RNAi

Genetic diseases that are accompanied by central nervous system involvement are often fatal. Among these are the autosomal dominant neurogenetic diseases caused by nucleotide repeat expansion. For example, Huntington's Disease (HD) and spino-cerebellar ataxia 1 (SCA1) are caused by expansion of a tract of CAGs encoding glutamine. Treatments for these disorders are limited to symptomatic intervention. RNA interference (RNAi) is a method for inhibiting target gene expression and provides a unique tool for therapy by attacking the fundamental problem directly.

RNA interference (RNAi) is a mechanism by which RNA can impart repressive activity on gene expression. It is now well established that interference of gene expression can occur in plant and mammalian cells either prior to transcription or post-transcriptionally. Fortunately, we can co-opt this naturally occurring system to accomplish RNAi against targets not normally silenced in a given population of cells. In our case, the target cells are neurons in situ and the mRNAs we wish to silence are encoded from genes that when mutant, cause disease.

In our laboratory, we have tested RNAi strategies for SCA1 and HD by creating short hairpin RNAs (shRNA) to the mRNA encoding by the Ataxia 1 gene and to the Huntington's gene. Our laboratory uses adeno-associated virus as a vehicle to get the shRNA into, and expressed, in cells of the brain. We have tested the effectiveness of these shRNAs in reducing transcripts in cell lines and in mouse brains. We have also shown improvements in the symptoms in mouse model systems for SCA1 (1) and HD (2). We are currently looking at ways to improve on the design, delivery, expression, and efficacy of these interfering RNAs in vivo.

References:

1. Xia H, Mao Q, Eliason SL, Harper SQ, Martins IH, Orr HT, Paulson HL, Yang L, Kotin RM, Davidson BL. RNAi suppresses polyglutamine-induced neurodegeneration in a model of spinocerebellar ataxia. Nat Med 10(8):775-776, 2004.

2. Harper SQ, Staber PD, He X, Eliason SL, Martins IH, Mao Q, Yang L, Kotin RM, Paulson HL, Davidson BL. RNA interference improves motor and neuropathological abnormalities in a Huntington's disease mouse model. PNAS 102(16):5820-5825, 2005.

Additional References:

Denovan-Wright EM, Davidson BL. RNAi: a potential therapy for the dominantly inherited nucleotide repeat diseases. Gene Ther 2005.

Davidson BL, Harper SQ. Viral delivery of recombinant short hairpin RNAs. Meth Enzymol 392:145-173, 2005.

Harper SQ, Davidson BL. Plasmid-based RNA interference: construction of small-hairpin RNA expression vectors. Meth Mol Biol 309:219-236, 2005.

Alisky JM, Davidson BL. Towards therapy using RNA interference. Am J Pharmacogenomics 4(1):45-51, 2004.