title: Increased neuronal nitric oxide synthase dimerisation is involved in rat and human pancreatic beta cell hyperactivity in obesity.
abstract: OBJECTIVE
  Pancreatic beta cell hyperactivity is known to occur in obesity, particularly in insulin-resistant states. Our aim was to investigate whether changes in neuronal nitric oxide synthase (nNOS) function affect beta cell compensation in two relevant models: the Zucker fa/fa rats and pancreatic islets from obese humans.
  
  
  METHODS
  Glucose-induced insulin response was evaluated in the isolated perfused rat pancreas and in human pancreatic islets from obese individuals. Expression of nNOS (also known as NOS1) and subcellular localisation of nNOS were studied by quantitative RT-PCR, immunoblotting, immunofluorescence and electron microscopy.
  
  
  RESULTS
  Pancreatic beta cells from Zucker fa/fa rats and obese individuals were found to be hyper-responsive to glucose. Pharmacological blockade of nNOS was unable to modify beta cell response to glucose in fa/fa rats and in islets from obese individuals, suggesting an abnormal control of insulin secretion by the enzyme. In both cases, nNOS activity in islet cell extracts remained unchanged, despite a drastic increase in nNOS protein and an enhancement in the dimer/monomer ratio, pointing to the presence of high amounts of catalytically inactive enzyme. This relative decrease in activity could be mainly related to increases in islet asymmetric dimethyl-arginine content, an endogenous inhibitor of nNOS activity. In addition, mitochondrial nNOS level was decreased, which contrasts with a strongly increased association with insulin granules.
  
  
  CONCLUSIONS
  Increased nNOS production and dimerisation, together with a relative decrease in catalytic activity and relocalisation, are involved in beta cell hyperactivity in insulin-resistant rats but also in human islets isolated from obese individuals.
authors.affiliation: University Montpellier 1, CNRS FRE 3400, Centre for Pharmacology and Innovation in Diabetes (CPID), Faculté de Pharmacie, 15 avenue Charles Flahault, BP 14491, 34093 Montpellier Cedex 5, France.
authors.forename: K
authors.initials: K
authors.lastname: Mezghenna
authors.forename: P
authors.initials: P
authors.lastname: Pomiès
authors.forename: A
authors.initials: A
authors.lastname: Chalançon
authors.forename: F
authors.initials: F
authors.lastname: Castex
authors.forename: J
authors.initials: J
authors.lastname: Leroy
authors.forename: N
authors.initials: N
authors.lastname: Niclauss
authors.forename: B
authors.initials: B
authors.lastname: Nadal
authors.forename: L
authors.initials: L
authors.lastname: Cambier
authors.forename: C
authors.initials: C
authors.lastname: Cazevieille
authors.forename: P
authors.initials: P
authors.lastname: Petit
authors.forename: R
authors.initials: R
authors.lastname: Gomis
authors.forename: T
authors.initials: T
authors.lastname: Berney
authors.forename: R
authors.initials: R
authors.lastname: Gross
authors.forename: A D
authors.initials: AD
authors.lastname: Lajoix
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D019281:Dimerization; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D008875:Middle Aged; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009765:Obesity / Q000378:metabolism*; D021381:Protein Transport; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011922:Rats, Mutant Strains; D011924:Rats, Zucker; D046509:Tissue Culture Techniques
chemical_list: D007328:Insulin; D012333:RNA, Messenger; C496320:NOS1 protein, human; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat