Cell Dysfunction In Type Research Articles

Connexin 40 Plays a Crucial Role in the Myocardial Ischemia Reperfusion Injury of Type 2 Diabetic Mice

Type 2 diabetes serves as an independent risk factor for the development of ischemic heart disease and ischemic heart diseases is a leading cause of high mortality in diabetes. In addition to atherosclerosis, microvascular disease due to endothelial dysfunction is implicated in the development and progression of ischemic heart disease. Connexin 40 (Cx40) predominantly expresses in vascular endothelial cells (ECs) and regulates endothelium‐dependent vascular relaxation and angiogenesis. We previously proved that downregulation of Cx40 is associated with coronary endothelial cell dysfunction in type 1 diabetic mice, however the involvement of Cx40 in cardiac ischemia reperfusion (I/R) injury in diabetes has never been revealed. In this study, we explore the role of Cx40 in cardiac I/R injury using type 2 diabetic mice (T2D mice). T2D mice were generated by a single injection of low‐dose streptozotocin (75 mg/kg) with a high‐fat diet (60 % kcal). T2D mice exhibited a significant decline of cardiac contractile function and larger infarction size after I/R compared to the control mice. T2D mice also showed attenuated endothelium‐dependent vascular relaxation in coronary arteries, decreased capillary density and enhanced endothelial apoptosis in the myocardium. Mouse coronary endothelial cells (MCECs) isolated from T2D mice exhibited significantly lower expression of Cx40 protein than in control MCECs. Therefore, we next examined the myocardial endothelial function using Cx40 knockout (Cx40−/−) mice. Our results demonstrated that a) Cx40 deletion impaired endothelium‐dependent relaxation via diminishing endothelium‐dependent hyperpolarization‐induced relaxation in coronary arteries, b) capillary density was decreased in the myocardium of Cx40−/− mice, c) cardiac contractility was attenuated in Cx40−/− mice, and d) infarction size after I/R was significantly increased in Cx40−/− mice compared to wild type mice. In conclusion, our data suggest that CX40 is an important protein to maintain myocardial endothelial function and decreased CX40 level might be one of crucial mechanisms which alter cardiac functions and lead to more severe damage after cardiac I/R in T2D mice.Support or Funding InformationNIH/HL115578

Urine Levels of Phthalate Metabolites and Bisphenol A in Relation to Main Metabolic Syndrome Components: Dyslipidemia, Hypertension and Type 2 Diabetes. A Pilot Study.

Human exposure to organic pollutants (some of them also called endocrine disruptors) can be associated with adverse metabolic health outcomes including type 2 diabetes. The goal of this study was to compare the urine levels of bisphenol A and phthalate metabolites in subgroups of patients with metabolic syndrome composed of patients with and without three important components of metabolic syndrome (hypertension, dyslipidemia and diabetes). We have investigated 24 hr urine samples of 168 patients with metabolic syndrome from the Metabolic Outpatient Department of General University Hospital in Prague. Using standard metabolic syndrome criteria, we classified patients as dyslipidemic (n=87), hypertensive (n=96), and type 2 diabetic (n=58). Bisphenol A and 15 metabolites of phthalates were evaluated in relation to creatinine excretion. Samples were analysed with enzymatic cleavage of glucuronide using ultra-high-performance liquid chromatography-electrospray ionization tandem mass spectrometry in one laboratory with external quality control. Four metabolites, mono-n-butyl phthalate, mono-(2-ethyl-5-hydroxyhexyl) phthalate, mono-(2-ethyl-5-oxohexyl) phthalate, and mono-(2-ethyl-5-carboxypentyl) phthalate showed significantly higher levels in diabetic compared to non-diabetic patients (p<0.001, p=0.002, p=0.002, and p=0.005, respectively). The differences remained significant after adjustment to hypertension, dyslipidemia, age, and BMI. No difference was found between either the hypertensive and non-hypertensive or dyslipidemic and non-dyslipidemic patients. There was no significant relation of bisphenol A level to diabetes, hypertension, dyslipidemia, age, and BMI. Urine levels of four phthalate metabolites were significantly higher in type 2 diabetics independently on specified predictors. Phthalate levels can be in relation to beta cell dysfunction in type 2 diabetic patients but this study is not able to show if the relation is causal.

