Each person, each rodent, each dog, has an unmistakable sign of aging: the loss of hair and fur. But why does this happen?
Rui Yi, professor of pathology at Northwestern University, decided to find out the answer.
A generally accepted hypothesis about why stem cells says that they replace tissues and organs, which includes hair, but they will end up exhausted and die in their place. The process is seen as an integral part of aging.
However, Yi and his colleagues made the surprising discovery that, at least for the hair of aging animals, stem cells escape those that surround them. .
It’s a new way of thinking about aging, said Cheng-Ming Chuong, a physician and professor of pathology at the University of Southern California, who researches since skin cells and did not participate in the study. Yi, published by the scientific journal Nature Aging.
The study also identifies two genes involved in the aging of the hair of laboratory rats and in human hair, which opens up new possibilities to stop the process by preventing it from because stem cells escape.
Charles Chan, a stem cell researcher at Stanford University, called the study very important, pointing out that, in science, everything related to aging seems so complicated that we don’t know where to start.
By showing u In the pathway and mechanism that explain hair aging, Yi and his colleagues may have provided an entry point.
Stem cells play an important role in the growth of animal hair and human hair. .
Hair follicles, miniaturized tunnel-shaped organs from which hairs grow, go through cyclical periods of growth in which a population of stem cells living in a specialized region called the bulb develops and transforms into rapidly growing hair cells.
Sarah Millar, director of the Black Family Stem Cell Institute, at the Icahn School of Medicine from Mount Sinai, who did not participate in the one led by Yi, explained that these cells from the origin of the hair shaft and its sheath.
Later, after a period of time that is short for a person’s body hair and much longer for the hair, the follicle becomes inactive and its lower part degenerates. The hair shaft stops growing and expels, and ends up replaced by a new strand of hair, when the cycle starts again.
But while the rest of the follicle dies, a collection of stem cells remains in the bulb , ready to start transforming into hair cells that will result in a new strand of hair.
Yi, like most scientists, assumed that with age since stem cells died, in a process known as exhausted stem cells.
He anticipated that the death of the stem cells in a follicle meant that the hair turned white and that, when enough stem cells were lost, that strand of hair would die. But his hypothesis had not been fully tested.
Working with a graduate student, Chi Zhang, Yi decided that in order to understand the hair aging process, he needed hair growth and aging. individual strands follow.
Usually, researchers who study aging remove portions of tissue from animals of different ages and examine for changes.
There are two downsides to this approach, he said Yi. What tissue is already dead first. And it’s not clear what led to the changes being observed, or what will come after them.
He decided that his team would use a different method. They followed the growth of individual hair follicles in the ears of laboratory rats using a wavelength laser capable of penetrating deep into long tissues.
Labeled the hair follicles with a green fluorescent protein , anesthetized the animals so they wouldn’t move, put their ears under a microscope, and repeated the observation several times in order to keep track of what was happening with the same follicle.
What they saw was A surprise: when the animals began to age, turn gray and lose hair, since stem cells escaped their small homes in the bulb. They changed shape, from round to an indefinite shape similar to an amoeba, and escaped through the small holes in the follicle. Then, they resumed their original form and started to move.
Sometimes, because fugitive cells took great leaps, in cellular terms, from the niche where they once lived.
If I hadn’t seen it with my own eyes, I wouldn’t have believed it, Yi said. In my mind, that sounded crazy.
And then since stem cells disappeared, perhaps consumed by the immune system.
Chan compared the animal’s body to the one car. If you wear it too long without replacing the parts, they wear out, he said. In the body, stem cells are like mechanics, which provide replacement parts, and in some organs, such as hair, blood and bones, this replacement happens continuously.
But in the case of hair, it looks like the stem cell mechanic just quits the job one day.
Why does this happen, though? The next step for Yi and his colleagues was to ask whether genes controlled the process. They found that two of them FOXC1 and NFATC1 were less active in older hair follicle cells.
Therefore, the researchers bred laboratory mice to create specimens lacking these genes in order to determine if they were the ones who functioned as master controllers.
The animals began to lose hair at four or five months of age. At months, when they were middle-aged, they looked old. They had lost a lot of hair and the few remaining hairs were gray.
Now the researchers sincerely want to save stem cells from the hair of aging animals.
The story of the discovery of a completely unexpected natural process makes Chuong wonder what remains to be learned about living creatures.
Translation by Paulo Migliacci