Type 2 diabetes: when insulin secretion fails to compensate for insulin resistance

Untargeted metabolic profiling identifies altered serum metabolites of type 2 diabetes mellitus in a prospective, nested case control study

BACKGROUND

Application of metabolite profiling could expand the etiological knowledge of type 2 diabetes mellitus (T2D). However, few prospective studies apply broad untargeted metabolite profiling to reveal the comprehensive metabolic alterations preceding the onset of T2D.

METHODS

We applied untargeted metabolite profiling in serum samples obtained from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam cohort comprising 300 individuals who developed T2D after a median follow-up time of 6 years and 300 matched controls. For that purpose, we used ultraperformance LC-MS with a protocol specifically designed for large-scale metabolomics studies with regard to robustness and repeatability. After multivariate classification to select metabolites with the strongest contribution to disease classification, we applied multivariable-adjusted conditional logistic regression to assess the association of these metabolites with T2D.

RESULTS

Among several alterations in lipid metabolism, there was an inverse association with T2D for metabolites chemically annotated as lysophosphatidylcholine(dm16:0) and phosphatidylcholine(O-20:0/O-20:0). Hexose sugars were positively associated with T2D, whereas higher concentrations of a sugar alcohol and a deoxyhexose sugar reduced the odds of diabetes by approximately 60% and 70%, respectively. Furthermore, there was suggestive evidence for a positive association of the circulating purine nucleotide isopentenyladenosine-5'-monophosphate with incident T2D.

CONCLUSIONS

This study constitutes one of the largest metabolite profiling approaches of T2D biomarkers in a prospective study population. The findings might help generate new hypotheses about diabetes etiology and develop further targeted studies of a smaller number of potentially important metabolites.

GDF15 Is a Novel Biomarker for Impaired Fasting Glucose

BACKGROUND

Growth differentiation factor-15 (GDF15) is a protein that belongs to the transforming growth factor β superfamily. An elevated serum level of GDF15 was found to be associated with type 2 diabetes mellitus (T2DM). T2DM is an inflammatory disease that progresses from normal glucose tolerance (NGT) to impaired fasting glucose (IFG). Hence, we aimed to validate the relationship between GDF15 and IFG.

METHODS

The participants were divided into the following three groups: NGT (n=137), IFG (n=29), and T2DM (n=75). The controls and T2DM outpatients visited the hospital for routine health check-ups. We used fasting blood glucose to detect IFG in nondiabetic patients. We checked the body mass index (BMI), C-reactive protein level, metabolic parameters, and fasting serum GDF15 level.

RESULTS

Age, BMI, triglyceride, insulin, glucose, homeostatic model assessment-insulin resistance (HOMA-IR), and GDF15 levels were elevated in the IFG and T2DM groups compared to the NGT group. In the correlation analysis between metabolic parameters and GDF15, age and HOMA-IR had a significant positive correlation with GDF15 levels. GDF15 significantly discriminated between IFG and NGT, independent of age, BMI, and HOMA-IR. The serum levels of GDF15 were more elevated in men than in women. As a biomarker for IFG based on the receiver operating characteristic curve analysis, the cutoff value of GDF15 was 510 pg/mL in males and 400 pg/mL in females.

CONCLUSION

GDF15 had a positive correlation with IR independent of age and BMI, and the serum level of GDF15 was increased in the IFG and T2DM groups. GDF15 may be a novel biomarker for detecting IFG in nondiabetic patients.

Dietary stimulators of GLUT4 expression and translocation in skeletal muscle: a mini-review

Chronic insulin resistance can lead to type II diabetes mellitus, which is also directly influenced by an individual's genetics as well as their lifestyle. Under normal circumstances, insulin facilitates glucose uptake in skeletal muscle and adipose tissue by stimulating glucose transporter 4 (GLUT4) translocation and activity. GLUT4 activity is directly correlated with the ability to clear elevated blood glucose and insulin sensitivity. In diabetes, energy excess and prolonged hyperinsulinemia suppress muscle and adipose response to insulin, in part through reduced GLUT4 membrane levels. This work uniquely describes much of the experimental data demonstrating the effects of various dietary components on GLUT4 expression and translocation in skeletal muscle. These observations implicate several individual dietary chemicals as potential adjuvant therapies in the maintenance of diabetes and insulin resistance.

Cross-fostering and improved lactation ameliorates deficits in endocrine pancreatic morphology in growth-restricted adult male rat offspring

Uteroplacental insufficiency and poor postnatal nutrition impair adult glucose tolerance and insulin secretion in male rat offspring, which can be partially ameliorated by improving postnatal nutrition. Uteroplacental insufficiency was induced in the WKY rat on day 18 of pregnancy (Restricted) compared to sham-operated Controls. Pups were then cross-fostered onto Control or Restricted mothers one day after birth resulting in: (Pup-on-Mother) Control-on-Control, Control-on-Restricted, Restricted-on-Control and Restricted-on-Restricted. Endocrine pancreatic morphology and markers of intrinsic β-cell function and glucose homeostasis were assessed in male offspring at 6 months. Pancreatic and hepatic gene expression was quantified at postnatal day 7 and 6 months. Restricted pups were born 10-15% lighter than Controls and remained lighter at 6 months. Relative islet and β-cell mass were 51-65% lower in Restricted-on-Restricted compared to Controls at 6 months. Non-fasting plasma C-reactive protein levels were also increased, suggestive of an inflammatory response. Overall, the average number of islets, small islets and proportion of β-cells per islet correlated positively with birth weight. Intrinsic β-cell function, estimated by insulin secretion relative to β-cell mass, was unaffected by Restriction, suggesting that the in vivo functional deficit was attributable to reduced mass, not function. Importantly, these deficits were ameliorated when lactational nutrition was normalized in Restricted-on-Control offspring, who also showed increased pancreatic Igf1r, Pdx1 and Vegf mRNA expression at 7 days compared to Control-on-Control and Restricted-on-Restricted. This highlights lactation as a critical period for intervention following prenatal restraint, whereby deficits in endocrine pancreatic mass and associated impaired in vivo insulin secretion can be ameliorated.

Nonalcoholic fatty liver disease: A main driver of insulin resistance or a dangerous liaison?

Insulin resistance is one of the key components of the metabolic syndrome and it eventually leads to the development of type 2 diabetes, making it one of the biggest medical problems of modern society. Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are tightly associated with insulin resistance. While it is fairly clear that insulin resistance causes hepatic steatosis, it is not known if NAFLD causes insulin resistance. Hepatic inflammation and lipid accumulation are believed to be the main drivers of hepatic insulin resistance in NAFLD. Here we give an overview of the evidence linking hepatic lipid accumulation to the development of insulin resistance, including the accumulation of triacylglycerol and lipid metabolites, such as diacylglycerol and ceramides. In particular, we discuss the role of obesity in this relation by reviewing the current evidence in terms of the reported changes in body weight and/or adipose tissue mass. We further discuss whether the activation or inhibition of inflammatory pathways, Kupffer cells and other immune cells influences the development of insulin resistance. We show that, in contrast to what is commonly believed, neither hepatic steatosis nor hepatic inflammation is sufficient to cause insulin resistance. Many studies show that obesity cannot be ignored as an underlying factor in this relationship and NAFLD is therefore less likely to be one of the main drivers of insulin resistance.

