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  • 1
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 140-142 (Oct. 1993), p. 641-658 
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    International journal of cosmetic science 27 (2005), S. 0 
    ISSN: 1468-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The biological effects of hormones on human melanocytes are still being investigated. Several kinds of hormones have mitogenic and/or melanogenic effects on human melanocytes. For example, melanotropic hormones, such as α-melanocyte-stimulating hormone (α-MSH) and adrenocorticotrophic hormone (ACTH), were shown to induce skin darkening some time ago, and more recently, the mechanism of up-regulation of tyrosinase activity in human normal melanocytes by melanotropins through the cyclic AMP (cAMP) signaling pathway has been reported. cAMP is now recognized to play a key role in the regulation of skin pigmentation. α-MSH is known to elevate intracellular cAMP levels through the melanocortin 1 receptor (MC1R) and this plays a critical role in the regulation of melanogenesis. Recently it has been recognized that cAMP elevating agents up-regulate transcription of the MITF gene that in turn stimulates expression of the tyrosinase gene via MITF binding to its M-box.Solar lentigo is a benign pigmented spot on sun-exposed skin especially on the back of the hands, arms and on the forehead. We have compared melanogenesis histological parameters in solar lentigo and in normal skin of Japanese women. We chose to analyze melanin distribution and expression of α-MSH as mediators of human pigmentation, in solar lentigo and normal skin biopsies of photo-exposed dorsal forearm. Punch biopsies were fixed with 4% formaldehyde and sections were stained with Fontana-Masson technique to evaluate melanin distribution. Immunohistochemistry was carried out to demonstrate α-MSH protein expression using rabbit polyclonal antibody anti-human α-MSH. Melanin distribution and relative expression of α-MSH were analyzed and quantified using semiquantitative computer-assisted image analysis. With this technique, we found that solar lentigo skin possessed 60% more α-MSH expression than normal skin (〈link href="#f1-11"〉Fig. 1).〈figure xml:id="f1-11"〉1〈mediaResource alt="image" href="urn:x-wiley:01425463:ICS254_11_11:ICS_254_f1-11"/〉Quantification of alpha MSH expression in solar lentigo and normal skin for 10 japanese subjects. Immunolocalization of alpha MSH in solar lentigo and normal skin. (a) Representative image of alpha MSH expression in solar lentigo. (b) Representative image of alpha MSH expression in normal skin. Alpha MSH expression was determined from the integrated intensity given areas of epidermis reported to the total surface of epidermis in each section. Four selected areas of each section were photographed and quantified. Statistical differences were evaluated using the paired Student's t-test. Data are presented as the mean of 10 biopsies.While it has been reported that human skin color is changed by castration or by injection of androgen and a recent in vitro study in contrast suggested that testosterone might reduce tyrosinase activities in human melanocytes through the decrease of the mRNA expression of MC1R, the precise mechanism involved in the regulation of skin pigmentation by androgens has remained unclear. To date, there have been few reports about the effects of androgens on human melanocytes. In a previous study, we demonstrated that human genital melanocytes are androgen target cells. Those melanocytes had androgen receptors (ARs) in their nuclei as detected by immunohistochemistry and they also had high levels of 5α -reductase activities, the enzyme that converts testosterone to its more active form, 5α-dihydrotestosterone (DHT). R1881 (methyltrienolone, a potent synthetic androgen) stimulated tyrosinase activity when melanocytes were cultured continuously with TPA, hydrocortisone and BPE and then were treated with FBS [1]. When melanocytes were deprived of FBS and BPE for a prolonged time, the effects of androgen on tyrosinase activity were reduced. Furthermore, when cultured without FBS, BPE or TPA, prolonged exposure to R1881 down-regulated tyrosinase activity when added together with FBS and BPE. These data suggest that FBS or BPE contain elements that inhibit tyrosinase activity when contacting melanocytes even if only briefly [2].Recent advances in the understanding of androgen signaling indicate the specific membrane-signaling pathway involved in Sex hormone-binding globulin (SHBG) as well as in the androgen-AR mechanism, a classical pathway. SHBG is a glycoprotein found in human plasma that possesses a high affinity