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

Subcellular Feature-Based Classification of α and β Cells Using Soft X-ray Tomography

The dysfunction of α and β cells in pancreatic islets can lead to diabetes. Many questions remain on the subcellular organization of islet cells during the progression of disease. Existing three-dimensional cellular mapping approaches face challenges such as time-intensive sample sectioning and subjective cellular identification. To address these challenges, we have developed a subcellular feature-based classification approach, which allows us to identify α and β cells and quantify their subcellular structural characteristics using soft X-ray tomography (SXT). We observed significant differences in whole-cell morphological and organelle statistics between the two cell types. Additionally, we characterize subtle biophysical differences between individual insulin and glucagon vesicles by analyzing vesicle size and molecular density distributions, which were not previously possible using other methods. These sub-vesicular parameters enable us to predict cell types systematically using supervised machine learning. We also visualize distinct vesicle and cell subtypes using Uniform Manifold Approximation and Projection (UMAP) embeddings, which provides us with an innovative approach to explore structural heterogeneity in islet cells. This methodology presents an innovative approach for tracking biologically meaningful heterogeneity in cells that can be applied to any cellular system.

The Importance of Intra-Islet Communication in the Function and Plasticity of the Islets of Langerhans during Health and Diabetes

Islets of Langerhans are anatomically dispersed within the pancreas and exhibit regulatory coordination between islets in response to nutritional and inflammatory stimuli. However, within individual islets, there is also multi-faceted coordination of function between individual beta-cells, and between beta-cells and other endocrine and vascular cell types. This is mediated partly through circulatory feedback of the major secreted hormones, insulin and glucagon, but also by autocrine and paracrine actions within the islet by a range of other secreted products, including somatostatin, urocortin 3, serotonin, glucagon-like peptide-1, acetylcholine, and ghrelin. Their availability can be modulated within the islet by pericyte-mediated regulation of microvascular blood flow. Within the islet, both endocrine progenitor cells and the ability of endocrine cells to trans-differentiate between phenotypes can alter endocrine cell mass to adapt to changed metabolic circumstances, regulated by the within-islet trophic environment. Optimal islet function is precariously balanced due to the high metabolic rate required by beta-cells to synthesize and secrete insulin, and they are susceptible to oxidative and endoplasmic reticular stress in the face of high metabolic demand. Resulting changes in paracrine dynamics within the islets can contribute to the emergence of Types 1, 2 and gestational diabetes.

Physically interacting beta-delta pairs in the regenerating pancreas revealed by single-cell sequencing

Objectives

Until recently, communication between neighboring cells in islets of Langerhans was overlooked by genomic technologies, which require rigorous tissue dissociation into single cells.

Methods

We utilize sorting of physically interacting cells (PICs) with single-cell RNA-sequencing to systematically map cellular interactions in the endocrine pancreas after pancreatectomy.

Results

The pancreas cellular landscape features pancreatectomy associated heterogeneity of beta-cells, including an interaction-specific program between paired beta and delta-cells.

Conclusions

Our analysis suggests that the particular cluster of beta-cells that pairs with delta-cells benefits from stress protection, implying that the interaction between beta- and delta-cells might safeguard against pancreatectomy associated challenges. The work encourages testing the potential relevance of physically-interacting beta-delta-cells also in diabetes mellitus.

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Single-cell RNA-sequencing systematically maps physically interacting endocrine cells in the pancreas.

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The landscape of pancreatectomy associated beta-cell heterogeneity is mapped in a single cell resolution.

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Interaction-specific beta - delta cellular program safeguards beta cells against pancreatectomy-associated stress.

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Physically interacting beta delta pairs were discovered in an injury model and may also be relevant in diabetes.

Gap junction coupling and islet delta-cell function in health and disease

The pancreatic islets contain beta-cells and alpha-cells, which are responsible for secreting two principal gluco-regulatory hormones; insulin and glucagon, respectively. However, they also contain delta-cells, a relatively sparse cell type that secretes somatostatin (SST). These cells have a complex morphology allowing them to establish an extensive communication network throughout the islet, despite their scarcity. Delta-cells are electrically excitable cells, and SST secretion is released in a glucose- and K_ATP-dependent manner. SST hyperpolarises the alpha-cell membrane and suppresses exocytosis. In this way, islet SST potently inhibits glucagon release. Recent studies investigating the activity of delta-cells have revealed they are electrically coupled to beta-cells via gap junctions, suggesting the delta-cell is more than just a paracrine inhibitor. In this Review, we summarize delta-cell morphology, function, and the role of SST signalling for regulating islet hormonal output. A distinguishing feature of this Review is that we attempt to use the discovery of this gap junction pathway, together with what is already known about delta-cells, to reframe the role of these cells in both health and disease. In particular, we argue that the discovery of gap junction communication between delta-cells and beta-cells provides new insights into the contribution of delta-cells to the islet hormonal defects observed in both type 1 and type 2 diabetes. This reappraisal of the delta-cell is important as it may offer novel insights into how the physiology of this cell can be utilised to restore islet function in diabetes.

