Kyoizumi, 1998  Title: Radiation sensitivity of human hair
follicles in SCID-hu mice.
Authors: Kyoizumi S, Suzuki T, Teraoka S, Seyama
T
Journal: Radiat Res 1998 Jan;149(1):11-8
PMID: 9421149, UI: 98081502
Affiliated institution: Department of Radiobiology,
Radiation Effects Research Foundation, Hiroshima, Japan.
We developed an experimental model for studying the growth and
epilation of the human hair follicle by implanting human scalp
tissue onto immunodeficient C.B-17 scid/scid mice. The skin grafts
showed continuous growth of black human hairs for at least 1 year
and maintained the normal histological structure of a human hair
follicle and other tissues associated with the skin. Using this
in vivo model, we evaluated the effect of irradiation on the function
of human hair follicles. Localized X irradiation (1 to 6 Gy) induced
hair loss dose-dependently and synchronously in the third week
after irradiation. The hairs undergoing epilation showed a gradual
decrease in width toward the root. The minimum width at the thinnest
portion of the surviving hair 4 weeks after irradiation suggested
that epilation resulted from the breaking of hairs when the hair
width decreased to less than 20 microm. After the highest-dose
irradiation, the normal structure of the hair bulb was totally
abrogated, and long and narrow epithelial tissues associated with
regressed papillary cells remained. The surviving epithelia were
morphologically similar to the outer epithelial sheath of the
follicle associated with palisadic basal cell layers. In the third
week some cells in the basal layers of the surviving epithelium
in each follicle expressed proliferating cell nuclear antigen.
By about 9 weeks after irradiation, the complete structure of
the follicle regenerated, with hair growth activity even in the
grafts irradiated at the highest dose, although about 30% of the
hairs did not regrow. These findings suggest that follicular stem
cells that survive high-dose exposure in the sheath-like epithelial
tissue can reproduce the complete follicle structure. This animal
model can be used to assess the effects of radiation exposure
on human skin and to identify and characterize human follicular
stem cells.
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