Imatinib prevents dexamethasone-induced pancreatic ß-cell apoptosis via decreased TRAIL and DR5.

Prolonged administration of dexamethasone, a potent anti-inflammatory drug, can lead to steroid-induced diabetes. Imatinib, a medication commonly prescribed for chronic myeloid leukemia (CML), has been shown to improve diabetes in CML patients. Our recent study demonstrated that dexamethasone induces pancreatic ß-cell apoptosis by upregulating the expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptor, death receptor 5 (DR5). We hypothesized that imatinib may protect against dexamethasone-induced pancreatic ß-cell apoptosis by reducing the expression of TRAIL and DR5, thereby favorably modulating downstream effectors in apoptotic pathways. We test this hypothesis by assessing the effects of imatinib on dexamethasone-induced apoptosis in rat insulinoma cell line cells. As anticipated, dexamethasone treatment led to increased TRAIL and DR5 expression, as well as an elevation in superoxide production. Conversely, expression of the TRAIL decoy receptor (DcR1) was decreased. Moreover, key effectors in the extrinsic and intrinsic apoptosis pathways, such as B-cell lymphoma 2 (BCL-2) associated X (BAX), nuclear factor kappa B (NF-κb), P73, caspase 8, and caspase 9, were upregulated, while the antiapoptotic protein BCL-2 was downregulated. Interestingly and importantly, imatinib at a concentration of 10 µM reversed the effect of dexamethasone on TRAIL, DR5, DcR1, superoxide production, BAX, BCL-2, NF-κB, P73, caspase 3, caspase 8, and caspase 9. Similar effects of imatinib on dexamethasone-induced TRAIL and DR5 expression were also observed in isolated mouse islets. Taken together, our findings suggest that imatinib protects against dexamethasone-induced pancreatic ß-cell apoptosis by reducing TRAIL and DR5 expression and modulating downstream effectors in the extrinsic and intrinsic apoptosis pathways.

Defective functions of HNF1A variants on BCL2L1 transactivation and beta-cell growth.

Maturity-onset diabetes of the young type 3 (MODY3) is caused by mutations in a gene encoding transcription factor hepatocyte nuclear factor 1-alpha (HNF1A). Although the roles of HNF1A in regulation of hepatic and pancreatic genes to maintain glucose homeostasis were investigated, the functions of HNF1A are not completely elucidated. To better understand the functions of HNF1A, we characterized mutations of HNF1A in Thai MODY3 patients and studied the functions of wild-type HNF1A and variant proteins. We demonstrate for the first time that HNF1A upregulates transactivation of an anti-apoptotic gene BCL2 Like 1 (BCL2L1) and that all the identified HNF1A variants including p.D80V, p.R203C, p.P475L, and p.G554fsX556, reduce this ability. The four HNF1A variants impair HNF1A function in promoting INS-1 cell transition from G1 to S phase of cell cycle, which thereby retard cell growth. This finding indicates the role of HNF1A in beta-cell viability by upregulation of anti-apoptotic gene expression and also reaffirms its role in beta-cell growth through cell cycle control.

13C-Acetic Acid Breath Test Monitoring of Gastric Emptying during Disease Progression in Diabetic Rats.

Gastric motility disturbance is commonly found in long-standing hyperglycemia. Both delayed and rapid gastric emptying has been reported in diabetes. However, very few studies have followed the changes in gastric emptying during disease progression in diabetes because of technical limitations. 13C-Acetic acid breath test is a validated method which is non-invasive and can be used repeatedly or serially to evaluate gastric emptying changes in animal. We investigated the gastric emptying changes in different stages of diabetes using 13C-acetic acid breath test, as well as its related mechanisms involving interstitial cells of Cajal (ICCs), and stem cell factor (SCF) in streptozotocin-induced diabetic rats. The results showed that gastric emptying was accelerated at the early stage (12 weeks of diabetes) whereas intramuscular ICCs (ICC-IM) networks were not different from normal group. At long-term stage (28 weeks of diabetes), gastric emptying had returned to normal pattern with no delayed. ICC-IM networks were decreased in the diabetic group compared to 12th weeks, and were lower than in the normal group at the same time point. SCF levels were constantly high in the diabetic group than in the normal group. This result indicated that 13C-acetic acid breath test is useful to track the alteration in gastric emptying during disease progression. The change of gastric emptying was not found to be significantly associated with ICC-IM. Elevated SCF may help to preserve ICC-IM, especially in the early phase of diabetes.

