A comparative immunohistochemical study of pancreatic islets in laboratory animals (rats, dogs, minipigs, nonhuman primates)

Machine-learning-guided recognition of α and β cells from label-free infrared micrographs of living human islets of Langerhans

Human islets of Langerhans are composed mostly of glucagon-secreting α cells and insulin-secreting β cells closely intermingled one another. Current methods for identifying α and β cells involve either fixing islets and using immunostaining or disaggregating islets and employing flow cytometry for classifying α and β cells based on their size and autofluorescence. Neither approach, however, allows investigating the dynamic behavior of α and β cells in a living and intact islet. To tackle this issue, we present a machine-learning-based strategy for identification α and β cells in label-free infrared micrographs of living human islets without immunostaining. Intrinsic autofluorescence is stimulated by infrared light and collected both in intensity and lifetime in the visible range, dominated by NAD(P)H and lipofuscin signals. Descriptive parameters are derived from micrographs for ~ 103 cells. These parameters are used as input for a boosted decision-tree model (XGBoost) pre-trained with immunofluorescence-derived cell-type information. The model displays an optimized-metrics performance of 0.86 (i.e. area under a ROC curve), with an associated precision of 0.94 for the recognition of β cells and 0.75 for α cells. This tool promises to enable longitudinal studies on the dynamic behavior of individual cell types at single-cell resolution within the intact tissue.

Heterogenous expression of endocrine and progenitor cells within the neonatal porcine pancreatic lobes-Implications for neonatal porcine islet xenotransplantation

Neonatal porcine islets (NPIs) are a source of islets for xenotransplantation. In the pig, the pancreatic lobes remain separate, thus, when optimizing NPI isolation, the pancreatic lobes included in the pancreatic digest should be specified. These lobes are the duodenal (DL), splenic (SL) and connecting (CL) lobe that correspond to the head, body-tail, and uncinate process of the human pancreas. In this study we are the first to evaluate all three neonatal porcine pancreatic lobes and NPIs isolated from these lobes. We report, a significant difference in endocrine and progenitor cell composition between lobes, and observed pancreatic duct glands (PDG) within the mesenchyme surrounding exocrine ducts in the DL and CL. Following in vitro differentiation, NPIs isolated from each lobe differed significantly in the percent increase of endocrine cells and final cell composition. Compared to other recipients, diabetic immunodeficient mice transplanted with NPIs isolated from the SL demonstrated euglycemic control as early as 4 weeks (p < 0.05) and achieved normoglycemia by 6 weeks post-transplant (p < 0.01). For the first time we report significant differences between the neonatal porcine pancreatic lobes and demonstrate that NPIs from these lobes differ in xenograft function.

The Role of Adiponectin during Pregnancy and Gestational Diabetes

Pregnancy involves a range of metabolic adaptations to supply adequate energy for fetal growth and development. Gestational diabetes (GDM) is defined as hyperglycemia with first onset during pregnancy. GDM is a recognized risk factor for both pregnancy complications and long-term maternal and offspring risk of cardiometabolic disease development. While pregnancy changes maternal metabolism, GDM can be viewed as a maladaptation by maternal systems to pregnancy, which may include mechanisms such as insufficient insulin secretion, dysregulated hepatic glucose output, mitochondrial dysfunction and lipotoxicity. Adiponectin is an adipose-tissue-derived adipokine that circulates in the body and regulates a diverse range of physiologic mechanisms including energy metabolism and insulin sensitivity. In pregnant women, circulating adiponectin levels decrease correspondingly with insulin sensitivity, and adiponectin levels are low in GDM. In this review, we summarize the current state of knowledge about metabolic adaptations to pregnancy and the role of adiponectin in these processes, with a focus on GDM. Recent studies from rodent model systems have clarified that adiponectin deficiency during pregnancy contributes to GDM development. The upregulation of adiponectin alleviates hyperglycemia in pregnant mice, although much remains to be understood for adiponectin to be utilized clinically for GDM.

Submilligram Level of Beetle Antifreeze Proteins Minimize Cold-Induced Cell Swelling and Promote Cell Survival

Hypothermic (cold) preservation is a limiting factor for successful cell and tissue transplantation where cell swelling (edema) usually develops, impairing cell function. University of Wisconsin (UW) solution, a standard cold preservation solution, contains effective components to suppress hypothermia-induced cell swelling. Antifreeze proteins (AFPs) found in many cold-adapted organisms can prevent cold injury of the organisms. Here, the effects of a beetle AFP from Dendroides canadensis (DAFP-1) on pancreatic β-cells preservation were first investigated. As low as 500 µg/mL, DAFP-1 significantly minimized INS-1 cell swelling and subsequent cell death during 4 °C preservation in UW solution for up to three days. However, such significant cytoprotection was not observed by an AFP from Tenebrio molitor (TmAFP), a structural homologue to DAFP-1 but lacking arginine, at the same levels. The cytoprotective effect of DAFP-1 was further validated with the primary β-cells in the isolated rat pancreatic islets in UW solution. The submilligram level supplement of DAFP-1 to UW solution significantly increased the islet mass recovery after three days of cold preservation followed by rewarming. The protective effects of DAFP-1 in UW solution were discussed at a molecular level. The results indicate the potential of DAFP-1 to enhance cell survival during extended cold preservation.

Comparative analysis of reconstructed architectures from mice and human islets

Intra-islet communication via electrical, paracrine and autocrine signals, is highly dependent on the organization of cells within the islets and is key for an adequate response to changes in blood glucose and other stimuli. In spite of the fact that relevant structural differences between mouse and human islet architectures have been described, the functional implications of these differences remain only partially understood. In this work, aiming to contribute to a better understanding of the relationship between structural and functional properties of pancreatic islets, we reconstructed human and mice islets in order to perform a structural comparison based on both morphologic and network-derived metrics. According to our results, human islets constitute a more efficient network from a connectivity viewpoint, mainly due to the higher proportion of heterotypic contacts between islet cells in comparison to mice islets.

Diagnosis and treatment of type 1 diabetes at the dawn of the personalized medicine era

Type 1 diabetes affects millions of people globally and requires careful management to avoid serious long-term complications, including heart and kidney disease, stroke, and loss of sight. The type 1 diabetes patient cohort is highly heterogeneous, with individuals presenting with disease at different stages and severities, arising from distinct etiologies, and overlaying varied genetic backgrounds. At present, the “one-size-fits-all” treatment for type 1 diabetes is exogenic insulin substitution therapy, but this approach fails to achieve optimal blood glucose control in many individuals. With advances in our understanding of early-stage diabetes development, diabetes stratification, and the role of genetics, type 1 diabetes is a promising candidate for a personalized medicine approach, which aims to apply “the right therapy at the right time, to the right patient”. In the case of type 1 diabetes, great efforts are now being focused on risk stratification for diabetes development to enable pre-clinical detection, and the application of treatments such as gene therapy, to prevent pancreatic destruction in a sub-set of patients. Alongside this, breakthroughs in stem cell therapies hold great promise for the regeneration of pancreatic tissues in some individuals. Here we review the recent initiatives in the field of personalized medicine for type 1 diabetes, including the latest discoveries in stem cell and gene therapy for the disease, and current obstacles that must be overcome before the dream of personalized medicine for all type 1 diabetes patients can be realized.

