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

Theoretical Studies of DNA Microarray Present Potential Molecular and Cellular Interconnectivity of Signaling Pathways in Immune System Dysregulation

Autoimmunity is defined as the inability to regulate immunological activities in the body, especially in response to external triggers, leading to the attack of the tissues and organs of the host. Outcomes include the onset of autoimmune diseases whose effects are primarily due to dysregulated immune responses. In past years, there have been cases that show an increased susceptibility to other autoimmune disorders in patients who are already experiencing the same type of disease. Research in this field has started analyzing the potential molecular and cellular causes of this interconnectedness, bearing in mind the possibility of advancing drugs and therapies for the treatment of autoimmunity. With that, this study aimed to determine the correlation of four autoimmune diseases, which are type 1 diabetes (T1D), psoriasis (PSR), systemic sclerosis (SSc), and systemic lupus erythematosus (SLE), by identifying highly preserved co-expressed genes among datasets using WGCNA. Functional annotation was then employed to characterize these sets of genes based on their systemic relationship as a whole to elucidate the biological processes, cellular components, and molecular functions of the pathways they are involved in. Lastly, drug repurposing analysis was performed to screen candidate drugs for repositioning that could regulate the abnormal expression of genes among the diseases. A total of thirteen modules were obtained from the analysis, the majority of which were associated with transcriptional, post-transcriptional, and post-translational modification processes. Also, the evaluation based on KEGG suggested the possible role of TH17 differentiation in the simultaneous onset of the four diseases. Furthermore, clomiphene was the top drug candidate for regulating overexpressed hub genes; meanwhile, prilocaine was the top drug for regulating under-expressed hub genes. This study was geared towards utilizing transcriptomics approaches for the assessment of microarray data, which is different from the use of traditional genomic analyses. Such a research design for investigating correlations among autoimmune diseases may be the first of its kind.

Waste to Medicine: Evidence from Computational Studies on the Modulatory Role of Corn Silk on the Therapeutic Targets Implicated in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and/or defective insulin production in the human body. Although the antidiabetic action of corn silk (CS) is well-established, the understanding of the mechanism of action (MoA) behind this potential is lacking. Hence, this study aimed to elucidate the MoA in different samples (raw and three extracts: aqueous, hydro-ethanolic, and ethanolic) as a therapeutic agent for the management of T2DM using metabolomic profiling and computational techniques. Ultra-performance liquid chromatography-mass spectrometry (UP-LCMS), in silico techniques, and density functional theory were used for compound identification and to predict the MoA. A total of 110 out of the 128 identified secondary metabolites passed the Lipinski's rule of five. The Kyoto Encyclopaedia of Genes and Genomes pathway enrichment analysis revealed the cAMP pathway as the hub signaling pathway, in which ADORA1, HCAR2, and GABBR1 were identified as the key target genes implicated in the pathway. Since gallicynoic acid (-48.74 kcal/mol), dodecanedioc acid (-34.53 kcal/mol), and tetradecanedioc acid (-36.80 kcal/mol) interacted well with ADORA1, HCAR2, and GABBR1, respectively, and are thermodynamically stable in their formed compatible complexes, according to the post-molecular dynamics simulation results, they are suggested as potential drug candidates for T2DM therapy via the maintenance of normal glucose homeostasis and pancreatic β-cell function.

Vascular endothelial growth factor B improves impaired glucose tolerance through insulin-mediated inhibition of glucagon secretion

BACKGROUND

Impaired glucose tolerance (IGT) is a homeostatic state between euglycemia and hyperglycemia and is considered an early high-risk state of diabetes. When IGT occurs, insulin sensitivity decreases, causing a reduction in insulin secretion and an increase in glucagon secretion. Recently, vascular endothelial growth factor B (VEGFB) has been demonstrated to play a positive role in improving glucose metabolism and insulin sensitivity. Therefore, we constructed a mouse model of IGT through high-fat diet feeding and speculated that VEGFB can regulate hyperglycemia in IGT by influencing insulin-mediated glucagon secretion, thus contributing to the prevention and cure of prediabetes.

AIM

To explore the potential molecular mechanism and regulatory effects of VEGFB on insulin-mediated glucagon in mice with IGT.

METHODS

We conducted in vivo experiments through systematic VEGFB knockout and pancreatic-specific VEGFB overexpression. Insulin and glucagon secretions were detected via enzyme-linked immunosorbent assay, and the protein expression of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) was determined using western blot. Further, mRNA expression of forkhead box protein O1, phosphoenolpyruvate carboxykinase, and glucose-6 phosphatase was detected via quantitative polymerase chain reaction, and the correlation between the expression of proteins was analyzed via bioinformatics.

RESULTS

In mice with IGT and VEGFB knockout, glucagon secretion increased, and the protein expression of PI3K/AKT decreased dramatically. Further, in mice with VEGFB overexpression, glucagon levels declined, with the activation of the PI3K/AKT signaling pathway.

CONCLUSION

VEGFB/vascular endothelial growth factor receptor 1 can promote insulin-mediated glucagon secretion by activating the PI3K/AKT signaling pathway to regulate glucose metabolism disorders in mice with IGT.

