Endocrine pancreatic cells of postnatal "diabetes" (db) mice in cell culture

Animal Models of Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is one of the most common complications associated with chronic hyperglycemia seen in patients with diabetes mellitus. While many facets of DR are still not fully understood, animal studies have contributed significantly to understanding the etiology and progression of human DR. This review provides a comprehensive discussion of the induced and genetic DR models in different species and the advantages and disadvantages of each model.

RECENT FINDINGS

Rodents are the most commonly used models, though dogs develop the most similar morphological retinal lesions as those seen in humans, and pigs and zebrafish have similar vasculature and retinal structures to humans. Nonhuman primates can also develop diabetes mellitus spontaneously or have focal lesions induced to simulate retinal neovascular disease observed in individuals with DR. DR results in vascular changes and dysfunction of the neural, glial, and pancreatic β cells. Currently, no model completely recapitulates the full pathophysiology of neuronal and vascular changes that occur at each stage of diabetic retinopathy; however, each model recapitulates many of the disease phenotypes.

Deletion of glycerol channel aquaporin-9 (Aqp9) impairs long-term blood glucose control in C57BL/6 leptin receptor-deficient (db/db) obese mice

Deletion of the glycerol channel aquaporin-9 (Aqp9) reduces postprandial blood glucose levels in leptin receptor–deficient (db/db) obese mice on a C57BL/6 × C57BLKS mixed genetic background. Furthermore, shRNA-mediated reduction of Aqp9 expression reduces liver triacylglycerol (TAG) accumulation in a diet-induced rat model of obesity. The aim of this study was to investigate metabolic effects of Aqp9 deletion in coisogenic db/db mice of the C57BL/6 background. Aqp9^wtdb/db and Aqp9^−/−db/db mice did not differ in body weight and liver TAG contents. On the C57BL/6 genetic background, we observed elevated plasma glucose in Aqp9^−/−db/db mice (+1.1 mmol/L, life-time average), while plasma insulin concentration was reduced at the time of death. Glucose levels changed similarly in pentobarbital anesthetized, glucagon challenged Aqp9^wtdb/db and Aqp9^−/−db/db mice. Liver transcriptional profiling did not detect differential gene expression between genotypes. Metabolite profiling revealed a sex independent increase in plasma glycerol (+55%) and glucose (+24%), and reduction in threonate (all at q < 0.1) in Aqp9^−/−db/db mice compared to controls. Metabolite profiling thus confirms a role of AQP9 in glycerol metabolism of obese C57BL/6 db/db mice. In this animal model of obesity Aqp9 gene deletion elevates plasma glucose and does not alleviate hepatosteatosis.

Type 1 diabetes in mice and men: gene expression profiling to investigate disease pathogenesis

Type 1 diabetes (T1D) is a complex polygenic disease that is triggered by various environmental factors in genetically susceptible individuals. The emphasis placed on genome-wide association studies to explain the genetics of T1D has failed to advance our understanding of T1D pathogenesis or identify biomarkers of disease progression or therapeutic targets. Using the nonobese diabetic (NOD) mouse model of T1D and the non-disease prone congenic NOD.B10 mice, our laboratory demonstrated striking tissue-specific and age-dependent changes in gene expression during disease progression. We established a "roadmap" of differential gene expression and used this to identify candidate genes in mice (and human orthologs) that play a role in disease pathology. Here, we describe two genes, Deformed epidermal autoregulatory factor 1 (Deaf1) and Adenosine A1 receptor (Adora1), that are differentially expressed and alternatively spliced in the pancreatic lymph nodes or islets of NOD mice and T1D patients to form dominant-negative non-functional isoforms. Loss of Deaf1 function leads to reduced peripheral tissue antigen expression in lymph node stromal cells and may contribute to a breakdown in peripheral tolerance, while reduced Adora1 function results in an early intrinsic alpha cell defect that may explain the hyperglucagonemia and resulting beta cell stress observed prior to the onset of diabetes. Remarkably, both genes were also alternatively spliced in the same tissues of auto-antibody positive prediabetic patients, and these splicing events resulted in similar downstream effects as those seen in NOD mice. These findings demonstrate the value of gene expression profiling in studying disease pathogenesis in T1D.