Pancreatic Islets and Gestalt Principles

The human brain has inherent methodology to efficiently interpret complex environmental stimuli into understanding. This visual perception is governed by the law of simplicity, which is fundamental to Gestalt theory. First introduced in a seminal article by Wertheimer in 1923, the theory explains how the mind groups similar images and fills in gaps in order to perceive an amenable version of reality. The world we see consists of complex visual scenes, but rarely is the entire picture visible to us. Since it is inefficient for all visual data to be analyzed at once, certain patterns are given higher importance and made to stand out from the rest of the field in our brain. Here we propose that Gestalt theory may explain why rodent islet architecture has historically been seen as having a core-mantle arrangement. By filling in apparent gaps in the non-β-cell lining, the mind interprets it as a "whole" mantle, which may have further led to widely accepted notions regarding islet microcirculation, intra-islet signaling, and islet development. They are largely based on the prevailing stereotypic islet architecture in which an enclosed structure is presumed. Three-dimensional analysis provides more integrated views of islet and pancreatic microcirculation.

Foetal development of endocrine organs in dog

The canine adenohypophysis starts to be identifiable from 25 day of pregnancy. ACTH-immunoreactive cells migrate until day 38 after which the number of ACTH-producing cells increases but their distribution does not change. The STH- and LH-producing cells first appear on day 38 of pregnancy. The primordium of the adrenal glands appears as a slender structure on day 27 and forms the definitive cortical structure on day 35. The histological pattern of the foetal adrenal cortex differs from the post-natal structure in so far as the three cortical zones (definitive zone, transitional zone and foetal zone) extend from the outside towards the inside of gland. The mass of foetal and neonatal adrenals is more than 10 times larger than the adult adrenals relative to body weight. The cortisol concentration in the amnion is slightly lower than in the allantois but the foetal serum cortisol concentration is significantly higher than in the maternal and foetal fluid compartments. The thyroxine concentrations in the allantois and amnion fluids exceed the foetal serum concentrations except in the ninth week of pregnancy, but thyroxine levels in foetal fluids and serum are below the physiological levels of adult animals. The exocrine and endocrine functions of the pancreas develop and act in parallel. Pancreatic cells are first detected at 30 days when the branched structure is clearly detectable immunohistochemically, and at that time, insulin-positive β-cells and α-cells are visible as well. The foetal serum glucose concentration exceeds the healthy adult range, but the glucose concentration in the allantois and amnion fluid remains below the physiological blood glucose concentration of mature dogs. The insulin concentration in the allantois fluid greatly exceeds the foetal serum and amnion insulin concentrations.

Characterization of Insulin and Glucagon Genes and Their Producing Endocrine Cells From Pygmy Sperm Whale (Kogia breviceps)

Insulin and glucagon are hormones secreted by pancreatic β and α cells, respectively, which together regulate glucose homeostasis. Dysregulation of insulin or glucagon can result in loss of blood glucose control, characterized by hyperglycemia or hypoglycemia. To better understand the endocrine physiology of cetaceans, we cloned and characterized the insulin and glucagon genes from pygmy sperm whale (Kogia breviceps). We obtained the complete coding sequences of the preproinsulin and preproglucagon genes, which encodes the preproinsulin protein of 110 amino acid (aa) residues and encodes the preproglucagon protein of 179 aa residues, respectively. Sequence comparison and phylogenetic analyses demonstrate that protein structures were similar to other mammalian orthologs. Immunohistochemistry and immunofluorescence staining using insulin, glucagon, and somatostatin antibodies allowed analysis of pygmy sperm whale islet distribution, architecture, and composition. Our results showed the pygmy sperm whale islet was irregularly shaped and randomly distributed throughout the pancreas. The architecture of α, β, and δ cells of the pygmy sperm whale was similar to that of artiodactyls species. This is the first report about insulin and glucagon genes in cetaceans, which provides new information about the structural conservation of the insulin and glucagon genes. Furthermore, offers novel information on the properties of endocrine cells in cetacean for further studies.

Immunohistochemical distribution of insulin-, glucagon- and somatostatin-containing cells in the pancreas of Lake Van fish (Alburnus tarichi Güldenstädt, 1814) (Cyprinidae)

The Lake Van fish (Alburnus tarichi) is a species that is endemic to Turkey’s Lake Van basin. In this study, the regional distribution, volume density, and relative frequency of some pancreatic endocrine cells in Lake Van fish were investigated via immunohistochemistry using specific mammalian antibodies. The pancreatic tissue was observed to be surrounded by adipose tissue, which was adjacent to the gall bladder or extrahepatic bile duct, or dispersed in the adipose tissue ranked among coils of post-esophageal swelling and intestine. The pancreatic endocrine cells were examined, including the islets, exocrine pancreas, and pancreatic ducts. According to the modified aldehyde fuchsin staining and immunohistochemistry, insulin-secreting beta cells were observed to localize throughout the islets. Glucagon immune-reactive (IR) cells were observed to be situated moderately on the islet periphery, and were rarely determined in the islet central region. A small number of somatostatin- IR cells were observed in the islet centers and peripheries. Similar distributions of those three endocrine cells were also determined in the secondary islets. Additionally, the endocrine cell percentages did not differ between the primary and secondary islets; insulin-, glucagon- and somatostatin-IR cells comprised approximately 54%, 29%, and 11% of the endocrine cells in the principal islets, whereas they comprised 52%, 27%, and 14% in the secondary islets, respectively. Insulin-, glucagon- and somatostatin-IR cells were also determined among the epithelium and subepithelial connective tissue in the pancreatic ducts or exocrine areas of the pancreas. With this study, the existence, regional distribution, and relative frequency of the insulin-, glucagon- and somatostatin-IR cells were first investigated in the pancreatic tissue of Lake Van fish and the results were discussed.

Isolation and Characterization of Pancreatic Canine Fetal Cells at the Final Stage of Gestation

The incidence of diabetes mellitus in dogs is increasing in recent years, mainly because of genetic and/or environmental factors, including endocrine disorders (like in humans); failure of suitable control of blood sugar levels, which triggers hyperglycemia; glycosuria and weight loss, which demands the development of innovative treatments to cure or treat this complex disease in dogs. The present study established for the first time a protocol to obtain and characterize cells derived from pancreas of canine fetuses. Those fetuses do not have a defined breed and were at the final stage of gestation. The protocol aims to provide morphological data to enable future applications of these cells for therapeutic approaches. In cell culture, pancreatic cells showed a fibroblast-like appearance with a mono-layered growth pattern and were not tumorigenic. They exhibited a positive expression for the pluripotent proliferation markers NANOG and PCNA and expressed PDX1, a transcription factor that is important for activation of the insulin gene promoter. In addition, Tyrosine Hydroxylase-positive (TH+) sympathetic nerve fibers were identified. Histologically, the pancreatic epithelium was developed, pancreatic glands in the fetuses were like those in the parenchyma of postconception dogs and pancreatic islets were unevenly distributed and organized in small clusters along the glands close to the vasculature. Staining with dithizone indicated the presence of insulin in the cells. A large number of beta cells were confirmed by immunofluorescence. In conclusion, the canine fetal pancreas cells could be an alternative and adequate source of cell lineages for stem cell therapies for diabetes treatment. Anat Rec, 302:1409-1418, 2019. © 2018 Wiley Periodicals, Inc.

