Inhibition of apoptosis signal-regulating kinase 1 reduces endoplasmic reticulum stress and nuclear huntingtin fragments in a mouse model of Huntington disease

Huntington's disease (HD) is characterized clinically by chorea, psychiatric disturbances, and dementia, while it is characterized pathologically by neuronal inclusions as well as striatal and cortical neurodegeneration. The neurodegeneration arises from the loss of long projection neurons in the cortex and striatum. In this study, we investigated the role of apoptosis signal-regulating kinase 1 (Ask1) in the pathogenesis of HD. We analyzed the expression of Ask1 and huntingtin (htt) within the striatum and cortex and also examined the interaction of Ask1 with htt fragments in HD (R6/2) mice. Additionally, we inhibited Ask1 and analyzed the resulting changes in brain-derived neurotrophic factor (BDNF) expression, motor function, and striatal atrophy. Ask1 activity was blocked using an Ask1 antibody raised against the C-terminus of the Ask1 protein. The anti-Ask1 antibody was infused into the striatum of the HD mice for four weeks using a micro-osmotic pump. The levels of Ask1 protein and endoplasmic reticulum (ER) stress were increased in HD mice. Binding of inactivated Ask1 to htt fragments was more prevalent in the cytosol than the nucleus of cortical neurons. Binding of inactivated Ask1 to htt fragments prevented translocation of the htt fragments into the nucleus, resulting in an improvement in motor dysfunction and atrophy. In the normal state, active Ask1 may help htt fragments enter the nucleus, while inactivated Ask1 hinders this translocation by binding to but not releasing fragmented htt into the nucleus. We propose that Ask1 may interact with htt fragments and subsequently induce ER stress. BDNF depletion may be prevented by targeting Ask1; this would decrease ER stress and possibly ameliorate behavioral or anatomical abnormalities that accompany HD. Therefore, regulating the amounts and activity of the Ask1 protein is a novel strategy for treatment of HD.

[1]  Y. Itoyama,et al.  Presenilin-1 mutations downregulate the signalling pathway of the unfolded-protein response , 1999, Nature Cell Biology.

[2]  K. Shimoke,et al.  Prevention of endoplasmic reticulum stress-induced cell death by brain-derived neurotrophic factor in cultured cerebral cortical neurons , 2004, Brain Research.

[3]  He Li,et al.  Amino-terminal fragments of mutant huntingtin show selective accumulation in striatal neurons and synaptic toxicity , 2000, Nature Genetics.

[4]  N. Hattori,et al.  An Unfolded Putative Transmembrane Polypeptide, which Can Lead to Endoplasmic Reticulum Stress, Is a Substrate of Parkin , 2001, Cell.

[5]  C. Cepeda,et al.  Pathological cell-cell interactions are necessary for striatal pathogenesis in a conditional mouse model of Huntington's disease , 2007, Molecular Neurodegeneration.

[6]  Blair R. Leavitt,et al.  Caspase Cleavage of Mutant Huntingtin Precedes Neurodegeneration in Huntington's Disease , 2002, The Journal of Neuroscience.

[7]  W. Min,et al.  AIP1 Is Critical in Transducing IRE1-mediated Endoplasmic Reticulum Stress Response* , 2008, Journal of Biological Chemistry.

[8]  G. Kim,et al.  Early nuclear translocation of endonuclease G and subsequent DNA fragmentation after transient focal cerebral ischemia in mice , 2005, Neuroscience Letters.

[9]  A. Chang,et al.  Heat shock response relieves ER stress , 2008, The EMBO journal.

[10]  S. Strickland,et al.  Neuronal Death in the Hippocampus Is Promoted by Plasmin-Catalyzed Degradation of Laminin , 1997, Cell.

[11]  Blair R. Leavitt,et al.  Loss of Huntingtin-Mediated BDNF Gene Transcription in Huntington's Disease , 2001, Science.

[12]  S. Rothman.  Excitotoxic neuronal death: mechanisms and clinical relevance , 1994 .

[13]  H. Ichijo,et al.  The ASK1-MAP kinase signaling in ER stress and neurodegenerative diseases. , 2006, Current molecular medicine.

[14]  H. Paulson,et al.  Suppression of polyglutamine-mediated neurodegeneration in Drosophila by the molecular chaperone HSP70 , 1999, Nature Genetics.

[15]  T. Dawson,et al.  Apoptosis-Inducing Factor Substitutes for Caspase Executioners in NMDA-Triggered Excitotoxic Neuronal Death , 2004, The Journal of Neuroscience.

[16]  H. Lehrach,et al.  Accumulation of mutant huntingtin fragments in aggresome-like inclusion bodies as a result of insufficient protein degradation. , 2001, Molecular biology of the cell.

[17]  Elena Cattaneo,et al.  Normal huntingtin function: an alternative approach to Huntington's disease , 2005, Nature Reviews Neuroscience.

[18]  G. Kim,et al.  Induction of apoptosis signal-regulating kinase 1 and oxidative stress mediate age-dependent vulnerability to 3-nitropropionic acid in the mouse striatum , 2008, Neuroscience Letters.

[19]  Christopher A. Ross,et al.  The antidepressant sertraline improves the phenotype, promotes neurogenesis and increases BDNF levels in the R6/2 Huntington's disease mouse model , 2008, Experimental Neurology.

[20]  Xianglin Shi,et al.  Brain‐derived neurotrophic factor suppresses tunicamycin‐induced upregulation of CHOP in neurons , 2007, Journal of neuroscience research.

[21]  A. Hackam,et al.  Specific caspase interactions and amplification are involved in selective neuronal vulnerability in Huntington's disease , 2004, Cell Death and Differentiation.

[22]  M. Beal,et al.  Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases , 2006, Nature.

[23]  D. Monté,et al.  ASK1 and MAP2K6 as modifiers of age at onset in Huntington’s disease , 2008, Journal of Molecular Medicine.

[24]  Kiyoshi Inoue,et al.  ASK1 is essential for endoplasmic reticulum stress-induced neuronal cell death triggered by expanded polyglutamine repeats. , 2002, Genes & development.

[25]  H. Ichijo,et al.  Apoptosis signal-regulating kinase 1 in stress and immune response. , 2008, Annual review of pharmacology and toxicology.

[26]  R. Kopito,et al.  Impairment of the ubiquitin-proteasome system by protein aggregation. , 2001, Science.

[27]  Jiankun Cui,et al.  A Highly Specific Inhibitor of Matrix Metalloproteinase-9 Rescues Laminin from Proteolysis and Neurons from Apoptosis in Transient Focal Cerebral Ischemia , 2005, The Journal of Neuroscience.