Different Populations of Melanocytes Are Present in Hair Follicles and Epidermis

Abstract

Melanocytes in human skin reside both in the epidermis and in the matrix and outer root sheath of anagen hair follicles. Comparative study of melanocytes in these different locations has been difficult as hair follicle melanocytes could not be cultured . In this study we used a recently described method of growing hair follicle melanocytes to characterize and compare hair follicle and epidermal melanocytes in the scalp of the same individual. Three morphologically and antigenically distinct types of melanocytes were observed in primary culture. These included (1) moderately pigmented and polydendritic melanocytes derived from epidermis; (2) small, bipolar, amelanotic melanocytes; and (3) large, intensely pigmented melanocytes; the latter two were derived from hair follicles. The three sub-populations of cells all reacted with melanocyte-specific monoclonal antibody. Epidermal and amelanotic hair follicle melanocytes proliferated well in culture, whereas the intensely pigmented hair follicle melanocytes did not. Amelanotic hair follicle melanocytes differed from epidermal melanocytes in being less differentiated, and they expressed less mature melanosome antigens. In addition, hair follicle melanocytes expressed some antigens associated with alopecia areata, but not antigens associated with vitiligo, whereas the reverse was true for epidermal melanocytes. Thus antigenically different populations of melanocytes are present in epidermis and hair follicle. This could account for the preferential destruction of hair follicle melanocytes in alopecia areata and of epidermal melanocytes in vitiligo.

Stem cell factor/c-Kit signalling in normal and androgenetic alopecia hair follicles

“…These antigens were also expressed by cultured human epidermal and hair follicle melanocytes. This concurs with earlier studies of human epidermis (Grichknik et al 1996, Norris et al 1996 and rodent hair follicles (Okura et al 1995, Botchkareva et al 2001, and with NKI/beteb distribution in human follicles (Horikawa et al 1996, Commo & Bernard 2000 and cultured melanocytes (Tobin & Bystryn 1996, Zhu et al 2004.…”

“…Thirdly, less differentiated cells, only expressing NKI/beteb, probably forms of melanocyte stem cell, were present in small numbers in all areas and were the majority in mid-follicle ORS. During follicular melanocyte culture two types were observed here and elsewhere (Hu et al 1957, Tobin & Bystryn, 1996, Na et al 2006, including less differentiated, bipolar forms with great dividing capacity. These SCF/c-Kitindependent cells in the mid-follicle ORS, the follicle stem cell niche, correspond to c-Kit-negative stem cells in mice (Nishimura et al 2002, Steingrimsson et al 2005.…”

Corticotropin releasing hormone and the skin

“…This discrepancy may be explained in part by changes induced during the enforced melanocyte proliferation in vitro. However, we have more recently also detected CRH-R2 protein expression in cultured follicular melanocytes using both immunocytochemistry ( Figure 12) and immunoblotting (99), which raises the alternative possibility that variation in melanocyte gene expression may reflect their heterogeneous differentiation status in the hair follicle in situ and in vitro (100,101). The Paus laboratory reported a similar distribution of CRH and CRH-R1 in human scalp hair follicles both at the gene and protein levels (73,74).…”

Behavior of Hair Follicles in Vitiligo: Clinical Presentation and Discussion

“…The famous c-Kit is required during the hair growth cycle for activation of melanocytes, although in stem cell compartment appears to exhibit stem cell factor SCF/c-Kit independence [15]. Some amelanotic dopa-negative melanocytes may also be distributed in the periphery of the bulb and the most proximal matrix [1,19]. All the dopa-positive cells, and also some dopa-negative melanocytes of the mid outer root sheath are (pre)melanosome gp100 positive [19].…”

“…Sharov et al stated that both bulge cells and follicular papilla cells may be the source of melanocytes during the new hair cycle as the original follicular melanocytes lose their functions during catagen [18]. The hair bulb may also possess a minor subpopulation of those poorly differentiated pigment cells [1].…”