Imaging of extracellular and intracellular ATP in pancreatic beta cells reveals correlation between glucose metabolism and purinergic signalling

Adenosine triphosphate (ATP) is a universal energy molecule and yet cells release it and extracellular ATP is an important signalling molecule between cells. Monitoring of ATP levels outside of cells is important for our understanding of physiological and pathophysiological processes in cells/tissues. Here, we focus on pancreatic beta cells (INS-1E) and test the hypothesis that there is an association between intra- and extracellular ATP levels which depends on glucose provision. We imaged real-time changes in extracellular ATP in pancreatic beta cells using two sensors tethered to extracellular aspects of the plasma membrane (eATeam3.10, iATPSnFR1.0). Increase in glucose induced fast micromolar ATP release to the cell surface, depending on glucose concentrations. Chronic pre-treatment with glucose increased the basal ATP signal. In addition, we co-expressed intracellular ATP sensors (ATeam1.30, PercevalHR) in the same cultures and showed that glucose induced fast increases in extracellular and intracellular ATP. Glucose and extracellular ATP stimulated glucose transport monitored by the glucose sensor (FLII12Pglu-700uDelta6). In conclusion, we propose that in beta cells there is a dynamic relation between intra- and extracellular ATP that depends on glucose transport and metabolism and these processes may be tuned by purinergic signalling. Future development of ATP sensors for imaging may aid development of novel approaches to target extracellular ATP in, for example, type 2 diabetes mellitus therapy.

KSRP improves pancreatic beta cell function and survival

Impaired insulin production and/or secretion by pancreatic beta cells can lead to high blood glucose levels and type 2 diabetes (T2D). Therefore, investigating new proteins involved in beta cell response to stress conditions could be useful in finding new targets for therapeutic approaches. KH-type splicing regulatory protein (KSRP) is a protein usually involved in gene expression due to its role in post-transcriptional regulation. Although there are studies describing the important role of KSRP in tissues closely related to glucose homeostasis, its effect on pancreatic beta cells has not been explored so far. Pancreatic islets from diet-induced obese mice (C57BL/6JUnib) were used to determine KSRP expression and we also performed in vitro experiments exposing INS-1E cells (pancreatic beta cell line) to different stressors (palmitate or cyclopiazonic acid-CPA) to induce cellular dysfunction. Here we show that KSRP expression is reduced in all the beta cell dysfunction models tested. In addition, when manipulated to knock down KSRP, beta cells exhibited increased death and impaired insulin secretion, whereas KSRP overexpression prevented cell death and increased insulin secretion. Taken together, our findings suggest that KSRP could be an important target to protect beta cells from impaired functioning and death.

Vildagliptin inhibits high fat and fetuin-A mediated DPP-4 expression, intracellular lipid accumulation and improves insulin secretory defects in pancreatic beta cells

Dipeptidyl peptidase-4 (DPP-4), a ubiquitous proteolytic enzyme, inhibits insulin secretion from pancreatic beta cells by inactivating circulating incretin hormones GLP-1 and GIP. High circulating levels of DPP-4 is presumed to compromise insulin secretion in people with type 2 diabetes (T2D). Our group recently reported lipid induced DPP-4 expression in pancreatic beta cells, mediated by the TLR4-NFkB pathway. In the present study, we looked at the role of Vildagliptin on pancreatic DPP-4 inhibition, preservation of islet mass and restoration of insulin secretion. MIN6 mouse insulinoma cells incubated with palmitate and fetuin-A, a proinflammatory organokine associated with insulin resistance, showed activation of TLR4-NFkB pathway, which was rescued on Vildagliptin treatment. In addition, Vildagliptin, by suppressing palmitate-fetuin-A mediated DPP-4 expression in MIN6, prevented the secretion of IL-1beta and fetuin-A in the culture media. DPP-4 siRNA abrogated TLR4-NFkB pathway mediated islet cell inflammation. Vildagliptin also reduced palmitate-fetuin-A mediated intracellular lipid accumulation in MIN6 and isolated islets from high fat fed (HFD) mice as observed by Oil O Red staining with downregulation of CD36 and PPARgamma. Vildagliptin also preserved islet mass and rescued insulin secretory defect in HFD mice. Our results suggest that inhibition of DPP-4 by Vildagliptin protects pancreatic beta cells from the deleterious effects of lipid and fetuin-A, preserves insulin secretory functions and improves hyperglycemia.

Didymin protects pancreatic beta cells by enhancing mitochondrial function in high-fat diet-induced impaired glucose tolerance

PURPOSE

Prolonged exposure to plasma free fatty acids (FFAs) leads to impaired glucose tolerance (IGT) which can progress to type 2 diabetes (T2D) in the absence of timely and effective interventions. High-fat diet (HFD) leads to chronic inflammation and oxidative stress, impairing pancreatic beta cell (PBC) function. While Didymin, a flavonoid glycoside derived from citrus fruits, has beneficial effects on inflammation dysfunction, its specific role in HFD-induced IGT remains yet to be elucidated. Hence, this study aims to investigate the protective effects of Didymin on PBCs.

METHODS

HFD-induced IGT mice and INS-1 cells were used to explore the effect and mechanism of Didymin in alleviating IGT. Serum glucose and insulin levels were measured during the glucose tolerance and insulin tolerance tests to evaluate PBC function and insulin resistance. Next, RNA-seq analysis was performed to identify the pathways potentially influenced by Didymin in PBCs. Furthermore, we validated the effects of Didymin both in vitro and in vivo. Mitochondrial electron transport inhibitor (Rotenone) was used to further confirm that Didymin exerts its ameliorative effect by enhancing mitochondria function.

RESULTS

Didymin reduces postprandial glycemia and enhances 30-minute postprandial insulin levels in IGT mice. Moreover, Didymin was found to enhance mitochondria biogenesis and function, regulate insulin secretion, and alleviate inflammation and apoptosis. However, these effects were abrogated with the treatment of Rotenone, indicating that Didymin exerts its ameliorative effect by enhancing mitochondria function.

CONCLUSIONS

Didymin exhibits therapeutic potential in the treatment of HFD-induced IGT. This beneficial effect is attributed to the amelioration of PBC dysfunction through improved mitochondrial function.

Deletion of Ascl1 in pancreatic β-cells improves insulin secretion, promotes parasympathetic innervation, and attenuates dedifferentiation during metabolic stress

OBJECTIVE

ASCL1, a pioneer transcription factor, is essential for neural cell differentiation and function. Previous studies have shown that Ascl1 expression is increased in pancreatic β-cells lacking functional KATP channels or after feeding of a high fat diet (HFD) suggesting that it may contribute to the metabolic stress response of β-cells.

METHODS

We generated β-cell-specific Ascl1 knockout mice (Ascl1βKO) and assessed their glucose homeostasis, islet morphology and gene expression after feeding either a normal diet or HFD for 12 weeks, or in combination with a genetic disruption of Abcc8, an essential KATP channel component.

RESULTS

Ascl1 expression is increased in response to both a HFD and membrane depolarization and requires CREB-dependent Ca2+ signaling. No differences in glucose homeostasis or islet morphology were observed in Ascl1βKO mice fed a normal diet or in the absence of KATP channels. However, male Ascl1βKO mice fed a HFD exhibited decreased blood glucose levels, improved glucose tolerance, and increased β-cell proliferation. Bulk RNA-seq analysis of islets from Ascl1βKO mice from three studied conditions showed alterations in genes associated with the secretory function. HFD-fed Ascl1βKO mice showed the most extensive changes with increased expression of genes necessary for glucose sensing, insulin secretion and β-cell proliferation, and a decrease in genes associated with β-cell dysfunction, inflammation and dedifferentiation. HFD-fed Ascl1βKO mice also displayed increased expression of parasympathetic neural markers and cholinergic receptors that was accompanied by increased insulin secretion in response to acetylcholine and an increase in islet innervation.

CONCLUSIONS

Ascl1 expression is induced by stimuli that cause Ca2+-signaling to the nucleus and contributes in a multifactorial manner to the loss of β-cell function by promoting the expression of genes associated with cellular dedifferentiation, attenuating β-cells proliferation, suppressing acetylcholine sensitivity, and repressing parasympathetic innervation of islets. Thus, the removal of Ascl1 from β-cells improves their function in response to metabolic stress.

Guf1 overexpression improves pancreatic β cell functions in type 2 diabetes mellitus rats with Roux-en-Y gastric bypass (RYGB) surgery

The Roux-en-Y gastric bypass (RYGB) is a one-of-a-kind treatment among contemporary bariatric surgical procedures, and its therapeutic effects for type 2 diabetes mellitus (T2DM) are satisfactory. The present study performed isobaric tags for relative and absolute quantification (iTRAQ) combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis identifying different proteomics between T2DM rats with or without Roux-en-Y gastric bypass (RYGB) surgery, and GTP binding elongation factor GUF1 (Guf1) was first found to be significantly upregulated in rats from the T2DM plus RYGB group. In the cellular lipotoxicity model induced by palmitic acid stimulation of rat pancreatic beta cell line, INS-1, palmitic acid treatment inhibited cell viability, suppressed GSIS, promoted lipid droplet formation, promoted cell apoptosis, and induced mitochondrial membrane potential loss. The effects of palmitic acid on INS-1 cells mentioned above could be partially eliminated by Guf1 overexpression but aggravated by Guf1 knockdown. Last, under palmitic acid treatment, Guf1 overexpression promotes the PI3K/Akt and NF-κB signaling but inhibits the AMPK activation. Guf1 is upregulated in T2DM rats who received RYGB, and Guf1 overexpression improves cell mitochondrial functions, increases cell proliferation, inhibits cell apoptosis, and promotes cell functions in palmitic acid-treated β cells.