Targeting inflammation in the treatment of type 2 diabetes: time to start

The role of inflammation in the pathogenesis of type 2 diabetes and associated complications is now well established. Several conditions that are driven by inflammatory processes are also associated with diabetes, including rheumatoid arthritis, gout, psoriasis and Crohn's disease, and various anti-inflammatory drugs have been approved or are in late stages of development for the treatment of these conditions. This review discusses the rationale for the use of some of these anti-inflammatory treatments in patients with diabetes and what we could expect from their use. Future immunomodulatory treatments may not target a specific disease, but could instead act on a dysfunctional pathway that causes several conditions associated with the metabolic syndrome.

ROCK1 isoform-specific deletion reveals a role for diet-induced insulin resistance

Rho kinase (ROCK) isoforms regulate insulin signaling and glucose metabolism negatively or positively in cultured cell lines and skeletal muscle. However, the in vivo function of the ROCK1 isoform in adipose tissue has not been addressed. To determine the specific role of the adipose ROCK1 isoform in the development of insulin resistance and obesity, mice lacking ROCK1 in adipose tissue globally or selectively were studied. Here, we show that insulin's ability to activate IRS-1/PI3K/Akt signaling was greatly enhanced in adipose tissue of ROCK1(-/-) mice compared with wild-type mice. These effects resulted from the inhibitory effect of ROCK1 on insulin receptor action, as evidenced by the fact that IR tyrosine phosphorylation was abolished in ROCK1(-/-) MEF cells when ROCK1 was reexpressed. Consistently, adipose-specific disruption of ROCK1 increased IR tyrosine phosphorylation in adipose tissue and modestly improved sensitivity to insulin in obese mice induced by high-fat feeding. This effect is independent of any changes in adiposity, number or size of adipocytes, and metabolic parameters, including glucose, insulin, leptin, and triglyceride levels, demonstrating a minimal effect of adipose ROCK1 on whole body metabolism. Enzymatic activity of ROCK1 in adipose tissue remained ∼50%, which likely originated from the fraction of stromal vascular cells, suggesting involvement of these cells for adipose metabolic regulation. Moreover, ROCK isoform activities were increased in adipose tissue of diet-induced or genetically obese mice. These data suggest that adipose ROCK1 isoform plays an inhibtory role for the regulation of insulin sensitivity in diet-induced obesity in vivo.

A network pharmacology approach to determine active compounds and action mechanisms of ge-gen-qin-lian decoction for treatment of type 2 diabetes

Traditional Chinese medicine (TCM) herbal formulae can be valuable therapeutic strategies and drug discovery resources. However, the active ingredients and action mechanisms of most TCM formulae remain unclear. Therefore, the identification of potent ingredients and their actions is a major challenge in TCM research. In this study, we used a network pharmacology approach we previously developed to help determine the potential antidiabetic ingredients from the traditional Ge-Gen-Qin-Lian decoction (GGQLD) formula. We predicted the target profiles of all available GGQLD ingredients to infer the active ingredients by clustering the target profile of ingredients with FDA-approved antidiabetic drugs. We also applied network target analysis to evaluate the links between herbal ingredients and pharmacological actions to help explain the action mechanisms of GGQLD. According to the predicted results, we confirmed that a novel antidiabetic ingredient from Puerariae Lobatae radix (Ge-Gen), 4-Hydroxymephenytoin, increased the insulin secretion in RIN-5F cells and improved insulin resistance in 3T3-L1 adipocytes. The network pharmacology strategy used here provided a powerful means for identifying bioactive ingredients and mechanisms of action for TCM herbal formulae, including Ge-Gen-Qin-Lian decoction.

Role of the mammalian target of rapamycin (mTOR) complexes in pancreatic β-cell mass regulation

Exquisite regulation of insulin secretion by pancreatic β-cells is essential to maintain metabolic homeostasis. β-Cell mass must be accordingly adapted to metabolic needs and can be largely modified under different situations. The mammalian target of rapamycin (mTOR) complexes has been consistently identified as key modulators of β-cell mass. mTOR can be found into two different complexes, mTORC1 and mTORC2. Under systemic insulin resistance, mTORC1/mTORC2 signaling in β-cells is needed to increase β-cell mass and insulin secretion. However, type 2 diabetes arises when these compensatory mechanisms fail, being the role of mTOR complexes still obscure in β-cell failure. In this chapter, we introduce the protein composition and regulation of mTOR complexes and their role in pancreatic β-cells. Furthermore, we describe their main signaling effectors through the review of numerous animal models, which indicate the essential role of mTORC1/mTORC2 in pancreatic β-cell mass regulation.

The onset of type 2 diabetes: proposal for a multi-scale model

Background

Type 2 diabetes mellitus (T2D) is a common age-related disease, and is a major health concern, particularly in developed countries where the population is aging, including Europe. The multi-scale immune system simulator for the onset of type 2 diabetes (MISSION-T2D) is a European Union-funded project that aims to develop and validate an integrated, multilevel, and patient-specific model, incorporating genetic, metabolic, and nutritional data for the simulation and prediction of metabolic and inflammatory processes in the onset and progression of T2D. The project will ultimately provide a tool for diagnosis and clinical decision making that can estimate the risk of developing T2D and predict its progression in response to possible therapies. Recent data showed that T2D and its complications, specifically in the heart, kidney, retina, and feet, should be considered a systemic disease that is sustained by a pervasive, metabolically-driven state of inflammation. Accordingly, there is an urgent need (1) to understand the complex mechanisms underpinning the onset of this disease, and (2) to identify early patient-specific diagnostic parameters and related inflammatory indicators.

Objective

We aim to accomplish this mission by setting up a multi-scale model to study the systemic interactions of the biological mechanisms involved in response to a variety of nutritional and metabolic stimuli and stressors.

Methods

Specifically, we will be studying the biological mechanisms of immunological/inflammatory processes, energy intake/expenditure ratio, and cell cycle rate. The overall architecture of the model will exploit an already established immune system simulator as well as several discrete and continuous mathematical methods for modeling of the processes critically involved in the onset and progression of T2D. We aim to validate the predictions of our models using actual biological and clinical data.

Results

This study was initiated in March 2013 and is expected to be completed by February 2016.

Conclusions

MISSION-T2D aims to pave the way for translating validated multilevel immune-metabolic models into the clinical setting of T2D. This approach will eventually generate predictive biomarkers for this disease from the integration of clinical data with metabolic, nutritional, immune/inflammatory, genetic, and gut microbiota profiles. Eventually, it should prove possible to translate these into cost-effective and mobile-based diagnostic tools.

Metabolic actions of Rho-kinase in periphery and brain

Obesity has increased at an alarming rate in recent years and is now a worldwide public health problem. Elucidating the mechanisms behind the metabolic dysfunctions associated with obesity is of high priority. The metabolic function of Rho-kinase (Rho-associated coiled-coil-containing kinase; ROCK) has been the subject of a great deal of investigation in metabolic-related diseases. It appears that inhibition of ROCK activity is beneficial for the treatment of a wide range of cardiovascular-related diseases. However, recent studies with genetic models of ROCK demonstrate that ROCK plays a positive role in insulin and leptin signaling. Here we discuss the newly identified functions of ROCK in regulating glucose and energy metabolism, with particular emphasis on metabolic actions of insulin and leptin.

