Like other mammals, humans are unable to regain the ability to hear once it is lost, but a new study by experts at the Washington University School of Medicine in St. Louis provided new insight that could bring us closer to reversing this tenant of medical science.
Writing in the online journal eLife, senior author and biology professor David M. Ornitz and his colleagues explained they have identified a pair of signaling molecules that are required for proper development of the cochlea– a part of the inner ear that forms early in development.
The cochlea plays a role in detecting sound and transmitting signals to the brain, and if either of these two newly identified signals is lost, the embryo is unable to produce a sufficient amount of the cells that eventually form the adult version of this spiral-shaped, hollow bone chamber.
This deficiency results in impaired hearing, the study authors explained in a statement. Their research has led to new insights into the processes of inner-ear development and is an essential first step towards the ultimate goal of recovering lost hearing in humans.
Goal is to regenerate sensory hair cells of the cochlea
“To eventually be able to restore hearing, we would like to be able to regenerate the sensory hair cells of the cochlea,” Dr. Ornitz explained. “If the inner ear in birds and fish is damaged… cells in the inner ear are naturally turned back into progenitor cells that are capable of replacing the sensory cells.”
Mammals, however, “are more complex” and have “a better sense of hearing over a wider range of sounds,” he added in a statement. “However, it is thought that in exchange for better hearing, we have lost the ability to regenerate sensory hair cells.”
As part of their research, Dr. Ornitz and his co-authors studied inner ear development in mice and found that it relies upon the presence of two signaling molecules, FGF9 and FGF20.
The inner ear’s hair cells detect sound vibrations and transmit those signals to the brain, and hearing loss occurs when these cells become damaged due to loud noise, medication, or aging. The new study found that FGF9 and FGF20 send signals to their receptors to promote the growth of sensory progenitor cells and directs proper cochlear development.
“We have discovered that an FGF signal is instructive in forming the cochlea,” said Dr. Ornitz. “These FGF signals tell the surrounding tissue to make a factor – we don’t know yet what that factor is – but we know it regulates progenitor cell growth. And being able to grow progenitor cells, or instruct cells that can become progenitor cells to grow, is one key to restoring hearing.”
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(Image credit: Thinkstock)
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