FFA-Fetuin-A regulates DPP-IV expression in pancreatic beta cells through TLR4-NFkB pathway

Dipeptidyl peptidase 4 (DPP-IV) is a ubiquitous proteolytic enzyme that cleaves incretin hormones, such as glucagon-like peptide 1 (GLP1) and gastric inhibitory protein (GIP), leading to reduced glucose stimulated insulin secretion from the pancreatic beta cells. The functionally active enzyme is present in a membrane bound form in several cell types as well as in a soluble form in the circulation. The present report deals with DPP-IV expression and its regulation in the pancreatic beta cells in presence of free fatty acids (FFAs) and Fetuin-A, a circulatory glycoprotein associated with insulin resistance in humans and animals. FFA and Fetuin-A individually or in combination trigger DPP-IV expression in MIN6 cells. Islets isolated from high fat diet fed (HFD) mice (16 weeks) showed higher levels of DPP-IV expression than standard diet (SD) fed mice. Fetuin-A increased DPP-IV expression in HFD mice (4 weeks). Inhibition of TLR4 or NFkB prevented palmitate-Fetuin-A mediated DPP-IV expression in MIN6. It has been seen that Fetuin-A alone also could trigger DPP-IV expression in MIN6 cells via NFkB. Additionally, palmitate treatment exhibited reduced level of soluble DPP-IV in the media of MIN6 culture, which corroborated with the expression pattern of its protease, KLK5 that cleaves and releases the membrane bound DPP-IV into the secretion. Our results demonstrate that FFA-Fetuin-A upregulates DPP-IV expression in the pancreatic beta cells through the TLR4-NFkB pathway.

Systematic Bayesian posterior analysis guided by Kullback-Leibler divergence facilitates hypothesis formation

Bayesian inference produces a posterior distribution for the parameters of a mathematical model that can be used to guide the formation of hypotheses; specifically, the posterior may be searched for evidence of alternative model hypotheses, which serves as a starting point for hypothesis formation and model refinement. Previous approaches to search for this evidence are largely qualitative and unsystematic; further, demonstrations of these approaches typically stop at hypothesis formation, leaving the questions they raise unanswered. Here, we introduce a Kullback-Leibler (KL) divergence-based ranking to expedite Bayesian hypothesis formation and investigate the hypotheses it generates, ultimately generating novel, biologically significant insights. Our approach uses KL divergence to rank parameters by how much information they gain from experimental data. Subsequently, rather than searching all model parameters at random, we use this ranking to prioritize examining the posteriors of the parameters that gained the most information from the data for evidence of alternative model hypotheses. We test our approach with two examples, which showcase the ability of our approach to systematically uncover different types of alternative hypothesis evidence. First, we test our KL divergence ranking on an established example of Bayesian hypothesis formation. Our top-ranked parameter matches the one previously identified to produce alternative hypotheses. In the second example, we apply our ranking in a novel study of a computational model of prolactin-induced JAK2-STAT5 signaling, a pathway that mediates beta cell proliferation. Within the top 3 ranked parameters (out of 33), we find a bimodal posterior revealing two possible ranges for the prolactin receptor degradation rate. We go on to refine the model, incorporating new data and determining which degradation rate is most plausible. Overall, while the effectiveness of our approach depends on having a properly formulated prior and on the form of the posterior distribution, we demonstrate that our approach offers a novel and generalizable quantitative framework for Bayesian hypothesis formation and use it to produce a novel, biologically-significant insight into beta cell signaling.

Importance of beta cell mass for glycaemic control in people with type 1 diabetes

AIMS/HYPOTHESIS

The role of beta cell mass in the balance of glucose control and hypoglycaemic burden in people with type 1 diabetes is unclear. We applied positron emission tomography (PET) imaging with radiolabelled exendin to compare beta cell mass among people with type 1 diabetes and either low glucose variability (LGV) or high glucose variability (HGV).

METHODS

All participants with either LGV (n=9) or HGV (n=7) underwent a mixed-meal tolerance test to determine beta cell function and wore a blinded continuous glucose monitor for a week. After an i.v. injection with [⁶⁸Ga]Ga-NODAGA-exendin-4, PET images were acquired for the quantification of pancreatic uptake of radiolabelled exendin. The mean standardised uptake value (SUVmean) of the pancreas was used to determine the amount of beta cell mass.

RESULTS

Participants with LGV had lower HbA_1c (46.0 mmol/mol [44.5-52.5] [6.4% (6.3-7)] vs 80 mmol/mol [69.0-110] [9.5% (8.5-12.2)], p=0.001) and higher time in range (TIR) (75.6% [73.5-90.3] vs 38.7% [25.1-48.5], p=0.002) than those with HGV. The SUVmean of the pancreas was higher for the LGV than for the HGV group (5.1 [3.6-5.6] vs 2.9 [2.1-3.4], p=0.008). The AUC_C-peptide:AUC_glucose ratio was numerically, but not statistically, higher in the LGV compared with the HGV group (2.7×10^-2 [6.2×10^-4-5.3×10^-2] vs 9.3×10^-4 [4.7×10^-4-5.2×10^-3], p=0.21). SUVmean correlated with the AUC_C-peptide:AUC_glucose ratio (Pearson r=0.64, p=0.01), as well as with the TIR (r=0.64, p=0.01) and the SD of interstitial glucose levels (r=-0.66, p=0.007).

CONCLUSION/INTERPRETATION

Our data show higher beta cell mass in people with type 1 diabetes and LGV than in those with HGV, independent of beta cell function.

miRNA Theranostic Nanoparticles Promote Pancreatic Beta Cell Proliferation in Type 1 Diabetes Model

Type 1 diabetes (T1D) is a chronic autoimmune disorder which affects the insulin-producing beta cells in the pancreas. A variety of strategies, namely, insulin replacement therapy, engineered vaccines, immunomodulators, etc., have been explored to correct this condition. Recent studies have attributed the development of T1D to the anomalous expression of microRNAs in the pancreatic islets. Here, we describe the protocol for the development of a theranostic approach to modify the expression of aberrant miRNAs. The MRI-based nanodrug consists of superparamagnetic iron oxide nanoparticles conjugated to microRNA-targeting oligonucleotides that can promote proliferation of pancreatic beta cells in a mouse model of T1D. This theranostic approach can successfully serve as a potential therapeutic approach for the targeted treatment of T1D with minimal side effects.

Selective ablation of P53 in pancreatic beta cells fails to ameliorate glucose metabolism in genetic, dietary and pharmacological models of diabetes mellitus

OBJECTIVE

Beta cell dysfunction and death are critical steps in the development of both type 1 and type 2 diabetes (T1D and T2D), but the underlying mechanisms are incompletely understood. Activation of the essential tumor suppressor and transcription factor P53 (also known as TP53 and Trp53 in mice) was linked to beta cell death in vitro and has been reported in several diabetes mouse models and beta cells of humans with T2D. In this article, we set out to determine the beta cell specific role of P53 in beta cell dysfunction, cell death and development of diabetes in vivo.

METHODS

We generated beta cell specific P53 knockout (P53^BKO) mice and used complementary genetic, dietary and pharmacological models of glucose intolerance, beta cell dysfunction and diabetes development to evaluate the functional role of P53 selectively in beta cells. We further analyzed the effect of P53 ablation on beta cell survival in isolated pancreatic islets exposed to diabetogenic stress inducers ex vivo by flow cytometry.

RESULTS

Beta cell specific ablation of P53/Trp53 failed to ameliorate glucose tolerance, insulin secretion or to increase beta cell numbers in genetic, dietary and pharmacological models of diabetes. Additionally, loss of P53 in beta cells did not protect against streptozotocin (STZ) induced hyperglycemia and beta cell death, although STZ-induced activation of classical pro-apoptotic P53 target genes was significantly reduced in P53^BKO mice. In contrast, Olaparib mediated PARP1 inhibition protected against acute ex vivo STZ-induced beta cell death and islet destruction.

CONCLUSIONS

Our study reveals that ablation of P53 specifically in beta cells is unexpectedly unable to attenuate beta cell failure and death in vivo and ex vivo. While during development and progression of diabetes, P53 and P53-regulated pathways are activated, our study suggests that P53 signaling is not essential for loss of beta cells or beta cell dysfunction. P53 in other cell types and organs may predominantly regulate systemic glucose homeostasis.

Liraglutide protects β-cells in novel human islet spheroid models of type 1 diabetes

To enable accurate, high-throughput and longer-term studies of the immunopathogenesis of type 1 diabetes (T1D), we established three in-vitro islet-immune injury models by culturing spheroids derived from primary human islets with proinflammatory cytokines, activated peripheral blood mononuclear cells or HLA-A2-restricted preproinsulin-specific cytotoxic T lymphocytes. In all models, β-cell function declined as manifested by increased basal and decreased glucose-stimulated insulin release (GSIS), and decreased intracellular insulin content. Additional hallmarks of T1D progression such as loss of the first-phase insulin response (FFIR), increased proinsulin-to-insulin ratios, HLA-class I expression, and inflammatory cytokine release were also observed. Using these models, we show that liraglutide, a glucagon-like peptide 1 receptor agonist, prevented loss of GSIS under T1D-relevant stress, by preserving the FFIR and decreasing immune cell infiltration and cytokine secretion. Our results corroborate that liraglutide mediates an anti-inflammatory effect that aids in protecting β-cells from the immune-mediated attack that leads to T1D.

Histamine H3 receptor antagonists - Roles in neurological and endocrine diseases and diabetes mellitus

Human histamine H3 receptor (H3R) was initially described in the brain of rat in 1983 and cloned in 1999. It can be found in the human brain and functions as a regulator of histamine synthesis and release. H3 receptors are predominantly resident in the presynaptic region of neurons containing histamine, where they modulate the synthesis and release of histamine (autoreceptor) or other neurotransmitters such as dopamine, norepinephrine, gamma-aminobutyric acid (GABA), glutamate, acetylcholine and serotonin (all heteroreceptors). The human histamine H3 receptor has twenty isoforms of which eight are functional. H3 receptor expression is seen in the cerebral cortex, neurons of the basal ganglia and hippocampus, which are important for process of cognition, sleep and homoeostatic regulation. In addition, histamine H3R antagonists stimulate insulin release, through inducing the release of acetylcholine and cause significant reduction in total body weight and triglycerides in obese subjects by causing a feeling of satiety in the hypothalamus. The ability of histamine H3R antagonist to reduce diabetes-induced hyperglycaemia is comparable to that of metformin. It is reasonable therefore, to claim that H3 receptor antagonists may play an important role in the therapy of disorders of cognition, the ability to sleep, oxidative stress, inflammation and anomaly of glucose homoeostasis. A large number of H3R antagonists are being developed by pharmaceutical companies and university research centres. As examples of these new drugs, this review will discuss a number of drugs, including the first histamine H3R receptor antagonist produced.

