Novel time-resolved reporter mouse reveals spatial and transcriptional heterogeneity during alpha cell differentiation.

AIMS/HYPOTHESIS: Glucagon-expressing pancreatic alpha cells have attracted much attention for their plasticity to transdifferentiate into insulin-producing beta cells; however, it remains unclear precisely when, and from where, alpha cells emerge and what regulates alpha cell fate. We therefore explored the spatial and transcriptional heterogeneity of alpha cell differentiation using a novel time-resolved reporter system. METHODS: We established the mouse model, 'Gcg-Timer', in which newly generated alpha cells can be distinguished from more-differentiated cells by their fluorescence. Fluorescence imaging and transcriptome analysis were performed with Gcg-Timer mice during the embryonic and postnatal stages. RESULTS: Fluorescence imaging and flow cytometry demonstrated that green fluorescence-dominant cells were present in Gcg-Timer mice at the embryonic and neonatal stages but not after 1 week of age, suggesting that alpha cell neogenesis occurs during embryogenesis and early neonatal stages under physiological conditions. Transcriptome analysis of Gcg-Timer embryos revealed that the mRNAs related to angiogenesis were enriched in newly generated alpha cells. Histological analysis revealed that some alpha cells arise close to the pancreatic ducts, whereas the others arise away from the ducts and adjacent to the blood vessels. Notably, when the glucagon signal was suppressed by genetic ablation or by chemicals, such as neutralising glucagon antibody, green-dominant cells emerged again in adult mice. CONCLUSIONS/INTERPRETATION: Novel time-resolved analysis with Gcg-Timer reporter mice uncovered spatiotemporal features of alpha cell neogenesis that will enhance our understanding of cellular identity and plasticity within the islets. DATA AVAILABILITY: Raw and processed RNA sequencing data for this study has been deposited in the Gene Expression Omnibus under accession number GSE229090.

Postprandial Plasma Glucagon Kinetics in Type 2 Diabetes Mellitus: Comparison of Immunoassay and Mass Spectrometry.

CONTEXT: Accurate glucagon level measurements are necessary for investigation of mechanisms for postprandial hyperglycemia in type 2 diabetes. OBJECTIVE: To evaluate the accuracy of postprandial glucagon level measurements using a sandwich ELISA vs a recently established liquid chromatography-high resolution mass spectrometry (LC-HRMS) method in type 2 diabetes mellitus. DESIGN AND PARTICIPANTS: Twenty patients with type 2 diabetes treated with insulin underwent a meal test before and after administration of the dipeptidyl peptidase-4 inhibitor anagliptin for 4 weeks. Blood samples were taken serially after the meal, and glucagon levels were measured using both ELISA and LC-HRMS. We compared the change from baseline to 4 weeks (Δ0-4W) using the area under the curve for plasma glucagon during the meal test [area under the curve (AUC)0-3h] measured using ELISA and LC-HRMS. RESULTS: ELISA-based glucagon AUC0-3h was higher than LC-HRMS-based AUC0-3h at baseline and 4 weeks. However, differences in Δ0-4W-AUC0-3h measured using ELISA and LC-HRMS were not statistically significant. Additionally, Δ0-4W-AUC0-3h measured using ELISA and LC-HRMS were strongly correlated (r = 0.87, P < 0.001). CONCLUSIONS: Plasma glucagon levels during a meal test in patients with type 2 diabetes measured using ELISA were consistently higher than those measured using LC-HRMS. However, given that the changes in glucagon levels measured using ELISA before and after dipeptidyl peptidase-4 inhibitor therapy were similar to those based on LC-HRMS, this ELISA seems to be useful for evaluating the effect of the drug interventions on postprandial glucagon levels.

Enhanced Expression of the Key Mitosis Regulator Cyclin B1 Is Mediated by PDZ-Binding Kinase in Islets of Pregnant Mice.

