References: Hair growth and hair loss
Int J Dev Biol. 1997 Jun;41(3):491-8.
Adult epidermal keratinocytes are endowed with pilosebaceous forming abilities.
Ferraris C, Bernard BA, Dhouailly D.
Equipe de Biologie de la Differenciation Epitheliale, UMR CNRS 5538 Laboratoire d'Etude de la Differenciation et de l'Adherence Cellulaires, Institut Albert Bonniot, Universite Joseph Fourier, Grenoble, France.
Pluristratified epithelia of adult vertebrate skin continuously regenerate from stem cells, and the question still arises as to whether those cells are committed to the production of only one cell lineage, or in contrast they conserve their embryonic pluripotentiality. In order to investigate the abilities of adult cultured as well as wound healing epidermis, heterospecific fibroblast-keratinocyte recombinations were performed, which allow unquestionable identification of the cells implicated in the structures that differentiate. Adult human cultured breast epidermal cells and full-thickness wound healing from human facial skin and foreskin were associated with either rabbit embryonic trichogenic dermis or cultured dermal papilla cells of adult rat, before grafting onto nude mice for two weeks to one month. In situ hybridization with a human specific sequence Alu probe labeled the human cells, whereas implanted rabbit or rat and host mouse cells were distinguished by the Hoechst staining of their nuclei. The results show that human adult cultured breast epidermal cells are able to form hair buds and to participate in hair follicle formation, while adult healing epidermis from a sparsely hairy skin as the human face or the dorsal skin of nude mouse, or even from a glabrous epidermis as the human foreskin, are able to differentiate pilosebaceous units. Although a follicular origin of the involved keratinocytes cannot be excluded in the three first cases, the formation of hair and sebaceous glands by foreskin keratinocytes of children 2 to 10 years-old establishes the cutaneous appendage ability of the interfollicular epidermal stem cells. The formation of interspecies mosaic follicles also highlights the fact that there must be a significant level of commonality in the interactive signaling molecules used by epithelial cells from different species.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9240566&dopt=Abstract
J Invest Dermatol. 1997 Aug;109(2):219-24.
Developmentally programmed expression of hyaluronan in human skin and its appendages.
Agren UM, Tammi M, Ryynanen M, Tammi R.
Department of Anatomy, University of Kuopio, Finland.
The expression of hyaluronan (HA) in fetal human skin was studied by using a biotinylated HA-binding probe. The uniform expression of HA in primitive skin was changed after the 9th week, when differentiation of the basement membrane zone increased HA in the subepidermal mesenchyme. Maturation of the papillary dermis at the 12-20th weeks led to the thickening of this HA-enriched zone; the underlying reticular layer was less intensely stained. In epidermis the number of cell layers rapidly increased after the 9th week. At first all epidermal layers were HA-positive. A complete loss of HA from the upper intermediate cells on the 18th week preceded the formation of mature granular and cornified layers. Peridermal cells remained HA-positive even when the underlying stratum corneum turned negative. The tightly apposed basal epithelial cells, the first stage of hair follicle and eccrine sweat gland formation, became almost completely depleted of HA. With advancing bulb development HA returned in the epithelial compartment, until maturation of the hair follicles restricted its expression to the outer root sheath and hair matrix. Maturation of the sebaceous glands led to the expression of HA pericellularly in the germinative cells and intracellularly in the mature sebocytes. Marked changes thus occur in the distribution of HA during fetal skin development; the primitive tissues exhibited a uniform widespread expression of HA, and maturing tissues showed distinct locally regulated patterns. The loss of epithelial HA in the hair follicle anlagen and upper intermediate cells turned out to be early differentiation markers.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9242511&dopt=Abstract
Arch Dermatol Res. 1997 Jun;289(7):384-8.
Lesional alopecia areata T lymphocytes downregulate epithelial cell proliferation.
Thein C, Strange P, Hansen ER, Baadsgaard O.
Department of Dermatology, Gentofte Hospital, University of Copenhagen, Hellerup, Denmark.
Alopecia areata is characterized by peribulbar infiltration by activated T cells. The function of these T cells in the pathogenesis is unknown. To elucidate the potential role of lesional T cells in the regulation of hair growth, T-cell clones from the margin of involved alopecia areata lesions from three patients were obtained by cloning, using the limiting dilution method. Of these T-cell clones, 31 were CD4+CD8-, 15 were CD8+CD4- and 2 were CD4-CD8-. The T-cell clones were activated and the supernatant harvested 24 h later and tested for its capacity to regulate proliferation of neonatal keratinocytes. The majority of the T-cell clone supernatants inhibited epithelial cell proliferation in a dose-dependent fashion. When the cytokine profiles of conditioned T-cell medium were compared with the growth-regulatory capacity, it was found that T-cell clones that released high amounts of interferon gamma and/or tumour necrosis factor alpha inhibited keratinocyte growth. In conclusion, T cells derived from the margin of active alopecia areata lesions are able to downregulate epithelial cell proliferation. This points to an important role of the immune system, especially the T cells, in this disease.
online pharmacy ref. source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9248616&dopt=Abstract
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