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May 6, 2021

Hopkins professor explores our understanding of the ear and what's left to discover

By DEANNA RAHMAN | February 5, 2021

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Paul Fuchs described how acoustic trauma and age-related hearing loss can lead to the degeneration of neurons connected to the hair cells in the ear.

Last Friday, Paul Fuchs gave a lecture as a part of the Hopkins at Home series titled “How the Ear Hears, and What We Can Do About It.” Fuchs is a David M. Rubenstein Research Professor of Otolaryngology-Head & Neck Surgery at the School of Medicine. His laboratory researches the structure and function of the inner ear.

In his lecture, Fuchs detailed the basic cellular and molecular mechanisms that give us our sense of hearing and how knowledge of these mechanisms affects the development of therapies. Fuchs also explained how humans’ perception of sound can go awry due to conductive hearing loss and the much more problematic sensorineural hearing loss.

He described the functioning of the cochlea, a structure in the ear that encodes the specific patterns of the varied frequency components of sound. Sound waves vibrate the cochlea, which causes hair cells on its surface to be pushed from side to side. The mechanical energy created by these movements is converted into an electrical signal by opening ion channels which allow the transport of charged particles. This process is referred to as mechanotransduction.

Understanding the gritty details of mechanotransduction is important, Fuchs said, because the several dozen proteins that participate in the process are affected by certain human deafness genes. Scientists are improving gene therapy techniques to correct impaired activity of transmembrane channel 1 (TMC1). Mutations in TMC1 lead to a form of deafness in humans and mice known as a monogenic form of deafness. Fuchs explained why this form of deafness is such a big target for gene therapy. 

“All you have to do is fix that one gene, and you can restore hearing,” he said.

One of the major questions still trying to be answered is how do you introduce the therapeutic gene into the ear? Gene therapy that is successful in other areas of the body, such as the retina, does not always translate to areas like the inner ear. In gene therapy for the retina, the corrective genetic material is injected right into the eye. According to Fuchs, this injection does not work for the ear because the inner ear is inside the skull’s very hard temporal bone.

“Thus far, people have been using surgical strategies to introduce genetic material or drugs into the inner ear by actually making a hole somewhere and then injecting the material directly in,” he said.

Fuchs believes that the most progress has been achieved by injecting the corrective material into the fluid spaces of the associated vestibular epithelium rather than injecting into the cochlea itself. Fuchs explained that this type of injection allows therapeutic agents to be put in without damaging one’s hearing. 

Fuchs also discussed new knowledge that has been gathered about the consequences of acoustic trauma and age-related hearing loss.

“Independent of genetic deafness, we know that another consequence of acoustic trauma and age-related hearing loss is not just the death of hair cells. It also turns out that the multiple synaptic connections onto an inner hair cell can degenerate and pull away,” he said.

This denervation of the cochlea, in addition to the loss of hair cells, is a critical factor in hearing loss, so much so that scientists are working to prevent this from happening and are investigating how to repair the connection between afferent neurons and their hair cells. 

During his lecture, Fuchs noted the correlation between acoustic trauma and hearing loss and emphasized the importance of avoiding loud sounds.

“Humans vary widely in their sensitivity to acoustic trauma, but as a general rule, the more very loud sound experienced (i.e., needing to shout to be understood), the greater the risk of accumulated damage and eventual hearing loss,” he wrote in an email to The News-Letter.

So how conscious should we be when it comes to the volume of our music, Netflix or Zoom meetings? Fuchs described a way to gauge if audio is harmfully loud.

“If a given listening experience gives you that feeling of ‘cotton wool’ in your ears afterwards, then you’ve caused temporary damage to the ear. Repeating such exposures increases the risk of early-onset age-related hearing loss,” he wrote.

Fuchs also shared his advice for headphone-wearers.

“If you wear ear-buds or headsets, and the sound is loud enough for someone else to hear, it’s too loud and likely to be damaging,” he wrote.

At the end of his lecture, Fuchs shared the pleasure of seeing the potential therapeutic benefits of his work after conducting basic science research for several decades.

“I feel very fortunate to be working in a field of study that has crossed the threshold to therapeutic intervention,” he wrote. “Now we have real possibilities for curing monogenic deafness.”

Learning about those possibilities through Fuchs’ lecture was exciting for Asha Duhan, a sophomore majoring in Neuroscience.

“It was amazing to see real-world applications of information I had learned in my neuroscience classes,” she wrote in an email to The News-Letter.

Fuchs noted that the progress made in his lab and indeed in the field of otolaryngology as a whole would not be possible without regular collaboration with other scientists. For his research projects Fuchs works with Ana Belén Elgoyhen at the University of Buenos Aires and Elisabeth Glowatzki, a professor at the School of Medicine.

“What is particularly gratifying is that our progress has resulted from the generous creativity of fellow scientists,” he wrote. “Extraordinary students and research fellows have powered our efforts throughout the years.”

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