Casein kinase 2 phosphorylates and stabilizes C/EBPß in pancreatic ß cells.

During the development of type 2 diabetes, endoplasmic reticulum (ER) stress leads to pancreatic ß cell failure. CCAAT/enhancer-binding protein (C/EBP) ß is highly induced by ER stress and AMP-activated protein kinase (AMPK) suppression in pancreatic ß cells, and its accumulation reduces pancreatic ß cell mass. We investigated the phosphorylation state of C/EBPß under these conditions. Casein kinase 2 (CK2) was found to co-localize with C/EBPß in MIN6 cells. It phosphorylated S222 of C/EBPß, a previously unidentified phosphorylation site. We found that C/EBPß is phosphorylated by CK2 under AMPK suppression and ER stress, which are important from the viewpoint of the worsening pathological condition of type 2 diabetes, such as decreased insulin secretion and apoptosis of pancreatic ß cells.

Paternal allelic mutation at the Kcnq1 locus reduces pancreatic ß-cell mass by epigenetic modification of Cdkn1c.

Genetic factors are important determinants of the onset and progression of diabetes mellitus. Numerous susceptibility genes for type 2 diabetes, including potassium voltage-gated channel, KQT-like subfamily Q, member1 (KCNQ1), have been identified in humans by genome-wide analyses and other studies. Experiments with genetically modified mice have also implicated various genes in the pathogenesis of diabetes. However, the possible effects of the parent of origin for diabetes susceptibility alleles on disease onset have remained unclear. Here, we show that a mutation at the Kcnq1 locus reduces pancreatic ß-cell mass in mice by epigenetic modulation only when it is inherited from the father. The noncoding RNA KCNQ1 overlapping transcript1 (Kcnq1ot1) is expressed from the Kcnq1 locus and regulates the expression of neighboring genes on the paternal allele. We found that disruption of Kcnq1 results in reduced Kcnq1ot1 expression as well as the increased expression of cyclin-dependent kinase inhibitor 1C (Cdkn1c), an imprinted gene that encodes a cell cycle inhibitor, only when the mutation is on the paternal allele. Furthermore, histone modification at the Cdkn1c promoter region in pancreatic islets was found to contribute to this phenomenon. Our observations suggest that the Kcnq1 genomic region directly regulates pancreatic ß-cell mass and that genomic imprinting may be a determinant of the onset of diabetes mellitus.

Compensatory hyperinsulinemia in high-fat diet-induced obese mice is associated with enhanced insulin translation in islets.

A high-fat diet (HF) is associated with obesity, insulin resistance, and hyperglycemia. Animal studies have shown compensatory mechanisms in pancreatic ß-cells after high fat load, such as increased pancreatic ß-cell mass, enhanced insulin secretion, and exocytosis. However, the effects of high fat intake on insulin synthesis are obscure. Here, we investigated whether insulin synthesis was altered in correlation with an HF diet, for the purpose of obtaining further understanding of the compensatory mechanisms in pancreatic ß-cells. Mice fed an HF diet are obese, insulin resistant, hyperinsulinemic, and glucose intolerant. In islets of mice fed an HF diet, more storage of insulin was identified. We analyzed insulin translation in mouse islets, as well as in INS-1 cells, using non-radioisotope chemicals. We found that insulin translational levels were significantly increased in islets of mice fed an HF diet to meet systemic demand, without altering its transcriptional levels. Our data showed that not only increased pancreatic ß-cell mass and insulin secretion but also elevated insulin translation is the major compensatory mechanism of pancreatic ß-cells.

Ablation of PDK1 in pancreatic beta cells induces diabetes as a result of loss of beta cell mass.