Diminished adenosine A1 receptor expression in pancreatic α-cells may contribute to the pathology of type 1 diabetes

Prediabetic NOD mice exhibit hyperglucagonemia, possibly due to an intrinsic α-cell defect. Here, we show that the expression of a potential glucagon inhibitor, the adenosine A1 receptor (Adora1), is gradually diminished in α-cells of NOD mice, autoantibody-positive (AA(+)) and overtly type 1 diabetic (T1D) patients during the progression of disease. We demonstrated that islet inflammation was associated with loss of Adora1 expression through the alternative splicing of Adora1. Expression of the spliced variant (Adora1-Var) was upregulated in the pancreas of 12-week-old NOD versus age-matched NOD.B10 (non-diabetes-susceptible) control mice and was detected in the pancreas of AA(+) patients but not in control subjects or overtly diabetic patients, suggesting that inflammation drives the splicing of Adora1. We subsequently demonstrated that Adora1-Var expression was upregulated in the islets of NOD.B10 mice after exposure to inflammatory cytokines and in the pancreas of NOD.SCID mice after adoptive transfer of activated autologous splenocytes. Adora1-Var encodes a dominant-negative N-terminal truncated isoform of Adora1. The splicing of Adora1 and loss of Adora1 expression on α-cells may explain the hyperglucagonemia observed in prediabetic NOD mice and may contribute to the pathogenesis of human T1D and NOD disease.

Ultra-structural study of insulin granules in pancreatic β-cells of db/db mouse by scanning transmission electron microscopy tomography

Insulin granule trafficking is a key step in the secretion of glucose-stimulated insulin from pancreatic β-cells. The main feature of type 2 diabetes (T2D) is the failure of pancreatic β-cells to secrete sufficient amounts of insulin to maintain normal blood glucose levels. In this work, we developed and applied tomography based on scanning transmission electron microscopy (STEM) to image intact insulin granules in the β-cells of mouse pancreatic islets. Using three-dimensional (3D) reconstruction, we found decreases in both the number and the grey level of insulin granules in db/db mouse pancreatic β-cells. Moreover, insulin granules were closer to the plasma membrane in diabetic β-cells than in control cells. Thus, 3D ultra-structural tomography may provide new insights into the pathology of insulin secretion in T2D.

Glucose homeostasis in pre-diabetic NOD and lymphocyte-deficient NOD/SCID mice during gestation

BACKGROUND

Unlike other strains, spontaneously type 1 non-obese diabetic (NOD) experience transient hyperinsulinemia after weaning. The same applies for NOD/SCID mice, which lack functional lymphocytes, and unlike NOD mice, do not develop insulitis and diabetes like NOD mice.

AIMS

Given that beta-cell stimulation is a natural feature of gestation, we hypothesized that glucose homeostasis is disturbed in gestate pre-diabetic NOD and non-diabetic NOD/SCID mice, which may accelerate the onset of diabetes and increase diabetes prevalence.

METHODS

During gestation and postpartum, mice were analyzed under basal feed conditions followed by glucose injection (1 g/kg, i.p.) after overnight fast, using glucose tolerance test (GTT). Glycemia, corticosteronemia, blood and pancreatic insulin, glucagon levels, islet size, and islet morphology were evaluated. Glycemia and mortality were assessed after successive gestations in NOD mice mated for the first time at 2 different ages.

RESULTS

1. Basal glucagonemia rose markedly in first-gestation fed NOD mice. 2. beta-cell hyperactivity was present earlier in first-gestation non-diabetic fasted NOD and NOD/SCID mice than in age-matched C57BL/6 mice, assessed by increased insulin/glucose ratio after GTT. 3. Overnight fasting increased corticosteronemia rapidly and sharply in pre-diabetic gestate NOD and NOD/SCID mice. 4. Islet size increased in non-diabetic gestate NOD mice compared with C57BL/6 mice. 5. Successive gestations accelerated diabetes onset, and contributed to increased mortality in NOD mice.

CONCLUSIONS

First-gestation pre-diabetic NOD and non-diabetic NOD/SCID mice exhibited beta-cell hyperactivity and deregulation of glucagon and/or corticosterone secretion. This amplified normally occurring insulin resistance, further exhausted maternal beta-cells, and accelerated diabetes in NOD mice.

