Ablation of 3-phosphoinositide-dependent protein kinase 1 (PDK1) in vascular endothelial cells enhances insulin sensitivity by reducing visceral fat and suppressing angiogenesis

The phosphatidylinositol 3-kinase signaling pathway in vascular endothelial cells is important for systemic angiogenesis and glucose metabolism. In this study, we addressed the precise role of the 3-phosphoinositide-dependent protein kinase 1 (PDK1)-regulated signaling network in endothelial cells in vivo, using vascular endothelial PDK1 knockout (VEPDK1KO) mice. Surprisingly, VEPDK1KO mice manifested enhanced glucose tolerance and whole-body insulin sensitivity due to suppression of their hepatic glucose production with no change in either peripheral glucose disposal or even impaired vascular endothelial function at 6 months of age. When mice were fed a standard diet at 6 months of age and a high-fat diet at 3 months of age, hypertrophy of epididymal adipose tissues was inhibited, adiponectin mRNA was significantly increased, and mRNA of MCP1, leptin, and TNFα was decreased in the white adipose tissue of VEPDK1KO mice in comparison with controls. Consequently, both the circulating adiponectin levels and the activity of hepatic AMP-activated protein kinase were significantly increased, subsequently enhancing whole-body insulin sensitivity and energy expenditure with increased hepatic fatty acid oxidation in VEPDK1KO mice. These results provide the first in vivo evidence that lowered angiogenesis through the deletion of PDK1 signaling not only interferes with the growth of adipose tissue but also induces increased energy expenditure due to amelioration of the adipocytokine profile. This demonstrates an unexpected role of PDK1 signaling in endothelial cells on the maintenance of proper glucose homeostasis through the regulation of adipocyte development.

Overexpression of KLF15 transcription factor in adipocytes of mice results in down-regulation of SCD1 protein expression in adipocytes and consequent enhancement of glucose-induced insulin secretion

Krüppel-like factor 15 (KLF15), a member of the Krüppel-like factor family of transcription factors, has been found to play diverse roles in adipocytes in vitro. However, little is known of the function of KLF15 in adipocytes in vivo. We have now found that the expression of KLF15 in adipose tissue is down-regulated in obese mice, and we therefore generated adipose tissue-specific KLF15 transgenic (aP2-KLF15 Tg) mice to investigate the possible contribution of KLF15 to various pathological conditions associated with obesity in vivo. The aP2-KLF15 Tg mice manifest insulin resistance and are resistant to the development of obesity induced by maintenance on a high fat diet. However, they also exhibit improved glucose tolerance as a result of enhanced insulin secretion. Furthermore, this enhancement of insulin secretion was shown to result from down-regulation of the expression of stearoyl-CoA desaturase 1 (SCD1) in white adipose tissue and a consequent reduced level of oxidative stress. This is supported by the findings that restoration of SCD1 expression in white adipose tissue of aP2-KLF15 Tg mice exhibited increased oxidative stress in white adipose tissue and reduced insulin secretion with hyperglycemia. Our data thus provide an example of cross-talk between white adipose tissue and pancreatic β cells mediated through modulation of oxidative stress.

Role of S6K1 in regulation of SREBP1c expression in the liver

The transcription factor sterol regulatory element-binding protein 1c (SREBP1c) plays an important role in the control of fatty acid metabolism in the liver. Evidence suggests that mammalian target of rapamycin (mTOR) complex 1 (mTORC1) contributes to the regulation of SREBP1c expression, but signaling downstream of mTORC1 remains unclear. We have now shown that medium rich in branched-chain amino acids stimulates expression of the SREBP1c gene in cultured hepatocytes in a manner sensitive both to rapamycin, a pharmacological inhibitor of mTORC1, and to a short hairpin RNA (shRNA) specific for S6 kinase 1 (S6K1), a downstream effector of mTORC1. The phosphorylation of S6K1 was increased in the liver of obese db/db mice. Furthermore, depletion of hepatic S6K1 in db/db mice with the use of an adenovirus vector encoding S6K1 shRNA resulted in down-regulation of SREBP1c gene expression in the liver as well as a reduced hepatic triglyceride content and serum triglyceride concentration. These results thus suggest that S6K1 regulates SREBP1c expression both in cultured hepatocytes and in mouse liver, and that increased hepatic activity of S6K1 contributes at least in part to the pathogenesis of obesity-induced hepatic steatosis and hypertriglyceridemia.

Report of the committee on the classification and diagnostic criteria of diabetes mellitus

