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.