PAX4 R192H and P321H polymorphisms in type 2 diabetes and their functional defects.

We have previously identified PAX4 mutations causing MODY9 and a recent genome-wide association study reported a susceptibility locus of type 2 diabetes (T2D) near PAX4. In this study, we aim to investigate the association between PAX4 polymorphisms and T2D in Thai patients and examine functions of PAX4 variant proteins. PAX4 rs2233580 (R192H) and rs712701 (P321H) were genotyped in 746 patients with T2D and 562 healthy normal control subjects by PCR and restriction-fragment length polymorphism method. PAX4 variant proteins were investigated for repressor function on human insulin and glucagon promoters and for cell viability and apoptosis upon high glucose exposure. Genotype and allele frequencies of PAX4 rs2233580 were more frequent in patients with T2D than in control subjects (P=0.001 and 0.0006, respectively) with odds ratio of 1.66 (P=0.001; 95% confidence interval, 1.22-2.27). PAX4 rs712701 was not associated with T2D but it was in linkage disequilibrium with rs2233580. The 192H/321H (A/A) haplotype was more frequent in T2D patients than in controls (9.5% vs 6.6%; P=0.009). PAX4 R192H, but not PAX4 P321H, impaired repression activities on insulin and glucagon promoters and decreased transcript levels of genes required to maintain ß-cell function, proliferation and survival. Viability of ß-cell was reduced under glucotoxic stress condition for the cells overexpressing either PAX4 R192H or PAX4 P321H or both. Thus these PAX4 polymorphisms may increase T2D risk by defective transcription regulation of target genes and/or decreased ß-cell survival in high glucose condition.

Cardiometabolic risk in Thai adults with type 2 diabetes mellitus: obese versus non-obese.

BACKGROUND: Adiposity is an inflammatory condition contributing to the morbidity and mortality of several disorders, including type 2 diabetes mellitus (T2D) and cardiovascular disease. OBJECTIVE: To compare cardiometabolic risk factors between obese and non-obese Thai patients with T2DM MATERIAL AND METHOD: The cross-sectional study was done in 20 obese (BM >25 kg/m2) and 20 non-obese (BMI 23 kg/m2) T2DM Researchers measured fasting plasma glucose and lipids, serum levels of insulin, leptin, adiponectin, and soluble tumor necrosis factor-alpha receptors type 1 and 2 (sTNF-R] andsTNF-R2). Insulin sensitivity check index (QUICIKI) and insulin resistance index (HOMA-IR) were calculated. RESULTS: Thai obese adults with T2DMhad greater amounts ofsTNF-R2 and HOMA-IR, higher ratios of leptin/adiponectin, and more incidences of hypertension and hypertriglyceridemia in comparison to non-obese counterparts. Additionally, HOMA-IR values in non-obese T2DMwere greater than those reported among non-diabetic Thai adults. A reverse association between inflammatory markers (both sTNF-Rs) andHDLC was detected. Leptin/adiponectin ratios correlated directly with HOMA-IR, serum insulin, plasma triglycerides and BMI, whereas HOMA-IR did not relate to any studied plasma lipid. CONCLUSION: The present study demonstrated an increased cardiometabolic risk in obese T2DM adults than non-obese T2DM adults among the Thai population. The leptin/adiponectin ratio may be more relevant to predict the risk of cardiovascular events in T2DMpatients than HOMA-IR.

Dengue virus disrupts Daxx and NF-κB interaction to induce CD137-mediated apoptosis.

Dengue virus (DENV) is a positive-strand RNA virus of the Flavivirus family with 4 different serotypes. Clinical manifestations of DENV infection include dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. Following DENV infection, apoptosis of hepatic cells is observed both in vitro and in vivo. However, the molecular mechanisms revealing how viral components affect cellular apoptosis remain unclear. In the present study, the role of death domain-associated protein 6 (Daxx) in DENV-mediated apoptosis was characterized by RNA interference and overexpression studies, and the anti-apoptotic function of Daxx during DENV infection was identified. Furthermore, the viral component, DENV capsid protein (DENV C), interacted with Daxx to disrupt interaction between Daxx and NF-κB. The liberated NF-κB activated the promoter of CD137, which is a member of the TNF family, and is previously shown to induce apoptosis during DENV infection. In summary, DENV C disrupts Daxx and NF-κB interaction to induce CD137-mediated apoptosis during DENV infection.