Alpha cell receptor for advanced glycation end products associate with glucagon expression in type 1 diabetes

Hypoglycemia in type 1 diabetes associates with changes in the pancreatic islet α cells, where the receptor for advanced glycation end products (RAGE) is highly expressed. This study compared islet RAGE expression in donors without diabetes, those at risk of, and those with type 1 diabetes. Laser-dissected islets were subject to RNA bioinformatics and adjacent pancreatic tissue were assessed by confocal microscopy. We found that islets from type 1 diabetes donors had differential expression of the RAGE gene (AGER) and its correlated genes, based on glucagon expression. Random forest machine learning revealed that AGER was the most important predictor for islet glucagon levels. Conversely, a generalized linear model identified that glucagon expression could be predicted by expression of RAGE signaling molecules, its ligands and enzymes that create or clear RAGE ligands. Confocal imaging co-localized RAGE, its ligands and signaling molecules to the α cells. Half of the type 1 diabetes cohort comprised of adolescents and a patient with history of hypoglycemia-all showed an inverse relationship between glucagon and RAGE. These data confirm an association between glucagon and islet RAGE, its ligands and signaling pathways in type 1 diabetes, which warrants functional investigation into a role for RAGE in hypoglycemia.

The human α cell in health and disease

In commemoration of 100 years since the discovery of glucagon, we review current knowledge about the human α cell. Alpha cells make up 30-40% of human islet endocrine cells and play a major role in regulating whole-body glucose homeostasis, largely through the direct actions of their main secretory product - glucagon - on peripheral organs. Additionally, glucagon and other secretory products of α cells, namely acetylcholine, glutamate, and glucagon-like peptide-1, have been shown to play an indirect role in the modulation of glucose homeostasis through autocrine and paracrine interactions within the islet. Studies of glucagon's role as a counterregulatory hormone have revealed additional important functions of the α cell, including the regulation of multiple aspects of energy metabolism outside that of glucose. At the molecular level, human α cells are defined by the expression of conserved islet-enriched transcription factors and various enriched signature genes, many of which have currently unknown cellular functions. Despite these common threads, notable heterogeneity exists amongst human α cell gene expression and function. Even greater differences are noted at the inter-species level, underscoring the importance of further study of α cell physiology in the human context. Finally, studies on α cell morphology and function in type 1 and type 2 diabetes, as well as other forms of metabolic stress, reveal a key contribution of α cell dysfunction to dysregulated glucose homeostasis in disease pathogenesis, making targeting the α cell an important focus for improving treatment.

Dual A1 and A2A adenosine receptor antagonists, methoxy substituted 2-benzylidene-1-indanone, suppresses intestinal postprandial glucose and attenuates hyperglycaemia in fructose-streptozotocin diabetic rats

BACKGROUND/AIM

Recent research suggests that adenosine receptors (ARs) influence many of the metabolic abnormalities associated with diabetes. A non-xanthine benzylidene indanone derivative 2-(3,4-dihydroxybenzylidene)-4-methoxy-2,3-dihydro-1 H-inden-1-one (2-BI), has shown to exhibit higher affinity at A₁/A_2A ARs compared to caffeine. Due to its structural similarity to caffeine, and the established antidiabetic effects of caffeine, the current study was initiated to explore the possible antidiabetic effect of 2-BI.

METHODS

The study was designed to assess the antidiabetic effects of several A₁ and/or A_2A AR antagonists, via intestinal glucose absorption and glucose-lowering effects in fructose-streptozotocin (STZ) induced diabetic rats. Six-week-old male Sprague-Dawley rats were induced with diabetes via fructose and streptozotocin. Rats were treated for 4 weeks with AR antagonists, metformin and pioglitazone, respectively. Non-fasting blood glucose (NFBG) was determined weekly and the oral glucose tolerance test (OGTT) was conducted at the end of the intervention period.

RESULTS

Dual A₁/A_2A AR antagonists (caffeine and 2-BI) decreased glucose absorption in the intestinal membrane significantly (p < 0.01), while the selective A_2A AR antagonist (Istradefylline), showed the highest significant (p < 0.001) reduction in intestinal glucose absorption. The selective A₁ antagonist (DPCPX) had the least significant (p < 0.05) reduction in glucose absorption. Similarly, dual A₁/A_2A AR antagonists and selective A_2A AR antagonists significantly reduced non-fast blood glucose and improved glucose tolerance in diabetic rats from the first week of the treatment. Conversely, the selective A₁ AR antagonist did not reduce non-fast blood glucose significantly until the 4th week of treatment. 2-BI, caffeine and istradefylline compared well with standard antidiabetic treatments, metformin and pioglitazone, and in some cases performed even better.

CONCLUSION

2-BI exhibited good antidiabetic activity by reducing intestinal postprandial glucose absorption and improving glucose tolerance in a diabetic animal model. The dual antagonism of A₁/A_2A ARs presents a positive synergism that could provide a new possibility for the treatment of diabetes.