Spatial and transcriptional heterogeneity of pancreatic beta cell neogenesis revealed by a time-resolved reporter system

AIMS/HYPOTHESIS

While pancreatic beta cells have been shown to originate from endocrine progenitors in ductal regions, it remains unclear precisely where beta cells emerge from and which transcripts define newborn beta cells. We therefore investigated characteristics of newborn beta cells extracted by a time-resolved reporter system.

METHODS

We established a mouse model, 'Ins1-GFP; Timer', which provides spatial information during beta cell neogenesis with high temporal resolution. Single-cell RNA-sequencing (scRNA-seq) was performed on mouse beta cells sorted by fluorescent reporter to uncover transcriptomic profiles of newborn beta cells. scRNA-seq of human embryonic stem cell (hESC)-derived beta-like cells was also performed to compare newborn beta cell features between mouse and human.

RESULTS

Fluorescence imaging of Ins1-GFP; Timer mouse pancreas successfully dissected newly generated beta cells as green fluorescence-dominant cells. This reporter system revealed that, as expected, some newborn beta cells arise close to the ducts (β^duct); unexpectedly, the others arise away from the ducts and adjacent to blood vessels (β^vessel). Single-cell transcriptomic analyses demonstrated five distinct populations among newborn beta cells, confirming spatial heterogeneity of beta cell neogenesis such as high probability of glucagon-positive β^duct, musculoaponeurotic fibrosarcoma oncogene family B (MafB)-positive β^duct and musculoaponeurotic fibrosarcoma oncogene family A (MafA)-positive β^vessel cells. Comparative analysis with scRNA-seq data of mouse newborn beta cells and hESC-derived beta-like cells uncovered transcriptional similarity between mouse and human beta cell neogenesis including microsomal glutathione S-transferase 1 (MGST1)- and synaptotagmin 13 (SYT13)-highly-expressing state.

CONCLUSIONS/INTERPRETATION

The combination of time-resolved histological imaging with single-cell transcriptional mapping demonstrated novel features of spatial and transcriptional heterogeneity in beta cell neogenesis, which will lead to a better understanding of beta cell differentiation for future cell therapy.

DATA AVAILABILITY

Raw and processed single-cell RNA-sequencing data for this study has been deposited in the Gene Expression Omnibus under accession number GSE155742.

The pro-radical hydrogen peroxide as a stable hydroxyl radical distributor: lessons from pancreatic beta cells

The toxic potential of H₂O₂ is limited, even if intracellular concentrations of H₂O₂ under conditions of oxidative stress increase to the micromolar concentration range. Its toxicity is mostly restricted to the oxidation of highly reactive thiol groups, some of which are functionally very important. Subsequently, the HO^· radical is generated spontaneously from H₂O₂ in the Fenton reaction. The HO^· radical is extremely toxic and destroys any biological structure. Due to the high reactivity, its action is limited to a locally restricted site of its generation. On the other hand, H₂O₂ with its stability and long half-life can reach virtually any site and distribute its toxic effect all over the cell. Thereby HO^·, in spite of its ultra-short half-life (10^-9 s), can execute its extraordinary toxic action at any target of the cell. In this oxidative stress scenario, H₂O₂ is the pro-radical, that spreads the toxic action of the HO^· radical. It is the longevity of the H₂O₂ molecule allowing it to distribute its toxic action from the site of origin all over the cell and may even mediate intercellular communication. Thus, H₂O₂ acts as a spreader by transporting it to sites where the extremely short-lived toxic HO^· radical can arise in the presence of "free iron". H₂O₂ and HO^· act in concert due to their different complementary chemical properties. They are dependent upon each other while executing the toxic effects in oxidative stress under diabetic metabolic conditions in particular in the highly vulnerable pancreatic beta cell, which in contrast to many other cell types is so badly protected against oxidative stress due to its extremely low H₂O₂ inactivating enzyme capacity.

TUDCA receptors and their role on pancreatic beta cells

Bile acids have received increasing attention over the past years as their multiple alternative roles became clearer. Tauroursodeoxycholic Acid (TUDCA) in specific has generated special interest due to its ability to promote pancreatic survival and function, as well as reduce endoplasmic reticulum stress. However, there are few studies explaining the molecular mechanisms behind TUDCA's beneficial actions on pancreatic beta cells. In this review, we decided to review the literature in order to craft a primer for researchers on what is known about TUDCA's receptors and the molecular pathways involved in this bile acid's function in the endocrine pancreas. We review the studies that focused on G protein-coupled bile acid receptor (TGR5), Sphingosine-1-phosphate receptor 2 (S1PR2) and α5β1 Integrin function in pancreatic cells. Our hope is to provide a basis for future studies to expand upon, especially considering the current lack of studies focusing on the importance of these receptors, either through TUDCA signaling or other signaling molecules.

Impact of moderate exercise on fatty acid oxidation in pancreatic β-cells and skeletal muscle

Fatty acids (FA) play a crucial role in glycaemia regulation in healthy and metabolic disorders conditions through various mechanisms. FA oxidation is one of the processes involved in lipid metabolism and can be modulated by exercise. Nowadays, physical activity is known to be an effective strategy for the prevention and treatment of Type 2 Diabetes. Moreover, its intensity, its duration, the sex-gender, the prandial state, exerkines… are as many parameters that can influence glycaemic control. However, the widely debated question is to determine the best type of exercise for patients with metabolic disorders. In this review, we will discuss the impact of exercise intensity, especially moderate activity, on glycaemic control by focussing on FA oxidation in pancreatic β-cells and skeletal muscle. Finally, thanks to all the recent data, we will determine whether moderate physical activity is a good therapeutic strategy and if FA oxidation represents a target of interest to treat diabetic, obese and insulin-resistant patients.

CARD9 mediates glucose-stimulated insulin secretion in pancreatic beta cells

Caspase recruitment domain containing protein 9 (CARD9) plays key regulatory role(s) in innate and adaptive immune responses. Recent evidence implicates CARD9 in the onset of metabolic diseases including insulin resistance. However, potential contributory roles of CARD9 in glucose-stimulated insulin secretion (GSIS) remain unknown. Herein, we report that CARD9 is expressed in human islets, rat islets, mouse islets and clonal INS-1 832/13 cells. Subcellularly, CARD9 is predominantly cytosolic (~75%) in INS-1 832/13 cells. siRNA-mediated depletion of CARD9 expression significantly (~50%) suppressed GSIS in INS-1 832/13 cells. Interestingly, glucose-induced activation of Rac1, a small G-protein, which is a requisite for GSIS to occur, is unaffected in CARD9-si transfected cells, suggesting that CARD9-mediates GSIS in a Rac1-independent fashion. Furthermore, insulin secretion promoted by KCl or mastoparan (a global G protein activator), remained resistant to CARD9 depletion in INS-1 832/13 cells. In addition, pharmacological inhibition (BRD5529) of interaction between CARD9 and TRIM62, its ubiquitin ligase, exerted no significant effects on GSIS. Lastly, depletion of CARD9 prevented glucose-induced p38, not ERK1/2 phosphorylation in beta cells. Based on these observations, we propose that CARD9 might regulate GSIS via a Rac1-independent and p38-dependent signaling module.

Pancreatic steatosis in adult rats induced by nicotine exposure during breastfeeding

PURPOSE

Maternal nicotine exposure negatively impacts offspring's health and metabolism, leading to obesity and insulin resistance. Here we investigated the pancreatic islet function, glycemic homeostasis, and insulin signaling in adult rat offspring that were nicotine-exposed during breastfeeding.

METHODS

For this, lactating Wistar rat dams were divided into two groups: Nicotine (implanted with osmotic minipumps containing 6 mg/Kg, NIC) and Control (saline, CON). Solutions were released from postnatal (PN) day 2-16. At PN110 and PN170, 10 offspring per litter/sex/group were submitted to the oral glucose tolerance test (OGTT). PN180 offspring were killed and glycemia, insulinemia, adiponectinemia, pancreas morphology as well as pancreatic islet protein expression (related to insulin secretion) and skeletal muscle (related to insulin action) were evaluated. Males and females were compared to their respective controls.

RESULTS

Adult NIC offspring of both sexes showed glucose intolerance in the OGTT. Despite normoglycemia, NIC males showed hyperinsulinemia while females, although normoinsulinemic, had hyperglycemia. Both sexes showed increased IRI, reduced adiponectin/visceral fat mass ratio and higher ectopic deposition of lipids in the pancreatic tissue adipocytes. In pancreatic islets, NIC males showed lower PDX-1 expression while females had higher PDX-1 and GLUT2 expressions plus lower α2 adrenergic receptor. In the muscle, NIC offspring of both sexes showed reduction of GLUT4 expression; NIC males also had lower insulin receptor and pAKT expressions.

CONCLUSIONS

Thus, glycemic homeostasis and peripheral insulin signaling in adult offspring of both sexes are affected by nicotine exposure through the milk, increasing the risk for type 2 diabetes development.

Low serum trypsinogen levels in chronic pancreatitis: Correlation with parenchymal loss, exocrine pancreatic insufficiency, and diabetes but not CT-based cambridge severity scores for fibrosis

BACKGROUND

Chronic pancreatitis (CP) is a complex inflammatory disorder of the pancreas affecting acinar cells, duct cells, islet cells and inflammatory cells including fibrosis-producing stellate cells. Serum trypsinogen is a biomarkers of acinar cell function.

AIM

To define the degree of correlation between low trypsinogen levels as a marker of acinar cell function and variable features of CP.

METHODS

Serum samples from previously ascertained and well phenotyped case and control subjects from the North American Pancreatitis Study II (NAPS2) were used to measure serum trypsinogen levels in a commercial laboratory. Control samples were used to define normal ranges and compared with levels in CP patients with defined features.