The total mass of islets of Langerhans is reduced in individuals with type 2 diabetes, possibly contributing to the pathogenesis of this condition. Although the regulation of islet mass is complex, recent studies have suggested the importance of a signaling pathway that includes the insulin or insulin-like growth factor-1 receptors, insulin receptor substrate and phosphatidylinositol (PI) 3-kinase. 3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a serine-threonine kinase that mediates signaling downstream of PI 3-kinase. Here we show that mice that lack PDK1 specifically in pancreatic beta cells (betaPdk1-/- mice) develop progressive hyperglycemia as a result of a loss of islet mass. The mice show reductions in islet density as well as in the number and size of cells. Haploinsufficiency of the gene for the transcription factor Foxo1 resulted in a marked increase in the number, but not the size, of cells and resulted in the restoration of glucose homeostasis in betaPdk1-/- mice. These results suggest that PDK1 is important in maintenance of pancreatic cell mass and glucose homeostasis.

The relationship between pancreatic atrophy after steroid therapy and diabetes mellitus in patients with autoimmune pancreatitis.

BACKGROUND/OBJECTIVES: Many patients with autoimmune pancreatitis (AIP) have an association with diabetes mellitus. It has not been clarified whether steroid therapy for AIP improves or worsens the condition of diabetes mellitus. The aim of this study was thus to investigate the relationship between pancreatic atrophy after steroid therapy and the clinical course of diabetes. METHODS: Thirty-one AIP patients, who were treated by steroid therapy, were included in this study during December 2005 to March 2013. Pancreatic atrophy 6 months after the beginning of steroid therapy was defined to be present when the width of the pancreatic body was less than 10 mm. The relationships between pancreatic atrophy and patient characteristics as well as the course of diabetes were examined. RESULTS: Steroid therapy was effective in all treated patients. Pancreatic atrophy was observed in 12 patients and not in 19 patients after the steroid therapy. AIP patients with pancreatic atrophy showed higher incidences of diabetes mellitus (p = 0.001, 9/12 vs. 2/19), diabetes control worsening (p = 0.007, 7/12 vs. 2/17), and new onset of diabetes (p = 0.02, 5/7 vs. 1/18) than those without atrophy. It was not associated with gender, other organ involvement, pattern of pancreas swelling (diffuse/focal), serum IgG4 level, alcohol intake, and pancreatic calcification on CT. Patients with new onset of diabetes needed insulin therapy, even in the maintenance therapy of AIP. CONCLUSIONS: AIP patients with pancreatic atrophy after steroid therapy have a high incidence of diabetes mellitus. New onset of diabetes is closely associated with pancreatic atrophy after steroid therapy.

Association of short-term changes in HbA1c with body composition and the importance of muscle maintenance in patients with Type 2 diabetes.

AIMS: This study aimed to investigate the relationship between changes in glucose metabolism and body composition in patients with diabetes. METHODS: We included 380 patients with type 2 diabetes, who underwent bioelectrical impedance analysis, in this longitudinal study. Changes in HbA1c (ΔHbA1c) levels and body composition indices were compared between baseline and 6 months. A multivariate analysis was performed to examine the relationship between ΔHbA1c and changes in body composition. RESULTS: HbA1c levels were significantly decreased at 6 months (P < 0.01), but there was no significant change in BMI. A linear multiple regression analysis showed that ΔHbA1c was negatively correlated with changes in muscle mass (ß = -0.18; P = 0.047) and bone mineral content (ß = -0.28; P < 0.001), but there was no significant association between ΔHbA1c levels and a change in body fat percentage. CONCLUSIONS: This study shows a limited association between short-term changes in glucose metabolism and changes in body composition in patients with type 2 diabetes. Therefore, interventions aimed at reducing adiposity may not affect glucose metabolism in the short term, while interventions focused on maintaining or enhancing muscle mass and bone mineral content may play an important role in diabetes management.

Association of scan frequency with CGM-derived metrics and influential factors in adults with type 1 diabetes mellitus.