δ-Cells: The Neighborhood Watch in the Islet Community

Somatostatin-secreting δ-cells have aroused great attention due to their powerful roles in coordination of islet insulin and glucagon secretion and maintenance of glucose homeostasis. δ-cells exhibit neuron-like morphology with projections which enable pan-islet somatostatin paracrine regulation despite their scarcity in the islets. The expression of a range of hormone and neurotransmitter receptors allows δ-cells to integrate paracrine, endocrine, neural and nutritional inputs, and provide rapid and precise feedback modulations on glucagon and insulin secretion from α- and β-cells, respectively. Interestingly, the paracrine tone of δ-cells can be effectively modified in response to factors released by neighboring cells in this interactive communication, such as insulin, urocortin 3 and γ-aminobutyric acid from β-cells, glucagon, glutamate and glucagon-like peptide-1 from α-cells. In the setting of diabetes, defects in δ-cell function lead to suboptimal insulin and glucagon outputs and lift the glycemic set-point. The interaction of δ-cells and non-δ-cells also becomes defective in diabetes, with reduces paracrine feedback to β-cells to exacerbate hyperglycemia or enhanced inhibition of α-cells, disabling counter-regulation, to cause hypoglycemia. Thus, it is possible to restore/optimize islet function in diabetes targeting somatostatin signaling, which could open novel avenues for the development of effective diabetic treatments.

Distribution and density of melatonin receptors in human main pancreatic islet cell types

Recent investigations of our group established that melatonin modulates hormone secretion of pancreatic islets via melatonin receptor types MT1 and MT2. Expression of MT1 and MT2 has been shown in mouse, rat, and human pancreatic islets as well as in the β-, α-, and δ-cell lines INS-1, αTC1.9, and QGP-1. In view of these earlier investigations, this study was performed to analyze in detail the distribution and density of melatonin receptors on the main islet cell types in human pancreatic tissue obtained from nondiabetic and type 2 diabetic patients. Immunohistochemical analysis established the presence of MT1 and MT2 in β-, α-, and δ-cells, but notably, with differences in receptor density. In general, the lowest MT1 and MT2 receptor density was measured in α-cells compared to the 2 other cell types. In type 2 diabetic islets, MT1 and MT2 receptor density was increased in δ-cells compared to normoglycemic controls. In human islets in batch culture of a nondiabetic donor, an increase of somatostatin secretion was observed under melatonin treatment while in islets of a type 2 diabetic donor, an inhibitory influence could be observed, especially in the presence of 5.5 mmol/L glucose. These data suggest the following: i) cell-type-specific density of MT1 and MT2 receptors in human pancreatic islets, which should be considered in context of the hormone secretion of islets, ii) the influence of diabetes on density of MT1 and MT2 as well as iii) the differential impact of melatonin on somatostatin secretion of nondiabetic and type 2 diabetic islets.

Distinct Shift in Beta-Cell Glutaredoxin 5 Expression Is Mediated by Hypoxia and Lipotoxicity Both In Vivo and In Vitro

Histomorphological and functional alterations in pancreatic islet composition directly correlate with hyperglycemia severity. Progressive deterioration of metabolic control in subjects suffering from type 2 diabetes is predominantly caused by impaired beta-cell functionality. The glutaredoxin system is supposed to wield protective properties for beta-cells. Therefore, we sought to identify a correlation between the structural changes observed in diabetic pancreatic islets with altered glutaredoxin 5 expression, in order to determine an underlying mechanism of beta-cell impairment. Islets of db/db mice presenting with uncontrolled diabetes were assessed in terms of morphological structure and insulin, glucagon, and glutaredoxin 5 expression. MIN6 cell function and glutaredoxin 5 expression were analyzed after exposure to oleic acid and hypoxia. Islets of diabese mice were marked by typical remodeling and distinct reduction of, and shifts, in localization of glutaredoxin 5-positive cells. These islets featured decreased glutaredoxin 5 as well as insulin and glucagon content. In beta-cell culture, glutaredoxin 5 protein and mRNA expression were decreased by hypoxia and oleic acid but not by leptin treatment. Our study demonstrates that glutaredoxin 5 expression patterns are distinctively altered in islets of rodents presenting with uncontrolled diabesity. In vitro, reduction of islet-cell glutaredoxin 5 expression was mediated by hypoxia and oleic acid. Thus, glutaredoxin 5-deficiency in islets during diabetes may be caused by lipotoxicity and hypoxia.

