TMC1-TMC2 Hidden Function Hearing loss

Scientists Uncover Hidden Role of Hearing Proteins Linked to Irreversible Deafness

Discovery of a Second Function in TMC Proteins

Proteins long recognized as vital to the sense of hearing have now been found to possess an unexpected second function: they serve as gatekeepers, transferring fatty molecules across cell membranes. When this newly identified role is disrupted—whether by genetic mutations, damage from excessive noise, or the effects of certain medications—it may trigger the death of the ear's fragile sensory cells, leading to irreversible hearing loss.

The findings were unveiled at the 70the Biophysical Society Annual Meeting, held in San Francisco from 21-25 February 2026.

How Hair Cells Convert Sound into Electrical signals

Deep within the inner ear, specialized sensory cells known as hair cells transform sound vibrations into electrical impulses that are transmitted to the brain. Their name derives from the minute, hair-like projections—called stereocilia—arranged in tight bundles resembling a narrow crest.

"When sound waves bend these delicate structures, ion channels open, allowing charged particles to enter the cell and initiate the electrical signal that conveys sound to the brain," explained Hubert Lee, a postdoctoral fellow working in the laboratory of Angela Ballesteros at the National Institute of Deafness and Other Communication Disorders (NIDCD), part of the National Institutes of Health.

He added that when defects arise in these channel proteins, the hair cells perish. As they lack the ability to regenerate, any resulting loss is permanent.

TMC1 and TMC2 - More Than Just Ion Channels

The channel proteins known as TMC1 and TMC2 have long been recognized as the molecular machinery responsible for converting sound vibrations into electrical signals. Mutations in TMC1 are among the principal causes of inherited deafness. However, researchers at the National Institute on Deafness and Other Communication Disorders have now identified an entirely separate function for these proteins.

"We discovered that TMC1 and TMC2 are not solely ion channels essential for hearing—they also play a role in regulating the cell membrane," said Ballesteros. "We believe it is this membrane-regulating function, rather than their channel activity, that triggers hair cell death when disrupted."

The Lipid Scramblase Discovery - A Critical Breakthrough

The channels also function as so-called lipid scramblases—molecular systems responsible for redistributing fatty molecules, known as phospholipids, between the inner and outer layers of a cell membrane. Under normal conditions, specific phospholipids remain confined to particular sides of the membrane. However, when phosphatidylserine shifts to the cell's outer surface, it typically signals that the cell is undergoing death.

"Hair cells in mouse models carrying TMC1 mutations associated with hearing loss display this membrane imbalance phosphatidylserine becomes externalized and the membrane begins to bleb and disintegrate," Ballesteros explained. "This is a recognized hallmark of apoptosis. It is what ultimately destroys the hair cells."

Why Some Antibiotics Can Cause Hearing Loss

The findings also help explain why some medications are associated with hearing loss as a side effect. Aminoglycosides, a widely used of antibiotics, have long been recognized for their ototoxic effects. Researchers discovered that these drugs activate the same membrane-disrupting scramblase activity within living systems.

"Scientists originally believed these drugs caused hearing loss by blocking the channel function of TMC proteins in vivo," Lee explained. "What we are observing instead is that, within the complex environment of a living hair cell, these compounds act as powerful disruptors, causing the collapse of membrane asymmetry. In contrast, within the controlled conditions of our reconstituted system, the protein appears unaffected, indicating that additional elements such as lipid specificity or absent protein partners—may be involved."

Cholesterol's Role in Protecting Hearing

The researchers further found that scramblase activity is influenced by the amount of cholesterol present within the cell membrane. This discovery may open the door to future strategies centred on dietary adjustments or cholesterol regulation, with the aim of safeguarding hearing against ototoxic medications or inherited forms of deafness.

"If we can fully understand how these drugs activate the scramblase, we may be able to develop new treatments that avoid triggering this effect," said Yein Christina Park, a graduate student in the NIH-JHU programme and co-first author of the study. "In time, it may be possible to produce antibiotics that do not carry the risk of permanent hearing loss."

