leydig cells, and uterine endometrial glands) were present at 4 years of age and beyond. Renal adenoma, uterine leiomyoma, and Leydig cell tumor were observed in several microminipigs. Moreover, glomerulosclerosis, renal interstitial fibrosis, thymic involution, and adrenocortical cell vacuolation were common in aging microminipigs. Since knowledge of age-related changes is helpful for pathologists, the basic information obtained in this study will be a useful reference for all future toxicity evaluations in microminipigs.

Evolution of pig intestinal stem cells from birth to weaning

Pig intestinal epithelium undergoes a complete renewal every 2 to 3 days that is driven by intestinal stem cells (ISCs) located at the crypt base in their niche. Intestinal stem cells generate a pool of highly proliferative transit-amplifying cells, which either migrate up the villus and differentiate into enterocytes and secretory cells or migrate towards the base of the crypt where they differentiate into Paneth cells that secrete antimicrobial peptides. The balance between ISCs' self-renewal and differentiation controls intestinal epithelial homeostasis; therefore, ISCs are essential for ensuring intestinal epithelial integrity. Detailed knowledge of these mechanisms in pig and other domestic species is very limited. Therefore, the aim of this work was to characterize ISC from birth to weaning. We analysed the duodenum, jejunum and colon of six piglets at birth, 6-day-old nursing piglets and 28-day-old weanlings, one week after weaning. We immunolocalized homeobox only protein+ (HOPX) and sex-determining region Y-box 9+ (SOX9) cells that identify quiescent and active ISC, respectively. The volume of ISCs was quantified with stereological methods and was compared to that of mitotic cells expressing proliferating cell nuclear antigen and apoptotic cells identified by the presence of cleaved caspase-3. Furthermore, we compared all these values with crypts and villi measurements and their ratio. Our results indicated that both quiescent and active ISCs are present in pig intestine from birth to weaning and are localized in the crypts of the small and large intestine. However, both markers were also observed along the villi and on the colon luminal epithelium, suggesting that at these stages, pig mucosa is still immature. Weaning induced a dramatic reduction of both HOPX+ and SOX9+ cells, but SOX9+ cells underwent a significantly greater reduction in the small intestine than in the colon. This suggests that the two ISC types are differentially regulated along the intestinal tracts. Overall, the pig ISC complex has many similarities with its murine counterpart, but also has some differences. These include active ISC not showing the typical columnar base morphology as well as the absence of bona fide Paneth cells. This is the first description of ISC dynamics during pig's early life and provides useful reference data for future studies, aimed at targeting ISC for the development of efficient alternatives to in-feed antibiotics for preserving intestinal integrity.

Dissection of the Trigeminal Ganglion of Nonrodent Species Used in Toxicology Studies

The ganglion of the trigeminal (V cranial) nerve is generally sampled at necropsy in nonrodent toxicology studies only when somatic or autonomic peripheral nervous system toxicity is suspected. The ganglion is far more difficult to locate in nonrodents than in rats and mice, and suitable methods to dissect it have been described only for swine. The trigeminal nerve caudal to the ganglion passes through a canal, roofed by bone in dogs and rabbits and by a tough layer of dura mater in swine and nonhuman primates. The ganglion is partly or wholly obscured by overlying dura mater. Of the 3 intracranial branches of the nerve, the ophthalmic is delicate and the maxillary and mandibular have extremely short courses within the cranial cavity. Methods that are practical in routine toxicologic pathology for the dissection of the ganglion in nonrodent laboratory species are illustrated and relevant species differences in the anatomy of the intracranial part of the trigeminal nerve are highlighted.

Multi-omics insights into functional alterations of the liver in insulin-deficient diabetes mellitus

OBJECTIVE

The liver regulates the availability of insulin to other tissues and is the first line insulin response organ physiologically exposed to higher insulin concentrations than the periphery. Basal insulin during fasting inhibits hepatic gluconeogenesis and glycogenolysis, whereas postprandial insulin peaks stimulate glycogen synthesis. The molecular consequences of chronic insulin deficiency for the liver have not been studied systematically.

METHODS

We analyzed liver samples of a genetically diabetic pig model (MIDY) and of wild-type (WT) littermate controls by RNA sequencing, proteomics, and targeted metabolomics/lipidomics.

