Role of ATP production and uncoupling protein-2 in the insulin secretory defect induced by chronic exposure to high glucose or free fatty acids and effects of peroxisome proliferator-activated receptor-gamma inhibition.
In rat pancreatic islets chronically exposed to high glucose or high free fatty acid (FFA) levels, glucose-induced insulin release and mitochondrial glucose oxidation are impaired. These abnormalities are associated with high basal ATP levels but a decreased glucose-induced ATP production (Delta of increment over baseline 0.7 +/- 0.5 or 0.5 +/- 0.3 pmol/islet in islets exposed to glucose or FFA vs. 12.0 +/- 0.6 in control islets, n = 3; P < 0.01) and, as a consequence, with an altered ATP/ADP ratio. To investigate further the mechanism of the impaired ATP formation, we measured in rat pancreatic islets glucose-stimulated pyruvate dehydrogenase (PDH) activity, a key enzyme for pyruvate metabolism and for the subsequent glucose oxidation through the Krebs cycle, and also the uncoupling protein-2 (UCP-2) content by Western blot. In islets exposed to high glucose or FFA, glucose-stimulated PDH activity was impaired and UCP-2 was overexpressed. Because UCP-2 expression is modulated by a peroxisome proliferator- activated receptor (PPAR)-dependent pathway, we measured PPAR-gamma contents by Western blot and the effects of a PPAR-gamma antagonist. PPAR-gamma levels were overexpressed in islets cultured with high FFA levels but unaffected in islets exposed to high glucose. In islets exposed to high FFA concentration, a PPAR-gamma antagonist was able to prevent UCP-2 overexpression and to restore insulin secretion and the ATP/ADP ratio. These data indicate that in rat pancreatic islets chronically exposed to high glucose or FFA, glucose-induced impairment of insulin secretion is associated with (and might be due to) altered mitochondrial function, which results in impaired glucose oxidation, overexpression of the UCP-2 protein, and a consequent decrease of ATP production. This alteration in FFA cultured islets is mediated by the PPAR-gamma pathway.
Institute of Internal Medicine, Endocrinology and Metabolism, "Signorelli" Diabetes Center, University of Catania, Ospedale Garibaldi and Ospedale Cannizzaro, Catania, Italy.
Giovanni
G
Patanè
Marcello
M
Anello
Salvatore
S
Piro
Riccardo
R
Vigneri
Francesco
F
Purrello
Agata Maria
AM
Rabuazzo
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000096:biosynthesis* / Q000378:metabolism; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005230:Fatty Acids, Nonesterified / Q000008:administration & dosage* / Q000494:pharmacology; D005947:Glucose / Q000008:administration & dosage* / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007473:Ion Channels; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008024:Ligands; D008297:Male; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D010084:Oxidation-Reduction; D011506:Proteins / Q000502:physiology*; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000071246:Uncoupling Protein 2
D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007473:Ion Channels; D008024:Ligands; D026901:Membrane Transport Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D011768:Pyruvate Dehydrogenase Complex; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C000604391:Ucp2 protein, rat; D000071246:Uncoupling Protein 2; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005947:Glucose