Rac1-NADPH oxidase signaling promotes CD36 activation under glucotoxic conditions in pancreatic beta cells

We recently reported that cluster determinant 36 (CD36), a fatty acid transporter, plays a pivotal role in glucotoxicity-induced β-cell dysfunction. However, little is known about how glucotoxicity influences CD36 expression. Emerging evidence suggests that the small GTPase Rac1 is involved in the pathogenesis of beta cell dysfunction in type 2 diabetes (T2D). The primary objective of the current study was to determine the role of Rac1 in CD36 activation and its impact on β-cell dysfunction in diabetes mellitus. To address this question, we subjected INS-1 cells and human beta cells (1.1B4) to high glucose conditions (30mM) in the presence or absence of Rac1 inhibition either by NSC23766 (Rac1 GTPase inhibitor) or small interfering RNA. High glucose exposure in INS-1 and human beta cells (1.1b4) resulted in the activation of Rac1 and induced cell apoptosis. Rac1 activation mediates NADPH oxidase (NOX) activation leading to elevated ROS production in both cells. Activation of the Rac1-NOX complex by high glucose levels enhanced CD36 expression in INS-1 and human 1.1b4 beta cell membrane fractions. The inhibition of Rac1 by NSC23766 inhibited NADPH oxidase activity and ROS generation induced by high glucose concentrations in INS-1 & human 1.1b4 beta cells. Inhibition of Rac1-NOX complex activation by NSC23766 significantly reduced CD36 expression in INS-1 and human 1.1b4 beta cell membrane fractions. In addition, Rac1 inhibition by NSC23766 significantly reduced high glucose-induced mitochondrial dysfunction. Furthermore, NADPH oxidase inhibition by VAS2870 also attenuated high glucose-induced ROS generation and cell apoptosis. These results suggest that Rac1-NADPH oxidase dependent CD36 expression contributes to high glucose-induced beta cell dysfunction and cell death.

Hypothalamic AMP-Activated Protein Kinase Regulates Biphasic Insulin Secretion from Pancreatic β Cells during Fasting and in Type 2 Diabetes

Glucose-stimulated insulin secretion (GSIS) by pancreatic β cells is biphasic. However, the physiological significance of biphasic GSIS and its relationship to diabetes are not yet fully understood. This study demonstrated that impaired first-phase GSIS follows fasting, leading to increased blood glucose levels and brain glucose distribution in humans. Animal experiments to determine a possible network between the brain and β cells revealed that fasting-dependent hyperactivation of AMP-activated protein kinase in the hypothalamus inhibited first-phase GSIS by stimulating the α-adrenergic pancreatic nerve. Furthermore, abnormal excitability of this brain-β cell neural axis was involved in diabetes-related impairment of first-phase GSIS in diabetic animals. Finally, pancreatic denervation improved first-phase GSIS and glucose tolerance and ameliorated severe diabetes by preventing β cell loss in diabetic animals. These results indicate that impaired first-phase GSIS is critical for brain distribution of dietary glucose after fasting. Furthermore, β cells in individuals with diabetes mistakenly sense that they are under conditions that mimic prolonged fasting. The present study provides additional insight into both β cell physiology and the pathogenesis of β cell dysfunction in type 2 diabetes.

Pharmacological Effects and Pharmacokinetic Properties of a Dual-Function Peptide 5rolGLP-HV.

In order to better understand the therapeutic mechanism of dual-function peptide 5rolGLP-HV in treatment of treat diabetes and its complication of thrombosis, the pharmacological effects and pharmacokinetic properties of 5rolGLP-HV were conducted in this study. 5rolGLP-HV was orally administered to diabetic mice, and the hypoglycemic mechanism was investigated. Thrombotic mice were applied to study the thrombus dissolving ability of 5rolGLP-HV. The concentration of rolGLP and rHV in rat plasma following single oral dose or intravenous injection of 5rolGLP-HV was measured. Treatment with 5rolGLP-HV decreased insulin resistance (2.96±1.43 vs. 9.35±1.51, p<0.05) of diabetic mice. 5rolGLP-HV shortened the length of thrombus in thrombosis mice (2.92±0.74 vs. 5.92±1.16cm, p<0.01) and extended the thrombin time (15.35±1.22 vs. 8.67±0.89s, p<0.01) of normal mice. Meanwhile, 5rolGLP-HV restored the damage of pancreatic, liver, kidney, and adipose tissues induced in the diabetic mice. 5rolGLP-HV exhibited a fast absorption and slow elimination phase after digested into rolGLP-1 and rHV in vivo. These results suggested that 5rolGLP-HV had an ideal therapeutic potential in the prevention of β cell dysfunction in type 2 diabetes and delay of the thrombus.