The proliferation of pancreatic ß cells is enhanced to enable an increase in ß-cell mass and to compensate for insulin resistance during pregnancy. To elucidate the mechanisms involved, we previously investigated islets from pregnant and nonpregnant mice by gene expression profiling and found that the expression of postsynaptic density-95/Discs large/zonula occludens-1 (PDZ)-binding kinase (Pbk), a member of the mitogen-activated protein kinase kinase family, is increased in pregnant mouse islets compared with control mouse islets. Among the pregnancy hormones, treatment with estradiol upregulated Pbk expression. Inhibition of Pbk expression using a small interfering RNA for Pbk reduced bromodeoxyuridine incorporation in mouse insulinoma 6 cells, which was accompanied by a decreased expression of Ccnb1, a regulatory gene involved in mitosis. Ccnb1 expression was augmented in mouse islets during pregnancy. The forced expression of Pbk using an adenovirus system in isolated mouse islets increased Ccnb1 expression, and the Pbk inhibitor HI-TOPK-032 suppressed Ccnb1 expression in islets isolated from pregnant mice. Our results suggest that Pbk contributes to the expansion of islets during pregnancy and that Ccnb1 may assist Pbk in its role in ß-cell proliferation.

Normal pancreatic ß-cell function in mice with RIP-Cre-mediated inactivation of p62/SQSTM1.

Recent studies have suggested that decreased pancreatic ß-cell function and mass are common features of patients with type 2 diabetes mellitus. Pancreatic ß-cell homeostasis is regulated by various types of signaling molecules and stress responses. Sequestosome 1/p62 (SQSTM1, hereafter referred to as p62) is a ubiquitin-binding adaptor protein involved in cell signaling, oxidative stress, and autophagy. Because p62 appears to play an important role in maintaining mitochondrial quality control, it is possible that the loss of p62 in pancreatic ß cells contributes to mitochondrial dysfunction, and thus leading to impaired glucose tolerance. In this study we investigated the physiological roles of p62 by inactivating p62 in a ß-cell specific manner. We found that firstly, rat insulin-2 promoter-Cre (RIP-Cre)-mediated p62 inactivation did not cause body weight gain, although ubiquitous inactivation of p62 was previously shown to result in severe obesity. Secondly, we found no gross structural disorganization of the islets of p62-deficient mice. Consistent with normal islet morphology, no impairment in glucose tolerance was observed in mice with RIP-Cre-mediated p62 deletion. These results suggest that p62 is dispensable for normal islet organization and ß-cell function.

One year follow-up after a randomized controlled trial of a 130 g/day low-carbohydrate diet in patients with type 2 diabetes mellitus and poor glycemic control.

BACKGROUND & AIMS: Recently, we conducted a prospective randomized controlled trial (RCT) showing that a 6-month 130g/day low-carbohydrate diet (LCD) reduced HbA1c and BMI more than a calorie restricted diet (CRD). [1] To assess whether the benefits of the LCD persisted after the intensive intervention, we compared HbA1c and BMI between the LCD and CRD groups at 1 year after the end of the 6-month RCT. METHODS: Following the end of the 6-month RCT, patients were allowed to manage their own diets with periodic outpatient visits. One year later, we analyzed clinical and nutrition data. RESULTS: Of the 66 participants in the original study, 27 in the CRD group and 22 in the LCD group completed this trial. One year after the end of the original RCT, the carbohydrate intake was comparable between the groups (215 [189-243]/day in the CRD group and 214 (176-262) g/day in the LCD group). Compared with the baseline data, HbA1c and BMI were decreased in both groups (CRD: HbA1c -0.4 [-0.9 to 0.3] % and BMI -0.63 [-1.20 to 0.18] kg/m2; LCD: HbA1c -0.35 [-1.0 to 0.35] % and BMI -0.77 [-1.15 to -0.12] kg/m2). There were no significant differences in HbA1c and BMI between the groups. CONCLUSIONS: One year after the diet therapy intervention, the beneficial effect of the LCD on reduction of HbA1c and BMI did not persist in comparison with CRD. However, combining the data of both groups, significant improvements in HbA1c and BMI from baseline were observed. Although the superiority of the LCD disappeared 1 year after the intensive intervention, these data suggest that well-constructed nutrition therapy programs, both CRD and LCD, were equally effective in improving HbA1c for at least 1 year. TRIAL REGISTRATION: University Hospital Medical Information Network (UMIN) ID000010663.

Safety and efficacy of metformin up-titration in Japanese patients with type 2 diabetes mellitus treated with vildagliptin and low-dose metformin.