An optical method to evaluate both mass and functional competence of pancreatic α- and β-cells

Imbalanced glucagon and insulin release leads to the onset of type 2 diabetes. To pinpoint the underlying primary driving force, here we have developed a fast, non-biased optical method to measure ratios of pancreatic α- and β-cell mass and function simultaneously. We firstly label both primary α- and β-cells with the red fluorescent probe ZinRhodaLactam-1 (ZRL1), and then highlight α-cells by selectively quenching the ZRL1 signal from β-cells. Based on the signals before and after quenching, we calculate the ratio of the α-cell to β-cell mass within live islets, which we found matched the results from immunohistochemistry. From the same islets, glucagon and insulin release capability can be concomitantly measured. Thus, we were able to measure the ratio of α-cell to β-cell mass and their function in wild-type and diabetic Lepr(db)/Lepr(db) (denoted db/db) mice at different ages. We find that the initial glucose intolerance that appears in 10-week-old db/db mice is associated with further expansion of α-cell mass prior to deterioration in functional β-cell mass. Our method is extendable to studies of islet mass and function in other type 2 diabetes animal models, which shall benefit mechanistic studies of imbalanced hormone secretion during type 2 diabetes progression.

Alpha-, Delta- and PP-cells: Are They the Architectural Cornerstones of Islet Structure and Co-ordination?

Islet non-β-cells, the α- δ- and pancreatic polypeptide cells (PP-cells), are important components of islet architecture and intercellular communication. In α-cells, glucagon is found in electron-dense granules; granule exocytosis is calcium-dependent via P/Q-type Ca(2+)-channels, which may be clustered at designated cell membrane sites. Somatostatin-containing δ-cells are neuron-like, creating a network for intra-islet communication. Somatostatin 1-28 and 1-14 have a short bioactive half-life, suggesting inhibitory action via paracrine signaling. PP-cells are the most infrequent islet cell type. The embryologically separate ventral pancreas anlage contains PP-rich islets that are morphologically diffuse and α-cell deficient. Tissue samples taken from the head region are unlikely to be representative of the whole pancreas. PP has anorexic effects on gastro-intestinal function and alters insulin and glucagon secretion. Islet architecture is disrupted in rodent diabetic models, diabetic primates and human Type 1 and Type 2 diabetes, with an increased α-cell population and relocation of non-β-cells to central areas of the islet. In diabetes, the transdifferentiation of non-β-cells, with changes in hormone content, suggests plasticity of islet cells but cellular function may be compromised. Understanding how diabetes-related disordered islet structure influences intra-islet cellular communication could clarify how non-β-cells contribute to the control of islet function.

Delta Cell Hyperplasia in Adult Goto-Kakizaki (GK/MolTac) Diabetic Rats

Reduced beta cell mass in pancreatic islets (PI) of Goto-Kakizaki (GK) rats is frequently observed in this diabetic model, but knowledge on delta cells is scarce. Aiming to compare delta cell physiology/pathology of GK to Wistar rats, we found that delta cell number increased over time as did somatostatin mRNA and delta cells distribution in PI is different in GK rats. Subtle changes in 6-week-old GK rats were found. With maturation and aging of GK rats, disturbed cytoarchitecture occurred with irregular beta cells accompanied by delta cell hyperplasia and loss of pancreatic polypeptide (PPY) positivity. Unlike the constant glucose-stimulation index for insulin PI release in Wistar rats, this index declined with GK age, whereas for somatostatin it increased with age. A decrease of GK rat PPY serum levels was found. GK rat body weight decreased with increasing hyperglycemia. Somatostatin analog octreotide completely blocked insulin secretion, impaired proliferation at low autocrine insulin, and decreased PPY secretion and mitochondrial DNA in INS-1E cells. In conclusion, in GK rats PI, significant local delta cell hyperplasia and suspected paracrine effect of somatostatin diminish beta cell viability and contribute to the deterioration of beta cell mass. Altered PPY-secreting cells distribution amends another component of GK PI's pathophysiology.

