Abstract
Sensorineural hearing loss is caused by the loss of sensory hair cells (HCs) or a damaged afferent nerve pathway to the auditory cortex. The most common option for the treatment of sensorineural hearing loss is hearing rehabilitation using hearing devices. Various kinds of hearing devices are available but, despite recent advancements, their perceived sound quality does not mimic that of the “naïve” cochlea. Damage to crucial cochlear structures is mostly irreversible and results in permanent hearing loss. Cochlear HC regeneration has long been an important goal in the field of hearing research. However, it remains challenging because, thus far, no medical treatment has successfully regenerated cochlear HCs. Recent advances in genetic modulation and developmental techniques have led to novel approaches to generating HCs or protecting against HC loss, to preserve hearing. In this review, we present and review the current status of two different approaches to restoring or protecting hearing, gene therapy, including the newly introduced CRISPR/Cas9 genome editing, and stem cell therapy, and suggest the future direction.
Highlights
The history of gene therapy began in the 1960s and early 1970s, when genetically marked cells were developed and used to understand the mechanism of cellular transformation by several viral vectors
Sensorineural hearing loss is caused by the loss of sensory hair cells (HCs) or damage involving the afferent nerve pathway to the auditory cortex
Similar outcome of gene therapy showing recovery of phenotype by delivery of gene using adenoassociated virus (AAV) vector was observed in animal model for Usher syndrome [37] and genetic hearing loss related to human DFNB7/11 and DFNA36 [38]
Summary
Hearing loss can be divided into sensorineural and conductive hearing loss. Conductive hearing loss is a biophysical problem, resulting from the fixation or disruption of the ossicular chain, middle ear effusion, and third window of the cochlea. Sensorineural hearing loss is caused by the loss of sensory hair cells (HCs) or damage involving the afferent nerve pathway to the auditory cortex. These types of damage are caused by a variety of ototoxic agents, such as aminoglycoside and cisplatin, acoustic overexposure, and mutations in the genes responsible for hearing and aging. They are mostly irreversible and result in permanent hearing loss. The second is stem-cell therapy (Figure 1(c)), in which cells capable of differentiating into HCs, such as induced pluripotent cells (IPCs) or embryonic stem cells (ESCs), are forced to differentiate into HCs by exposure to the responsible factors
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