Proteasomal-dependent aggregate reversal and absence of cell death in a conditional mouse model of Huntington's disease.
Neuronal intranuclear inclusions are a histopathological hallmark of Huntington's disease. Nevertheless, the precise mechanism by which they are formed and their relevance to neuronal cell death and/or dysfunction remains unclear. We recently generated a conditional mouse model of Huntington's disease (HD94) in which silencing expression of mutated huntingtin led to the disappearance of intranuclear aggregates and amelioration of the behavioral phenotype. Here, we analyze primary striatal neuronal cultures from HD94 mice to explore the dynamics of aggregate formation and reversal, the possible mechanisms involved, and the correlation between aggregates and neuronal death. In parallel, we examine symptomatic adult HD94 mice in similar studies and explored the relationship between aggregate clearance and behavioral reversal. We report that, in culture, aggregate formation and reversal were rapid processes, such that 2 d of transgene expression led to aggregate formation, and 5 d of transgene suppression led to aggregate disappearance. In mice, full reversal of aggregates and intranuclear mutant huntingtin was more rapid than reported previously and preceded the motor recovery by several weeks. Furthermore, the proteasome inhibitor lactacystin inhibited the aggregate clearance observed in culture, thus indicating that aggregate formation is a balance between the rate of huntingtin synthesis and its degradation by the proteasome. Finally, neither expression of the mutant huntingtin nor aggregates compromised the viability of HD94 cultures. This correlated with the lack of cell death in symptomatic HD94 mice, thus demonstrating that neuronal dysfunction, and not cell loss, triggered by mutant huntingtin underlies symptomatology.
Martín-Aparicio
E
E
Centro de Biologia Molecular "Severo Ochoa," Consejo Superior de Investigaciones Cientificas-Universidad Autónoma de Madrid, 28049 Madrid, Spain.
Yamamoto
A
A
Hernández
F
F
Hen
R
R
Avila
J
J
Lucas
J J
JJ
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D004195:Disease Models, Animal; D020868:Gene Silencing / Q000187:drug effects; D005799:Genes, Dominant; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D008124:Locomotion / Q000187:drug effects / Q000235:genetics; D046911:Macromolecular Substances; D051379:Mice; D008818:Mice, Neurologic Mutants; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex; D012074:Remission Induction; D013752:Tetracycline / Q000494:pharmacology; D019076:Transgenes; D025801:Ubiquitin / Q000378:metabolism
C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D025801:Ubiquitin; C067713:lactacystin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D013752:Tetracycline; D000111:Acetylcysteine