In vivo reprogramming of pancreatic acinar cells to three islet endocrine subtypes

Direct lineage conversion of adult cells is a promising approach for regenerative medicine. A major challenge of lineage conversion is to generate specific cell subtypes. The pancreatic islets contain three major hormone-secreting endocrine subtypes: insulin(+) β-cells, glucagon(+) α-cells, and somatostatin(+) δ-cells. We previously reported that a combination of three transcription factors, Ngn3, Mafa, and Pdx1, directly reprograms pancreatic acinar cells to β-cells. We now show that acinar cells can be converted to δ-like and α-like cells by Ngn3 and Ngn3+Mafa respectively. Thus, three major islet endocrine subtypes can be derived by acinar reprogramming. Ngn3 promotes establishment of a generic endocrine state in acinar cells, and also promotes δ-specification in the absence of other factors. δ-specification is in turn suppressed by Mafa and Pdx1 during α- and β-cell induction. These studies identify a set of defined factors whose combinatorial actions reprogram acinar cells to distinct islet endocrine subtypes in vivo. DOI: http://dx.doi.org/10.7554/eLife.01846.001.

Effects of long-term treatment with the dipeptidyl peptidase-4 inhibitor vildagliptin on islet endocrine cells in non-obese type 2 diabetic Goto-Kakizaki rats

Reduced β cell mass is a characteristic feature of type 2 diabetes and incretin therapy is expected to prevent this condition. However, it is unknown whether dipeptidyl peptidase-4 inhibitors influence β and α cell mass in animal models of diabetes that can be translated to humans. Therefore, we examined the long-term effects of treatment with the dipeptidyl peptidase-4 inhibitor vildagliptin on islet morphology in Goto-Kakizaki (GK) rats, a spontaneous, non-obese model of type 2 diabetes, and explored the underlying mechanisms. Four-week-old GK rats were orally administered with vildagliptin (15 mg/kg) twice daily for 18 weeks. Glucose tolerance was monitored during the study. After 18 weeks, β and α cell morphology and the expression of molecules involved in cell proliferation and cell death were examined by immunohistochemistry and morphometric analysis. We found that vildagliptin improved glucose tolerance and insulin secretion, and suppressed hyperglucagonemia by increasing plasma active glucagon-like peptide-1 concentrations. β cell mass was reduced in GK rats to 40% of that in Wistar rats, but was restored to 80% by vildagliptin. Vildagliptin enhanced β and α cell proliferation, and increased the number of small neogenetic islets. Vildagliptin also reduced the number of 8-hydroxy-2'-deoxyguanosine-positive cells and forkhead box protein O1 expression, inhibited macrophage infiltration, and enhanced S6 ribosomal protein, molecule of target of rapamycin, and pancreatic duodenal homeobox 1 expression. These results indicate that starting vildagliptin treatment from an early age improved glucose tolerance and preserved islet β cell mass in GK rats by facilitating the proliferation of islet endocrine cells.

R-type Ca(2+)-channel-evoked CICR regulates glucose-induced somatostatin secretion

Pancreatic islets have a central role in blood glucose homeostasis. In addition to insulin-producing beta-cells and glucagon-secreting alpha-cells, the islets contain somatostatin-releasing delta-cells. Somatostatin is a powerful inhibitor of insulin and glucagon secretion. It is normally secreted in response to glucose and there is evidence suggesting its release becomes perturbed in diabetes. Little is known about the control of somatostatin release. Closure of ATP-regulated K(+)-channels (K(ATP)-channels) and a depolarization-evoked increase in cytoplasmic free Ca(2+) concentration ([Ca(2+)](i)) have been proposed to be essential. Here, we report that somatostatin release evoked by high glucose (>or=10 mM) is unaffected by the K(ATP)-channel activator diazoxide and proceeds normally in K(ATP)-channel-deficient islets. Glucose-induced somatostatin secretion is instead primarily dependent on Ca(2+)-induced Ca(2+)-release (CICR). This constitutes a novel mechanism for K(ATP)-channel-independent metabolic control of pancreatic hormone secretion.

Mitochondrial metabolism reveals a functional architecture in intact islets of Langerhans from normal and diabetic Psammomys obesus

