Abstract
Targeting specific cell types in the mammalian inner ear is important for treating genetic hearing loss due to the different cell type-specific functions. Adeno-associated virus (AAV) is an efficient in vivo gene transfer vector, and it has demonstrated promise for treating genetic hearing loss. Although more than 100 AAV serotypes have been identified, few studies have investigated whether AAV can be distributed to specific inner ear cell types. Here we screened three EGFP-AAV reporter constructs (serotypes DJ, DJ8, and PHP.B) in the neonatal mammalian inner ear by injection via the round window membrane to determine the cellular specificity of the AAV vectors. Sensory hair cells, supporting cells, cells in Reissner’s membrane, interdental cells, and root cells were successfully transduced. Hair cells in the cochlear sensory epithelial region were the most frequently transduced cell type by all tested AAV serotypes. The recombinant DJ serotype most effectively transduced a range of cell types at a high rate. Our findings provide a basis for improving treatment of hereditary hearing loss using targeted AAV-mediated gene therapy.
Highlights
Sensorineural hearing loss (SNHL) involves damage to the cochlea and the auditory nerve, and it accounts for approximately 90% of hearing loss cases, over half of which have an underlying genetic etiology.[1]
Numerous associated virus (AAV) serotypes have been engineered by directed evolution,[20,21,22] including the serotypes DJ and DJ8, which carry a heparin-binding domain and exhibit tropism for the liver and brain, similar to that of serotypes AAV8 and AAV9.22 The engineered AAV9 variant PHP.B contains a randomized insert of seven amino acids, and it has shown broader transduction distribution following intravenous infusion into the central nervous system (CNS) of mice compared to AAV9.23
There was only a slight difference between the inner ears of the mice injected with saline and those of the mice injected with rAAV2/DJ at 8 and 16 kHz (*p < 0.05; Figures 1B and 1C)
Summary
Sensorineural hearing loss (SNHL) involves damage to the cochlea and the auditory nerve, and it accounts for approximately 90% of hearing loss cases, over half of which have an underlying genetic etiology.[1]. Several successful studies of gene therapy in SNHL mouse models have demonstrated that cochlear gene therapy is a potentially effective strategy for ameliorating hereditary hearing loss in humans.[4,5,6,7,8,9] despite the initial success, a system in which the therapeutic gene would be transported to the correct native locus is still to be developed.[3]. Adeno-associated virus (AAV) is an effective nonpathogenic gene transfer vector that can be used for treating hereditary hearing loss.[10] The function of an AAV vector is determined mainly by the capsid protein,[11,12,13] and because viral replication and packaging proteins are generally interchangeable, researchers can quickly investigate various serotypes in animal models to determine which serotype best suits their needs. Numerous AAV serotypes have been engineered by directed evolution,[20,21,22] including the serotypes DJ and DJ8, which carry a heparin-binding domain and exhibit tropism for the liver and brain, similar to that of serotypes AAV8 and AAV9.22 The engineered AAV9 variant PHP.B contains a randomized insert of seven amino acids, and it has shown broader transduction distribution following intravenous infusion into the central nervous system (CNS) of mice compared to AAV9.23
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