Understanding Hair Transplants and Hair Loss - Pacific Hair

munocytochemical analysis of various proliferation and differentiation markers . Surpris-
ingly, keratinocytes of all fragments, as shown by expression of high-molecular-weight
cytokeratins and filaggrin, were capable of terminal differentiation. These data indicate
that cells with long life spans are localized in central parts of the outer root sheath close
to the bulge area and that cells with high colony-forming ability are localized in the lower
central parts . The latter are usually removed by plucking and may therefore not represent
stem cells but rather cells important for hair growth during a single cycle . Cells with
long life spans—also included in plucked hair follicles—may be immediate progeny of
stem cells that will be segregated in the bulge area . Finally, our results are important
for gene transfer and stem cell gene therapy in genodermatoses, because plucked hair
follicles are easily available and keratinocytes close to the bulge area should be used
selectively .
Yang (1993), reported that corneal keratinocyte stem cells can proliferate in vitro better
than their progeny cells. In this paper, we applied this approach to the identification of
hair follicular stem cells . When human scalp hair follicles were placed in explant culture,
the bulge area yielded best outgrowths. In another experiment, we isolated different
subpopulations of human follicular keratinocytes by micro-dissection, dispersed them
by trypsin/EDTA into single cells, and grew them in the presence of 3T3 feeder cells .
The keratinocytes were then subcultured under identical conditions to compare their in
vitro life span . Our results indicate that the life span of keratinocytes of the upper follicle
(containing mainly the isthmus area)>sebaceous gland> lower follicle (between
the bulge and bulb) > bulb (containing the matrix cells) . The cultured upper follicular
keratinocytes tend to be small and relatively uniform in size . The poor in vitro growth of
matrix cells may reflect their non-stem cell nature and/or special growth requirement(s)
satisfied in vivo by the neighboring dermal papilla cells. Unexpectedly, we found that
the upper follicular keratinocytes grow even better than epidermal keratinocytes . The
existence of a subpopulation of keratinocytes with an in vitro growth potential superior
than other known keratinocytes of the skin supports the hypothesis that follicular stem
cells reside in the upper follicle . Our data also raise the possibility that putative follicular
stem cells are involved not only in forming the follicle, but also in the long-term maintenance
of the epidermis . Finally, we discuss the possibility that keratinocyte stem cells,
as defined by their in vivo slow-cycling nature, are absent in culture.
Hung et al ., (2001), reported that human Frizzled-3 is important to developing hair follicle
and identified the mRNA for human Frizzled-3 in epidermal keratinocytes and in
the HaCaT keratinocyte cell line . Human Frizzled-3 mRNA encodes a 666 amino acid
U n d e r s t a n d i n g H a i r T r a n s p l a n t s a n d H a i r L o s s
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