CONCEPT OF DIABETES MELLITUS

Diabetes mellitus is a group of diseases associated with various metabolic disorders, the main feature of which is chronic hyperglycemia due to insufficient insulin action. Its pathogenesis involves both genetic and environmental factors. The long-term persistence of metabolic disorders can cause susceptibility to specific complications and also foster arteriosclerosis. Diabetes mellitus is associated with a broad range of clinical presentations, from being asymptomatic to ketoacidosis or coma, depending on the degree of metabolic disorder. CLASSIFICATION TABLES 1 AND 2 AND FIGURE 1: [Table: see text] [Table: see text] Figure 1 A scheme of the relationship between etiology (mechanism) and patho-physiological stages (states) of diabetes mellitus. Arrows pointing right represent worsening of glucose metabolism disorders (including onset of diabetes mellitus). Among the arrow lines, indicates the condition classified as 'diabetes mellitus'. Arrows pointing left represent improvement in the glucose metabolism disorder. The broken lines indicate events of low frequency. For example, in type 2 diabetes mellitus, infection can lead to ketoacidosis and require temporary insulin treatment for survival. Also, once diabetes mellitus has developed, it is treated as diabetes mellitus regardless of improvement in glucose metabolism, therefore, the arrow lines pointing left are filled in black. In such cases, a broken line is used, because complete normalization of glucose metabolism is rare.imageThe classification of glucose metabolism disorders is principally derived from etiology, and includes staging of pathophysiology based on the degree of deficiency of insulin action. These disorders are classified into four groups: (i) type 1 diabetes mellitus; (ii) type 2 diabetes mellitus; (iii) diabetes mellitus due to other specific mechanisms or diseases; and (iv) gestational diabetes mellitus. Type 1 diabetes is characterized by destruction of pancreatic β-cells. Type 2 diabetes is characterized by combinations of decreased insulin secretion and decreased insulin sensitivity (insulin resistance). Glucose metabolism disorders in category (iii) are divided into two subgroups; subgroup A is diabetes in which a genetic abnormality has been identified, and subgroup B is diabetes associated with other pathologic disorders or clinical conditions. The staging of glucose metabolism includes normal, borderline and diabetic stages depending on the degree of hyperglycemia occurring as a result of the lack of insulin action or clinical condition. The diabetic stage is then subdivided into three substages: non-insulin- requiring, insulin-requiring for glycemic control, and insulin-dependent for survival. The two former conditions are called non-insulin-dependent diabetes and the latter is known as insulin-dependent diabetes. In each individual, these stages may vary according to the deterioration or the improvement of the metabolic state, either spontaneously or by treatment. DIAGNOSIS TABLES 3–7 AND FIGURE 2: [Table: see text] [Table: see text] [Table: see text] [Table: see text] [Table: see text] Figure 2 Flow chart outlining steps in the clinical diagnosis of diabetes mellitus. *The value for HbA1c (%) is indicated with 0.4% added to HbA1c (JDS) (%).imageCategories of the State of Glycemia:  Confirmation of chronic hyperglycemia is essential for the diagnosis of diabetes mellitus. When plasma glucose levels are used to determine the categories of glycemia, patients are classified as having a diabetic type if they meet one of the following criteria: (i) fasting plasma glucose level of ≥126 mg/dL (≥7.0 mmol/L); (ii) 2-h value of ≥200 mg/dL (≥11.1 mmol/L) in 75 g oral glucose tolerance test (OGTT); or (iii) casual plasma glucose level of ≥200 mg/dL (≥11.1 mmol/L). Normal type is defined as fasting plasma glucose level of <110 mg/dL (<6.1 mmol/L) and 2-h value of <140 mg/dL (<7.8 mmol/L) in OGTT. Borderline type (neither diabetic nor normal type) is defined as falling between the diabetic and normal values. According to the current revision, in addition to the earlier listed plasma glucose values, hemoglobin A1c (HbA1c) has been given a more prominent position as one of the diagnostic criteria. That is, (iv) HbA1c≥6.5% is now also considered to indicate diabetic type. The value of HbA1c, which is equivalent to the internationally used HbA1c (%) (HbA1c [NGSP]) defined by the NGSP (National Glycohemoglobin Standardization Program), is expressed by adding 0.4% to the HbA1c (JDS) (%) defined by the Japan Diabetes Society (JDS). Subjects with borderline type have a high rate of developing diabetes mellitus, and correspond to the combination of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) noted by the American Diabetes Association (ADA) and WHO. Although borderline cases show few of the specific complications of diabetes mellitus, the risk of arteriosclerosis is higher than those of normal type. When HbA1c is 6.0-6.4%, suspected diabetes mellitus cannot be excluded, and when HbA1c of 5.6-5.9% is included, it forms a group with a high risk for developing diabetes mellitus in the future, even if they do not have it currently. Clinical Diagnosis: 1 If any of the criteria for diabetic type (i) through to (iv) is observed at the initial examination, the patient is judged to be 'diabetic type'. Re-examination is conducted on another day, and if 'diabetic type' is reconfirmed, diabetes mellitus is diagnosed. However, a diagnosis cannot be made only by the re-examination of HbA1c alone. Moreover, if the plasma glucose values (any of criteria [i], [ii], or [iii]) and the HbA1c (criterion [iv]) in the same blood sample both indicate diabetic type, diabetes mellitus is diagnosed based on the initial examination alone. If HbA1c is used, it is essential that the plasma glucose level (criteria [i], [ii] or [iii]) also indicates diabetic type for a diagnosis of diabetes mellitus. When diabetes mellitus is suspected, HbA1c should be measured at the same time as examination for plasma glucose.2 If the plasma glucose level indicates diabetic type (any of [i], [ii], or [iii]) and either of the following conditions exists, diabetes mellitus can be diagnosed immediately at the initial examination.• The presence of typical symptoms of diabetes mellitus (thirst, polydipsia, polyuria, weight loss)• The presence of definite diabetic retinopathy3 If it can be confirmed that the above conditions 1 or 2 existed in the past, diabetes mellitus can be diagnosed or suspected regardless of the current test results.4 If the diagnosis of diabetes cannot be established by these procedures, the patient is followed up and re-examined after an appropriate interval.5 The physician should assess not only the presence or absence of diabetes, but also its etiology and glycemic stage, and the presence and absence of diabetic complications or associated conditions. Epidemiological Study:  For the purpose of estimating the frequency of diabetes mellitus, 'diabetes mellitus' can be substituted for the determination of 'diabetic type' from a single examination. In this case, HbA1c≥6.5% alone can be defined as 'diabetes mellitus'. Health Screening:  It is important not to misdiagnose diabetes mellitus, and thus clinical information such as family history and obesity should be referred to at the time of screening in addition to an index for plasma glucose level. Gestational Diabetes Mellitus:  There are two hyperglycemic disorders in pregnancy: (i) gestational diabetes mellitus (GDM); and (ii) diabetes mellitus. GDM is diagnosed if one or more of the following criteria is met in a 75 g OGTT during pregnancy: 1 Fasting plasma glucose level of ≥92 mg/dL (5.1 mmol/L)2 1-h value of ≥180 mg/dL (10.0 mmol/L)3 2-h value of ≥153 mg/dL (8.5 mmol/L) However, diabetes mellitus that is diagnosed by the clinical diagnosis of diabetes mellitus defined earlier is excluded from GDM. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00074.x, 2010).

A genome-wide association study in the Japanese population identifies susceptibility loci for type 2 diabetes at UBE2E2 and C2CD4A-C2CD4B

We conducted a genome-wide association study of type 2 diabetes (T2D) using 459,359 SNPs in a Japanese population with a three-stage study design (stage 1, 4,470 cases and 3,071 controls; stage 2, 2,886 cases and 3,087 controls; stage 3, 3,622 cases and 2,356 controls). We identified new associations in UBE2E2 on chromosome 3 and in C2CD4A-C2CD4B on chromosome 15 at genome-wide significant levels (rs7612463 in UBE2E2, combined P = 2.27 × 10⁻⁹; rs7172432 in C2CD4A-C2CD4B, combined P = 3.66 × 10⁻⁹). The association of these two loci with T2D was replicated in other east Asian populations. In the European populations, the C2CD4A-C2CD4B locus was significantly associated with T2D, and a combined analysis of all populations gave P = 8.78 × 10⁻¹⁴, whereas the UBE2E2 locus did not show association to T2D. In conclusion, we identified two new loci at UBE2E2 and C2CD4A-C2CD4B associated with susceptibility to T2D.

Role of KLF15 in regulation of hepatic gluconeogenesis and metformin action

OBJECTIVE

An increase in the rate of gluconeogenesis is largely responsible for the hyperglycemia in individuals with type 2 diabetes, with the antidiabetes action of metformin being thought to be achieved at least in part through suppression of gluconeogenesis.

RESEARCH DESIGN AND METHODS

We investigated whether the transcription factor KLF15 has a role in the regulation of gluconeogenesis and whether KLF15 participates in the antidiabetes effect of metformin.

RESULTS

Here we show that KLF15 regulates the expression of genes for gluconeogenic or amino acid-degrading enzymes in coordination with the transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1alpha. Liver-specific ablation of KLF15 in diabetic mice resulted in downregulation of the expression of genes for gluconeogenic or amino acid catabolic enzymes and in amelioration of hyperglycemia. Exposure of cultured hepatocytes to metformin reduced the abundance of KLF15 through acceleration of its degradation and downregulation of its mRNA. Metformin suppressed the expression of genes for gluconeogenic or amino acid-degrading enzymes in cultured hepatocytes, and these effects of metformin were attenuated by restoration of KLF15 expression. Administration of metformin to mice inhibited both the expression of KLF15 and glucose production in the liver, the latter effect also being attenuated by restoration of hepatic KLF15 expression.

CONCLUSIONS

KLF15 plays an important role in regulation of the expression of genes for gluconeogenic and amino acid-degrading enzymes and that the inhibitory effect of metformin on gluconeogenesis is mediated at least in part by downregulation of KLF15 and consequent attenuation of the expression of such genes.