How biologics targeting the IL-1 system are being considered for the treatment of type 2 diabetes

Metabolic diseases are associated with activation of the innate immune system in various tissues and characterized by elevated inflammatory factors and the presence of immune cells. Type 2 diabetes develops when islet beta cells are deficient in producing sufficient insulin to overcome peripheral insulin resistance. Intra-islet IL-1β activity diminishes beta cell function and survival and governs islet inflammation. Targeting the IL-1 system with the IL-1 receptor antagonist IL1Ra improved insulin secretion, glycaemia and reduced systemic inflammation in a proof of concept study with patients with type 2 diabetes. Currently, long lasting and specific IL-1β blocking antibodies are being evaluated in clinical trials and this may lead to a novel cytokine-based treatment for type 2 diabetes.

DC260126: a small-molecule antagonist of GPR40 that protects against pancreatic β-Cells dysfunction in db/db mice

G protein-coupled receptor 40 (GPR40) mediates both acute and chronic effects of free fatty acids (FFAs) on insulin secretion. However, it remains controversial whether inhibition of GPR40 would be beneficial in prevention of type 2 diabetes. This study is designed to evaluate the potential effects of DC260126, a small molecule antagonist of GPR40, on β-cell function following administration of 10 mg/kg dose of DC260126 to obese diabetic db/db mice. Oral glucose tolerance test, glucose stimulated insulin secretion and insulin tolerance test were used to investigate the pharmacological effects of DC260126 on db/db mice after 21-days treatment. Immunohistochemistry and serum biochemical analysis were also performed in this study. Although no significant change of blood glucose levels was found in DC260126-treated mice, DC260126 significantly inhibited glucose stimulated insulin secretion, reduced blood insulin level and improved insulin sensitivity after 3 weeks administration in db/db mice. Moreover, DC260126 reduced the proinsulin/insulin ratio and the apoptotic rate of pancreatic β-cells remarkably in DC260126-treated db/db mice compared to vehicle-treated mice (p<0.05, n = 8). The results suggest that although DC260126 could not provide benefit for improving hyperglycemia, it could protect against pancreatic β-cells dysfunction through reducing overload of β-cells, and it increases insulin sensitivity possibly via alleviation of hyperinsulinemia in db/db mice.

Antidiabetic potential of phycocyanin: effects on KKAy mice

CONTEXT

Phycocyanin (PC) has been proven to have many therapeutic properties, but its effects on diabetes have not been investigated.

OBJECTIVE

Antidiabetic activity of PC isolated from Spirulina platensis was evaluated in this study.

MATERIALS AND METHODS

Oral administration of PC (100 mg/kg, once per day for 3 weeks) on KKAy mice were investigated by monitoring the changes in body weight, food intake, fasting plasma glucose level, 24 h random blood glucose levels, oral glucose tolerance tests (OGTTs), glycosylated serum protein (GSP), fasting serum insulin (FINS), glycogen, triglyceride (TG), total cholesterol (TC), total antioxidative capability (T-AOC) and malondialdehyde (MDA). Histopathological changes in the pancreas were also examined with hematoxylin-eosin staining.

RESULTS

Administration of PC significantly decreased the body weight, fasting plasma glucose, 24 h random blood glucose levels, FINS and GSP levels, TG and TC content in serum and livers, MDA content in livers (p < 0.05 or p < 0.01). On the other hand, glucose tolerance to glucose administration, T-AOC, and the content of glycogen in liver and muscle were enhanced following PC treatment (p < 0.05 or p < 0.01). Histopathological results showed that PC administration suppressed the abnormal enlargement of islets observed in the pancreas of KKAy mice.

DISCUSSION AND CONCLUSION

The antidiabetic effect of PC on KKAy mice is most likely due to its ability to enhance insulin sensitivity, amelioration of insulin resistance of peripheral target tissues and regulation of glucolipide metabolism. Therefore, PC may have a potential clinical utility in combating type-2 diabetes.

Iron and diabetes risk

Iron overload is a risk factor for diabetes. The link between iron and diabetes was first recognized in pathologic conditions-hereditary hemochromatosis and thalassemia-but high levels of dietary iron also impart diabetes risk. Iron plays a direct and causal role in diabetes pathogenesis mediated both by β cell failure and insulin resistance. Iron also regulates metabolism in most tissues involved in fuel homeostasis, with the adipocyte in particular serving an iron-sensing role. The underlying molecular mechanisms mediating these effects are numerous and incompletely understood but include oxidant stress and modulation of adipokines and intracellular signal transduction pathways.

The role of aging upon β cell turnover

Preservation and regeneration of β cell endocrine function is a long-sought goal in diabetes research. Defective insulin secretion from β cells underlies both type 1 and type 2 diabetes, thus fueling considerable interest in molecules capable of rebuilding β cell secretion capacity. Though early work in rodents suggested that regeneration might be possible, recent studies have revealed that aging powerfully restricts cell cycle entry of β cells, which may limit regeneration capacity. Consequently, aging has emerged as an enigmatic challenge that might limit β cell regeneration therapies. This Review summarizes recent data regarding the role of aging in β cell regeneration and proposes models explaining these phenomena.

An exploratory study of the association between KCNB1 rs1051295 and type 2 diabetes and its related traits in Chinese Han population

Since the KCNB1 encoding Kv2.1 channel accounts for the majority of Kv currents modulating insulin secretion by pancreatic islet beta-cells, we postulated that KCNB1 is a plausible candidate gene for genetic variation contributing to the variable compensatory secretory function of beta-cells in type-2 diabetes (T2D). We conducted two studies, a case-control study and a cross-section study, to investigate the association of common single-nucleotide polymorphisms (SNPs) in KCNB1 with T2D and its linking traits. In the case-control study, we first examined the association of 20 tag SNPs of KCNB1 with T2D in a population with 226 T2D patients and non-diabetic subjects (screening study). We then identified the association in an enlarged population of 412 T2D patients and non-diabetic subjects (replication study). In the cross-sectional study, we investigated the linkage between the candidate SNP rs1051295 and T2D by comparing beta-cell function and insulin sensitivity among rs1051295 genotypes in a general population of 1051 subjects at fasting and after glucose loading (oral glucose tolerance tests, OGTT) in 84 fasting glucose impaired subjects, and several T2D-related traits. We found that among the 19 available tag SNPs, only the KCNB1 rs1051295 was associated with T2D (P = 0.027), with the rs1051295 TT genotype associated with an increased risk of T2D compared with genotypes CC (P = 0.009). At fasting, rs1051295 genotype TT was associated with a 9.8% reduction in insulin sensitivity compared to CC (P = 0.008); along with increased plasma triglycerides (TG) levels (TT/CC: P = 0.046) and increased waist/hip (W/H) ratio (TT/CC: P = 0.013; TT/TC: P = 0.002). OGTT confirmed that genotype TT exhibited reduced insulin sensitivity by 16.3% (P = 0.030) compared with genotype TC+CC in a fasting glucose impaired population. The KCNB1 rs1051295 genotype TT in the Chinese Han population is associated with decreased insulin sensitivity and increased plasma TG and W/H ratio, which together contribute to an increased risk for T2D.

