Losing Your Hair? You Can Blame the Massive Stem Cell Escape.


Every person, every mouse, every dog ​​has only one sign of aging: hair loss. But why is this happening?

Rui Yi, a professor of pathology at Northwestern University, set out to answer the question.

One generally accepted hypothesis about stem cells says that they regenerate tissues and organs, including hair, but will eventually run out and then die in place. This process is seen as an integral part of aging.

Instead, Dr. Yi and colleagues have surprisingly discovered that, at least in the hair of aging animals, stem cells escape the structures that house them.

A skin cell researcher and professor of pathology at the University of Southern California, and Dr. Not participating in Yi’s study published Monday, Dr. “It’s a new way of thinking about aging,” said Cheng-Ming Chuong. magazine Nature Aging.

The study also identifies two genes involved in hair aging, opening up new possibilities to stop the process by preventing stem cells from escaping.

Charles KF Chan, a stem cell researcher at Stanford University, called the paper “very important”, noting that “in science, everything about aging seems so complicated and we don’t know where to start.” By demonstrating a way and mechanism to explain aging hair, Dr. Yi and his colleagues may have provided a foothold.

Stem cells play a crucial role in hair growth in mice and humans. Hair follicles, which are tunnel-shaped miniature organs from which hair grows, go through periods of cyclical growth where the stem cell population living in a special area called a bulge divides and becomes rapidly growing hair cells.

Director of the Black Family Stem Cell Institute at the Icahn School of Medicine in Mount Sinai and Dr. Sarah Millar, who was not involved in Yi’s article, explained that these cells make up the hair shaft and sheath. Then, after a period of time, which is short for human body hair and much longer for hair on the person’s head, the follicle becomes inactive and its lower part degenerates. The hair shaft stops growing and falls out, only to be replaced by a new strand as the cycle repeats.

But while the rest of the follicle dies, a collection of stem cells remains in the ridge, ready to turn into hair cells to grow a new strand of hair.

Dr. Yi, like most scientists, assumed that stem cells die with age in a process known as stem cell depletion. He hoped that the death of stem cells from a hair follicle would mean that the hair would turn white and that once enough stem cells were lost, the hair shaft would die. However, this hypothesis was not fully tested.

Along with graduate student Chi Zhang, Dr. Yi decided that to understand the aging process in hair, he had to monitor individual strands as they grow and age.

Normally, researchers who study aging take tissue pieces from animals of different ages and study the changes. Dr. Yi said this approach has two drawbacks. First, the tissue is already dead. And it’s unclear what led to the observed changes or what will happen after them.

He decided that his team would use a different method. Using a long-wavelength laser that can penetrate deep into tissue, they tracked the growth of individual hair follicles in the mice’s ears. They labeled the hair follicles with a green fluorescent protein, anesthetized the animals so they wouldn’t move, put their ears under a microscope, and went over and over to watch what happened to the same hair follicle.

What they found was a surprise: As the animals began to age, turn gray and lose hair, stem cells began to escape from their tiny home on the ledge. The cells changed their shape from round to amoeba-like and squeezed through tiny holes in the follicle. Then they regained their normal shape and took off.

Sometimes, escaping stem cells travel long cellular distances from their niche.

Dr. “I wouldn’t have believed it if I hadn’t seen it myself,” Yi said. “It’s almost crazy in my mind.”

The stem cells were then destroyed, perhaps consumed by the immune system.

Dr. Chan likened the body of an animal to a car. “If you run it long enough and don’t replace parts, things will wear out,” he said. In the body, stem cells are like a mechanic, providing spare parts and change is constant in some organs such as hair, blood and bone.

But with the hair, it looks like the mechanic now – stem cells – will one day quit the job.

But why? Dr. Yi and colleagues’ next step was to ask whether genes control the process. They discovered two less active ones, FOXC1 and NFATC1, in older hair follicle cells. Their role was to trap the stem cells in the protrusion. So the researchers bred mice lacking these genes to see if they could become master controllers.

When the mice were 4 to 5 months old, they started losing their hair. At 16 months, the animals looked old when they were middle-aged: they had lost a lot of hair, and the sparse strands of hair that remained were grey.

Now the researchers want to save hair stem cells from aging mice.

This story about the discovery of a completely unexpected natural process, by Dr. It makes Chuong wonder what is left to learn about living things.

Nature has endless surprises waiting for us. “You can see fantastic things.”



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