Age-related deafness is caused by some mix of loss of sensory hair cells of the inner ear, and loss of connections between those cells and the brain. A range of potential approaches to restore those cells are under development, and the work here is an example of this sort of work. Researchers have constructed an AAV viral vector that has some specificity for hair cells and nearby supporting cells, and which can be used to deliver a gene therapy payload that converts those supporting cells into new hair cells.
Cells of the cochlea, such as hair cells (HCs) and supporting cells (SCs), are essential for hearing. While sensorineural hearing loss can result from genetic mutations in both HCs and SCs, non-genetic stresses, such as noise, ototoxic medicines, or aging, can also induce deafness through damaging HCs. In either case, these damages are irreversible in mammals who do not have the ability to regenerate cochlear cells. Notably, SCs have the potential to transdifferentiate into HC-like cells.
Gene therapies have emerged as important treatments for genetic diseases, and current progress also demonstrates their potential for treating hearing loss. Several genes, such as tmc1, clrn, and otof, when being delivered to cochleae, can restore hearing function in animal models. Adeno-associated viruses (AAVs) have been shown to possess high safety in both animal models and humans. Previously, we developed a synthetic AAV, AAV-ie, which targets SCs and HCs. AAV-ie can regenerate HC-like cells through delivering the transcription factor, Atoh1, which transdifferentiates SCs into HC-like cells. However, its targeting efficiencies for SCs or HCs need to be improved, especially in the basal region of cochleae.
In the present study, we performed mutational screening on the AAV-ie capsid. We generated a repertoire of mutants on the amino acid sequence of AAV-ie capsids to manipulate phosphorylation/ubiquitination of AAVs in cells. We demonstrated that a particular amino acid-mutant AAV-ie capsid, AAV-ie-K558R, can transduce SCs with high efficiency and is suitable for correcting dysfunctional genetic mutations or for HC-like regeneration.