title: Hypoxia reduces ER-to-Golgi protein trafficking and increases cell death by inhibiting the adaptive unfolded protein response in mouse beta cells.
abstract: Hypoxia may contribute to beta cell failure in type 2 diabetes and islet transplantation. The adaptive unfolded protein response (UPR) is required for endoplasmic reticulum (ER) homeostasis. Here we investigated whether or not hypoxia regulates the UPR in beta cells and the role the adaptive UPR plays during hypoxic stress.
  
  
  
  Mouse islets and MIN6 cells were exposed to various oxygen (O2) tensions. DNA-damage inducible transcript 3 (DDIT3), hypoxia-inducible transcription factor (HIF)1α and HSPA5 were knocked down using small interfering (si)RNA; Hspa5 was also overexpressed. db/db mice were used.
  
  
  
  Hypoxia-response genes were upregulated in vivo in the islets of diabetic, but not prediabetic, db/db mice. In isolated mouse islets and MIN6 cells, O2 deprivation (1-5% vs 20%; 4-24 h) markedly reduced the expression of adaptive UPR genes, including Hspa5, Hsp90b1, Fkbp11 and spliced Xbp1. Coatomer protein complex genes (Copa, Cope, Copg [also known as Copg1], Copz1 and Copz2) and ER-to-Golgi protein trafficking were also reduced, whereas apoptotic genes (Ddit3, Atf3 and Trb3 [also known as Trib3]), c-Jun N-terminal kinase (JNK) phosphorylation and cell death were increased. Inhibition of JNK, but not HIF1α, restored adaptive UPR gene expression and ER-to-Golgi protein trafficking while protecting against apoptotic genes and cell death following hypoxia. DDIT3 knockdown delayed the loss of the adaptive UPR and partially protected against hypoxia-induced cell death. The latter response was prevented by HSPA5 knockdown. Finally, Hspa5 overexpression significantly protected against hypoxia-induced cell death.
  
  
  
  Hypoxia inhibits the adaptive UPR in beta cells via JNK and DDIT3 activation, but independently of HIF1α. Downregulation of the adaptive UPR contributes to reduced ER-to-Golgi protein trafficking and increased beta cell death during hypoxic stress.
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Bensellam
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Maxwell
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.
authors.forename: Jeng Yie
authors.initials: JY
authors.lastname: Chan
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.
authors.forename: Jude
authors.initials: J
authors.lastname: Luzuriaga
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.
authors.forename: Phillip K
authors.initials: PK
authors.lastname: West
authors.affiliation: Université catholique de Louvain, Institut de recherche expérimentale et clinique, Pôle d'endocrinologie, diabète et nutrition, Brussels, Belgium.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Jonas
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia.|Westmead Hospital, Sydney, NSW, Australia.|The Westmead Millennium Institute for Medical Research, The University of Sydney, Sydney, NSW, Australia.
authors.forename: Jenny E
authors.initials: JE
authors.lastname: Gunton
authors.affiliation: Garvan Institute of Medical Research, St Vincent's Hospital, UNSW Australia, 384 Victoria Street, Darlinghurst, Sydney, NSW, 2010, Australia. r.laybutt@garvan.org.au.
authors.forename: D Ross
authors.initials: DR
authors.lastname: Laybutt
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D016923:Cell Death / Q000502:physiology; D002460:Cell Line; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006056:Golgi Apparatus / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D021381:Protein Transport / Q000502:physiology; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D056811:Unfolded Protein Response / Q000502:physiology
chemical_list: C497250:Ddit3 protein, mouse; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D051742:Transcription Factor CHOP
keywords: Apoptosis; Beta cell; Hypoxia; Islet of Langerhans; Protein trafficking; Type 2 diabetes; Unfolded protein response