RESULTS

Cross-omics analyses revealed increased activities in amino acid metabolism, oxidation of fatty acids, ketogenesis, and gluconeogenesis in the MIDY samples. In particular, the concentrations of the ketogenic enzyme 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2) and of retinol dehydrogenase 16 (RDH16), which catalyzes the first step in retinoic acid biogenesis, were highly increased. Accordingly, elevated levels of retinoic acid, which stimulates the expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PCK1), were measured in the MIDY samples. In contrast, pathways related to extracellular matrix and inflammation/pathogen defense response were less active than in the WT samples.

CONCLUSIONS

The first multi-omics study of a clinically relevant diabetic large animal model revealed molecular signatures and key drivers of functional alterations of the liver in insulin-deficient diabetes mellitus. The multi-omics data set provides a valuable resource for comparative analyses with other experimental or clinical data sets.

Pathology Study Design, Conduct, and Reporting to Achieve Rigor and Reproducibility in Translational Research Using Animal Models

In translational research, animal models are an important tool to aid in decision-making when taking potential therapies into human clinical trials. Recently, there have been a number of papers that have suggested limited concordance of preclinical animal experiments with subsequent human clinical experience. Assessments of preclinical animal studies have led to concerns about the reproducibility of data and have highlighted the need for an emphasis on rigor and quality in the planning, conduct, analysis, and reporting of such studies. The incorporation of a wider role for the comparative pathologist using pathology best practices in the planning and conduct of animal model-based research is one way to increase the quality and reproducibility of data. The use of optimal design and planning of tissue collection, incorporation of pathology methods into written protocols, conduct of pathology procedures using accepted best practices, and the use of optimal pathology analysis and reporting methods enhance the quality of the data acquired from many types of preclinical animal models and studies. Many of these pathology practices are well established in the discipline of toxicologic pathology and have a proven and useful track record in enhancing the data from animal-based studies used in safety assessment of human therapeutics. Some of this experience can be adopted by the wider community of preclinical investigators to increase the reproducibility of animal study data.

Generation of an equine biobank to be used for Functional Annotation of Animal Genomes project

The Functional Annotation of Animal Genomes (FAANG) project aims to identify genomic regulatory elements in both sexes across multiple stages of development in domesticated animals. This study represents the first stage of the FAANG project for the horse, Equus caballus. A biobank of 80 tissue samples, two cell lines and six body fluids was created from two adult Thoroughbred mares. Ante-mortem assessments included full physical examinations, lameness, ophthalmologic and neurologic evaluations. Complete blood counts and serum biochemistries were also performed. At necropsy, in addition to tissue samples, aliquots of serum, ethylenediaminetetraacetic acid (EDTA) plasma, heparinized plasma, cerebrospinal fluid, synovial fluid, urine and microbiome samples from all regions of the gastrointestinal and urogenital tracts were collected. Epidermal keratinocytes and dermal fibroblasts were cultured from skin samples. All tissues were grossly and histologically evaluated by a board-certified veterinary pathologist. The results of the clinical and pathological evaluations identified subclinical eosinophilic and lymphocytic infiltration throughout the length of the gastrointestinal tract as well as a mild clinical lameness in both animals. Each sample was cryo-preserved in multiple ways, and nuclei were extracted from selected tissues. These samples represent the first published systemically healthy equine-specific biobank with extensive clinical phenotyping ante- and post-mortem. The tissues in the biobank are intended for community-wide use in the functional annotation of the equine genome. The use of the biobank will improve the quality of the reference annotation and allow all equine researchers to elucidate unknown genomic and epigenomic causes of disease.

Metabolic syndrome and extensive adipose tissue inflammation in morbidly obese Göttingen minipigs

OBJECTIVE

The worldwide prevalence of obesity has increased to 10% in men and 15% in women and is associated with severe comorbidities such as diabetes, cancer, and cardiovascular disease. Animal models of obesity are central to experimental studies of disease mechanisms and therapeutic strategies. Diet-induced obesity (DIO) models in rodents have provided important insights into the pathophysiology of obesity and, in most instances, are the first in line for exploratory pharmacology studies. To deepen the relevance towards translation to human patients, we established a corresponding DIO model in Göttingen minipigs (GM).

METHODS

Young adult female ovariectomized GM were fed a high-fat/high-energy diet for a period of 70 weeks. The ration was calculated to meet the requirements and maintain body weight (BW) of lean adult minipigs (L-GM group) or increased stepwise to achieve an obese state (DIO-GM group). Body composition, blood parameters and intravenous glucose tolerance were determined at regular intervals. A pilot chronic treatment trial with a GLP1 receptor agonist was conducted in DIO-GM. At the end of the study, the animals were necropsied and a biobank of selected tissues was established.

