Therapeutic Regulation of Gene Expression in the Inner Ear using RNA Interference

Abstract

Targeting and down-regulating specific genes with antisense and decoy oligonucleotides, ribozymes or RNA interference (RNAi) offers the theoretical potential of altering a disease phenotype. This article reviews the molecular mechanism behind the in-vivo application of RNAi-mediated gene silencing, focusing on its application to the inner ear. RNAi is a physiological phenomenon in which small, double-stranded RNA molecules (small interfering RNA, siRNA) reduce expression of homologous genes. Notable for its exquisite sequence specificity, it is ideally applied to diseases caused by a gain-of-function mechanism of action. Types of deafness in which gain-of-function mutations are observed include DFNA2 (KCNQ4), DFNA3 (GJB2) and DFNA5 (DFNA5). Several strategies can be used to deliver siRNA into the inner ear, including cationic liposomes, adenoassociated and lentiviral vectors, and adenoviral vectors. Transduction efficiency with cationic liposomes is low and the effect is transient; with adeno-associated and lentiviral vectors, long-term transfection is possible using a small hairpin RNA (shRNA) expression cassette.

Sound Strategies for Hearing Restoration

“…Several novel alternatives for treating dominant deafness are on the horizon. One such approach would involve viral delivery of siRNA sequences designed to suppress expression of the mutant sequence but not the correct, wild-type sequence (72). Since many forms of dominant deafness result in single point mutations, the design of effective and specific siRNAs, with only one nucleotide mismatch, will be challenging.…”

Restoration of Hearing in the VGLUT3 Knockout Mouse Using Virally Mediated Gene Therapy

“…In such a scenario, even successfully regenerated hair cells will still be subject to the innate genetic mutation that led to hair cell loss in the first place. To date, efforts to restore hearing in this type of hearing loss with gene therapy have been met with limited success (Maeda et al, 2009), and no study has reported the reversal of deafness in an animal model of genetic deafness.…”

Cochlear gene therapy

“…According to Maeda et al, types of deafness in which these ‘gain-of-function’ mutations which would potentially be amenable to such RNAi techniques include DFNA2 (KCNQ4), DFNA3 (GJB2) and DFNA5 (DFNA5). (29) Another study reported that connexin-26 expressed in a bacterial artificial chromosome in a connexin-30 knockout mouse was able to restore hearing in this model. Since connexin-related deafness accounts for a majority of cases of genetic deafness, these results represent promising, though preliminary breakthroughs in this arena.…”

“…In one of the few studies to document some successful results, Maeda et al , attempted to restore the hearing loss in a model of Connexin 26-induced deafness using AAV-transduced antisense oligonucleotides for RNA interference (RNAi). (29) In this model, the hearing loss was induced first by introducing the defective gene in a normal animal, and then using RNAi to suppress the defective gene and reverse the hearing loss. According to Maeda et al, types of deafness in which these ‘gain-of-function’ mutations which would potentially be amenable to such RNAi techniques include DFNA2 (KCNQ4), DFNA3 (GJB2) and DFNA5 (DFNA5).…”