Islet proteomics reveals genetic variation in dopamine production resulting in altered insulin secretion

The mouse is a critical model in diabetes research, but most research in mice has been limited to a small number of mouse strains and limited genetic variation. Using the eight founder strains and both sexes of the Collaborative Cross (C57BL/6J (B6), A/J, 129S1/SvImJ (129), NOD/ShiLtJ (NOD), NZO/HILtJ (NZO), PWK/PhJ (PWK), WSB/EiJ (WSB), and CAST/EiJ (CAST)), we investigated the genetic dependence of diabetes-related metabolic phenotypes and insulin secretion. We found that strain background is associated with an extraordinary range in body weight, plasma glucose, insulin, triglycerides, and insulin secretion. Our whole-islet proteomic analysis of the eight mouse strains demonstrates that genetic background exerts a strong influence on the islet proteome that can be linked to the differences in diabetes-related metabolic phenotypes and insulin secretion. We computed protein modules consisting of highly correlated proteins that enrich for biological pathways and provide a searchable database of the islet protein expression profiles. To validate the data resource, we identified tyrosine hydroxylase (Th), a key enzyme in catecholamine synthesis, as a protein that is highly expressed in β-cells of PWK and CAST islets. We show that CAST islets synthesize elevated levels of dopamine, which suppresses insulin secretion. Prior studies, using only the B6 strain, concluded that adult mouse islets do not synthesize l-3,4-dihydroxyphenylalanine (l-DOPA), the product of Th and precursor of dopamine. Thus, the choice of the CAST strain, guided by our islet proteomic survey, was crucial for these discoveries. In summary, we provide a valuable data resource to the research community, and show that proteomic analysis identified a strain-specific pathway by which dopamine synthesized in β-cells inhibits insulin secretion.

Regulatory Forum Opinion Piece: Review-Toxicological Pathology Profile and Regulatory Expectations for Nonclinical Development of Insulins and Insulin Analogues

The toxicological profile of insulins is exclusively due to exaggerated pharmacology resulting in hypoglycemic findings. Insulin analogues displaying modifications and aimed at improving pharmacokinetics do not induce different toxicity. The main target is the brain displaying neuronal necrosis. Wallerian degeneration of nerves occurs rarely after severe hypoglycemia. These findings are of potential human relevance; nevertheless, these changes are induced in normoglycemic animals whereas diabetic patients suffer from hyperglycemia. Therefore, it is usually not difficult to achieve a therapeutic window for subsequent use in patients. Based upon this and in the absence of classical toxicity, there has been no scientific need for diabetic animal models. A greater challenge is the mitogenicity already inherent with regular insulin. Thus, the focus for preclinical safety evaluation of analogues is to demonstrate that modifications in regular insulin do not result in enhanced mitogenicity. The approaches used to assess the mitogenic potential of insulin analogues have changed over time driven by scientific progression and changes within the regulatory environment. Therefore, in vitro and in vivo evaluation of cell proliferation has become common practice, and to date there has been no evidence that the mitogenic potential of insulin analogues may be increased compared to regular insulin.

Improved yield of canine islet isolation from deceased donors

BACKGROUND

Canine diabetes is a strikingly prevalent and growing disease, and yet the standard treatment of a twice-daily insulin injection is both cumbersome to pet owners and only moderately effective. Islet transplantation has been performed with repeated success in canine research models, but has unfortunately not been made available to companion animals. Standard protocols for islet isolation, developed primarily for human islet transplantation, include beating-heart organ donation, vascular perfusion of preservation solutions, specialized equipment. Unfortunately, these processes are prohibitively complex and expensive for veterinary use. The aim of the study was to develop a simplified approach for isolating canine islets that is compatible with the financial and logistical restrictions inherent to veterinary medicine for the purpose of translating islet transplantation to a clinical treatment for canine diabetes.

RESULTS

Here, we describe simplified strategies for isolating quality islets from deceased canine donors without vascular preservation and with up to 90 min of cold ischemia time. An average of more than 1500 islet equivalents per kg of donor bodyweight was obtained with a purity of 70% (N = 6 animals). Islets were 95% viable and responsive to glucose stimulation for a week. We found that processing only the body and tail of the pancreas increased isolation efficiency without sacrificing islet total yield. Islet yield per gram of tissue increased from 773 to 1868 islet equivalents when the head of the pancreas was discarded (N = 3/group).

CONCLUSIONS

In summary, this study resulted in the development of an efficient and readily accessible method for obtaining viable and functional canine islets from deceased donors. These strategies provide an ethical means for obtaining donor islets.

Endogenous Pancreatic Enzyme Activity Levels Show no Significant Effect on Human Islet Isolation Yield

Despite advances in human islet isolation, islet yield remains inconsistent and unreliable. In recent studies, it has been suggested that serine proteases, in particular trypsin, have been shown to have a damaging effect on islet yield. This study evaluated enzyme activity levels throughout 42 human islet isolation procedures. Trypsin, chymotrypsin, and elastase activity was determined spectrophotometrically using suitable chromophoric substrates. The results of the islet isolations were rated as successful (n = 19) or unsuccessful (n = 23) based on the islet yield and functionality. The enzyme activity profiles of the isolations were compared. No significant differences in donor-related variables were found in this study. However, in the successful isolations, a significantly greater amount (85.6 ± 1.9%; p = 0.0017) of the pancreas was digested in a significantly shorter digestion time (19.7 ± 0.6 min; p = 0.0054) compared with 74.8 ± 2.5% of digested tissue in 22.6 ± 0.7 min in the poor isolations. This study showed no significant effect of serine protease levels on the outcome of islet isolations, regardless of enzyme inhibitor supplementation. These data suggest that serine protease activity does not sufficiently affect islet yield. However, the data show that the most successful human islet isolations are achieved when the maximum amount of tissue is digested in the shortest amount of time. This suggests that further understanding of the isolation process should focus on the role of the collagenase digestion solution in the dissociation of the endocrine–exocrine tissue connection.

Comparative Pathogenesis of Autoimmune Diabetes in Humans, NOD Mice, and Canines: Has a Valuable Animal Model of Type 1 Diabetes Been Overlooked?

Despite decades of research in humans and mouse models of disease, substantial gaps remain in our understanding of pathogenic mechanisms underlying the development of type 1 diabetes. Furthermore, translation of therapies from preclinical efforts capable of delaying or halting β-cell destruction has been limited. Hence, a pressing need exists to identify alternative animal models that reflect human disease. Canine insulin deficiency diabetes is, in some cases, considered to follow autoimmune pathogenesis, similar to NOD mice and humans, characterized by hyperglycemia requiring lifelong exogenous insulin therapy. Also similar to human type 1 diabetes, the canonical canine disorder appears to be increasing in prevalence. Whereas islet architecture in rodents is distinctly different from humans, canine pancreatic endocrine cell distribution is more similar. Differences in breed susceptibility alongside associations with MHC and other canine immune response genes parallel that of different ethnic groups within the human population, a potential benefit over NOD mice. The impact of environment on disease development also favors canine over rodent models. Herein, we consider the potential for canine diabetes to provide valuable insights for human type 1 diabetes in terms of pancreatic histopathology, impairment of β-cell function and mass, islet inflammation (i.e., insulitis), and autoantibodies specific for β-cell antigens.

