Caspase-6 activity in a BACHD mouse modulates steady-state levels of mutant huntingtin protein but is not necessary for production of a 586 amino acid proteolytic fragment.

TitleCaspase-6 activity in a BACHD mouse modulates steady-state levels of mutant huntingtin protein but is not necessary for production of a 586 amino acid proteolytic fragment.
Publication TypeJournal Article
Year of Publication2012
AuthorsGafni, J, Papanikolaou T, Degiacomo F, Holcomb J, Chen S, Menalled L, Kudwa A, Fitzpatrick J, Miller S, Ramboz S, Tuunanen PI, Lehtimäki KK, Yang WX, Park L, Kwak S, Howland D, Park H, Ellerby LM
JournalThe Journal of neuroscience : the official journal of the Society for Neuroscience
Volume32
Issue22
Pagination7454-65
Date Published2012 May 30
ISSN1529-2401
KeywordsAge Factors, Amino Acids, Animals, Aspartic Acid, Body Weight, Brain, Caspase 6, Cells, Cultured, Corpus Striatum, Disease Models, Animal, Embryo, Mammalian, Exploratory Behavior, Female, Gene Expression Regulation, Huntington Disease, Magnetic Resonance Imaging, Mice, Mice, Inbred C57BL, Mice, Knockout, Mice, Mutant Strains, Motor Activity, Nerve Tissue Proteins, Neurons, Proteolysis, RNA, Small Interfering, Rotarod Performance Test, Trinucleotide Repeat Expansion, Ubiquitination
Abstract

Huntington's disease (HD) is caused by a mutation in the huntingtin (htt) gene encoding an expansion of glutamine repeats at the N terminus of the Htt protein. Proteolysis of Htt has been identified as a critical pathological event in HD models. In particular, it has been postulated that proteolysis of Htt at the putative caspase-6 cleavage site (at amino acid Asp-586) plays a critical role in disease progression and pathogenesis. However, whether caspase-6 is indeed the essential enzyme that cleaves Htt at this site in vivo has not been determined. To evaluate, we crossed the BACHD mouse model with a caspase-6 knock-out mouse (Casp6(-/-)). Western blot and immunocytochemistry confirmed the lack of caspase-6 protein in Casp6(-/-) mice, regardless of HD genotype. We predicted the Casp6(-/-) mouse would have reduced levels of caspase-6 Htt fragments and increased levels of full-length Htt protein. In contrast, we found a significant reduction of full-length mutant Htt (mHtt) and fragments in the striatum of BACHD Casp6(-/-) mice. Importantly, we detected the presence of Htt fragments consistent with cleavage at amino acid Asp-586 of Htt in the BACHD Casp6(-/-) mouse, indicating that caspase-6 activity cannot fully account for the generation of the Htt 586 fragment in vivo. Our data are not consistent with the hypothesis that caspase-6 activity is critical in generating a potentially toxic 586 aa Htt fragment in vivo. However, our studies do suggest a role for caspase-6 activity in clearance pathways for mHtt protein.

DOI10.1038/npp.2012.42
Alternate JournalJ. Neurosci.