Introduction: This study aimed to investigate the association between scan frequency and intermittently scanned continuous glucose monitoring (isCGM) metrics and to clarify the factors affecting scan frequency in adults with type 1 diabetes mellitus (T1D). Methods: We enrolled adults with T1D who used FreeStyle® Libre. Scan and self-monitoring of blood glucose (SMBG) frequency and CGM metrics from the past 90-day glucose data were collected. The receiver operating characteristic curve was plotted to obtain the optimal cutoff values of scan frequency for the target values of time in range (TIR), time above range (TAR), and time below range (TBR). Results: The study was conducted on 211 adults with T1D (mean age, 50.9 ± 15.2 years; male, 40.8%; diabetes duration, 16.4 ± 11.9 years; duration of CGM use, 2.1 ± 1.0 years; and mean HbA1c, 7.6 ± 0.9%). The average scan frequency was 10.5 ± 3.3 scan/day. Scan frequency was positively correlated with TIR and negatively correlated with TAR, although it was not significantly correlated with TBR. Scan frequency was positively correlated with the hypoglycemia fear survey-behavior score, while it was negatively correlated with some glycemic variability metrics. Adult patients with T1D and good exercise habits had a higher scan frequency than those without exercise habits. The AUC for > 70% of the TIR was 0.653, with an optimal cutoff of 11 scan/day. Conclusions: In real-world conditions, frequent scans were linked to improved CGM metrics, including increased TIR, reduced TAR, and some glycemic variability metrics. Exercise habits and hypoglycemia fear-related behavior might affect scan frequency. Our findings could help healthcare professionals use isCGM to support adults with T1D.Clinical Trial Registry No. UMIN000039376.

Determinants of phase angle in Japanese patients with diabetes.

Phase angle, obtained using bioelectrical impedance analysis, non-invasively reflects the whole-body cellular condition and nutritional status and may be helpful as a prognostic factor. Patients with diabetes had a smaller phase angle than healthy subjects. However, the clinical significance of phase angle has not yet been elucidated. Therefore, the purpose of this study was to clarify the relationship between phase angle and HbA1c in patients with diabetes and the clinical relevance of phase angle. A retrospective, multicenter, cross-sectional study was conducted with Japanese patients with diabetes. Body composition was determined with bioelectrical impedance analysis, and this was used to obtain phase angle. Phase angle was assessed in relation to clinical parameters, body composition parameters, and HbA1c levels. A total of 655 patients were enrolled (400 men and 255 women, aged 57.1 ± 14.8 years, body mass index 25.6 ± 5.2 kg/m2, HbA1c 8.1 ± 1.9%). Even in patients with diabetes, the phase angle was higher in men than in women and did not differ between the types of diabetes. Multiple regression analysis, performed with phase angle as the objective variable, and age, sex, diabetes type, HbA1c, albumin level, and body mass index as explanatory variables, revealed that phase angle was negatively affected by HbA1c (B = - 0.043, 95% Confidence interval: - 0.07 to - 0.02, p < 0.001). HbA1c, age, sex, albumin level, and body mass index were independent determinants of phase angle in participants with diabetes.

To Use or Not to Use a Self-monitoring of Blood Glucose System? Real-world Flash Glucose Monitoring Patterns Using a Cluster Analysis of the FGM-Japan Study.

Objective This study investigated self-monitoring of blood glucose (SMBG) adherence and flash glucose monitoring patterns using a cluster analysis in Japanese type 1 diabetes (T1D) patients with intermittently scanned continuous glucose monitoring (isCGM). Methods We measured SMBG adherence and performed a data-driven cluster analysis using a hierarchical clustering in T1D patients from Japan using the FreeStyle Libre system. Clusters were based on three variables (testing glucose frequency and referred Libre data for hyperglycemia or hypoglycemia). Patients We enrolled 209 participants. Inclusion criteria were patients with T1D, duration of isCGM use ≥3 months, age ≥20 years old, and regular attendance at the collaborating center. Results The rate of good adherence to SMBG recommended by a doctor was 85.0%. We identified three clusters: cluster 1 (low SMBG test frequency but high reference to Libre data, 17.7%), cluster 2 (high SMBG test frequency but low reference to Libre data, 34.0%), and cluster 3 (high SMBG test frequency and high reference to Libra data, 48.3%). Compared with other clusters, individuals in cluster 1 were younger, those in cluster 2 had a shorter Libre duration, and individuals in cluster 3 had lower time-in-range, higher severe diabetic distress, and high intake of snacks and sweetened beverages. There were no marked differences in the incidence of diabetic complications and rate of wearing the Libre sensor among the clusters. Conclusion We stratified the patients into three subgroups with varied clinical characteristics and CGM metrics. This new substratification might help tailor diabetes management of patients with T1D using isCGM.