The Different Faces of the Pancreatic Islet

Type 1 diabetes (T1D) patients who receive pancreatic islet transplant experience significant improvement in their quality-of-life. This comes primarily through improved control of blood sugar levels, restored awareness of hypoglycemia, and prevention of serious and potentially life-threatening diabetes-associated complications, such as kidney failure, heart and vascular disease, stroke, nerve damage, and blindness. Therefore, beta cell replacement through transplantation of isolated islets is an important option in the treatment of T1D. However, lasting success of this promising therapy depends on durable survival and efficacy of the transplanted islets, which are directly influenced by the islet isolation procedures. Thus, isolating pancreatic islets with consistent and reliable quality is critical in the clinical application of islet transplantation.Quality of isolated islets is important in pre-clinical studies as well, as efforts to advance and improve clinical outcomes of islet transplant therapy have relied heavily on animal models ranging from rodents, to pigs, to nonhuman primates. As a result, pancreatic islets have been isolated from these and other species and used in a variety of in vitro or in vivo applications for this and other research purposes. Protocols for islet isolation have been somewhat similar across species, especially, in mammals. However, given the increasing evidence about the distinct structural and functional features of human and mouse islets, using similar methods of islet isolation may contribute to inconsistencies in the islet quality, immunogenicity, and experimental outcomes. This may also contribute to the discrepancies commonly observed between pre-clinical findings and clinical outcomes. Therefore, it is prudent to consider the particular features of pancreatic islets from different species when optimizing islet isolation protocols.In this chapter, we explore the structural and functional features of pancreatic islets from mice, pigs, nonhuman primates, and humans because of their prevalent use in nonclinical, preclinical, and clinical applications.

Development of the Endocrine Pancreas in the Beagle Dog: From Fetal to Adult Life

Our objectives were to describe, in Beagle dogs, the ontogenesis of beta (insulin-producing) and alpha (glucagon-producing) cells from fetal to early postnatal life and adulthood. In addition, to have some insight into interspecies comparison, Beagle dog pancreases were compared to pancreases from a Labrador and Chow Chow. At midgestation, the epithelium was dense, beta cells scarce, and alpha cells numerous and concentrated in the center of the pancreatic bud. From 36 to 45 days post conception (pc), beta cell numbers increased and the epithelium expanded and branched out. At 55 days pc, large beta cell aggregates were seen. At weaning, the islets were similar to those in adults, with limited alpha cells intermingled with numerous beta cells. Quantification of the Alpha to Beta cells ratio has shown a gradual increase of beta cells proportion throughout development. Similar findings were obtained in the two other breeds. In conclusion, in the fetal Beagle dog beta cells emerge from the pancreatic bud at midgestation, but the endocrine structure is mature only in early postnatal life. The ontogenesis of the endocrine pancreas demonstrated in dogs resembles that reported in rats and mice. In contrast, human beta cells appear earlier, at the beginning of the second trimester of gestation. Our study provides a detailed morphological description of pancreatic development in dogs but supplies no information on alpha- or beta-cell function during fetal life. The morphological data reported here provide a foundation for building physiological studies. Anat Rec, 300:1429-1438, 2017. © 2017 Wiley Periodicals, Inc.

Dynamic self-organization of microwell-aggregated cellular mixtures

Cells with different cohesive properties self-assemble in a spatiotemporal and context-dependent manner. Previous studies on cell self-organization mainly focused on the spontaneous structural development within a short period of time during which the cell numbers remained constant. However the effect of cell proliferation over time on the self-organization of cells is largely unexplored. Here, we studied the spatiotemporal dynamics of self-organization of a co-culture of MDA-MB-231 and MCF10A cells seeded in a well defined space (i.e. non-adherent microfabricated wells). When cell-growth was chemically inhibited, high cohesive MCF10A cells formed a core surrounded by low cohesive MDA-MB-231 cells on the periphery, consistent with the differential adhesion hypothesis (DAH). Interestingly, this aggregate morphology was completely inverted when the cells were free to grow. At an initial seeding ratio of 1 : 1 (MDA-MB-231 : MCF10A), the fast growing MCF10A cells segregated in the periphery while the slow growing MDA-MB-231 cells stayed in the core. Another morphology developed at an inequal seeding ratio (4 : 1), that is, the cell mixtures developed a side-by-side aggregate morphology. We conclude that the cell self-organization depends not only on the cell cohesive properties but also on the cell seeding ratio and proliferation. Furthermore, by taking advantage of the cell self-organization, we purified human embryonic stem cells-derived pancreatic progenitors (hESCs-PPs) from co-cultured feeder cells without using any additional tools or labels.

The types of endocrine cells in the pancreas of Sunda porcupine (Hystrix javanica)

Aim:

To identify the types of endocrine cells in the pancreas of the Sunda porcupine (Hystrix javanica) and its immunolocalization.

Materials and Methods:

Five adult H. javanica were used without sexual distinction. The presences of endocrine cells (glucagon, insulin, somatostatin, and pancreatic polypeptide [PP]) in pancreatic tissues were detected using the avidin-biotin-peroxidase complex method.

Results:

The fusiform, round, and oval form endocrine cells were detected in the islets of Langerhans and exocrine parts. Most of the insulin cells were found in the central area, glucagon cells were identified in the central and peripheral areas, and somatostatin and PP cells were detected in the mantle area of the islets of Langerhans. Glucagon and somatostatin cells were also detected in smaller numbers of peripheral parts of the islet. In all of the islet parts, glucagon endocrine cells were most prevalent cell type and then, somatostatin, insulin, and PP. In the exocrine parts, PP, somatostatin, glucagon, and insulin endocrine cells were found in the inter-acinus part with moderate, moderate, a few and rare numbers, in that order. In the pancreatic duct, glucagon and somatostatin cells were found between epithelial cells in rare numbers.

Conclusion:

The pancreas of Sunda porcupine (H. javanica) contains four types of major pancreatic endocrine cells with approximately similar distribution patterns to the other rodents, except for abundant glucagon cells in the peripheral area of the islets of Langerhans.

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.

A comparison of the anatomical structure of the pancreas in experimental animals

As basic knowledge for evaluation of pancreatic toxicity, anatomical structures were compared among experimental animal species, including rats, dogs, monkeys, and minipigs. In terms of gross anatomy, the pancreases of dogs, monkeys, and minipigs are compact and similar to that of humans. The rat pancreas is relatively compact at the splenic segment, but the duodenal segment is dispersed within the mesentery. In terms of histology, the islet of each animal is characterized by a topographic distribution pattern of α- versus β-cells. β-cells occupy the large central part of the rat islet, and α-cells are located in the periphery and occasionally exhibit cuffing. In dog islets, β-cells are distributed in all parts and α-cells are scattered in the center or periphery of the islet (at body and left lobe); whereas β-cells occupy all parts of the islet and no α-cells are present in the islet (at right lobe). Monkey islets show two distinct patterns, that is, α-cell-rich or β-cell-rich islets, and the former represent peripheral β-cells forming an irregular ring. Minipig islets show an irregular outline, and both α- and β-cells are present in all parts of the islet, intermingling with each other. According to morphometry, the endocrine tissue accounts for <2% of the pancreas roughly in rats and minipigs, and that of monkeys accounts for >7% of the pancreas (at tail). The endocrine tissue proportion tends to increase as the position changes from right to left in the pancreas in each species.

Evaluation of isolated caprine pancreatic islets cytoarchitecture by laser scanning confocal microscopy and flow cytometry

BACKGROUND

Pancreatic islets are composed of different hormone-secreting cell types. A finely balanced combination of endocrine cells in the islets regulates intraportal vein secretions and plasma nutrient levels. Every islet cell type is distinguished by its specific secretory granule pattern and hormone content, endocrine and cell signaling mechanisms, and neuronal interactions. The scarcity of pancreatic islet donors for patients with diabetes has caused a considerable interest in the field of islet xenotransplantation. Previous studies have shown that cell arrangement in the pancreatic islets of ruminants differs from that of other mammals; however, caprine islet cytoarchitecture has not yet been comprehensively described. This investigation aimed to characterize caprine islets in regard to better understanding of caprine islet structure and compare with previously reported species, by conducting a detailed analysis of islet architecture and composition using confocal microscopy and immunofluorescence staining for pancreatic islet hormones.

