Delta cell death in the islet of Langerhans and the progression from normal glucose tolerance to type 2 diabetes in non-human primates (baboon, Papio hamadryas).
ABSTRACT: The cellular composition of the islet of Langerhans is essential to ensure its physiological function. Morphophysiological islet abnormalities are present in type 2 diabetes but the relationship between fasting plasma glucose (FPG) and islet cell composition, particularly the role of delta cells, is unknown. We explored these questions in pancreases from baboons (Papio hamadryas) with FPG ranging from normal to type 2 diabetic values.We measured the volumes of alpha, beta and delta cells and amyloid in pancreatic islets of 40 baboons (Group 1 [G1]: FPG < 4.44 mmol/l [n = 10]; G2: FPG = 4.44-5.26 mmol/l [n = 9]; G3: FPG = 5.27-6.94 mmol/l [n = 9]; G4: FPG > 6.94 mmol/l [n = 12]) and correlated islet composition with metabolic and hormonal variables. We also performed confocal microscopy including TUNEL, caspase-3, and anti-caspase cleavage product of cytokeratin 18 (M30) immunostaining, electron microscopy, and immuno-electron microscopy with anti-somatostatin antibodies in baboon pancreases.Amyloidosis preceded the decrease in beta cell volume. Alpha cell volume increased ? 50% in G3 and G4 (p < 0.05), while delta cell volume decreased in these groups by 31% and 39%, respectively (p < 0.05). In G4, glucagon levels were higher, while insulin and HOMA index of beta cell function were lower than in the other groups. Immunostaining of G4 pancreatic sections with TUNEL, caspase-3 and M30 showed apoptosis of beta and delta cells, which was also confirmed by immuno-electron microscopy with anti-somatostatin antibodies.In diabetic baboons, changes in islet composition correlate with amyloid deposition, with increased alpha cell and decreased beta and delta cell volume and number due to apoptosis. These data argue for an important role of delta cells in type 2 diabetes.
Project description:beta-Cell dysfunction is an important factor in the development of hyperglycemia of type-2 diabetes mellitus, and pancreatic islet amyloidosis (IA) has been postulated to be one of the main contributors to impaired insulin secretion. The aim of this study was to evaluate the correlation of IA with metabolic parameters and its effect on islets of Langerhans remodeling and relative endocrine-cell volume in baboons. We sequenced the amylin peptide, determined the fibrillogenic propensities, and evaluated pancreatic histology, clinical and biochemical characteristics, and endocrine cell proliferation and apoptosis in 150 baboons with different metabolic status. Amylin sequence in the baboon was 92% similar to humans and showed superimposable fibrillogenic propensities. IA severity correlated with fasting plasma glucose (FPG) (r = 0.662, P < 0.001) and HbA1c (r = 0.726, P < 0.001), as well as with free fatty acid, glucagon values, decreased homeostasis model assessment (HOMA) insulin resistance, and HOMA-B. IA severity was associated with a decreased relative beta-cell volume, and increased relative alpha-cell volume and hyperglucagonemia. These results strongly support the concept that IA and beta-cell apoptosis in concert with alpha-cell proliferation and hypertrophy are key determinants of islets of Langerhans "dysfunctional remodeling" and hyperglycemia in the baboon, a nonhuman primate model of type-2 diabetes mellitus. The most important determinants of IA were age and FPG (R(2) = 0.519, P < 0.0001), and different FPG levels were sensitive and specific to predict IA severity. Finally, a predictive model for islet amyloid severity was generated with age and FPG as required variables.