Anti-diabetic activities of Gegen Qinlian Decoction in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes

Gegen Qinlian Decoction (GGQLD) is one of the well-known traditional Chinese medicines. Recently, it was reported that GGQLD had good clinical effects on type 2 diabetes mellitus. However, few studies have confirmed in detail the anti-diabetic activities of GGQLD in vivo and in vitro. In the present study, we investigated the anti-diabetic effects of GGQLD in high-fat diet combined with streptozotocin-induced diabetic rats and in 3T3-L1 adipocytes. The present results suggested GGQLD (4.95, 11.55 and 18.15 g/kg) decreased significantly fasting blood glucose, glycosylated serum protein, and glycosylated hemoglobin of diabetic rats (p<0.05), and GGQLD (4.95 and 18.15 g/kg) decreased significantly fasting serum insulin levels of diabetic rats (p<0.05); in 3T3-L1 adipocytes, Gegen Qinlian Decoction-containing serum (GGQLD-CS) (4%, 8% and 16%) enhanced glucose consumption, triglyceride (TG) content, adiponectin protein concentration and the mRNA expression of adiponectin. Adiponectin contributes to the regulation of lipid and glucose metabolism, and can play a critical role in the development of diabetes mellitus; the mechanisms of action of GGQLD might be related to augmentation of adiponectin protein concentration and up-regulation of the mRNA expression of adiponectin. However, the multi-target mechanisms of action of GGQLD need to be clarified further. The present study further validated the beneficial effects of GGQLD as an anti-diabetic agent. These findings provide a new insight into the anti-diabetic application for GGQLD in clinic and display the potential of GGQLD as a new drug candidate for the treatment of diabetes mellitus.

Insulin resistance is not necessarily an essential element of metabolic syndrome

Type 2 diabetes is frequently associated with metabolic syndrome (MetS). Insulin resistance (IR) is thought to be the underlying pathophysiology of MetS. The purpose of this study is to examine the association of MetS with IR and beta cell function. This is a cross-sectional study in NHANES 1999-2000 participants who were at least 18 years old, including 911 non-Hispanic whites (NHW), 398 non-Hispanic blacks (NHB), and 595 Mexican-Americans (MA). MetS was defined based on the revised ATP III. IR and beta cell function were calculated using homeostasis model assessment (HOMA-IR and HOMA-B). The high-risk tertile was defined as the highest HOMA-IR and lowest HOMA-B. The odds ratio (OR) was calculated against the other two tertiles. The relationship of HOAM-IR and HOMA-B with the components of MetS was also examined. IR was a risk factor of MetS in all three ethnic groups (OR 4.17-12.01, P < 0.0001). Fasting glucose, triglycerides, and HDL cholesterol were associated with IR (P < 0.001) and correlated with HOMA-IR (P < 0.001), while inconsistent results were noted in blood pressure and waist circumference among three racial/ethnic groups. However, in the MetS subjects, 32 % of NHW, 28 % of NHB, and 44 % of MA were not in the IR tertile and in the IR subjects, 25 % of NHW, 36 % NHB, and 30 % of MA did not have MetS. No relationship was found between beta cell function and MetS. Although IR is a risk factor for MetS, IR is neither necessary nor required for MetS.

Syntaxin-3 regulates newcomer insulin granule exocytosis and compound fusion in pancreatic beta cells

AIMS/HYPOTHESIS

The molecular basis of the exocytosis of secretory insulin-containing granules (SGs) during biphasic glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells remains unclear. Syntaxin (SYN)-1A and SYN-4 have been shown to mediate insulin exocytosis. The insulin-secretory function of SYN-3, which is particularly abundant in SGs, is unclear.

METHODS

Mouse pancreatic islets and INS-1 cells were treated with adenovirus carrying Syn-3 (also known as Stx3) or small interfering RNA targeting Syn-3 in order to examine insulin secretion by radioimmunoassay. The localisation and distribution of insulin granules were examined by confocal and electron microscopy. Dynamic single-granule fusion events were assessed using total internal reflection fluorescence microscopy (TIRFM).

RESULTS

Depletion of endogenous SYN-3 inhibited insulin release. TIRFM showed no change in the number or fusion competence of previously docked SGs but, instead, a marked reduction in the recruitment of newcomer SGs and their subsequent exocytotic fusion during biphasic GSIS. Conversely, overexpression of Syn-3 enhanced both phases of GSIS, owing to the increase in newcomer SGs and, remarkably, to increased SG-SG fusion, which was confirmed by electron microscopy.

CONCLUSIONS/INTERPRETATION

In insulin secretion, SYN-3 plays a role in the mediation of newcomer SG exocytosis and SG-SG fusion that contributes to biphasic GSIS.

Alteration of 11β-hydroxysteroid dehydrogenase type 1 and glucocorticoid receptor by ethanol in rat liver and mouse hepatoma cells

Alcohol is a potential risk factor of type 2 diabetes, but its underlying mechanism is unclear. To explore this issue, Wistar rats and mouse hepatoma cells (Hepa 1-6) were exposed to ethanol, 8 g·kg(-1) ·d(-1) for 3 months and 100 mM for 48 h, respectively. Glucose and insulin tolerance tests in vivo were performed, and protein levels of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) and glucocorticoid receptor (GR) in liver and Hepa 1-6 cells were measured. Alterations of key enzymes of gluconeogenesis phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6 phosphatase (G6Pase), as well as glycogen synthase kinase 3a (GSK3 α ), were also examined. The results revealed that glucose levels were increased, and insulin sensitivity was impaired accompanied with liver injury in rats exposed to ethanol compared with controls. The 11β-HSD1, GR, PEPCK, G6Pase, and GSK3 α proteins were increased in the liver of rats treated with ethanol compared with controls. Ethanol-exposed Hepa 1-6 cells also showed higher expression of 11β-HSD1, GR, PEPCK, G6Pase, and GSK3 α proteins than control cells. After treatment of Hepa 1-6 cells exposed to ethanol with the GR inhibitor RU486, the expression of 11β-HSD1 and GR was significantly decreased. At the same time the increases in PEPCK, G6Pase, and GSK3 α levels induced by ethanol in Hepa 1-6 cells were also attenuated by RU486. The results indicate that ethanol causes glucose intolerance by increasing hepatic expression of 11β-HSD1 and GR, which leads to increased expression of gluconeogenic and glycogenolytic enzymes.

MicroRNA expression profiling of human islets from individuals with and without type 2 diabetes: promises and pitfalls

Recent studies in mouse, involving the β-cell-specific deletion of Dicer1, have highlighted the crucial role of miRNAs (microRNAs) in regulating insulin secretion and consequently Type 2 diabetes. Identifying the individual miRNAs involved in human islet dysfunction may be of diagnostic and therapeutic interest. miRNA expression profiling of human islets isolated from donors with and without Type 2 diabetes may represent one of the first steps in the discovery of these specific miRNAs. The present review discusses some of the potential pitfalls and promises of such an approach.

Insulin resistance and the polycystic ovary syndrome revisited: an update on mechanisms and implications

Polycystic ovary syndrome (PCOS) is now recognized as an important metabolic as well as reproductive disorder conferring substantially increased risk for type 2 diabetes. Affected women have marked insulin resistance, independent of obesity. This article summarizes the state of the science since we last reviewed the field in the Endocrine Reviews in 1997. There is general agreement that obese women with PCOS are insulin resistant, but some groups of lean affected women may have normal insulin sensitivity. There is a post-binding defect in receptor signaling likely due to increased receptor and insulin receptor substrate-1 serine phosphorylation that selectively affects metabolic but not mitogenic pathways in classic insulin target tissues and in the ovary. Constitutive activation of serine kinases in the MAPK-ERK pathway may contribute to resistance to insulin's metabolic actions in skeletal muscle. Insulin functions as a co-gonadotropin through its cognate receptor to modulate ovarian steroidogenesis. Genetic disruption of insulin signaling in the brain has indicated that this pathway is important for ovulation and body weight regulation. These insights have been directly translated into a novel therapy for PCOS with insulin-sensitizing drugs. Furthermore, androgens contribute to insulin resistance in PCOS. PCOS may also have developmental origins due to androgen exposure at critical periods or to intrauterine growth restriction. PCOS is a complex genetic disease, and first-degree relatives have reproductive and metabolic phenotypes. Several PCOS genetic susceptibility loci have been mapped and replicated. Some of the same susceptibility genes contribute to disease risk in Chinese and European PCOS populations, suggesting that PCOS is an ancient trait.

