A study shows how repeated exposure to loud music, noise can be damaging
Biophysicist Dr Sabyasachi Rakshit with researcher Pritam Saha in
the lab at IISER.
Over a decade back,
doctors at the Ear, Nose and Throat (ENT) Department in the Postgraduate
Institute of Medical Education and Research (PGIMER), Chandigarh, were baffled
to discover hearing loss in 20-year-old patients. These were not cases of
temporary damage or infection, but young patients showing symptoms of old age.
Around the same time, the
then head of the ENT Department, Prof Naresh Panda, met Dr Sabyasachi Rakshit,
a biophysicist at the Indian Institute of Science Education and Research
(IISER), Mohali, who had recently returned after his postdoctoral stint in the
US. Dr Panda shared the riddle, urging him to look deeper.
A cue from Prof Panda set
Dr Sabyasachi on a path of exploration. “Dr Panda had identified certain
genetic mutations in proteins related to hearing among the affected patients
and suspected their association with the disease. He guided us in using
Progressive Hearing Loss (PHL) as a model for studying Age-Related Hearing Loss
(ARHL),” he says. From there on, it took several years for Dr Sabyasachi and
his team to solve the riddle, but the hard work paid off, with the discoveries
getting published in Nature Communications, a peer-reviewed, open access,
scientific journal.
“There were relentless challenges throughout.
Preparing proteins and creating in-vitro conditions alone took more than three
years. However, I remained focused as the goal was bigger than the hurdles,”
says Dr Sabyasachi, who got fascinated with the science of hearing as he
watched doctors testing his newborn’s ears for otoacoustic emissions — whispers
from within the inner ear itself.
The DBT/Wellcome Trust
India Alliance contributed Rs 3.5 crore for the study, along with Rs 80 lakh
from the Science and Engineering Research Board, besides generous help from
IISER for setting up the laboratory equipment.
How hearing works
There are microscopic
protein structures called tip-links deep inside our ears; these play a crucial
role in hearing. These tip-links act as gatekeepers for the tiny ion channels
in our ear cells. When sound waves reach them, these stretch the tip-links,
which then open the ion channels. This allows ions to flow, changing the cell’s
charge and sending electrical signals to the brain, and letting us perceive the
sound.
Even the buzz of a
mosquito creates just enough force (10 picoNewtons) to trigger the system,
explains Dr Sabyasachi. However, what will be the impact of, say, a
high-decibel show of singer Diljit Dosanjh on these tip-links, or of the roar
of the city’s traffic at peak hour, or a mother’s shrieking call waking you up
in the morning?
Giving an analogy of the
problem at hand, Dr Sabyasachi says, “You can open the door with a thread,
which will let the process of hearing reach the brain. But what will happen if
you ask the elephant to open the door? It can remove the door rightaway,
causing serious and permanent damage. This is what can happen with constant
exposure to loud sound or headphones.” Something similar had happened with the
youngsters who reported hearing loss at PGIMER.
The breakthrough
Dr Sabyasachi and his
students — Pritam Saha (biology); Vishavdeep Vashisht (physics); Ojas Singh,
Gaurav Bhati and Surbhi Garg (chemistry); and Dr Amin Sagar (ex-postdoctoral
student) — built a special device called magnetic tweezers in their lab, but on
a tight budget, especially during the difficult pandemic years. This tool
allowed them to create intermittent beep sounds of various intensities that
tip-links experience and study their behaviour under repeated stress.
In their first
breakthrough (Nature Communications, 2024), the team discovered that tip-links
behave like “smart seat belts”. These safely allow sound forces to reach our
hearing cells but can also absorb stronger, potentially damaging forces.
“However, if the sound is too loud, the tip-links temporarily disengage — like
seat belts unbuckling in extreme situations — to protect our hearing cells from
permanent damage,” says Dr Sabyasachi.
The second breakthrough
(Nature Communications, 2025) revealed what happens over time with repeated
exposure to loud music or noise. “The tip-links lose their force-filtering
ability, which could explain how age-related hearing loss develops. The
repetitive inputs of loud sound induced fatigue in the tip-links, making them
more prone to unfolding and losing their critical force-filtering function.
Studying this was no easy task, given the time ARHL takes to occur naturally,”
says Dr Sabyasachi.
After examining mutations
linked to PHL, Pritam Saha, a doctoral researcher and part of Dr Sabyasachi’s
team, said, “We have found that even small genetic mutations can alter how
these proteins fold and unfold under force, leading to hearing problems.”
What’s next
The IISER team wants to
push the boundaries even further. Its goal? To translate songs into mechanical
signals that can speak directly to the tip-link proteins, communicating with
them in their biomechanical language to better understand their response to
music and sound stimuli.
As Dr Sabyasachi puts it,
this line of research brings them one step closer to understanding the
intricate dance between sound and biology, and perhaps, one day, to develop
ways to slow or even prevent hearing loss altogether.
What inner ear feels
The study explains how
the protein Cadherin-23, which is involved in hearing, changes shape when it is
pulled or stretched by a physical force — like the forces your inner ear feels
when you hear sound — and explains why some people lose their hearing faster
than others.
Alarming rate
The silent pandemic of
hearing loss has been rising, and according to the World Health Organisation
(WHO), it is estimated that by 2050, over 700 million people — or 1 in every 10
persons — will be affected by it.
Decoding the science
The breakthrough explains
how human beings lose hearing ability over time, thus simplifying the
sound-biology interaction. If the protein, important for sensing sound
vibrations, can’t handle stress, it breaks down, leading to hearing loss. The
findings explain that how well a protein handles mechanical stress might also
be a result of evolution, depending on the environment where a creature lives.
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