Insulin counteracts glucotoxic effects by suppressing thioredoxin-interacting protein production in INS-1E beta cells and in Psammomys obesus pancreatic islets (original) (raw)
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Cellular Physiology and Biochemistry, 2010
Background and aims: Recently, thioredoxin-interacting protein (Txnip) expression has been implicated in a number of cellular events associated with diabetes, with increased Txnip levels associated with reduced glucose uptake into peripheral tissues, increased reactive oxygen species (ROS) in endothelial cells, beta cell glucotoxicity and apoptosis. The potential relevance of Txnip with regards to glucoseregulated insulin secretion (GSIS), a fundamentally important characteristic of beta cells and insulin-producing cells being considered as a possible cell therapy for diabetes, has not yet been investigated. Methods: Here, studying glucose-responsive MIN6 B1(GSIS) and cells which had significantly reduced response to glucose after time in culture i.e. MIN6 B1(Non-GSIS), using ELISAs; qRT-PCR; immunoprecipitation and Western blotting; transient and stable (siRNA/shRNA and cDNA) approaches to achieve Txnip knock-down or over-expression, respectively,we established a direct association between Txnip ex-pression and GSIS. Results: Specifically, increasing Txnip levels correlate with increased intracellular ROS levels and with significant GSIS loss.Conversely, both transient and stable knock-down of Txnip expression was associated with GSIS recovery. Conclusion: This, we believe, is another reason in favour of targeting Txnip as a novel approach for diabetesrelated therapy.
Prolonged insulin treatment sensitizes apoptosis pathways in pancreatic beta cells
Journal of Endocrinology, 2016
Insulin resistance results from impaired insulin signaling in target tissues that leads to increased levels of insulin required to control plasma glucose levels. The cycle of hyperglycemia and hyperinsulinemia eventually leads to pancreatic cell deterioration and death by a mechanism that is yet unclear. Insulin induces ROS formation in several cell types. Furthermore, death of pancreatic cells induced by oxidative stress could be potentiated by insulin. Here, we investigated the mechanism underlying this phenomenon. Experiments were done on pancreatic cell lines (Min-6, RINm, INS-1), isolated mouse and human islets, and on cell lines derived from nonpancreatic sources. Insulin (100nM) for 24h selectively increased the production of ROS in pancreatic cells and isolated pancreatic islets, but only slightly affected the expression of antioxidant enzymes. This was accompanied by a time- and dose-dependent decrease in cellular reducing power of pancreatic cells induced by insulin and al...
Insulin increases H2O2-induced pancreatic beta cell death
Apoptosis, 2010
Insulin resistance results, in part, from impaired insulin signaling in insulin target tissues. Consequently, increased levels of insulin are necessary to control plasma glucose levels. The effects of elevated insulin levels on pancreatic beta (b) cell function, however, are unclear. In this study, we investigated the possibility that insulin may influence survival of pancreatic b cells. Studies were conducted on RINm, RINm5F and Min-6 pancreatic bcells. Cell death was induced by treatment with H 2 O 2 , and was estimated by measurements of LDH levels, viability assay (Cell-Titer Blue), propidium iodide staining and FACS analysis, and mitochondrial membrane potential (JC-1). In addition, levels of cleaved caspase-3 and caspase activity were determined. Treatment with H 2 O 2 increased cell death; this effect was increased by simultaneous treatment of cells with insulin. Insulin treatment alone caused a slight increase in cell death. Inhibition of caspase-3 reduced the effect of insulin to increase H 2 O 2-induced cell death. Insulin increased ROS production by pancreatic b cells and increased the effect of H 2 O 2. These effects were increased by inhibition of IR signaling, indicative of an effect independent of the IR cascade. We conclude that elevated levels of insulin may act to exacerbate cell death induced by H 2 O 2 and, perhaps, other inducers of apoptosis. Keywords Apoptosis Á ROS Á IR signaling Á Beta cell death Á Oxidative stress Abbreviations ROS Reactive oxygen species T1DM Type 1 diabetes mellitus T2DM Type 2 diabetes mellitus
TXNIP Regulates Peripheral Glucose Metabolism in Humans
PLoS Medicine, 2007
Type 2 diabetes mellitus (T2DM) is characterized by defects in insulin secretion and action. Impaired glucose uptake in skeletal muscle is believed to be one of the earliest features in the natural history of T2DM, although underlying mechanisms remain obscure.
