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.
We also have to distinguish once again 2 populations of matrix cells:
- trichocytes of matrix
- germinative epithelium of matrix.
1. In vitro DP fibroblasts stimulate GE cells proliferation and aggregation. In collagen gel, in 3-D culture DP +GE produce root-like structures. In 2-D cultures, when GE cells were seeded above DP cells aggregates they form dome-like structures, that were raised up above the culture, or, more usually compact lines, tensions, that elongated with time. Less common was the assembly of “organotypic” structures. Here, GE cells had become completely surrounded by DP cells. Between them a basal membrane was identified. At the same time GE cells morphologically remained small and round. In all other types of cultures [lacking DP cells], GE cells were not activated in that way. They remained quiescent, in G0-phase, don’t proliferate and don’t express several keratins, that are characteristic for terminally differentiating trichocytes.
REYNOLDS A.J., JAHODA C.A., Hair follicle stem cells? A distinct germinative epidermal cells population is activated in vitro by the presence of hair dermal papilla cells. // J. Cell. Sci., vol.99(pt.2)., p.373-385., 1991
JAHODA CA., REYNOLDS AJ ., Dermal- epidermal interaction . Follicle derived cell populations in the study of hair growth mechanism . // J. Invest. Dermatol. 1993 vol. 101 p. 33s-38s .
2. These authors in studies with human HFs confirmed their results. Here again, “organotypic” structures with basal membrane were formed.
REYNOLDS A.J., LAURENCE C.M., JAHODA C.A., Human hair follicle germinative epidermal cell culture. // j. Invest. Dermatol., vol.10194)., p.634-638., 1993
3. When trichocytes, isolated from plucked human scalp HFs were propagated on feeder layers of DP cells epidermoid differentiation was largely prevented while still allowing growth and stratification [in case of dermal fibroblasts trichocytes undergo keratinization]. Co-culture of trichocytes together with DP cells in 3-D Matrigel suppressed almost completely epidermal keratinization stratification [in case of dermal fibroblasts large spheroidal structures with inward-directed differentiation and all the epidermal markers found in 'surface' cultures were developed]. Therefore, DP fibroblasts don’t induce even typical hair proteins in cultured trichocytes.
LIMAT A., BREITKREUTZ D., THIEKOETTER G., NOSER F., HUNZIKER T., BRATHEN L.R., FUSENIG N.E. Phenotypic modulation of human hair matrix cells (trichocytes0 by environmental influence in vitro & in vivo. // Epitelial Cell biol., vol.2(2)., p.55-65., 1993
Therefore, 2 independent research groups give practically 2 opposite results:
First group confirm that GE cells in association with DP fibroblasts form complex 3-D structures with basal membrane. Yet, presence of HF specific keratins wasn’t tested.
Others point to the inability of matrix trichocytes to form any kind of complex structure, but undifferentiated spheroid bodies, surrounded by DP cells. Therefore, DP fibroblasts in culture are only able to suppress alternative directions of differentiation [keratinization] of trichocytes. They aren’t even able to induce typical hair keratins |
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