Sustained effects of nonallele‐specific Huntingtin silencing

Objective Huntington's disease (HD) is a fatal autosomal dominant neurodegenerative disorder caused by a polyglutamine expansion in the huntingtin (htt) protein. No cure is available to date to alleviate neurodegeneration. Recent studies have demonstrated that RNA interference represents a promising approach for the treatment of autosomal dominant disorders. But whether an allele‐specific silencing of mutant htt or a nonallele‐specific silencing should be considered has not been addressed. Methods We developed small hairpin RNA targeting mutant or wild‐type htt transcripts, or both. Results We confirmed the therapeutic potential of sihtt administered with lentiviral vectors in rodent models of HD and showed that initiation of small interfering RNA treatment after the onset of HD symptoms is still efficacious and reduces the HD‐like pathology. We then addressed the question of the impact of nonallele‐specific silencing and demonstrated that silencing of endogenous htt to 25 to 35% in vivo is altering several pathways associated with known htt functions but is not inducing overt toxicity or increasing striatal vulnerability up to 9 months after treatment. Interpretation These data indicate that the coincident silencing of the wild‐type and mutant htt may be considered as a therapeutic tool for HD. Ann Neurol 2009;65:276–285