A landmark study, led by researchers from Massachusetts Eye and Ear, presents a novel hypothesis to explain age-related hearing loss, challenging the prevailing view that has dominated over half a century of medical science. The new research offers evidence to suggest age-related hearing loss is primarily caused by accumulated damage to inner ear sensory hair cells, and hair-regeneration technologies may offer new treatments.
Presbycusis, or age-related hearing loss, is generally thought to be caused by a slowly degenerating stria vascularis, an important part of the cochlea. Prior animal research has revealed age-related atrophy in the stria vascularis does cause hearing loss, and the general assumption amongst many scientists has been this process also applies to age-related hearing loss in humans.
Closely investigating a human inner ear can only be done using autopsied post-mortem specimens. A new study set out to perform the largest and most rigorous analysis of autopsy specimens to understand the pathology of age-related hearing loss.
The study chronicles the close examination of more than 120 human inner ear autopsy specimens. Most of the specimens were accompanied by audiogram data collected while the subjects were alive, allowing the researchers to clearly correlate the anatomical data with patterns of hearing loss.
The big finding in the study was damage to the stria vascularis did not correlate with the severity or pattern of hearing loss. Instead, the most accurate predictor of hearing loss was the degree and location of hair cell death.
What this implies is that damage to the sensory hair cells in the cochlea may be the primary cause of presbycusis, and that suggests age-related hearing loss is not an inevitable consequence of aging but instead more related to a lifetime of acoustic overexposure.
“The greater hair cell death in human ears suggests that the high-frequency hearing losses that define presbycusis may be avoidable, reflecting mainly accumulated damage from environmental noise exposures,” explains M. Charles Liberman, co-author on the new study. “It’s likely that if we were more careful about protecting our ears during prolonged noisy activities, or completely avoiding them, we could all hear better into old age.”
Peizhe Wu, lead author on the new study, says this novel research finding significantly expands the potential for future treatments to improve hearing in elderly subjects. If this kind of hair cell damage is indeed the primary cause of presbycusis, then it's possible recent advances in hair cell regeneration could be repurposed to treat hearing loss.
“Our study upends the dogma about the major cause of age-related hearing loss,” says Wu. “Documenting the dominant role of progressive hair cell loss in the hearing impairment of normal aging means that the millions who suffer with this condition could benefit from the hair cell regenerative therapies that are the focus of ongoing research across the world.”
The new study was published in the journal JNeurosci.
Source: Massachusetts Eye and Ear