RESULTS

DIO-GM developed severe subcutaneous and visceral adiposity (body fat >50% of body mass vs. 22% in L-GM), increased plasma cholesterol, triglyceride, and free fatty acid levels, insulin resistance (HOMA-IR >5 vs. 2 in L-GM), impaired glucose tolerance and increased heart rate when resting and active. However, fasting glucose concentrations stayed within normal range throughout the study. Treatment with a long-acting GLP1 receptor agonist revealed substantial reduction of food intake and body weight within four weeks, with increased drug sensitivity relative to observations in other DIO animal models. Extensive adipose tissue inflammation and adipocyte necrosis was observed in visceral, but not subcutaneous, adipose tissue of DIO-GM.

CONCLUSIONS

The Munich DIO-GM model resembles hallmarks of the human metabolic syndrome with extensive adipose tissue inflammation and adipocyte necrosis reported for the first time. DIO-GM may be used for evaluating novel treatments of obesity and associated comorbidities. They may help to identify triggers and mechanisms of fat tissue inflammation and mechanisms preventing complete metabolic decompensation despite morbid obesity.

Growth hormone receptor-deficient pigs resemble the pathophysiology of human Laron syndrome and reveal altered activation of signaling cascades in the liver

OBJECTIVE

Laron syndrome (LS) is a rare, autosomal recessive disorder in humans caused by loss-of-function mutations of the growth hormone receptor (GHR) gene. To establish a large animal model for LS, pigs with GHR knockout (KO) mutations were generated and characterized.

METHODS

CRISPR/Cas9 technology was applied to mutate exon 3 of the GHR gene in porcine zygotes. Two heterozygous founder sows with a 1-bp or 7-bp insertion in GHR exon 3 were obtained, and their heterozygous F1 offspring were intercrossed to produce GHR-KO, heterozygous GHR mutant, and wild-type pigs. Since the latter two groups were not significantly different in any parameter investigated, they were pooled as the GHR expressing control group. The characterization program included body and organ growth, body composition, endocrine and clinical-chemical parameters, as well as signaling studies in liver tissue.

RESULTS

GHR-KO pigs lacked GHR and had markedly reduced serum insulin-like growth factor 1 (IGF1) levels and reduced IGF-binding protein 3 (IGFBP3) activity but increased IGFBP2 levels. Serum GH concentrations were significantly elevated compared with control pigs. GHR-KO pigs had a normal birth weight. Growth retardation became significant at the age of five weeks. At the age of six months, the body weight of GHR-KO pigs was reduced by 60% compared with controls. Most organ weights of GHR-KO pigs were reduced proportionally to body weight. However, the weights of liver, kidneys, and heart were disproportionately reduced, while the relative brain weight was almost doubled. GHR-KO pigs had a markedly increased percentage of total body fat relative to body weight and displayed transient juvenile hypoglycemia along with decreased serum triglyceride and cholesterol levels. Analysis of insulin receptor related signaling in the liver of adult fasted pigs revealed increased phosphorylation of IRS1 and PI3K. In agreement with the loss of GHR, phosphorylation of STAT5 was significantly reduced. In contrast, phosphorylation of JAK2 was significantly increased, possibly due to the increased serum leptin levels and increased hepatic leptin receptor expression and activation in GHR-KO pigs. In addition, increased mTOR phosphorylation was observed in GHR-KO liver samples, and phosphorylation studies of downstream substrates suggested the activation of mainly mTOR complex 2.

CONCLUSION

GHR-KO pigs resemble the pathophysiology of LS and are an interesting model for mechanistic studies and treatment trials.

Sampling Strategies and Processing of Biobank Tissue Samples from Porcine Biomedical Models

In translational medical research, porcine models have steadily become more popular. Considering the high value of individual animals, particularly of genetically modified pig models, and the often-limited number of available animals of these models, establishment of (biobank) collections of adequately processed tissue samples suited for a broad spectrum of subsequent analyses methods, including analyses not specified at the time point of sampling, represent meaningful approaches to take full advantage of the translational value of the model. With respect to the peculiarities of porcine anatomy, comprehensive guidelines have recently been established for standardized generation of representative, high-quality samples from different porcine organs and tissues. These guidelines are essential prerequisites for the reproducibility of results and their comparability between different studies and investigators. The recording of basic data, such as organ weights and volumes, the determination of the sampling locations and of the numbers of tissue samples to be generated, as well as their orientation, size, processing and trimming directions, are relevant factors determining the generalizability and usability of the specimen for molecular, qualitative, and quantitative morphological analyses. Here, an illustrative, practical, step-by-step demonstration of the most important techniques for generation of representative, multi-purpose biobank specimen from porcine tissues is presented. The methods described here include determination of organ/tissue volumes and densities, the application of a volume-weighted systematic random sampling procedure for parenchymal organs by point-counting, determination of the extent of tissue shrinkage related to histological embedding of samples, and generation of randomly oriented samples for quantitative stereological analyses, such as isotropic uniform random (IUR) sections generated by the "Orientator" and "Isector" methods, and vertical uniform random (VUR) sections.