PDK-1/FoxO1 pathway in POMC neurons regulates Pomc expression and food intake

Both insulin and leptin signaling converge on phosphatidylinositol 3-OH kinase [PI(3)K]/3-phosphoinositide-dependent protein kinase-1 (PDK-1)/protein kinase B (PKB, also known as Akt) in proopiomelanocortin (POMC) neurons. Forkhead box-containing protein-O1 (FoxO1) is inactivated in a PI(3)K-dependent manner. However, the interrelationship between PI(3)K/PDK-1/Akt and FoxO1, and the chronic effects of the overexpression of FoxO1 in POMC neurons on energy homeostasis has not been elucidated. To determine the extent to which PDK-1 and FoxO1 signaling in POMC neurons was responsible for energy homeostasis, we generated POMC neuron-specific Pdk1 knockout mice (POMCPdk1(-/-)) and mice selectively expressing a constitutively nuclear (CN)FoxO1 or transactivation-defective (Delta256)FoxO1 in POMC neurons (CNFoxO1(POMC) or Delta256FoxO1(POMC)). POMCPdk1(-/-) mice showed increased food intake and body weight accompanied by decreased expression of Pomc gene. The CNFoxO1(POMC) mice exhibited mild obesity and hyperphagia compared with POMCPdk1(-/-) mice. Although expression of the CNFoxO1 made POMCPdk1(-/-) mice more obese due to excessive suppression of Pomc gene, overexpression of Delta256FoxO1 in POMC neurons had no effects on metabolic phenotypes and Pomc expression levels of POMCPdk1(-/-) mice. These data suggest a requirement for PDK-1 and FoxO1 in transcriptional regulation of Pomc and food intake.

Effect of intrauterine undernutrition during late gestation on pancreatic beta cell mass

We analyzed the effect of low birth weight on pancreatic beta cell mass. We used pregnant C57BL6J mice, and we reduced their food supply by 30% during the late gestational period and examined the changes in the metabolism and pancreatic beta cell mass. Pancreatic beta cell mass at birth was greatly decreased in the mice of the food restriction group (RG) as compared to the mice of the control group (CG). The body weight of RG mice exhibited a "catch-up growth" pattern and became equivalent to that of CG mice 7 days after birth, and thereafter exceeded that of CG mice; however, the pancreatic beta cell mass in RG mice remained lower than that in CG mice at the age of 4 weeks. A high-fat diet significantly increased the pancreatic beta cell mass in RG mice as compared to that in CG mice at 12 weeks of age. However, RG mice fed on high-fat diets tended to exhibit a decrease in the pancreatic beta cell mass at approximately 20 weeks of age. The plasma insulin concentrations also tended to be decreased in RG mice after 24 weeks of age as compared to those of CG mice. These results thus indicate that the growth of pancreatic beta cells is insufficient in RG mice, and pancreatic beta cell failure can easily develop as a consequence of insulin resistance.

An increase in the circulating concentration of monocyte chemoattractant protein-1 elicits systemic insulin resistance irrespective of adipose tissue inflammation in mice

Chronic inflammation in adipose tissue is thought to be important for the development of insulin resistance in obesity. Furthermore, the level of monocyte chemoattractant protein-1 (MCP-1) is increased not only in adipose tissue but also in the circulation in association with obesity. However, it has remained unclear to what extent the increased circulating level of MCP-1 contributes to insulin resistance. We have now examined the relevance of circulating MCP-1 to the development of insulin resistance in mice. The plasma concentration of MCP-1 was increased chronically or acutely in mice to the level observed in obese animals by chronic subcutaneous infusion of recombinant MCP-1 with an osmotic pump or by acute intravenous infusion of MCP-1 with an infusion pump, respectively. Whole-body metabolic parameters as well as inflammatory changes in adipose tissue were examined. A chronic increase in the circulating level of MCP-1 induced insulin resistance, macrophage infiltration into adipose tissue, and an increase in hepatic triacylglycerol content. An acute increase in the circulating MCP-1 concentration also induced insulin resistance but not macrophage infiltration into adipose tissue. In addition, inhibition of signaling by MCP-1 and its receptor CCR2 by administration of a novel CCR2 antagonist ameliorated insulin resistance in mice fed a high-fat diet without affecting macrophage infiltration into adipose tissue. These data indicate that an increase in the concentration of MCP-1 in the circulation is sufficient to induce systemic insulin resistance irrespective of adipose tissue inflammation.

Identification of KCNJ15 as a susceptibility gene in Asian patients with type 2 diabetes mellitus

Recent advances in genome research have enabled the identification of new genomic variations that are associated with type 2 diabetes mellitus (T2DM). Via fine mapping of SNPs in a candidate region of chromosome 21q, the current study identifies potassium inwardly-rectifying channel, subfamily J, member 15 (KCNJ15) as a new T2DM susceptibility gene. KCNJ15 is expressed in the beta cell of the pancreas, and a synonymous SNP, rs3746876, in exon 4 (C566T) of this gene, with T allele frequency among control subjects of 3.1%, showed a significant association with T2DM affecting lean individuals in three independent Japanese sample sets (p = 2.5 x 10(-7), odds ratio [OR] = 2.54, 95% confidence interval [CI] = 1.76-3.67) and with unstratified T2DM (p = 6.7 x 10(-6), OR = 1.76, 95% CI = 1.37-2.25). The diabetes risk allele frequency was, however, very low among Europeans in whom no association between this variant and T2DM could be shown. Functional analysis in human embryonic kidney 293 cells demonstrated that the risk allele of the synonymous SNP in exon 4 increased KCNJ15 expression via increased mRNA stability, which resulted in the higher expression of protein as compared to that of the nonrisk allele. We also showed that KCNJ15 is expressed in human pancreatic beta cells. In conclusion, we demonstrated a significant association between a synonymous variant in KCNJ15 and T2DM in lean Japanese patients with T2DM, suggesting that KCNJ15 is a previously unreported susceptibility gene for T2DM among Asians.

Effects of coffee on inflammatory cytokine gene expression in mice fed high-fat diets

In order to investigate the risk-reducing effects of coffee in metabolic syndrome, we performed a study in mice fed a high-fat diet with added coffee and analyzed gene expression in liver and adipose tissues using cDNA microarray. Male C57BL/6J mice were raised for 8 weeks on either a normal diet (N group), a high-fat diet (HF group), or a high-fat diet with 1.1% decaffeinated (HF+DC group) or 1.1% caffeine-containing instant coffee (HF+CC group). The body weights of mice in the HF+DC and HF+CC groups were mostly intermediate between the N and HF groups, even if there were no difference in the amount of diet consumption in each group. Mesenteric fat weight was lower in the HF+DC group than in the HF group (p < 0.05) and tended to become lower in the HF+CC group than in the HF group. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were significantly lower in the HF+DC and HF+CC groups than in the HF group (p < 0.05). Inflammatory cytokine interleukin (IL)-1beta gene expression in liver was up-regulated in the HF group and significantly down-regulated in the HF+DC and HF+CC groups (p < 0.01), while MCP-1 gene expression in white adipose tissue was also significantly suppressed in the HF+DC group (p < 0.01). The induction of these anti-inflammatory responses by coffee consumption may contribute to reducing the risks of metabolic syndrome.