Differential Activation of Innate Immune Pathways by Distinct Islet Amyloid Polypeptide (IAPP) Aggregates

Aggregation of islet amyloid polypeptide (IAPP) contributes to beta cell dysfunction in type 2 diabetes and islet transplantation. Like other amyloidogenic peptides, human IAPP induces macrophage IL-1β secretion by stimulating both the synthesis and processing of proIL-1β, a pro-inflammatory cytokine that (when chronically elevated) impairs beta cell insulin secretion. We sought to determine the specific mechanism of IAPP-induced proIL-1β synthesis. Soluble IAPP species produced early during IAPP aggregation provided a Toll-like-receptor-2- (TLR2-) dependent stimulus for NF-κB activation in HEK 293 cells and bone marrow-derived macrophages (BMDMs). Non-amyloidogenic rodent IAPP and thioflavin-T-positive fibrillar amyloid produced by human IAPP aggregation failed to activate TLR2. Blockade of TLR6 but not TLR1 prevented hIAPP-induced TLR2 activation, consistent with stimulation of a TLR2/6 heterodimer. TLR2 and its downstream adaptor protein MyD88 were required for IAPP-induced cytokine production by BMDMs, a process that is partially dependent on autoinduction by IL-1. BMDMs treated with soluble but not fibrillar IAPP provided a TLR2-dependent priming stimulus for ATP-induced IL-1β secretion, whereas late IAPP aggregates induced NLRP3-dependent IL-1β secretion by LPS-primed macrophages. Moreover, inhibition of TLR2 and depletion of islet macrophages prevented up-regulation of Il1b and Tnf expression in human IAPP-expressing transgenic mouse islets. These data suggest participation by both soluble and fibrillar aggregates in IAPP-induced islet inflammation. IAPP-induced activation of TLR2 and secretion of IL-1 may be important therapeutic targets to prevent amyloid-associated beta cell dysfunction.

Islet-specific monoamine oxidase A and B expression depends on MafA transcriptional activity and is compromised in type 2 diabetes

Lack or dysfunction of insulin producing β cells results in the development of type 1 and type 2 diabetes mellitus, respectively. Insulin secretion is controlled by metabolic stimuli (glucose, fatty acids), but also by monoamine neurotransmitters, like dopamine, serotonin, and norepinephrine. Intracellular monoamine levels are controlled by monoamine oxidases (Mao) A and B. Here we show that MaoA and MaoB are expressed in mouse islet β cells and that inhibition of Mao activity reduces insulin secretion in response to metabolic stimuli. Moreover, analysis of MaoA and MaoB protein expression in mouse and human type 2 diabetic islets shows a significant reduction of MaoB in type 2 diabetic β cells suggesting that loss of Mao contributes to β cell dysfunction. MaoB expression was also reduced in β cells of MafA-deficient mice, a mouse model for β cell dysfunction, and biochemical studies showed that MafA directly binds to and activates MaoA and MaoB transcriptional control sequences. Taken together, our results show that MaoA and MaoB expression in pancreatic islets is required for physiological insulin secretion and lost in type 2 diabetic mouse and human β cells. These findings demonstrate that regulation of monoamine levels by Mao activity in β cells is pivotal for physiological insulin secretion and that loss of MaoB expression may contribute to the β cell dysfunction in type 2 diabetes.

