Extracellular matrix derived from hair and skin fibroblasts stimulates human skin melanocyte tyrosinase activity

There is indirect evidence that both skin and hair melanocytes are regulated by the activity of adjacent cells. In hair, the specialized fibroblasts (dermal papilla cells) appear to play a role in the regulation of hair growth. Hair pigmentation may relate to hair growth. In skin, melanocytes are located adjacent to the basement membrane zone. As far as we are aware, direct interactions of fibroblasts with melanocytes have not previously been investigated. Accordingly, the objective of this study was to develop co-culture conditions in which to investigate whether dermal fibroblasts from skin or hair could influence melanocyte differentiation. The influence of fibroblast-conditioned media, co-culture with fibroblasts, and fibroblast-derived extracellular matrix (ECM) on normal human skin melanocyte tyrosinase activity was examined. Fibroblasts from both skin and hair were capable of altering melanocyte morphology and significantly increasing tyrosinase activity when melanocytes were cultured in the absence, but not the presence, of the major proliferative drives. Although stimulation of tyrosinase activity was detectable with conditioned medium and co-culture with fibroblasts, the most striking result was obtained with the fibroblast-produced ECM which, on average, produced a four-fold increase in tyrosinase activity within 6 days. Thus, the study describes co-culture conditions in which the stimulatory effect of the fibroblast on melanocyte differentiation can be examined.     

Update on the regulation of mammalian melanocyte function and skin pigmentation

Melanogenesis is the unique process of producing pigmented biopolymers that are sequestered within melanosomes, which provides color to the skin, hair and eyes of animals and, in the case of human skin, also protects the underlying tissues from UV damage. We review the current understanding of melanogenesis, focusing on factors important to the biochemistry of pigment synthesis, the biogenesis of melanosomes, signaling pathways and factors that regulate melanogenesis, intramelanosomal pH, transport and transfer of melanosomes, and pigmentary disorders related to the dysfunction of melanosome-related proteins. Although it has been known for some time that many of the factors that affect melanogenesis are derived from keratinocytes, fibroblasts, endothelial cells, hormones, inflammatory cells and nerves, a number of new factors that are involved in that regulation have recently been reported, such as factors that regulate melanosome pH and ion transport.     

Structure and function of ethnic skin and hair

Differences have been found among blacks, whites, Asians, and Hispanics in various areas of skin structure and function. Among them is the stratum corneum lipid (ceramide) content, which is highest in Asians, then Hispanics, then whites, and lowest in blacks. Melanosomal packaging and percutaneous absorption rates for specific compounds also vary among the different races. Reports supporting the occurrence of difference in TEWL, tyrosinase levels, skin elasticity, and water absorption rates between blacks and whites, and reaction to skin irritation have been conflicting. No significant differences in corneocyte size, skin thickness, and skin biomechanics have been reported.     

Functional characterization of melanocyte stem cells in hair follicles

In mice, coat pigmentation requires a stem cell (SC) system in which the survival, proliferation, and differentiation of melanocytes (MCs) are regulated by microenvironments in hair follicles (HFs). In vitro systems are required to analyze the behavior of single melanocyte stem cells (MCSCs) and their potential to form SC systems in vivo. We describe here an experimental system for the isolation, self-renewal, and differentiation of MCSCs, as well as an in vivo reconstitution assay for assessing their potential. Using Dct(tm1(Cre)Bee)/CAG-CAT-GFP mice, we show that, in the presence of stem cell factor and basic fibroblast growth factor and the XB2 feeder cell line, purified MCSCs can undergo clonogenic proliferation, resulting in c-Kit(low) side scatter(low) cells. In culture, these cells maintain their capacity to differentiate and reconstitute an MCSC system in HFs. As these cells are present in the upper part of the HF near the bulge region, express only low levels of housekeeping genes, and are resistant to neonatal treatment with ACK2, it is likely that only MCSCs that are quiescent in vivo have clonogenic activity in vitro. We also found that MCSCs can be purified from wild-type mice by fluorescent cell sorting and can be characterized in vitro.     

Neonatal skin barrier: structure, function, and disorders

The development of the human skin from intrauterine to extrauterine life is a balletic interplay of maturing layers and interlocking structures. We discuss this transition and then branch out to touch on issues of premature infant as well as neonatal skin care. Disruption of the barrier function due to toxins and development errors are expounded upon. Staph scalded skin syndrome, collodion membrane, bullous congenital ichthyosiform erythroderma, autosomal recessive ichthyosis (lamellar and congenital ichthyosiform erythroderma), and harlequin fetus are used as examples of these disruptions. Discussion of therapy with the authors' experience highlights each disease.     