for binding of sex hormones. It has been recognized that unbound, free steroids function on target cells through their intracellular receptors. Recently, it has been speculated that SHBG participates in steroid signaling pathways by binding to SHBG-receptors (RSHBG) located on the target cell membranes. SHBG that is bound to a steroid cannot bind to its receptor, but free SHBG that first binds to the RSHBG can subsequently bind steroids. Several studies on human tissues and cultured cells, such as prostate and breast cancer cells, have revealed that the SHGB–RSHBG complex is involved in the steroid-activated signal transduction pathway that results in the accumulation of intracellular cAMP. SHBG–RSHBG complexes on the cell membrane combine with some types of sex hormones and then induce the accumulation of intracellular cAMP in those tissues and cells. Further, some steroids antagonize the activation of SHBG–RSHBG induced by other steroids. FBS contains high endogenous levels of SHBG, which can confuse the study of steroid effects. We formed the hypothesis that androgen function in melanocytes is effected through the cell membrane signaling pathway via the SHBG–RSHBG complex. Immunohistochemistry was used to demonstrate the co-staining of SHBG and testosterone with specific monoclonal antibodies. There was a dramatic increase in positive staining following SHBG pre-treatment. Generally, staining for testosterone is much stronger when staining for SHBG is stronger. These immunohistochemical results strongly suggest the existence of the RSHBG on the surface of normal human melanocytes.The responses of intracellular levels of cAMP to various androgens and hydrocortisone were studied. After the saturation of RSHBG on the cell membranes by SHBG and then washing to remove excess SHBG, a decrease in intracellular cAMP levels within 30 min of incubation with testosterone was observed in a dose-dependent manner, but not in the absence of SHBG pre-treatment. Those findings suggest the possibility that normal human melanocytes might utilize the cell membrane transduction pathway of androgen via the SHBG–RSHBG complex to regulate intracellular cAMP. They further suggest that strong androgens, such as testosterone and DHT, might act as antagonists in this pathway. We have already reported that human melanocytes possess significant levels of 5α -reductase activities and that testosterone is predominantly metabolized to DHT, a stronger androgen. DHT might work as a negative feedback factor against cAMP accumulation via the SHBG–RSHBG complex, since the affinity of DHT to SHBG is higher than that of testosterone.Tyrosinase activity was decreased by the physiological concentration of testosterone after 4 days of treatment. As the decreases in tyrosinase activity coincided with decreases of intracellular cAMP, those intracellular cAMP levels (regulated through cell membrane signaling) might regulate tyrosinase activity influenced by androgens after treatment with SHBG. Tyrosinase activity was stimulated by R1881 when the melanocytes were cultured continuously in medium containing FBS and hydrocortisone. FBS and hydrocortisone that are endogenous in the medium might work against the effect of strong androgens that may be antagonists in the cell membrane signaling pathway, because high concentrations of unbound SHBG found in FBS can easily bind to the cell surface and high concentrations of hydrocortisone added to the culture medium might have already occupied the SHBG–RSHBG complex on the cell membrane.Further, we studied the expression of tyrosinase mRNA
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    International journal of cosmetic science 27 (2005), S. 0 
    ISSN: 1468-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The extent of changes with aging depends largely on how much the skin is exposed to sunlight and also on the genetic disposition of the individual. There are thus two main processes, extrinsic aging because of environmental stress, and intrinsic genetically programmed aging [1]. Hence, the processes of aging depends on a person's ethnic origin and the part of the world in which they live.〈section xml:id="abs1-1"〉〈title type="main"〉MethodsThe present study investigates the influence of age and exposure to sunlight on the facial skin of 31 healthy Japanese women, aged 20–78 years old, living in Osaka city. Skin samples were obtained during plastic surgery from the face, from areas exposed to varying intensities of sunlight (forehead, cheek, nose, upper eyelid). Samples were fixed in formalin and embedded in paraffin. Sections (5–7 μm) were cut and stained with hematoxylin–phloxyn–safran, orcein or Masson's trichrome. Others were immunostained for p63, β1-integrin, type IV collagen CD1a and AQP3. Statistical analysis of quantitative and qualitative parameters were performed by analysis of variance (anova) with linear regressions, and the chi-squared test.