The Value of Neutrophil Lymphocyte Ratio in Predicting the Degree of Insulin Resistance and β Cell Dysfunction in Type 2 Diabetic Patients

Objective:Insulin resistance and progressive pancreatic β-cell failure are key factors in the development of type 2 diabetes.The aim of the present study was to define the relationship between Neutrophil Lymphocyte Ratio (NLR) and the degree of insulin resistance and β cell dysfunction in Type 2Diabetus Mellitus.Methods: This study was carried out on seventy diabetic patient attended the outpatient clinic of the diabetes and metabolism unit in Alexandria Main University Hospital (AMUH)and thirty t healthy subjects with matched age, sex and socioeconomic status as a control group. Subjects were interviewed in order to collect data using predesigned questionnaire, anthropometric measures were measured, blood samples were collected from each subject for chemical analysis. Results: NLR was higher in diabetic subjects than non-diabetic one. NLR showed significant positive correlation with HOMA-IR and no significant negative correlation with HOMA-β.Conclusion: the relation between inflammation and adipose tissue is extremely complex in diabetic patients. However, simple calculation of NLR and measurement of waist circumference can reveal inflammation in the diabetic population.

Relationship between serum secreted Frizzled-related protein 4 and the pancreatic β cell function

Objective To investigate the relationship between serum secreted frizzled-related protein 4(SFRP4) and the first-phase of glucose-stimulated insulin secretion from pancreatic β cell under different glucose tolerance statuses. Methods Fifty-six patients with newly diagnosed type 2 diabetes mellitus(T2DM group), 52 patients with impaired glucose tolerance(IGT group), and 42 subjects with normal glucose tolerance(NGT group)underwent intravenous glucose tolerance test. Fasting serum SFRP4 and interleukin(IL)-1β were assayed by ELISA. Acute insulin response(AIR), the area under the curve of the first-phase(0-10 min)insulin secretion(AUC), glucose disposition index(GDI), homeostasis model assessment for β cell function index(HOMA-β), and insulin resistance index(HOMA-IR)were calculated. Results (1)The levels of SFRP4 and IL-1β in T2DM group and IGT group were significantly higher than that in NGT group[(184.38±61.34 or 141.64±40.46 or 95.46±20.13)ng/ml, P<0.01]. AIR, AUC, and GDI in T2DM group and IGT group were significantly lower than those in NGT group(P<0.01), and these results were more significantly reduced in T2DM group compared with those in IGT group.(2)SFRP4 was negatively correlated with AIR, AUC, GDI, HOMA-β(P<0.01), and positively correlated with fasting plasma glucose, 2 h plasma glucose after glucose loading, HbA1C, IL-1β, and high sensitive C-reactive protein(P<0.01). (3)Multiple stepwise regression analysis showed that AUC, HOMA-IR, and serum IL-1β level were independently associated with SFRP4. Conclusion The concentration of serum SFRP4 is closely correlated with the glycolipid metabolic disorder, the first-phase of glucose-stimulated insulin secretion, and chronic low-grade inflammation. SFRP4 may be involved in the mechanism of β cell dysfunction in type 2 diabetes mellitus. Key words: Secreted frizzled-related protein 4; β-cell function; Intravenous glucose tolerance test; Interleukin-1β; Diabetes mellitus, type 2

Altered serotonin (5-HT) 1D and 2A receptor expression may contribute to defective insulin and glucagon secretion in human type 2 diabetes

Islet produced 5-hydroxy tryptamine (5-HT) is suggested to regulate islet hormone secretion in a paracrine and autocrine manner in rodents. Hitherto, no studies demonstrate a role for this amine in human islet function, nor is it known if 5-HT signaling is involved in the development of beta cell dysfunction in type 2 diabetes (T2D). To clarify this, we performed a complete transcriptional mapping of 5-HT receptors and processing enzymes in human islets and investigated differential expression of these genes in non-diabetic and T2D human islet donors. We show the expression of fourteen 5-HT receptors as well as processing enzymes involved in the biosynthesis of 5-HT at the mRNA level in human islets. Two 5-HT receptors (HTR1D and HTR2A) were over-expressed in T2D islet donors. Both receptors (5-HT1d and 5-HT2a) were localized to human alpha, beta and delta cells. 5-HT inhibited both insulin and glucagon secretion in non-diabetic islet donors. In islets isolated from T2D donors the amine significantly increased release of insulin in response to glucose. Our results suggest that 5-HT signaling participates in regulation of overall islet hormone secretion in non- diabetic individuals and over-expression of HTR1D and HTR2A may either contribute to islet dysfunction in T2D or arise as a consequence of an already dysfunctional islet.