Identification of Novel Disease-Relevant Genes and Pathways in the Pathogenesis of Type 1 Diabetes: A Potential Defect in Pancreatic Iron Homeostasis

Multiple pathways contribute to the pathophysiological development of type 1 diabetes (T1D); however, the exact mechanisms involved are unclear. We performed differential gene expression analysis in pancreatic islets of NOD mice versus age-matched congenic NOD.B10 controls to identify genes that may contribute to disease pathogenesis. Novel genes related to extracellular matrix development and glucagon and insulin signaling/secretion were changed in NOD mice during early inflammation. During "respective" insulitis, the expression of genes encoding multiple chemosensory olfactory receptors were upregulated, and during "destructive" insulitis, the expression of genes involved in antimicrobial defense and iron homeostasis were downregulated. Islet inflammation reduced the expression of Hamp that encodes hepcidin. Hepcidin is expressed in β-cells and serves as the key regulator of iron homeostasis. We showed that Hamp and hepcidin levels were lower, while iron levels were higher in the pancreas of 12-week-old NOD versus NOD.B10 mice, suggesting that a loss of iron homeostasis may occur in the islets during the onset of "destructive" insulitis. Interestingly, we showed that the severity of NOD disease correlates with dietary iron intake. NOD mice maintained on low-iron diets had a lower incidence of hyperglycemia, while those maintained on high-iron diets had an earlier onset and higher incidence of disease, suggesting that high iron exposure combined with a loss of pancreatic iron homeostasis may exacerbate NOD disease. This mechanism may explain the link seen between high iron exposure and the increased risk for T1D in humans.

Potential Therapeutic Targeting Neurotransmitter Receptors in Diabetes

Neurotransmitters are signaling molecules secreted by neurons to coordinate communication and proper function among different sections in the central neural system (CNS) by binding with different receptors. Some neurotransmitters as well as their receptors are found in pancreatic islets and are involved in the regulation of glucose homeostasis. Neurotransmitters can act with their receptors in pancreatic islets to stimulate or inhibit the secretion of insulin (β cell), glucagon (α cell) or somatostatin (δ cell). Neurotransmitter receptors are either G-protein coupled receptors or ligand-gated channels, their effects on blood glucose are mainly decided by the number and location of them in islets. Dysfunction of neurotransmitters receptors in islets is involved in the development of β cell dysfunction and type 2 diabetes (T2D).Therapies targeting different transmitter systems have great potential in the prevention and treatment of T2D and other metabolic diseases.

Multipotent Stromal Cells from Subcutaneous Adipose Tissue of Normal Weight and Obese Subjects: Modulation of Their Adipogenic Differentiation by Adenosine A1 Receptor Ligands

Adenosine A₁ receptor (A₁R) activation, stimulating lipogenesis and decreasing insulin resistance, could be useful for metabolic syndrome management in obese subjects. Since full A₁R agonists induce harmful side-effects, while partial agonists show a better pharmacological profile, we investigated the influence of two derivatives of the full A₁R agonist 2-chloro-N⁶-cyclopentyladenosine (CCPA), C1 and C2 behaving as A₁R partial agonists in animal models, on the adipogenic differentiation of stromal/stem cells (ASCs) from human subcutaneous adipose tissue, which mainly contribute to increase fat mass in obesity. The ASCs from normal-weight subjects showed increased proliferation and A₁R expression but reduced adipogenic differentiation compared to obese individual-derived ASCs. Cell exposure to CCPA, C1, C2 or DPCPX, an A₁R antagonist, did not affect ASC proliferation, while mainly C2 and DPCPX significantly decreased adipogenic differentiation of both ASC types, reducing the activity of glycerol-3-phosphate dehydrogenase and the expression of PPARγ and FABP-4, all adipogenic markers, and phosphorylation of Akt in the phosphatidylinositol-3-kinase pathway, which plays a key-role in adipogenesis. While requiring confirmation in in vivo models, our results suggest that A₁R partial agonists or antagonists, by limiting ASC differentiation into adipocytes and, thereby, fat mass expansion, could favor development/worsening of metabolic syndrome in obese subjects without a dietary control.

Adenosine A1 receptor is dispensable for hepatocyte glucose metabolism and insulin sensitivity

Hepatic insulin resistance (IR) and enhanced hepatic glucose production (HGP) are key features of type 2 diabetes (T2D), contributing to fasting hyperglycemia. Adenosine receptors (ARs) are G protein-coupled and expressed in hepatocytes. Here, we explored the role of hepatic Gi/o-coupled A1AR on insulin resistance and glucose fluxes associated with obesity. We generated a mouse model with hepatocyte-specific deletion of A1AR (A1LΔ/Δ), which was compared with whole body knockout of A1AR or A1AR/A3AR (both Gi-coupled). Selective deletion of hepatic A1AR resulted in a modest improvement in insulin sensitivity. In addition, HFD A1LΔ/Δ mice showed decreased fasting glucose levels. Hyperinsulinemic-euglycemic clamp studies demonstrated enhanced insulin sensitivity with no change in HGP in HFD A1LΔ/Δ mice. Similar to A1LΔ/Δ, fasting blood glucose levels were significantly reduced in whole body A1Δ/Δ and A1Δ/ΔA3Δ/Δ compared to wild-type mice. Taken together, our data support the concept that blocking hepatic A1AR may decrease fasting blood glucose levels without directly affecting hepatocyte glucose metabolism and insulin sensitivity.