Practicable methods for histological section thickness measurement in quantitative stereological analyses

The accuracy of quantitative stereological analysis tools such as the (physical) disector method substantially depends on the precise determination of the thickness of the analyzed histological sections. One conventional method for measurement of histological section thickness is to re-embed the section of interest vertically to its original section plane. The section thickness is then measured in a subsequently prepared histological section of this orthogonally re-embedded sample. However, the orthogonal re-embedding (ORE) technique is quite work- and time-intensive and may produce inaccurate section thickness measurement values due to unintentional slightly oblique (non-orthogonal) positioning of the re-embedded sample-section. Here, an improved ORE method is presented, allowing for determination of the factual section plane angle of the re-embedded section, and correction of measured section thickness values for oblique (non-orthogonal) sectioning. For this, the analyzed section is mounted flat on a foil of known thickness (calibration foil) and both the section and the calibration foil are then vertically (re-)embedded. The section angle of the re-embedded section is then calculated from the deviation of the measured section thickness of the calibration foil and its factual thickness, using basic geometry. To find a practicable, fast, and accurate alternative to ORE, the suitability of spectral reflectance (SR) measurement for determination of plastic section thicknesses was evaluated. Using a commercially available optical reflectometer (F20, Filmetrics^®, USA), the thicknesses of 0.5 μm thick semi-thin Epon (glycid ether)-sections and of 1–3 μm thick plastic sections (glycolmethacrylate/ methylmethacrylate, GMA/MMA), as regularly used in physical disector analyses, could precisely be measured within few seconds. Compared to the measured section thicknesses determined by ORE, SR measures displayed less than 1% deviation. Our results prove the applicability of SR to efficiently provide accurate section thickness measurements as a prerequisite for reliable estimates of dependent quantitative stereological parameters.

Retinopathy with central oedema in an INS C94Y transgenic pig model of long-term diabetes

AIMS/HYPOTHESIS

Diabetic retinopathy is a severe complication of diabetes mellitus that often leads to blindness. Because the pathophysiology of diabetic retinopathy is not fully understood and novel therapeutic interventions require testing, there is a need for reliable animal models that mimic all the complications of diabetic retinopathy. Pig eyes share important anatomical and physiological similarities with human eyes. Previous studies have demonstrated that INS ^C94Y transgenic pigs develop a stable diabetic phenotype and ocular alterations such as cataracts. The aim of this study was to conduct an in-depth analysis of pathological changes in retinas from INS ^C94Y pigs exposed to hyperglycaemia for more than 2 years, representing a chronic diabetic condition.

METHODS

Eyes from six INS ^C94Ypigs and six age-matched control littermates were analysed via histology and immunohistochemistry. For histological analyses of retinal (layer) thickness, sections were stained with H&E or Mallory's trichrome. For comparison of protein expression patterns and vessel courses, sections were stained with different antibodies in immunohistochemistry. Observed lesions were compared with reported pathologies in human diabetic retinopathy.

RESULTS

INS ^C94Ypigs developed several signs of diabetic retinopathy similar to those seen in humans, such as intraretinal microvascular abnormalities, symptoms of proliferative diabetic retinopathy and central retinal oedema in a region that is cone rich, like the human macula.

CONCLUSIONS/INTERPRETATION

The INS ^C94Ypig is an interesting model for studying the pathophysiology of diabetic retinopathy and for testing novel therapeutic strategies.

The Munich MIDY Pig Biobank - A unique resource for studying organ crosstalk in diabetes

OBJECTIVE

The prevalence of diabetes mellitus and associated complications is steadily increasing. As a resource for studying systemic consequences of chronic insulin insufficiency and hyperglycemia, we established a comprehensive biobank of long-term diabetic INSC94Y transgenic pigs, a model of mutant INS gene-induced diabetes of youth (MIDY), and of wild-type (WT) littermates.