SET7/9 Enzyme Regulates Cytokine-induced Expression of Inducible Nitric-oxide Synthase through Methylation of Lysine 4 at Histone 3 in the Islet β Cell

SET7/9 is an enzyme that methylates histone 3 at lysine 4 (H3K4) to maintain euchromatin architecture. Although SET7/9 is enriched in islets and contributes to the transactivation of β cell-specific genes, including Ins1 and Slc2a, SET7/9 has also been reported to bind the p65 subunit of nuclear factor κB in non-β cells and modify its transcriptional activity. Given that inflammation is a central component of β cell dysfunction in Type 1 and Type 2 diabetes, the aim of this study was to elucidate the role of SET7/9 in proinflammatory cytokine signaling in β cells. To induce inflammation, βTC3 insulinoma cells were treated with IL-1β, TNF-α, and IFN-γ. Cytokine treatment led to increased expression of inducible nitric-oxide synthase, which was attenuated by the diminution of SET7/9 using RNA interference. Consistent with previous reports, SET7/9 was co-immunoprecipitated with p65 and underwent cytosolic to nuclear translocation in response to cytokines. ChIP analysis demonstrated augmented H3K4 mono- and dimethylation of the proximal Nos2 promoter with cytokine exposure. SET7/9 was found to occupy this same region, whereas SET7/9 knockdown attenuated cytokine-induced histone methylation of the Nos2 gene. To test this relationship further, islets were isolated from SET7/9-deficient and wild-type mice and treated with IL-1β, TNF-α, and IFN-γ. Cytokine-induced Nos2 expression was reduced in the islets from SET7/9 knock-out mice. Together, our findings suggest that SET7/9 contributes to Nos2 transcription and proinflammatory cytokine signaling in the pancreatic β cell through activating histone modifications.

The anti-diabetic effects of GLP-1-gastrin dual agonist ZP3022 in ZDF rats

Aims/hypothesisCombination treatment with exendin-4 and gastrin has proven beneficial in treatment of diabetes and preservation of beta cell mass in diabetic mice. Here, we examined the chronic effects of a GLP-1-gastrin dual agonist ZP3022 on glycemic control and beta cell dysfunction in overtly diabetic Zucker Diabetic Fatty (ZDF) rats. MethodsZDF rats aged 11 weeks were dosed s.c., b.i.d. for 8 weeks with vehicle, ZP3022, liraglutide, exendin-4, or gastrin-17 with or without exendin-4. Glycemic control was assessed by measurements of HbA1c and blood glucose levels, as well as glucose tolerance during an oral glucose tolerance test (OGTT). Beta cell dynamics were examined by morphometric analyses of beta and alpha cell fractions. ResultsZP3022 improved glycemic control as measured by terminal HbA1c levels (6.2±0.12 (high dose) vs. 7.9±0.07% (vehicle), P<0.001), as did all treatments, except gastrin-17 monotherapy. In contrast, only ZP3022, exendin-4 and combination treatment with exendin-4 and gastrin-17 significantly improved glucose tolerance and increased insulin levels during an OGTT. Moreover, only ZP3022 significantly enhanced the beta cell fraction in ZDF rats, a difference of 41%, when compared to the vehicle group (0.31±0.03 vs. 0.22±0.02%, respectively, P<0.05). ConclusionThese data suggest that ZP3022 may have therapeutic potential in the prevention/delay of beta cell dysfunction in type 2 diabetes.