RESULTS

A final cohort of 279 CP patients and 262 controls from the NAPS2 studies were evaluated. In controls trypsinogen had a mean of 34.96 ng/ml and SD = 11.99. Cut-off values for low trypsinogen ranged from <20 to 10 ng/ml and very low trypsinogen at <10 ng/ml. Compared to controls, CP was associated with very low trypsinogen levels (p < 0.0001). Within CP, very low trypsinogen levels correlated with parenchymal loss (pancreatic surgery [p < 0.05]; atrophy with calcifications, [p < 0.001]), EPI (p < 0.01, trend p < 0.001) and diabetes (trend p < 0.01) but not CT-based criteria for fibrosis (pancreatic duct dilation, irregularity, strictures).

CONCLUSIONS

Very low serum trypsinogen levels correlate with measures of acinar cell loss including surgical resection, atrophic-calcific CP, diabetes and functional symptoms EPI but not duct morphology criteria. Serum trypsinogen levels correlate with decreased acinar cell function and therefore have biomarker utility clinical management.

Targeted pancreatic beta cell imaging for early diagnosis

Pancreatic beta cells are important in blood glucose level regulation. As type 1 and 2 diabetes are getting prevalent worldwide, we need to explore new methods for early detection of beta cell-related afflictions. Using bioimaging techniques to measure beta cell mass is crucial because a decrease in beta cell density is seen in diseases such as diabetes and thus can be a new way of diagnosis for such diseases. We also need to appraise beta cell purity in transplanted islets for type 1 diabetes patients. Sufficient amount of functional beta cells must also be determined before being transplanted to the patients. In this review, indirect imaging of beta cells will be discussed. This includes membrane protein on pancreatic beta cells whereby specific probes are designed for different imaging modalities mainly magnetic resonance imaging, positron emission tomography and fluorescence imaging. Direct imaging of insulin is also explored though probes synthesized for such function are relatively fewer. The path for successful pancreatic beta cell imaging is fraught with challenges like non-specific binding, lack of beta cell-restricted targets, the requirement of probes to cross multiple lipid layers to bind to intracellular insulin. Hence, there is an urgent need to develop new imaging techniques and innovative probing constructs in the entire imaging chain of bioengineering to provide early detection of beta cell-related pathology.

A mitophagic response to iron overload-induced oxidative damage associated with the PINK1/Parkin pathway in pancreatic beta cells

BACKGROUND

Iron overload can result in a disorder in glucose metabolism. However, the underlining mechanism through which iron overload induces beta cell death remains unknown.

METHODS

According to the concentration of ferric ammonium citrate (FAC) and N-acetylcysteine, INS-1 cells were randomly divided into four groups: normal control (FAC 0 μM) group, FAC 80 μM group, FAC 160 μM group, FAC 160μM + NAC group. Cell proliferation was assessed by Cell Counting Kit-8. Reactive oxygen species (ROS) level was further evaluated using flow cytometer with a fluorescent probe. The mitochondrial membrane potential was detected by JC-1 kit, and transmission electron microscopy was used to observe the mitochondrial changes. The related protein expressions were detected by western bolt to evaluate mitophagy status.

RESULTS

It was shown that FAC treatment decreased INS-1 cell viability in vitro, resulted in a decline in mitochondrial membrane potential, increased oxidative stress level and suppressed mitophagy. Furthermore, these effects could be alleviated by the ROS scavenger.

CONCLUSIONS

We proved that increased iron overload primarily increased oxidative stress and further suppressed mitophagy via PTEN-induced putative kinase 1/Parkin pathway, resulting in cytotoxicity in INS-1 cells.

Atf6α impacts cell number by influencing survival, death and proliferation

Background

A growing body of literature suggests the cell–intrinsic activity of Atf6α during ER stress responses has implications for tissue cell number during growth and development, as well as in adult biology and tumorigenesis [1]. This concept is important, linking the cellular processes of secretory protein synthesis and endoplasmic reticulum stress response with functional tissue capacity and organ size. However, the field contains conflicting observations, especially notable in secretory cell types like the pancreatic beta cell.

Scope of review

Here we summarize current knowledge of the basic biology of Atf6α, along with the pleiotropic roles Atf6α plays in cell life and death decisions and possible explanations for conflicting observations. We include studies investigating the roles of Atf6α in cell survival, death and proliferation using well-controlled methodology and specific validated outcome measures, with a focus on endocrine and metabolic tissues when information was available.

Major conclusions

The net outcome of Atf6α on cell survival and cell death depends on cell type and growth conditions, the presence and degree of ER stress, and the duration and intensity of Atf6α activation. It is unquestioned that Atf6α activity influences the cell fate decision between survival and death, although opposite directions of this outcome are reported in different contexts. Atf6α can also trigger cell cycle activity to expand tissue cell number through proliferation. Much work remains to be done to clarify the many gaps in understanding in this important emerging field.

Combination of ferric ammonium citrate with cytokines involved in apoptosis and insulin secretion of human pancreatic beta cells related to diabetes in thalassemia

Background

Diabetes mellitus (DM) is a common complication found in β-thalassemia patients. The mechanism of DM in β-thalassemia patients is still unclear, but it could be from an iron overload and increase of some cytokines, such as interleukin1-β (IL-1β) and tumor necrosis factor-α (TNF-α). The objective of this study was to study the effect of interaction between ferric ammonium citrate (FAC) and cytokines, IL-1β and TNF-α, on 1.1B4 human pancreatic β-cell line.

Methods

The effect of the combination of FAC and cytokines on cell viability was studied by MTT assay. Insulin secretion was assessed by the enzyme-linked immunosorbent assay (ELISA). The reactive oxygen species (ROS) and cell apoptosis in normal and high glucose condition were determined by flow cytometer. In addition, gene expression of apoptosis, antioxidant; glutathione peroxidase 1 (GPX1) and superoxide dismutase 2 (SOD2), and insulin secretory function were studied by real-time polymerase chain reaction (Real-time PCR).

Results

The findings revealed that FAC exposure resulted in the decrease of cell viability and insulin-release, and the induction of ROS and apoptosis in pancreatic cells. Interestingly, a combination of FAC and cytokines had an additive effect on SOD2 antioxidants' genes expression and endoplasmic reticulum (ER) stress. In addition, it reduced the insulin secretion genes expression; insulin (INS), glucose kinase (GCK), protein convertase 1 (PSCK1), and protein convertase 2 (PSCK2). Moreover, the highest ROS and the lowest insulin secretion were found in FAC combined with IL-1β and TNF-α in the high-glucose condition of human pancreatic beta cell, which could be involved in the mechanism of DM development in β-thalassemia patients.

Regulation of lipid metabolism in pancreatic beta cells by interferon gamma: A link to anti-viral function

Interferons (IFN) have been shown to alter lipid metabolism in immune and some non-hematopoietic cells and this affects host cell response to pathogens. In type 1 diabetes, IFNγ acts as a proinflammatory cytokine that, along with other cytokines, is released during pancreatic beta cell autoinflammation and contributes to immune response and beta cell dysfunction. The hypothesis tested herein is that IFN modifies beta cell lipid metabolism and this is associated with enhanced anti-viral response and beta cell stress. Treatment of INS-1 cells with IFNγ for 6 to 24 h led to a dynamic change in TAG and lipid droplet (LD) levels, with a decrease at 6 h and an increase at 24 h. The later accumulation of TAG was associated with increased de novo lipogenesis (DNL), and impaired mitochondrial fatty acid oxidation (FAO). Gene expression results suggested that IFNγ regulates lipolytic, lipogenic, LD and FAO genes in a temporal manner. The changes in lipid gene expression are dependent on the classical Janus kinase (JAK) pathway. Pretreatment with IFNγ robustly enhanced anti-viral gene expression induced by the viral mimetic polyinosinic: polycytidylic acid (PIC), and this potentiating effect of IFNγ was markedly attenuated by inhibitors of DNL. The IFNγ-induced accumulation of lipid, however, was insufficient to cause endoplasmic reticulum (ER) stress. These studies demonstrated a non-canonical effect of IFNγ in regulation of pancreatic beta cell lipid metabolism that is intimately linked with host cell defense and might alter cellular function early in the progression to type 1 diabetes.

Beta cell identity changes with mild hyperglycemia: Implications for function, growth, and vulnerability

OBJECTIVE

As diabetes develops, marked reductions of insulin secretion are associated with very modest elevations of glucose. We wondered if these glucose changes disrupt beta cell differentiation enough to account for the altered function.

METHODS

Rats were subjected to 90% partial pancreatectomies and those with only mild glucose elevations 4 weeks or 10 weeks after surgery had major alterations of gene expression in their islets as determined by RNAseq.

RESULTS

Changes associated with glucose toxicity demonstrated that many of the critical genes responsible for insulin secretion were downregulated while the expression of normally suppressed genes increased. Also, there were marked changes in genes associated with replication, aging, senescence, stress, inflammation, and increased expression of genes controlling both class I and II MHC antigens.

CONCLUSIONS

These findings suggest that mild glucose elevations in the early stages of diabetes lead to phenotypic changes that adversely affect beta cell function, growth, and vulnerability.

SUMOylation, a multifaceted regulatory mechanism in the pancreatic beta cells

SUMOylation is an evolutionarily conserved post-translational modification (PTM) that regulates protein subcellular localization, stability, conformation, transcription and enzymatic activity. Recent studies indicate that SUMOylation plays a key role in insulin gene expression, glucose metabolism and insulin exocytosis under physiological conditions in the pancreatic beta cells. Furthermore, SUMOylation is implicated in beta cell survival and recovery following exposure to oxidative stress, ER stress and inflammatory mediators under pathological situations. SUMOylation is closely regulated by the cellular redox status, and it collaborates with other PTMs such as phosphorylation, ubiquitination, and NEDDylation, to maintain beta cellular homeostasis. We hereby provide an update on recent findings regarding the role of SUMOylation in the regulation of pancreatic beta cell viability and function, and discuss its potential implication in beta cell senescence and RNA processing (e.g., pre-mRNA splicing and mRNA methylation). Through which we intend to provide novel insights into this fundamental biological process regarding both maintenance of beta cell viability and functionality, and beta cell dysfunction in diabetes mellitus.