METHODS

Female MIDY pigs (n = 4) were maintained with suboptimal insulin treatment for 2 years, together with female WT littermates (n = 5). Plasma insulin, C-peptide and glucagon levels were regularly determined using specific immunoassays. In addition, clinical chemical, targeted metabolomics, and lipidomics analyses were performed. At age 2 years, all pigs were euthanized, necropsied, and a broad spectrum of tissues was taken by systematic uniform random sampling procedures. Total beta cell volume was determined by stereological methods. A pilot proteome analysis of pancreas, liver, and kidney cortex was performed by label free proteomics.

RESULTS

MIDY pigs had elevated fasting plasma glucose and fructosamine concentrations, C-peptide levels that decreased with age and were undetectable at 2 years, and an 82% reduced total beta cell volume compared to WT. Plasma glucagon and beta hydroxybutyrate levels of MIDY pigs were chronically elevated, reflecting hallmarks of poorly controlled diabetes in humans. In total, ∼1900 samples of different body fluids (blood, serum, plasma, urine, cerebrospinal fluid, and synovial fluid) as well as ∼17,000 samples from ∼50 different tissues and organs were preserved to facilitate a plethora of morphological and molecular analyses. Principal component analyses of plasma targeted metabolomics and lipidomics data and of proteome profiles from pancreas, liver, and kidney cortex clearly separated MIDY and WT samples.

CONCLUSIONS

The broad spectrum of well-defined biosamples in the Munich MIDY Pig Biobank that will be available to the scientific community provides a unique resource for systematic studies of organ crosstalk in diabetes in a multi-organ, multi-omics dimension.

Missense Mutation of POU Domain Class 3 Transcription Factor 3 in Pou3f3L423P Mice Causes Reduced Nephron Number and Impaired Development of the Thick Ascending Limb of the Loop of Henle

During nephrogenesis, POU domain class 3 transcription factor 3 (POU3F3 aka BRN1) is critically involved in development of distinct nephron segments, including the thick ascending limb of the loop of Henle (TAL). Deficiency of POU3F3 in knock-out mice leads to underdevelopment of the TAL, lack of differentiation of TAL cells, and perinatal death due to renal failure. Pou3f3L423P mutant mice, which were established in the Munich ENU Mouse Mutagenesis Project, carry a recessive point mutation in the homeobox domain of POU3F3. Homozygous Pou3f3L423P mutants are viable and fertile. The present study used functional, as well as qualitative and quantitative morphological analyses to characterize the renal phenotype of juvenile (12 days) and aged (60 weeks) homo- and heterozygous Pou3f3L423P mutant mice and age-matched wild-type controls. In both age groups, homozygous mutants vs. control mice displayed significantly smaller kidney volumes, decreased nephron numbers and mean glomerular volumes, smaller TAL volumes, as well as lower volume densities of the TAL in the kidney. No histological or ultrastructural lesions of TAL cells or glomerular cells were observed in homozygous mutant mice. Aged homozygous mutants displayed increased serum urea concentrations and reduced specific urine gravity, but no evidence of glomerular dysfunction. These results confirm the role of POU3F3 in development and function of the TAL and provide new evidence for its involvement in regulation of the nephron number in the kidney. Therefore, Pou3f3L423P mutant mice represent a valuable research model for further analyses of POU3F3 functions, or for nephrological studies examining the role of congenital low nephron numbers.

Comparative aspects of rodent and nonrodent animal models for mechanistic and translational diabetes research

The prevalence of diabetes mellitus, which currently affects 387 million people worldwide, is permanently rising in both adults and adolescents. Despite numerous treatment options, diabetes mellitus is a progressive disease with severe comorbidities, such as nephropathy, neuropathy, and retinopathy, as well as cardiovascular disease. Therefore, animal models predictive of the efficacy and safety of novel compounds in humans are of great value to address the unmet need for improved therapeutics. Although rodent models provide important mechanistic insights, their predictive value for therapeutic outcomes in humans is limited. In recent years, the pig has gained importance for biomedical research because of its close similarity to human anatomy, physiology, size, and, in contrast to non-human primates, better ethical acceptance. In this review, anatomic, biochemical, physiological, and morphologic aspects relevant to diabetes research will be compared between different animal species, that is, mouse, rat, rabbit, pig, and non-human primates. The value of the pig as a model organism for diabetes research will be highlighted, and (dis)advantages of the currently available approaches for the generation of pig models exhibiting characteristics of metabolic syndrome or type 2 diabetes mellitus will be discussed.