MicroRNA miR-124a, a negative regulator of insulin secretion, is hyperexpressed in human pancreatic islets of type 2 diabetic patients

MicroRNAs are a class of negative regulators of gene expression, which have been demonstrated to be involved in the development of endocrine pancreas and in the regulation of insulin secretion. Type 2 Diabetes (T2D) is a metabolic disease characterized by insulin-resistance in target tissues and by the functional alteration of pancreatic insulin-secreting beta-cells. Recently, we characterized the expression levels of microRNAs miR-124a and miR-375, both involved in the control of beta cell function, in human pancreatic islets obtained from T2D and from age-matched non-diabetic organ donors. We observed the hyperexpression of miR-124a in human pancreatic islets obtained from T2D patients vs non-diabetic subjects, while miR-375 did not result differentially expressed. Moreover, we demonstrated that miR-124a overexpression in MIN6-pseudoislets reduced glucose-stimulated insulin secretion. Among predicted miR-124a target genes we focused on Foxa2 and Mtpn, which are both involved in the regulation of insulin secretion and of glucose sensing. Indeed, using luciferase assay, we validated miR-124a targeting Foxa2 and Mtpn 3’UTR sequences. Accordingly, upon miR-124a inhibition in MIN6 pseudoislets, we detected the upregulation of Foxa2 and Mtpn and of other selected miR-124a predicted target genes such as Akt3, Flot2, Sirt1, and NeuroD1, indicating a possible role for such a microRNA in the control of several beta-cell functions. In conclusion, we uncovered a major hyperexpression of miR-124a in T2D islets, whose silencing resulted in increased expression of target genes of major importance for beta cell function and whose overexpression impaired glucose stimulated insulin secretion, leading to the hypothesis that an altered miR-124a expression may contribute to beta cell dysfunction in type 2 diabetes

IL-1 mediates amyloid-associated islet dysfunction and inflammation in human islet amyloid polypeptide transgenic mice.

Aggregation of islet amyloid polypeptide (IAPP) to form amyloid contributes to beta cell dysfunction in type 2 diabetes. Human but not non-amyloidogenic rodent IAPP induces islet macrophage proIL-1β synthesis. We evaluated the effect of IL-1 receptor antagonist (IL-1Ra) on islet inflammation and dysfunction in a mouse model of type 2 diabetes with amyloid formation. Lean and obese male mice (A/a or A(vy)/A at the agouti locus, respectively) with or without beta cell human IAPP expression (hIAPP(Tg/0)) were treated with PBS or IL-1Ra (50 mg kg(-1) day(-1)) from 16 weeks of age. Intraperitoneal glucose and insulin tolerance tests were performed after 8 weeks. Pancreases were harvested for histology and gene expression analysis. Aggregation of human IAPP was associated with marked upregulation of proinflammatory gene expression in islets of obese hIAPP(Tg/0) mice, together with amyloid deposition and fasting hyperglycaemia. IL-1Ra improved glucose tolerance and reduced plasma proinsulin:insulin in both lean and obese hIAPP(Tg/0) mice with no effect on insulin sensitivity. The severity and prevalence of islet amyloid was reduced by IL-1Ra in lean hIAPP (Tg/0) mice, suggesting a feed-forward mechanism by which islet inflammation promotes islet amyloid at the early stages of disease. IL-1Ra limited Il1a, Il1b, Tnf and Ccl2 expression in islets from obese hIAPP(Tg/0) mice, suggesting an altered islet inflammatory milieu. These data provide the first in vivo evidence—using a transgenic mouse model with amyloid deposits resembling those found in human islets—that IAPP-induced beta cell dysfunction in type 2 diabetes may be mediated by IL-1. Anti-IL-1 therapies may limit islet inflammation and dysfunction associated with amyloid formation.

MicroRNA-124a is hyperexpressed in type 2 diabetic human pancreatic islets and negatively regulates insulin secretion.

MicroRNAs are a class of negative regulators of gene expression, which have been shown to be involved in the development of endocrine pancreas and in the regulation of insulin secretion. Since type 2 diabetes (T2D) is characterized by beta cell dysfunction, we aimed at evaluating expression levels of miR-124a and miR-375, both involved in the control of beta cell function, in human pancreatic islets obtained from T2D and from age-matched non-diabetic organ donors. We analyzed miR-124a and miR-375 expression by real-time qRT-PCR in human pancreatic islets and evaluated the potential role of miR-124a by overexpressing or silencing such miRNA in MIN6 pseudoislets. We identified a major miR-124a hyperexpression in T2D human pancreatic islets with no differential expression of miR-375. Of note, miR-124a overexpression in MIN6 pseudoislets resulted in an impaired glucose-induced insulin secretion. In addition, miR-124a silencing in MIN6 pseudoislets resulted in increased expression of predicted target genes (Mtpn, Foxa2, Flot2, Akt3, Sirt1 and NeuroD1) involved in beta cell function. For Mtpn and Foxa2, we further demonstrated the actual binding of miR-124a to their 3UTR sequences by luciferase assay. We uncovered a major hyperexpression of miR-124a in T2D islets, whose silencing resulted in increased expression of target genes of major importance for beta cell function and whose overexpression impaired glucose-stimulated insulin secretion, leading to the hypothesis that an altered miR-124a expression may contribute to beta cell dysfunction in type 2 diabetes.