The cells within the intact islet of Langerhans function as a metabolic syncytium, secreting insulin in a coordinated and oscillatory manner in response to external fuel. With increased glucose, the oscillatory amplitude is enhanced, leading to the hypothesis that cells within the islet are secreting with greater synchronization. Consequently, non-insulin-dependent diabetes mellitus (NIDDM; type 2 diabetes)-induced irregularities in insulin secretion oscillations may be attributed to decreased intercellular coordination. The purpose of the present study was to determine whether the degree of metabolic coordination within the intact islet was enhanced by increased glucose and compromised by NIDDM. Experiments were performed with isolated islets from normal and diabetic Psammomys obesus. Using confocal microscopy and the mitochondrial potentiometric dye rhodamine 123, we measured mitochondrial membrane potential oscillations in individual cells within intact islets. When mitochondrial membrane potential was averaged from all the cells in a single islet, the resultant waveform demonstrated clear sinusoidal oscillations. Cells within islets were heterogeneous in terms of cellular synchronicity (similarity in phase and period), sinusoidal regularity, and frequency of oscillation. Cells within normal islets oscillated with greater synchronicity compared with cells within diabetic islets. The range of oscillatory frequencies was unchanged by glucose or diabetes. Cells within diabetic (but not normal) islets increased oscillatory regularity in response to glucose. These data support the hypothesis that glucose enhances metabolic coupling in normal islets and that the dampening of oscillatory insulin secretion in NIDDM may result from disrupted metabolic coupling.

Pancreatic islet fibrosis in rock hyrax (Procavia capensis), Part 2: Pathology, immunohistochemistry, and electron microscopy

Pancreatic islet fibrosis with varying degrees of islet cell hyperplasia or islet effacement was diagnosed histologically in 19 rock hyraxes (Procavia capensis) from seven zoological parks. Some, but not all, affected hyraxes were from a common lineage. The condition was associated with apparent hyperglycemia in seven and diabetes mellitus in two. Immunohistochemistry revealed hyperplasia of beta, alpha, and delta cells proportional to the degree of the fibrosis. Electron microscopy revealed collagen deposition and fibroplasia within and around the islets. Special stains and electron microscopy were negative for the presence of amyloid. Beta cell depletion was never identified. The condition has morphologic features that resemble islet fibrosis of human infants born to diabetic mothers.

Functional characterization of somatostatin receptors expressed on hamster glucagonoma cells

We characterized somatostatin receptors expressed in hamster glucagonoma INR1G9 cells and the effects of somatostatin on glucagon secretion, proglucagon gene expression, and the adenosine 3',5'-cyclic monophosphate (cAMP)-dependent signal-transduction cascade. 125I-labeled somatostatin was displaced by somatostatin-14 and somatostatin-28 with a dissociation constant of 2 nmol/l. Stable GTP analogues decreased binding of 125I-somatostatin to its receptors, suggesting an interaction of somatostatin receptors with G proteins. Chemical cross-linking of 125I-somatostatin to its receptor revealed a molecular mass of the ligand-receptor complex of 47 kDa. Somatostatin inhibited forskolin-stimulated activation of adenylate cyclase [2.5 microM forskolin (161%) + 1 microM somatostatin (128%); P < 0.05] and protein kinase A [10 microM forskolin (143%) + 1 microM somatostatin (114%); P < 0.05] but did not influence basal activities of these enzymes. Forskolin-induced stimulation of cAMP generation was reduced by somatostatin [2.5 microM forskolin (306%) + 1 microM somatostatin (145%); P < 0.05]. Somatostatin inhibited forskolin, theophylline, and arginine stimulation of glucagon secretion. Basal as well as forskolin-, theophylline-, and isobutyl methylxanthine-induced proglucagon gene expression was significantly reduced by somatostatin. Our data show that, in INR1G9 cells, somatostatin receptors are at least in part coupled to the adenylate cyclase system. Somatostatin is a potent negative regulator of both basal and forskolin-stimulated proglucagon gene expression. The interaction with forskolin occurs at the level of adenylate cyclase. The effect of somatostatin on basal proglucagon gene transcription is most probably mediated by an unrelated second messenger system. Somatostatin may influence several functions of the pancreatic A cell.

Quantitative immunocytochemical study of islet cell populations in diabetic calmodulin-transgenic mice

The present study describes the changes in the endocrine pancreas of severely diabetic calmodulin-transgenic mice using light microscopic immunocytochemical and morphometric techniques. A marked reduction in the number and volume of islets, together with distortion of their normal architecture, was found in diabetic mice. In addition, the volume density of both endocrine tissue and B-cells was decreased. An irregular distribution of non-B-cells was also observed in diabetic animals. The volume density and the percentage of A-cells appeared increased. However, when quantified per area unit, the number of all the islet cell types diminished, although only the decrease in B-cell number was statistically significant. The decrease in B-cell mass might account for the diabetic state developed in this animal model.