Ablation of C/EBPbeta alleviates ER stress and pancreatic beta cell failure through the GRP78 chaperone in mice

Pancreatic beta cell failure is thought to underlie the progression from glucose intolerance to overt diabetes, and ER stress is implicated in such beta cell dysfunction. We have now shown that the transcription factor CCAAT/enhancer-binding protein beta (C/EBPbeta) accumulated in the islets of diabetic animal models as a result of ER stress before the onset of hyperglycemia. Transgenic overexpression of C/EBPbeta specifically in beta cells of mice reduced beta cell mass and lowered plasma insulin levels, resulting in the development of diabetes. Conversely, genetic ablation of C/EBPbeta in the beta cells of mouse models of diabetes, including Akita mice, which harbor a heterozygous mutation in Ins2 (Ins2WT/C96Y), and leptin receptor-deficient (Lepr-/-) mice, resulted in an increase in beta cell mass and ameliorated hyperglycemia. The accumulation of C/EBPbeta in pancreatic beta cells reduced the abundance of the molecular chaperone glucose-regulated protein of 78 kDa (GRP78) as a result of suppression of the transactivation activity of the transcription factor ATF6alpha, thereby increasing the vulnerability of these cells to excess ER stress. Our results thus indicate that the accumulation of C/EBPbeta in pancreatic beta cells contributes to beta cell failure in mice by enhancing susceptibility to ER stress.

Regulation of SREBP1c expression by mTOR signaling in hepatocytes

The transcription factor sterol regulatory element-binding protein 1c (SREBP1c) plays an important role in the regulation of fatty acid metabolism in the liver. Although the importance of phosphoinositide 3-kinase in the regulation of SREBP1c expression is widely accepted, the role of mammalian target of rapamycin (mTOR) in such regulation has remained unclear. We have now shown that the insulin-induced increase in the abundance of SREBP1c mRNA in cultured AML12 mouse hepatocytes was largely abolished by LY294002, an inhibitor of phosphoinositide 3-kinase, but was reduced only slightly by rapamycin, an inhibitor of mTOR. Forced expression of a constitutively active form of Akt containing a myristoylation signal sequence (MyrAkt) in these cells with the use of an adenoviral vector resulted in the phosphorylation of p70 S6 kinase, a downstream target of mTOR signaling, and this effect was inhibited by rapamycin. MyrAkt also increased the abundance of SREBP1c mRNA and protein as well as the expression of the SREBP1c target genes for fatty acid synthase and stearoyl-CoA desaturase 1. These effects of MyrAkt were also markedly inhibited by LY294002 and by rapamycin. These results thus suggest that mTOR signaling plays a major role in Akt-mediated up-regulation of SREBP1c expression but that it plays only a minor role in insulin-induced expression of this transcription factor.

Angiopoietin-like protein 2 promotes chronic adipose tissue inflammation and obesity-related systemic insulin resistance

Recent studies of obesity have provided new insights into the mechanisms underlying insulin resistance and metabolic dysregulation. Numerous efforts have been made to identify key regulators of obesity-linked adipose tissue inflammation and insulin resistance. We found that angiopoietin-like protein 2 (Angptl2) was secreted by adipose tissue and that its circulating level was closely related to adiposity, systemic insulin resistance, and inflammation in both mice and humans. Angptl2 activated an inflammatory cascade in endothelial cells via integrin signaling and induced chemotaxis of monocytes/macrophages. Constitutive Angptl2 activation in vivo induced inflammation of the vasculature characterized by abundant attachment of leukocytes to the vessel walls and increased permeability. Angptl2 deletion ameliorated adipose tissue inflammation and systemic insulin resistance in diet-induced obese mice. Conversely, Angptl2 overexpression in adipose tissue caused local inflammation and systemic insulin resistance in nonobese mice. Thus, Angptl2 is a key adipocyte-derived inflammatory mediator that links obesity to systemic insulin resistance.

[Diabetes susceptibility genes]

Type 2 diabetes mellitus is a complex polygenic disorder in which common genetics variants interact with environmental factors. Genome-wide association study(GWAS) revealed more than 10 diabetes susceptibility loci for type 2 diabetes mellitus including SNPs in KCNQ1, which was first identified in Japanese by two independent Japanese groups. However, these variants identified by GWAS showed low O.R. (odds ratio) such as 1.1-1.5 suggesting low penetrance of these variants. Diabetes mellitus is also caused by a mutation in one gene such as glucokinase and HNF-1 alpha, which showed high penetrance. Therefore, next challenge will be to identify low-frequency variants with intermediate penetrance, which may be associated with diabetes mellitus.

Muscle-specific overexpression of heparin-binding epidermal growth factor-like growth factor increases peripheral glucose disposal and insulin sensitivity

Physical exercise ameliorates metabolic disorders such as type 2 diabetes mellitus and obesity, but the molecular basis of these effects remains elusive. In the present study, we found that exercise up-regulates heparin-binding epidermal growth factor-like growth factor (HB-EGF) in skeletal muscle. To address the metabolic consequences of such gain of HB-EGF function, we generated mice that overexpress this protein specifically in muscle. The transgenic animals exhibited a higher respiratory quotient than did wild-type mice during indirect calorimetry, indicative of their selective use of carbohydrate rather than fat as an energy substrate. They also showed substantial increases in glucose tolerance, insulin sensitivity, and glucose uptake by skeletal muscle. These changes were accompanied by increased kinase activity of Akt in skeletal muscle and consequent inhibition of Forkhead box O1-dependent expression of the pyruvate dehydrogenase kinase 4 gene. Furthermore, mice with a high level of transgene expression were largely protected from obesity, hepatic steatosis, and insulin resistance, even when maintained on a high-fat diet. Our results suggest that HB-EGF produced by contracting muscle acts as an insulin sensitizer that facilitates peripheral glucose disposal.

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

AIM

To study the changes in gene expression by pancreatic beta cells under insulin resistance conditions.

METHOD

An exhaustive gene expression analysis was performed, using isolated pancreatic islets of obese diabetic model Lepr(-/-) mice. Overexpression of cyclin D2 was induced in cells from the pancreatic beta cell line, namely, INS-1.

RESULTS

Through a gene expression analysis using islets isolated from db/db mice, we found a significant increase in the expression of ribosome-related molecules. In addition, increased expression of cyclin D2 was found at certain protein levels. As INS-1 cells were induced to overexpress cyclin D2, we found an increase in the expression of ribosome-related molecules. Concurrently, an increase in the expression of endoplasmic reticulum stress (ER stress)-related molecules was also found.

CONCLUSION

In cases of pancreatic beta cell hyperplasia associated with insulin resistance, ribosomal biogenesis is increased, and ER stress is induced.

