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Research groups studying different types of hearing loss have gained new insight into its causes and possible treatments from experiments using mice. One group, led by Zheng-Yi Chen (Harvard Medical School and Massachusetts Eye and Ear Infirmary, Boston, MA), investigated age-related hearing loss (ARHL) and noise-induced hearing loss (NIHL), the two most common forms of deafness. Both are caused by the irreversible loss of inner ear outer hair cells, and although hearing aids and cochlear implants can help some affected individuals, they do not work for everyone, and there is no cure. Chen's team hypothesized that ARHL and NIHL might have similar causes and set out to determine whether protecting hair cells from damage could reduce either form of hearing loss. They zeroed in on the transcription factor islet 1 (Isl1) as a potential protector because it is expressed in developing hair cells. They created transgenic mice overexpressing Isl1 only in hair cells and evaluated their hair cells and hearing function as they aged to 17 months. Isl1 overexpression protected hair cells from age-related degeneration and promoted hair cell survival after exposure to loud noise. As a result, transgenic mice had better hearing than wild-type mice of similar age or with similar exposure to loud noise (J. Neurosci. 33, 15086–15094; 2013). These results suggest that ARHL and NIHL likely share a common mechanism and, furthermore, that Isl1 expression can protect against the hearing loss that occurs with age and noise exposure.

A separate team headed by Kerry A. Miller and based at Murdoch Childrens Research Institute and University of Melbourne (Melbourne, Australia) approached the problem of hearing loss from a different angle. As part of a large-scale mutagenesis screen, they created mice with severe hearing loss, located the genetic region that was affected and characterized the condition as a model for human hereditary deafness. Their objective was to identify deafness-related genes that could become therapeutic targets for hereditary hearing loss in people. The mutant mice developed congenital hearing loss by 4 weeks of age, progressing to profound deafness within the next 8 weeks. They had abnormal cochlear structure and morphology. The causative mutation was located within a 21.6-Mb region of chromosome 18 that has not previously been associated with deafness but contains several candidates for further analysis, including the genes encoding aquaporin 4, cadherin 2 and myosin 7b (PLoS ONE 8, e74243; 2013).

Both groups hope their work will lead to better understanding and treatment of hearing loss in humans.