Researchers at Indiana University School of Medicine have successfully developed a method to grow hairy skin from mouse pluripotent stem cells — a discovery that could lead to new approaches to model disease and new therapies for the treatment of skin disorders and cancers.
This research, recently published online in the journal Cell Reports, marks the first demonstration that hair follicles can be grown in cultures of stem cells. The study was led by Karl Koehler, PhD, assistant professor of otolaryngology-head and neck surgery at IU School of Medicine, and a postdoctoral fellow in his lab, Jiyoon Lee, PhD.
“The skin is a complex organ that has been difficult to fully recreate and maintain in culture for research purposes,” says Koehler, who explains more in a blog post. “Our study shows how to encourage hair development from lab grown mouse skin, which has been particularly troublesome for researchers to recreate in culture.”
Koehler and his team’s findings build on their past work creating a technique for growing inner ear cells from stem cells, in which mouse stem cells are cultured in a three-dimensional ball and treated with specific signaling molecules to coax the cells into producing inner ear tissue. The researchers noticed that skin was a byproduct of the inner ear growth process.
“In the developing embryo, the inner ear comes from the same layer of cells as the top layer of the skin, [the epidermis], so it was no surprise that skin and inner ear tissue formed in tandem,” Koehler says. “We were surprised to find that the bottom layer of the skin [the dermis] also develops.”
In the current study, Koehler and his team show how the epidermis and dermis cells form a sphere-like cluster of cells, called a skin “organoid.” The cells in skin organoids are organized much like cells in normal skin, but inside-out, meaning the top layer of the skin faces the interior of the organoid.
The team identified culture conditions that allowed skin organoids to proceed through the stages of development much like skin in the embryo.
“After about 20 days, we were amazed to see that skin organoids sprouted hair follicles,” Koehler says. “The roots of the follicles protrude from the skin organoids in all directions.”
The researchers confirmed that the timing of development and expression of key proteins closely match skin and hair development in the mouse embryo. To validate their findings, the IU team collaborated with Stefan Heller, PhD, Edward C. and Amy H. Sewall Professor of Otolaryngology-Head and Neck Surgery at Stanford University, whose lab members confirmed that the technique was reproducible with stem cells from other mouse strains.
“In addition to the major epidermal and dermal cell types we also found specialized cell types, such as melanocytes [pigment cells], Merkel cells [touch sensing cells], adipocytes [fat cells], sebaceous gland cells, and hair follicle stem cells in organoids,” Koehler says. “This is fascinating because it shows that if we derive the basic building blocks of skin together in culture, then these diverse cell types will self-assemble on their own.”
Lee, first author on the study, says these findings serve as a blueprint for how to make from scratch the entire skin organ using stem cells.
“My hope is that by improving skin-in-a-dish models we can greatly diminish the sacrifice of experimental animals and ultimately help patients with skin-related issues live a better life,” Lee says.
Koehler says he cautions that there are several technical hurdles that they have yet to overcome for the skin organoid model to reach its full potential as a drug discovery tool. For instance, the skin organoids are missing immune cells, blood vessels, and nerve endings found in normal skin.
“The shape of skin organoids is another problem that needs to be addressed in the future,” he says. “Because the organoids are inside-out compared to normal skin, the layers of dead cells and hairs cannot be shed as they are normally, so we need to find a way to flip the structure of skin organoids.”
Without these changes, the skin organoids have a shelf life of about a month, which is just long enough to study the complete development of mouse skin and hair.
Koehler and his team are currently using the mouse organoids as a template to derive hairy skin from human pluripotent stem cells. This work has the potential to lead to new skin grafting techniques — incorporating hair follicles — and therapies for human diseases, including alopecia, acne, and skin cancers.