Stem cells can shift from hair growth to skin healing

Hair has a hidden job: helping your skin heal. Normally, skin stem cells focus on repairing wounds, while hair follicle stem cells focus on growing hair.

But when the skin is injured – and the regular stem cells are damaged or depleted – the hair stem cells switch jobs. They stop making hair and start repairing the skin instead.

This surprising switch, discovered by scientists at Rockefeller University, isn’t random. It’s driven by stress- and more specifically, a stress response that cells use to ration their energy in tough conditions.

Stress tells cells to pivot

The researchers found that a signal called the “integrated stress response,” or ISR, tells hair follicle stem cells when to pause hair growth and help repair the skin. This signal kicks in when the cells sense a shortage of a specific nutrient: serine.

Serine, a nonessential amino acid found in meat, grains, and milk, triggers the integrated stress response (ISR) when its levels drop – either due to dietary deficiency or because the body diverts it for other needs.

That causes the hair follicle stem cells (HFSCs) to pull back on hair production. If there’s also a skin injury, the ISR gets even stronger, pushing these cells fully into skin-repair mode.

“Serine deprivation triggers a highly sensitive cellular ‘dial’ that fine-tunes the cell’s fate – toward skin and away from hair,” says Jesse Novak, the study’s first author. “Our findings suggest that we might be able to speed up the healing of skin wounds by manipulating serine levels through diet or medications.”

Wounds recruit hair helpers

Stem cells are the body’s utility players. They maintain tissues, grow new cells, and repair damage. But how they fuel themselves – especially when conditions change – hasn’t been fully understood.

The team at Rockefeller University studied how HFSCs behave when skin is injured to learn more.

“Most skin wounds that we get are from abrasions, which destroy the upper part of the skin,” said Novak. “That area is home to a pool of stem cells that normally takes charge in wound repair. But when these cells are destroyed, it forces hair follicle stem cells to take the lead in repair.”

The researchers saw this as a perfect chance to track how metabolism affects what stem cells do – and when.

Starved cells pick survival

Previous research from the same lab showed that precancerous skin cells rely heavily on serine. Taking serine out of the diet could slow or stop their growth. That got scientists wondering: What happens to normal cells if you take away serine?

To find out, they put HFSCs through a series of stress tests. In one set of experiments, mice were fed a diet without serine. In another, the scientists used genetic tools to stop stem cells from making serine on their own.

The results were clear in both cases: when serine is low, the ISR tells HFSCs to put hair growth on hold. The body shifts its priorities.

Then they added another challenge – wounding the skin. The stress response got even stronger. Hair production slowed further, and healing sped up. The ISR seemed to be acting like a control tower, directing traffic during a crisis.

“No one likes to lose hair, but when it comes down to survival in stressful times, repairing the epidermis takes precedence,” said Elaine Fuchs, head of the lab. “A missing patch of hair isn’t a threat to an animal, but an unhealed wound is.”

What about boosting hair growth?

If cutting back on serine slows hair growth, could a high-serine diet do the opposite? Not really.

The researchers tried feeding mice six times the normal amount of serine. Their bodies barely noticed – serine levels only increased by about 50 percent. The body seems to regulate it tightly.

Still, there was a small win. “We did see that if we prevented a stem cell from making its own serine and replenished its losses through a high-serine diet, we were able to partially rescue hair regeneration,” Novak said.

What’s next for stem cell research

The team now wants to explore whether reducing dietary serine or changing ISR activity through medications could help wounds heal faster. They’re also curious if other amino acids might have similar effects.

“Overall, the ability of stem cells to make cell fate decisions based upon the levels of stress they experience is likely to have broad implications for how tissues optimize their regenerative capacities in times where resources are scarce,” said Fuchs.

In other words, your cells know when to prioritize survival over style. When food is low and the skin is hurt, hair can wait.

The full study was published in the journal Cell Metabolism.

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