1 Management of Immunocompromised and Infected Animals

This chapter discusses the management of immunocompromized and infected animals. The microbiological quality of laboratory animals is a direct result of colony management practices, and monitoring provides an after-the-fact assessment of the adequacy of those practices. In the case of immunocompromised animals or in infection experiments, however, monitoring for a comprehensive list of micro-organisms is reasonable. The testing of animals usually starts with necropsy and blood sampling for serology, followed by microscopic examination for parasites and sampling of organs for bacteriology, pathology, and, in rare cases, virological examinations. Biological materials represent a high risk, if they originate from or have been propagated in animals. In particular, tumors, viruses, or parasites that are serially passaged in animals often pick up pathogens, and therefore a high percentage of these are contaminated. It has been shown in mice and rats that all preimplantational stages can be revitalized successfully upon freezethaw procedures. For long-term storage, eight-cell stages have been recommended in the chapter, while two-cell stages were considered to be less suitable. One embryo batch (inbred strain) derived from a single pedigree donor pair may be regarded as a prospective breeding nucleus, if one fertile breeding pair is obtained upon revitalization. Assuming an average revitalization rate of 20% (fertile breeders), one embryo batch should contain a minimum number of 10 embryos to obtain at least one breeding pair with a 50% chance of revitalization.

Mouse pancreatic acinar/ductular tissue gives rise to epithelial cultures that are morphologically, biochemically, and functionally indistinguishable from interlobular duct cell cultures

Most of the pancreatic exocrine epithelium consists of acinar and intralobular duct (ductular) cells, with the balance consisting of interlobular and main duct cells. Fragments of mouse acinar/ductular epithelium can be isolated by partial digestion with collagenase and purified by Ficoll density gradient centrifugation. We investigated whether previously developed culture conditions used for duct epithelium would result in the selective survival and proliferation of ductular cells from the acinar/ductular fragments. The fragments were cultured on nitrocellulose filters coated with extracellular matrix. After 2 to 4 wk the filters were covered with proliferating cells resembling parallel cultures of duct epithelium by the following criteria: protein/DNA ratio, light and electron microscopic appearance, the presence of duct markers (carbonic anhydrase [CA] activity, CA II mRNA, the cystic fibrosis transmembrane conductance regulator), the near absence of acinar cell markers (amylase and chymotrypsin), a similar polypeptide profile after sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the presence of spontaneous and secretin-stimulated electrogenic ion transport. Both duct and ductular epithelia formed fluid-filled cysts in collagen gels and both could be subcultured. We conclude that acinar/ductular tissue gives rise to ductular cells in culture by some combination of acinar cell death and/or transdifferentiation to a ductular phenotype, accompanied by proliferation of these cells and preexisting ductular cells. These cultures may be used to investigate the properties of this part of the pancreatic duct system, from which most of the pancreatic juice water and electrolytes probably originates.

Glucose induces intracisternal type A retroviral gene transcription and translation in pancreatic beta cells

C57BL/KsJ (BKs) and CBA/J, but not C57BL/6J (B6) mice are susceptible to the diabetogenic action of the obesity gene, "diabetes" (db). BKs and CBA/J, but not B6 mice, constitutively express intracisternal type A particles (IAP), an endogenous class of retrovirus, in beta cells and in cortical thymocytes. IAP genetic expression in these cell types included production of the group-specific antigen, p73, as well as higher-molecular mass p73-related antigens (p114-120). We used islet culture techniques to show that both transcription and translation of IAP genomes in beta cells in enhanced by glucose. Maintenance of CBA/J islets for 48 h in 16.5 mM glucose-containing medium effected a fivefold induction of IAP protein synthesis in comparison to islets cultured in low- (5.5 mM) glucose medium. Analysis of RNA from 16.5 mM glucose-cultured islets revealed induction of 7.2 and 5.4 kbp transcripts known to code for p73 and the p114-120 polypeptides, respectively. This induction in CBA/J islets was 10-15-fold on a tissue basis, and 5-7-fold on an RNA basis. Glucose induction of preproinsulin mRNA levels was also analyzed in the same samples. Islets cultured in 16.5 mM glucose showed an eightfold higher level on a tissue basis, and a fourfold increase in terms of total recovered RNA. Comparison of these glucose-inducible parameters in islets isolated from the diabetes-susceptible BKs strain vs. the resistant B6 strain revealed that expression of the group-specific retroviral p73 antigen was limited to BKs beta cells. This inbred strain control of p73 expression was also found in cortical thymocytes, with B6 thymocytes producing a 117 kD component to the exclusion of p73, while both components were expressed in thymocytes from normal BKs mice. In comparison to normal BKs males, thymocytes from four week-old genetically diabetic (db/db) BKs males showed no change in labeling of p117, but showed a sharply diminished incorporation into p73. This suggested that accelerated thymic involution characteristic of db/db mice may entail selective elimination of p73-producing cells. The possibility that glucose-stressed BKs pancreatic beta cells are marked for autoimmune elimination by the elaboration of p73 or other IAP-related proteins is discussed.