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Key Takeaways from the Study

• TMC1 and TMC2 proteins have a newly identified membrane-regulating function.
• Disruption of this function may cause irreversible hair cell death.
• Aminoglycoside antibiotics may trigger hearing loss by activating lipid scramblase activity.
• Cholesterol levels in cell membranes may influence vulnerability to damage.
• Future treatments could focus on preventing membrane imbalance rather than blocking ion channels.

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Human Chin Evolutionary Accident Spandrel Study

The Human Chin May Be an Evolutionary Accident, Not a Design

Dashiell Hammett famously opened The Maltese Falcon by drawing attention to Sam Spade's jutting chin. It was one of several features used to sketch the detective's sharp profile. Yet, from an evolutionary standpoint, emphasizing the chin may have been unintentionally repetitive—because every human chin is distinctive. Indeed, humans are the only primates to possess one at all.

A Feature Unique to Homo sapiens

Our closest living relatives, chimpanzees, lack chins entirely. So too did Neanderthals, Denisovans and every other extinct human lineage. The ability to quite literally "take it on the chin" is uniquely ours. This singular trait makes the chin a defining marker of Homo sapiens in the fossil record.

Put simply, a chin is the forward projection of the lower jawbone. But why does it exist? What evolutionary forces shaped its emergence?

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New Study Questions the Purpose of the Chin

A study published in PLOS One, lead by a biological anthropologist at the University at Buffalo, suggests that the human chin may not have evolved for any specific purpose at all. Instead, the findings contribute to a broader understanding of the human body as a complex blend of adaptive traits and incidental evolutionary byproducts.

Evolution by Chance, Not Selection

"The chin evolved largely by chance rather than through direct selection," explained Noreen von Cramon-Taubadel, PhD, Professor and Chair of the University at Buffalo's Department of Anthropology within the College of Arts and Sciences.

"It appears to be an evolutionary byproduct arising from selection acting on other regions of the skull."

The Chin as an Evolutionary 'Spandrel'

In evolutionary biology, such a feature is known as a "spandrel"—a trait that emerges unintentionally. Much like the empty space beneath a staircase, which exists not by design but as a consequence of construction, the chin may simply be the architectural side-effect of other structural changes in the human skull.

The concept of a "spandrel", first popularized by evolutionary biologist Stephen Jay Gould, was inspired by the triangular spaces formed when arches were constructed to support the dome of St Mark's Basilica in Venice. These spaces serve no architectural function of their own; they simply exist as an inevitable consequence of the arches above them.

The same principle, researchers suggest, applies to the human chin.

Why the Chin Is Unlikely to Be an Adaptation

"Possessing a unique trait such as the chin does not automatically mean it evolved through natural selection to improve survival," explained Professor Noreen von Cramon-Taubadel.

"It is unlikely to function as a structural reinforcement for the lower jaw or to dissipate the forces of chewing. The chin is more plausibly a secondary structure rather than an adaptation.

"It is only by examining the organism as a whole that we can distinguish which traits serve a functional role and which arise as secondary consequences," Professor von Cramon-Taubadel explained.

Testing the 'Null Hypothesis' of Neutral Evolution

Although her team is not the first to propose that the chin represents a spandrel, their approach departs from earlier studies that largely assumed natural selection directly shaped the lower jaw.

Instead, the researchers tested what is known as the null hypothesis of neutrality:

• Cranial characteristics were compared between apes and humans
• The study examined whether chin formation occurred without targeted selection
• Evolutionary changes were analyzed across multiple regions of the skull

"While we identified evidence of direct selection in certain regions of the human skull, the traits specific to the chin align more closely with the spandrel model," she noted.

"The changes that occurred after our divergence from chimpanzees were likely due to selection acting on other areas of the skull and jaw—not on the chin itself."

Rethinking Adaptation in Human Evolution

Within anthropology, there has long been an adaptationist tendency to interpret physical traits as purposeful outcomes of natural selection. Differences observed between species often encourage the assumption that every characteristic has been deliberately shaped to serve a specific function.

"One of the central aims of this research—and of biological anthropology more broadly—is to provide empirical evidence that challenges that assumption," Professor von Cramon-Taubadel explained.

"Our findings highlight the importance of examining how traits are integrated with one another when evaluating their evolutionary history."

