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Hair follicle stem cells were found to have the ability to
regenerate all the follicle cell types and glands.
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Using an animal model, a research team led by Yann
Barrandon at the EPFL (Ecole Polytechnique Federale de
Lausanne) and the CHUV (Lausanne University Hospital) has
discovered that certain cells inside the hair follicle are
true multipotent stem cells, capable of developing into the
many different cell types needed for hair growth and
follicle replacement.
In an article appearing in the Oct 3 advance online edition of
the Proceedings of the National Academy of Sciences, they
demonstrate that these holoclones can be used for long-term follicle
renewal.
In 2001, Barrandon was part of a French research team who
reported in the scientific journal Cell that stem cells could be
used to generate skin containing hair and sebaceous glands in mice.
But at that time it was unclear whether the stem cells in hair
follicles were true stem cells, capable of long-term renewal, or
multipotent progenitor cells that would not permanently engraft in
the follicle.
In the current PNAS study, the Swiss researchers have answered
that question, using rat whisker hair follicles to demonstrate that
the clonogenic keratinocytes in hair follicles are true stem cells.
Barrandon's group isolated stem cells from rat whisker follicles,
labelled them, and grew them in culture for 140 generations. They
then implanted progeny cells into the skin of newborn mice whose
hair follicles were just being formed. This skin was then grafted
onto athymic (nude) mice. Some cells were incorporated into
developing follicles, but other follicles were completely made up of
labelled cells. Each progeny cell contributed to the formation of
eight different types of cell in the follicle, including those of
the outer root sheath, inner root sheath, the hair shaft, the
sebaceous gland and the epidermis.
After 125 days, a biopsy was taken from the graft, and labelled
stem cells were isolated, subcloned, cultivated and then once again
transplanted. The rat whisker stem cells participated again in
forming all the cell types needed to form the hair follicle and
sebaceous glands, resulting in hair bulbs that underwent repeated
normal phases of growth, rest and regeneration. The fact that the
transplanted cells participate in the hair cycle over long periods
of time shows that they are true multipotent stem cells and not
progeniture cells.
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"With the progeny of a single stem cell, it would be theoretically
possible to generate the complete hair bulb of a human being, and
one that would last for years," explains Barrandon.
The ability of the stem cells in hair follicles to repeatedly
regenerate all the different cell types of the follicle and
sebaceous glands has important implications for regenerative
medicine. The method could one day be used to regenerate hair on
patients with severe burns. This study is a logical complement to
other work in Barrandon's Laboratory of Stem Cell Dynamics,
recognized for research into the reconstruction of injured tissues
and organs.
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