Factors associated with hemoglobin glycation index in adults with type 1 diabetes mellitus: The FGM-Japan study.

AIMS/INTRODUCTION: The discrepancy between HbA1c and glucose exposure may have significant clinical implications; however, the association between the hemoglobin glycation index (HGI) and clinical parameters in type 1 diabetes remains controversial. This study aimed to find the factors associated with HGI (laboratory HbA1c - predicted HbA1c derived from the continuous glucose monitoring [CGM]). MATERIALS AND METHODS: We conducted a cross-sectional study of adults with type 1 diabetes (n = 211, age 50.9 ± 15.2 years old, female sex = 59.2%, duration of CGM use = 2.1 ± 1.0 years). All subjects wore the CGM for 90 days before HbA1c measurement. Data derived from the FreeStyle Libre sensor were used to calculate the glucose management indicator (GMI) and glycemic variability (GV) parameters. HGI was defined as the difference between the GMI and the laboratory HbA1c levels. The participants were divided into three groups according to the HGI tertile (low, moderate, and high). Multivariate regression analyses were performed. RESULTS: The female sex ratio, HbA1c, and % coefficient of variation (%CV) significantly increased over the HGI tertile, while eGFR and Hb decreased over the HGI tertile. In multivariate analysis, the factors associated with HGI were %CV and eGFR, after adjusting for HbA1c level and sex (R2  = 0.44). CONCLUSIONS: This study demonstrated that HGI is associated with female sex, eGFR, and some glycemic variability indices, independently of HbA1c. Minimizing glycemic fluctuations might reduce HGI. This information provides diabetic health professionals and patients with personalized diabetes management for adults with type 1 diabetes.

Deletion of Cdkn1b ameliorates hyperglycemia by maintaining compensatory hyperinsulinemia in diabetic mice.

The protein p27(Kip1) regulates cell cycle progression in mammals by inhibiting the activity of cyclin-dependent kinases (CDKs). Here we show that p27(Kip1) progressively accumulates in the nucleus of pancreatic beta cells in mice that lack either insulin receptor substrate 2 (Irs2(-/-)) or the long form of the leptin receptor (Lepr(-/-) or db/db). Deletion of the gene encoding p27(Kip1) (Cdkn1b) ameliorated hyperglycemia in these animal models of type 2 diabetes mellitus by increasing islet mass and maintaining compensatory hyperinsulinemia, effects that were attributable predominantly to stimulation of pancreatic beta-cell proliferation. Thus, p27(Kip1) contributes to beta-cell failure during the development of type 2 diabetes in Irs2(-/-) and Lepr(-/-) mice and represents a potential new target for the treatment of this condition.

Diabetes-related shame among people with type 2 diabetes: an internet-based cross-sectional study.