METHODOLOGY

After collection and purification of caprine islets with Euro-Ficoll density gradients, islets were considered for viability and functionality procedures with DTZ (dithizone) staining and GSIST (glucose-stimulated insulin secretion test) subsequently. Batches of islet were selected for immunostaining and study through confocal microscopy and flow cytometry.

RESULTS

Histological sections of caprine pancreatic islets showed that α-cells were segregated at the periphery of β-cells. In caprine islets, α- and δ-cells remarkably were intermingled with β-cells in the mantle. Such cytoarchitecture was observed in all examined caprine pancreatic islets and was also reported for the islets of other ruminants. In both small and large caprine islets (< 150 and > 150 μm in diameter, respectively), the majority of β-cells were positioned at the core and α-cells were arranged at the mantle, while some single α-cells were also observed in the islet center. We evaluated the content of β-, α-, and δ-cells by confocal microscopy (n = 35, mean ± SD; 38.01 ± 9.50%, 30.33 ± 10.11%, 2.25 ± 1.10%, respectively) and flow cytometry (n = 9, mean ± SD; 37.52 ± 9.74%, 31.72 ± 4.92%, 2.70 ± 2.81%, respectively). Our findings indicate that the caprine islets are heterogeneous in cell composition. The difference could be attributed to species-specific interaction between endocrine cells and blood.

CONCLUSIONS

Comparative studies of islet architecture may lead to better understanding of islet structure and cell type population arrangement. These results suggest the use of caprine islets as an addition to the supply of islets for diabetes research.

Increased androgen levels in rats impair glucose-stimulated insulin secretion through disruption of pancreatic beta cell mitochondrial function

Although insulin resistance is recognized to contribute to the reproductive and metabolic phenotypes of polycystic ovary syndrome (PCOS), pancreatic beta cell dysfunction plays an essential role in the progression from PCOS to the development of type 2 diabetes. However, the role of insulin secretory abnormalities in PCOS has received little attention. In addition, the precise changes in beta cells and the underlying mechanisms remain unclear. In this study, we therefore attempted to elucidate potential mechanisms involved in beta cell alterations in a rat model of PCOS. Glucose-induced insulin secretion was measured in islets isolated from DHT-treated and control rats. Oxygen consumption rate (OCR), ATP production, and mitochondrial copy number were assayed to evaluate mitochondrial function. Glucose-stimulated insulin secretion is significantly decreased in islets from DHT-treated rats. On the other hand, significant reductions are observed in the expression levels of several key genes involved in mitochondrial biogenesis and in mitochondrial OCR and ATP production in DHT-treated rat islets. Meanwhile, we found that androgens can directly impair beta cell function by inducing mitochondrial dysfunction in vitro in an androgen receptor dependent manner. For the first time, our study demonstrates that increased androgens in female rats can impair glucose-stimulated insulin secretion partly through disruption of pancreatic beta cell mitochondrial function. This work has significance for hyperandrogenic women with PCOS: excess activation of the androgen receptor by androgens may provoke beta cell dysfunction via mitochondrial dysfunction.

Development, growth and maintenance of β-cell mass: models are also part of the story

Pancreatic β-cells in the islets of Langerhans play a crucial role in regulating glucose homeostasis in the circulation. Loss of β-cell mass or function due to environmental, genetic and immunological factors leads to the manifestation of diabetes mellitus. The mechanisms regulating the dynamics of pancreatic β-cell mass during normal development and diabetes progression are complex. To fully unravel such complexity, experimental and clinical approaches need to be combined with mathematical and computational models. In the natural sciences, mathematical and computational models have aided the identification of key mechanisms underlying the behavior of systems comprising multiple interacting components. A number of mathematical and computational models have been proposed to explain the development, growth and death of pancreatic β-cells. In this review, we discuss some of these models and how their predictions provide novel insight into the mechanisms controlling β-cell mass during normal development and diabetes progression. Lastly, we discuss a handful of the major open questions in the field.

The human GLP-1 analogs liraglutide and semaglutide: absence of histopathological effects on the pancreas in nonhuman primates

Increased pancreas mass and glucagon-positive adenomas have been suggested to be a risk associated with sitagliptin or exenatide therapy in humans. Novo Nordisk has conducted extensive toxicology studies, including data on pancreas weight and histology, in Cynomolgus monkeys dosed with two different human glucagon-like peptide-1 (GLP-1) receptor agonists. In a 52-week study with liraglutide, a dose-related increase in absolute pancreas weight was observed in female monkeys only. Such dose-related increase was not found in studies of 4, 13, or 87 weeks' duration. No treatment-related histopathological abnormalities were observed in any of the studies. Quantitative histology of the pancreas from the 52-week study showed an increase in the exocrine cell mass in liraglutide-dosed animals, with normal composition of endocrine and exocrine cellular compartments. Proliferation rate of the exocrine tissue was low and comparable between groups. Endocrine cell mass and proliferation rates were unaltered by liraglutide treatment. Semaglutide showed no increase in pancreas weight and no treatment-related histopathological findings in the pancreas after 13 or 52 weeks' dosing. Overall, results in 138 nonhuman primates showed no histopathological changes in the pancreas associated with liraglutide or semaglutide, two structurally different GLP-1 receptor agonists.

Streptozotocin-induced diabetes models: pathophysiological mechanisms and fetal outcomes

Glucose homeostasis is controlled by endocrine pancreatic cells, and any pancreatic disturbance can result in diabetes. Because 8% to 12% of diabetic pregnant women present with malformed fetuses, there is great interest in understanding the etiology, pathophysiological mechanisms, and treatment of gestational diabetes. Hyperglycemia enhances the production of reactive oxygen species, leading to oxidative stress, which is involved in diabetic teratogenesis. It has also been suggested that maternal diabetes alters embryonic gene expression, which might cause malformations. Due to ethical issues involving human studies that sometimes have invasive aspects and the multiplicity of uncontrolled variables that can alter the uterine environment during clinical studies, it is necessary to use animal models to better understand diabetic pathophysiology. This review aimed to gather information about pathophysiological mechanisms and fetal outcomes in streptozotocin-induced diabetic rats. To understand the pathophysiological mechanisms and factors involved in diabetes, the use of pancreatic regeneration studies is increasing in an attempt to understand the behavior of pancreatic beta cells. In addition, these studies suggest a new preventive concept as a treatment basis for diabetes, introducing therapeutic efforts to minimize or prevent diabetes-induced oxidative stress, DNA damage, and teratogenesis.

Comparative Pancreatic Pathology

Spontaneous pathologies of the pancreas are important causes of morbidity and mortality in some veterinary species and rare in others. As in human beings, the pancreas of most domestic and exotic animals is a composite organ with both endocrine and exocrine functions. The similarities between structure and function of porcine, canine, and human pancreata are such that the pig and dog serve as valuable models in basic and translational studies, most recently for efforts aimed at modeling pancreatitis and diabetes, developing functional and sustainable replacement of endocrine functions, and in imaging and manipulation studies.

