Mitochondrial reactive oxygen species are obligatory signals for glucose-induced insulin secretion.
OBJECTIVE
Insulin secretion involves complex events in which the mitochondria play a pivotal role in the generation of signals that couple glucose detection to insulin secretion. Studies on the mitochondrial generation of reactive oxygen species (ROS) generally focus on chronic nutrient exposure. Here, we investigate whether transient mitochondrial ROS production linked to glucose-induced increased respiration might act as a signal for monitoring insulin secretion.


METHODS
ROS production in response to glucose was investigated in freshly isolated rat islets. ROS effects were studied using a pharmacological approach and calcium imaging.


RESULTS
Transient glucose increase from 5.5 to 16.7 mmol/l stimulated ROS generation, which was reversed by antioxidants. Insulin secretion was dose dependently blunted by antioxidants and highly correlated with ROS levels. The incapacity of beta-cells to secrete insulin in response to glucose with antioxidants was associated with a decrease in ROS production and in contrast to the maintenance of high levels of ATP and NADH. Then, we investigated the mitochondrial origin of ROS (mROS) as the triggering signal. Insulin release was mimicked by the mitochondrial-complex blockers, antimycin and rotenone, that generate mROS. The adding of antioxidants to mitochondrial blockers or to glucose was used to lower mROS reversed insulin secretion. Finally, calcium imaging on perifused islets using glucose stimulation or mitochondrial blockers revealed that calcium mobilization was completely reversed using the antioxidant trolox and that it was of extracellular origin. No toxic effects were present using these pharmacological approaches.


CONCLUSIONS
Altogether, these complementary results demonstrate that mROS production is a necessary stimulus for glucose-induced insulin secretion.
Leloup
Corinne
C
Department of Metabolism, Plasticity, and Mitochondria, Unité Mixte de Recherche 5241, Centre National de la Recherche Scientifique-Université Paul Sabatier, Institut Fédératif de Recherche 31, Toulouse, France. coleloup@toulouse.inserm.fr
Tourrel-Cuzin
Cécile
C
Magnan
Christophe
C
Karaca
Melis
M
Castel
Julien
J
Carneiro
Lionel
L
Colombani
Anne-Laure
AL
Ktorza
Alain
A
Casteilla
Louis
L
Pénicaud
Luc
L
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002839:Chromans / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D009243:NAD / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction; D013482:Superoxide Dismutase / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology
D002839:Chromans; D007328:Insulin; D017382:Reactive Oxygen Species; D009243:NAD; D013481:Superoxides; D019284:Thapsigargin; D000255:Adenosine Triphosphate; D013482:Superoxide Dismutase; D005947:Glucose; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D002118:Calcium