Inhibition of endoplasmic reticulum stress counteracts neuronal cell death and protein aggregation caused by N-terminal mutant huntingtin proteins

• Published in: Experimental cell research 2008-03, Vol.314 (5), p.950-960
• Main Authors: Reijonen, Sami, Putkonen, Noora, Nørremølle, Anne, Lindholm, Dan, Korhonen, Laura
• Format: Article
• Language: English
• Subjects: Brain; Caspase; Cell death; Cell Death - drug effects; Cell Line; Cellular biology; Cinnamates - pharmacology; Endoplasmic Reticulum - pathology; Endoplasmic reticulum stress; Heat-Shock Proteins; Humans; Huntingtin Protein; Huntington Disease - etiology; Huntington Disease - pathology; Huntington's disease; JNK Mitogen-Activated Protein Kinases; MEDICIN; MEDICINE; Molecular Chaperones; Mutant Proteins - metabolism; Mutant Proteins - physiology; Mutation; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - physiology; Neurological disorders; Neurons - drug effects; Neurons - pathology; Nuclear Proteins - genetics; Nuclear Proteins - physiology; PC6.3 cell; Peptide Fragments; Proteins; Salubrinal; Thiourea - analogs & derivatives; Thiourea - pharmacology; Transcription Factor CHOP; Transfection
• ISSN: 0014-4827; 1090-2422; 1090-2422
• DOI: 10.1016/j.yexcr.2007.12.025

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-α (eIF2α) 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.