Glucose-responsive artificial promoter-mediated insulin gene transfer improves glucose control in diabetic mice

AIM: To investigate the effect of insulin gene therapy using a glucose-responsive synthetic promoter in type 2 diabetic obese mice.

METHODS: We employed a recently developed novel insulin gene therapy strategy using a synthetic promoter that regulates insulin gene expression in the liver in response to blood glucose level changes. We intravenously administered a recombinant adenovirus expressing furin-cleavable rat insulin under the control of the synthetic promoter (rAd-SP-rINSfur) into diabetic Lepr^db/db mice. A recombinant adenovirus expressing β-galactosidase under the cytomegalovirus promoter was used as a control (rAd-CMV-βgal). Blood glucose levels and body weights were monitored for 50 d. Glucose and insulin tolerance tests were performed. Immunohistochemical staining was performed to investigate islet morphology and insulin content.

RESULTS: Administration of rAd-SP-rINSfur lowered blood glucose levels and normoglycemia was maintained for 50 d, whereas the rAd-CMV-βgal control virus-injected mice remained hyperglycemic. Glucose tolerance tests showed that rAd-SP-rINSfur-treated mice cleared exogenous glucose from the blood more efficiently than control virus-injected mice at 4 wk [area under the curve (AUC): 21  508.80 ± 2248.18 vs 62  640.00 ± 5014.28, P < 0.01] and at 6 wk (AUC: 29  956.60 ± 1757.33 vs 60  016.60 ± 3794.47, P < 0.01). In addition, insulin sensitivity was also significantly improved in mice treated with rAd-SP-rINSfur compared with rAd-CMV-βgal-treated mice (AUC: 9150.17 ± 1007.78 vs 11  994.20 ± 474.40, P < 0.05). The islets from rAd-SP-rINSfur-injected mice appeared to be smaller and to contain a higher concentration of insulin than those from rAd-CMV-βgal-injected mice.

CONCLUSION: Based on these results, we suggest that insulin gene therapy might be one therapeutic option for remission of type 2 diabetes.

Dual role of VAMP8 in regulating insulin exocytosis and islet β cell growth

Optimal insulin secretion required to maintain glucose homeostasis is the summation of total pancreatic islet β cell mass and intrinsic secretory capacity of individual β cells, which are regulated by distinct mechanisms that could be amplified by glucagon-like-peptide-1 (GLP-1). Because of these actions of GLP-1 on islet β cells, GLP-1 has been deployed to treat diabetes. We employed SNARE protein VAMP8-null mice to demonstrate that VAMP8 mediates insulin granule recruitment to the plasma membrane, which partly accounts for GLP-1 potentiation of glucose-stimulated insulin secretion. VAMP8-null mice also exhibited increased islet β cell mass from increased β cell mitosis, with β cell proliferative activity greatly amplified by GLP-1. Thus, despite the β cell exocytotic defect, VAMP8-null mice have an increased total insulin secretory capacity, which improved glucose homeostasis. We conclude that these VAMP8-mediated events partly underlie the therapeutic actions of GLP-1 on insulin secretion and β cell growth.

Hepatitis C virus induced a novel apoptosis-like death of pancreatic beta cells through a caspase 3-dependent pathway

Epidemiological and experimental studies have suggested that Hepatitis C virus (HCV) infection is associated with the development of type 2 diabetes. Pancreatic beta cell failure is central to the progression of type 2 diabetes. Using virus infection system, we investigate the influence of HCV infection on the fate of the insulinoma cell line, MIN6. Our experiments demonstrate that the HCV virion itself is indispensable and has a dose- and time-dependent cytopathic effect on the cells. HCV infection inhibits cell proliferation and induces death of MIN6 cells with apoptotic characteristics, including cell surface exposure of phosphatidylserine, decreased mitochondrial membrane potential, activation of caspase 3 and poly (ADP-ribose) polymerase, and DNA fragmentation in the nucleus. However, the fact that HCV-infected cells exhibit a dilated, low-density nucleus with intact plasma and nuclear membrane indicates that a novel apoptosis-like death occurs. HCV infection also causes endoplasmic reticulum (ER) stress. Further, HCV RNA replication was detected in MIN6 cells, although the infection efficiency is very low and no progeny virus particle generates. Taken together, our data suggest that HCV infection induces death of pancreatic beta cells through an ER stress-involved, caspase 3-dependent, special pathway.

Group VIA PLA2 (iPLA2β) is activated upstream of p38 mitogen-activated protein kinase (MAPK) in pancreatic islet β-cell signaling

Group VIA phospholipase A(2) (iPLA(2)β) in pancreatic islet β-cells participates in glucose-stimulated insulin secretion and sarco(endo)plasmic reticulum ATPase (SERCA) inhibitor-induced apoptosis, and both are attenuated by pharmacologic or genetic reductions in iPLA(2)β activity and amplified by iPLA(2)β overexpression. While exploring signaling events that occur downstream of iPLA(2)β activation, we found that p38 MAPK is activated by phosphorylation in INS-1 insulinoma cells and mouse pancreatic islets, that this increases with iPLA(2)β expression level, and that it is stimulated by the iPLA(2)β reaction product arachidonic acid. The insulin secretagogue D-glucose also stimulates β-cell p38 MAPK phosphorylation, and this is prevented by the iPLA(2)β inhibitor bromoenol lactone. Insulin secretion induced by d-glucose and forskolin is amplified by overexpressing iPLA(2)β in INS-1 cells and in mouse islets, and the p38 MAPK inhibitor PD169316 prevents both responses. The SERCA inhibitor thapsigargin also stimulates phosphorylation of both β-cell MAPK kinase isoforms and p38 MAPK, and bromoenol lactone prevents both events. Others have reported that iPLA(2)β products activate Rho family G-proteins that promote MAPK kinase activation via a mechanism inhibited by Clostridium difficile toxin B, which we find to inhibit thapsigargin-induced β-cell p38 MAPK phosphorylation. Thapsigargin-induced β-cell apoptosis and ceramide generation are also prevented by the p38 MAPK inhibitor PD169316. These observations indicate that p38 MAPK is activated downstream of iPLA(2)β in β-cells incubated with insulin secretagogues or thapsigargin, that this requires prior iPLA(2)β activation, and that p38 MAPK is involved in the β-cell functional responses of insulin secretion and apoptosis in which iPLA(2)β participates.

Nifedipine protects INS-1 β-cell from high glucose-induced ER stress and apoptosis

Sustained high concentration of glucose has been verified toxic to β-cells. Glucose augments Ca²⁺-stimulated insulin release in pancreatic β-cells, but chronic high concentration of glucose could induce a sustained level of Ca²⁺ in β-cells, which leads to cell apoptosis. However, the mechanism of high glucose-induced β-cell apoptosis remains unclear. In this study, we use a calcium channel blocker, nifedipine, to investigate whether the inhibition of intracellular Ca²⁺ concentration could protect β-cells from chronic high glucose-induced apoptosis. It was found that in a concentration of 33.3 mM, chronic stimulation of glucose could induce INS-1 β-cells apoptosis at least through the endoplasmic reticulum stress pathway and 10 μM nifedipine inhibited Ca²⁺ release to protect β-cells from high glucose-induced endoplasmic reticulum stress and apoptosis. These results indicated that inhibition of Ca²⁺ over-accumulation might provide benefit to attenuate islet β-cell decompensation in a high glucose environment.