Effects of dissociation and culture on the maintenance of insulin, glucagon and somatostatin release by neonatal rat islets of Langerhans

The ability of the principal islet cell types to maintain their differentiated function in vitro was assessed in a tissue culture system using neonatal rat pancreata. The effects of tissue dissociation and culture on the yield of islet tissue was measured at various times during the preparation and maintenance of cultures for 8 days. As estimated by the radioimmunoassay of insulin, glucagon and somatostatin in tissue extracts, the amount of islet tissue available for culture was reduced 50-70% following dissociation; an additional loss occurred after the first day in vitro. Only the insulin content of the tissue increased during culture. The hormone content of the media indicated that B-, A- and D-cell function was maintained throughout the culture period. The concentrations of insulin and glucagon in the medium approximately doubled and somatostatin increased 3-fold. This system has been shown to be a useful tool for the simultaneous study of the three major islet cell types and their secretory products.

Microtubules and beta cell function: effect of colchicine on microtubules and insulin secretion in vitro by mouse beta cells

A monolayer culture system was developed to study the role of microtubules in insulin secretion. Cultured cells were obtained to study the role of microtubules in insulin secretion. Cultured cells were obtained by enzymatic digestion of pancreases from C57BL-KsJ mice 6-12 wk of age. On day 4 of culture, the medium was changed, control or treatment medium added, and frequent samples were removed for insulin assay. Microtubules and beta cells were identified by indirect immunofluorescence with monospecific antibodies to tubulin and insulin. An extensive microtubule network radiates from the perinuclear region of the beta cell to the plasma membrane. Although alterations in the calcium concentration of the medium did not affect the microtubule pattern, the absence of calcium or glucose in the medium inhibited insulin secretion (P less than 0.001). Optimum insulin release occurred at a calcium concentration of 2.5 mM. Colchicine, in concentrations of 10(-10) M, did not affect the microtubule immunofluorescent pattern, whereas concentrations of 1 and 5 x 10(-7) M decreased the number of microtubules, and microtubules could not be identified in cultures treated with 10(-6) M colchicine for 2 h. After a 2-h preincubation, the prolonged release of insulin at either 2.0 or 4.5 mg/ml of glucose was decreased by 10(-6) M colchicine (P less than 0.02). The immediate release of insulin was similar to that in control plates and occurred in cultures with no identifiable microtubules. Microtubules and insulin secretion were not altered by 10(-6) M lumicolchicine and prolonged insulin secretion recovered 24 h after removal of colchicine. These studies show that the microtubules facilitate sustained secretion of insulin but are not required for the immediate release of the hormone. Alterations in the extracellular calcium concentration which play an essential role in insulin secretion do not alter the microtubule pattern in the beta cell.

A new mutation (db3J) at the diabetes locus in strain 129/J mice. I. Physiological and histological characterization

