Role of nicotinamide nucleotide transhydrogenase in the acute glucose regulation of glutathione redox state in mouse pancreatic islets

Santos, Laila R.B.;Takahashi, Hilton;Souza, Arnaldo H.;Jonas, Jean-Christophe
(2014) EASD Islet Study Group 2014 “Pancreatic Islet Cells Plasticity in Health and Diabetes” — Location: Lausanne, Switzerland (12.September.2014)

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  • Santos, Laila R.B.UCLouvain
    Author
  • Takahashi, HiltonUCLouvain
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  • Souza, Arnaldo H.UCLouvain
    Author
  • Jonas, Jean-Christopheorcid-logoUCLouvain
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Abstract
Background and aim: Using GRX1‐roGFP2 as a reporter for changes in glutathione redox state, we recently showed that glucose acutely reduces mitochondrial glutathione in rat islet cell clusters and human islets. Interestingly, this glucose effect was inversely correlated with the increase in NAD(P)H autofluorescence, suggesting a possible link between both events. Among the enzymes involved in mitochondrial NADPH production, nicotinamide nucleotide transhydrogenase (NNT) may play a critical role in beta‐cell function by contributing to mitochondrial ROS detoxification and to the rise in cytosolic NADPH. Here, we tested the impact of NNT inactivation on glucose and H2O2‐mediated changes in cytosolic and mitochondrial glutathione redox state by comparing changes in (mt‐)GRX1‐ roGFP2 fluorescence ratio in islets from C57BL/6J mice with truncated NNT and from C57BL/6N mice with wild‐type NNT (J vs. N islets). Results: 1) The mutation of the NNT gene in J but not N mice was confirmed by PCR on tail DNA. 2) At 10 mM glucose, micromolar amounts of exogenous H2O2 similarly oxidized mitochondrial and cytosolic GRX1‐roGFP2 in J and N islets. 3) At low glucose, mt‐GRX1‐roGFP2 fluorescence ratio was higher in N than J islets. Upon stepwise glucose stimulation, it rapidly decreased in N islets while slightly increasing in J islets. Overexpressing NNT in J islets restored the glucose responsiveness of mt‐GRX1‐roGFP2 fluorescence ratio. 4) In N but not J islets, cytosolic GRX1‐roGFP2 fluorescence ratio slightly increased upon glucose removal and decreased upon stimulation with 2 and 5 mM glucose. 5) Glucose induced a larger increase in NAD(P)H autofluorescence in N vs. J islets. Conclusion: The lack of NNT in islets from C57BL/6J mice is associated with a lower glucose‐induced rise in NAD(P)H autofluorescence and a lack of glucose reduction of the glutathione redox state in the mitochondrial matrix and the cytosol. It does not, however, increase their sensitivity to exogenous H2O2.
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Santos, L. R. B., Takahashi, H., Souza, A. H., & Jonas, J.-C. (2014). Role of nicotinamide nucleotide transhydrogenase in the acute glucose regulation of glutathione redox state in mouse pancreatic islets. EASD Islet Study Group 2014 “Pancreatic Islet Cells Plasticity in Health and Diabetes”, Lausanne, Switzerland. https://hdl.handle.net/2078.5/189024