Oligonucleotide-based strategies to combat polyglutamine diseases.
Bottom Line: The latter include targeting SNP variants associated with mutations or targeting the pathologically expanded CAG repeat directly.We compare gene silencing effectors of various types in a number of aspects, including their design, efficiency in cell culture experiments and pre-clinical testing.We discuss advantages, current limitations and perspectives of various ON-based strategies used to treat polyQ diseases.
Affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland.Show MeSH
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Mentions: The possible ways to block the pathogenic pathway in polyQ diseases include the following: genome editing, transcription inhibition, transcript degradation or modification, translation arrest, and inhibition or degradation of toxic protein (Figure 2). To prevent the activation of pathogenic pathways, the mutation should be eliminated or blocked at the earliest step of mutant gene expression, i.e. in the DNA sequence. The technologies designed for DNA editing are developing rapidly (71–73) and were already tested for therapeutic use (74–79). In the case of polyQ diseases, gene editing tools can be directly targeted to expanded CAG sequences in genomic DNA. Zinc finger nucleases that recognize and cleave CAG repeat sequences were tested in mammalian cells (80). More recently, the CAG repeat-targeting zinc finger proteins (ZFPs) were used in a R6/2 HD mouse model to achieve efficient and specific repression of mutant HTT (81). The ZFP-mediated mutant transgene repression likely involved steric blockade formation for RNA polymerase during transcription and resulted in a substantial correction of the molecular and behavioral pathogenic hallmarks. In attempts to therapeutically regulate gene transcription, the promoter sequence may be targeted with short RNA duplexes (82–85). The feasibility of this approach is supported by growing evidence that core RNA interference (RNAi) proteins are present and operate in the nucleus (86–89). It is not clear whether the observed changes in the histone code are caused by short RNAs targeting DNA or RNA (sense or antisense) covering the promoter sequence, but clearly Argonaute proteins are involved in these processes (90,91). In the case of polyQ diseases, this strategy would likely result in silencing both alleles of the gene.
Affiliation: Department of Molecular Biomedicine, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-704 Poznan, Poland.