Huntington's disease (HD) is a fatal, dominant neurogenetic disorder. HD results from polyglutamine repeat expansion (CAG codon, Q) in exon 1 of HD, conferring a toxic gain of function on the protein huntingtin (htt). Currently, no preventative treatment exists for HD. RNA interference (RNAi) has emerged as a potential therapeutic tool for treating dominant diseases by directly reducing disease gene expression. Here, we show that RNAi directed against mutant human htt reduced htt mRNA and protein expression in cell culture and in HD mouse brain. Importantly, htt gene silencing improved behavioral and neuropathological abnormalities associated with HD. Our data provide support for the further development of RNAi for HD therapy.short hairpin RNAs ͉ triplet repeat diseases ͉ gene therapy ͉ nanomedicine

The dominant polyglutamine expansion diseases, which include spinocerebellar ataxia type 1 (SCA1) and Huntington disease, are progressive, untreatable, neurodegenerative disorders. In inducible mouse models of SCA1 and Huntington disease, repression of mutant allele expression improves disease phenotypes. Thus, therapies designed to inhibit expression of the mutant gene would be beneficial. Here we evaluate the ability of RNA interference (RNAi) to inhibit polyglutamine-induced neurodegeneration caused by mutant ataxin-1 in a mouse model of SCA1. Upon intracerebellar injection, recombinant adeno-associated virus (AAV) vectors expressing short hairpin RNAs profoundly improved motor coordination, restored cerebellar morphology and resolved characteristic ataxin-1 inclusions in Purkinje cells of SCA1 mice. Our data demonstrate in vivo the potential use of RNAi as therapy for dominant neurodegenerative disease.

Recombinant adeno-associated virus vectors based on serotype 2 (rAAV2) can direct transgene expression in the central nervous system (CNS), but it is not known how other rAAV serotypes perform as CNS gene transfer vectors. Serotypes 4 and 5 are distinct from rAAV2 and from each other in their capsid regions, suggesting that they may direct binding and entry into different cell types. In this study, we examined the tropisms and transduction efficiencies of ␤-galactosidase-encoding vectors made from rAAV4 and rAAV5 compared with similarly designed rAAV2-based vectors. Injection of rAAV5 ␤-galactosidase (␤gal) or rAAV4␤gal into the lateral ventricle resulted in stable transduction of ependymal cells, with approximately 10-fold more positive cells than in mice injected with rAAV2␤gal. Major differences between the three vectors were revealed upon striatal injections. Intrastriatal injection of rAAV4␤gal resulted again in striking ependyma-specific expression of transgene, with a notable absence of transduced cells in the parenchyma. rAAV2␤gal and rAAV5␤gal intrastriatal injections led to ␤-gal-positive parenchymal cells, but, unlike rAAV2␤gal, rAAV5␤gal transduced both neurons and astrocytes. The number of transgene-positive cells in rAAV5␤gal-injected brains was 130 and 5,000 times higher than in rAAV2␤gal-injected brains at 3 and 15 wk, respectively. Moreover, transgene-positive cells were widely dispersed throughout the injected hemisphere in rAAV5␤gal-transduced animals. Together, our data provide in vivo support for earlier in vitro work, suggesting that rAAV4 and rAAV5 gain cell entry by means of receptors distinct from rAAV2. These differences could be exploited to improve gene therapy for CNS disorders.