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PMID: 19118173 Published · ppublish English Journal Article Research Support, Non-U.S. Gov't

Cytoplasmic inclusions of Htt exon1 containing an expanded polyglutamine tract suppress execution of apoptosis in sympathetic neurons.

The Journal of neuroscience : the official journal of the Society for Neuroscience ·Vol. 28 ·No. 53 ·2008-12-31 ·Pages 14401-15

King MA, Goemans CG, Hafiz F, Prehn JH, Wyttenbach A, Tolkovsky AM

Abstract

Proteins containing extended polyglutamine repeats cause at least nine neurodegenerative disorders, but the mechanisms of disease-related neuronal death remain uncertain. We show that sympathetic neurons containing cytoplasmic inclusions formed by 97 glutamines expressed within human huntingtin exon1-enhanced green fluorescent protein (Q97) undergo a protracted form of nonapoptotic death that is insensitive to Bax deletion or caspase inhibition but is characterized by mitochondrial dysfunction. By treating the neurons with combined cytosine arabinoside and NGF withdrawal, we demonstrate that Q97 confers a powerful resistance to apoptosis at multiple levels: despite normal proapoptotic signaling (elevation of P-ser15-p53 and BimEL), there is no increase of Puma mRNA or Bax activation, both necessary for apoptosis. Even restoration of Bax translocation with overexpressed Puma does not activate apoptosis. We demonstrate that this robust inhibition of apoptosis is caused by Q97-mediated accumulation of Hsp70, which occurs through inhibition of proteasomal activity. Thus, apoptosis is reinstated by short hairpin RNA-mediated knockdown of Hsp70. These findings explain the rarity of apoptotic death in Q97-expressing neurons. Given the proteasomal blockade, we test whether enhancing lysosomal-mediated degradation with rapamycin reduces Q97 accumulation. Rapamycin reduces the amount of nonpathological Q25 by 70% over 3 d, but Q97 accumulation is unaffected. Interestingly, Q47 inclusions form more slowly as a result of constitutive lysosomal degradation, but faster-forming Q97 inclusions escape lysosomal control. Thus, cytoplasmic Q97 inclusions are refractory to clearance by proteasomal and lysosomal systems, leading to a toxicity that dominates over neuroprotective Hsp70. Our findings may explain the rarity of apoptosis but the inevitable cell death associated with polyQ inclusion diseases.

MeSH Terms
Analysis of Variance Animals Animals, Newborn Apoptosis/drug effects,physiology Cyclosporine/pharmacology Enzyme Inhibitors/pharmacology Exons/genetics Green Fluorescent Proteins/genetics HSP70 Heat-Shock Proteins/genetics,metabolism Humans Inclusion Bodies/metabolism,pathology Lysosomes/drug effects,metabolism Nerve Growth Factor/pharmacology Neurons/cytology,physiology Peptides/genetics,metabolism,pharmacology Rats Rats, Wistar Receptor, trkA/metabolism Serotonin Plasma Membrane Transport Proteins/genetics,metabolism Signal Transduction/drug effects Superior Cervical Ganglion/cytology Time Factors Transfection bcl-2-Associated X Protein/metabolism
Chemicals
Enzyme Inhibitors HSP70 Heat-Shock Proteins Peptides SLC6A4 protein, human Serotonin Plasma Membrane Transport Proteins bcl-2-Associated X Protein enhanced green fluorescent protein Green Fluorescent Proteins polyglutamine Cyclosporine Nerve Growth Factor Receptor, trkA
Authors & Affiliations
6 authors, click to expand affiliations / ORCID
King Matthew A
Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
Goemans Christoph G
Hafiz Farida
Prehn Jochen H M
Wyttenbach Andreas
Tolkovsky Aviva M
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Article Info
Journal
The Journal of neuroscience : the official journal of the Society for Neuroscience
Abbr.
J Neurosci
ISSN
1529-2401
DOI
10.1523/JNEUROSCI.4751-08.2008
Published
2008-12-31
Pages
14401-15
Language
English
Region
United States
NLM ID
8102140
PMCID
PMC6671245
Subset
IM
Grants
Wellcome Trust · 064232 · United Kingdom
Wellcome Trust · 070430 · United Kingdom
Medical Research Council · United Kingdom
External Links
PubMed source DOI: 10.1523/JNEUROSCI.4751-08.2008 PMC Full Text View journal details
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