Diet-induced up-regulation of gene expression in adipocytes without changes in DNA methylation

The expansion of white adipose tissue (WAT) mass during the development of obesity is mediated in part through an increase in adipocyte size. Although gene expression profiles associated with adipogenesis in vitro and the development of obesity in vivo have been characterized by DNA microarray analysis, the role of chromatin and chromatin-modifying proteins in the regulation of gene expression related to adipocyte hypertrophy has remained unclear. We have now shown that maintenance of C57BL/6J mice on a high-fat diet for 16 weeks resulted in marked up-regulation of the expression of leptin, Mest (mesoderm specific transcript; also known as paternally expressed gene 1, or Peg1), and sFRP5 (secreted frizzled-related protein 5) genes in WAT. Furthermore, the demethylating agent 5-aza-2'-deoxycytidine increased the amount of Mest/Peg1 mRNA, but not that of leptin or sFRP5 mRNAs, in mouse 3T3-L1 adipocytes. However, analysis by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry revealed that maintenance of mice on a high-fat diet for various times did not affect the level of methylation at specific CpG sites in the promoter regions of leptin, Mest/Peg1, and sFRP5 genes in WAT. Our results indicate that the diet-induced up-regulation of leptin, Mest/Peg1, and sFRP5 gene expression in WAT during the development of obesity in mice is not mediated directly by changes in DNA methylation.

Two related cases of type A insulin resistance with compound heterozygous mutations of the insulin receptor gene

We describe two sisters with type A insulin resistance. In contrast to common situation for this genetic disorder, the sisters harbored compound heterozygous mutations in the insulin receptor gene associated with mild glucose intolerance. The cases highlight the diversity of clinical phenotypes associated with mutations of the insulin receptor gene.

Identification and characterization of an alternative promoter of the human PGC-1alpha gene

The transcriptional regulator peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) controls mitochondrial biogenesis and energy homeostasis. Although physical exercise induces PGC-1alpha expression in muscle, the underlying mechanism of this effect has remained incompletely understood. We recently identified a novel muscle-enriched isoform of PGC-1alpha transcript (designated PGC-1alpha-b) that is derived from a previously unidentified first exon. We have now cloned and characterized the human PGC-1alpha-b promoter. The muscle-specific transcription factors MyoD and MRF4 transactivated this promoter through interaction with a proximal E-box motif. Furthermore, either forced expression of Ca(2+)- and calmodulin-dependent protein kinase IV (CaMKIV), calcineurin A, or the p38 mitogen-activated protein kinase (p38 MAPK) kinase MKK6 or the intracellular accumulation of cAMP activated the PGC-1alpha-b promoter in cultured myoblasts through recruitment of cAMP response element (CRE)-binding protein (CREB) to a putative CRE located downstream of the E-box. Our results thus reveal a potential molecular basis for isoform-specific regulation of PGC-1alpha expression in contracting muscle.

Variants in KCNQ1 are associated with susceptibility to type 2 diabetes mellitus

We carried out a multistage genome-wide association study of type 2 diabetes mellitus in Japanese individuals, with a total of 1,612 cases and 1,424 controls and 100,000 SNPs. The most significant association was obtained with SNPs in KCNQ1, and dense mapping within the gene revealed that rs2237892 in intron 15 showed the lowest Pvalue (6.7 x 10(-13), odds ratio (OR) = 1.49). The association of KCNQ1 with type 2 diabetes was replicated in populations of Korean, Chinese and European ancestry as well as in two independent Japanese populations, and meta-analysis with a total of 19,930 individuals (9,569 cases and 10,361 controls) yielded a P value of 1.7 x 10(-42) (OR = 1.40; 95% CI = 1.34-1.47) for rs2237892. Among control subjects, the risk allele of this polymorphism was associated with impairment of insulin secretion according to the homeostasis model assessment of beta-cell function or the corrected insulin response. Our data thus implicate KCNQ1 as a diabetes susceptibility gene in groups of different ancestries.

Role of the E3 ubiquitin ligase gene related to anergy in lymphocytes in glucose and lipid metabolism in the liver

Gene related to anergy in lymphocytes (GRAIL) is an E3 ubiquitin ligase that regulates energy in T-lymphocytes. Whereas, the relevance of GRAIL to T lymphocyte function is well established, the role of this protein in other cell types remains unknown. Given that GRAIL is abundant in the liver, we investigated the potential function of GRAIL in nutrient metabolism by generating mice in which the expression of GRAIL is reduced specifically in the liver. Adenovirus-mediated transfer of a short hairpin RNA specific for GRAIL mRNA markedly reduced the amounts of GRAIL mRNA and protein in the liver. Blood glucose levels of the mice with hepatic GRAIL deficiency did not differ from those of control animals in the fasted or fed states. However, these mice manifested glucose intolerance in association with a normal increase in plasma insulin levels during glucose challenge. The mice also manifested an increase in the serum concentration of free fatty acids, whereas the serum levels of cholesterol and triglyceride were unchanged. The hepatic abundance of mRNAs for glucose-6-phosphatase, catalytic (a key enzyme in hepatic glucose production) and for sterol regulatory element-binding transcription factor 1 (an important transcriptional regulator of lipogenesis) was increased in the mice with hepatic GRAIL deficiency, possibly contributing to the metabolic abnormalities of these animals. Our results thus demonstrate that GRAIL in the liver is essential for maintenance of normal glucose and lipid metabolism in living animals.

[Obesity and insulin resistance]

The worldwide epidemic of obesity is a serious threat to public health, because obesity results in insulin resistance, which leads to metabolic syndrome. Obesity is determined by both adipocyte size (adipocyte hypertrophy) and adipocyte number (adipocyte hyperplasia). Recent studies have begun to clarify the mechanism which regulates the size and number of adipocytes. In addition, chronic inflammation in insulin sensitive tissues receives much attention as the mediator between obesity and insulin resistance. In particular, excess triacylglycerol storage in adipocytes induces macrophage infiltration into adipose tissues, which results in inflammation and alters the expression and secretion of various adipokines. Inflammation pathway is also activated in liver. In addition, myeloid cells are tightly involved in inflammation in adipose tissues and liver. Inflammation in these tissues results in systemic insulin resistance. Intervention which decreases inflammation may be useful treatment for insulin resistance.

A case of hypothalamic panhypopituitarism with empty sella syndrome: case report and review of the literature

Empty sella syndrome is frequently accompanied with pituitary dysfunction. Most of the patients with empty sella syndrome demonstrate primary pituitary or stalk dysfunction and few cases show hypothalamic dysfunction. A 71-year-old man manifested appetite loss, nausea and vomiting with hyponatremia and adrenal insufficiency. Hormonal evaluation and cranial MRI revealed a panhypopituitarism with empty sella. Intriguingly, while the response of ACTH to CRH administration was exaggerated, the response to insulin hypoglycemia was blunted. Serum PRL levels were normal. Further, decreased level of fT4, slightly elevated basal levels of TSH, and delayed response of TSH to TRH administration were observed. These findings strongly suggest that the panhypopituitarism is caused by hypothalamic dysfunction. The presence of autoantibodies to pituitary and cerebrum in the patient's serum implies an autoimmune mechanism as a pathogenesis.