This article will provide a brief review of spontaneous veterinary diseases and their underlying mechanisms and the morphological features that reflect these alterations. Several species- or breed-specific conditions and the effects of selected systemic diseases on the pancreas are also discussed. The contributions to our knowledge of pancreatic physiology and pathology by small mammal (rodent) and engineered animal models and the in-depth mechanisms homologous to those in the human pancreas are covered in other sections of this article.

Sympathetic innervation during development is necessary for pancreatic islet architecture and functional maturation

Sympathetic neurons depend on target-derived neurotrophic cues to control their survival and growth. However, whether sympathetic innervation contributes reciprocally to the development of target tissues is less clear. Here, we report that sympathetic innervation is necessary for the formation of the pancreatic islets of Langerhans and for their functional maturation. Genetic or pharmacological ablation of sympathetic innervation during development resulted in altered islet architecture, reduced insulin secretion, and impaired glucose tolerance in mice. Similar defects were observed with pharmacological blockade of β-adrenergic signaling. Conversely, the administration of a β-adrenergic agonist restored islet morphology and glucose tolerance in deinnervated animals. Furthermore, in neuron-islet cocultures, sympathetic neurons promoted islet cell migration in a β-adrenergic-dependent manner. This study reveals that islet architecture requires extrinsic inductive cues from neighboring tissues such as sympathetic nerves and suggests that early perturbations in sympathetic innervation might underlie metabolic disorders.

The effect of experimentally induced chronic hyperglycaemia on serum and pancreatic insulin, pancreatic islet IGF-I and plasma and urinary ketones in the domestic cat (Felis felis)

Like in humans, diabetes mellitus is on the rise in cats. Feline diabetes is a suitable model for human type-2 diabetes. We investigated magnitude and timing of insulin suppression with induced hyperglycaemia and its relationship to plasma and urinary ketones and to pancreatic islet insulin. IGF-I is under discussion as a protective mechanism but little is known about its role in diabetes in general and its distinct localisation in feline pancreatic islets in particular. Thirteen healthy, adult cats were allocated to 2 groups and infused with glucose to maintain their blood glucose at a high or moderate concentration for 42 days resulting in insulin secretion suppression. After initial increase, insulin levels declined to baseline but were still detectable in the blood at a very low level after 6 weeks of glucose infusion and then increased after a 3 week recovery period. While IGF-I in healthy cats was primarily located in glucagon cells, in hyperglycaemia-challenge IGF-I was pronounced in the β-cells 3 weeks after ceasation of infusion. Six/8 cats developing glucose toxicity became ketonuric after 3-4 weeks. Gross lipaemia occurred approx 1 week prior to ketonuria. Ketonuric cats required 1-2 weeks of insulin therapy after-infusion until β-cell recovery. In conclusion, ketosis and hyperlipidaemia are likely to occur in diabetic cats with glucose at 30 mmol/L, especially after ≥2 weeks. Three weeks after ceasation of infusions, clinical and morphological recovery occurred. We propose a local protective effect of IGF-I to support survival and insulin production in the hyperglycaemic state and recovery period.

Embryonic stem cells of the non-human primate Callithrix jacchus can be differentiated into definitive endoderm by Activin-A but not IDE-1/2

Pluripotent stem cells hold great promise for regenerative medicine, due to their unlimited self-renewal potential and the ability to differentiate into all somatic cell types. Differences between the rodent disease models and the situation in humans can be narrowed down with non-human primate models. The common marmoset monkey (Callithrix jacchus) is an interesting model for biomedical research because these animals are easy to breed, get relatively old (≤ 13 years), are small in size, are relatively cost-effective and have a high genetic proximity to the human. In particular, diseases of the liver and pancreas are interesting for cell replacement therapies but the in vitro differentiation of ESCs into the definitive endoderm germ layer is still a demanding task. Membrane-permeable, chemically defined small molecules can possibly replace recombinant growth factors used in most directed differentiation protocols. However, the potent small molecules IDE-1 and IDE-2 were not able to induce definitive endoderm-like cells when ESCs from the common marmoset were treated with these compounds, whereas the recombinant growth factor Activin A could force the differentiation into this lineage. Our results indicate that ESCs from the common marmoset are less sensitive or even insensitive to these small molecules. Thus, differences between the species of human ESCs and ESCs of this non-human primate might be a useful model to further evaluate the exact mode of action of these compounds.

Islet microarchitecture and glucose transporter expression of the pancreas of the marmoset monkey display similarities to the human

The common marmoset New World monkey (Callithrix jacchus), is a primate model with great potential for scientific research, including research on diabetes. However, in opposite to Rhesus and Java monkeys (Macaca mulatta and Macaca fascicularis) little is known about the marmosets islet microarchitecture, glucose transporter and pancreatic marker gene expression. In this work we analyze differences and similarities in size, shape, cellular composition and intra-islet topography between the common marmoset and the human endocrine pancreas. Different sized, circular and a-circular shaped islets of the common marmoset and human display α-cells in the whole islet organ leading to a ribbon-like islet type. The number of islets was significantly higher in the common marmoset compared with humans. However, the area of insulin-producing cells was significantly higher in the human pancreas. Intra-islet distribution pattern of δ- and β-cells was similar in both species. The morphology of the exocrine pancreas regarding acinar and ductal cells was quite similar as confirmed by ultrastructural analysis. Additionally the ultrastructure of secretory granules from α-, δ- and β-cells of human and non-human primate pancreas showed the same characteristics. Molecular analysis showed the presence of endocrine pancreatic marker genes like PMCA2, NCX1, SUR1, KIR6.2, MAFA, NGN3 and PDX1 also expressed in the human. For the first time we could show presence of Glut 5 and 9 transporters in addition to the low abundance transporter Glut2 and the highly expressed Glut1 glucose transporter. We propose that Callithrix jacchus displays a new animal model for diabetes research and regenerative medicine.

Ultrastructural analysis, zinc transporters, glucose transporters and hormones expression in New world primate (Callithrix jacchus) and human pancreatic islets

The New world primates (NWP) Callithrix jacchus separated from man approximately 50 million years ago and is a potential alternative small non-human primate model for diabetes research. Ultrastructure, and gene expression of pancreatic islets and the recently described diabetes auto antigenic zinc transporters families in human, NWP and pig pancreas were studied. Morphologically NWP islets were larger than pig islets and similar in size to human islets. NWP islets alpha cells had high dense core surrounded by a limiting membrane, beta cells by the mixed morphology of the granule core, and delta cells by moderate opaque core. Antibody staining for insulin, glucagon, somatostatin and Glucagon-like peptide-1 (GLP-1) showed that the distribution pattern of the different cell types within islets was comparable to pig and human islets. In all three species protein expression of zinc transporter ZnT8 was detected in most of the insulin producing beta cells whereas Zip14 expression was widely expressed in alpha and beta cells. In both human and NWP little or no expression of Glut2 was observed compared to Glut1 and glucokinase at the protein level, however the messenger RNA level of Glut2 was greater than Glut1 and glucokinase. In contrast all three glucose transporters were expressed in pig islets at the protein level. The expression of Zip14 in islets is reported for the first time. In conclusion NWP pancreatic islets express comparable islet cell types and distribution to humans and pigs. Importantly, marmosets have a similar glucose transporter profile to humans, making this non-endangered primate species a useful animal model for pancreatic biology.

