Therapeutic silencing of mutant huntingtin with siRNA attenuates striatal and cortical neuropathology and behavioral deficits

doi:10.1073/pnas.0708285104

Therapeutic silencing of mutant huntingtin with siRNA attenuates striatal and cortical neuropathology and behavioral deficits

*Department of Neurology, Massachusetts General Hospital, Charlestown, MA 02114;
Departments of ^†Medicine and
^§Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01655; and
^‡Alnylam Pharmaceuticals, Cambridge, MA 02142

Communicated by Craig Mello, University of Massachusetts Medical School, Worcester, MA, August 31, 2007 (received for review May 4, 2007)

Abstract

Huntington's disease (HD) is a neurodegenerative disorder caused by expansion of a CAG repeat in the huntingtin (Htt) gene. HD is autosomal dominant and, in theory, amenable to therapeutic RNA silencing. We introduced cholesterol-conjugated small interfering RNA duplexes (cc-siRNA) targeting human Htt mRNA (siRNA-Htt) into mouse striata that also received adeno-associated virus containing either expanded (100 CAG) or wild-type (18 CAG) Htt cDNA encoding huntingtin (Htt) 1–400. Adeno-associated virus delivery to striatum and overlying cortex of the mutant Htt gene, but not the wild type, produced neuropathology and motor deficits. Treatment with cc-siRNA-Htt in mice with mutant Htt prolonged survival of striatal neurons, reduced neuropil aggregates, diminished inclusion size, and lowered the frequency of clasping and footslips on balance beam. cc-siRNA-Htt was designed to target human wild-type and mutant Htt and decreased levels of both in the striatum. Our findings indicate that a single administration into the adult striatum of an siRNA targeting Htt can silence mutant Htt, attenuate neuronal pathology, and delay the abnormal behavioral phenotype observed in a rapid-onset, viral transgenic mouse model of HD.

Footnotes

^¶To whom correspondence should be addressed at:
University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655.
E-mail: neil.aronin{at}umassmed.edu
Author contributions: M.D., M.S.-E., D.W.Y.S., P.D.Z., and N.A. designed research; M.D., M.S.-E., K.C., E.S., E.P., M.S., J.Y., P.R., and N.A. performed research; M.D., M.S.-E., R.K.P., K.G.R., M.M., D.W.Y.S., and N.A. contributed new reagents/analytic tools; M.D., K.C., E.S., E.P., P.D.Z., and N.A. analyzed data; and M.D., M.S.-E., D.W.Y.S., P.D.Z., and N.A. wrote the paper.
Conflict of interest statement: P.D.Z. is a cofounder and scientific advisory board member of Alnylam Pharmaceuticals. D.W.Y.S., M.M., K.G.R., and R.K.P. are employees of Alnylam Pharmaceuticals.
This article contains supporting information online at www.pnas.org/cgi/content/full/0708285104/DC1.
Abbreviations:

AAV,

adeno-associated virus;

AAVHtt18Q,

AAV containing Htt cDNA producing Htt with 18 polyglutamines;

HD,

Huntington's disease;

Luc,

luciferase;

shRNA,

short hairpin RNA;

siRNA,

small interfering RNA.
Freely available online through the PNAS open access option.