FASEB Journal, 2008
Pancreatic beta-cell loss through apoptosis represents a key factor in the pathogenesis of diabetes; however, no effective approaches to block this process and preserve endogenous beta-cell mass are currently available. To study the role of thioredoxin-interacting protein (TXNIP), a proapoptotic beta-cell factor we recently identified, we used HcB-19 (TXNIP nonsense mutation) and beta-cell-specific TX-NIP knockout (bTKO) mice. Interestingly, HcB-19 mice demonstrate increased adiposity, but have lower blood glucose levels and increased pancreatic beta-cell mass (as assessed by morphometry). Moreover, HcB-19 mice are resistant to streptozotocin-induced diabetes. When intercrossed with obese, insulin-resistant, and diabetic mice, double-mutant BTBRlep ob/ob txnip hcb/hcb are even more obese, but are protected against diabetes and beta-cell apoptosis, resulting in a 3-fold increase in beta-cell mass. Beta-cell-specific TXNIP deletion also enhanced beta-cell mass (P<0.005) and protected against diabetes, and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) revealed a ϳ50-fold reduction in beta-cell apoptosis in streptozotocin-treated bTKO mice. We further discovered that TXNIP deficiency induces Akt/Bcl-xL signaling and inhibits mitochondrial beta-cell death, suggesting that these mechanisms may mediate the beta-cell protective effects of TXNIP deficiency. These results suggest that lowering beta-cell TXNIP expression could serve as a novel strategy for the treatment of type 1 and type 2 diabetes by promoting endogenous beta-cell survival.
Thioredoxin-Interacting Protein: A Critical Link Between Glucose Toxicity and -Cell Apoptosis
Diabetes, 2008
OBJECTIVE—In diabetes, glucose toxicity affects different organ systems, including pancreatic islets where it leads to β-cell apoptosis, but the mechanisms are not fully understood. Recently, we identified thioredoxin-interacting protein (TXNIP) as a proapoptotic β-cell factor that is induced by glucose, raising the possibility that TXNIP may play a role in β-cell glucose toxicity. RESEARCH DESIGN AND METHODS—To assess the effects of glucose on TXNIP expression and apoptosis and define the role of TXNIP, we used INS-1 β-cells; primary mouse islets; obese, diabetic BTBR.ob mice; and a unique mouse model of TXNIP deficiency (HcB-19) that harbors a natural nonsense mutation in the TXNIP gene. RESULTS—Incubation of INS-1 cells at 25 mmol/l glucose for 24 h led to an 18-fold increase in TXNIP protein, as assessed by immunoblotting. This was accompanied by increased apoptosis, as demonstrated by a 12-fold induction of cleaved caspase-3. Overexpression of TXNIP revealed that TXNIP induces ...
Journal of Clinical Investigation, 1996
This study demonstrates that rat islet  cells constitutively express an apoptotic program which is activated when mRNA or protein synthesis is blocked. Apoptotic  cells were detectable by electron microscopy after treatment with actinomycin D or cycloheximide. With a fluorescence microscopic assay both agents were found to increase the number of apoptotic  cells dose-and time-dependently, up to 70% after 1 wk of culture; virtually no apoptotic  cells occurred in control preparations or in conditions leading to primary necrosis. Thus, survival of  cells seems dependent on synthesis of proteins which suppress an endogenous suicide program. This mechanism explains earlier observed effects of glucose on survival of cultured  cells. Glucose is known to dose-dependently increase the percentage of  cells in active biosynthesis and the percentage that survives during culture. It is now demonstrated that the glucose-induced survival of  cells cultured for 1 wk results from a dose-dependent reduction in the percentage of  cells dying in apoptosis (49% at 3 mM glucose, 40% at 6 mM, 9% at 10 mM). Thus, intercellular differences in glucose sensitivity appear responsible for the heterogeneity in  cell sensitivity to apoptotic conditions. These data indicate that glucose promotes survival of  cells by activating synthesis of proteins which suppress apoptosis. The present model allows for further investigation of the regulation of apoptosis in  cells and the identification of agents which induce or prevent  cell death. ( J. Clin. Invest. 1996. 98:1568-1574.) Key words: apoptosis • insulin • endocrine pancreas • diabetes • islets of Langerhans 1. Abbreviations used in this paper: AMD, actinomycin D; CHX, cycloheximide; HO 342, Hoechst 33342; PI, propidium iodide.