Analysis of factors affecting increase in bone mineral density at lumbar spine by bisphosphonate treatment in postmenopausal osteoporosis

Bisphosphonate is an effective drug to reduce fracture risk in osteoporotic patients; however, factors affecting the efficacy of bisphosphonate treatment are not fully known, especially in Japanese patients. In the present study, we examined the relationships between an increase in lumbar spine bone mineral density (BMD) by bisphosphonates and several pretreatment parameters, including biochemical, bone/mineral, and body composition indices, in 85 postmenopausal osteoporotic patients treated with alendronate or risedronate. BMD increase was measured by dual-energy X-ray absorptiometry at the lumbar spine before and 2 years after treatment. BMD increase at the lumbar spine was observed as independent of age, height, weight, body mass index, and fat mass, although lean body mass seemed slightly related. On the other hand, fasting plasma glucose (FPG) levels were significantly and positively related to BMD increase at the lumbar spine. In multiple regression analysis, FPG levels were not significantly related to BMD increase at the lumbar spine when lean body mass was considered. As for bone/mineral parameters, BMD increase at the lumbar spine was not significantly related to serum levels of calcium, parathyroid hormone (PTH), and alkaline phosphatase or urinary levels of deoxypiridinoline and calcium excretion. As for BMD parameters, Z-scores of BMD at any site and bone geometry parameters obtained by forearm peripheral quantitative computed tomography were not significantly related to BMD increase at the lumbar spine. BMD increases at the lumbar spine were similar between groups with or without vertebral fractures. In conclusion, BMD increase at the lumbar spine by bisphosphonate treatment was not related to any pretreatment parameters, including body size, body composition, and bone/mineral metabolism in postmenopausal Japanese women with primary osteoporosis, although FPG correlated partly to BMD through lean body mass.

Skp2 promotes adipocyte differentiation via a p27Kip1-independent mechanism in primary mouse embryonic fibroblasts

Skp2, the substrate-binding subunit of an SCF ubiquitin ligase complex, is a key regulator of cell cycle progression that targets substrates for degradation by the 26S proteasome. We have now shown that ablation of Skp2 in primary mouse embryonic fibroblasts (MEFs) results both in impairment of adipocyte differentiation and in the accumulation of the cyclin-dependent kinase inhibitor p27(Kip1), a principal target of the SCF(Skp2) complex. Genetic ablation of p27(Kip1) in MEFs promoted both lipid accumulation and adipocyte-specific gene expression. However, depletion of p27(Kip1) by adenovirus-mediated RNA interference failed to correct the impairment of adipocyte differentiation in Skp2(-/-) MEFs. In contrast, troglitazone, a high-affinity ligand for peroxisome proliferator-activated receptor gamma (PPARgamma), largely restored lipid accumulation and PPARgamma gene expression in Skp2(-/-) MEFs. Our data suggest that Skp2 plays an essential role in adipogenesis in MEFs in a manner that is at least in part independent of regulation of p27(Kip1) expression.

The Krüppel-like factor KLF15 inhibits transcription of the adrenomedullin gene in adipocytes

KLF15 (Krüppel-like factor 15) plays a key role in adipocyte differentiation and glucose transport in adipocytes through activation of its target genes. We have now identified six target genes regulated directly by KLF15 in 3T3-L1 mouse adipocytes with the use of a combination of microarray-based chromatin immunoprecipitation and gene expression analyses. We confirmed the direct regulation by KLF15 of one of these genes, that for adrenomedullin, with the use of a luciferase reporter assay in 3T3-L1 preadipocytes and adipocytes. Such analysis revealed that the most proximal CACCC element in the promoter of the human adrenomedullin gene (located in the region spanning nucleotides -70 and -29) is required for trans-inhibition by KLF15. Furthermore, chromatin immunoprecipitation showed that KLF15 binds to this region of the human adrenomedullin gene promoter in cultured human adipocytes. These results thus implicate KLF15 in the regulation of adrenomedullin expression in adipose tissue.

Overexpression of the transcriptional coregulator Cited2 protects against glucocorticoid-induced atrophy of C2C12 myotubes

In patients with various catabolic conditions, glucocorticoid excess induces skeletal muscle wasting by accelerating protein degradation via the ubiquitin-proteasome pathway. Although the transcriptional coactivator p300 has been implicated in this pathological process, regulatory mechanisms and molecular targets of its action remain unclear. Here we show that CREB-binding protein (CBP)/p300-interacting transactivator with ED-rich tail 2 (Cited2), which binds to the cysteine-histidine-rich region 1 of p300 and CBP, regulates muscle mass in vitro. Adenovirus-mediated overexpression of wild-type Cited2 significantly blocked morphological alterations of C2C12 myotubes with a concomitant decrease in myosin heavy chain protein in response to synthetic glucocorticoid dexamethasone, which were attributable to the reduced induction of atrophy-related ubiquitin ligases MuRF1 and MAFbx. These myotube-sparing effects were less pronounced, however, with a carboxyl-terminally truncated mutant of Cited2 that lacked the ability to bind p300. These results suggest that the gain of Cited2 function counteracts glucocorticoid-induced muscle atrophy through inhibition of proteolysis mediated by p300-dependent gene transcription.

Insulin-stimulated fusion of GLUT4 vesicles to plasma membrane is dependent on wortmannin-sensitive insulin signaling pathway in 3T3-L1 adipocytes

It is established that wortmannin which completely inhibits class IA PI 3-kinase activation abrogated the insulin-dependent translocation of GLUT4 to the plasma membrane in adipocytes and skeletal muscle. However, it was not clear which steps wortmannin inhibited during the whole translocation process of GLUT4. We have now dissected the each steps of the GLUT4 trafficking in 3T3-L1 adipocytes using exogenously-expressed GLUT4 reporter in combination with plasma membrane lawn assay. We showed that 100 nM wortmannin inhibited the fusion of GLUT4 vesicles to the plasma membrane without affecting the movement and the subsequent tethering/docking event of GLUT4 vesicles to the membrane in 3T3-L1 adipocytes. These results suggest that wortmannin-sensitive insulin signaling pathway plays a crucial role in the fusion step of GLUT4 vesicles to the plasma membrane in 3T3-L1 adipocytes.

Role of hepatic STAT3 in the regulation of lipid metabolism

Regulation of hepatic gene expression is largely responsible for the control of nutrient metabolism. We previously showed that the transcription factor STAT3 regulates glucose homeostasis by suppressing the expression of gluconeogenic genes in the liver. However, the role of STAT3 in the control of lipid metabolism has remained unknown. We have now investigated the effects of hepatic overexpression of STAT3, achieved by adenovirus-mediated gene transfer, on glucose and lipid metabolism in insulin-resistant diabetic mice. Forced expression of STAT3 reduced blood glucose and plasma insulin concentrations as well as the hepatic abundance of mRNA for phosphoenolpyruvate carboxykinase. However, it also increased the plasma levels of triglyceride and total cholesterol without affecting those of low density lipoprotein- or high density lipoprotein-cholesterol. The hepatic abundance of mRNAs for fatty acid synthase and acetyl-CoA carboxylase, both of which catalyze the synthesis of fatty acids, was increased by overexpression of STAT3, whereas that of mRNAs for sterol regulatory element-binding proteins 1a, 1c, or 2 was unaffected. Moreover, the amount of mRNA for acyl-CoA oxidase, which contributes to beta-oxidation, was decreased by forced expression of STAT3. These results indicate that forced activation of STAT3 signaling in the liver of insulin-resistant diabetic mice increased the circulating levels of atherogenic lipids through changes in the hepatic expression of genes involved in lipid metabolism. Furthermore, these alterations in hepatic gene expression likely occurred through a mechanism independent of sterol regulatory element-binding proteins.