毛囊黑素干细胞研究进展

基于每个毛发循环中产生一个色素性毛干的观察,人们推测在毛囊中存在黑素干细胞(melanocyte stem cells,MSCs),后来的研究证实这一推测,并确定这种MSCs 起源于神经嵴,发育期间随机移行到毛囊.MSCs 位于隆突区内,在毛发生长期,产生大量的子代进入毛母质.MSCs 的不完全维持引起毛发灰化,pax3和Mitf 是调节MSCs 维持与分化之间平衡的关键分子.近年人们采用多种方法分离和培养MSCs,以期更好地构建含色素人工皮肤,拓展组织工程皮肤代用品的应用范围,提高色素脱失皮肤病的治疗水平.     

Determinants of melanocyte density in adult human skin

Abstract The distribution of melanocytes in human skin has been observed to vary within and among individuals, yet little is known of the factors that determine the density of these pigment cells. These factors were explored in a molecular epidemiological study conducted among a population-based sample of 97 male subjects aged over 50 years in Queensland, Australia. Information relating to environmental and phenotypic factors was collected through face-to-face interviews and physical examination of all participants. In addition, 2-mm biopsies of representative skin were taken from the dorsum of the hand and another anatomical site. Melanocytes were identified by cytoplasmic staining with the B8G3 (anti-TRP1) monoclonal antibody using standard immunohistochemical techniques. Melanocyte counts were performed blind by two observers. On crude analysis, melanocyte density decreased with advancing age (P = 0.0002), and increased with increasing number of naevi (P = 0.01). Other pigmentary characteristics (such as hair and eye colour and depth of tan) were not associated with epidermal melanocyte density. Melanocyte density varied significantly by anatomical site (P = 0.02), with highest densities observed on the back/shoulders (n = 50, 17.1 ± 8.8 cells/mm, mean ± SD) followed by the upper limbs (n = 11, 12.6 ± 8.8 cells/mm) and lower limbs (n = 14, 14.4 ± 5.9 cells/mm). Lowest melanocyte densities were recorded on the anterior trunk (n = 3, 3.2 ± 2.4 cells/mm). These findings confirm the results of earlier studies in which site-specific differences in melanocyte density have been found. We speculate that the unequal distribution of melanocytes may partially explain the site-specific incidence of melanoma, offering fresh perspectives on the aetiology of this cancer. Received: 21 January 1999 / Received after revision: 26 May 1999 / Accepted: 27 May 1999     

Urinary excretion of 5-S-cysteinyldopa in relation to skin type, UVB-induced erythema, and melanocyte proliferation in human skin

5-S-Cysteinyldopa (5-S-CD) is found in all pigment-producing cells and is the major precursor of phaeomelanin. However, the melanocyte specificity of the compound has been questioned. In order to elucidate the origin of 5-S-CD, we have now systematically studied the relationship between the 5-S-CD excretion in urine and the size of the melanocyte organ, UV-induced melanocyte proliferation, skin type, and the erythemal reaction. The skin type had no influence on the basal excretion of 5-S-CD. There was no significant correlation between the basal 5-S-CD excretion and the size of the melanocyte organ; that is, the number of skin melanocytes and nevi. During the irradiation, subjects with skin type II developed a more pronounced erythema (p less than 0.01) and had a significantly higher 5-S-CD excretion than those with skin type III-IV (p less than 0.01). No correlation was found between 5-S-CD excretion and UV-induced melanocyte proliferation. The lack of correlation between the basal 5-S-CD excretion and skin type or number of melanocytes suggests that the basal 5-S-CD in urine is mainly of extra-melanocytic origin. Our findings favor the view that the increase in 5-S-CD excretion during UV irradiation is due to UV damage.     

Fas and c-kit are involved in the control of hair follicle melanocyte apoptosis and migration in chemotherapy-induced hair loss

Chemotherapy alters the structure and function of hair follicle melanocytes. Molecular mechanisms controlling melanocyte responses during chemotherapy-induced hair loss, however, remain largely unknown. Using immunohistology and multicolor confocal microscopy, we show here that cyclophosphamide administration to C57BL/6 mice alters the activity and fate of hair follicle melanocytes. After 24-48 h, hair bulb melanocytes expressing Fas undergo apoptosis. The number of apoptotic follicular melanocytes is significantly reduced (p<0.01) in cyclophosphamide-treated Fas knockout mice compared to wild-type controls, suggesting that Fas signaling contributes to chemotherapy-induced melanocyte death. After 3-5 d, surviving hair bulb melanocytes express c-kit receptor, proliferate, and appear to migrate up the outer root sheath. Tyrosinase-positive and melanogenically active cells then appear in the epidermis. By Western blotting and immunohistochemistry, expression levels of the c-kit ligand, stem cell factor, in skin and epidermis are strongly increased after cyclophosphamide treatment. Cyclophosphamide-induced migration of the hair follicle melanocytes into epidermis is completely abrogated by administration of c-kit neutralizing antibody. These data suggest that chemotherapy induces a complex response in the hair follicle melanocytes, which includes apoptosis, proliferation, and migration. Pharmacologic manipulation of Fas and c-kit signaling pathways might be useful for the correction of skin hyperpigmentation as a side-effect of chemotherapy.     