Differential contribution of dietary fat and monosaccharide to metabolic syndrome in the common marmoset (Callithrix jacchus)

There is a critical need for animal models to study aspects type 2 diabetes (T2D) pathogenesis and prevention. While the rhesus macaque is such an established model, the common marmoset has added benefits including reduced zoonotic risks, shorter life span, and a predisposition to birth twins demonstrating chimerism. The marmoset as a model organism for the study of metabolic syndrome has not been fully evaluated. Marmosets fed high-fat or glucose-enriched diets were followed longitudinally to observe effects on morphometric and metabolic measures. Effects on pancreatic histomorphometry and vascular pathology were examined terminally. The glucose-enriched diet group developed an obese phenotype and a prolonged hyperglycemic state evidenced by a rapid and persistent increase in mean glycosylated hemoglobin (HgbA1c) observed as early as week 16. In contrast, marmosets fed a high-fat diet did not maintain an obese phenotype and demonstrated a delayed increase in HgbA1) that did not reach statistical significance until week 40. Consumption of either diet resulted in profound pancreatic islet hyperplasia suggesting a compensation for increased insulin requirements. Although the high-fat diet group developed atherosclerosis of increased severity, the presence of lesions correlated with glucose intolerance only in the glucose-enriched diet group. The altered timing of glucose dysregulation, differential contribution to obesity, and variation in vascular pathology suggests mechanisms of effect specific to dietary nutrient content. Feeding nutritionally modified diets to common marmosets recapitulates aspects of metabolic disease and represents a model that may prove instrumental to elucidating the contribution of nutrient excess to disease development.

Effect of different obesogenic diets on pancreatic histology in Ossabaw miniature swine

OBJECTIVE

Obesity is a factor in the outcome and severity of pancreatic conditions. We examined the effect of hypercaloric diets on the pancreata of Ossabaw swine, a large animal model of metabolic syndrome and obesity.

METHODS

Swine were fed with 1 of 4 diets: high-fructose (n = 9), atherogenic (n = 10), modified atherogenic (n = 6), or eucaloric standard diet (n = 12) for 24 weeks. Serum chemistries were measured, and pancreata were examined for histological abnormalities including steatosis, inflammation or fibrosis, insulin content, and oxidative stress.

RESULTS

The fructose, atherogenic, and modified atherogenic diet groups exhibited obesity, metabolic syndrome, islet enlargement, and significantly increased pancreatic steatosis (22.9% ± 7.5%, 19.7% ± 7.7%, and 38.7% ± 15.3% fat in total tissue area, respectively) compared with controls (9.3% ± 1.9%; P < 0.05). The modified atherogenic diet group showed significantly increased oxidative stress levels as evidenced by elevated serum malondialdehyde (3.0 ± 3.3 vs 1.5 ± 0.3 μmol/L in controls; P = 0.006) and pancreatic malondialdehyde (0.1 ± 0.12 vs 0.04 ± 0.01 nmol/mg protein in controls; P = 0.01). None of the swine exhibited pancreatitis or cellular injury.

CONCLUSIONS

Ossabaw swine fed with a modified atherogenic diet developed significant pancreatic steatosis and increased oxidative stress, but no other histological abnormalities were observed.

An immunohistochemical study of the pancreatic endocrine cells of the ddN mouse

The regional distribution and frequency of the pancreatic endocrine cells in the ddN mouse were studied using specific antisera against insulin, glucagon, somatostatin and human pancreatic polypeptide (hPP). In the pancreatic islets, most of insulin-immunoreactive (IR) cells were located in the central region, and glucagon-, somatostatin and hPP-IR cells were located in the peripheral region regardless of the lobe. In the splenic part, glucagon-IR cells were also located in the central regions, and more numerous somatostatin-IR cells were detected in the central regions as compared with the duo-denal part. hPP-IR cells were restricted to the peripheral regions in both lobes but more numerous cells were detected in the duodenal portion. In the exocrine parenchyma of the splenic lobe, only insulin- and glucagon-IR cells were detected but all four kinds of IR cells were observed in the duodenal portion. In addition, insulin and hPP-IR cells were also demonstrated in the pancreatic duct regions. In conclusion, some strain-dependent characteristic distributional patterns of pancreatic endocrine cells were found in the ddN mouse with somewhat different distributional patterns between the two pancreatic lobes.

Pancreatic islet plasticity: interspecies comparison of islet architecture and composition

The pancreatic islet displays diverse patterns of endocrine cell arrangement. The prototypic islet, with insulin-secreting beta-cells forming the core surrounded by other endocrine cells in the periphery, is largely based on studies of normal rodent islets. Recent reports on large animals, including humans, show a difference in islet architecture, in which the endocrine cells are randomly distributed throughout the islet. This particular species difference has raised concerns regarding the interpretation of data based on rodent studies to humans. On the other hand, further variations have been reported in marsupials and some nonhuman primates, which possess an inverted ratio of beta-cells to other endocrine cells. This review discusses the striking plasticity of islet architecture and cellular composition among various species including changes in response to metabolic states within a single species. We propose that this plasticity reflects evolutionary acquired adaptation induced by altered physiological conditions, rather than inherent disparities between species.

The comparative anatomy of islets

In the past 20 years, numerous publications on a variety of mammalian and non-mammalian species have appeared in the literature to supplement the excellent comparative work performed in the 70s and 80s by the Falkmer, Epple, and Youson groups. What emerges is that islets are much more complex than once thought and show a lot of similarities in rodents and higher primates. The diversity of lifestyles, metabolic demands, and diets has most likely influenced the great diversity in both structure and cell-type content of islets in lower vertebrate species. In this chapter, I try to provide an overview of the evolution from endocrine cell types in invertebrates to the higher mammals and focus on what has been reported in the literature and some of our own experiences and also include a description of other hormones reported to be found in islets.

Islet architecture: A comparative study

Emerging reports on the organization of the different hormone-secreting cell types (alpha, glucagon; beta, insulin; and delta, somatostatin) in human islets have emphasized the distinct differences between human and mouse islets, raising questions about the relevance of studies of mouse islets to human islet physiology. Here, we examine the differences and similarities between the architecture of human and mouse islets. We studied islets from various mouse models including ob/ob and db/db and pregnant mice. We also examined the islets of monkeys, pigs, rabbits and birds for further comparisons. Despite differences in overall body and pancreas size as well as total beta-cell mass among these species, the distribution of their islet sizes closely overlaps, except in the bird pancreas in which the delta-cell population predominates (both in singlets and clusters) along with a small number of islets. Markedly large islets (>10,000 mum(2)) were observed in human and monkey islets as well as in islets from ob/ob and pregnant mice. The fraction of alpha-, beta- and delta-cells within an islet varied between islets in all the species examined. Furthermore, there was variability in the distribution of alpha- and delta-cells within the same species. In summary, human and mouse islets share common architectural features that may reflect demand for insulin. Comparative studies of islet architecture may lead to a better understanding of islet development and function.

The immunohistochemical localization of synaptophysin protein (p38) in the gastro-entero-pancreatic (GEP) system of reptiles

The gastro-entero-pancreatic (GEP) system of four reptilian species: turtle (Emys orbicularis), lizards (Lacerta viridis and Lacerta agilis) and snake (Natrix natrix) has been investigated immunohistochemically for the presence and topographic distribution of synaptophysin. Among the studied reptiles, only in turtles were neural, glial and neuroendocrine elements labelled for this marker protein. Semi-quantitative evaluation of the immunolabelled neural structures distributed throughout the gastroenteric wall revealed, with two exceptions, highly significant mean differences between the successive gut segments. Significant mean differences were noted also between myenteric and submucosal neurons immunolabelled in the various gastroenteric regions. Moreover, the comparison of ganglionic perikarya groups showed, at least in the stomach, significant mean differences. The amounts of immunopositive glial cells seemed to vary similarly to those of nerve fibers along the entire gastrointestinal tract. Finally, every "closed" and "open" population of immunopositive epithelial cells showed typical fluctuations along the gut. In addition to the distribution of synaptophysin in the GEP system of turtles, the above findings furnish evidence that this marker protein, which is widespread in mammals, is only occasionally expressed in reptiles and probably in most poikilothermic vertebrates.