Pathways of Glucagon Secretion and Trafficking in the Pancreatic Alpha Cell: Novel Pathways, Proteins, and Targets for Hyperglucagonemia

Patients with diabetes mellitus exhibit hyperglucagonemia, or excess glucagon secretion, which may be the underlying cause of the hyperglycemia of diabetes. Defective alpha cell secretory responses to glucose and paracrine effectors in both Type 1 and Type 2 diabetes may drive the development of hyperglucagonemia. Therefore, uncovering the mechanisms that regulate glucagon secretion from the pancreatic alpha cell is critical for developing improved treatments for diabetes. In this review, we focus on aspects of alpha cell biology for possible mechanisms for alpha cell dysfunction in diabetes: proglucagon processing, intrinsic and paracrine control of glucagon secretion, secretory granule dynamics, and alterations in intracellular trafficking. We explore possible clues gleaned from these studies in how inhibition of glucagon secretion can be targeted as a treatment for diabetes mellitus.

Alternative Splicing: A New Cause and Potential Therapeutic Target in Autoimmune Disease

Alternative splicing (AS) is a complex coordinated transcriptional regulatory mechanism. It affects nearly 95% of all protein-coding genes and occurs in nearly all human organs. Aberrant alternative splicing can lead to various neurological diseases and cancers and is responsible for aging, infection, inflammation, immune and metabolic disorders, and so on. Though aberrant alternative splicing events and their regulatory mechanisms are widely recognized, the association between autoimmune disease and alternative splicing has not been extensively examined. Autoimmune diseases are characterized by the loss of tolerance of the immune system towards self-antigens and organ-specific or systemic inflammation and subsequent tissue damage. In the present review, we summarized the most recent reports on splicing events that occur in the immunopathogenesis of systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) and attempted to clarify the role that splicing events play in regulating autoimmune disease progression. We also identified the changes that occur in splicing factor expression. The foregoing information might improve our understanding of autoimmune diseases and help develop new diagnostic and therapeutic tools for them.

Diabetes and hypertension: Pivotal involvement of purinergic signaling

Diabetes mellitus (DM) and hypertension are highly prevalent worldwide health problems and frequently associated with severe clinical complications, such as diabetic cardiomyopathy, nephropathy, retinopathy, neuropathy, stroke, and cardiac arrhythmia, among others. Despite all existing research results and reasonable speculations, knowledge about the role of purinergic system in individuals with DM and hypertension remains restricted. Purinergic signaling accounts for a complex network of receptors and extracellular enzymes responsible for the recognition and degradation of extracellular nucleotides and adenosine. The main components of this system that will be presented in this review are: P1 and P2 receptors and the enzymatic cascade composed by CD39 (NTPDase; with ATP and ADP as a substrate), CD73 (5'-nucleotidase; with AMP as a substrate), and adenosine deaminase (ADA; with adenosine as a substrate). The purinergic system has recently emerged as a central player in several physiopathological conditions, particularly those linked to inflammatory responses such as diabetes and hypertension. Therefore, the present review focuses on changes in both purinergic P1 and P2 receptor expression as well as the activities of CD39, CD73, and ADA in diabetes and hypertension conditions. It can be postulated that the manipulation of the purinergic axis at different levels can prevent or exacerbate the insurgency and evolution of diabetes and hypertension working as a compensatory mechanism.

Adenosine Signaling in Autoimmune Disorders

The molecular components of the purinergic system (i.e., receptors, metabolizing enzymes and membrane transporters) are widely expressed in the cells of the immune system. Additionally, high concentrations of adenosine are generated from the hydrolysis of ATP in any "danger" condition, when oxygen and energy availability dramatically drops. Therefore, adenosine acts as a retaliatory metabolite to counteract the nucleotide-mediated boost of the immune reaction. Based on this observation, it can be foreseen that the recruitment with selective agonists of the receptors involved in the immunomodulatory effect of adenosine might represent an innovative anti-inflammatory approach with potential exploitation in autoimmune disorders. Quite surprisingly, pro-inflammatory activity exerted by some adenosine receptors has been also identified, thus paving the way for the hypothesis that at least some autoimmune disorders may be caused by a derailment of adenosine signaling. In this review article, we provide a general overview of the roles played by adenosine on immune cells with a specific focus on the development of adenosine-based therapies for autoimmune disorders, as demonstrated by the exciting data from concluded and ongoing clinical trials.

Reversal of Hyperglycemia and Suppression of Type 1 Diabetes in the NOD Mouse with Apoptotic DNA Immunotherapy™ (ADi™), ADi-100

The antigen-specific apoptotic DNA immunotherapeutic, ADi-100, is designed to suppress type 1 diabetes and consists of two DNA plasmids encoding genetic sequences of the apoptosis-inducing molecule, BAX, and the secreted form of the autoantigen, glutamic acid decarboxylase 65, that is CpG hyper-methylated to avoid inflammatory signaling (msGAD55). Upon a four-day treatment with ADi-100 of young female non-obese diabetic (NOD) mice, the frequency of various tolerogenic dendritic cell populations increased in draining lymph nodes; these cells lost the capacity to stimulate glutamic acid decarboxylase (GAD)-specific CD4⁺ T lymphocytes and were associated with the previously demonstrated enhancement of GAD-specific regulatory T cells. The efficacy of two ADi-100 formulations containing different proportions of BAX and msGAD55, 1:4 (10/40 µg) and 1:2 (17/33 µg), was evaluated in mildly hyperglycemic pre-diabetic NOD female mice. Both formulations suppressed the incidence of diabetes by 80% in an antigen-specific manner, while all untreated mice developed diabetes. However, treatment of pre-diabetic mice with significantly higher hyperglycemia, denoting progressive disease, showed that ADi-100 1:2 strongly suppressed diabetes incidence by 80% whereas the ADi-100 1:4 was less effective (50%). As an antigen-specific monotherapy, ADi-100 is highly efficacious in reversing elevated hyperglycemia to prevent diabetes, in which increasing apoptosis-inducing BAX content is a promising immune tolerance feature.

Gene Expression Analysis of the Pre-Diabetic Pancreas to Identify Pathogenic Mechanisms and Biomarkers of Type 1 Diabetes

Type 1 Diabetes (T1D) occurs as a result of the autoimmune destruction of pancreatic β-cells by self-reactive T cells. The etiology of this disease is complex and difficult to study due to a lack of disease-relevant tissues from pre-diabetic individuals. In this study, we performed gene expression analysis on human pancreas tissues obtained from the Network of Pancreatic Organ Donors with Diabetes (nPOD), and showed that 155 genes were differentially expressed by ≥2-fold in the pancreata of autoantibody-positive (AA+) at-risk individuals compared to healthy controls. Only 48 of these genes remained changed by ≥2-fold in the pancreata of established T1D patients. Pathway analysis of these genes showed a significant association with various immune pathways. We were able to validate the differential expression of eight disease-relevant genes by QPCR analysis: A significant upregulation of CADM2, and downregulation of TRPM5, CRH, PDK4, ANGPL4, CLEC4D, RSG16, and FCGR2B was confirmed in the pancreata of AA+ individuals versus controls. Studies have already implicated FCGR2B in the pathogenesis of disease in non-obese diabetic (NOD) mice. Here we showed that CADM2, TRPM5, PDK4, and ANGPL4 were similarly changed in the pancreata of pre-diabetic 12-week-old NOD mice compared to NOD.B10 controls, suggesting a possible role for these genes in the pathogenesis of both T1D and NOD disease. The loss of the leukocyte-specific gene, FCGR2B, in the pancreata of AA+ individuals, is particularly interesting, as it may serve as a potential whole blood biomarker of disease progression. To test this, we quantified FCGR2B expression in peripheral blood samples of T1D patients, and AA+ and AA- first-degree relatives of T1D patients enrolled in the TrialNet Pathway to Prevention study. We showed that FCGR2B was significantly reduced in the peripheral blood of AA+ individuals compared to AA- controls. Together, these findings demonstrate that gene expression analysis of pancreatic tissue and peripheral blood samples can be used to identify disease-relevant genes and pathways and potential biomarkers of disease progression in T1D.

Expression of Adenosine Receptors in Rodent Pancreas

Adenosine regulates exocrine and endocrine secretions in the pancreas. Adenosine is considered to play a role in acini-to-duct signaling in the exocrine pancreas. To identify the molecular basis of functional adenosine receptors in the exocrine pancreas, immunohistochemical analysis was performed in the rat, mouse, and guinea pig pancreas, and the secretory rate and concentration of HCO₃⁻ in pancreatic juice from the rat pancreas were measured. The A_2A adenosine receptor colocalized with ezrin, an A-kinase anchoring protein, in the luminal membrane of duct cells in the mouse and guinea pig pancreas. However, a strong signal ascribed to A_2B adenosine receptors was detected in insulin-positive β cells in islets of Langerhans. The A_2A adenosine receptor agonist 4-[2-[[6-Amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid (CGS 21680) stimulated HCO₃⁻-rich fluid secretion from the rat pancreas. These results indicate that A_2A adenosine receptors may be, at least in part, involved in the exocrine secretion of pancreatic duct cells via acini-to-duct signaling. The adenosine receptors may be a potential therapeutic target for cancer as well as exocrine dysfunctions of the pancreas.

Transcriptomic and methylomic analysis reveal the toxicological effect of 2,3,7,8-Tetrachlorodibenzodioxin on human embryonic stem cell

Cumulating epidemiological studies demonstrated that environmental exposure to endocrine disrupting chemicals (EDCs) during the early stages of fetal development is associated with the increase in disease susceptibility in later life. The fetal developmental plasticity is considered as a protective mechanism against an undesirable prenatal environment. Dioxin is one of the environmental contaminants and is considered a diabetogenic factor. Experimental animal and human epidemiological studies have revealed that dioxin exposure was associated with insulin resistance and altered beta cell function. But the effect of dioxin exposure in early stage of fetal development is still largely unknown. In this report, we used the human embryonic stem cell (hESC) line, VAL-3, as a model, together with Methyl-CpG Binding Domain (MBD) protein-enriched genome sequencing and transcriptome sequencing (RNA-seq), in order to determine the dynamic changes of the epigenetic landscape and transcriptional dysregulation in hESC upon dioxin exposure. The bioinformatics analyses including the Database for Annotation, Visualization and Integrated Discovery (DAVID) analysis and Ingenuity Pathway Analysis (IPA) highlighted the predisposed neural, hepatic, cardiac and metabolic toxicological effects of dioxin during the fetal development.