Project description:Aims:Basal insulin plus oral hypoglycemic agents (OHAs) has not been investigated for early intensive antihyperglycemic treatment in people with newly diagnosed type 2 diabetes. This study is aimed at comparing the short-term (over a period of 12 days) effects of basal insulin glargine plus OHAs and continuous subcutaneous insulin infusion (CSII) on glycemic control and beta-cell function in this setting. Methods:An open-label parallel-group study. Newly diagnosed hospitalized patients with type 2 diabetes and fasting plasma glucose (FPG) ?11.1?mmol/L or glycated hemoglobin (HbA1c) ?9% (75?mmol/mol) were randomized to CSII or insulin glargine in combination with metformin and gliclazide. The primary outcome measure was the mean amplitude of glycemic excursions (MAGE), and secondary endpoints included time to reach glycemic control target (FPG?<?7?mmol/L and 2-hour postprandial plasma glucose?<?10?mmol/L), markers of ?-cell function, and hypoglycemia. Results:Subjects in the CSII (n = 35) and basal insulin plus OHA (n = 33) groups had a similar significant reduction from baseline to end of treatment in glycated albumin (-6.44?±?3.23% and-?6.42?±?3.56%, P = 0.970). Groups A and B have comparable time to glycemic control (3.6?±?1.2 days and 4.0?±?1.4 days), MAGE (3.40?±?1.40?mmol/L vs. 3.16?±?1.38?mmol/L; p = 0.484), and 24-hour mean blood glucose (7.49?±?0.96?mmol/L vs. 7.02?±?1.03?mmol/L). Changes in the C-peptide reactivity index, the secretory unit of islet in transplantation index, and insulin secretion-sensitivity index-2 indicated a greater ?-cell function improvement with basal insulin plus OHAs versus CSII. Conclusions:Short-term insulin glargine plus OHAs may be an alternative to CSII for initial intensive therapy in people with newly diagnosed type 2 diabetes.
Project description:PURPOSE:To evaluate the effects of metreleptin in patients with partial lipodystrophy (PL). METHODS:Patients aged???6 months with PL, circulating leptin?<?12.0?ng/mL, and diabetes mellitus, insulin resistance, or hypertriglyceridemia received metreleptin doses (once or twice daily) titrated to a mean of 0.124?mg/kg/day. Changes from baseline to month 12 in glycated hemoglobin (HbA1c) and fasting serum triglycerides (TGs; co-primary endpoints), fasting plasma glucose (FPG), and liver volume were evaluated. Additional assessments included the proportions of patients achieving target decreases in HbA1c or fasting TGs at month 12, long-term treatment effects, and treatment-emergent adverse events (TEAEs). RESULTS:Significant (p?<?0.05) reductions in HbA1c (-0.6%), fasting TGs (-20.8%), FPG (-1.2?mmol/L), and liver volume (-13.4%) were observed in the overall PL population at month 12. In a subgroup of patients with baseline HbA1c???6.5% or TGs???5.65?mmol/L, significant (p?<?0.05) reductions were seen in HbA1c (-0.9%), fasting TGs (-37.4%), FPG (-1.9?mmol/L), and liver volume (-12.4%). In this subgroup, 67.9% of patients had a???1% decrease in HbA1c or???30% decrease in fasting TGs, and 42.9% had a???2% decrease in HbA1c or???40% decrease in fasting TGs. Long-term treatment in this subgroup led to significant (p?<?0.05) reductions at months 12, 24, and 36 in HbA1c, fasting TGs, and FPG. Metreleptin was well tolerated with no unexpected safety signals. The most common TEAEs were abdominal pain, hypoglycemia, and nausea. CONCLUSIONS:In patients with PL, treatment with metreleptin was well tolerated and resulted in improvements in glycemic control, hypertriglyceridemia, and liver volume.
Project description:HbA(1c) levels are higher in most ethnic groups compared with white Europeans (WEs) independent of glycemic control. This comparison has not been performed between South Asians (SAs) and WEs. We analyzed the independent effect of ethnicity on HbA(1c) and fasting and 2-h plasma glucose (FPG and 2 hrPG, respectively) between these groups.Analysis of the ADDITION-Leicester study, in which 4,688 WEs and 1,352 SAs underwent oral glucose tolerance testing, HbA(1c), and other risk factor measurements.Significant associations with HbA(1c) included ethnicity, FPG, 2 hrPG, and homeostasis model assessment of β-cell function (P < 0.001); age and sex (P < 0.01); and fasting insulin and potassium (P < 0.05). After adjusting for these and other risk factors, SAs demonstrated higher HbA(1c) (6.22 and 6.02%, mean difference 0.20%, 0.10-0.30, P < 0.001), FPG (5.15 and 5.30 mmol/L, mean difference 0.15 mmol/L, 0.09-0.21, P < 0.001), and 2 hrPG (5.82 and 6.57 mmol/L, mean difference 0.75 mmol/L, 0.59-0.92, P < 0.001) compared with WEs, respectively.HbA(1c), FPG, and 2 hrPG levels were higher in SAs independent of factors affecting glycemic control.