Use of Streptozotocin in Rodent Models of Islet Transplantation

Streptozotocin (STZ) selectively destroys beta cells and is widely used to induce experimental diabetes in rodents. Rodent beta cells are very sensitive to the toxic effects of STZ, while human beta cells are highly resistant to STZ. Taking advantage of this characteristic, here, we describe two protocols for the induction of STZ-diabetes. In the first model, hyperglycemia is induced prior to islet transplantation, whereas in the second model, STZ is injected after islet transplantation. The former model has many applications and thus is the most commonly used method. However, when implanting human islets into mice, there are clear benefits to administering STZ after the transplantation. It reduces the cost and burden of experiments and the number of human islets needed for transplantation and improves the welfare and survival of animals used in the experiments. In both methods, a key step in the experimental protocol is to remove the graft-bearing kidney at the end of the experiment and monitor onset of hyperglycemia. This can be used to demonstrate that the glycemic control of the animal is due to the engrafted islets and not regeneration of endogenous beta cells. This chapter outlines protocols of administering streptozotocin pre- and post-islet transplantation in mice as well as nephrectomy to remove the graft-bearing kidney.

Effects on pancreatic Beta and other Islet cells of the glucose-dependent insulinotropic polypeptide

Glucose-dependent insulinotropic polypeptide (GIP) is a gut-derived incretin that, in common with glucagon-like peptide-1 (GLP-1), has both insulin releasing and extra-pancreatic glucoregulatory actions. GIP is released in response to glucose or fat absorption and acts on the GIP receptor (GIPR) to potentiate insulin release from pancreatic beta cells. GIP has also been shown to promote beta cell survival and stimulate the release of GLP-1 from islet alpha cells. There is now evidence to suggest that low levels of GIP are secreted from alpha cells and may act in a paracrine manner to prime neighboring beta cells for insulin release. In addition, GIP acts on adipocytes to stimulate fat storage and can exert anorexigenic effects via actions in the hypothalamus. Contrary to GLP-1, the development of effective GIP-based T2D treatments has been hindered by poor bioavailability and attenuation of beta cell responses to GIP in some patients with sub-optimally controlled T2D. Recently, longer-acting GIP agonists that exhibit enzymatic stability, as well as dual GLP-1/GIP agonists which provide simultaneous improvement in glucose and weight control have been generated and successfully tested in animal T2D models. This, together with reports on GIP antagonists that may protect against obesity, has revived the interest on the GIP/GIPR axis as a potential anti-diabetic pathway. In this review, we summarize the known aspects of the effects of GIP on beta and other islet cells and discuss the most recent developments on GIP-based therapeutic agents for the improvement of beta cell function in T2D patients.

Stearoyl CoA desaturase is a gatekeeper that protects human beta cells against lipotoxicity and maintains their identity

AIMS/HYPOTHESIS

During the onset of type 2 diabetes, excessive dietary intake of saturated NEFA and fructose lead to impaired insulin production and secretion by insulin-producing pancreatic beta cells. The majority of data on the deleterious effects of lipids on functional beta cell mass were obtained either in vivo in rodent models or in vitro using rodent islets and beta cell lines. Translating data from rodent to human beta cells remains challenging. Here, we used the human beta cell line EndoC-βH1 and analysed its sensitivity to a lipotoxic and glucolipotoxic (high palmitate with or without high glucose) insult, as a way to model human beta cells in a type 2 diabetes environment.

METHODS

EndoC-βH1 cells were exposed to palmitate after knockdown of genes related to saturated NEFA metabolism. We analysed whether and how palmitate induces apoptosis, stress and inflammation and modulates beta cell identity.

RESULTS

EndoC-βH1 cells were insensitive to the deleterious effects of saturated NEFA (palmitate and stearate) unless stearoyl CoA desaturase (SCD) was silenced. SCD was abundantly expressed in EndoC-βH1 cells, as well as in human islets and human induced pluripotent stem cell-derived beta cells. SCD silencing induced markers of inflammation and endoplasmic reticulum stress and also IAPP mRNA. Treatment with the SCD products oleate or palmitoleate reversed inflammation and endoplasmic reticulum stress. Upon SCD knockdown, palmitate induced expression of dedifferentiation markers such as SOX9, MYC and HES1. Interestingly, SCD knockdown by itself disrupted beta cell identity with a decrease in mature beta cell markers INS, MAFA and SLC30A8 and decreased insulin content and glucose-stimulated insulin secretion.

CONCLUSIONS/INTERPRETATION

The present study delineates an important role for SCD in the protection against lipotoxicity and in the maintenance of human beta cell identity.

DATA AVAILABILITY

Microarray data and all experimental details that support the findings of this study have been deposited in in the GEO database with the GSE130208 accession code.

Death versus dedifferentiation: The molecular bases of beta cell mass reduction in type 2 diabetes

Diabetes Mellitus is currently affecting more than 425 million people worldwide, among which over 90 % of the cases belong to type 2 diabetes. The number is growing quickly every year. Together with its many complications, the disease is causing tremendous social and economic burden and is classified as one of the leading causes of high morbidity and mortality rate. Residing in the islets of Langerhans, pancreatic beta cell serves as a central mediator in glucose homeostasis through secreting insulin, the only hormone that could reduce glucose level in the body, into the blood. Abnormality in pancreatic beta cell is generally considered as the fundamental reason which is responsible for the development of diabetes. Evidence shows that beta cell mass is greatly reduced in the biopsy of type 2 diabetic patients. Since then, large amount of research was conducted in order to decipher the molecular mechanisms behind the phenotype above and enormous progression has been made. The aim of this review is to summarize and provide a rudimentary molecular road map for beta cell mass reduction from the aspects of apoptosis and dedifferentiation based on recent research advances. Hopefully, this review could give the community some enlightenment for the next-step research and, more importantly, could provide avenues for developing novel and effective therapies to restrain or reverse beta cell loss in type 2 diabetes in the clinic.

Zinc deficiency alters the susceptibility of pancreatic beta cells (INS-1) to arsenic exposure

Pancreatic beta cells produce and release insulin, a hormone that regulates blood glucose levels, and their dysfunction contributes to the development of diabetes mellitus. Zinc deficiency and inorganic arsenic exposure both independently associate with the development of diabetes, although the effects of their combination on pancreatic beta cell health and function remain unknown. We hypothesized zinc deficiency increases the toxicity associated with arsenic exposure, causing an increased susceptibility to DNA damage and disruption of insulin production. Zinc deficiency decreased cell proliferation by 30% in pancreatic INS-1 rat insulinoma cells. Arsenic exposure (0, 50 or 500 ppb exposures) significantly decreased cell proliferation, and increased mRNA levels of genes involved in stress response (Mt1, Mt2, Hmox1) and DNA damage (p53, Ogg1). When co-exposed to both zinc deficiency and arsenic, zinc deficiency attenuated this response to arsenic, decreasing the expression of Mt1, Hmox1, and Ogg1, and significantly increasing DNA double-strand breaks 2.9-fold. Arsenic exposure decreased insulin expression, but co-exposure did not decrease insulin levels beyond the arsenic alone condition, but did result in a further 33% decline in cell proliferation at the 500 ppb arsenic dose, and a significant increase in beta cell apoptosis. These results suggest zinc deficiency and arsenic, both independently and in combination, adversely affect pancreatic beta cell health and both factors should be considered in the evaluation of health outcomes for susceptible populations.

Metabolic signatures suggest o-phosphocholine to UDP-N-acetylglucosamine ratio as a potential biomarker for high-glucose and/or palmitate exposure in pancreatic β-cells

INTRODUCTION

Chronic exposure to high-glucose and free fatty acids (FFA) alone/or in combination; and the resulting gluco-, lipo- and glucolipo-toxic conditions, respectively, have been known to induce dysfunction and apoptosis of β-cells in Diabetes. The molecular mechanisms and the development of biomarkers that can be used to predict similarities and differences behind these conditions would help in easier and earlier diagnosis of Diabetes.

OBJECTIVES

This study aims to use metabolomics to gain insight into the mechanisms by which β-cells respond to excess-nutrient stress and identify associated biomarkers.

METHODS

INS-1E cells were cultured in high-glucose, palmitate alone/or in combination for 24 h to mimic gluco-, lipo- and glucolipo-toxic conditions, respectively. Biochemical and cellular experiments were performed to confirm the establishment of these conditions. To gain molecular insights, abundant metabolites were identified and quantified using ¹H-NMR.

RESULTS

No loss of cellular viability was observed in high-glucose while exposure to FFA alone/in combination with high-glucose was associated with increased ROS levels, membrane damage, lipid accumulation, and DNA double-strand breaks. Forty-nine abundant metabolites were identified and quantified using ¹H-NMR. Chemometric pair-wise analysis in glucotoxic and lipotoxic conditions, when compared with glucolipotoxic conditions, revealed partial overlap in the dysregulated metabolites; however, the dysregulation was more significant under glucolipotoxic conditions.

CONCLUSION

The current study compared gluco-, lipo- and glucolipotoxic conditions in parallel and elucidated differences in metabolic pathways that play major roles in Diabetes. o-phosphocholine and UDP-N-acetylglucosamine were identified as common dysregulated metabolites and their ratio was proposed as a potential biomarker for these conditions.

DEXI, a candidate gene for type 1 diabetes, modulates rat and human pancreatic beta cell inflammation via regulation of the type I IFN/STAT signalling pathway

AIMS/HYPOTHESIS

The initial stages of type 1 diabetes are characterised by an aberrant islet inflammation that is in part regulated by the interaction between type 1 diabetes susceptibility genes and environmental factors. Chromosome 16p13 is associated with type 1 diabetes and CLEC16A is thought to be the aetiological gene in the region. Recent gene expression analysis has, however, indicated that SNPs in CLEC16A modulate the expression of a neighbouring gene with unknown function named DEXI, encoding dexamethasone-induced protein (DEXI). We therefore evaluated the role of DEXI in beta cell responses to 'danger signals' and determined the mechanisms involved.

