Wednesday January 4 2012
The FGF20 protein contributes to inner ear development
Gene research may provide a clue to the causes of deafness, according to today’s Daily Mirror. The Daily Mail suggested that “the discovery of deafness gene brings treatment for hearing loss a step closer”.
The news is based on an animal study investigating how the hearing of mice was affected when they were deliberately bred to be born without a protein called FGF20. The researchers were specifically interested in the way the protein controlled the development of the hair-like cells (hair cells) of the inner ear, which are essential to hearing. Damage to and loss of these hair cells is responsible for the majority of age-related deafness in humans.
Researchers found that mice lacking the FGF20 protein were deaf from birth. This was because the area of the inner ear containing a type of hair cell had not developed normally, as it became stuck in an earlier developmental stage. This suggests FGF20 is essential for the normal development of these important cells.
The findings may provide a new target for researchers aiming for a better understanding of deafness due to hair cell defects in humans. However, this study does not provide a mechanism to repair or regrow the hair cells in humans or mice. Much more research is needed before these findings could lead to treatments for deafness.
Where did the story come from?
The study was carried out by researchers from Washington University School of Medicine and funded by various sources, including academic department grants, hearing foundations and hearing loss charities.
The study was published in the peer-reviewed scientific journal Public Library of Science (PLoS) Biology.
The media generally reported the story accurately, stating clearly that the research was done in mice and that further research in humans is required to understand the role of the gene in age-related hearing loss in people.
What kind of research was this?
This was an animal study using mice. It aimed to understand the biology behind the growth of the hair cells in the inner ear that are essential for normal hearing. These hair cells are very small and fine and are hidden out of sight, deep within the structures of the inner ear. They are not the hairs you can see if you peer down someone's ear canal.
Outer and inner hair cells in the inner ear play a part in human and animal hearing. The researchers say that a large proportion of age-related hearing loss in humans is caused by loss or damage to the outer hair cells. This type of hearing loss is reported to affect about one-third of people over the age of 65.
Surprisingly, humans and other mammals cannot regrow hair cells damaged through excess noise, whereas birds and some amphibians can. This means any hearing impairment caused by the death of these hair cells is irreversible in humans. The researchers suggested that a better understanding of how the hair cells develop may provide clues on how new hair cells might be stimulated to grow or repair when they are lost or damaged, as is the case in age-related hearing loss.
Animal studies are helpful for developing a better understanding of how a particular biological process occurs, as it is often easier to obtain and study animal cells than human cells. The results can give an indication of how the processes may occur in human cells, but there may also be some differences. If such exploratory research does suggest potential treatments for deafness, these would have to be tried first in animals. Further studies in humans can follow, but only after safety concerns are comprehensively addressed through rounds of animal research.
What did the research involve?
Fibroblast growth factor 20 (FGF20) is a protein that is essential at several stages of inner ear development. To investigate what this protein does in the ear, the researchers bred mice that were genetically modified to lack this protein.
The researchers compared these mice with normal mice to see the effect of not having FGF20 protein. They assessed whether the mice survived at birth, how healthy they were, whether they were deaf and how the inner and outer hairs of the ear were affected at different stages of development. This included counting the hair cells of the inner ear.
What were the basic results?
The researchers found that mice lacking the FGF20 protein were healthy and survived normally but were deaf from birth.
Specifically, they were deaf because the area of the inner ear containing the outer hairs and supporting cells had not developed normally. The researchers found that the cells that would normally develop into outer hair cells became stuck in an earlier developmental stage and could not progress to become mature hair cells.
However, the inner hair cells of the inner ear had developed normally. This suggested the development process of the inner and outer hair cells differed and required different chemical signals at different times.
How did the researchers interpret the results?
The researchers concluded that the biological development of the inner and outer hair cells is separate, and that FGF20 protein is much more important for the development of the outer hair cells than the inner.
They concluded that FGF20 is required for the normal development of the outer hair cells in mice and that this protein could be a target for future research into age-related human deafness due to damage or loss of the outer hair cells.
They also say that because the mice lacking FGF20 were deaf from birth, mutations in the gene that produces this protein might also be a cause of inherited deafness in humans who are also born deaf.
This research provides important new information about the role that the FGF20 protein plays in the development of the outer hair cells in the ears of mice. As the majority of age-related deafness is caused by damage or loss to these cells, the findings may provide a new target for future research focused on improving our understanding of this type of deafness in humans.
While this is a useful scientific development, there are limitations. We cannot be certain, for instance, that FGF20 plays exactly the same role in the development of the human hair cells as it does in mice. Ideally, further research would look into FGF20 using human cells to see if similar results are found. It might also be worth examining the genetics of people who are born deaf in order to understand further the role of the gene in producing the FGF20 protein.
This study does provide important information in the understanding of the biology of hair cells in the inner ear, but it does not provide a mechanism to repair or stimulate their growth in mice or humans. This will require more research.
The ultimate goal of future research would be to develop a way to stimulate the regrowth or repair of the hair cells that are damaged or abnormal, in an effort to restore normal hearing. The current animal study represents one of the first steps on the long road that may lead to new treatments. However, it is likely to take a significant amount of time and research before we know if the final goal is achievable.