Immunohistochemical, ultrastructural, and hormonal studies on the endocrine pancreas of voles (Microtus arvalis) with monosodium aspartate-induced diabetes

A single subcutaneous administration of monosodium aspartate (MSA) to 30 neonatal voles, Microtus arvalis Pallas, induced a diabetes mellitus in 50% of the treated animals in early adulthood. The voles (18 males and 12 females) were weaned at 3 weeks of age and fed pellets for Herbivora and cubed hay. Diabetic voles with glycosuria (nine males and six females) were classified into two groups according to the duration and grade of glycosuria. One group had slight diabetes with glycosuria (+: 0.1%) for 1 week and the other severe diabetes with marked glycosuria ( : greater than or equal to 0.5%) for over 4 weeks. Pancreatic islets of diabetic voles (n = 7) were examined immunohistochemically, light microscopically, and electron microscopically. Blood glucose concentration and tissue content of insulin, glucagon, and somatostatin were also measured. Slightly diabetic voles (n = 3) had enlarged islets, that, viewed by light microscopy, were characterized by hypertrophy and hyperplasia of beta cells with moderate degranulation. No changes were observed in the peripherally located alpha and delta cells; the voles were moderately hyperglycemic, and they had decreased pancreatic insulin content. Severely diabetic voles (n = 4) that had marked hyperglycemia and almost complete loss of insulin content showed marked vacuolation and degranulation of beta cells. In addition, altered distribution of alpha and delta cells from the periphery of the islets to their interior was noted. Ultrastructural examination revealed features compatible with those of hyperfunction of beta cells in the slightly diabetic voles and marked degeneration of beta cells with glycogen accumulation in the severely diabetic voles.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of somatostatin and its analogues in the pathogenesis and treatment of diabetes mellitus

Somatostatin secreted by pancreatic D cells is a potent inhibitor of insulin, glucagon and growth hormone secretion, as well as other cells. The role of abnormal pancreatic D-cell function in diabetes mellitus is unclear. However, development of long-acting selective somatostatin analogs might prove useful in the treatment of diabetes.

The effect of prednisolone on cyclosporin-induced damage of pancreatic B cells in Wistar rats

The combined effects of cyclosporin (CYA) and prednisolone (PSL) on the function and morphology of pancreatic B cells of Wistar rats were investigated. Four 13-day treatment groups were compared; these were the O group (olive oil alone, p.o.), the P group (PSL 3 mg/kg/day, i.m.), the C group (CYA 20 mg/kg/day, p.o.), and the PC group (PSL 3 mg/kg/day, i.m. plus CYA 20 mg/kg/day, p.o.). Glucose tolerance was equally impaired in the C and PC groups. The pancreatic insulin content in the C group was 49.7% of that of the O group, whereas that in the PC group was 81.1%. Morphometric analysis using modified aldehyde-fuchsin staining revealed that 'percent beta-granule area' in the islet was 17.5%, 15.0%, 6.5%, and 7.8% in the O, P, C, and PC groups, respectively. Ultrastructurally, pancreatic B cells in the PC group showed CYA damage; however, a significant number of B cells exhibited hypertrophy of the rough endoplasmic reticulum and the Golgi apparatus, suggesting concomitant B cell hyperactivity in this group. These findings suggest that PSL does not aggravate the toxic effects of CYA on pancreatic B cells during short-term treatment; rather, it might be protective.

Quantitative morphological changes in endocrine pancreas of rats with spontaneous diabetes mellitus

The present study describes the cytopathology of the pancreatic islets in 18-old male eSS rats with spontaneous diabetes mellitus as compared to aged-matched normal animals. Light-microscopic immunocytochemical and morphometric techniques were used to study islet-cell populations, while quantitative methods were employed specifically for the analysis of B-cell ultrastructure. The diabetic rats showed disruption of the islet structure and fibrosis in the stroma. The volume density (Vvi) of endocrine tissue and the Vvi and percentage of B cells were diminished, whereas the Vvi of exocrine tissue and the Vvi and percentage of D cells were increased. The number of medium and large islets as well as their mean volume (micron3) decreased in these animals. Pancreatic B cells from eSS rats showed an increase in the Vvi of endoplasmic reticulum, immature secretory granules and lysosomes. Conversely, the Vvi of total secretory granules and microtubules appeared diminished. The current observations contribute to our understanding of this useful animal model of diabetes mellitus, in the attempt to clarify the pathogenesis of the disease.