Certain hormonal markers in urban Thai adults with metabolic syndrome.

BACKGROUND: The prevalence of metabolic syndrome (MS) accompanied with cardiometabolic complications has progressively increased in Thailand. The roles of insulin resistance, leptin, adiponectin, and free testosterone as prognostic indicators of MS among Thai population were evaluated MATERIAL AND METHOD: Men and women aged 34 to 89 years (n = 308) having 0-5 criteria of MS according to NCEP III with Asian-specific cut-points for waist circumference were enrolled in this cross-sectional study. Blood glucose, lipids, insulin, leptin, adiponectin, and free testosterone were measured RESULTS: Each component of MS, especially the enlarged waist, adversely affected insulin sensitivity. MS subjects were at higher risk for developing insulin resistance, decreasing of plasma adiponectin, and increasing of leptin and the leptin/ adiponectin ratio in comparison to non-MS individuals. The hormonal changes that have been shown to be associated with increased cardiometabolic risk were amplifiedas more MS criteria have been met. Odds ratios of increased leptin/adiponectin ratio among MS group were highest in comparison to others. Free testosterone levels declined with age and did not discriminate men with MS. CONCLUSION: The results indicate the benefit of hormonal assessment, particularly the leptin/adiponectin ratio in identifying MS individuals with high cardiometabolic disease risk.

Obesity and appetite-related hormones.

OBJECTIVE: Alterations of hormones involved in food intake can lead to obesity and related-diseases. The aim of the present study was to measure plasma levels of appetite-related hormones: insulin, leptin, adiponectin, acylated ghrelin, and cortisol in connection with eating behaviors among obese and non-obese women. MATERIAL AND METHOD: The present study was performed in 53 non-obese and 33 obese Thai women (BMI < 23 and > or = 25 kg/m2 respectively), aged 25 to 45 years. Saliva and fasting blood samples were collected for hormone measurements. Subjects 'eating behavior was evaluated using Thai version of the Three-factor eating questionnaire (TFEQ) and their stress status was assessed by the Thai stress test (TST). RESULTS: In comparison to non-obese individuals, obese women showed higher disinhibition eating, plasma glucose, insulin, HOMA insulin resistance index, leptin, and triglyceride levels but lesser plasma adiponectin and HDLC. Lower adiponectin was directly associated with higher disinhibition eating. Plasma leptin related positively to fat mass and insulin resistance but negatively to acylated ghrelin level. The trend towards increased acylated ghrelin after adjusted for age, obesity and eating behaviors was shown in stress women. CONCLUSION: Increased insulin resistance, high leptin, and reduced adiponectin accompanied with disinhibition eating have been detected in obese women.

Cytoprotective effect of genistein against dexamethasone-induced pancreatic ß-cell apoptosis.

Steroid-induced diabetes is a well-known metabolic side effect of long-term use of glucocorticoid (GC). Our group recently demonstrated dexamethasone-induced pancreatic ß-cell apoptosis via upregulation of TRAIL and TRAIL death receptor (DR5). Genistein protects against pancreatic ß-cell apoptosis induced by toxic agents. This study aimed to investigate the cytoprotective effect of genistein against dexamethasone-induced pancreatic ß-cell apoptosis in cultured rat insulinoma (INS-1) cell line and in isolated mouse islets. In the absence of genistein, dexamethasone-induced pancreatic ß-cell apoptosis was associated with upregulation of TRAIL, DR5, and superoxide production, but downregulation of TRAIL decoy receptor (DcR1). Dexamethasone also activated the expression of extrinsic and intrinsic apoptotic proteins, including Bax, NF-κB, caspase-8, and caspase-3, but suppressed the expression of the anti-apoptotic Bcl-2 protein. Combination treatment with dexamethasone and genistein protected against pancreatic ß-cell apoptosis, and reduced the effects of dexamethasone on the expressions of TRAIL, DR5, DcR1, superoxide production, Bax, Bcl-2, NF-κB, caspase-8, and caspase-3. Moreover, combination treatment with dexamethasone and genistein reduced the expressions of TRAIL and DR5 in isolated mouse islets. The results of this study demonstrate the cytoprotective effect of genistein against dexamethasone-induced pancreatic ß-cell apoptosis in both cell line and islets via reduced TRAIL and DR5 protein expression.

