Hearing loss and all the processes connected to it is a widespread problem that has concerned scientists for many decades. Once incurred, sensorineural hearing damage cannot be reversed and is not treatable, as the hair cells in the cochlea do not regenerate. These hair cells are responsible for receiving the sound vibrations from the inner ear fluid and translating them into electrical signals for the brain to process.
Constant research has been conducted to try to find a way to change their inevitable and irreversible demise and look for alternative methods for proliferation or restoration of hair cells such as gene supply or the use of stem cells. Hearing loss can occur during birth or due to genetic or other diseases, ototoxic drugs or head traumas but the most common cause remains ageing.
With time, many cells in our body gradually lose their ability to reproduce without mistakes, while others cannot reproduce at all - as in the case of sensory hair cells in the cochlea. What is interesting, however, is that only mammals (including humans) lack that ability in contrast to birds and other vertebrae, which have proven to be able to regenerate damaged hair cells. This evidence has led scientists to believe that mammals, which must have lost that capability during a time in the evolutionary cycle, may be able to restore it with the right combination of therapy and stimuli.
This type of research gives hope to many to regain their hearing or at least improve their current condition. Many institutions have embarked on the search for a regeneration formula whilst experimenting with various methods and testing them mainly on mice. One such group of researchers is that of Emory University School of Medicine. Researchers there believe that gene therapy is the key to the solution. The experiment consists of treating mice with the gene Atoh1 that can stimulate the growth of new sensory hair cells. The results are optimistic but there is still a long away to go as the gene has an effect only on young mice so far and not on adult ones.
Another study, by Dr Dave Furness from Keele University in North Staffordshire, is focusing on using stem cells for restoring lost hearing due to old age. Dr Furness and his team have discovered that fibrocytes, responsible for the composition of the fluid in the cochlea, vitiate with age. In addition, damaged fibrocytes are believed to affect parts of the inner ear and cause their deterioration as well eventually resulting in hearing loss. The research aims to grow fibrocytes from stem cells and to transplant them in the ear when they begin to degrade, hopefully before inflicting additional damage to the inner ear. Other researchers are also looking at the possibilities stem cells can offer for regeneration purposes. A challenge they are currently concentrating on is to find a way to make embryonic stem cells and adult cells transform into hair cells in the inner ear.
Stefan Heller from the Stanford University School of Medicine believes that the extended study of the little known molecular basis of the hearing cells and the correct drug stimuli will help in finding a way to restore damaged sensory cells and activate their lost natural mechanism for regeneration.