Timothy C. Hain, MD Last revision: December 30, 2007
Many processes that affect the inner ear kill the main sensory part of the ear, hair cells. While it would seem reasonable that hair cells should be replaced when they are lost, this seems to be species specific. Hair cells of birds, both auditory and vestibular, regenerate but hair cells of humans are generally felt to not regenerate. In birds, auditory hair cells regenerate after exposure to ototoxic aminoglycoside antibiotics, and noise.
Vestibular hair cells also regenerate in birds, with both the vestibulocollic and vestibuloocular reflexes recovering full functionality after aminoglycoside exposure in chickens (Goode et al, 1999; Carey et al, 1996; Boyle et al, 2001). Hair cell regeneration in birds depends on a gene missing from Humans, Math 1.
If birds can regenerate their hair cells, it seems reasonable that people might also be able to do this, perhaps with the correct growth factor or genetic trigger. This is an ongoing subject of research. An promising method that has some experimental verification is to transvect the Math 1 gene into mammalian hair cells. (Staecker, Praetorius et al. 2007)
A recent study indicated that stereocilia, a part of the hair cell, "turns over" in cell cultures of rat inner ears over roughly 48 hours (Schneider and others, 2002). It is not surprising to find that damaged cells can repair themselves and this process offers evidence for short-term repair processes in the ear.
If we could regenerate hair cells in humans, it seems likely that much hearing and balance disease might simply disappear. Imagine - -instead of getting a hearing aid when one is 70 years old, one simply had an injection through the ear drum and restoration of hearing after a few months !
There are relatively few references concerning hair cell regeneration in the medical literature. In our opinion, considering the extremely high potential of this area, there should be more funding directed in this direction.
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