METHODS

Functional studies based on silencing or overexpression of DEXI were performed in rat and human pancreatic beta cells. Beta cell inflammation and apoptosis, driven by a synthetic viral double-stranded RNA, were evaluated by real-time PCR, western blotting and luciferase assays.

RESULTS

DEXI-silenced beta cells exposed to a synthetic double-stranded RNA (polyinosinic:polycytidylic acid [PIC], a by-product of viral replication) showed reduced activation of signal transducer and activator of transcription (STAT) 1 and lower production of proinflammatory chemokines that was preceded by a reduction in IFNβ levels. Exposure to PIC increased chromatin-bound DEXI and IFNβ promoter activity. This effect on IFNβ promoter was inhibited in DEXI-silenced beta cells, suggesting that DEXI is implicated in the regulation of IFNβ transcription. In a mirror image of knockdown experiments, DEXI overexpression led to increased levels of STAT1 and proinflammatory chemokines.

CONCLUSIONS/INTERPRETATION

These observations support DEXI as the aetiological gene in the type 1 diabetes-associated 16p13 genomic region, and provide the first indication of a link between this candidate gene and the regulation of local antiviral immune responses in beta cells. Moreover, our results provide initial information on the function of DEXI.

Acute pancreatic beta cell apoptosis by IL-1β is responsible for postburn hyperglycemia: Evidence from humans and mice

BACKGROUND

Acute hyperglycemia is regarded as a risk factor for critically ill patients; however, insufficient understanding of its nature and underlying mechanisms hinders widespread adoption of glycemic control in critical care units.

METHODS

A single center, prospective cohort study recruiting 107 burn patients and 62 controls was conducted to characterize the early phase of acute hyperglycemia in burn patients. A total of 1643 blood samples were collected and analyzed over the entire postburn 200 h. A mouse severe burn model was used to study the underlying mechanisms of acute hyperglycemia postburn.

RESULTS

The dynamic change of postburn blood glucose represented a distinctive pattern in amplitude and duration that was in parallel with the degree of burn injury. Multiple linear regressions revealed that serum insulin, glucagon and glucocorticoid were the major factors affecting blood glucose postburn. Particularly, extensive burns impaired capacity and responsiveness of pancreatic insulin secretion, which was associated with increased serum IL-1β in burn patients. Mechanistically, acute IL-1β elevation specifically induced pancreatic beta cell apoptosis and dampened capacity of insulin secretion, leading to postburn hyperglycemia in burned mice. More importantly, inhibition of IL-1β not only alleviated pancreatic beta cell apoptosis, but also attenuated hyperglycemia and improved survival of burned mice.

CONCLUSIONS

Our findings reveal a novel mechanism of acute hyperglycemia postburn in which impaired insulin secretory capacity mediated by IL-1β leads to acute hyperglycemia. These data suggest that targeting IL-1β to restore endogenous insulin secretory function may be a novel glycemic control strategy to improve outcomes for burn patients.

Activation of GLP-1 receptor signalling alleviates cellular stresses and improves beta cell function in a mouse model of Wolfram syndrome

AIMS/HYPOTHESIS

Loss of functional beta cells results in a gradual progression of insulin insufficiency in Wolfram syndrome caused by recessive WFS1 mutations. However, beta cell dysfunction in Wolfram syndrome has yet to be fully characterised, and there are also no specific treatment recommendations. In this study, we aimed to characterise beta cell secretory defects and to examine the potential effects of a glucagon-like peptide-1 (GLP-1) receptor agonist on diabetes in Wolfram syndrome.

METHODS

Insulin secretory function was assessed by the pancreatic perfusion method in mice used as a model of Wolfram syndrome. In addition, granule dynamics in living beta cells were examined using total internal reflection fluorescence microscopy. Acute and chronic effects of exendin-4 (Ex-4) on glucose tolerance and insulin secretion were examined in young Wfs1^-/- mice without hyperglycaemia. Molecular events associated with Ex-4 treatment were investigated using pancreatic sections and isolated islets. In addition, we retrospectively observed a woman with Wolfram syndrome who had been treated with liraglutide for 24 weeks.

RESULTS

Treatment with liraglutide ameliorated our patient's glycaemic control and resulted in a 20% reduction of daily insulin dose along with an off-drug elevation of fasting C-peptide immunoreactivity. Glucose-stimulated first-phase insulin secretion and potassium-stimulated insulin secretion decreased by 53% and 59%, respectively, in perfused pancreases of 10-week-old Wfs1^-/- mice compared with wild-type (WT) mice. The number of insulin granule fusion events in the first phase decreased by 41% in Wfs1^-/- beta cells compared with WT beta cells. Perfusion with Ex-4 increased insulin release in the first and second phases by 3.9-fold and 5.6-fold, respectively, in Wfs1^-/- mice compared with perfusion with saline as a control. The physiological relevance of the effects of Ex-4 was shown by the fact that a single administration potentiated glucose-stimulated insulin secretion and improved glucose tolerance in Wfs1^-/- mice. Four weeks of administration of Ex-4 resulted in an off-drug amelioration of glucose excursions after glucose loading in Wfs1^-/- mice, with insulin secretory dynamics that were indistinguishable from those in WT mice, despite the fact that there was no alteration in beta cell mass. In association with the functional improvements, Ex-4 treatment reversed the increases in phosphorylated eukaryotic initiation factor (EIF2α) and thioredoxin interacting protein (TXNIP), and the decrease in phosphorylated AMP-activated kinase (AMPK), in the beta cells of the Wfs1^-/- mice. Furthermore, Ex-4 treatment modulated the transcription of oxidative and endoplasmic reticulum stress-related markers in isolated islets, implying that it was able to mitigate the cellular stresses resulting from Wfs1 deficiency.

CONCLUSIONS/INTERPRETATION

Our study provides deeper insights into the pathophysiology of beta cell dysfunction caused by WFS1 deficiency and implies that activation of the GLP-1 receptor signal may alleviate insulin insufficiency and aid glycaemic control in Wolfram syndrome.

Vegf-A mRNA transfection as a novel approach to improve mouse and human islet graft revascularisation

AIMS/HYPOTHESIS

The initial avascular period following islet transplantation seriously compromises graft function and survival. Enhancing graft revascularisation to improve engraftment has been attempted through virus-based delivery of angiogenic triggers, but risks associated with viral vectors have hampered clinical translation. In vitro transcribed mRNA transfection circumvents these risks and may be used for improving islet engraftment.

METHODS

Mouse and human pancreatic islet cells were transfected with mRNA encoding the angiogenic growth factor vascular endothelial growth factor A (VEGF-A) before transplantation under the kidney capsule in mice.

RESULTS

At day 7 post transplantation, revascularisation of grafts transfected with Vegf-A (also known as Vegfa) mRNA was significantly higher compared with non-transfected or Gfp mRNA-transfected controls in mouse islet grafts (2.11- and 1.87-fold, respectively) (vessel area/graft area, mean ± SEM: 0.118 ± 0.01 [n = 3] in Vegf-A mRNA transfected group (VEGF) vs 0.056 ± 0.01 [n = 3] in no RNA [p < 0.05] vs 0.063 ± 0.02 [n = 4] in Gfp mRNA transfected group (GFP) [p < 0.05]); EndoC-bH3 grafts (2.85- and 2.48-fold. respectively) (0.085 ± 0.02 [n = 4] in VEGF vs 0.030 ± 0.004 [n = 4] in no RNA [p < 0.05] vs 0.034 ± 0.01 [n = 5] in GFP [p < 0.05]); and human islet grafts (3.17- and 3.80-fold, respectively) (0.048 ± 0.013 [n = 3] in VEGF vs 0.015 ± 0.0051 [n = 4] in no RNA [p < 0.01] vs 0.013 ± 0.0046 [n = 4] in GFP [p < 0.01]). At day 30 post transplantation, human islet grafts maintained a vascularisation benefit (1.70- and 1.82-fold, respectively) (0.049 ± 0.0042 [n = 8] in VEGF vs 0.029 ± 0.0052 [n = 5] in no RNA [p < 0.05] vs 0.027 ± 0.0056 [n = 4] in GFP [p < 0.05]) and a higher beta cell volume (1.64- and 2.26-fold, respectively) (0.0292 ± 0.0032 μl [n = 7] in VEGF vs 0.0178 ± 0.0021 μl [n = 5] in no RNA [p < 0.01] vs 0.0129 ± 0.0012 μl [n = 4] in GFP [p < 0.001]).

CONCLUSIONS/INTERPRETATION

Vegf-A mRNA transfection before transplantation provides a promising and safe strategy to improve engraftment of islets and other cell-based implants.

Circadian dysrhythmia-linked diabetes mellitus: Examining melatonin’s roles in prophylaxis and management

Diabetes mellitus is a chronic, life-threatening metabolic disorder that occurs worldwide. Despite an increase in the knowledge of the risk factors that are associated with diabetes mellitus, its worldwide prevalence has continued to rise; thus, necessitating more research into its aetiology. Recent researches are beginning to link a dysregulation of the circadian rhythm to impairment of intermediary metabolism; with evidences that circadian rhythm dysfunction might play an important role in the aetiology, course or prognosis of some cases of diabetes mellitus. These evidences thereby suggest possible relationships between the circadian rhythm regulator melatonin, and diabetes mellitus. In this review, we discuss the roles of the circadian rhythm in the regulation of the metabolism of carbohydrates and other macronutrients; with emphasis on the importance of melatonin and the impacts of its deficiency on carbohydrate homeostasis. Also, the possibility of using melatonin and its analogs for the “prophylaxis” or management of diabetes mellitus is also considered.

Deactivation of the NLRP3 inflammasome in infiltrating macrophages by duodenal-jejunal bypass surgery mediates improvement of beta cell function in type 2 diabetes

OBJECTIVE

Bariatric surgery could improve pancreatic beta cell function, thereby leading to the remission of the type 2 diabetes mellitus (T2DM). However, the specific mechanism underlying this phenomenon is yet to be revealed. The aim of this study is to test the hypothesis that Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome in infiltrating macrophages plays an important role in the modulation of beta cell function after duodenal-jejunal bypass (DJB) surgery.

