Persistent oxidative stress due to absence of uncoupling protein 2 associated with impaired pancreatic beta-cell function.
ABSTRACT Uncoupling protein (UCP) 2 is a widely expressed mitochondrial protein whose precise function is still unclear but has been linked to mitochondria-derived reactive oxygen species production. Thus, the chronic absence of UCP2 has the potential to promote persistent reactive oxygen species accumulation and an oxidative stress response. Here, we show that Ucp2-/- mice on three highly congenic (N >10) strain backgrounds (C57BL/6J, A/J, 129/SvImJ), including two independently generated sources of Ucp2-null animals, all exhibit increased oxidative stress. Ucp2-null animals exhibit a decreased ratio of reduced glutathione to its oxidized form in blood and tissues that normally express UCP2, including pancreatic islets. Islets from Ucp2-/- mice exhibit elevated levels of numerous antioxidant enzymes, increased nitrotyrosine and F4/80 staining, but no change in insulin content. Contrary to results in Ucp2-/- mice of mixed 129/B6 strain background, glucose-stimulated insulin secretion in Ucp2-/- islets of each congenic strain was significantly decreased. These data show that the chronic absence of UCP2 causes oxidative stress, including in islets, and is accompanied by impaired glucose-stimulated insulin secretion.
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ABSTRACT: In pancreatic β-cells, uncoupling protein 2 (UCP2) is thought to negatively regulate insulin secretion; however, its role is still debated, in part due to the confounding effects of long-term UCP2 deletion in current knockout mouse models. We have now generated an inducible β-cell-specific UCP2 deletion model by crossing loxUCP2 mice with those that express a Cre recombinase-estrogen receptor fusion protein driven by the mouse insulin promoter (MIPCreER). Because tamoxifen, which was used to induce UCP2 deletion, is an uncoupling agent, we initially determined whether tamoxifen affected glycemia. Initially, C57BL/6 control mice were injected intraperitoneally with tamoxifen or vehicle (corn oil [CO]) 3 times in 1 week, and the mice examined 2 weeks postinjection. Both groups of mice displayed similar glucose tolerance and in vivo and in vitro insulin secretion, suggesting no effects of tamoxifen on glucose homeostasis and β-cell function. MIPCreER×loxUCP2 male littermates were then injected with tamoxifen to induce β-cell-specific UCP2 deletion (ind.UCP2BKO) or with CO as described above. UCP2 deletion was confirmed by polymerase chain reaction (PCR) analysis of islets. There were no differences in fasting glucose, glucagon or insulin in ind.UCP2BKO mice and glucose (OGTT) and insulin tolerance tests revealed similar levels of glucose and insulin sensitivity. However, ind.UCP2BKO mice sustained significantly higher plasma insulin levels during an OGTT and isolated islets secreted more insulin in response to high glucose. Together, these results suggest that short-term deletion of β-cell UCP2 in adult mice leads to the direct enhancement of insulin secretion.Canadian Journal of Diabetes 10/2012; 36(5):237-243. DOI:10.1016/j.jcjd.2012.08.004 · 0.46 Impact Factor
Article: Pharmacogenomics of glinides[Show abstract] [Hide abstract]
ABSTRACT: Glinides, including repaglinide, nateglinide and mitiglinide, are a type of fasting insulin secretagogue that could help to mimic early-phase insulin release, thus providing improved control of the postprandial glucose levels. Glinides stimulate insulin secretion by inhibiting ATP-sensitive potassium channels in the pancreatic β-cell membrane. Although glinides have been widely used clinically and display excellent safety and efficacy, the response to glinides varies among individuals, which is partially due to genetic factors involved in drug absorption, distribution, metabolism and targeting. Several pharmacogenomic studies have demonstrated that variants of genes involved in the pharmacokinetics or pharmacodynamics of glinides are associated with the drug response. Polymorphisms of genes involved in drug metabolism, such as CYP2C9, CYP2C8 and SLCO1B1, may influence the efficacy of glinides and the incidence of adverse effects. In addition, Type 2 diabetes mellitus susceptibility genes, such as KCNQ1, PAX4 and BETA2, also influence the efficacy of glinides. In this article, we review and discuss current pharmacogenomics researches on glinides, and hopefully provide useful data and proof for clinical application.Pharmacogenomics 01/2015; 16(1):45-60. DOI:10.2217/pgs.14.152 · 3.43 Impact Factor
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ABSTRACT: Aims: The inability of pancreatic β-cells to secrete sufficient insulin in response to glucose stimulation is a major contributing factor to the development of Type 2 diabetes (T2D). We investigated the in vitro and in vivo effects of deficiency of nuclear factor-erythroid 2-related factor 1 (Nrf1) in β-cells on β-cell function and glucose homeostasis. Results: Silencing of Nrf1 in β-cells leads to a pre-T2D phenotype with disrupted glucose metabolism and impaired insulin secretion. Specifically, MIN6 β-cells with stable knockdown of Nrf1 (Nrf1-KD) and isolated islets from β-cell-specific Nrf1-knockout [Nrf1(b)-KO] mice displayed impaired glucose responsiveness, including elevated basal insulin release and decreased glucose-stimulated insulin secretion (GSIS). Nrf1(b)-KO mice exhibited severe fasting hyperinsulinemia, reduced GSIS and glucose intolerance. Silencing of Nrf1 in MIN6 cells resulted in oxidative stress and altered glucose metabolism, with increases in both glucose uptake and aerobic glycolysis, which is associated with the elevated basal insulin release and reduced glucose responsiveness. The elevated glycolysis and reduced glucose responsiveness due to Nrf1 silencing likely result from altered expression of glucose metabolic enzymes, with induction of high-affinity hexokinase 1 and suppression of low-affinity glucokinase. Innovation: Our study demonstrated a novel role of Nrf1 in regulating glucose metabolism and insulin secretion in β-cells and characterized Nrf1 as a key transcription factor that regulates the coupling of glycolysis and mitochondrial metabolism and GSIS. Conclusion: Nrf1 plays critical roles in regulating glucose metabolism, mitochondrial function and insulin secretion, suggesting that Nrf1 may be a novel target to improve the function of insulin-secreting β-cells.Antioxidants and Redox Signaling 01/2015; 22(10). DOI:10.1089/ars.2014.6017 · 7.67 Impact Factor