Hair-follicle stem cells have a second job. Elaine Fuchs's lab at Rockefeller University has spent years documenting how these cells, best known for cycling through phases of hair growth, can pivot in an emergency — abandoning their follicle role to rush to injured skin and accelerate repair. In a 2025 paper, her team pinned down exactly what triggers that switch.
The signal is serine, a simple amino acid that cells use both as a building block for proteins and as a nutrient sensor. When serine levels are normal and the skin is intact, hair-follicle stem cells stay in their lane. But when serine becomes scarce — either because of dietary restriction or because a wound is consuming local resources — the cells read that scarcity as an instruction to change behavior.
In experiments using mouse models, the researchers showed that serine deprivation alone was enough to slow hair growth, redirecting the cells' energy. When serine restriction was combined with a wound, the cells transitioned fully into repair mode, migrating out of the follicle and into the wound site, where they contributed to new tissue formation.
The connection works through a well-known metabolic sensing pathway. Serine feeds into the one-carbon metabolism network, which supplies building blocks for DNA and proteins during periods of rapid cell division. When that supply drops, the stem cells sense it as a broader sign that resources are constrained — and behave accordingly.
This matters beyond hair biology. It adds serine to a growing list of metabolites that serve as environmental signals for stem cell behavior — linking diet, metabolism, and tissue repair in a concrete, mechanistic way. It also raises the possibility that metabolic interventions could be used to enhance wound healing in patients where normal repair mechanisms are compromised, such as in diabetes or aging.
The work from Fuchs's lab contributes to a broader shift in how researchers think about stem cells — not as static populations waiting to be activated by growth factors, but as cells continuously monitoring the nutritional and metabolic state of their environment and adjusting accordingly.