As we age, the chances are that many of us will lose some hearing ability, either through environmental insults to the ears or as a result of the genes we inherit. The most common cause of hearing loss occurs through damage to the sensory hair cells found within the organ of Corti, the auditory sensory epithelium in mammalian ears. These cells are essential for our perception of sound and when lost, they do not regenerate. In a report to be published in the May issue of Nature Cell Biology, researchers identify one key gene that seems to be closely linked to progressive hearing loss in mice.
There are two types of cell in the organ of Corti that are important for sound perception: sensory hair cells and supporting cells. Sensory hair cells have become specialized in the detection of sound waves, which are transmitted through liquid in the auditory canals. As the sensory hair cells move and bend in this liquid, the movement is translated into a nerve impulse that is sent to the brain. During embryogenesis, these cells divide constantly, a process that continues until just after birth. Therefore, these cells cannot regenerate once they have been lost.
Neil Segil and colleagues have now demonstrated that a mouse gene called Ink4d is involved in this process. Deletion of Ink4d allows the sensory hair cells to divide again within the adult ear. However, this is not good news for the mice or their hearing. These dividing cells undergo programmed cell death, or apoptosis, which seems to cause progressive hearing loss in the mutant mice. Although Ink4d is a good candidate gene for inherited progressive hearing loss, it remains unclear if it is mutated in patients who are losing their ability to hear.
Ink4d is known to inhibit important regulators of cell division and also has important roles in stopping other cell types from dividing. These new results imply that removing inhibitors of cell division can lead to progressive hearing loss in mice. As the easiest way to reverse human hearing loss may involve the generation of new sensory hair cells by encouraging the cells to divide, this work has important implications for the treatment of human deafness.
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(C) Nature Cell Biology press release.
Message posted by: Trevor M. D'Souza