Protective effect of Schisandrae chinensis oil on pancreatic β-cells in diabetic rats.

Islet cell dysfunction in type 2 diabetes is primarily attributed to increased apoptosis of pancreatic β-Cells. The aim of the present study was to investigate the effects of Schisandrae chinensis oil on pancreatic β-Cells in type 2 diabetes mellitus rats and the associated molecular mechanisms of action. Wistar rats were randomly divided into diabetic rats and control rats, diabetic rats treated with Schisandrae chinensis oil (1mg/kg), and control rats treated with Schisandrae chinensis oil. The serum fasting blood glucose, insulin, total cholesterol, and triglyceride levels along with MDA content, SOD and CAT activities in pancreatic tissues were measured. TUNEL was used to observe the apoptosis of rat pancreatic cells. Western blot was used to determine specific protein expression. The results showed that the oil significantly decreased fasting blood glucose, total cholesterol, triglyceride levels as well as the pancreatic MDA, but increased SOD and CAT activities. The protein expression of Bcl-2, PDX-1, GLUT-2, and GCK but not caspase 3 was significantly enhanced in the oil-treated rats compared with diabetic rats. However, Bax content was not significantly different between the control and DM groups. Schisandra chinensis oil improves pancreatic β-cell function by enhancing antioxidant potential of the pancreas, upregulating the expression of anti-apoptotic genes, increasing expression of glucose metabolism, and delaying islet cell apoptosis.

Islet amyloid formation is an important determinant for inducing islet inflammation in high-fat-fed human IAPP transgenic mice.

Amyloid deposition and inflammation are characteristic of islet pathology in type 2 diabetes. The aim of this study was to determine whether islet amyloid formation is required for the development of islet inflammation in vivo. Human islet amyloid polypeptide transgenic mice and non-transgenic littermates (the latter incapable of forming islet amyloid) were fed a low-fat (10%) or high-fat (60%) diet for 12 months; high-fat feeding induces islet amyloid formation in transgenic mice. At the conclusion of the study, glycaemia, beta cell function, islet amyloid deposition, markers of islet inflammation and islet macrophage infiltration were measured. Fasting plasma glucose levels did not differ by diet or genotype. Insulin release in response to i.v. glucose was significantly greater in both high vs low fat groups, and significantly lower in both transgenic compared with non-transgenic groups. Only high-fat-fed transgenic mice developed islet amyloid and showed a trend towards reduced beta cell area. Compared with islets from low-fat-fed transgenic or high-fat-fed non-transgenic mice, islets of high-fat-fed transgenic mice displayed a significant increase in the expression of genes encoding chemokines (Ccl2, Cxcl1), macrophage/dendritic cell markers (Emr1, Itgax), NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome components (Nlrp3, Pycard, Casp1) and proinflammatory cytokines (Il1b, Tnf, Il6), as well as increased F4/80 staining, consistent with increased islet inflammation and macrophage infiltration. Our results indicate that islet amyloid formation is required for the induction of islet inflammation in this long-term high-fat-diet model, and thus could promote beta cell dysfunction in type 2 diabetes via islet inflammation.

TLR2/6 and TLR4-activated macrophages contribute to islet inflammation and impair beta cell insulin gene expression via IL-1 and IL-6.

