title: Impact of scavenging hydrogen peroxide in the endoplasmic reticulum for β cell function.
abstract: Oxidative folding of nascent proteins in the endoplasmic reticulum (ER), catalysed by one or more members of the protein disulfide isomerase family and the sulfhydryl oxidase ER oxidoreductin 1 (ERO1), is accompanied by generation of hydrogen peroxide (H2O2). Because of the high rate of insulin biosynthesis and the low expression of H2O2-inactivating enzymes in pancreatic β cells, it has been proposed that the luminal H2O2 concentration might be very high. As the role of this H2O2 in ER stress and proinsulin processing is still unsolved, an ER-targeted and luminal-active catalase variant, ER-Catalase N244, was expressed in insulin-secreting INS-1E cells. In these cells, the influence of ER-specific H2O2 removal on cytokine-mediated cytotoxicity and ER stress, insulin gene expression, insulin content and secretion was analysed. The expression of ER-Catalase N244 reduced the toxicity of exogenously added H2O2 significantly with a threefold increase of the EC50 value for H2O2. However, the expression of cytokine-induced ER stress genes and viability after incubation with β cell toxic cytokines (IL1β alone or together with TNFα+IFNγ) was not affected by ER-Catalase N244. In control and ER-Catalase N244 expressing cells, insulin secretion and proinsulin content was identical, while removal of luminal H2O2 reduced insulin gene expression and insulin content in ER-Catalase N244 expressing cells. These data show that ER-Catalase N244 reduced H2O2 toxicity but did not provide protection against pro-inflammatory cytokine-mediated toxicity and ER stress. Insulin secretion was not affected by decreasing H2O2 in the ER in spite of a reduced insulin transcription and processing.
authors.affiliation: Hannover Medical SchoolInstitute of Clinical Biochemistry, 30623 Hannover, Germany Lortz.Stephan@mh-hannover.de.
authors.forename: S
authors.initials: S
authors.lastname: Lortz
authors.affiliation: Hannover Medical SchoolInstitute of Clinical Biochemistry, 30623 Hannover, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Lenzen
authors.affiliation: Hannover Medical SchoolInstitute of Clinical Biochemistry, 30623 Hannover, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Mehmeti
mesh_terms: D000818:Animals; D002374:Catalase / Q000378:metabolism; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D059865:Endoplasmic Reticulum Stress / Q000502:physiology; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D010088:Oxidoreductases / Q000378:metabolism; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000378:metabolism; D017510:Protein Folding; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D046509:Tissue Culture Techniques
chemical_list: D002374:Catalase; D006861:Hydrogen Peroxide; D007328:Insulin; D010088:Oxidoreductases; D050862:Oxidoreductases Acting on Sulfur Group Donors; D017382:Reactive Oxygen Species
keywords: catalase; endoplasmic reticulum; insulin-secreting cells; pro-inflammatory cytokines; protein folding; reactive oxygen species