METHODS

DJB and sham surgery were performed in diabetic Sprague-Dawley (SD) rats induced by high-fat diet (HFD) and streptozotocin (STZ). Body weight, food intake, and glucose tolerance test (GTT) were measured at indicated time points. Apoptosis of the beta cells was measured by Terminal deoxynucleotidyl transferase mediated dUTP Nick End Labeling (TUNEL) assay. We also assessed the macrophage content and NLRP3 expression in the rat model. Furthermore, macrophage reconstitution was performed after DJB surgery. Beta cell function and NLRP3 inflammasome pathway were re-evaluated in wild-type macrophage reconstitution group and NLRP3-knockdown macrophage reconstitution group.

RESULTS

DJB surgery group rats displayed rapid and sustained improvement in glucose tolerance. Decreased apoptosis and improved secretion function of the beta cells were observed in DJB surgery group. NLRP3 inflammasome pathway in infiltrating macrophages was also suppressed after DJB surgery. Moreover, diabetic remission acquired by DJB sustained in NLRP3-knockdown macrophage reconstitution group, while extinguished in group reconstituted with wild-type macrophage.

CONCLUSIONS

NLRP3 inflammasome deactivation in infiltrating macrophages is involved in marked beta cell function improvement after DJB surgery.

Both conditional ablation and overexpression of E2 SUMO-conjugating enzyme (UBC9) in mouse pancreatic beta cells result in impaired beta cell function

AIMS/HYPOTHESIS

Post-translational attachment of a small ubiquitin-like modifier (SUMO) to the lysine (K) residue(s) of target proteins (SUMOylation) is an evolutionary conserved regulatory mechanism. This modification has previously been demonstrated to be implicated in the control of a remarkably versatile regulatory mechanism of cellular processes. However, the exact regulatory role and biological actions of the E2 SUMO-conjugating enzyme (UBC9)-mediated SUMOylation function in pancreatic beta cells has remained elusive.

METHODS

Inducible beta cell-specific Ubc9 (also known as Ube2i) knockout (KO; Ubc9^Δbeta) and transgenic (Ubc9^Tg) mice were employed to address the impact of SUMOylation on beta cell viability and functionality. Ubc9 deficiency or overexpression was induced at 8 weeks of age using tamoxifen. To study the mechanism involved, we closely examined the regulation of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) through SUMOylation in beta cells.

RESULTS

Upon induction of Ubc9 deficiency, Ubc9^Δbeta islets exhibited a 3.5-fold higher accumulation of reactive oxygen species (ROS) than Ubc9^f/f control islets. Islets from Ubc9^Δbeta mice also had decreased insulin content and loss of beta cell mass after tamoxifen treatment. Specifically, at day 45 after Ubc9 deletion only 40% of beta cell mass remained in Ubc9^Δbeta mice, while 90% of beta cell mass was lost by day 75. Diabetes onset was noted in some Ubc9^Δbeta mice 8 weeks after induction of Ubc9 deficiency and all mice developed diabetes by 10 weeks following tamoxifen treatment. In contrast, Ubc9^Tg beta cells displayed an increased antioxidant ability but impaired insulin secretion. Unlike Ubc9^Δbeta mice, which spontaneously developed diabetes, Ubc9^Tg mice preserved normal non-fasting blood glucose levels without developing diabetes. It was noted that SUMOylation of NRF2 promoted its nuclear expression along with enhanced transcriptional activity, thereby preventing ROS accumulation in beta cells.

CONCLUSIONS/INTERPRETATION

SUMOylation function is required to protect against oxidative stress in beta cells; this mechanism is, at least in part, carried out by the regulation of NRF2 activity to enhance ROS detoxification. Homeostatic SUMOylation is also likely to be essential for maintaining beta cell functionality.

Inositol hexakisphosphate kinase 1 is a metabolic sensor in pancreatic β-cells

Diphosphoinositol pentakisphosphate (IP₇) is critical for the exocytotic capacity of the pancreatic β-cell, but its regulation by the primary instigator of β-cell exocytosis, glucose, is unknown. The high K_m for ATP of the IP₇-generating enzymes, the inositol hexakisphosphate kinases (IP6K1 and 2) suggests that these enzymes might serve as metabolic sensors in insulin secreting β-cells and act as translators of disrupted metabolism in diabetes. We investigated this hypothesis and now show that glucose stimulation, which increases the ATP/ADP ratio, leads to an early rise in IP₇ concentration in β-cells. RNAi mediated knock down of the IP6K1 isoform inhibits both glucose-mediated increase in IP₇ and first phase insulin secretion, demonstrating that IP6K1 integrates glucose metabolism and insulin exocytosis. In diabetic mouse islets the deranged ATP/ADP levels under both basal and glucose-stimulated conditions are mirrored in both disrupted IP₇ generation and insulin release. Thus the unique metabolic sensing properties of IP6K1 guarantees appropriate concentrations of IP₇ and thereby both correct basal insulin secretion and intact first phase insulin release. In addition, our data suggest that a specific cell signaling defect, namely, inappropriate IP₇ generation may be an essential convergence point integrating multiple metabolic defects into the commonly observed phenotype in diabetes.

•

Glucose increases IP7 levels transiently through IP6K1 in pancreatic β-cells.

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IP6K1 decodes glucose-driven increases in ATP/ADP ratio into 1st phase insulin release.

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IP7 production and insulin release mirror perturbed metabolism in diabetic islets.

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IP6K1 acts as a β-cell metabolic sensor under normal and pathological conditions.

Urtica Dioica Distillate Regenerates Pancreatic Beta Cells in Streptozotocin-Induced Diabetic Rats

BACKGROUND

Urtica dioica is known as an anti-hyperglycemic plant. Urtica dioica distillate (UD) is a traditional Iranian drink, locally known as "aragh gazaneh". In spite of its widespread consumption in Iran, according to traditional Iranian medicine, there is no scientific report on the usefulness of UD for diabetic patients. This survey was designed to evaluate its protective effects for the recovery from diabetes by determining the serum insulin, blood glucose, volume of pancreatic islets, and the number and volume of β-cells in diabetic rats.

METHODS

A total of 48 Sprague-Dawley male rats (200-250 g) were randomly distributed into 6 groups (n=8), including non-diabetic plus distilled water (DW), non-diabetic plus UD, diabetic plus DW, diabetic plus UD, diabetic plus insulin, and diabetic plus glibenclamide. DW, UD, and glibenclamide were administered via intragastric gavage and insulin was injected subcutaneously. After four weeks of experiments, blood samples were collected for serum insulin and blood glucose assay. Pancreas was also evaluated using stereological method. The SPSS software was used for statistical analysis. Kruskal-Wallis, repeated measurements, and Mann-Whitney U test were applied for comparisons between the groups.

RESULTS

The treatment of diabetic rats with UD reduced the blood glucose dramatically (P<0.001) and increased serum insulin levels significantly (P=0.03) in comparison to the diabetic plus DW rats. Treatment with UD did not affect the mean β-cell volumes in the diabetic rats when compared to the diabetic plus DW rats, but the islet volumes and β-cell numbers were significantly recovered.

CONCLUSION

UD treatment in diabetic rats improves hyperglycemia by partially restoring plasma insulin levels. The data suggest that UD prevents islet atrophy and/or regenerate pancreatic β-cells.

Rat Pancreatic Beta-Cell Culture

In this chapter, we describe the methods used to culture mainly rat pancreatic beta cells. We consider necessary to use this approach to get more information about physiological, biophysical, and molecular biology characteristics of primary beta cells. Most of the literature published has been developed in murine and human beta-cell lines. However, there are many differences between tumoral cell lines and native cells because, in contrast to cell lines, primary cells do not divide. Moreover, cell lines can be in various stages of the cell cycle and thus have a different sensitivity to glucose, compared to primary cells. Finally, for these reasons, cell lines can be heterogeneous, as the primary cells are. The main problem in using primary beta cells is that despite that they are a majority within a culture they appear mixed with other kinds of pancreatic islet cells. If one needs to identify single cells or has an only beta-cell composition, it is necessary to process the sample further. For example, one may obtain an enriched population of beta cells using fluorescence-activated cell sorting or identify single cells with the reverse hemolytic plaque assay. The other problem is that cells change with time in culture, becoming old and losing some characteristics, and so must be used preferentially during the first week. The development of human beta-cell cultures is of importance in medicine because we hope one day to be able to transplant viable beta cells to patients with diabetes mellitus type 1.

Disentangling the Role of Melatonin and its Receptor MTNR1B in Type 2 Diabetes: Still a Long Way to Go?

PURPOSE OF REVIEW

Type 2 diabetes (T2D) is a complex genetic metabolic disorder. T2D heritability has been estimated around 40-70%. In the last decade, exponential progress has been made in identifying T2D genetic determinants, through genome-wide association studies (GWAS). Among single-nucleotide polymorphisms mostly associated with T2D risk, rs10830963 is located in the MTNR1B gene, encoding one of the two receptors of melatonin, a neurohormone involved in circadian rhythms. Subsequent studies aiming to disentangle the role of MTNR1B in T2D pathophysiology led to controversies. In this review, we will tackle them and will try to give some directions to get a better view of MTNR1B contribution to T2D pathophysiology.

RECENT FINDINGS

Recent studies either based on genetic/genomic analyses, clinical/epidemiology data, functional analyses at rs10830963 locus, insulin secretion assays in response to melatonin (involving or not MTNR1B) or animal model analyses have led to strong controversies at each level of interpretation. We discuss possible caveats in these studies and present ways to go beyond these issues, towards a better understanding of T2D molecular mechanisms, keeping in mind that melatonin is a versatile hormone and regulates many functions via its primary role in the body clock.