Inflammation contributes to pancreatic beta cell dysfunction in type 2 diabetes. Toll-like receptor (TLR)-2 and -4 ligands are increased systemically in recently diagnosed type 2 diabetes patients, and TLR2- and TLR4-deficient mice are protected from the metabolic consequences of a high-fat diet. Here we investigated the role of macrophages in TLR2/6- and TLR4-mediated effects on islet inflammation and beta cell function. Genetic and pharmacological approaches were used to determine the effects of TLR2/6 and TLR4 ligands on mouse islets, human islets and purified rat beta cells. Islet macrophages were depleted and sorted by flow cytometry and the effects of TLR2/6- and TLR4-activated bone-marrow-derived macrophages (BMDMs) on beta cell function were assessed. Macrophages contributed to TLR2/6- and TLR4-induced islet Il1a/IL1A and Il1b/IL1B mRNA expression in mouse and human islets and IL-1β secretion from human islets. TLR2/6 and TLR4 ligands also reduced insulin gene expression; however, this occurred in a non-beta cell autonomous manner. TLR2/6- and TLR4-activated BMDMs reduced beta cell insulin secretion partly via reducing Ins1, Ins2, and Pdx1 mRNA expression. Antagonism of the IL-1 receptor and neutralisation of IL-6 completely reversed the effects of activated macrophages on beta cell gene expression. We conclude that islet macrophages are major contributors to islet IL-1β secretion in response to TLR2/6 and TLR4 ligands. BMDMs stimulated with TLR2/6 and TLR4 ligands reduce insulin secretion from pancreatic beta cells, partly via IL-1β- and IL-6-mediated decreased insulin gene expression.

Distinct actions of oligomers and fibrils of islet amyloid polypeptide on Toll-like receptor 2 and NLRP3 inflammasome activation (INM7P.423)

Abstract Aggregation of islet amyloid polypeptide (IAPP) to form amyloid contributes to beta cell dysfunction in type 2 diabetes. Human but not non-amyloidogenic rodent IAPP activates TLR2 and NLRP3 to induce IL-1β secretion by islet macrophages. It is unclear which form of IAPP aggregate induces IL-1β and whether this pathway is relevant to disease pathogenesis. We therefore evaluated the contributions of soluble and fibrillar IAPP to IL-1β secretion by bone marrow-derived macrophages (BMDMs) and assessed the effects of IL-1 receptor antagonist (IL-1Ra) on glucose homeostasis in transgenic mice with beta cell expression of human IAPP. BMDMs treated with soluble but not fibrillar IAPP provided a TLR2-dependent priming stimulus for ATP-induced IL-1β secretion, suggesting that pre-fibrillar species interact with TLR2. Fibrillar but not soluble IAPP aggregates were required for IL-1β secretion in LPS-primed BMDMs and are therefore likely the principal stimulus for NLRP3. Moreover, IL-1Ra (50 mg/kg/d for 8 weeks) improved glucose tolerance in obese human IAPP transgenic mice (AUC=1360±110 vs. 880±70; p&amp;lt;0.05) with no effect in wild-type littermates. These data provide the first in vivo evidence that IAPP-induced islet dysfunction in type 2 diabetes is mediated by IL-1, and suggest that both soluble and fibrillar IAPP aggregates participate in this process. Islet inflammation and amyloid formation are therefore important therapeutic targets to improve beta cell function in type 2 diabetes.

The Fractalkine/CX3CR1 System Regulates β Cell Function and Insulin Secretion

Here, we demonstrate that the fractalkine (FKN)/CX3CR1 system represents a regulatory mechanism for pancreatic islet β cell function and insulin secretion. CX3CR1 knockout (KO) mice exhibited a marked defect in glucose and GLP1-stimulated insulin secretion, and this defect was also observed invitro in isolated islets from CX3CR1 KO mice. Invivo administration of FKN improved glucose tolerance with an increase in insulin secretion. Invitro treatment of islets with FKN increased intracellular Ca(2+) and potentiated insulin secretion inboth mouse and human islets. The KO islets exhibited reduced expression of a set of genes necessary for the fully functional, differentiated β cell state, whereas treatment of wild-type (WT) islets with FKN led to increased expression of these genes. Lastly, expression of FKN in islets was decreased by aging and high-fat diet/obesity, suggesting that decreased FKN/CX3CR1 signaling could be a mechanism underlying β cell dysfunction in type 2 diabetes.