New source of multipotent adult stem cells discovered in human hair follicles

Researchers at the University of Pennsylvania School of Medicine have isolated a new source of adult stem cells that appear to have the potential to differentiate into several cell types. If their approach to growing these cells can be scaled up and proves to be safe and effective in animal and human studies, it could one day provide the tissue needed by an individual for treating a host of disorders, including peripheral nerve disease, Parkinson's disease, and spinal cord injury.

“We are very excited about this new source of adult stem cells that has the potential for a variety of applications,” says senior author Xiaowei (George) Xu, MD, PhD, Assistant Professor of Pathology. “A number of reports have pointed to the fact that adult stem cells may be more flexible in what they become than previously thought, so we decided to look in the hair follicle bulge, a niche for these cells.” Xu and colleagues report their findings in the latest issue of the American Journal of Pathology.

Hair follicles are well known to be a source for adult stem cells. Using human embryonic stem cell culture conditions, the researchers isolated and grew a new type of multipotent adult stem cell from scalp tissue obtained from the National Institute of Health's Cooperative Human Tissue Network.

The mutipotent stem cells grow as masses the investigators call hair spheres. After growing the “raw” cells from the hair spheres in different types of growth factors, the investigators were able to differentiate the stem cells into multiple lineages, including nerve cells, smooth muscle cells, and melanocytes (skin pigment cells).

The differentiated cells acquired lineage-specific markers and demonstrated appropriate functions in tissue culture, according to each cell type. For example, after 14 days, 20% to 40% of the cells in the melanocyte media took on a weblike shape typical of melanocytes. The new cells also expressed biomarkers typical of pigment cells and when placed in an artificial human skin construct, produced melanin and responded to chemical cues from normal epidermis skin cells.

After 14 days, about 10% of the stem cells in the neuronal cell line — a type of cell not present in skin or hair — grew dendrites, the long extensions typical of nerve cells and expressed neuronal proteins. The neurotransmitter glutamate was also present in the cells, but the neurotransmitter dopamine was not detected.

Thirdly, about 80% of the stem cells grown in the muscle media differentiated into smooth muscle cells. These new muscle cells also contracted when placed in a collagen matrix.

Overall, the researchers showed that human embryonic stem cell media could be used to isolate and expand a novel population of multipotent adult stem cells from human hair follicles. “Although we are just at the start of this research, our findings suggest that human hair follicles may provide an accessible, individualized source of stem cells,” says Xu. The researchers are now working on inducing other cell types from the hair sphere cells and testing the cells in animal models. Study co-authors are Hong Yu, Suresh M. Kumar, and Geza Acs, all from Penn; and Dong Fang, Ling Li, Thiennga K. Nguyen, and Meenhard Herlyn, all from the Wistar Institute, Philadelphia.