Dexamethasone induces pancreatic ß-cell apoptosis through upregulation of TRAIL death receptor.

Long-term medication with dexamethasone - a synthetic glucocorticoid (GC) drug - results in hyperglycemia, or steroid-induced diabetes. Although recent studies revealed that dexamethasone directly induces pancreatic ß-cell apoptosis, its molecular mechanisms remain unclear. In our initial analysis of mRNA transcripts, we discovered the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway may be involved in dexamethasone-induced pancreatic ß-cell apoptosis. In the present study, a mechanism of dexamethasone-induced pancreatic ß-cell apoptosis through the TRAIL pathway was investigated in cultured cells and isolated mouse islets. INS-1 cells were cultured with and without dexamethasone in the presence or absence of a glucocorticoid receptor (GR) inhibitor, RU486. We found that dexamethasone induced pancreatic ß-cell apoptosis in association with the upregulation of TNSF10 (TRAIL) mRNA and protein expression. Moreover, dexamethasone upregulated the TRAIL death receptor (DR5) protein but suppressed the decoy receptor (DcR1) protein. Similar findings were observed in mouse isolated islets: dexamethasone increased TRAIL and DR5 compared to that of control mice. Furthermore, dexamethasone stimulated pro-apoptotic signaling including superoxide production, caspase-8, -9, and -3 activities, NF-κB, and Bax but repressed the anti-apoptotic protein, Bcl-2. All these effects were inhibited by the GR-inhibitor, RU486. Furthermore, knock-down DR5 decreased dexamethasone-induced caspase 3 activity. Caspase-8 and caspase-9 inhibitors protected pancreatic ß-cells from dexamethasone-induced apoptosis. Taken together, dexamethasone induced pancreatic ß-cell apoptosis by binding to the GR and inducing DR5 and TRAIL pathway.

Functional defect of truncated hepatocyte nuclear factor-1alpha (G554fsX556) associated with maturity-onset diabetes of the young.

A novel frameshift mutation attributable to 14-nucleotide insertion in hepatocyte nuclear factor-1alpha (HNF-1alpha) encoding a truncated HNF-1alpha (G554fsX556) with 76-amino acid deletion at its carboxyl terminus was identified in a Thai family with maturity-onset diabetes of the young (MODY). The wild-type and mutant HNF-1alpha proteins were expressed by in vitro transcription and translation (TNT) assay and by transfection in HeLa cells. The wild-type and mutant HNF-1alpha could similarly bind to human glucose-transporter 2 (GLUT2) promoter examined by electrophoretic mobility shift assay (EMSA). However, the transactivation activities of mutant HNF-1alpha on human GLUT2 and rat L-type pyruvate kinase (L-PK) promoters in HeLa cells determined by luciferase reporter assay were reduced to approximately 55-60% of the wild-type protein. These results suggested that the functional defect of novel truncated HNF-1alpha (G554fsX556) on the transactivation of its target-gene promoters would account for the beta-cell dysfunction associated with the pathogenesis of MODY.

Estradiol Prevents High Glucose-Induced ß-cell Apoptosis by Decreased BTG2 Expression.

Hyperglycemia stimulates several pathways to induce pancreatic ß-cell apoptosis. In our previous study by mRNA analysis, we demonstrated that B-cell translocation gene 2 (BTG2) expression was up-regulated in INS-1 cells cultured under high glucose conditions, but this effect was reversed by estrogen. In the present study, we demonstrated that BTG2 mRNA and protein expressions in both INS-1 cells and mouse pancreatic islets increased under high glucose conditions compared to those cultured under basal glucose conditions, while in the presence of estrogen, the BTG2 mRNA and protein expressions decreased. SiRNA-BTG2 significantly reduced cell apoptosis, cleaved-caspase 3, and Bax, compared to the siRNA-control in INS-1 cultured under high glucose conditions. We further demonstrated that BTG2 promoter activity was activated under high glucose conditions whereas estrogen significantly reduced it. The effects of estrogen on BTG2 expression were inhibited by estrogen receptor inhibitors. Also, under high glucose conditions, p53 and Bax mRNA and protein expressions increased, but they decreased in the presence of estrogen. Again, the effect of estrogen on p53 and Bax expression was inhibited by estrogen receptor inhibitors. Taken together, this study demonstrates that estrogen reduces pancreatic ß-cell apoptosis under high glucose conditions via suppression of BTG2, p53, and Bax expressions.

