title: Overexpression of the antioxidant enzyme catalase does not interfere with the glucose responsiveness of insulin-secreting INS-1E cells and rat islets.
abstract: OBJECTIVE
  Hydrogen peroxide (H2O2)-inactivating enzymes such as catalase are produced in extraordinarily low levels in beta cells. Whether this low expression might be related to a signalling function of H2O2 within the beta cell is unknown. A high level of H2O2-inactivating enzymes could potentially be incompatible with glucose-induced insulin secretion. Therefore the effect of catalase overexpression on mitochondrial function and physiological insulin secretion was studied in insulin-secreting INS-1E and primary islet cells.
  
  
  METHODS
  INS-1E and rat islet cells were lentivirally transduced to overexpress catalase in the cytosol (CytoCat) or in mitochondria (MitoCat). Cell viability and caspase-3 activation were assessed after cytokine incubation and hypoxia. Insulin secretion was quantified and expression of the gene encoding the mitochondrial uncoupling protein 2 (Ucp2) was measured in parallel to mitochondrial membrane potential and reactive oxygen species (ROS) formation.
  
  
  RESULTS
  The ability to secret insulin in a glucose-dependent manner was not suppressed by catalase overexpression, although the glucose-dependent increase in the mitochondrial membrane potential was attenuated in MitoCat cells along with an increased Ucp2 expression and reduced mitochondrial ROS formation. In addition, MitoCat overexpressing cells were significantly more resistant against pro-inflammatory cytokines and hypoxia than CytoCat and control cells.
  
  
  CONCLUSIONS
  The results demonstrate that an improved antioxidative defence status of insulin-secreting cells allowing efficient H2O2 inactivation is not incompatible with proper insulin secretory responsiveness to glucose stimulation and provide no support for a signalling role of H2O2 in insulin-secreting cells. Interestingly, the results also document for the first time that the decreased ROS formation with increasing glucose concentrations is of mitochondrial origin.
authors.affiliation: Institute of Clinical Biochemistry, Hannover Medical School, 30623 Hannover, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Lortz
authors.forename: E
authors.initials: E
authors.lastname: Gurgul-Convey
authors.forename: O
authors.initials: O
authors.lastname: Naujok
authors.forename: S
authors.initials: S
authors.lastname: Lenzen
mesh_terms: D019297:2,4-Dinitrophenol / Q000494:pharmacology; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002374:Catalase / Q000378:metabolism*; D016207:Cytokines / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D005434:Flow Cytometry; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology*; D008297:Male; D008564:Membrane Potentials; D008928:Mitochondria / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D018384:Oxidative Stress; D051381:Rats; D011917:Rats, Inbred Lew; D017382:Reactive Oxygen Species; D015398:Signal Transduction; D000071246:Uncoupling Protein 2
chemical_list: D001786:Blood Glucose; D016207:Cytokines; D007328:Insulin; D007473:Ion Channels; D024101:Mitochondrial Proteins; D017382:Reactive Oxygen Species; C000604391:Ucp2 protein, rat; D000071246:Uncoupling Protein 2; D006861:Hydrogen Peroxide; D002374:Catalase; D005947:Glucose; D019297:2,4-Dinitrophenol