BACKGROUND: This study investigated the safety and efficacy of metformin up-titration in Japanese patients with type 2 diabetes mellitus treated with vildagliptin (100 mg/day) and low-dose metformin (500 or 750 mg/day). RESEARCH DESIGN AND METHODS: Fifty patients were randomly allocated to the control group (maintaining the initial low-dose of metformin) and the dose increase group (up-titrating of metformin to 1,500-2,250 mg/day) for 24 weeks. The primary outcome was change in HbA1c from baseline to 24 weeks. RESULTS: Among the 25 patients allocated to the dose increase group, four patients were not able to complete the study protocol because of gastrointestinal symptoms. HbA1c in the dose increase group was significantly but modestly lower than in the control group (change in HbA1c: 0.22 ± 0.57 vs. -0.15 ± 0.58%, group comparison, P < 0.05). The dose increase group did not gain weight during the study period, and no hypoglycemic events were reported in both groups. The rate of gastrointestinal symptoms in the dose increase group was profoundly higher than in the control group (32 vs. 0%, P < 0.01). CONCLUSIONS: In Japanese patients with type 2 diabetes treated with vildagliptin and low-dose metformin, metformin up-titration significantly but modestly improved glycemic control without hypoglycemia and weight gain.

Relationships between lifestyle patterns and cardio-renal-metabolic parameters in patients with type 2 diabetes mellitus: A cross-sectional study.

INTRODUCTION: While individuals tend to show accumulation of certain lifestyle patterns, the effect of such patterns in real daily life on cardio-renal-metabolic parameters remains largely unknown. This study aimed to assess clustering of lifestyle patterns and investigate the relationships between such patterns and cardio-renal-metabolic parameters. PARTICIPANTS AND METHODS: The study participants were 726 Japanese type 2 diabetes mellitus (T2DM) outpatients free of history of cardiovascular diseases. The relationship between lifestyle patterns and cardio-renal-metabolic parameters was investigated by linear and logistic regression analyses. RESULTS: Factor analysis identified three lifestyle patterns. Subjects characterized by evening type, poor sleep quality and depressive status (type 1 pattern) had high levels of HbA1c, alanine aminotransferase and albuminuria. Subjects characterized by high consumption of food, alcohol and cigarettes (type 2 pattern) had high levels of γ-glutamyl transpeptidase, triglycerides, HDL-cholesterol, blood pressure, and brachial-ankle pulse wave velocity. Subjects characterized by high physical activity (type 3 pattern) had low uric acid and mild elevation of alanine aminotransferase and aspartate aminotransferase. In multivariate regression analysis adjusted by age, gender and BMI, type 1 pattern was associated with higher HbA1c levels, systolic BP and brachial-ankle pulse wave velocity. Type 2 pattern was associated with higher HDL-cholesterol levels, triglycerides, aspartate aminotransferase, ɤ- glutamyl transpeptidase levels, and diastolic BP. CONCLUSIONS: The study identified three lifestyle patterns that were associated with distinct cardio-metabolic-renal parameters in T2DM patients. TRIAL REGISTRATION: UMIN000010932.

Efficacy and Safety of Vildagliptin as an Add-On Therapy in Inadequately Controlled Type 2 Diabetes Patients Treated With Basal Insulin.

BACKGROUND: The aim of this study was to investigate the efficacy and safety of vildagliptin as an add-on therapy for patients with type 2 diabetes mellitus inadequately controlled with basal insulin. METHODS: Twenty-four patients treated with basal insulin and oral anti-diabetes drugs were randomly allocated into two groups: the control group (did not receive any add-on drugs) and vildagliptin group (received vildagliptin 100 mg/day for 6 months). The primary outcome was changes in hemoglobin A1c (HbA1c) from baseline to end of study. RESULTS: Treatment with vildagliptin significantly reduced HbA1c from 8.1±0.7% at baseline to 7.1±0.7% (P < 0.01), while there was no significant change of HbA1c in the control group. Vildagliptin group showed significant reduction of HbA1c compared with control group (-1.0±0.3% vs. 0.2±0.8%, P < 0.01). In addition, vildagliptin group showed a significant increase in 1,5-anhydroglucitol compared with the control group (4.5 ± 3.4 vs. 0.5 ± 4.1 µg/mL, P < 0.05). Mild hypoglycemia was reported in one patient of the vildagliptin group and two patients of the control group. CONCLUSION: Vildagliptin improved glycemic control without increasing hypoglycemia in Japanese type 2 diabetes inadequately controlled with basal insulin treatment and other oral anti-diabetes drugs. This study was registered with UMIN (University Hospital Medical Information Network ID#000010849).

A randomized controlled trial of 130 g/day low-carbohydrate diet in type 2 diabetes with poor glycemic control.

BACKGROUND & AIMS: The usefulness of low-carbohydrate diet (LCD) for Japanese patients with type 2 diabetes mellitus (T2DM) has not been fully investigated. Therefore, we compared the effectiveness and safety of LCD with calorie restricted diet (CRD). METHODS: This prospective, randomized, open-label, comparative study included 66 T2DM patients with HbA1c >7.5% even after receiving repeated education programs on CRD. They were randomly allocated to either the 130g/day LCD group (n = 33) or CRD group (n = 33). Patients received personal nutrition education of CRD or LCD for 30 min at baseline, 1, 2, 4, and 6 months. Patients of the CRD group were advised to maintain the intake of calories and balance of macronutrients (28× ideal body weight calories per day). Patients of the LCD group were advised to maintain the intake of 130 g/day carbohydrate without other specific restrictions. Several parameters were assessed at baseline and 6 months after each intervention. The primary endpoint was a change in HbA1c level from baseline to the end of the study. RESULTS: At baseline, BMI and HbA1c were 26.5 (24.6-30.1) and 8.3 (8.0-9.3), and 26.7 (25.0-30.0) kg/m2 and 8.0 (7.6-8.9) %, in the CRD and LCD, respectively. At the end of the study, HbA1c decreased by -0.65 (-1.53 to -0.10) % in the LCD group, compared with 0.00 (-0.68 to 0.40) % in the CRD group (p < 0.01). Also, the decrease in BMI in the LCD group [-0.58 (-1.51 to -0.16) kg/m2] exceeded that observed in the CRD group (p = 0.03). CONCLUSIONS: Our study demonstrated that 6-month 130 g/day LCD reduced HbA1c and BMI in poorly controlled Japanese patients with T2DM. LCD is a potentially useful nutrition therapy for Japanese patients who cannot adhere to CRD. This trial was registered at http://www.umin.ac.jp/english/ (University Hospital Medical Information Network: study ID number 000010663).

Effect of treatment guidance using a retrospective continuous glucose monitoring system on glycaemic control in outpatients with type 2 diabetes mellitus: A randomized controlled trial.

OBJECTIVES: To assess the effect of treatment guidance based on data from a continuous glucose monitoring (CGM) device on glycaemic control, and patient satisfaction, in patients with type 2 diabetes mellitus (T2DM). METHODS: Patients with poorly-controlled T2DM treated with insulin were randomly assigned to the intervention or nonintervention group. Continuous blood-glucose levels were recorded for 4-5 days using a CGM device on three separate occasions during the 8-month study period. The intervention group received treatment guidance based on the CGM data; the nonintervention group received advice based on blood glucose and glycosylated haemoglobin (HbA1c) levels. RESULTS: A total of 34 patients were enrolled in the study. The mean ± SD baseline HbA1c was 8.2 ± 1.2% in the intervention group and 8.2 ± 0.9% in the nonintervention group. At the study end, there was no significant difference in the change from baseline of HbA1c between the two groups. There was also no significant difference in the change from baseline in the Diabetes Treatment Satisfaction Questionnaire score between the two groups. CONCLUSIONS: The present study did not demonstrate that treatment guidance using retrospective CGM data was effective for improving glycaemic control and therapeutic satisfaction in Japanese patients with T2DM.

Switching from Twice-Daily Basal Insulin Injections to Once-Daily Insulin Degludec Injection for Basal-Bolus Insulin Regimen in Japanese Patients with Type 1 Diabetes: A Pilot Study.

