Today's open access paper is a review of present progress towards regenerative therapies that can reverse hearing loss. Progressive hearing loss is pervasive in old age, and accelerates considerable in the later stages of life. Hearing loss correlates with cognitive decline, and while it is plausible that this is because of degeneration of central nervous system function, there is also the consideration that loss of hearing isolates people and deprives them of interactions that stimulate brain activity. It is well demonstrated in mice that environment richness has a strong impact on the brain and its pace of aging.

Much of the research into age-related hearing loss is focused on the sensory hair cells of the inner ear. These detect the pressure waves of sound and in response pass impulses into nervous system connections leading to the brain. There is some evidence for loss of these cells to be the problem, and some evidence for the cells to survive in sufficient numbers, but lose their connections to the brain. Numerous research teams over the past decade or more have worked on producing regenerative therapies to regrow functional hair cells in the aged inner ear. Numerous strategies have been attempted, such as adapting mechanisms from regenerative species that can regrow hair cells as adults, or direct stimulation of pathways such as Notch that are associated with growth. Varying degrees of success have been demonstrated in mice, but as is often the case, progress towards the clinic remains frustratingly slow.

Hearing regeneration and regenerative medicine: present and future approaches