title: Inhibition of endoplasmic reticulum stress counteracts neuronal cell death and protein aggregation caused by N-terminal mutant huntingtin proteins.
abstract: Accumulation of abnormal proteins occurs in many neurodegenerative diseases including Huntington's disease (HD). However, the precise role of protein aggregation in neuronal cell death remains unclear. We show here that the expression of N-terminal huntingtin proteins with expanded polyglutamine (polyQ) repeats causes cell death in neuronal PC6.3 cell that involves endoplasmic reticulum (ER) stress. These mutant huntingtin fragment proteins elevated Bip, an ER chaperone, and increased Chop and the phosphorylation of c-Jun-N-terminal kinase (JNK) that are involved in cell death regulation. Caspase-12, residing in the ER, was cleaved in mutant huntingtin expressing cells, as was caspase-3 mediating cell death. In contrast, cytochrome-c or apoptosis inducing factor (AIF) was not released from mitochondria after the expression of these proteins. Treatment with salubrinal that inhibits ER stress counteracted cell death and reduced protein aggregations in the PC6.3 cells caused by the mutant huntingtin fragment proteins. Salubrinal upregulated Bip, reduced cleavage of caspase-12 and increased the phosphorylation of eukaryotic translation initiation factor-2 subunit-alpha (eIF2alpha) that are neuroprotective. These results show that N-terminal mutant huntingtin proteins activate cellular pathways linked to ER stress, and that inhibition of ER stress by salubrinal increases cell survival. The data suggests that compounds targeting ER stress may be considered in designing novel approaches for treatment of HD and possibly other polyQ diseases.
authors.affiliation: Medical Research Institute Minerva, Biomedicum Helsinki, Haartmaninkatu 8, Helsinki, Finland.
authors.forename: Sami
authors.initials: S
authors.lastname: Reijonen
authors.forename: Noora
authors.initials: N
authors.lastname: Putkonen
authors.forename: Anne
authors.initials: A
authors.lastname: Nørremølle
authors.forename: Dan
authors.initials: D
authors.lastname: Lindholm
authors.forename: Laura
authors.initials: L
authors.lastname: Korhonen
mesh_terms: D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D002934:Cinnamates / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000473:pathology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000209:etiology / Q000473:pathology*; D048031:JNK Mitogen-Activated Protein Kinases; D018832:Molecular Chaperones; D050505:Mutant Proteins / Q000378:metabolism / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000473:pathology*; D009687:Nuclear Proteins / Q000235:genetics / Q000502:physiology*; D010446:Peptide Fragments; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D051742:Transcription Factor CHOP; D014162:Transfection
chemical_list: D002934:Cinnamates; D000091342:Endoplasmic Reticulum Chaperone BiP; C086055:HTT protein, human; D006360:Heat-Shock Proteins; D000071058:Huntingtin Protein; D018832:Molecular Chaperones; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments; C496827:salubrinal; D051742:Transcription Factor CHOP; D048031:JNK Mitogen-Activated Protein Kinases; D013890:Thiourea