In 2001, Barrandon was part of aFrench research team who reported in the scientific journal Cell thatstem cells could be used to generate skin containing hair and sebaceousglands in mice. But at that time it was unclear whether the stem cellsin hair follicles were true stem cells, capable of long-term renewal,or multipotent progenitor cells that would not permanently engraft inthe follicle.
In the current PNAS study, the Swiss researchershave answered that question, using rat whisker hair follicles todemonstrate that the clonogenic keratinocytes in hair follicles aretrue stem cells.
Barrandon's group isolated stem cells from ratwhisker follicles, labelled them, and grew them in culture for 140generations. They then implanted progeny cells into the skin of newbornmice whose hair follicles were just being formed. This skin was thengrafted onto athymic (nude) mice. Some cells were incorporated intodeveloping follicles, but other follicles were completely made up oflabelled cells. Each progeny cell contributed to the formation of eightdifferent types of cell in the follicle, including those of the outerroot sheath, inner root sheath, the hair shaft, the sebaceous gland andthe epidermis.
After 125 days, a biopsy was taken from the graft,and labelled stem cells were isolated, subcloned, cultivated and thenonce again transplanted. The rat whisker stem cells participated againin forming all the cell types needed to form the hair follicle andsebaceous glands, resulting in hair bulbs that underwent repeatednormal phases of growth, rest and regeneration. The fact that thetransplanted cells participate in the hair cycle over long periods oftime shows that they are true multipotent stem cells and notprogeniture cells.
"With the progeny of a single stem cell, itwould be theoretically possible to generate the complete hair bulb of ahuman being, and one that would last for years," explains Barrandon.
Theability of the stem cells in hair follicles to repeatedly regenerateall the different cell types of the follicle and sebaceous glands hasimportant implications for regenerative medicine. The method could oneday be used to regenerate hair on patients with severe burns. Thisstudy is a logical complement to other work in Barrandon's Laboratoryof Stem Cell Dynamics, recognized for research into the reconstructionof injured tissues and organs.
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