Association study of the effect of WFS1 polymorphisms on risk of type 2 diabetes in Japanese population

Mutations of WFS1 gene cause Wolfram syndrome, which is a rare autosomal recessive disorder characterized by juvenile diabetes mellitus, optic atrophy, deafness and diabetes insipidus. The product encoded by WFS1 gene, wolframin, could be involved in ER stress response causing beta-cell loss through impaired cell cycle progression and increased apoptosis. Recently, polymorphisms in the WFS1 gene were strongly associated with type 2 diabetes in Caucasians. The aim of the present study was to examine whether the variants of WFS1 are associated with risk of type 2 diabetes in Japanese individuals. Four single nucleotide polymorphisms, rs6446482, rs12511742, rs1801208 (R456H) and rs734312 (H611R) were genotyped in a total of 536 diabetic patients and 398 nondiabetic control subjects. Among the four variants, rs12511742 showed a marginal association with susceptibility to type 2 diabetes (odds ratio = 1.32, 95% confidence interval = 1.02-1.71, P = 0.033). Carriers of the risk allele at rs12511742 exhibited lower pancreas beta-cell function (P = 0.017). However, this association disappeared after adjustment for sex, age and BMI (Adjusted P = 0.24). Although we found no evidence for a substantial effect of WFS1 polymorphisms on risk of type 2 diabetes or clinical characteristics of diabetic subjects in Japanese population, this gene is still a good candidate for a type 2 diabetes susceptibility gene, potentially, through impaired insulin secretion.

FSP27 contributes to efficient energy storage in murine white adipocytes by promoting the formation of unilocular lipid droplets

White adipocytes are unique in that they contain large unilocular lipid droplets that occupy most of the cytoplasm. To identify genes involved in the maintenance of mature adipocytes, we expressed dominant-negative PPARgamma in 3T3-L1 cells and performed a microarray screen. The fat-specific protein of 27 kDa (FSP27) was strongly downregulated in this context. FSP27 expression correlated with induction of differentiation in cultured preadipocytes, and the protein localized to lipid droplets in murine white adipocytes in vivo. Ablation of FSP27 in mice resulted in the formation of multilocular lipid droplets in these cells. Furthermore, FSP27-deficient mice were protected from diet-induced obesity and insulin resistance and displayed an increased metabolic rate due to increased mitochondrial biogenesis in white adipose tissue (WAT). Depletion of FSP27 by siRNA in murine cultured white adipocytes resulted in the formation of numerous small lipid droplets, increased lipolysis, and decreased triacylglycerol storage, while expression of FSP27 in COS cells promoted the formation of large lipid droplets. Our results suggest that FSP27 contributes to efficient energy storage in WAT by promoting the formation of unilocular lipid droplets, thereby restricting lipolysis. In addition, we found that the nature of lipid accumulation in WAT appears to be associated with maintenance of energy balance and insulin sensitivity.

Pancreatic beta cell mass preserved in heterozygous PDK1 knockout mice

We have demonstrated that 3-phosphoinositide-dependent protein kinase 1 (PDK1) contributes to signaling by insulin or insulin-like growth factor-1 (IGF-1) that is responsible for the regulation of both the number and size of pancreatic beta cells in mice. Complete ablation of PDK1 in pancreatic beta cells leads to progressive hyperglycemia as a result of loss of beta cell mass. In this study, we generated heterozygous pancreatic beta cell-specific PDK1 knockout (betaPDK1+/-) mice and fed them a high-fat diet as a model of human type 2 diabetes. The betaPDK1+/- mice exhibited normal glucose tolerance even on a high-fat diet. Further, islet morphology and beta cell mass were normal in betaPDK1+/- mice, and haploinsufficiency of PDK1 did not impair the compensatory hyperplasia of beta cells on a high-fat diet. The phosphorylation and expression of the molecules that are expressed downstream of PDK1 were similar in the islets of the betaPDK1+/- and control mice. Eventually, we concluded that glucose homeostasis and islet mass were maintained in betaPDK1+/- mice.

Lack of association of LRP5 and LRP6 polymorphisms with type 2 diabetes mellitus in the Japanese population

AIMS

A missense mutation in the low density lipoprotein receptor-related protein 6 gene (LRP6) was recently shown to be responsible for a disorder characterized by early-onset coronary artery disease as well as diabetes mellitus (DM), hyperlipidemia, hypertension, and osteoporosis. Mice deficient in LRP5, a closely related paralog of LRP6, manifest a marked impairment in glucose tolerance. The aim of the present study was to examine whether common variants of LRP5 and LRP6 are associated with Type 2 DM or dyslipidemia in Japanese individuals.

METHODS

Thirteen single nucleotide polymorphisms (SNPs) of LRP6 and nine SNPs of LRP5 were genotyped in a total of 608 Type 2 DM patients and 366 nondiabetic control subjects (initial study). An association analysis was then performed for each SNP and for haplotypes. For some of the SNPs, we provided another sample panel of 576 cases and 576 controls for the replication study. The relation to clinical characteristics was also examined in diabetic subjects.

RESULTS

In the initial study, three SNPs of LRP6 were found to be associated with susceptibility to Type 2 DM. However, this association was not detected in the replication panel. None of SNPs in LRP5 were associated with Type 2 DM in the initial panel. Neither LRP6 nor LRP5 was associated with body mass index, HOMA-beta, HOMA-IR or serum lipid concentrations.

CONCLUSIONS

We found no evidence for a substantial effect of LRP5 or LRP6 SNPs on susceptibility to type 2 diabetes or clinical characteristics of diabetic subjects in Japanese population.

Role of metallothionein in Helicobacter pylori-positive gastric mucosa with or without early gastric cancer and the effect on its expression after eradication therapy

BACKGROUND AND AIM

Metallothionein (MT) has a proven relationship with various kinds of cancer and reduces tissue damage. Helicobacter pylori (H. pylori) infection is associated with the alteration of gastric epithelial cell cycle events, a condition implicated in the initiation and development of gastric cancer. This study investigates the role of MT in H. pylori-induced gastritis with or without early gastric cancer (ECG) and evaluates the effect on MT expression after eradication therapy.

METHODS

Gastric biopsy samples were immunohistochemically examined for MT expression in 36 H. pylori-negative patients without ECG and 98 positive patients with or without ECG. Real time polymerase chain reaction was performed in 14 antral biopsy samples with or without H. pylori. The severity of gastritis was also evaluated according to the updated Sydney System. In 31 successfully eradicated patients, the above assessment was repeated for two consecutive years.

RESULTS

MT expression was higher in H. pylori-negative patients than in positive patients (P < 0.01). Moreover, in the corpus it was higher in H. pylori-positive patients without ECG compared to those with ECG (P < 0.05). The MT labeling index had a negative correlation with the severity of gastritis (P < 0.01). A positive correlation was shown between the MT labeling index and apoptosis: proliferation ratio (r = 0.41, P < 0.01). The MT labeling index in H. pylori-positive patients was gradually recovered after eradication (P < 0.05).

CONCLUSION

The decrease of MT expression cannot prevent tissue damage in H. pylori-positive gastric mucosa and leads to more severe gastritis. This phenomenon may be attributed to gastric carcinogenesis. H. pylori eradication increases MT expression and may reduce the risk of ECG.

Replication of genome-wide association studies of type 2 diabetes susceptibility in Japan

BACKGROUND

In Europeans and populations of European origin, several groups have recently identified novel type 2 diabetes susceptibility genes, including FTO, SLC30A8, HHEX, CDKAL1, CDKN2B, and IGF2BP2, none of which were in the list of functional candidates.