INTRODUCTION: Emerging evidence suggests that diabetes stigma and negative emotions associated with it may impair the quality of life of people with diabetes. Among these psychological distresses, shame is considered the most distressing of all human emotional experiences and may be a condition to which diabetes clinicians should pay attention. This epidemiological study focused on diabetes-related shame and aimed to determine the prevalence of diabetes-related shame, its factors, and its association with psychological indicators. RESEARCH DESIGN AND METHODS: A cross-sectional online survey was conducted among people with type 2 diabetes preregistered with a research firm. The questionnaire included experience of diabetes-related shame and demographic data such as age, clinical characteristic measures such as hemoglobin A1c (HbA1c), and psychological indicators, including the WHO Five Well-Being Index (WHO-5) and Problem Areas In Diabetes-5 (PAID-5). Differences in each indicator between people with diabetes who experienced shame and those who did not were analyzed with the unpaired t-test. As supplemental analysis, binomial logistic regression analysis was used to identify factors associated with the prevalence of diabetes-related shame. RESULTS: Of the 510 participants, 32.9% experienced diabetes-related shame and 17.5% concealed their disease from colleagues or friends. Those who had experienced diabetes-related shame showed significantly lower WHO-5 and higher PAID-5 scores (p<0.001). However, no significant difference was found in HbA1c (p=0.36). Binomial logistic regression revealed that women, young adults, those without a college degree, those with low self-efficacy, and those with a strong sense of financial burden or external pressure were at higher risk of experiencing diabetes-related shame. CONCLUSIONS: Among people with type 2 diabetes mellitus, diabetes-related shame was associated with diabetes-specific emotional distress and low psychological well-being. Further research and care development are needed to address diabetes-related shame and improve the quality of life of people with diabetes.

Analysis of time-dependent alterations of parameters related to erythrocytes after ipragliflozin initiation.

Sodium-glucose cotransporter 2 (SGLT2) inhibitors often increase the hematocrit. It remains unclear whether this increase would be observed in all patients administered SGLT2 inhibitors, however. We therefore used the data from the previous study and investigated time-dependent alterations of various outcomes related to erythrocytes, erythropoiesis, and clinical outcome in type 2 diabetes subjects (n = 89) treated with ipragliflozin for 16 weeks. Among a total of 89 participants, 71 subjects (80.0% of total participants) showed the elevation of the hematocrit and 18 subjects (20.0% of total participants) did not at 16 weeks. Although the hematocrit levels at baseline were significantly lower in hematocrit-elevated group than non-elevated group, they reached the same levels 4 weeks after the onset of treatment. Binomial logistic regression analysis demonstrated that a lower baseline hematocrit level was related to the elevation of hematocrit at 16 weeks. Optimal cutoff hematocrit levels at baseline to predict hematocrit elevation were 46.9% (male) and 41.7% (female) in ROC analysis. Random intercept model analysis revealed the serum erythropoietin level increased in both hematocrit-elevated and non-elevated groups, whereas only the former group showed an increase in the percentage of reticulocytes during the first 4 weeks. These results suggest that the ipragliflozin-induced increase in hematocrit which is affected by the baseline hematocrit level is attributable to the responsiveness to, but not to the production of, erythropoietin. Collectively, Ht elevation observed in administration of SGLT2 inhibitors can result from erythropoietin-induced erythropoiesis, which is determined by the pre-treatment Ht level. Trial registration: This trial has been registered with University Hospital Medical Information Network Clinical Trial Registry (UMIN-CTR no. 000015478).

GCN2 regulates pancreatic ß cell mass by sensing intracellular amino acid levels.

EIF2AK4, which encodes the amino acid deficiency-sensing protein GCN2, has been implicated as a susceptibility gene for type 2 diabetes in the Japanese population. However, the mechanism by which GCN2 affects glucose homeostasis is unclear. Here, we show that insulin secretion is reduced in individuals harboring the risk allele of EIF2AK4 and that maintenance of GCN2-deficient mice on a high-fat diet results in a loss of pancreatic ß cell mass. Our data suggest that GCN2 senses amino acid deficiency in ß cells and limits signaling by mechanistic target of rapamycin complex 1 to prevent ß cell failure during the consumption of a high-fat diet.

Increased ribosomal biogenesis induces pancreatic beta cell failure in mice model of type 2 diabetes.

AIM: To study the changes in gene expression by pancreatic beta cells under insulin resistance conditions. METHOD: An exhaustive gene expression analysis was performed, using isolated pancreatic islets of obese diabetic model Lepr(-/-) mice. Overexpression of cyclin D2 was induced in cells from the pancreatic beta cell line, namely, INS-1. RESULTS: Through a gene expression analysis using islets isolated from db/db mice, we found a significant increase in the expression of ribosome-related molecules. In addition, increased expression of cyclin D2 was found at certain protein levels. As INS-1 cells were induced to overexpress cyclin D2, we found an increase in the expression of ribosome-related molecules. Concurrently, an increase in the expression of endoplasmic reticulum stress (ER stress)-related molecules was also found. CONCLUSION: In cases of pancreatic beta cell hyperplasia associated with insulin resistance, ribosomal biogenesis is increased, and ER stress is induced.