Local and systemic effects on the epidermal melanocyte population in UV-irradiated mouse skin.

Local and systemic effects of repeated UVB irradiation on the epidermal melanocytes have been studied in the C57Bl mice. A daily dose of 0.1 joule/cm2 for 10 days induced a 4-fold increase in the epidermal melanocyte population of the irradiated right ear. During the first weeks after the irradiation period, there was a gradual increase in the number of melanocytes also in the shielded left ear, up to about 3 times the age control values. Thereafter, the population density slowly decreased in both ears, but it remained well above original values as late as 20 weeks after the irradiation. Thus, a short UVB irradiation period induces a long-lasting increase in the number of epidermal melanocytes in irradiated skin areas, as well as in covered skin regions. It is suggested that the population increase in the shielded ear is initiated by one or more systemic factors originating from the UVB irradiated skin. Such factors may be involved in the regulation of a balanced melanocyte population over the entrie body surface.     

不同黑素细胞群在有色毛囊重建中作用的研究

目的观察不同种属小鼠的毛囊细胞能否嵌合重建有色毛囊, 探讨不同黑素细胞群在小鼠有色毛囊重建中的作用。方法选取C57BL/6J、BALB/C胎鼠或乳鼠皮肤, 分离出表皮细胞群、毛囊上皮细胞群和真皮细胞群, 培养、纯化从表皮细胞群获得的表皮黑素细胞。实验包含三部分, ①乳鼠C57BL/6J毛囊重建实验:分为表皮细胞+毛囊上皮细胞组、真皮细胞组;②嵌合毛囊重建实验:分为乳鼠C57BL/6J真皮细胞组、乳鼠BALB/C真皮细胞组、乳鼠BALB/C真皮+乳鼠C57BL/6J真皮细胞组、胎鼠BALB/C真皮细胞+胎鼠C57BL/6J真皮细胞组;③有色毛囊重建实验:分为乳鼠BALB/C真皮细胞+乳鼠C57BL/6J表皮细胞组、乳鼠BALB/C真皮细胞+乳鼠C57BL/6J毛囊上皮细胞组、乳鼠BALB/C真皮细胞+培养的C57BL/6J表皮黑素细胞组。采用小室移植法将不同细胞接种于裸鼠的背部, 每组4只。于移植后4周和8周, 通过大体观察、组织学及免疫荧光评估毛囊重建情况。结果移植后4周和8周, 乳鼠C57BL/6J毛囊重建实验中(本部分实验2组共8只BALB/C裸鼠, 7只存活, 1只因创面感染死亡...     

The structure of human hair

The process of hair formation involves keratinization. Hair and its sheaths undergo keratinization at different speeds and with different modes. In the hair bulb, the matrix of hair and its follicle are composed of similar-looking immature cells, eg, they all contain a small number of wispy tonofilaments and weakly developed desmosomes. Except for their topographic location, there is no clue as to which cell layer they will eventually form. The cells that are located most centrally, just above the dermal papilla, most likely produce the medulla (Fig. 2-1). A large mass of immature cells located peripheral to the medullary matrix and above the shoulders of the dome-shaped dermal papilla are most likely the matrix cells of the future cortex. Further toward the periphery and down the slope of the dermal papilla are the matrix cells of the cuticle of the cortex, cuticle of the inner root sheath, and inner root sheath (Huxley and Henle). Outermost and close to the bottom of the dermal papilla are the matrix cells of the outer root sheath. As the matrix cells move toward the surface of the skin, more definitive alignment of each layer becomes apparent, the timetable of keratinization of each layer is set, and the matrix cells of each layer follow a distinct mode of keratinization.^1–3     

Tenascin is overexpressed in vitiligo lesional skin and inhibits melanocyte adhesion

The aetiology of vitiligo remains obscure. In this study, the role of integrins in the observed inability of melanocytes to repopulate lesional skin was investigated. Antibodies directed to α₂, α₃, α₅, α_v, α₆, β₁ and β₃ integrin subunits were used. Immunohistology revealed no marked differences in the overall levels of expression of integrins between control, non-lesional, perilesional or lesional skin. Moreover, no differences were noted in the level of expression of integrins or the adhesive capacity between cultured control cells derived from three separate donors and vitiligo-derived melanocytes from two donors. Rather, it was clearly observed that towards the lesion, vitiligo skin contains increasing amounts of tenascin in the basal membrane and papillary dermis in five patients employing T2H5 antihuman tenascin antibody. The anti-adhesive effect observed in vitro for this extracellular matrix molecule using normal melanocytes may contribute to loss of pigment cells in vitiligo or to ineffective repopulation of the lesions.