The aim of this study was to investigate the efficacy of insulin degludec used for basal-bolus insulin regimen after switching from twice-daily basal insulin in Japanese patients with type 1 diabetes mellitus. The subjects were 22 type 1 diabetes patients treated with basal-bolus insulin regimen with twice-daily basal insulin. Basal insulin was switched to once-daily injection of insulin degludec with 10% dose reduction. HbA1c and fasting plasma glucose (FPG) were measured before and 12 weeks after switching. The frequency of hypoglycemic episodes, standard deviation (SD) of blood glucose, and mean of daily difference (MODD) were evaluated by continuous glucose monitoring (CGM) before and 4 weeks after switching. HbA1c and FPG before and 12 weeks after switching were comparable (HbA1c 8.5 ± 1.4 versus 8.7 ± 1.6%, P = 0.28; FPG 203.2 ± 81.2 versus 206.5 ± 122.4 mg/dL, P = 0.91). The frequency of hypoglycemia during nighttime was not significantly different at 4 weeks after switching (14.4 ± 17.0 versus 11.1 ± 15.0%, P = 0.45). In addition, SD and MODD before and 4 weeks after switching were also comparable. In conclusion, glycemic control under once-daily insulin degludec injection was almost comparable to that under twice-daily basal insulin injections in Japanese type 1 diabetes patients. This study was registered with ID: UMIN000010474.

Expression mechanism of tryptophan hydroxylase 1 in mouse islets during pregnancy.

Serotonin signaling plays key roles in augmentation of pancreatic ß-cell function during pregnancy. Increased expression of tryptophan hydroxylase 1 (Tph1), a rate-limiting enzyme for serotonin synthesis by lactogenic hormones, is involved in this phenomenon. To investigate its mechanisms, we here performed 5'-RACE and identified ß-cell-specific transcription initiation sites for Tph1. Prolactin enhanced the expression of mRNA containing these exons; however, reporter gene plasmids containing the proximal 5'-flanking region of these exons did not show prolactin responsiveness in MIN6 cells. Prolactin-induced Tph1 expression was inhibited by a Jak2 inhibitor and was partially inhibited by an MEK1/2 or PI3K inhibitor. Therefore, we analyzed interferon γ-activated sequences (GAS) and found GAS-A about 9-kbp upstream of the transcription start site. The reporter gene plasmid containing the GAS-A region linked to a heterologous promoter showed increased promoter activity by prolactin, which was inhibited by the forced expression of a dominant-negative mutant form of Stat5A and a Jak2 inhibitor. Chromatin immunoprecipitation analysis showed that prolactin treatment augmented Stat5 binding to the GAS-A region in MIN6 cells, as well as in isolated mouse islets, and that Stat5 recognized the GAS-A region in pregnant mouse islets. In addition, the transactivation activity of Stat5 was enhanced by prolactin through the Erk and PI3K pathways in MIN6 cells. Finally, serotonin expression was attenuated in islets of ß-cell-specific Stat5-deficient mice compared with that of control littermates during pregnancy. Our findings suggest that prolactin-induced Tph1 expression is mediated by the activation of Jak2/Stat5, Erk, and PI3K pathways in ß cells.

SET7/9 Enzyme Regulates Cytokine-induced Expression of Inducible Nitric-oxide Synthase through Methylation of Lysine 4 at Histone 3 in the Islet ß 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 ß cell-specific genes, including Ins1 and Slc2a, SET7/9 has also been reported to bind the p65 subunit of nuclear factor κB in non-ß cells and modify its transcriptional activity. Given that inflammation is a central component of ß 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 ß cells. To induce inflammation, ßTC3 insulinoma cells were treated with IL-1ß, 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-1ß, 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 ß cell through activating histone modifications.

Increased expression of ERp57/GRP58 is protective against pancreatic beta cell death caused by autophagic failure.

Autophagy is a tightly regulated self-digestion system. As in other cell types, autophagy plays an essential role in the homeostasis of pancreatic beta cells. However, the mechanisms involved in the deterioration of beta cell function caused by autophagic failure have not yet been fully elucidated. To gain insight into its mechanisms, we compared the protein expression of islets from beta cell-specific Atg7-deficient mice (Atg7(Δß-cell) mice) and their controls (Atg7(f/f) mice). Liquid chromatography/mass spectrometry after 1-dimensional electrophoresis identified the increased expression of ERp57/GRP58 in islets isolated from Atg7(Δß-cell) mice compared with those from Atg7(f/f) mice. The expression level of ERp57 was also elevated in rat insulinoma INS-1 cells by inducible knock-down of the atg7-gene. In Atg7 knock-down INS-1 cells, the suppression of ERp57 expression by siRNA resulted in an increase in the level of cleaved Caspase-3 protein and a decrease in the number of live cells. Furthermore, cell cycle analyses demonstrated that the suppressed expression of ERp57 increased the sub-G1 population. These data reveal that increased expression of ERp57 may contribute to the protection from beta cell death caused by autophagic failure.