OBJECTIVE AND DESIGN

The aim of this study was to replicate in a Japanese population previously identified associations of single nucleotide polymorphisms (SNPs) within 10 candidate loci with type 2 diabetes using a relatively large sample size: 1921 subjects with type 2 diabetes and 1622 normal controls.

RESULTS

A total of 15 SNPs were genotyped. Eight SNPs in five loci were found to be associated with type 2 diabetes: rs3802177 [odds ratio (OR) = 1.16 (95% confidence interval (CI) 1.05-1.27); P = 4.5 x 10(-3)] in SLC30A8; rs1111875 [OR = 1.27 (95% CI 1.14-1.40); P = 1.4 x 10(-5)] and rs7923837 [OR = 1.27 (95% CI 1.13-1.43); P = 1.0 x 10(-4)] in HHEX; rs10811661 [OR = 1.27 (95% CI 1.15-1.40); P = 1.9 x 10(-6)] in CDKN2B; rs4402960 [OR = 1.23 (95% CI 1.11-1.36); P = 8.1 x 10(-5)] and rs1470579 [OR = 1.18 (95% CI 1.07-1.31); P = 8.3 x 10(-4)] in IGF2BP2; and rs7754840 [OR = 1.28 (95% CI 1.17-1.41); P = 4.5 x 10(-7)] and rs7756992 [OR = 1.27 (95% CI 1.15-1.40); P = 9.8 x 10(-7)] in CDKAL1. The first and second strongest associations were found at variants in CDKAL1 and CDKN2B, both of which are involved in the regenerative capacity of pancreatic beta-cells.

CONCLUSION

Some of these variants represent common type 2 diabetes-susceptibility genes in both Japanese and Europeans.

Reduced insulin signaling and endoplasmic reticulum stress act synergistically to deteriorate pancreatic beta cell function

The total pancreatic beta cell mass is reduced in individuals with type 2 diabetes. We analyzed the islets of leptin receptor-deficient (Lepr-/-) mice, a model animal for type 2 diabetes with obesity. The plasma insulin levels in Lepr-/- mice peaked at approximately 7 weeks, an age at which the animals manifest normoglycemia to moderate hyperglycemia. Consistent with this, the beta cell mass was enlarged as compared with Lepr+/- mice, and it decreased thereafter. Thus, we focused on the islets of Lepr-/- mice at 7 weeks to elucidate the mechanism underlying beta cell failure. Endoplasmic reticulum (ER) stress was enhanced in beta cells of Lepr-/- mice at 7 weeks, as indicated by the increase in c-Jun and eIF2 alpha phosphorylation. Lepr-/- mice also exhibited a reduction in insulin signaling in beta cells at 7 weeks, as indicated by the decrease in Akt phosphorylation. These results indicate that both augmented ER stress and reduced insulin signaling occur before the onset of frank diabetes. Next, to examine the mutual effect of ER stress and insulin signaling in beta cells in vitro, we used MIN6 insulinoma cells. Tunicamycin induced ER stress as well as inhibited insulin signaling. Conversely, the PI-3 kinase inhibitor, LY294002, enhanced ER stress. Furthermore, the reduction in insulin signaling by LY294002 facilitated the induction of ER stress with tunicamycin. Taken together, we concluded that both ER stress and reduced insulin signaling might synergistically affect pancreatic beta cell dysfunction.

Autoantibodies to insulin receptors in man: immunological determinants and mechanism of action

The insulin receptor is a membrane glycoprotein of high Mr which binds insulin with high affinity and specificity and transmits some intracellular signal(s) that initiate(s) insulin action. Antibodies to the receptor have been identified in patients with a syndrome characterized by severe resistance to endogenous and exogenous insulin, varying degrees of glucose intolerance, and the skin lesion acanthosis nigricans. The syndrome is most common in non-Caucasian, middle-aged women, but occurs in patients of all races, both sexes, and spanning the ages of 12-62. Most patients have evidence of other autoimmune disease with increased erythrocyte sedimentation rate and gamma globulins, anti-DNA and anti-nuclear antibodies, leucopenia, and other signs and symptoms of autoimmune disease. Antibodies to the insulin receptor are detected by their ability to inhibit 125I-insulin binding or to immunoprecipitate solubilized insulin receptors. In vitro these antibodies acutely mimic most of insulin's metabolic effects. This insulin-like activity depends on antibody bivalence; monovalent Fab fragments block insulin binding and action but lack intrinsic activity. With prolonged exposure of cells to anti-receptor antibody the insulin-like effect is lost and a state of insulin resistance ensues. This is due to both a blockage of insulin binding and a form of post-receptor desensitization. The possible causation of anti-receptor antibodies in this condition is discussed.

Taurine administration after appearance of proteinuria retards progression of diabetic nephropathy in rats

Oxidative stress has been postulated to be involved in the development of diabetic nephropathy. In the present study, we evaluated the effect of taurine, an endogenous antioxidant, on diabetic nephropathy by mixing it with the daily drinking water (1%w/v) of streptozotocin-induced diabetic rats from the beginning of the fourth month after the induction of diabetes, during which the urinary protein excretion in untreated diabetic rats showed significant increase in comparison with nondiabetic rats. The taurine administration significantly suppressed further increase in urinary protein excretion in diabetic rats, accompanied by the reduction of mesangial extracellular matrix expansion and TGF-beta expression in the renal glomerulus. Immunohistochemical study showed that taurine administration suppressed the intensified stainings to the three different types of oxidative stress markers, such as 8-hydroxyl-2'-deoxyguanosine (8-OHdG), pentosidine, and nitrotyrosine observed in the renal tissues of untreated diabetic rats. These findings suggest that taurine has the ability to suppress the progression of diabetic nephropathy at least in part by its antioxidant property. Since this beneficial effect of taurine was obtained even if its administration was started after the time point when urinary protein excretion already became apparently higher than that of age-matched nondiabetic animals, taurine administration was potentially expected to be applied in clinical field to retard the development of nephropathy in diagnosed diabetic patients.

Insulin-induced GLUT4 movements in C2C12 myoblasts: evidence against a role of conventional kinesin motor proteins

Insulin induces translocation of the glucose transporter GLUT4 from intracellular storage compartment to the plasma membrane via complex mechanisms that require intact cytoskeletal networks. In cultured adipocytes, conventional kinesin motor proteins have been proposed to mediate GLUT4 movements on microtubules. It remains, however, unclear whether kinesin motor system plays a similar regulatory role in myocytes. We addressed this issue using C2C12 myoblasts, which have now been shown to express both heavy and light chains of conventional kinesin. In these cells, overexpression of either wild-type kinesin light chain 2 (KLC2) or its phosphorylation-defective mutant did not significantly affect insulin-stimulated translocation of exofacial Myc-tagged GLUT4-green fluorescent protein to the cell surface and its subsequent externalization. Likewise, a dominant-negative mutant of KLC2 had no marked effect on GLUT4 movements in this cell type. These results suggest that conventional kinesin is dispensable for insulin-induced GLUT4 translocation in cultured myoblasts and may thus reveal a cell-type specific role of the microtubules-based cytoskeleton in glucose transport in response to insulin.