Confluence does not affect the expression of miR-375 and its direct targets in rat and human insulin-secreting cell lines

MicroRNAs are small non-coding RNAs, which negatively regulate the expression of target genes. They have emerged as important modulators in beta cell compensation upon increased metabolic demand, failure of which leads to reduced insulin secretion and type 2 diabetes. To elucidate the function of miRNAs in beta cells, insulin-secreting cell lines, such as the rat insulinoma INS-1 832/13 and the human EndoC-βH1, are widely used. Previous studies in the cancer field have suggested that miRNA expression is influenced by confluency of adherent cells. We therefore aimed to investigate whether one of the most enriched miRNAs in the pancreatic endocrine cells, miR-375, and two of its validated targets in mouse, Cav1 and Aifm1, were differentially-expressed in cell cultures with different confluences. Additionally, we measured the expression of other miRNAs, such as miR-152, miR-130a, miR-132, miR-212 and miR-200a, with known roles in beta cell function. We did not see any significant expression changes of miR-375 nor any of the two targets, in both the rat and human beta cell lines at different confluences. Interestingly, among the other miRNAs measured, the expression of miR-132 and miR-212 positively correlated with confluence, but only in the INS-1 832/13 cells. Our results show that the expression of miR-375 and other miRNAs with known roles in beta cell function is independent of, or at least minimally influenced by the density of proliferating adherent cells, especially within the confluence range optimal for functional assays to elucidate miRNA-dependent regulatory mechanisms in the beta cell.

Diabetes recurrence after metabolic surgeries correlates with re-impaired insulin sensitivity rather than beta-cell function

AIM

To investigate factors causing diabetes recurrence after sleeve gastrectomy (SG) and duodenal-jejunal bypass (DJB).

METHODS

SG and DJB were performed on rats with diabetes induced by high-fat diet (HFD) and streptozotocin (STZ). HFD was used to induce diabetes recurrence at 4 wk postoperatively. Body weight, oral glucose tolerance test, homeostatic model assessment of insulin resistance (HOMA-IR), insulin signaling [IR, insulin receptor substrate (IRS)1, IRS2, phosphatidylinositol 3-kinase and AKT in liver and skeletal muscle], oral glucose stimulated insulin secretion, beta-cell morphology (mass, apoptosis and insulin secretion), glucagon-like peptide (GLP)-1, PYY and ghrelin were compared among SG rats with common low-fat diet (SG-LFD), SG with HFD (SG-HFD), DJB rats with LFD (DJB-LFD), DJB with HFD (DJB-HFD) and sham-operation with LFD (Sham) at targeted postoperative times.

RESULTS

SG and DJB resulted in significant improvement in glucose tolerance, lower HOMA-IR, up-regulated hepatic and muscular insulin signaling, higher levels of oral glucose-stimulated insulin secretion, bigger beta-cell mass, higher immunofluorescence intensity of insulin, fewer transferase-mediated dUTP-biotin 3’ nick end-labeling (TUNEL)-positive beta cells and higher postprandial GLP-1 and PYY levels than in the Sham group. The improvement in glucose tolerance was reversed at 12 wk postoperatively. Compared with the SG-LFD and DJB-LFD groups, the SG-HFD and DJB-HFD groups showed higher HOMA-IR, down-regulated hepatic and muscular insulin signaling, and more TUNEL-positive beta cells. No significant difference was detected between HFD and LFD groups for body weight, glucose-stimulated insulin secretion, beta-cell mass, immunofluorescence intensity of insulin, and postprandial GLP-1 and PYY levels. Fasting serum ghrelin decreased in SG groups, and there was no difference between HFD-SG and LFD-SG groups.

CONCLUSION

HFD reverses the improvement in glucose homeostasis after SG and DJB. Diabetes recurrence may correlate with re-impaired insulin sensitivity, but not with alterations of beta-cell function and body weight.

Intraocular in vivo imaging of pancreatic islet cell physiology/pathology

Background

Diabetes mellitus has reached epidemic proportions and requires new strategies for treatment. Unfortunately, the efficacy of treatment regimens on maintaining/re-gaining functional beta cell mass can, at the present, only be determined indirectly. Direct monitoring of beta cell mass is complicated by the anatomy of the endocrine pancreas, which consists of thousands to a million of discrete micro-organs, i.e. islets of Langerhans, which are scattered throughout the pancreas.

Scope of review

Here, we review the progress made over the last years using the anterior chamber of the eye as a transplantation site for functional imaging of pancreatic islet cells in the living organism. Islets engrafted on the iris are vascularized and innervated and the cornea, serving as a natural body-window, allows for microscopic, non-invasive, longitudinal evaluation of islet/beta cell function and survival with single-cell resolution in health and disease.

Major conclusions

Data provided by us and others demonstrate the high versatility of this imaging platform. The use of ‘reporter islets’ engrafted in the eye, reporting on the status of in situ endogenous islets in the pancreas of the same animal, allows the identification of key-events in the development and progression of diabetes. This will not only serve as a versatile research tool but will also lay the foundation for a personalized medicine approach and will serve as a screening platform for new drugs and/or treatment protocols. ‘Metabolic’ islet transplantation, in which islets engrafted in the eye replace the endogenous beta cells, will allow for the establishment of islet-specific transgenic models and ‘humanized’ mouse models as well as serving as the basis for a new clinical transplantation site for the cure of diabetes.

LXR activation causes G1/S arrest through inhibiting SKP2 expression in MIN6 pancreatic beta cells

Liver X receptors (LXRs) are nuclear hormone receptors with central roles in lipid homeostasis. We previously showed that LXR activation induced aberrant lipid metabolism and G1 cell cycle arrest in pancreatic beta cells. In this study, we aimed to identify the molecular target of LXR causing G1 arrest. LXR activation was induced by its agonist, T0901317. A series of luciferase reporters of truncated Skp2 promoter were analyzed in MIN6 cells. mRNA and protein levels of SKP2 and P27 were detected. Flow cytometry assay was used to determine the cell cycle distribution. MTT assay was used to evaluate cell viability. LXR activation increased cell distribution in G1 phase and lipid accumulation. Since dominant-negative Srebp1c could clear the deposited lipid rather than recover the G1 arrest, we identified S-phase kinase-associated protein 2 (Skp2) as a potential target gene of LXR. In deed, LXR activation significantly inhibited Skp2 gene expression and protein amount. We also observed that the luciferase activity of Skp2 promoter was suppressed by T0901317 and the potential LXR regulatory site was narrowed down to a region of nt -289 to -38. Silencing Lxrα and Lxrβ rescued SKP2 protein level and recovered the cellular growth repressed by LXR activation. Moreover, SKP2 overabundance reduced P27 protein level by promoting its degradation, consequently overcame the G1 arrest caused by T0901317. Our findings demonstrate that transrepressing Skp2 expression by LXR activation resulted in defective SKP2-mediated P27 degradation and inhibitory cell growth in beta cells.

Duodenal-jejunal bypass attenuates progressive failure of pancreatic islets in streptozotocin-induced diabetic rats

BACKGROUND

Preservation of pancreatic beta cell function has been increasingly appealing in the treatment of type 2 diabetes. Evidence is still limited on how bariatric surgery affects pancreatic beta cell apoptosis.

SETTING

University medical center.

OBJECTIVE

The study aimed to investigate the effect of a major component of Roux-en-Y gastric bypass, duodenal-jejunal bypass, on protecting pancreatic beta cells from progressive loss.

METHODS

Forty-five normal Sprague-Dawley rats were randomly assigned into 3 groups: duodenal-jejunal bypass (DJB) group (n = 16) and sham (S) group (n = 17), based upon the procedure received, and a control (C) group (n = 12) without any procedure performed, to eliminate potential traumatic effects from surgery. Ten days after surgery, streptozotocin (STZ, 45 mg/kg weight) was injected intraperitoneally into each animal, including the control animals, to selectively induce pancreatic beta cell apoptosis. Weight, food intake, plasma glucose level, and the results of an oral glucose tolerance test were measured before surgery, pre-STZ injection, and up to 4 weeks after STZ injection. Plasma insulin and glucagon-like peptide-1 levels were also assayed during oral glucose tolerance test. At the end, pancreatic tissues were sliced and stained for beta cell analysis.

RESULTS

There were no significant differences in weight among all groups at any time points measured, despite rats in the S and C groups consuming more food than those in the DJB group as measured on day 10 (P<.05) and day 20 (P<.01) after STZ injection. Animals undergoing DJB did not experience symptoms typical of uncompensated diabetes, including hyperphagia and progressive weight loss. After STZ injection, fasting plasma glucose levels in the DJB group were significantly lower than those in the C and S groups (P<.001). When challenged by glucose load, DJB rats also had a better glycemic excursion (P<.01) and incretin response compared with C and S rats (P<.05). In addition, pancreatic beta cell size and mass was better preserved in DJB rats (P< .001).

CONCLUSION

DJB is able to protect pancreatic beta cells from apoptosis, which leads to better glycemic control and delayed onset of diabetes. These results imply the necessity of including a DJB component when designing bariatric procedure to achieve a better long-term outcome.

Islet biology, the CDKN2A/B locus and type 2 diabetes risk

Type 2 diabetes, fuelled by the obesity epidemic, is an escalating worldwide cause of personal hardship and public cost. Diabetes incidence increases with age, and many studies link the classic senescence and ageing protein p16(INK4A) to diabetes pathophysiology via pancreatic islet biology. Genome-wide association studies (GWASs) have unequivocally linked the CDKN2A/B locus, which encodes p16 inhibitor of cyclin-dependent kinase (p16(INK4A)) and three other gene products, p14 alternate reading frame (p14(ARF)), p15(INK4B) and antisense non-coding RNA in the INK4 locus (ANRIL), with human diabetes risk. However, the mechanism by which the CDKN2A/B locus influences diabetes risk remains uncertain. Here, we weigh the evidence that CDKN2A/B polymorphisms impact metabolic health via islet biology vs effects in other tissues. Structured in a bedside-to-bench-to-bedside approach, we begin with a summary of the evidence that the CDKN2A/B locus impacts diabetes risk and a brief review of the basic biology of CDKN2A/B gene products. The main emphasis of this work is an in-depth look at the nuanced roles that CDKN2A/B gene products and related proteins play in the regulation of beta cell mass, proliferation and insulin secretory function, as well as roles in other metabolic tissues. We finish with a synthesis of basic biology and clinical observations, incorporating human physiology data. We conclude that it is likely that the CDKN2A/B locus influences diabetes risk through both islet and non-islet mechanisms.