Human IAPP-induced pancreatic ß cell toxicity and its regulation by autophagy.

Pancreatic islets in patients with type 2 diabetes mellitus (T2DM) are characterized by loss of ß cells and formation of amyloid deposits derived from islet amyloid polypeptide (IAPP). Here we demonstrated that treatment of INS-1 cells with human IAPP (hIAPP) enhances cell death, inhibits cytoproliferation, and increases autophagosome formation. Furthermore, inhibition of autophagy increased the vulnerability of ß cells to the cytotoxic effects of hIAPP. Based on these in vitro findings, we examined the pathogenic role of hIAPP and its relation to autophagy in hIAPP-knockin mice. In animals fed a standard diet, hIAPP had no toxic effects on ß cell function; however, hIAPP-knockin mice did not exhibit a high-fat-diet-induced compensatory increase in ß cell mass, which was due to limited ß cell proliferation and enhanced ß cell apoptosis. Importantly, expression of hIAPP in mice with a ß cell-specific autophagy defect resulted in substantial deterioration of glucose tolerance and dispersed cytoplasmic expression of p62-associated toxic oligomers, which were otherwise sequestrated within p62-positive inclusions. Together, our results indicate that increased insulin resistance in combination with reduced autophagy may enhance the toxic potential of hIAPP and enhance ß cell dysfunction and progression of T2DM.

Gut dysbiosis and detection of "live gut bacteria" in blood of Japanese patients with type 2 diabetes.

OBJECTIVE: Mounting evidence indicates that the gut microbiota are an important modifier of obesity and diabetes. However, so far there is no information on gut microbiota and "live gut bacteria" in the systemic circulation of Japanese patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: Using a sensitive reverse transcription-quantitative PCR (RT-qPCR) method, we determined the composition of fecal gut microbiota in 50 Japanese patients with type 2 diabetes and 50 control subjects, and its association with various clinical parameters, including inflammatory markers. We also analyzed the presence of gut bacteria in blood samples. RESULTS: The counts of the Clostridium coccoides group, Atopobium cluster, and Prevotella (obligate anaerobes) were significantly lower (P < 0.05), while the counts of total Lactobacillus (facultative anaerobes) were significantly higher (P < 0.05) in fecal samples of diabetic patients than in those of control subjects. Especially, the counts of Lactobacillus reuteri and Lactobacillus plantarum subgroups were significantly higher (P < 0.05). Gut bacteria were detected in blood at a significantly higher rate in diabetic patients than in control subjects (28% vs. 4%, P < 0.01), and most of these bacteria were Gram-positive. CONCLUSIONS: This is the first report of gut dysbiosis in Japanese patients with type 2 diabetes as assessed by RT-qPCR. The high rate of gut bacteria in the circulation suggests translocation of bacteria from the gut to the bloodstream.

Beneficial effects of vildagliptin combined with miglitol on glucose tolerance and islet morphology in diet-controlled db/db mice.

Dipeptidyl peptidase-4 (DPP-4) inhibitors improve glycemic control in patients with type 2 diabetes primarily by increasing plasma active glucagon-like peptide-1 (GLP-1) levels. While various combination therapies based on DPP-4 inhibitors have been proposed for treatment of type 2 diabetes, the effects of combination therapy of DPP-4 inhibitors and alpha-glucosidase inhibitors on ß-cell function are less characterized. We evaluated the effects of long-term treatment with vildagliptin, a DPP-4 inhibitor, on metabolic parameters and ß-cell function, in combination with miglitol, an alpha-glucosidase inhibitor, in diet-controlled db/db mice. In this study, 6-week-old male db/db mice were provided with standard chow twice a day for 6 weeks. Meal tolerance tests and glucose tolerance tests showed that the combination therapy of vildagliptin with miglitol, but not each alone, suppressed postprandial glycemic excursion, enhanced postprandial active GLP-1 levels and prevented deterioration of glucose tolerance in the db/db mice. The combination treatment did not alter ß-cell mass, but resulted in preserved expression of glucose transporter 2, Zinc transporter 8 and MafA and reduced the number of α cells. These results suggest that the combination of vildagliptin and miglitol prevents the development of overt diabetes in diet-controlled pre-diabetic db/db mice by normalizing postprandial glucose and incretin response, and by preserving ß-cell structure and the expression of factors essential for ß-cell function.