Project description:Obesity is associated with high insulin and glucagon plasma levels. Enhanced ?-cell function and ?-cell expansion are responsible for insulin hypersecretion. It is unknown whether hyperglucagonemia is due to ?-cell hypersecretion or to an increase in ?-cell mass. In this study, we investigated the dynamics of the ?-cell and ?-cell function and mass in pancreas of obese normoglycemic baboons.Pancreatic ?- and ?-cell volumes were measured in 51 normoglycemic baboons divided into six groups according to overweight severity or duration. Islets morphometric parameters were correlated to overweight and to diverse metabolic and laboratory parameters.Relative ?-cell volume (R?V) and relative islet ?-cell volume (RI?V) increased significantly with both overweight duration and severity. Conversely, in spite of the induction of insulin resistance, overweight produced only modest effects on relative ?-cell volume (R?V) and relative islet ?-cell volume (RI?V). Of note, RI?V did not increase neither with overweight duration nor with overweight severity, supposedly because of the concomitant, greater increase in RI?V. Baboons' body weights correlated with serum levels of interleukin-6 and tumor necrosis factor-? soluble receptors, demonstrating that overweight induces abnormal activation of the signaling of two cytokines known to impact differently ?- and ?-cell viability and replication.In conclusion, overweight and insulin resistance induce in baboons a significant increase in ?-cell volumes (R?V, RI?V), whereas have minimal effects on the ? cells. This study suggests that an increase in the ?-cell mass may precede the loss of ? cells and the transition to overt hyperglycemia and diabetes.
Project description:Complex local crosstalk amongst endocrine cells within the islet ensures tight coordination of their endocrine output. This is illustrated by the recent demonstration that the negative feedback control by delta cells within pancreatic islets determines the homeostatic set-point for plasma glucose during mouse postnatal development. However, the close association of islet endocrine cells that facilitates paracrine crosstalk also complicates the distinction between effects mediated directly on beta cells from indirect effects mediated via local intermediates, such as somatostatin from delta cells.To resolve this problem, we generated reporter mice that allow collection of pure pancreatic delta cells along with alpha and beta cells from the same islets and generated comprehensive transcriptomes for each islet endocrine cell type. These transcriptomes afford an unparalleled view of the receptors expressed by delta, alpha and beta cells, and allow the prediction of which signal targets which endocrine cell type with great accuracy.From these transcriptomes, we discovered that the ghrelin receptor is expressed exclusively by delta cells within the islet, which was confirmed by fluorescent in situ hybridization and qPCR. Indeed, ghrelin increases intracellular calcium in delta cells in intact mouse islets, measured by GCaMP6 and robustly potentiates glucose-stimulated somatostatin secretion on mouse and human islets in both static and perfusion assays. In contrast, des-acyl-ghrelin at the same dose had no effect on somatostatin secretion and did not block the actions of ghrelin.These results offer a straightforward explanation for the well-known insulinostatic actions of ghrelin. Rather than engaging beta cells directly, ghrelin engages delta cells to promote local inhibitory feedback that attenuates insulin release. These findings illustrate the power of our approach to resolve some of the long-standing conundrums with regard to the rich feedback that occurs within the islet that is integral to islet physiology and therefore highly relevant to diabetes.
Project description:Intra-islet and gut-islet crosstalk are critical in orchestrating basal and postprandial metabolism. The aim of this study was to identify regulatory proteins and receptors underlying somatostatin secretion though the use of transcriptomic comparison of purified murine alpha, beta and delta cells.Sst-Cre mice crossed with fluorescent reporters were used to identify delta cells, while Glu-Venus (with Venus reported under the control of the Glu [also known as Gcg] promoter) mice were used to identify alpha and beta cells. Alpha, beta and delta cells were purified using flow cytometry and analysed by RNA sequencing. The role of the ghrelin receptor was validated by imaging delta cell calcium concentrations using islets with delta cell restricted expression of the calcium reporter GCaMP3, and in perfused mouse pancreases.A database was constructed of all genes expressed in alpha, beta and delta cells. The gene encoding the ghrelin receptor, Ghsr, was highlighted as being highly expressed and enriched in delta cells. Activation of the ghrelin receptor raised cytosolic calcium levels in primary pancreatic delta cells and enhanced somatostatin secretion in perfused pancreases, correlating with a decrease in insulin and glucagon release. The inhibition of insulin secretion by ghrelin was prevented by somatostatin receptor antagonism.Our transcriptomic database of genes expressed in the principal islet cell populations will facilitate rational drug design to target specific islet cell types. The present study indicates that ghrelin acts specifically on delta cells within pancreatic islets to elicit somatostatin secretion, which in turn inhibits insulin and glucagon release. This highlights a potential role for ghrelin in the control of glucose metabolism.