Control of spontaneous glucose intolerance, hyperinsulinemia, and islet hyperplasia in nonobese C3H.SW male mice by Y-linked locus and adrenal gland

An inbred strain predisposition to maturity-onset impairment of glucose tolerance was discovered in C3H.SW/SnJ inbred male mice. Males were group-caged from weaning and subjected to repetitive handling stress; deterioration of glucose tolerance developed between 5 and 8 months of age in association with extreme hyperinsulinemia. Some males developed transient chemical diabetes in which plasma glucose concentrations were inappropriately high in relation to the high levels of plasma insulin. By 12 months of age, males previously glucose intolerant had regained a normal glucose tolerance. At death, a massive hypertrophy and hyperplasia of the islet beta-cells was documented in these mice. The impaired glucose tolerance could be circumvented by adrenalectomy at weaning. Although these finding suggested the presence of an obesity gene, the C3H.SW group-caged males were not obese when compared with C3HeB/FeJ males which, although moderately hyperinsulinemic, did not develop the glucose intolerance syndrome. Transfer of the Y chromosome from the C3HeB/FeChp background into the C3H.SW inbred background led to a reduction in the hyperinsulinemic and hyperglycemic stress on the pancreatic islets. Thus the extrinsic environment (caging and handling stress), mediated in part via the adrenal gland, could interact with sex-linked genetic susceptibility modifiers to stimulate hyperplasia of the pancreatic islets and produce a transient insulin resistant state of impaired glucose tolerance in the absence of obesity.

Analysis of pancreatic islet cells and hormone content in the spontaneously diabetic KKAy mouse by morphometry, immunocytochemistry and radioimmunoassay

The splenic pancreas of 165 day old diabetic KKAy and age-matched nondiabetic C57BL/6 mice was examined by morphometry and immunocytochemistry at the light microscopic level and by radioimmunoassay to evaluate the morphology, surface area, endocrine cell composition and hormone content of the pancreatic islets. The insulin cells of the diabetic mice were severely degranulated and many of the glucagon, somatostatin and pancreatic polypeptide cells were displaced from the mantle to the core of the islet tissue where the non-insulin cells appeared to lose their continuity. The topography of some of the islets of KKAy mice was further deranged by acinar cells among the endocrine tissue. Morphometric analysis revealed that the surface area of the islets of KKAy mice was significantly expanded in comparison with that of C57BL/6 mice. The volume and numerical percents of the insulin cells were significantly increased whereas those of the glucagon and somatostatin cells were decreased in the KKAy mice. Since only the mean absolute number of insulin cells was elevated in the diabetic mice, the alteration in the relative proportions of the non-insulin cells and hypertrophy of the islets seemed to be a manifestation of insulin cell hyperplasia. Pancreatic insulin and somatostatin contents were markedly diminished in the islets of KKAy compared with those of C57BL/6 mice. These results demonstrate that the microscopic anatomy, endocrine cell populations and hormone content of the pancreatic islets are deranged in the KKAy mouse with severe hyperinsulinemia and hyperglycemia.

Secretion and effect of somatostatin in early stages of the diabetic syndrome in C57BL/KsJ-mdb mice

In a previous study in C57BL/KsJ (mdb) mice aged 12 to 90 days, we observed alterations in the secretion of insulin and somatostatin and in the inhibitory effect of the latter upon insulin secretion. This study explores whether hormonal alterations are to be found in the very early stages of the diabetic syndrome, i.e. between ages 4 and 12 days. The results demonstrate two distinct phases in the development of the syndrome: up to age 6 days, the perifused slices of pancreata of control animals present biphasic glucose-induced patterns of insulin and somatostatin secretion, whereas the diabetic animals show a diminished first peak of insulin secretion, but a similar pattern of somatostatin secretion, to that of the control animals; between ages 7 and 12 days, the pancreata of diabetic mice exhibit insulin hypersecretion in basal conditions, and an absence of the first secretion peak and insulin hypersecretion in the second phase in response to glucose stimulation. The glucose-induced pattern of somatostatin secretion presents hormonal hypersecretion in both phases. B-cell sensitivity to the inhibitory effect of somatostatin is diminished in mdb mice of the above-mentioned groups, an alteration which becomes more evident as diabetes evolves. The results show that, in very early stages of the evolution of the diabetic syndrome in C57BL/KsJ (mdb) mice, there are already alterations in insulin and somatostatin secretion patterns and in the inhibitory effect of the latter on insulin secretion.