Effects of exenatide and liraglutide on postchallenge glucose disposal in individuals with normal glucose tolerance.

PURPOSE: Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are categorized as short- or long-acting types, but information regarding differences in the effects of these two types on postprandial glucose disposal has been limited. We have now investigated the effects of exenatide and liraglutide (short- and long-acting GLP-1RAs, respectively) on glucose disposal during an oral glucose tolerance test (OGTT). METHODS: Fourteen healthy volunteers with normal glucose tolerance underwent three OGTTs, which were performed without pharmacological intervention or after a single administration of exenatide or liraglutide at 30 min and 10 h, respectively, before test initiation. The three OGTTs were performed with intervals of at least 7 days between successive tests and within a period of 2 months. RESULTS: Exenatide, but not liraglutide, markedly decelerated the peak of both plasma glucose and serum insulin levels during the OGTT, with the peaks of both glucose and insulin concentrations occurring at 150 min after test initiation with exenatide compared with 30 min in the control condition or with liraglutide. Exenatide and liraglutide reduced the area under the curve for plasma glucose levels during the OGTT by similar extents, whereas that for serum insulin levels was reduced only by exenatide. CONCLUSIONS: Our results suggest that exenatide decelerates the increase in plasma glucose levels through inhibition of glucose absorption and that it exerts an insulin-sparing action after glucose challenge.

Early administration of dapagliflozin preserves pancreatic ß-cell mass through a legacy effect in a mouse model of type 2 diabetes.

AIMS/INTRODUCTION: The preservation of pancreatic ß-cell mass is an essential factor in the onset and development of type 2 diabetes mellitus. Recently, sodium-glucose cotransporter 2 inhibitors have been launched as antihyperglycemic agents, and their organ-protective effects are attracting attention. They are also reported to have favorable effects on the preservation of pancreatic ß-cell mass, but the appropriate timing for the administration of sodium-glucose cotransporter 2 inhibitors is obscure. MATERIALS AND METHODS: In the present study, we administered a sodium-glucose cotransporter 2 inhibitor, dapagliflozin, to an animal model of type 2 diabetes mellitus, db/db mice, and investigated the adequate timing and duration for its administration. We also carried out microarray analysis using pancreatic islets from db/db mice. RESULTS: We found that dapagliflozin preserved pancreatic ß-cell mass depending on the duration of administration and markedly improved blood glucose levels. If the duration was the same, the earlier administration of dapagliflozin was more effective in preserving pancreatic ß-cell mass, increasing serum insulin levels and improving blood glucose levels. From microarray analysis, we discovered that the expression of Agr2, Tff2 and Gkn3 was significantly upregulated after the early administration of dapagliflozin. This upregulated gene expression might provide a legacy effect for the preservation of pancreatic ß-cell mass. CONCLUSIONS: We expect that the early administration of dapagliflozin would provide a long-lasting effect in preserving pancreatic ß-cell mass.

Effects of ipragliflozin on glycemic control, appetite and its related hormones: A prospective, multicenter, open-label study (SOAR-KOBE Study).