EBF proteins participate in transcriptional regulation of Xenopus muscle development

EBF proteins have diverse functions in the development of multiple lineages, including neurons, B cells and adipocytes. During Drosophila muscle development EBF proteins are expressed in muscle progenitors and are required for muscle cell differentiation, but there is no known function of EBF proteins in vertebrate muscle development. In this study, we examine the expression of ebf genes in Xenopus muscle tissue and show that EBF activity is necessary for aspects of Xenopus skeletal muscle development, including somite organization, migration of hypaxial muscle anlagen toward the ventral abdomen, and development of jaw muscle. From a microarray screen, we have identified multiple candidate targets of EBF activity with known roles in muscle development. The candidate targets we have verified are MYOD, MYF5, M-Cadherin and SEB-4. In vivo overexpression of the ebf2 and ebf3 genes leads to ectopic expression of these candidate targets, and knockdown of EBF activity causes downregulation of the endogenous expression of the candidate targets. Furthermore, we found that MYOD and MYF5 are likely to be direct targets. Finally we show that MYOD can upregulate the expression of ebf genes, indicating the presence of a positive feedback loop between EBF and MYOD that we find to be important for maintenance of MYOD expression in Xenopus. These results suggest that EBF activity is important for both stabilizing commitment and driving aspects of differentiation in Xenopus muscle cells.

Antidiabetic effect and mechanism of chitooligosaccharides

The aim of this study was to observe the antidiabetic effect and mechanism of chitooligosaccharides (COS). Type 2 diabetic rats were fed a high-energy diet together with an injection of streptozotocin (STZ). After 8 weeks of COS treatment, the changes in glycometabolism, insulin sensitivity, serum hepatic marker enzyme levels, liver glycogen content, expressions of glucose transporter GLUT-4, malonaldehyde content, superoxide dismutase activity and morphology of the pancreas were observed. The results showed that COS significantly reduced fasting blood glucose (FBG), fasting insulin (FINS), increased the insulin sensitivity index (ISI) and improved oral glucose tolerance. COS increased liver glucokinase activity and glycogen content and upregulated the expressions of GLUT-4 mRNA in adipose and soleus muscle. They also raised the superoxide dismutase activity and reduced the malonaldehyde content in pancreas homogenate. Pancreas hematoxylin/eosin (HE) staining of the diabetic rats showed ruptured islet, but changes of pancreatic islet in the animals were minimized by administration of COS. The effect of COS on pancreatic beta cell (INS-1) in vitro was also examined. It was found that COS played important roles in INS-1 cells by promoting proliferation, increasing glucose stimulated insulin release, upregulating the expressions of GLUT-2 mRNA and protecting against STZ-induced apoptosis. The results from the present study indicate COS have protective effect for type 2 diabetes by ameliorating insulin resistance, promoting the proliferation of beta cells, increasing insulin secretion and protecting beta cells.

Growth hormone can improve insulin resistance and differentiation in pancreas of senescence accelerated prone male mice (SAMP8)

OBJECTIVE

The aim of the present study was to investigate the effect of aging on several parameters related to glucose metabolism, proliferation and differentiation in the pancreas and how GH administration to old SAMP8 mice could affect these parameters.

MATERIALS AND METHODS

Pancreas samples were obtained from two types of male mice models: senescence-accelerated prone (SAMP8) and senescence-accelerated-resistant (SAMR1) mice SAMP8 and SAMR1 mice and the influence of exogenous administration of GH (2mgs.c./kg/day) on SAMP8 mice. RNA was isolated from pancreas samples of male mice using the kit RNeasy total RNA kit Ref. 50974104 (Qiagen). Insulin was measured in plasma by RIA kit and glucose was measured in plasma by an assay kit.

RESULTS

Aging decreases the expression of differentiation in the pancreas of Pdx-1, FoxO 1 and FoxO 3A but not of Sirt 1 or of the expression of the proliferative genes PCNA and Sei1. The expression of glucagon and GLUT2 were increased with aging and no differences were observed in somatostatin and insulin expressions. Insulin levels in plasma were increased with aging in SAMP8 mice. IGF-1 expression was reduced with aging. The treatment with GH was able to increase the expression of Sirt 1, Pdx-1, FoxO 3A and IGF-1. On the other hand, the treatment decreased the expression of glucagon, GLUT2, somatostatin and insulin, furthermore GH was able to decrease the plasma levels of insulin in old male SAMP8 mice (p<0.0004).

CONCLUSION

The present study has shown that aging is associated with significant alterations in the relative expression of pancreatic genes involved in insulin secretion as well as in the differentiation and in the intra islet glucose metabolism. According to our results, GH administration to old SAMP8 mice was able to improve the pancreatic function of the old SAMP8 mice and to decrease insulin and glucagon expressions in the pancreas improving instead insulin levels and glucose metabolism.

Type 2 diabetes as an inflammatory disease

Components of the immune system are altered in obesity and type 2 diabetes (T2D), with the most apparent changes occurring in adipose tissue, the liver, pancreatic islets, the vasculature and circulating leukocytes. These immunological changes include altered levels of specific cytokines and chemokines, changes in the number and activation state of various leukocyte populations and increased apoptosis and tissue fibrosis. Together, these changes suggest that inflammation participates in the pathogenesis of T2D. Preliminary results from clinical trials with salicylates and interleukin-1 antagonists support this notion and have opened the door for immunomodulatory strategies for the treatment of T2D that simultaneously lower blood glucose levels and potentially reduce the severity and prevalence of the associated complications of this disease.

Effects of a Therapeutic Lifestyle Modification Program on Inflammatory Chemokines and Insulin Resistance in Subjects With Metabolic Syndrome

Background. Although therapeutic lifestyle modification (TLM) effectively improves the values of diagnostic biomarkers of metabolic syndrome, less is known about its effects on inflammatory chemokines and insulin resistance (IR) in patients with this syndrome. Objectives. To examine the effects of a short-term TLM program on inflammatory chemokines (monocyte chemoattractant protein-1 [MCP-1], retinol binding protein-4 [RBP-4]) and IR in subjects with metabolic syndrome. Method. Twenty-nine women (aged 66.5 ± 9.5 years) with metabolic syndrome were randomly assigned to the TLM intervention group (n = 16) or control group (n = 13). The TLM intervention group was provided with 4 weeks of health screening, education, exercise, diet, and counseling. Participants in the control group were instructed to maintain their usual lifestyle behavior. Outcome variables measured included MCP-1, RBP-4, fasting glucose, fasting insulin, and homeostasis model assessment (HOMA). An intention-to-treat strategy was not followed, and the final number of subjects in the analysis was 22 (14 in the TLM group and 8 in the control group). Results. After a 4-week TLM program, MCP-1, fasting insulin, and HOMA were significantly decreased in the TLM group compared to those in the control group (all p < .05). Conclusions. We conclude that a short-term TLM program could be effective for improving inflammatory state and IR, which are significant preceding biomarkers for cardiovascular complications in subjects with metabolic syndrome.