Temporal changes in pancreatic islet composition in C57BL/6J-db/db (diabetes) mice

Temporal changes in non-B cell populations were determined during the period of B cell hyperplasia in diabetes-resistant C57BL/6J mice. Pancreases from normal and db/db mice between 3 and 20 weeks of age were stained immunocytochemically for glucagon, somatostatin and pancreatic polypeptide (PP), and changes in A, D and PP cell volume densities quantified by image analysis. Further, islet volumes, D cell volumes and actual D cell numbers per islet were determined by analysis of serial sections through entire islets. The volume of db/db islets was three- and ten-fold elevated above normal by 8 and 20 weeks, respectively, due mainly to B cell hyperplasia. D cell volume density exhibited a transient increase during the initial phase of B cell hyperplasia, but then showed a gradual reduction; the average number and absolute volume of D cells per islet was comparable in db/db and normal islets from older mice. In contrast, PP cell volume density remained stable throughout, suggesting that this cell type kept pace with B cell hyperplasia. A cells showed a reduced volume density throughout and were distinguished from other islet cells which all responded positively to a degree, albeit non-coordinately, to the mitogenic stimulus exerted by db gene expression. The finding that A cells shared with certain neuroectodermally-derived cell types a differentially high concentration of sn-glycerol-3-phosphate dehydrogenase further underscored the uniqueness of the A cell from other cell types.

Lessons from studies with genetic forms of diabetes in the mouse

Genetically defined animal models of diabetes have many advantages over models in which the genetic component has not been established. Such models permit predictable numbers of normal and afflicted animals, differing by only a single gene, to be produced at will. Maintenance of these individual mutations in inbred strains of mice permits an evaluation of any gene-host interactions that act by modifying the severity of the diabetic condition. These genetic models provide precision tools for research in which the mutant gene itself, the inbred background, and the environment can be manipulated at will. In addition there is sufficient knowledge about the arrangement of individual genes in chromosomes in the mouse to permit one to identify, and use, closely linked markers in order to predict with confidence the mice destined to become diabetic. Such studies on the preclinical stages are of utmost importance and cannot be undertaken conveniently in any other model. Our studies with genetic mouse models have established that there are at least six genes in the mouse that can cause diabetes and obesity syndromes. The severity of the diabetes produced depends on the interaction of the mutant gene with the host inbred background as well as with other environmental factors. Establishing the nature of these interactions and the possible primary lesions involved in each genetic syndrome should have major ramifications in studies dealing with human diabetes.

Dietary control of pathogenesis in C57BL/KsJ db/db diabetes mice

Weanling C57BL/KsJ homozygous diabetic (db/db) and normal littermate (+/+ or +/db) mice were maintained for 5 mon on isocaloric diets containing either 60% sucrose, 23% casein, 8% corn oil (diet C) or 0% sucrose, 83% casein, 8% corn oil (diet B). Diabetic homozygotes consumed more diet C than normals, but ate control amounts of diet B. Diabetic mice fed diet C exhibited 57% mortality between 4 or 5 mo of age. All diabetic mutants fed the carbohydrate-free diet B appeared healthy at 6 mo of age; mutant females were normoglycemic and mutant males were only moderately hyperglycemic. Histological examination of pancreatic islets confirmed the absence of islet degeneration. In diet B maintained mutants, increased carcass fat composition, plasma and pancreatic content of insulin and glucagon, and thymidine incorporation into islets, all established that the db gene was being fully expressed. These results indicate that dietary protein stimulates islet growth and function in db/db mice, while high levels of refined carbohydrate in the diet predispose islet beta cells to undefined changes that culminate in necrosis. Restricting mutants' intake of a carbohydrate-containing diet to one-half the caloric intake of normal mice failed to block onset of beta cell necrosis. Thus, dietary composition rather than total caloric intake appears to be critical in the induction of islet necrosis and atrophy in this animal model of genetically transmitted diabetes.

Role of Ca2+ in impaired insulin release from islets of diabetic (C57BL/KsJ-db/db) mice

The involvement of Ca2+ in the impaired insulin release of diabetic C57BL/KsJ-db/db mice was studied. Twenty-week-old severely hyperglycemic mice were compared to nondiabetic C57BL/KsJ mice as controls. Collagenase-isolated islets were maintained for 46 h in tissue culture allowing for equilibration at the same glucose concentration (8.3) mM). The insulin content of both types of islets was similar. In control islets preloaded during culture with 45Ca2+ glucose-induced insulin release was associated with increased 45Ca2+ effux. Islets from diabetic mice showed markedly reduced insulin response to glucose and a smaller increase in 45Ca2+ efflux. Because insulin release was strikingly potentiated by 3-isobutyl-1-methylxanthine (IBMX), even more than in control islets, there was no generalized release defect. In both types of islets, IBMX potentiation was accompanied by a further enhanced 45Ca2+ efflux, possibly suggesting that cAMP effects are associated with increased cytosol Ca2+% concentrations. As Ca2+ uptake was stimulated by glucose in both types of islets, a defect may lie in the mechanism by which glucose uses cellulr calcium to raise cytosol Ca2+ in the beta-cell of these diabetic mice.