Exercise-induced enhancement of insulin sensitivity is associated with accumulation of M2-polarized macrophages in mouse skeletal muscle.

Exercise enhances insulin sensitivity in skeletal muscle, but the underlying mechanism remains obscure. Recent data suggest that alternatively activated M2 macrophages enhance insulin sensitivity in insulin target organs such as adipose tissue and liver. Therefore, the aim of this study was to determine the role of anti-inflammatory M2 macrophages in exercise-induced enhancement of insulin sensitivity in skeletal muscle. C57BL6J mice underwent a single bout of treadmill running (20 m/min, 90 min). Twenty-four hours later, ex vivo insulin-stimulated 2-deoxy glucose uptake was found to be increased in plantaris muscle. This change was associated with increased number of CD163-expressing macrophages (i.e. M2-polarized macrophages) in skeletal muscle. Systemic depletion of macrophages by pretreatment of mice with clodronate-containing liposome abrogated both CD163-positive macrophage accumulation in skeletal muscle as well as the enhancement of insulin sensitivity after exercise, without affecting insulin-induced phosphorylation of Akt and AS160 or exercise-induced GLUT4 expression. These results suggest that accumulation of M2-polarized macrophages is involved in exercise-induced enhancement of insulin sensitivity in mouse skeletal muscle, independently of the phosphorylation of Akt and AS160 and expression of GLUT4.

Exendin-4 improves ß-cell function in autophagy-deficient ß-cells.

Autophagy is cellular machinery for maintenance of ß-cell function and mass. The implication of autophagy failure in ß-cells on the pathophysiology of type 2 diabetes and its relation to the effect of treatment of diabetes remains elusive. Here, we found increased expression of p62 in islets of db/db mice and patients with type 2 diabetes mellitus. Treatment with exendin-4, a glucagon like peptide-1 receptor agonist, improved glucose tolerance in db/db mice without significant changes in p62 expression in ß-cells. Also in ß-cell-specific Atg7-deficient mice, exendin-4 efficiently improved blood glucose level and glucose tolerance mainly by enhanced insulin secretion. In addition, we found that exendin-4 reduced apoptotic cell death and increased proliferating cells in the Atg7-deficient islets, and that exendin-4 counteracted thapsigargin-induced cell death of isolated islets augmented by autophagy deficiency. Our results suggest the potential involvement of reduced autophagy in ß-cell dysfunction in type 2 diabetes. Without altering the autophagic state in ß-cells, exendin-4 improves glucose tolerance associated with autophagy deficiency in ß-cells. This is mainly achieved through augmentation of insulin secretion. In addition, exendin-4 prevents apoptosis and increases the proliferation of ß-cells associated with autophagy deficiency, also without altering the autophagic machinery in ß-cells.

The diabetes-susceptible gene SLC30A8/ZnT8 regulates hepatic insulin clearance.

Recent genome-wide association studies demonstrated that common variants of solute carrier family 30 member 8 gene (SLC30A8) increase susceptibility to type 2 diabetes. SLC30A8 encodes zinc transporter-8 (ZnT8), which delivers zinc ion from the cytoplasm into insulin granules. Although it is well known that insulin granules contain high amounts of zinc, the physiological role of secreted zinc remains elusive. In this study, we generated mice with ß cell-specific Slc30a8 deficiency (ZnT8KO mice) and demonstrated an unexpected functional linkage between Slc30a8 deletion and hepatic insulin clearance. The ZnT8KO mice had low peripheral blood insulin levels, despite insulin hypersecretion from pancreatic ß cells. We also demonstrated that a substantial amount of the hypersecreted insulin was degraded during its first passage through the liver. Consistent with these findings, ZnT8KO mice and human individuals carrying rs13266634, a major risk allele of SLC30A8, exhibited increased insulin clearance, as assessed by c-peptide/insulin ratio. Furthermore, we demonstrated that zinc secreted in concert with insulin suppressed hepatic insulin clearance by inhibiting clathrin-dependent insulin endocytosis. Our results indicate that SLC30A8 regulates hepatic insulin clearance and that genetic dysregulation of this system may play a role in the pathogenesis of type 2 diabetes.