The unfolded protein response is required to maintain the integrity of the endoplasmic reticulum, prevent oxidative stress and preserve differentiation in β-cells

Diabetes is an epidemic of worldwide proportions caused by β-cell failure. Nutrient fluctuations and insulin resistance drive β-cells to synthesize insulin beyond their capacity for protein folding and secretion and thereby activate the unfolded protein response (UPR), an adaptive signalling pathway to promote cell survival upon accumulation of unfolded protein in the endoplasmic reticulum (ER). Protein kinase-like endoplasmic reticulum kinase (PERK) signals one component of the UPR through phosphorylation of eukaryotic initiation factor 2 on the α-subunit (eIF2α) to attenuate protein synthesis, thereby reducing the biosynthetic burden. β-Cells uniquely require PERK-mediated phosphorylation of eIF2α to preserve cell function. Unabated protein synthesis in β-cells is sufficient to initiate a cascade of events, including oxidative stress, that are characteristic of β-cell failure observed in type 2 diabetes. In contrast to acute adaptive UPR activation, chronic activation increases expression of the proapoptotic transcription factor CAAT/enhancer-binding protein homologous protein (CHOP). Chop deletion in insulin-resistant mice profoundly increases β-cell mass and prevents β-cell failure to forestall the progression of diabetes. The findings suggest an unprecedented link by which protein synthesis and/or misfolding in the ER causes oxidative stress and should encourage the development of novel strategies to treat diabetes.

Mechanism of anti-hyperglycemic action of Vatairea macrocarpa (Leguminosae): investigation in peripheral tissues

AIM OF THE STUDY

Previous studies in our laboratory have demonstrated that the treatment of diabetic rats during 21 days with V. macrocarpa stem-bark ethanolic extract (VmE), reduced glycemia, urinary glucose and urea, increased liver glycogen content and improved other parameters diabetes related. The objective of this study was to evaluate if the anti-hyperglycemic mechanisms of VmE could be caused by improvement in the insulin signaling pathway in the peripheral tissues (liver, adipose and skeletal muscle).

MATERIAL AND METHODS

Streptozotocin-diabetic rats were separated into two groups: diabetic control (DC) and diabetic treated with VmE (DT) during 21 days. The alterations on the insulin signaling in liver, retroperitoneal adipose tissue (RET) and extensor digitorum longus (EDL) muscles were investigated through determination of insulin receptor (IR), protein kinase B/AKT content and AKT phosphorylation levels using Western blotting analysis. This same methodology was used to evaluate the phosphoenolpyruvate carboxykinase (PEPCK) levels in the liver from these animals.

RESULTS

The treatment with the extract increased the content of IR and the basal phosphorylation of AKT in the three tissues. In the liver from diabetic treated group, the insulin-stimulated AKT phosphorylation was higher and the PEPCK protein levels were reduced.

CONCLUSIONS

Data from this work suggest that the anti-hyperglycemic activity of stem-bark extract of V. macrocarpa can occur through stimulation of insulin signaling pathways in peripheral tissues from diabetic rats, mainly in liver and adipose tissue, probably promoting increase in the glucose uptake and liver glycogen synthesis. The concomitant decreasing in hepatic PEPCK levels could be associated to inhibition of gluconeogenesis, which can also contribute to glycemia reduction.

The double-stranded RNA-dependent protein kinase differentially regulates insulin receptor substrates 1 and 2 in HepG2 cells

The RNA-dependent protein kinase (PKR), initially known as a virus infection response protein, is found to differentially regulate two major players in the insulin signaling pathway, IRS1 and IRS2. PKR up-regulates the inhibitory phosphorylation of IRS1 and the expression of IRS2 at the transcriptional level.

Initially identified to be activated upon virus infection, the double-stranded RNA–dependent protein kinase (PKR) is best known for triggering cell defense responses by phosphorylating eIF-2α, thus suppressing RNA translation. We as well as others showed that the phosphorylation of PKR is down-regulated by insulin. In the present study, we further uncovered a novel function of PKR in regulating the IRS proteins. We found that PKR up-regulates the inhibitory phosphorylation of IRS1 at Ser312, which suppresses the tyrosine phosphorylation of IRS1. This effect of PKR on the phosphorylation of IRS1 is mediated by two other protein kinases, JNK and IKK. In contrast, PKR regulates IRS2, another major IRS family protein in the liver, at the transcriptional rather than the posttranslational level, and this effect is mediated by the transcription factor, FoxO1, which has been previously shown to be regulated by insulin and plays a significant role in glucose homeostasis and energy metabolism. In summary, we found for the first time that initially known as a virus infection response gene, PKR regulates the upstream central transmitters of insulin signaling, IRS1 and IRS2, through different mechanisms.

Direct evidence for susceptibility genes for type 2 diabetes on mouse chromosomes 11 and 14

AIMS/HYPOTHESIS

Diabetogenic loci for type 2 diabetes have been mapped to mouse chromosome (Chr) 11 and 14 in the Nagoya-Shibata-Yasuda (NSY) mouse, an animal model of type 2 diabetes. We aimed to obtain direct evidence of these genes on each chromosome and to clarify their function and interaction in conferring susceptibility to type 2 diabetes.

METHODS

We established three consomic strains homozygous for diabetogenic NSY-Chr11, NSY-Chr14 or both on the control C3H background (C3H-11(NSY), C3H-14(NSY) and C3H-11(NSY)14(NSY), respectively), and monitored diabetes-related phenotypes longitudinally. The glucokinase gene was sequenced as a positional candidate gene on Chr11.

RESULTS

C3H-11(NSY) mice showed hyperglycaemia associated with impaired insulin secretion and age-dependent insulin resistance without obesity. C3H-14(NSY) mice exhibited hyperglycaemia mainly due to insulin resistance, with a slight increase in percentage body fat. C3H-11(NSY)14(NSY) double consomic mice showed marked hyperglycaemia and obesity, which was not observed in single consomic strains. Sequences of the glucokinase gene were allelically variant between NSY and C3H mice.

CONCLUSIONS/INTERPRETATION

These data provide direct evidence that Chr11 and Chr14 harbour major susceptibility genes for type 2 diabetes. These two chromosomes interact to cause more severe hyperglycaemia and obesity, which was not observed with the presence of either single chromosome, indicating different modes of gene-gene interaction depending on the phenotype. Marked changes in the phenotypes retained in the consomic strains will facilitate fine mapping and the identification of the responsible genes and their interaction with each other, other genes and environmental factors.

Islet inflammation impairs the pancreatic beta-cell in type 2 diabetes

Onset of Type 2 diabetes occurs when the pancreatic beta-cell fails to adapt to the increased insulin demand caused by insulin resistance. Morphological and therapeutic intervention studies have uncovered an inflammatory process in islets of patients with Type 2 diabetes characterized by the presence of cytokines, immune cells, beta-cell apoptosis, amyloid deposits, and fibrosis. This insulitis is due to a pathological activation of the innate immune system by metabolic stress and governed by IL-1 signaling. We propose that this insulitis contributes to the decrease in beta-cell mass and the impaired insulin secretion observed in patients with Type 2 diabetes.