PAX4 mutations in Thais with maturity onset diabetes of the young.

CONTEXT: Six maturity onset diabetes of the young (MODY) genes have been discovered to date but account for a small proportion of MODY among Asians, suggesting the existence of other MODY genes in this racial group. OBJECTIVE: The aim of this study was to investigate whether or not genetic variants in PAX4, a crucial transcription factor in beta-cell development, contribute to MODY in Thais. DESIGN AND METHODS: We screened PAX4 coding sequences in 46 MODY probands without mutation in known MODY genes and in 74 nondiabetic controls using PCR-single-stranded conformational polymorphism analysis followed by direct sequencing. Genotyping of variants identified was done by PCR-restriction fragment length polymorphism analysis. RESULTS: Eight sequence differences were identified. Two novel variations (R164W and IVS7-1G>A) were found in two different probands. Neither was found in the 74 nondiabetic controls and additional 270 healthy subjects of Thai origin. R164W segregated with diabetes in the family of the proband and in vitro studies showed that it impairs the repressor activity of PAX4 on the insulin and glucagon promoters. The remaining six variants were previously described and observed in both groups. One of them, R192H, was three times more frequent in MODY probands than in 342 nondiabetic controls (minor allele frequency = 0.196 vs. 0.064; P < 0.00001). The same variant was associated with a younger age at diagnosis among 254 Thai subjects with adult-onset type 2 diabetes (44.6 +/- 15 vs. 49.7 +/- 11 yr; P = 0.048). CONCLUSIONS: We have identified two possible pathogenic mutations of PAX4, R164W, and IVS7-1G>A. For one of these, we have shown evidence of segregation with diabetes and a functional impact on PAX4 activity. Single-nucleotide polymorphism R192H might influence the age at onset of diabetes.

Estrogen increases glucose-induced insulin secretion from mouse pancreatic islets cultured in a prolonged high glucose condition.

BACKGROUND: It is known that males are more susceptible to develop type 2 diabetes than females. Estrogen has a protective effect on pancreatic islet against toxic agent such as amyloid. The role of estrogen in protection pancreatic islet against high glucose is still unknown. OBJECTIVE: Administration of estrogen in an ovariectomised animal shows a protective effect against type 2 diabetes. The present study aimed to determine the direct effect of estrogen on the islet function after prolonged culture in high glucose. MATERIAL AND METHOD: Estrogen (10-1 M in ethanol) was co-cultured with mouse pancreatic islets in normal glucose medium (11.1 mM) for 3 hours or with normal and high glucose medium (40 mM) for 10 days. RESULTS: Estrogen increased glucose-induced insulin secretion in islet culture in normal glucose medium for both 3-hour and 10-day culture. Prolonged exposure of pancreatic islet to high glucose generated impaired glucose-induced insulin secretion, which was partially abrogated by the presence of 10(-5) M estrogen. CONCLUSION: These results indicated a direct effect of estrogen on improving insulin secretion from mouse pancreatic islets that has been impaired by prolonged exposure to high glucose.

Glycemic and lipid responses to glucomannan in Thais with type 2 diabetes mellitus.

OBJECTIVE: To evaluate the benefits of glucomannan supplement on glycemic and lipid controls in type 2 diabetic patients. MATERIAL AND METHOD: A single-blind, placebo-controlled, crossover trial with two treatments separated by a 2-week washout period was performed in 10 men and 10 women with type 2 diabetes mellitus. Two separated protocols of experiments were sequentially followed. Initially, purified glucomannan (1 g) or placebo was ingested 30 min before 75-g glucose load to evaluate their effects on glucose absorption and insulin secretion in oral glucose tolerance test (OGTT). Later, the glycemic and lipid changes after 4-week intervention with 3 g/day glucomannan comparing to the placebo were determined. The standard OGTT was performed before and after ending of each intervention. RESULTS: Glucomannan taken before performing the OGTT can lower the rise of blood glucose and insulin from 1 to 2 hour in comparison with the placebo, though a statistically significance of insulin was not achieved. Long-term glucomannan supplement significantly reduced the 120-min glucose area under the curve of OGTT. Glucomannan also decreased the rise of low-density lipoprotein cholesterol (LDL-C). Reductions of HOMA-insulin resistance index and body mass index were detected in glucomannan-treated group though the former was shown only in females. No within- and between-group differences of insulin, fructosamine, and other lipids were observed in glucomannan- nor placebo- treated groups. CONCLUSION: In type 2 diabetes, pre-prandial glucomannan ingestion attenuated a rise of blood glucose without significantly affecting insulin levels. Long-term supplement of glucomannan to the regular diabetic regimen lessened post challenge glucose AUC and impeded the rise of LDL-C. Supplement of glucomannan may be beneficial to the glycemic and lipid controls in type 2 diabetes mellitus.