A spontaneous recessive mutation appearing in strain 129/J mice at the diabetes (db) locus on Chromosome 4 has been characterized. The new allele, designated db3J, produced hyperphagia and severe obesity. Mutants weighed in excess of 70 g by 6 months of age, compared to 22-28 g for lean littermates. Although the disease was similar to the mild hyperglycaemia-severe obesity syndrome exhibited by db gene presentation on the C57BL/6J inbred background, the syndrome in 129/J mice reduced lifespan, with mutants exhibiting sudden weight loss, hypoglycaemia, and a 67% mortality between 6 and 14 months of age. Mutant males, but not females, were transiently hyperglycaemic between 2 to 4 months of age, attaining a maximum mean blood sugar of 196 +/- 27 (SEM) mg/dl. Thereafter glucose levels declined to normoglycaemic values (80-100 mg/dl), and with increasing age, mutants of both sexes became hypoglycaemic (60 mg/dl at 9 months). Mutants of both sexes were extremely hyperinsulinaemic at the earlier ages, with mean plasma insulin at months 5 reflecting 30-fold elevations above normal for males and 18-fold for females. These levels diminished with age, the decline being more marked in males. Plasma glucagon levels were 3-fold elevated in the younger mutants of both sexes (86 pg/ml versus 28 pg/ml in normal mice), mean levels increasing to almost 5-fold above mean control vaues in the older age group (198 pg/ml versus 41 pg/ml in normal mice). Histopathological findings were limited to pancreas. Increasing necrosis of the exocrine, but not endocrine, pancreas was noted in aging mutants. Aldehyde fushsin staining of the mutant pancreas revealed hyperplastic islets filled with heavily granulated B-cells. B-cell hyperplasia was accompanied by a 30-fold increase over controls in pancreatic insulin content in the 8 month old mutants, whereas pancreatic glucagon content was only doubled. Morphometric analysis showed less than a 2-fold increase in the mean number of A-cells per islet. Thus, an interesting feature of expression of the diabetes gene in the 129/J strain is the persisting hyperglucagonaemia in the face of moderating hyperinsulinaemia.

A new mutation (db3J) at the diabetes locus in strain 129/J mice. II. Studies of pancreatic alpha cell function in culture

Monolayer cell cultures from pancreatic islets of aging 129/J strain diabetes (db3J/db3J) and lean littermate control mice were tested for differences in glucagon and insulin secretion in either serum-free Eagle's minimal essential medium (MEM) or Dulbecco's modified minimal essential medium (DMEM). There was a highly significant (p less than 0.0001) main effect of genotype and type of culture medium on glucagon secretion with time. Thus, although numbers of A-cells were not demonstrably increased in db3J/db3J cultures in DMEM, mean medium glucagon levels increased 2.7-, 18-, and 32-fold above littermate normal culture levels at days 4, 6, and 8 respectively. In MEM, the two populations could not be discriminated on the basis of glucagon secretion. By contrast, insulin secretion over culture days showed a highly significant (p less than 0.0001) dependence on genotype, but not type of medium, with the B-cell enriched db3J/db3J preparations secreting between 20 and 30 times as much insulin as controls in both medida. Analysis revealed that the heightened secretory responsiveness of mutatn A-cells in DMEM as compared to MEM was primarily elicited by the elevated DMEM amino acid concentration and specifically lysine (0.8 mmol/l in DMEM versus 0.4 mmol/l in MEM). In pulse-chase experiments using 14 day db3J/db3J cultures, incorporation of 3H-tryptophan into protein that eluted from Biogel P-10 columns in the native glucagon peak indicates that DMEM stimulated glucagon biosynthesis as well as secretion. This study reveals an augmented sensitivity of db3J/db3J A-cells to stimulation by basic amino acids in long-term culture.

Ultrastructural and morphometric studies of delta cells in pancreatic islets from C57BL/Ks diabetes mice

An ultrastructural and immunocytochemical study was undertaken to elucidate the temporal and quantitative aspects of the changes occurring in the delta cells in the pancreatic islets of C57BL/KsJ db/db (diabetes) mice. Electron microscopy revealed that prior to the major topographical redistribution of delta cells from their peripheral location to the islet interior, long delta cell filopodial extensions penetrated into the islet, greatly increasing the area of surface contact between delta cells and hypersecretory beta cells. Coincident with delta cells redistribution in islets of 8 to 10 week diabetes mice, the mean number of delta cells per islet had increased significantly. In contrast, their volume density had decreased, indicating incomplete compensation for beta cell hyperplasia which had commenced approximately 4 weeks earlier. In the 14 week mutants, numbers of delta cells per islet and islet volume reached maximum values while delta cell volume density had been restored to a control level. Delta cell volume density exhibited a 2-fold increase in the mutants at 20 weeks that coincided with massive beta cell necrosis. However, a decline in the number of delta cells per islet (173.6 +/- 20.9 at 14 weeks versus 91.2 +/- 20 weeks) suggests that islet degeneration in terminal stages of the syndrome also includes some loss of these cells.