Note: Among cell populations of HF the folloving are the most important:
- Cells of epithelial origin: matrix trichocytes [M] and ORS [outer root sheath] cells.
- Cells of dermal origin: DP fibroblasts and dermal sheath [DS] fibroblasts.
The last play in HF predominantly regulation role, while the former represent mitotically active populations.
1. J. Cohen in his early investigations has been studying HF regeneration from DP +M [structure defined as whole papilla]. Whole papillae were transplanted into micro-incision of ear skin. From 62 implants 25 regenerate new HF that produce several generations of fibres of vibrissae type. The vast majority of them have a pigmentation pattern of donor type. At the same time histologically new HFs were defective: their peripheral blood sinuses were weak, glassy membrane and ringwulst were absent. IN general, HFs morphology was defined by author as mosaic, combining signs of vibrissae and pelage HFs.
J. COHEN. The transplantation of individual rat & guinea-pig whisker papillae . // J. Embryol. exp. Morph. Vol. 9 , part 1 , p. 177-127 . 1961
Results of this experiments are difficult to interpret because local HFs of ear skin can contributed in regeneration process both directly and indirectly. Nevertheless, on the basis of these experiments we can do the following conclusions and pose several questions:
We can suppose, that new HFs regenerate only on the basis of transplanted DP and M cells. The last cells are defined as transient amplifiers and are already predetermined to become trichocytes.
At the same time, if they are transient amplifiers and their proliferation potentialities are limited how can 5 generations of fibres have been produced? In intact HFs at the end of telogen /beginning of anagen a pool of matrix cells is substituted by new pool of migrating cells from bulge region. But at transplantation whole papilla do not include own bulge region. We can suggest the following solutions:
Taking in account that ear skin contain many local HFs of pelage type, their bulge regions could be involved in regeneration process. They could be the source of stem cells.
On the other hand it is known that at the very base of vibrissae HF matrix a germinative cells reside. This is specific population of cells, whose proliferation status is poorly defined. The are believed to be intermediate between stem cells and trichocytes of matrix. On the base of light microscopy and TEM their morphology is closer to stem cells rather than to matrix’s trichocytes. SDS-RAGE study showed that keratins’ pattern of GE cells differs from that of ORS and M cells. Therefore, theoretically GE cells can support several growth cycles.
2. In other experiments, high-passage DP and GE cells were transplanted together into micro-incision of ear pinna. They repeatedly induced giant vibrissa-type follicles and fibres. It was concluded, that the adult GE cells enable non-inductive adult dermal cells [high-passage DP cells become non-inductive in other systems] to stimulate hair follicle neogenesis, effectively, by altering their 'status', causing the sheath cells to 'specialize' and the 'aged' papilla cells to 'rejuvenate'.
C. A. JAHODA., F. J. REYNOLDS ., Hair matrix germinative epidermal cells confer follicle-inducing capabilities on dermal sheath & high passage papilla cells. // Development., vol.122(10)., p.3085-3094., 1996 |
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