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Why This Matters Beyond Anthropology

Understanding how traits like the chin emerged reshapes how scientists interpret:

• Human evolutionary history
• Fossil identification and classification
• The balance between adaptation and chance in biology

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• Natural science and evolutionary understanding

Brain Signal Complete Fat Loss WashU Medicine

Brain-Controlled Signal Triggers Complete Fat Loss Without Eating Less

Breakthrough Discovery from WashU Medicine

Scientists at WashU Medicine have uncovered a powerful biological pathway that originates in the brain and triggers the complete depletion of body fat—without any reduction in food consumption. The breakthrough findings have been published in Nature Metabolism.

Research Team Behind the Groundbreaking Study

The research was led by senior investigator Erica L. Scheller, DDS, PhD. Associate Professor in the Division of Bone and Mineral Diseases within the Department of Medicine. She was joined by Xiao Zhang, PhD, formerly a doctoral researcher in Scheller's laboratory and now a postdoctoral fellow at the University of Pennsylvania School of Medicine, alongside graduate researcher Sree Panicker. Their work was inspired by a rare group of fat cells embedded deep within the skeleton.

The Mystery of Bone Marrow Fat

"Roughly 70% of bone marrow consists of fat that appears resistant to diet and exercise," explained Professor Scheller. "We were determined to understand the biological reason behind this."

The researchers discovered that a unique group of cells—known as constitutive bone marrow adipocytes—produce unusually high levels of proteins that block the breakdown of fat. As a result, these cells remain resistant to fat loss under normal daily conditions. "We refer to them as stable adipocytes," explained Xiao Zhang, the study's lead author.

Scientific Insights from the Study

• Approximately 70% of bone marrow is composed of fat
• These fat cells resist traditional weight-loss mechanisms
• Constitutive bone marrow adipocytes block fat breakdown
• Researchers identified them as "stable adipocytes"

How the Brain Unlocks Fat Loss

In laboratory mice, prolonged injections of the hormone leptin directly into the brain succeeded in "unlocking" these stable adipocytes. The treatment shifted the body into a low-glucose, low-insulin state, reducing the proteins that prevent fat breakdown. Within days, the mice experienced a complete loss of body fat—despite continuing to eat as usual.

This discovery highlights a previously unrecognized brain-to-fat biological signaling axis that may reshape scientific understanding of metabolism regulation.

Why Leptin Signaling Matters

• Direct brain-based hormone intervention
• Shift to low-glucose, low-insulin metabolic state
• Reduction of fat-protective proteins
• Complete fat depletion observed in animal models

Researchers Urge Caution Before Human Application

However, researchers warn that the pathway's strength makes it unsuitable for human application until it is fully understood. Stable adipocytes are found in bone marrow, the hands and feet, and surrounding essential glands. In patients suffering from severe wasting conditions, the depletion of fat from these areas in linked to bone fractures and a diminished quality of life.

The team emphasizes that while the discovery is scientifically transformative, careful evaluation is required before any clinical translation.

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Broader Health Implications

• Potential impact on osteoporosis and fracture risk
• Relevance to severe metabolic and wasting disorders
• Need for deeper safety evaluation before human trials

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Dopamine Gut Brain Vagus Nerve Reward Addiction

Gut-Brain Vagus Nerve Rewrites Dopamine Science, Challenging Brain-Only Addition Models

Dopamine, the neurotransmitter that shapes motivation, pleasure, mood and learning, has gained unexpected celebrity in recent years, becoming a buzzword for the fleeting highs of social media, comfort food and impulse shopping. This popularity has reinforced the idea that dopamine operates solely within the brain, where it is best known for its role in the mesolimbic pathway—a reward circuit linking the Ventral Tegmental Area (VTA) with the Nucleus Accumbens (NAc), amygdala and hippocampus.

However, new research published in Science Advances challenges this narrow view. The study reveals that the vagus nerve, which forms a vital communication bridge between the brain and the gut, also plays a crucial role in regulating motivation and reward-related behaviour.

The Gut-Brain-Vagal Axis Explained

The vagus nerve serves as the primary communication highway of the gut-brain axis, a sophisticated network that links peripheral organs to the brain. Through this pathway, the body continuously sends internal signals related to mood, digestion, inflammation and stress, shaping how the brain interprets physical states.