Elevated serum retinol-binding protein 4 is associated with insulin resistance in older women

Retinol-binding protein 4 (RBP4), a molecule secreted from adipocytes and hepatocytes, may contribute to insulin resistance and is a potential predictor for type 2 diabetes mellitus. We investigated the association between serum RBP4 concentrations and insulin resistance in perimenopausal women. In addition, we examined associations of serum RBP4 concentrations with age, risk factors of cardiovascular disease, and metabolic syndrome. A total of 73 healthy women were included in this study. Subjects' anthropometric measurements were taken, and body mass index and waist-hip ratio were calculated. Fasting glucose, fasting insulin, serum RBP4, and lipid parameters were examined. These various parameters were compared in subjects younger than and older than 50 years. Serum RBP4 concentrations in women at least 50 years of age were significantly higher than those in women younger than 50 years. In all subjects, serum RBP4 concentrations positively correlated with age, diastolic blood pressure, fasting glucose, and homeostatic assessment model of insulin resistance. After subgroup analysis, serum RBP4 concentrations positively correlated with age, fasting glucose, and homeostatic assessment model of insulin resistance in women at least 50 years of age. In women younger than 50 years, serum RBP4 concentrations positively correlated only with fasting glucose. Serum RBP4 appears to identify age-induced insulin resistance by physiologic changes due to aging or menopause and by increasing hepatic glucose production. However, the clinical implication of RBP4 for detecting cardiovascular disease and metabolic syndrome is not clear.

The roles of telomeres and telomerase in beta-cell regeneration

Telomerase is a specialized reverse transcriptase that is responsible for extending and preserving the end of the chromosomes (telomeres). Telomerase plays a key role in regulating the lifespan of mammalian cells and is involved in critical aspects of cellular ageing processes. In this review, we will briefly summarize our current understanding of the functions of telomeres, telomerase and their regulation. Considering that compensatory islet hyperplasia and beta-cell regeneration play important roles in the prevention and/or delay of the onset of overt diabetes, we will also examine current literature regarding the effects of diabetes on telomere shortening and provide insights from our own studies on the role of telomerase in beta-cell regeneration.

Transcription factor AP-2beta inhibits glucose-induced insulin secretion in cultured insulin-secreting cell-line

AIM

We previously identified the transcription factor activating enhancer-binding protein-2beta (AP-2beta) gene as a new candidate for conferring susceptibility to type 2 diabetes. To ascertain the possible involvement of AP-2beta in the pathogenesis of type 2 diabetes we examined the effects of AP-2beta on glucose-induced insulin secretion.

METHODS

We measured the insulin secretion stimulated by glucose, tolbutamide, or KCl in the HIT-T15 cells infected with adenovirus vectors encoding AP-2beta or LacZ (control).

RESULTS

We identified clear expression of AP-2beta in isolated rat pancreatic islets and in HIT-T15 cells. Glucose-induced increase in insulin secretion was significantly inhibited in AP-2beta-overexpressing cells (LacZ, 5.0+/-0.8 ng h(-1)mg(-1) protein; AP-2beta, 1.7+/-0.2 ng h(-1)mg(-1) protein; P=0.0015), whereas insulin expression was the same in both types of cells. Tolbutamide-induced insulin secretion was also suppressed in the AP-2beta-overexpressing cells, but KCl-induced insulin secretion was not affected by AP-2beta overexpression. In addition, Kir6.2 and glucokinase expression was significantly decreased in the AP-2beta-overexpressing cells.

CONCLUSION

We identified for the first time that AP-2beta expressed and functioned in insulin-secreting cell-line HIT-T15. These results suggest that AP-2beta contributes to susceptibility to type 2 diabetes by inhibiting glucose-induced insulin secretion in pancreatic beta cells.

Positional cloning of zinc finger domain transcription factor Zfp69, a candidate gene for obesity-associated diabetes contributed by mouse locus Nidd/SJL

Polygenic type 2 diabetes in mouse models is associated with obesity and results from a combination of adipogenic and diabetogenic alleles. Here we report the identification of a candidate gene for the diabetogenic effect of a QTL (Nidd/SJL, Nidd1) contributed by the SJL, NON, and NZB strains in outcross populations with New Zealand Obese (NZO) mice. A critical interval of distal chromosome 4 (2.1 Mbp) conferring the diabetic phenotype was identified by interval-specific congenic introgression of SJL into diabetes-resistant C57BL/6J, and subsequent reporter cross with NZO. Analysis of the 10 genes in the critical interval by sequencing, qRT–PCR, and RACE–PCR revealed a striking allelic variance of Zfp69 encoding zinc finger domain transcription factor 69. In NZO and C57BL/6J, a retrotransposon (IAPLTR1a) in intron 3 disrupted the gene by formation of a truncated mRNA that lacked the coding sequence for the KRAB (Krüppel-associated box) and Znf-C2H2 domains of Zfp69, whereas the diabetogenic SJL, NON, and NZB alleles generated a normal mRNA. When combined with the B6.V-Lep^ob background, the diabetogenic Zfp69^SJL allele produced hyperglycaemia, reduced gonadal fat, and increased plasma and liver triglycerides. mRNA levels of the human orthologue of Zfp69, ZNF642, were significantly increased in adipose tissue from patients with type 2 diabetes. We conclude that Zfp69 is the most likely candidate for the diabetogenic effect of Nidd/SJL, and that retrotransposon IAPLTR1a contributes substantially to the genetic heterogeneity of mouse strains. Expression of the transcription factor in adipose tissue may play a role in the pathogenesis of type 2 diabetes.

Type 2 diabetes in humans as well as in obese mice is caused by a combination of adipogenic and diabetogenic gene variants. We have identified a gene that appears to be involved in the pathogenesis of hyperglycaemia in obese mice: in some mouse strains, the gene Zfp69 is disrupted by a retroviral transposon (IAPLTR1a), which generates a truncated mRNA. Disruption of the gene was associated with a reduced susceptibility for diabetes, whereas the normal allele enhanced hyperglycaemia in obese mice. Zfp69 encodes a transcription factor which appears to interfere with lipid storage in adipose tissue, and thereby enhances lipid deposition in liver. In humans with type 2 diabetes, mRNA levels of the human orthologue of Zfp69 (ZNF642) were increased in adipose tissue. Thus, the transcription factor ZFP69/ZNF642 may be involved in the pathogenesis of obesity-associated diabetes.

Targeted disruption of ROCK1 causes insulin resistance in vivo

Insulin signaling is essential for normal glucose homeostasis. Rho-kinase (ROCK) isoforms have been shown to participate in insulin signaling and glucose metabolism in cultured cell lines. To investigate the physiological role of ROCK1 in the regulation of whole body glucose homeostasis and insulin sensitivity in vivo, we studied mice with global disruption of ROCK1. Here we show that, at 16-18 weeks of age, ROCK1-deficient mice exhibited insulin resistance, as revealed by the failure of blood glucose levels to decrease after insulin injection. However, glucose tolerance was normal in the absence of ROCK1. These effects were independent of changes in adiposity. Interestingly, ROCK1 gene ablation caused a significant increase in glucose-induced insulin secretion, leading to hyperinsulinemia. To determine the mechanism(s) by which deletion of ROCK1 causes insulin resistance, we measured the ability of insulin to activate phosphatidylinositol 3-kinase and multiple distal pathways in skeletal muscle. Insulin-stimulated phosphatidylinositol 3-kinase activity associated with IRS-1 or phospho-tyrosine was also reduced approximately 40% without any alteration in tyrosine phosphorylation of insulin receptor in skeletal muscle. Concurrently, serine phosphorylation of IRS-1 at serine 632/635, which is phosphorylated by ROCK in vitro, was also impaired in these mice. Insulin-induced phosphorylation of Akt, AS160, S6K, and S6 was also decreased in skeletal muscle. These data suggest that ROCK1 deficiency causes systemic insulin resistance by impairing insulin signaling in skeletal muscle. Thus, our results identify ROCK1 as a novel regulator of glucose homeostasis and insulin sensitivity in vivo, which could lead to new treatment approaches for obesity and type 2 diabetes.