Functional changes in vascular reactivity to adenosine receptor activation in type I diabetic mice

Activation of adenosine receptors has been implicated in several biological functions, including cardiovascular and renal function. Diabetes causes morphological and functional changes in the vasculature, resulting in abnormal responses to various stimuli. Recent studies have suggested that adenosine receptor expression and signaling are altered in disease states such as hypertension, diabetes. Using a streptozotocin (STZ) mouse model of type I diabetes (T1D), we investigated the functional changes in aorta and resistance mesenteric arteries to adenosine receptor agonist activation in T1D. Organ baths and DMT wire myographs were used for muscle tension measurements in isolated vascular rings, and western blotting was used for protein analysis. Concentration response curves to selective adenosine receptor agonists, including CCPA (A₁ receptor agonist), Cl-IBMECA (A₃ receptor agonist), CGS-21680 (A_2A receptor agonist), and BAY 60-6583 (A_2B receptor agonist), were performed. We found that diabetes did not affect adenosine receptor agonist-mediated relaxation or contraction in mesenteric arteries. However, aortas from diabetic mice exhibited a significant decrease (P < 0.05) in A₁ receptor-mediated vasoconstriction. In addition, the aortas from STZ-treated mice exhibited an increase in phenylephrine-mediated contraction (EC₅₀ 7.40 ± 0.08 in STZ vs 6.89 ± 0.14 in vehicle; P < 0.05), while relaxation to A_2A receptor agonists (CGS-21680) tended to decrease in aortas from the STZ-treated group (not statistically significant). Our data suggest that changes in adenosine receptor(s) vascular reactivity in T1D is tissue specific, and the decrease in A₁ receptor-mediated aortic contraction could be a compensatory mechanism to counterbalance the increased adrenergic vascular contractility observed in aortas from diabetic mice.

The role of adenosinergic pathway in human autoimmune diseases

Autoimmune diseases are characterized by the abnormal immune response against self-tissue, which are caused by the failure of nature immune homeostasis. Nature immune homeostasis represents the normal state of appropriate immune response to nonself-antigen and unresponsiveness to self-antigens. In normal situation, immune homeostasis is regulated by immunosuppressive signal and immunostimulating signal together. Accumulating data have demonstrated that the adenosinergic pathway played key roles in immune suppression and shield body from an excessive inflammatory response. The deficiency of adenosinergic pathway results in the imbalance between the pro- and anti-inflammatory activities. Thus, researchers pay much attention to the role of adenosinergic pathway in autoimmune diseases development. To date, accumulating data have suggested an important role of adenosinergic pathway-related molecules (i.e., CD39, CD73, ADA, adenosine receptors, etc.) in many types of human autoimmune diseases. More importantly, these findings have presented potential value of adenosinergic pathway analysis to be used for autoimmune diseases diagnosis, monitoring and treatment. In this review, we will provide a comprehensive description of the role of adenosinergic pathway in human autoimmune diseases.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

Oligofructose as an adjunct in treatment of diabetes in NOD mice

In type 1 diabetes, restoration of normoglycemia can be achieved if the autoimmune attack on beta cells ceases and insulin requirement is met by the residual beta cells. We hypothesize that an adjunctive therapy that reduces insulin demand by increasing insulin sensitivity will improve the efficacy of an immunotherapy in reversing diabetes. We tested the gut microbiota-modulating prebiotic, oligofructose (OFS), as the adjunctive therapy. We treated non-obese diabetic mice with an immunotherapy, monoclonal anti-CD3 antibody (aCD3), with or without concurrent dietary supplement of OFS. After 8 weeks of OFS supplement, the group that received both aCD3 and OFS (aCD3 + OFS) had a higher diabetes remission rate than the group that received aCD3 alone. The aCD3 + OFS group had higher insulin sensitivity accompanied by reduced lymphocytic infiltrate into the pancreatic islets, higher beta-cell proliferation rate, higher pancreatic insulin content, and secreted more insulin in response to glucose. The addition of OFS also caused a change in gut microbiota, with a higher level of Bifidobacterium and lower Clostridium leptum. Hence, our results suggest that OFS can potentially be an effective therapeutic adjunct in the treatment of type 1 diabetes by improving insulin sensitivity and beta-cell function, leading to improved glycemic control.

Adenosine production: a common path for mesenchymal stem-cell and regulatory T-cell-mediated immunosuppression

Adenosine is an important molecule that exerts control on the immune system, by signaling through receptors lying on the surface of immune cells. This nucleotide is produced, in part, by the action of the ectoenzymes CD39 and CD73. Interestingly, these proteins are expressed on the cell surface of regulatory T-cells (Tregs) and mesenchymal stromal cells (MSCs)-two cell populations that have emerged as potential therapeutic tools in the field of cell therapy. In fact, the production of adenosine constitutes a mechanism used by both cell types to control the immune response. Recently, great scientific progress was obtained regarding the role of adenosine in the inflammatory environment. In this context, the present review focuses on the advances related to the impact of adenosine production over the immune modulatory activity of Tregs and MSCs, and how this nucleotide controls the biological functions of these cells. Finally, we mention the main challenges and hurdles to bring such molecule to clinical settings.