Insulin feedback actions: complex effects involving isoforms of islet nitric oxide synthase
Regulatory Peptides, 2004
The present study examined the effects of exogenous insulin on C-peptide release in relation to islet activities of neural constitutive nitric oxide synthase (ncNOS) and inducible NOS (iNOS). The dose-response curves for glucose-stimulated insulin and C-peptide release from isolated islets were practically identical: 0.05-0.1 nmol/l insulin stimulated, 1-100 nmol/l had no effect, whereas concentrations z 250 nmol/l (''high insulin''), inhibited C-peptide release. Both the stimulatory and inhibitory effects were abolished by the phosphatidylinositol 3V-kinase inhibitor wortmannin. Addition of a NOS inhibitor partially reversed the inhibitory action of high insulin, but had no effect on the stimulatory action of low insulin (0.1 nmol/l). Moreover, high insulin markedly increased islet ncNOS activity and induced a strong iNOS activity. As shown biochemically and with confocal microscopy, the stimulatory action of high insulin on NOS activities and the associated inhibition of C-peptide release were reversed by raising cyclic AMP through addition of either glucagon-like peptide 1 (GLP-1) or dibutyryl cyclic AMP (Bt 2 cAMP) to the incubated islets. We conclude that the positive feedback mechanisms of action of insulin are independent of islet NOS activities and remain unclear. The negative feedback action of insulin, however, can be explained by its ability to stimulate both islet ncNOS activity and the expression and activity of iNOS. The effects on iNOS are most likely transduced through phosphatidylinositol 3V-kinase and are counteracted by raising islet cyclic AMP levels.
Emerging Role of Pancreatic β-Cells during Insulin Resistance
Type 2 Diabetes [Working Title], 2019
In today's world, type 2 diabetes has become a part of every household and leads to various complications including high blood sugar level, diabetic retinopathy, diabetic foot, diabetic nephropathy and diabetic neuropathy. Yet people lack awareness about this disease and its detrimental effects. For a better understanding of this disease we must know about the causes and preventive measures since the medications used in treating type 2 diabetes have moderate to severe side effects. Type 2 diabetes is characterized by loss of insulin receptor activity in skeletal muscle and adipocytes, compensatory insulin secretion from pancreatic β-cells, β-cell dysfunction and death. The proper functioning of β-cells is a major criterion for preventing advent of type 2 diabetes. The different natural or physiological insulin secretagogues include glucose, amino acids and fatty acids, which stimulate insulin secretion under the influence of various hormones like incretins, leptin, growth hormone, melatonin and estrogen. However, excess of nutrients lead to β-cell dysfunction and dearth of insulin involving various signal molecules like SIRT1, PPARγ, TLR4, NF-ΚB, Wnt, mTOR, inflammasomes, MCP1, EGFR, and Nrf2. A deeper insight into the functioning of these signaling molecules will also create new avenues for therapeutic interventions of curing β-cell dysfunction and death.
Biochemical and Biophysical Research Communications, 2001
Cytokines may participate in islet destruction during the development of type 1 diabetes. Expression of inducible nitric oxide synthase (iNOS) and subsequent NO formation induced by IL-1 or (IL-1 ؉ IFN-␥) may impair islet function in rodent islets. Inhibition of iNOS or a deletion of the iNOS gene (iNOS ؊/؊ mice) protects against cytokine-induced -cell suppression, although cytokines might also induce NO-independent impairment. Presently, we exposed wild-type (wt, C57BL/6 ؋ 129SvEv) and iNOS ؊/؊ islets to IL-1 (25 U/ml) and (IL-1 (25 U/ml) ؉ IFN-␥ (1000 U/ml)) for 48 h. IL-1 and (IL-1 ؉ IFN-␥) induced a significant increase in NO formation in wt but not in iNOS ؊/؊ islets. Both IL-1 and (IL-1 ؉ IFN-␥) impaired glucose-stimulated insulin release and reduced the insulin content of wt islets, while (IL-1 ؉ IFN-␥) reduced glucose oxidation rates and cell viability. IL-1 exposure to iNOS ؊/؊ islets impaired glucosestimulated insulin release, increased insulin accumulation and reduced the insulin content, without any increase in cell death. Exposure to (IL-1 ؉ IFN-␥) had no effect on iNOS ؊/؊ islets except reducing the insulin content. Our data suggest that IL-1 may inhibit glucose-stimulated insulin release by pathways that are not NO-dependent and not related to glucose metabolism or cell death.