Estrogen attenuates AGTR1 expression to reduce pancreatic ß-cell death from high glucose.

Chronic exposure of pancreatic ß-cells to high glucose levels results in ß-cell dysfunction and death. These effects can be protected by estrogen. The local pancreatic renin-angiotensin system (RAS) has been shown as a novel pathological pathway of high-glucose-induced cell death. The effect of estrogen on pancreatic RAS is still unknown. This study examines whether estrogen protects against pancreatic ß-cell death caused by glucotoxicity via a decrease in the pancreatic ß-cell RAS pathway. When INS-1 cells were cultured in a high glucose medium, cell death was significantly higher than when the cells were cultured in a basal glucose medium; similarly, there were also higher levels of AGTR1 and p47 ph ° x mRNA, and protein expression. Moreover, the addition of 10-8 M 17ß-estradiol to INS-1 cells cultured in a high glucose medium markedly reduced cell death, AGTR1 and p47 ph ° x mRNA levels, and protein expression. Similar results were demonstrated in the pancreatic islets. The presence of 10-8 M 17ß-estradiol, losartan, or a combination of both, in a high glucose medium had similar levels of reduction of p47 ph ° x mRNA and protein expression, compared with those cultured in high glucose. Taken together, estrogen protected pancreatic ß-cells from high-glucose-induced cell death by reducing the AGTR1 pathway.

Aberrant mRNA splicing of paired box 4 (PAX4) IVS7-1G>A mutation causing maturity-onset diabetes of the young, type 9.

AIMS: Paired box 4 (PAX4) mutations cause maturity-onset diabetes of the young, type 9 (MODY9). The molecular defect and alteration of PAX4 function associated with the mutation PAX4 IVS7-1G>A in a family with MODY9 and severe diabetic complications were studied. METHODS: We investigated the functional consequences of PAX4 IVS7-1G>A on mRNA splicing using minigene assays. Wild-type and mutant PAX4 were expressed in mouse pancreatic ß- and α-cell lines, and protein levels and translocation of PAX4 into the nucleus were determined. We also examined transcriptional repression of PAX4 target-gene promoters and ß-cell viability under diabetic-like (high-glucose) conditions. RESULTS: PAX4 IVS7-1G>A disrupts an acceptor splice site, causing an adjacent cryptic splice site within exon 8 to be used, resulting in a three-nucleotide deletion and glutamine deletion at position 250 (p.Q250del). Wild-type and PAX4 Q250del proteins were expressed at similar levels and could translocate normally into the nucleus in ßTC3 and αTC1.9 cells. However, the repressor functions of PAX4 Q250del on human insulin and glucagon promoters in INS-1 832/13 and αTC1.9 cells were significantly decreased, compared with that of wild-type PAX4. Moreover, the rate of apoptosis was increased in INS-1 cells over-expressing PAX4 Q250del when cultured in high-glucose conditions. CONCLUSIONS: PAX4 IVS7-1G>A caused aberrant mRNA splicing and PAX4 Q250 deletion. The mutation impaired PAX4 repressor functions on target-gene promoters and increased susceptibility to apoptosis upon high glucose exposure. Thus, PAX4 IVS7-1G>A contributes to the pathogenesis of diabetes in this MODY9 family through ß-cell dysfunction.

High glucose-induced impairment in insulin secretion is associated with reduction in islet glucokinase in a mouse model of susceptibility to islet dysfunction.

