Engineering better hair transplants

Cell-based approach to new follicles takes hold in skin

A hair-raising trick may lead to better hair transplants. Engineered hair follicles patched into skin can be coaxed to connect to surrounding tissue and to grow hair in an organized way, a study in mice finds.

Bioengineered follicles can grow hair (as seen on the mouse’s head) when transplanted into normally hairless mice, a new study shows. Takashi Tsuji/Tokyo University of Science

Unlike current hair transplant methods, which simply move existing hair follicles from one area of the scalp to another to cover a bald region, the approach would spur the creation of new hair follicles from existing cells.

“It’s exciting because it shows a cell-based approach for treating hair loss is maybe feasible,” says George Cotsarelis, a dermatologist at the University of Pennsylvania in Philadelphia.

The results also mark a step forward in efforts to regenerate organs such as salivary glands that form in a process similar to hair early in their development, says study coauthor Takashi Tsuji of Tokyo University of Science in Chiba, Japan. Tsuji and his colleagues describe the findings in the April 17 Nature Communications.

Hair follicles develop when two different types of cells — epithelial and mesenchymal cells — interact with each other. Epithelial cells grow very quickly and shed, while mesenchymal cells direct epithelial cells to make a follicle.

Previously, Tsuji and colleagues had bioengineered follicles and hair shafts in the lab using epithelial and mesenchymal cells from mouse embryos. Until now, it was unclear whether these organized clusters of cells would make normal hair if inserted into mouse skin.

In the new work, the team transplanted a group of the engineered follicles into the skin on the backs of hairless mice. After about two weeks, hairs began to sprout. Under the microscope, the hair grown from the bioengineered mouse follicles resembled normal hair, scientists found. And the mouse follicles went through the normal cycle of growing hair, shedding and making new hair.

When researchers injected the region around the bioengineered follicle with acetylcholine, a drug that causes muscles to contract, the hairs perked up. This suggests that the transplanted follicles had integrated with surrounding muscle and nerves like normal hair follicles do.

Importantly, the researchers were able to ensure hair didn’t become ingrown or point in the wrong direction by attaching a nylon thread to the engineered follicles and guiding the hair to grow outward.

“You have to make hair that is positioned right,” says Cheng-Ming Chuong, a stem cell and regeneration researcher at the University of Southern California in Los Angeles. Chuong notes that the new study succeeded in getting the follicles to grow in an organized way. Previous studies involving transplanted follicles produced hair that grew in random directions or formed cysts, which isn’t very useful clinically.

Tsuji and his colleagues also created functional follicles from adult mouse cells. The team harvested epithelial stem cells and mesenchymal cells from adult mouse hair follicles. Growing the two cell types together, the team engineered follicles that, when transplanted, made whisker-type hair.

The scientists then turned to human cells. Applying similar methods to cells collected from the scalps of men with male pattern baldness, researchers created individual follicles that grew hair once transplanted into hairless mice.

Still, Cotsarelis adds that these findings do not show whether the number of human hair follicles can be amplified, so that more hair is produced.

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