Explaining their findings, the study's authors highlight the gut as a central coordinator of this body-brain dialogue. They note that metabolically active organs, particularly the gut, influence brain function through hormonal signals, metabolites produced by gut microbes and a complex web of local and long-distance neural connections.

While previous research has largely focused on brain-centered models of reward, some studies have shown that gut-to-brain signaling via the vagus nerve can influence dopamine activity linked to food and eating behaviour. Until now, however, it remained unclear whether these gut-driven signals also affect other dopamine-fueled addictions.

Disrupted Vagal Signaling Alters Dopamine Activity

To investigate how strongly the gut-brain-vagal axis influences dopamine-driven reward, researchers carried out a series of experiments using mice. In some trials, the vagus nerve was surgically severed through a Subdiaphragmatic Vagotomy (SDV), allowing scientists to compare food-and drug-related reward behaviours between SDV mice and unaltered, or "Sham", mice. Dopamine activity inside the brain was tracked in real time using fiber photometry, alongside molecular testing and electrophysiological measurements.

The findings revealed that the gut-brain vagal axis plays a critical role in both food-and drug-induced reward. When offered foods typically considered addictive, SDV mice ate more slowly and consumed les overall, while unaltered mice showed a rapid rise in intake over a ten-day period.

Behavioural Changes in Food Motivation

The researchers observed heightened excitement in sham mice, a response that was notably absent in SDV mice. Using their experimental model alongside telemetric monitoring of movement, they found that sham mice showed increased activity both before eating—reflecting food anticipation — and during consumption itself.

By contrast, SDV mice displayed markedly reduced movement during both phases. Crucially, this difference was not linked to any underlying mobility problems, as sham and SDV mice showed comparable activity levels during the dark, foraging period and under normal baseline conditions.

Drug Experiments Reveal Similar Patterns

Comparable patterns emerged in drug-related experiments involving substances such as cocaine, morphine and amphetamines. SDV mice showed diminished locomotor responses to both morphine and cocaine, suggesting the vagus nerve plays a role in shaping dopamine signaling or its integration in the brain. Amphetamines, however, produced no consistent differences and showed dose-dependent effects in conditioning tests.

The researchers report that while sham mice developed a clear preference for cocaine, SDV mice showed no such conditioning. The response to amphetamine, however, varied with dose. At 2 mg/kg, both SDV and sham mice displayed positive conditioning.

At a lower dose of 1 mg/kg, the picture changed. SDV mice showed a reduced conditioning response compared with controls, indicating that the neural adaptations linked to SDV may be masked when dopamine levels rise sufficiently at higher doses.

Dopamine Signaling Inside the Brain

Further in vivo experiments revealed that an intact vagus nerve is essential for:

• Normal dopamine neuron firing
• Dopamine-driven molecular changes
• Structural plasticity within the brain's reward circuits

Using fiber photometry, the researchers found that severing the vagus nerve delayed dopamine signaling in the nucleus accumbens and reduced dopamine responses during food anticipation, eating and following drug exposure.

Despite these changes, dopamine function was not entirely lost. Movement-related processes remained intact, although overall activity was diminished, with dopamine neurons firing less frequently and receiving weaker excitatory input.

Implications for Addiction Treatment in Humans

The findings strengthen the case that the gut, acting through the vagus nerve, plays a direct and vital role in shaping reward and motivation. However, treatment for addiction that rely on reducing vagal signaling remain a distant prospect.

Surgically severing the vagus nerve, as done in the mouse experiments, is neither practical nor desirable in humans and could carry significant side effects. The researchers also caution that the gut may adapt over time, developing compensatory mechanisms to offset the loss of signaling.

As a result, further research is essential. The team suggests future studies should focus on more precise genetic or vital techniques to isolate specific vagal circuits, or explore alternative ways of modulating vagal activity. With further refinement, such approaches could one day contribute to treatments for eating disorders and addition.

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Key Takeaways for Readers

• Dopamine is influenced not only by the brain but also by gut-brain signaling.
• The vagus nerve plays a critical role in food and drug reward behaviour.
• Disrupting vagal signaling alters dopamine activity without eliminating movement.
• Future addiction treatments may target gut-brain communication rather than the brain alone.

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