Jenny Carmichael

Huntington's disease: from pathology and genetics to potential therapies

Huntingtons disease (HD) is a devastating autosomal dominant neurodegenerative disease caused by a CAG trinucleotide repeat expansion encoding an abnormally long polyglutamine tract in the huntingtin protein. Much has been learnt since the mutation was identified in 1993. We review the functions of wild-type huntingtin. Mutant huntingtin may cause toxicity via a range of different mechanisms. The primary consequence of the mutation is to confer a toxic gain of function on the mutant protein and this may be modified by certain normal activities that are impaired by the mutation. It is likely that the toxicity of mutant huntingtin is revealed after a series of cleavage events leading to the production of N-terminal huntingtin fragment(s) containing the expanded polyglutamine tract. Although aggregation of the mutant protein is a hallmark of the disease, the role of aggregation is complex and the arguments for protective roles of inclusions are discussed. Mutant huntingtin may mediate some of its toxicity in the nucleus by perturbing specific transcriptional pathways. HD may also inhibit mitochondrial function and proteasome activity. Importantly, not all of the effects of mutant huntingtin may be cell-autonomous, and it is possible that abnormalities in neighbouring neurons and glia may also have an impact on connected cells. It is likely that there is still much to learn about mutant huntingtin toxicity, and important insights have already come and may still come from chemical and genetic screens. Importantly, basic biological studies in HD have led to numerous potential therapeutic strategies.

The bacterial chaperonin GroEL requires GroES to reduce aggregation and cell death in a COS-7 cell model of Huntington's disease.

Huntingtons disease (HD) is caused by expansions of more than 35 CAG repeats in the HD gene. These repeats are translated into a long polyglutamine tract that confers a deleterious gain-of-function on the mutant protein. Intraneuronal inclusions comprising mutant huntingtin are found in HD patient brains. Here we show that the bacterial chaperonin GroEL can reduce aggregation of mutant huntingtin in COS-7 cells and requires GroES for efficient activity, analogous to what has been described in bacteria. The reduction in aggregation of mutant huntingtin by GroEL/GroES was associated with protection against polyglutamine-induced cell death.