Project description:Blood glucose levels are tightly controlled by the coordinated action of at least four cell types constituting pancreatic islets. Changes in the proportion and/or function of these cells are associated with genetic and molecular pathophysiology of monogenic, type 1, and type 2 (T2D) diabetes. Cellular heterogeneity impedes precise understanding of the molecular components of each islet cell type that govern islet (dys)function, particularly the less abundant delta and gamma/pancreatic polypeptide (PP) cells. Here, we report single-cell transcriptomes for 638 cells from nondiabetic (ND) and T2D human islet samples. Analyses of ND single-cell transcriptomes identified distinct alpha, beta, delta, and PP/gamma cell-type signatures. Genes linked to rare and common forms of islet dysfunction and diabetes were expressed in the delta and PP/gamma cell types. Moreover, this study revealed that delta cells specifically express receptors that receive and coordinate systemic cues from the leptin, ghrelin, and dopamine signaling pathways implicating them as integrators of central and peripheral metabolic signals into the pancreatic islet. Finally, single-cell transcriptome profiling revealed genes differentially regulated between T2D and ND alpha, beta, and delta cells that were undetectable in paired whole islet analyses. This study thus identifies fundamental cell-type-specific features of pancreatic islet (dys)function and provides a critical resource for comprehensive understanding of islet biology and diabetes pathogenesis.
Project description:Long-term exposure to NEFAs leads to inhibition of glucose-induced insulin secretion. We tested whether the release of somatostatin and glucagon, the two other major islet hormones, is also affected.Mouse pancreatic islets were cultured for 72 h at 4.5 or 15 mmol/l glucose with or without 0.5 mmol/l oleate or palmitate. The release of glucagon and somatostatin during subsequent 1 h incubations at 1 or 20 mmol/l glucose as well as the islet content of the two hormones were determined. Lipid-induced changes in islet cell ultrastructure were assessed by electron microscopy.Culture at 15 mmol/l glucose increased islet glucagon content by approximately 50% relative to that observed following culture at 4.5 mmol/l glucose. Inclusion of oleate or palmitate reduced islet glucagon content by 25% (at 4.5 mmol/l glucose) to 50% (at 15 mmol/l glucose). Long-term exposure to the NEFA increased glucagon secretion at 1 mmol/l glucose by 50% (when islets had been cultured at 15 mmol/l glucose) to 100% (with 4.5 mmol/l glucose in the culture medium) and abolished the inhibitory effect of 20 mmol/l glucose on glucagon secretion. Somatostatin content was unaffected by glucose and lipids, but glucose-induced somatostatin secretion was reduced by approximately 50% following long-term exposure to either of the NEFA, regardless of whether the culture medium contained 4.5 or 15 mmol/l glucose. Ultrastructural evidence of lipid deposition was seen in <10% of non-beta cells but in >80% of the beta cells.Long-term exposure to high glucose and/or NEFA affects the release of somatostatin and glucagon. The effects on glucagon secretion are very pronounced and in type 2 diabetes in vivo may aggravate the hyperglycaemic effects due to lack of insulin.
Project description:Little is known about the role of islet delta cells in regulating blood glucose homeostasis in vivo. Delta cells are important paracrine regulators of beta cell and alpha cell secretory activity, however the structural basis underlying this regulation has yet to be determined. Most delta cells are elongated and have a well-defined cell soma and a filopodia-like structure. Using in vivo optogenetics and high-speed Ca2+ imaging, we show that these filopodia are dynamic structures that contain a secretory machinery, enabling the delta cell to reach a large number of beta cells within the islet. This provides for efficient regulation of beta cell activity and is modulated by endogenous IGF-1/VEGF-A signaling. In pre-diabetes, delta cells undergo morphological changes that may be a compensation to maintain paracrine regulation of the beta cell. Our data provides an integrated picture of how delta cells can modulate beta cell activity under physiological conditions.