Hair loss: Significant factor ‘impairs hair follicle stem cells’ – and we are all at risk

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Harvard University researchers identified a significant factor that “impairs hair follicle stem cells”, putting them into an extended resting phase, preventing regeneration of the hair or follicle. A factor that we are all at risk of could lead to hair loss – the risk factor is stress. “My lab is interested in understanding how stress affects stem cell biology and tissue biology,” said Ya-Chieh Hsu.

The professor of stem cell and regenerative biology at Harvard continued: “The skin offers a tractable and accessible system to study this important problem in depth.

“And, in this work, we found that stress does actually delay stem-cell activation.”

The senior author of the study added that stress “fundamentally changes how frequently hair follicle stem cells regenerate tissues”.

The hair follicle is one of the few mammalian tissues that can undergo round of regeneration throughout life – just think of the hair life cycle.

Hair life cycle

  • Anagen – growing phase
  • Catagen – transition phase
  • Telegen – resting phase
  • Exogen – shedding phase.

The natural hair cycle between growth and rest is a process fuelled by hair follicle stem cells.

During the growth stage, the hair follicle stem cells become activated to regenerate the follicle and hair.

However, during the resting phase, hairs shed more easily, and new hair is not growing.

Hair loss can occur if the hairs shed but the stem cells remain inactive, not producing new tissue.

Conducting a mouse model, the researchers investigated the effect of chronic stress on hair follicle stem cells.

Giving mice corticosterone – the equivalent of cortisol in humans – was shown to force follicle stem cells to stay in a resting phase for a long time without regenerating tissues.

“This result suggests that elevated stress hormones indeed have a negative effect on hair follicle stem cells,” Professor Hsu said.

“But the real surprise came when we took out the source of the stress hormones.”

Under normal conditions, hair follicle regeneration slows over time, as the resting phase becomes longer and longer.

However, when the researchers removed the stress hormones from the mice, the stem cell’s resting phase became extremely short.

The mice were shown to constantly enter the hair growth phase throughout their lifetime, even when the mice were really old.

“So even the baseline level of stress hormone that’s normally circulating in the body is an important regulator of the resting phase,” Hsu theorised.

“Stress essentially just elevates this pre-existing ‘adrenal gland–hair follicle axis’,” he concluded.

This is thought to make it “even more difficult” for hair follicle stem cells to generate new hair follicles.

Further research discovered that stress prevents the dermal papilla cells from secreting Gas6 – a molecule that can activate hair follicle stem cells.

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