A hidden reason inner ear cells die—and what it means for preventing hearing loss

Sensory hair cells of the mouse inner ear stained with phalloidin to highlight actin-rich structures called stereocilia, which are arranged in bundles forming the mechanosensory organelle of the inner ear sensory cells. Three rows of outer hair cells (top) and a single row of inner hair cells (bottom) are visible, illustrating the precise cellular organization required for sound detection. Credit: Angela Ballesteros.

Proteins long known to be essential for hearing have been hiding a talent: they also act as gatekeepers that shuffle fatty molecules across cell membranes. When this newly discovered function goes haywire—due to genetic mutations, noise-induced damage, or certain medications—it may be what kills the delicate sensory cells in our ears, causing permanent hearing loss.

The research was presented at the 70th Biophysical Society Annual Meeting held in San Francisco from February 21–25, 2026.

How hair cells sense sound

Deep inside our ears, specialized cells called hair cells convert sound vibrations into electrical signals that travel to the brain. These cells get their name from tiny hair-like projections, called stereocilia, arranged in bundles that resemble a mohawk.

“When sound vibrations bend these hair-like structures, it opens channels that let ions flow into the cell, triggering a signal that carries sound to the brain,” explained Hubert Lee, a postdoctoral fellow in the lab of Angela Ballesteros at the National Institute on Deafness and Other Communication Disorders (NIDCD) at the National Institutes of Health.

“But when there’s a problem with these channel proteins, the hair cells die. And these cells don’t regenerate—so the hearing loss is permanent.”

A second job for key proteins

The channel proteins in question, called TMC1 and TMC2, have been studied for years as the molecular machinery that converts sound into electrical signals. Mutations in TMC1 are a leading cause of genetic deafness. But the NIDCD team has now discovered these proteins have an entirely separate job.

“We found that TMC1 and TMC2 are not only ion channels important for hearing—they also regulate the cell membrane,” said Ballesteros. “And we think this membrane regulatory function, not the channel function, is what leads to hair cell death when things go wrong.”

Scramblase activity and cell death

The channels also act as “lipid scramblases”—molecular machines that move fatty molecules called phospholipids from one side of a cell membrane to the other. Normally, different types of phospholipids are kept on specific sides of the membrane. When one particular phospholipid, called phosphatidylserine, gets flipped to the outer surface of a cell, it’s often a signal that the cell is dying.

“Hair cells from mouse models carrying mutations in TMC1 that cause hearing loss exhibit this membrane dysregulation—phosphatidylserine gets externalized, and the membrane starts blebbing and falling apart,” Ballesteros said. “This is an apoptotic hallmark. It’s what’s killing the hair cells.”

Why some antibiotics damage hearing

The discovery also sheds light on why certain medications cause hearing loss as a side effect. Common antibiotics called aminoglycosides are known to damage hearing, and the researchers found these drugs activate the same membrane-disrupting scramblase activity in vivo.

“Scientists initially thought these drugs caused hearing loss by blocking the channel function of TMCs in vivo,” Lee said. “But what we’re seeing now is that in the chaotic environment of the living hair cell, these drugs act as potent disruptors, triggering a collapse of membrane asymmetry. Yet, in the serene isolation of our reconstituted system, the protein remains indifferent to them, suggesting that other factors, such as lipid specificity or missing protein partners, are at play.”

Cholesterol clues and future therapies

The team also discovered that the scramblase activity depends on cholesterol levels in the cell membrane—a finding that could point toward future treatments based on diet or cholesterol management that could someday help protect our ears from ototoxic medications or genetic hearing loss.

“If we understand the mechanism by which these drugs activate the scramblase, we might be able to design new drugs that lack this effect,” said Yein Christina Park, graduate student at the NIH-JHU program and co-first author of this work. “We could potentially have antibiotics that don’t cause permanent hearing loss.”