Type 2 diabetes is characterized by islet dysfunction resulting in hyperglycemia, which can then lead to further deterioration in islet function. A possible mechanism for hyperglycemia-induced islet dysfunction is the accumulation of advanced glycation end products (AGE). The DBA/2 mouse develops pancreatic islet dysfunction when exposed to a high glucose environment and/or obesity-induced insulin resistance. To determine the biochemical cause of dysfunction, DBA/2 and C57BL/6 control islets were incubated in 11.1 mM or 40 mM glucose in the absence or presence of the AGE inhibitor aminoguanidine (AG) for 10 days. Basal (2.8 mM glucose) insulin release was increased in both DBA/2 and C57BL/6 islets incubated with 40 mM vs 11.1 mM glucose for 10 days. Chronic exposure to hyperglycemia decreased glucose (20 mM)-stimulated insulin secretion in DBA/2 but not in C57BL/6 islets. AG significantly increased fold-induced insulin release in high glucose cultured DBA/2 mouse islets, but did not affect C57BL/6 islet function. DBA/2 islet glucokinase was significantly reduced following 40 mM glucose culture, compared with 11.1 mM glucose cultured DBA/2 islets and 40 mM glucose cultured C57BL/6 islets. Incubation of islets with AG resulted in a normalization of DBA/2 islet glucokinase levels. In conclusion, chronic high glucose-induced increases in AGE can result in islet dysfunction and this is associated with reduced glucokinase levels in a mouse model with susceptibility to islet failure.

Testosterone reduces AGTR1 expression to prevent ß-cell and islet apoptosis from glucotoxicity.

Hypogonadism in men is associated with an increased incidence of type 2 diabetes. Supplementation with testosterone has been shown to protect pancreatic ß-cell against apoptosis due to toxic substances including streptozotocin and high glucose. One of the pathological mechanisms of glucose-induced pancreatic ß-cell apoptosis is the induction of the local rennin-angiotensin-aldosterone system (RAAS). The role of testosterone in regulation of the pancreatic RAAS is still unknown. This study aims to investigate the protective action of testosterone against glucotoxicity-induced pancreatic ß-cell apoptosis via alteration of the pancreatic RAAS pathway. Rat insulinoma cell line (INS-1) cells or isolated male mouse islets were cultured in basal and high-glucose media in the presence or absence of testosterone, losartan, and angiotensin II (Ang II), then cell apoptosis, cleaved caspase 3 expression, oxidative stress, and expression of angiotensin II type 1 receptor (AGTR1) and p47(phox) mRNA and protein were measured. Testosterone and losartan showed similar effects in reducing pancreatic ß-cell apoptosis. Testosterone significantly reduced expression of AGTR1 protein in INS-1 cells cultured in high-glucose medium or high-glucose medium with Ang II. Testosterone decreased the expression of AGTR1 and p47(phox) mRNA and protein in comparison with levels in cells cultured in high-glucose medium alone. Furthermore, testosterone attenuated superoxide production when co-cultured with high-glucose medium. In contrast, when cultured in basal glucose, supplementation of testosterone did not have any effect on cell apoptosis, oxidative stress, and expression of AGT1R and p47(phox). In addition, high-glucose medium did not increase cleaved caspase 3 in AGTR1 knockdown experiments. Thus, our results indicated that testosterone prevents pancreatic ß-cell apoptosis due to glucotoxicity through reduction of the expression of ATGR1 and its signaling pathway.

NF-κB is required for dengue virus NS5-induced RANTES expression.

Dengue virus (DENV) infection associates with renal disorders. Patients with dengue hemorrhagic fever and acute kidney injury have a high mortality rate. Increased levels of cytokines may contribute to the pathogenesis of DENV-induced kidney injury. Currently, molecular mechanisms how DENV induces kidney cell injury has not been thoroughly investigated. Excessive cytokine production may be involved in this process. Using human cytokine RT(2) Profiler PCR array, 14 genes including IP-10, RANTES, IL-8, CXCL-9 and MIP-1ß were up-regulated more than 2 folds in DENV-infected HEK 293 cells compared to that of mock-infected HEK 293 cells. In the present study, RANTES was suppressed by the NF-κB inhibitor, compound A (CpdA), in DENV-infected HEK 293 cells implying the role of NF-κB in RANTES expression. Chromatin immunoprecipitation (ChIP) assay showed that NF-κB binds more efficiently to its binding sites on the RANTES promoter in NS5-transfected HEK 293 cells than in HEK 293 cells expressing the vector lacking NS5 gene. To further examine whether the NS5-activated RANTES promoter is mediated through NF-κB, the two NF-κB binding sites on the RANTES promoter were mutated and this promoter was coupled to the luciferase cDNA. The result showed that when both binding sites of NF-κB in the RANTES promoter were mutated, the ability of NS5 to induce the luciferase activity was significantly decreased. Therefore, DENV NS5 activates RANTES production by increasing NF-κB binding to its binding sites on the RANTES promoter.