Expression-Based Genome-Wide Association Study Links Vitamin D-Binding Protein With Autoantigenicity in Type 1 Diabetes

Type 1 diabetes (T1D) is caused by autoreactive T cells that recognize pancreatic islet antigens and destroy insulin-producing β-cells. This attack results from a breakdown in tolerance for self-antigens, which is controlled by ectopic antigen expression in the thymus and pancreatic lymph nodes (PLNs). The autoantigens known to be involved include a set of islet proteins, such as insulin, GAD65, IA-2, and ZnT8. In an attempt to identify additional antigenic proteins, we performed an expression-based genome-wide association study using microarray data from 118 arrays of the thymus and PLNs of T1D mice. We ranked all 16,089 protein-coding genes by the likelihood of finding repeated differential expression and the degree of tissue specificity for pancreatic islets. The top autoantigen candidate was vitamin D-binding protein (VDBP). T-cell proliferation assays showed stronger T-cell reactivity to VDBP compared with control stimulations. Higher levels and frequencies of serum anti-VDBP autoantibodies (VDBP-Abs) were identified in patients with T1D (n = 331) than in healthy control subjects (n = 77). Serum vitamin D levels were negatively correlated with VDBP-Ab levels in patients in whom T1D developed during the winter. Immunohistochemical localization revealed that VDBP was specifically expressed in α-cells of pancreatic islets. We propose that VDBP could be an autoantigen in T1D.

A run on the biobank: what have we learned about type 1 diabetes from the nPOD tissue repository?

PURPOSE OF REVIEW

Since the inaugural year of its biobank in 2007, the Network for Pancreatic Organ Donors with Diabetes program has provided 70 370 human samples to 127 investigators worldwide for projects focused on the pathogenesis of type 1 diabetes (T1D). The purpose of this review was to highlight major advances in our understanding of T1D using works that contain original data from experiments utilizing biospecimens provided by the Network for Pancreatic Organ Donors with Diabetes program. A total of 15 studies, published between 1 June 2013 and 31 December 2014, were selected using various search and filter strategies.

RECENT FINDINGS

The type and frequency of B and/or T-cell immune markers in both the endocrine and exocrine compartments vary in T1D. Enterovirus signals have been identified as having new proteins in the extracellular matrix around infiltrated islets. Novel genes within human islet cell types have been shown to play a role in immunity, infiltration, inflammation, disease progression, cell mass and function. Various cytokines and a complement degradation product have also been detected in the blood or surrounding pancreatic ducts/vasculature.

SUMMARY

These findings, from T1D donors across the disease spectrum, emphasize the notion that pathogenic heterogeneity is a hallmark of the disorder.

Glucagon - the new 'insulin' in the pathophysiology of diabetes

PURPOSE OF REVIEW

Autoimmune destruction of the β cells is considered the key abnormality in type 1 diabetes mellitus and insulin replacement the primary therapeutic strategy. However, a lack of insulin is accompanied by disturbances in glucagon release, which is excessive postprandially, but insufficient during hypoglycaemia. In addition, replacing insulin alone appears insufficient for adequate glucose control. This review focuses on the growing body of evidence that glucagon abnormalities contribute significantly to the pathophysiology of diabetes and on recent efforts to target the glucagon axis as adjunctive therapy to insulin replacement.

RECENT FINDINGS

This review discusses recent (since 2013) advances in abnormalities of glucagon regulation and their link to the pathophysiology of diabetes; new mechanisms of glucagon action and regulation; manipulation of glucagon in diabetes treatment; and analytical and systems biology tools to study glucagon regulation.

SUMMARY

Recent efforts 'resurrected' glucagon as a key hormone in the pathophysiology of diabetes. New studies target its abnormal regulation and action that is key for improving diabetes treatment. The progress is promising, but major questions remain, including unravelling the mechanism of loss of glucagon counterregulation in type 1 diabetes mellitus and how best to manipulate glucagon to achieve more efficient and safer glycaemic control.

Glucagon-reactive islet-infiltrating CD8 T cells in NOD mice

Type 1 diabetes is characterized by T-cell-mediated destruction of the insulin-producing β cells in pancreatic islets. A number of islet antigens recognized by CD8 T cells that contribute to disease pathogenesis in non-obese diabetic (NOD) mice have been identified; however, the antigenic specificities of the majority of the islet-infiltrating cells have yet to be determined. The primary goal of the current study was to identify candidate antigens based on the level and specificity of expression of their genes in mouse islets and in the mouse β cell line MIN6. Peptides derived from the candidates were selected based on their predicted ability to bind H-2K(d) and were examined for recognition by islet-infiltrating T cells from NOD mice. Several proteins, including those encoded by Abcc8, Atp2a2, Pcsk2, Peg3 and Scg2, were validated as antigens in this way. Interestingly, islet-infiltrating T cells were also found to recognize peptides derived from proglucagon, whose expression in pancreatic islets is associated with α cells, which are not usually implicated in type 1 diabetes pathogenesis. However, type 1 diabetes patients have been reported to have serum autoantibodies to glucagon, and NOD mouse studies have shown a decrease in α cell mass during disease pathogenesis. Our finding of islet-infiltrating glucagon-specific T cells is consistent with these reports and suggests the possibility of α cell involvement in development and progression of disease.

