Cleavage at the 586 amino acid caspase-6 site in mutant huntingtin influences caspase-6 activation in vivo.
Caspase cleavage of huntingtin (htt) and nuclear htt accumulation represent early neuropathological changes in brains of patients with Huntington's disease (HD). However, the relationship between caspase cleavage of htt and caspase activation patterns in the pathogenesis of HD remains poorly understood. The lack of a phenotype in YAC mice expressing caspase-6-resistant (C6R) mutant htt (mhtt) highlights proteolysis of htt at the 586 aa caspase-6 (casp6) site as a key mechanism in the pathology of HD. The goal of this study was to investigate how proteolysis of htt at residue 586 plays a role in the pathogenesis of HD and determine whether inhibiting casp6 cleavage of mhtt alters cell-death pathways in vivo. Here we demonstrate that activation of casp6, and not caspase-3, is observed before onset of motor abnormalities in human and murine HD brain. Active casp6 levels correlate directly with CAG size and inversely with age of onset. In contrast, in vivo expression of C6R mhtt attenuates caspase activation. Increased casp6 activity and apoptotic cell death is evident in primary striatal neurons expressing caspase-cleavable, but not C6R, mhtt after NMDA application. Pretreatment with a casp6 inhibitor rescues the apoptotic cell death observed in this paradigm. These data demonstrate that activation of casp6 is an early marker of disease in HD. Furthermore, these data provide a clear link between excitotoxic pathways and proteolysis and suggest that C6R mhtt protects against neurodegeneration by influencing the activation of neuronal cell-death and excitotoxic pathways operative in HD.
Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, Department of Medical Genetics , Brain Research Centre, University of British Columbia, Vancouver, British Columbia, Canada V5Z 4H4.
Rona K
RK
Graham
Yu
Y
Deng
Jeffery
J
Carroll
Kuljeet
K
Vaid
Catherine
C
Cowan
Mahmoud A
MA
Pouladi
Martina
M
Metzler
Nagat
N
Bissada
Lili
L
Wang
Richard L M
RL
Faull
Michelle
M
Gray
X William
XW
Yang
Lynn A
LA
Raymond
Michael R
MR
Hayden
D000704:Analysis of Variance; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D015153:Blotting, Western; D053178:Caspase 6 / Q000235:genetics / Q000378:metabolism*; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D018450:Disease Progression; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D007150:Immunohistochemistry; D051379:Mice; D008822:Mice, Transgenic; D016202:N-Methylaspartate / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*
C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D016202:N-Methylaspartate; D053178:Caspase 6