These data indicate that the coincident silencing of the wild-type and mutant htt may be considered as a therapeutic tool for HD.

The insulin-like growth factor I (IGF-1)/Akt pathway plays a crucial role in Huntington's disease by phosphorylating the causative protein, polyQ-huntingtin, and abolishing its toxic properties [Humbert et al. (2002)Dev. Cell, 2, 831-837; Rangone et al. (2004)Eur. J. Neurosci., 19, 273-279]. Therefore, dysregulation of this pathway may be essential for disease progression. In the present report, we thus aimed to analyse the status of Akt in brain or in peripheral tissues in Huntington's disease. Using a genetic model of Huntington's disease in rat that reproduces neuronal dysfunction and death, we show a progressive alteration of Akt during neuronal dysfunction and prior neurodegeneration. By analysing a limited number of lymphoblasts and lymphocytes, we detected modifications of Akt in Huntington's disease patients confirming a dysregulation of Akt in the disease process. Finally, we demonstrate that during late stages of the disease, Akt is cleaved into an inactive form by caspase-3. These observations demonstrate a progressive but marked alteration of this pro-survival pathway in Huntington's disease, and further implicate it as a key transduction pathway regulating the toxicity of huntingtin.

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an expansion of glutamine repeats in the huntingtin (htt) protein. Abnormal protein folding and the accumulation of mutated htt are hallmarks of HD neuropathology. Heat-shock proteins (hsps), which refold denatured proteins, might therefore mitigate HD. We show here that hsp104 and hsp27 rescue striatal dysfunction in primary neuronal cultures and HD rat models based on lentiviral-mediated overexpression of a mutated htt fragment. In primary rat striatal cultures, production of hsp104 or hsp27 with htt171-82Q restored neuronal nuclei (NeuN)-positive cell density to that measured after infection with vector expressing the wild-type htt fragment (htt171-19Q). In vivo, both chaperones significantly reduced mutated-htt-related loss of DARPP-32 expression. Furthermore, hsps affected the distribution and size of htt inclusions, with the density of neuritic aggregates being remarkably increased in striatal neurons overexpressing hsps. We also found that htt171-82Q induced the up-regulation of endogenous hsp70 that was co-localized with htt inclusions, and that the overexpression of hsp104 and hsp27 modified the subcellular localization of hsp70 that became cytoplasmic. Finally, hsp104 induced the production of endogenous hsp27. These data demonstrate the protective effects of chaperones in mammalian models of HD.

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