AIMS/INTRODUCTION: Sodium-glucose cotransporter 2 (SGLT-2) inhibitors improve blood glucose control, as well as reducing bodyweight by promoting urinary glucose excretion. The weight loss is less than expected from urinary glucose loss, however, likely because of an increase in food intake. To investigate whether SGLT-2 inhibitors might increase appetite by affecting related hormones, we examined the effects of the SGLT-2 inhibitor, ipragliflozin, including those on appetite-regulating hormones, in individuals with suboptimally controlled type 2 diabetes. MATERIALS AND METHODS: The present prospective, multicenter, open-label study was carried out with 96 patients with a body mass index of ≥22 kg/m2 who were treated with ipragliflozin (50 mg/day) for 16 weeks. Parameters including glycated hemoglobin level, bodyweight, circulating leptin and active ghrelin concentrations, and appetite as assessed with a visual analog scale were measured before and during treatment. RESULTS: Both glycated hemoglobin level (from 7.9 ± 0.8 to 7.1 ± 0.7%) and bodyweight (from 75.2 ± 12.6 to 72.6 ± 12.4 kg) were significantly decreased after treatment for 16 weeks. The fasting serum leptin level was significantly decreased after 2 weeks (from 19.5 ± 13.1 to 18.1 ± 12.4 ng/mL) and remained decreased up to 16 weeks, even after adjustment for bodyweight, whereas the plasma active ghrelin level showed no significant change. The visual analog scale score for hunger was significantly increased at 2 and 8 weeks. CONCLUSIONS: The present results suggest that ipragliflozin improved glycemic control and reduced bodyweight, but also reduced serum leptin levels and might thereby have increased appetite.

PKClambda regulates glucose-induced insulin secretion through modulation of gene expression in pancreatic beta cells.

Altered regulation of insulin secretion by glucose is characteristic of individuals with type 2 diabetes mellitus, although the mechanisms that underlie this change remain unclear. We have now generated mice that lack the lambda isoform of PKC in pancreatic beta cells (betaPKClambda(-/-) mice) and show that these animals manifest impaired glucose tolerance and hypoinsulinemia. Furthermore, insulin secretion in response to high concentrations of glucose was impaired, whereas the basal rate of insulin release was increased, in islets isolated from betaPKClambda(-/-) mice. Neither the beta cell mass nor the islet insulin content of betaPKClambda(-/-) mice differed from that of control mice, however. The abundance of mRNAs for Glut2 and HNF3beta was reduced in islets of betaPKClambda(-/-) mice, and the expression of genes regulated by HNF3beta was also affected (that of Sur1 and Kir6.2 genes was reduced, whereas that of hexokinase 1 and hexokinase 2 genes was increased). Normalization of HNF3beta expression by infection of islets from betaPKClambda(-/-) mice with an adenoviral vector significantly reversed the defect in glucose-stimulated insulin secretion. These results indicate that PKClambda plays a prominent role in regulation of glucose-induced insulin secretion by modulating the expression of genes important for beta cell function.

Docosahexaenoic Acid Reduces Palmitic Acid-Induced Endoplasmic Reticulum Stress in Pancreatic Β Cells.

Endoplasmic reticulum (ER) stress leads to peripheral insulin resistance and the progression of pancreatic beta cell failure in type 2 diabetes. Although ER stress plays an important role in the pathogenesis of diabetes, it is indispensable for cellular activity. Therefore, when assessing the pathological significance of ER stress, it is important to monitor and quantify ER stress levels. Here, we have established a novel system to monitor ER stress levels quickly and sensitively, and using this method, we have clarified the effect of differences in glucose concentration and various fatty acids on the ER of pancreatic ß cells. First, we developed a cell system that secretes Gaussia luciferase in culture medium depending on the activation of the GRP78 promoter. This system could sensitively monitor ER stress levels that could not be detected with real-time RT-PCR and immunoblotting. This system revealed that hyperglycemia does not induce unfolded protein response (UPR) in a short period of time in MIN6 cells, a mouse pancreatic ß cell line. Physiological concentrations of palmitic acid, a saturated fatty acid, induced ER stress quickly, while physiological concentrations of oleic acid, an unsaturated fatty acid, did not. Docosahexaenoic acid, an n-3 unsaturated fatty acid, inhibited palmitic acid-induced ER stress. In this study, we have established a system that can sensitively detect ER stress levels of living cells in a short period of time. This system can be used to monitor the state of the ER in living cells and lead to the investigation of the significance of physiological or pathological ER stress levels.