Tissue surface tensions guide in vitro self-assembly of rodent pancreatic islet cells

The organization of endocrine cells in pancreatic islets is established through a series of morphogenetic events involving cell sorting, migration, and re-aggregation processes for which intercellular adhesion is thought to play a central role. In animals, these morphogenetic events result in an islet topology in which insulin-secreting cells form the core, while glucagon, somatostatin, and pancreatic polypeptide-secreting cells segregate to the periphery. Isolated pancreatic islet cells self-assemble in vitro into pseudoislets with the same cell type organization as native islets. It is widely held that differential adhesion between cells of the pancreatic islets generates this specific topology. However, this differential adhesion has never been rigorously quantified. In this manuscript, we use tissue surface tensiometry to measure the cohesivity of spherical aggregates from three immortalized mouse pancreatic islet cell lines. We show that, as predicted by the differential adhesion hypothesis, aggregates of the internally segregating INS-1 and MIN6 beta-cell lines are substantially more cohesive than those of the externally segregating alpha-TC line. Furthermore, we show that forced overexpression of P-cadherin by alpha-TC cells significantly perturbs the sorting process. Collectively, the data indicate that differential adhesion can drive the in vitro organization of immortalized rodent pancreatic islet cells.

Endoderm and Pancreatic Islet Lineage Differentiation from Human Embryonic Stem Cells

Human embryonic stem cells (HESCs) are a potential source of insulin-producing tissue for transplantation. Recent studies have begun to define factors that promote definitive endoderm formation from HESCs, but conditions permitting complete islet specification in vitro have not been described. Here, we study spontaneous differentiation of HESCs to definitive endoderm and pancreatic progenitor cells, and begin to determine which aspects of the protocol are required for this cell fate commitment. HESCs were differentiated in culture for up to 10 weeks, including an embryoid body (EB) formation step. Modifications to the protocol included elimination of the EB phase, varying initial cell cluster size when forming EBs, and addition of mesoderm-derived cells to EBs. Differentiated cells were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. HESCs are capable of spontaneous differentiation to cells expressing the definitive endoderm and pancreatic progenitor markers Foxa2, Sox17, and Pdx1, and ultimately, some cells express islet endocrine hormones. This differentiation occurs to a much greater extent when an EB formation step is included. Increased expression of endoderm markers during and after EB formation also correlated strongly with the size of cell clusters used to start EBs, as well as the addition of mesoderm- derived embryonic cells. This study demonstrates that a subset of differentiated HESC progeny adopt an endoderm fate and exhibit the capacity for further pancreatic lineage specification in vitro. Basal conditions were established for examining factors that can commit HESC-derived endoderm cells to specific pancreatic lineages.

The unique cytoarchitecture of human pancreatic islets has implications for islet cell function

The cytoarchitecture of human islets has been examined, focusing on cellular associations that provide the anatomical framework for paracrine interactions. By using confocal microscopy and multiple immunofluorescence, we found that, contrary to descriptions of prototypical islets in textbooks and in the literature, human islets did not show anatomical subdivisions. Insulin-immunoreactive beta cells, glucagon-immunoreactive alpha cells, and somatostatin-containing delta cells were found scattered throughout the human islet. Human beta cells were not clustered, and most (71%) showed associations with other endocrine cells, suggesting unique paracrine interactions in human islets. Human islets contained proportionally fewer beta cells and more alpha cells than did mouse islets. In human islets, most beta, alpha, and delta cells were aligned along blood vessels with no particular order or arrangement, indicating that islet microcirculation likely does not determine the order of paracrine interactions. We further investigated whether the unique human islet cytoarchitecture had functional implications. Applying imaging of cytoplasmic free Ca2+ concentration, [Ca2+]i, we found that beta cell oscillatory activity was not coordinated throughout the human islet as it was in mouse islets. Furthermore, human islets responded with an increase in [Ca2+]i when lowering the glucose concentration to 1 mM, which can be attributed to the large contribution of alpha cells to the islet composition. We conclude that the unique cellular arrangement of human islets has functional implications for islet cell function.

The effect of global SSTR5 gene ablation on the endocrine pancreas and glucose regulation in aging mice

INTRODUCTION

The purpose of this study was to examine the effect of global gene ablation of SSTR5 on the endocrine pancreas, insulin secretion, and glucose tolerance in aging mice, as SSTR5 is a primary regulator of insulin secretion in the mouse pancreas.

METHODS

Global SSTR5-/- mice were generated and genotypes were verified using Southern blot and RT-PCR. Glucose tolerance and in vivo insulin secretion in SSTR5-/- and WT mice were examined using intraperitoneal glucose tolerance test (IPGTT;1.2-2.0 mg/kg) at 3 and 12 months of age (n = 8 per group). Basal and glucose-stimulated insulin secretion in vitro was studied using the isolated perfused mouse pancreas model at 3 and 12 months. Pancreata were removed and levels of insulin, glucagon, somatostatin, and SSTR1 were studied using immunohistochemical analysis along with H&E staining of the pancreata.

RESULTS

Genotyping verified the absence of SSTR5 in SSTR5-/- mice. IPGTT demonstrated that 3-month-old SSTR5-/- mice were glucose intolerant despite similar insulin secretion both in vivo and in vitro and enlarged islets. At 12 months of age, SSTR5-/- mice had basal hypoglycemia and improved glucose intolerance associated with hyperinsulinemia in vivo and in vitro and enlarged islets. SSTR5-/- mice had increased insulin clearance at 3 and 12 months of age. SSTR1 expression was significantly increased in islets at 3 months of age, but was nearly absent in islets at 12 months of age, as was somatostatin staining in SSTR5-/- mice.

CONCLUSIONS

These results suggest that both SSTR5 and SSTR1 play a pivotal role in insulin secretion and glucose regulation in mice and that their regulatory effects are age-related.

Somatostatin receptors and autoimmune-mediated diabetes

Somatostatin (SST) peptide is produced by various SST-secreting cells throughout the body and acts as a neurotransmitter or paracrine/autocrine regulator in response to ions, nutrients, peptides hormones and neurotransmitters. SST is also widely distributed in the periphery to regulate the inflammatory and immune cells in response to hormones, growth factors, cytokines and other secretive molecules. SST peptides are considered the most important physiologic regulator of the islet cell, gastrointestinal cell and immune cell functions, and the importance of SST production levels has been implicated in several diseases including diabetes. The expression of SST receptors has also been found in T lymphocytes and primary immunologic organs. Interaction of SST and its receptors is also involved in T-cell proliferation and thymocyte selection. SSTR gene-ablated mice developed diabetes with morphologic, physiologic and immunologic alterations in the endocrine pancreas. Increased levels of mononuclear cell infiltration of the islets are associated with the increased levels of antigen-presenting cells located in the islets and peripancreatic lymph nodes. Increased levels of SST were also found in antigen-presenting cells and are associated with a significant increase of CD8 expression levels on CD4(+)/CD8(+) immature thymocytes. These findings highlight the crucial role of this neuroendocrine peptide and its receptors in regulating autoimmune functions.