Adenosine signalling in diabetes mellitus--pathophysiology and therapeutic considerations

Adenosine is a key extracellular signalling molecule that regulates several aspects of tissue function by activating four G-protein-coupled receptors, A1, A2A, A2B and A1 adenosine receptors. Accumulating evidence highlights a critical role for the adenosine system in the regulation of glucose homeostasis and the pathophysiology of type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). Although adenosine signalling is known to affect insulin secretion, new data indicate that adenosine signalling also contributes to the regulation of β-cell homeostasis and activity by controlling the proliferation and regeneration of these cells as well as the survival of β cells in inflammatory microenvironments. Furthermore, adenosine is emerging as a major regulator of insulin responsiveness by controlling insulin signalling in adipose tissue, muscle and liver; adenosine also indirectly mediates effects on inflammatory and/or immune cells in these tissues. This Review critically discusses the role of the adenosine-adenosine receptor system in regulating both the onset and progression of T1DM and T2DM, and the potential of pharmacological manipulation of the adenosinergic system as an approach to manage T1DM, T2DM and their associated complications.

Inflammation and hyperglycemia mediate Deaf1 splicing in the pancreatic lymph nodes via distinct pathways during type 1 diabetes

Peripheral tolerance is partially controlled by the expression of peripheral tissue antigens (PTAs) in lymph node stromal cells (LNSCs). We previously identified a transcriptional regulator, deformed epidermal autoregulatory factor 1 (Deaf1), that can regulate PTA expression in LNSCs of the pancreatic lymph nodes (PLNs). During the pathogenesis of type 1 diabetes (T1D), Deaf1 is spliced to form the dominant-negative isoform Deaf1-Var1. Here we show that Deaf1-Var1 expression correlates with the severity of disease in NOD mice and is reduced in the PLNs of mice that do not develop hyperglycemia. Inflammation and hyperglycemia independently drive Deaf1 splicing through activation of the splicing factors Srsf10 and Ptbp2, respectively. Inflammation induced by injection of activated splenocytes increased Deaf1-Var1 and Srsf10, but not Ptbp2, in the PLNs of NOD.SCID mice. Hyperglycemia induced by treatment with the insulin receptor agonist S961 increased Deaf1-Var1 and Ptbp2, but not Srsf10, in the PLNs of NOD.B10 and NOD mice. Overexpression of PTBP2 and/or SRSF10 also increased human DEAF1-VAR1 and reduced PTA expression in HEK293T cells. These data suggest that during the progression of T1D, inflammation and hyperglycemia mediate the splicing of DEAF1 and loss of PTA expression in LNSCs by regulating the expression of SRSF10 and PTBP2.

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

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

Regulatory role of adenosine in insulin secretion from pancreatic β-cells--action via adenosine A₁ receptor and beyond

Under physiological conditions, insulin secretion from pancreatic β-cells is tightly regulated by different factors, including nutrients, nervous system, and other hormones. Pancreatic β-cells are also influenced by paracrine and autocrine interactions. The results of rodent studies indicate that adenosine is present within pancreatic islets and is implicated in the regulation of insulin secretion; however, effects depend on adenosine and glucose concentrations. Moreover, species differences in adenosine action were found. In rat islets, low adenosine was demonstrated to decrease glucose-induced insulin secretion and this effect is mediated via adenosine A1 receptor. In the presence of high adenosine concentrations, other mechanisms are activated and glucose-induced insulin secretion is increased. It is also well established that suppression of adenosine action increases insulin-secretory response of β-cells to glucose. In mouse islets, low adenosine concentrations do not significantly affect insulin secretion. However, in the presence of higher adenosine concentrations, potentiation of glucose-induced insulin secretion was demonstrated. It is also known that upon stimulation of insulin secretion, both rat and mouse islets release ATP. In rat islets, ATP undergoes extracellular conversion to adenosine. However, mouse islets are unable to convert extracellularly ATP to adenosine and adenosine arises from intracellular ATP degradation.

Self-antigen expression in the peripheral immune system: roles in self-tolerance and type 1 diabetes pathogenesis

Type 1 diabetes (T1D) may result from a breakdown in peripheral tolerance that is partially controlled by the ectopic expression of peripheral tissue antigens (PTAs) in lymph nodes. Various subsets of lymph node stromal cells and certain hematopoietic cells play a role in maintaining T cell tolerance. These specialized cells have been shown to endogenously transcribe, process, and present a range of PTAs to naive T cells and mediate the clonal deletion or inactivation of autoreactive cells. During the progression of T1D, inflammation leads to reduced PTA expression in the pancreatic lymph nodes and the production of novel islet antigens that T cells are not tolerized against. These events allow for the escape and activation of autoreactive T cells and may contribute to the pathogenesis of T1D. In this review, we discuss recent findings in this area and propose possible therapies that may help reestablish self-tolerance during T1D.