Researchers have succeeded in developing near-perfect skin samples with colored hair and scalp, sebaceous glands, oil, and sensory cells. A discovery that is due to chance and will be of great interest to the cosmetic industry, which is looking for models to test its products. The researchers also plan to produce hair follicles for the treatment of baldness.
Hair Loss
For more than 40 years, researchers have been trying to reconstruct human skin as best as possible to treat burns or to test drugs and cosmetic products without the need for animal testing. Most of these methods use stem cells that are propagated in the laboratory to produce skin.
Unfortunately, the skin is much more complex than a simple collection of skin cells; it is woven from nerve, fat, pigment cells, etc. The “mini-organoids” embedded in the skin give it its appearance and give it the ability to feel heat, touch, and sweat. The human skin obtained until now lacked an essential element: hair. Researchers at the Children’s Hospital Boston Research Laboratory published a study in Nature in which they claim to have succeeded in producing “mini-organoids” from human skin with sebaceous glands and hair follicles.
A chance discovery
Although the team had been working on this project for years (in 2018, they published an article on hairy skin based on mouse stem cells), their discovery was a stroke of luck. Karl Koehler, then a researcher at Indiana University, tried to recreate the hearing cells to reconstruct the inner ear system. His goal was to create cells sensitive to auditory stimuli to test gene therapies for hearing loss and balance disorders.
By testing a “chemical cocktail” of growth factors and different molecules, he discovered that skin tissue formed in connection with the inner ear tissue. Even more surprising was that the hair follicles protruded from the cultivated skin. First, we tried to get rid of the skin cells as if they were weeds,” joked Karl Koehler, co-author of the Nature study. But when we realized the scientific value of hairy skin, we changed our tactics and tried to remove the inner ear organoids in favor of skin growth.
A real piece of skin
The researchers started with pluripotent stem cells reduced to the embryonic form and then applied their “recipe” to obtain the skin cells. A “recipe” that allows the simultaneous development of two layers of skin, the epidermis and the dermis, whose interaction promotes the appearance of hair follicles. By day 70, the hair has grown to the surface, which is the stage where hair appears on the fetus. Even better: the skin sample is equipped with melanocytes, which participate in the coloring of the skin and hair, as well as fat, sensory nerves, and Merkel cells, which participate in the sensation of touch.
A cure for baldness
After 140 days of culture, the cultured skin was implanted in mice, 55% of which developed hairs of 2 to 5 mm. When comparing the transplanted skin with real human skin, researchers found many similarities, such as the fact that the hair trunks were aligned perpendicular to the surface. Above all, the transplanted hair cells developed sebaceous glands from which sebum is produced, which contributes to the lipid film that protects the skin.
Therefore, the technique will probably “generate an almost unlimited number of hair follicles for transplantation,” said Karl Koehler. Hair à la carte! Every surgeon’s dream for patients suffering from baldness
A dream that is still a long way off, the authors warn. Rejection by the immune system is a major obstacle, says Karl Koehler. The generation of individually adapted hair follicles will be incredibly expensive and will take a year or more. As with hair transplants, this technique will probably still be reserved for the wealthy.
References
Lee, J., Rabbani, C.C., Gao, H. et al. Hair-bearing human skin generated entirely from pluripotent stem cells. Nature 582, 399–404 (2020). https://doi.org/10.1038/s41586-020-2352-3
