title: Oleate rescues INS-1E β-cells from palmitate-induced apoptosis by preventing activation of the unfolded protein response.
abstract: BACKGROUND
  Saturated free fatty acids (FFAs), such as palmitate, cause β-cell apoptosis whereas unsaturated FFAs, e.g. oleate, are not harmful. The toxicity of palmitate could be mediated through endoplasmic reticulum (ER) stress which triggers the activation of a signal responding cascade also called unfolded protein response (UPR). We investigated whether or not palmitate induced β-cell apoptosis through UPR activation and whether or not oleate as a monounsaturated fatty acid could counteract these effects.
  
  
  METHODS
  INS-1E β-cells were incubated with palmitate [0.5mM], oleate [1mM] or the combination [0.5/1mM] for 1, 6 and 24h. Viability and induction of apoptosis were measured by WST-1 assay and FITC-Annexin/PI-staining, respectively. Western blot analyses were performed for UPR specific proteins and mRNA expression of target molecules was determined by qPCR.
  
  
  RESULTS
  Palmitate significantly decreased viability (29±8.8%) of INS-1E β-cells compared to controls after 24h. Stimulation with oleate showed no effect on viability but the combination of oleate and palmitate improved viability compared to palmitate treated cells (55±9.3%) or controls (26±5.3%). The number of apoptotic cells was increased 2-fold after 24h incubation with palmitate compared to controls. Again, oleate showed no effect but in combination ameliorated the effect of palmitate to control level. Phosphorylation of eIF2α was increased after 6 and 24h incubation with palmitate. In contrast, oleate had no effect and in combination prevented phosphorylation of eIF2α. Increased Xbp1 splicing was visible already 6h after palmitate treatment and remained elevated at 24h. The combination with oleate abolished Xbp1 splicing. Interestingly, mRNA expression of the chaperones Bip, Pdi, Calnexin and Grp94 was not altered by FFA treatment. Only the proapoptotic transcription factor Chop was significantly enhanced by palmitate incubation. In accordance with sustained cell survival the combination as well as oleate alone, did not result in increased Chop levels compared to controls. In summary, we showed that oleate protects INS-1E β-cells from palmitate-induced apoptosis by the suppression of ER stress which was independent of chaperone activation.
authors.affiliation: Center for Pediatric Research Leipzig (CPL), Hospital for Children and Adolescents, University of Leipzig, Germany.
authors.forename: Dietlind
authors.initials: D
authors.lastname: Sommerweiss
authors.forename: Theresa
authors.initials: T
authors.lastname: Gorski
authors.forename: Sandy
authors.initials: S
authors.lastname: Richter
authors.forename: Antje
authors.initials: A
authors.lastname: Garten
authors.forename: Wieland
authors.initials: W
authors.lastname: Kiess
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D019610:Cytoprotection; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000473:pathology; D018832:Molecular Chaperones / Q000378:metabolism; D019301:Oleic Acid / Q000494:pharmacology*; D010168:Palmitates / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051381:Rats; D051742:Transcription Factor CHOP / Q000037:antagonists & inhibitors; D056811:Unfolded Protein Response / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C497251:Ddit3 protein, rat; D018832:Molecular Chaperones; D010168:Palmitates; D051742:Transcription Factor CHOP; D019301:Oleic Acid
keywords: ATF6; Apoptosis; Beta cell; Bip/Grp78; C/EBP homologous protein; Chop; ER; ER stress; FFA; Grp94; IRE1; MUFA; Oleate; PERK; Palmitate; Pdi; SCD1; SFA; UPR; X-box-binding protein 1; Xbp1; activating-transcription-factor 6; eIF2α; endoplasmic reticulum; eukaryotic initiation factor 2α; free fatty acid; glucose-regulated protein 94kDa; immunoglobulin heavy-chain binding protein; inositol-requiring-enzyme1; monounsaturated fatty acid; protein disulfide isomerase; protein-kinase-regulated-by-RNA-like-ER-associated-kinase; saturated fatty acid; stearoyl-CoA desaturase 1; unfolded protein response