〈section xml:id="abs1-2"〉〈title type="main"〉Results and discussion〈section xml:id="abs1-3"〉〈title type="main"〉Epidermis and dermal-epidermal junction: histological organizationWe confirmed that the whole living epidermis becomes thinner with increasing age, with an average decrease of about 5 μm per decade. This thinning is mainly because of a significant reduction in the number of keratinocyte layers. The thinning of the epidermis and the reduction of the keratinocytes layers in Japanese skin do not seem to be reflected in the thickness of the stratum corneum, which appears to remain constant whatever the age in the sample studied.The epidermal papillary structures also became flatter with age, associated with an increase in the thickness of the dermal–epidermal junction (DEJ). Thus, in addition to the loss of epidermal cells, the epidermis and dermis become less overlapped, so reducing the surface area for exchange between the two compartments. The DEJ also become thicker as Japanese ages and the expression of type IV collagen, the main constituent of the lamina densa and anchoring plaques is reduced in the most photoexposed skin areas. This accounts for the major changes in the function and molecular structure of DEJ components, as in aged Caucasian skin [2].〈section xml:id="abs1-4"〉〈title type="main"〉Keratinocyte growth and differentiation –β1-integrin and p63There is no doubt that the rate of cell turnover decreases in the flat aged epidermis, as indicated by the smaller number of proliferative cells [3, 4]. This study focused on two key regulatory proteins. One was p63, that is involved in maintaining the proliferative potential of basal keratinocytes and blocking their calcium-induced differentiation [5]. The other was β1-integrin, an adhesion protein present in basal keratinocytes and linked to their clonogenic potential [6].We found p63-positive cells in the basal layer of the epidermis and in the suprabasal layers (〈link href="#f1-7"〉Fig. 1a), in agreement with others [7]. The used pan anti-p63 antibody suggest that other isoforms of the protein in addition to the major ΔNp63α mainly expressed in the basal cells, could take part to other functions like differentiation in the suprabasal layers [5]. The great interindividual variation in the staining intensity for p63 in the samples studied made it impossible to detect significant changes in the number of p63-positive cells with age. Only an increase of p63 was observed in photoexposed areas compared to others within this case, a possible relation to the epidermal thickening.〈figure xml:id="f1-7"〉1〈mediaResource alt="image" href="urn:x-wiley:01425463:ICS254_7_7:ICS_254_f1-7"/〉Immunostaining of Japanese facial skin showing AQP3 expression at the plasma membrane of keratinocytes throughout the living epidermis (a) and the age-related change in AQP3 (b).β1-integrin was detected only in the basal keratinocytes, and the staining intensity varied from one segment of the basal layer to another. We evaluated the length of immune-labeled epidermis and the intensity of labeling in each fragment, using an arbitrary colorimetric scale (0–5). We observed a significant decrease in the intermediate intensities (equal to 2 only) with age in the zone least exposed to sunlight. This is consistent with the loss of adhesive properties of freshly isolated epidermal cells in aged skin [2] and the existence of different pools of basal keratinocytes [6]. It suggests that the effect of aging could affect particularly on the transit amplifying cells containing intermediate quantities of β1-integrin.〈section xml:id="abs1-5"〉〈title type="main"〉Osmotic and water homeostasis – aquaporin-3In addition to the stratum corneum (SC) that limits transepidermal water loss, the osmotic equilibrium inside the epidermis and hydration is controlled by the aquaglyceroporins 3 (AQP3) [8, 9]. Immunostaining for AQP-3 confirmed the presence of the protein in the plasma membranes of keratinocytes throughout the epidermis, together with AQP-3 cytoplasmic expression of the basal layer cells (〈link href="#f1-7"〉Fig. 1a). There was no immunostaining in the SC (〈link href="#f1-7"〉Fig. 1a) to retain water in the epidermis via the tight junction proteins [10], so maintaining the water-lipid barrier within the SC. The immunostaining for AQP3 decreased significantly with the skin age (〈link href="#f1-7"〉Fig. 1b), but there was no significant difference between areas exposed to sunlight and those not exposed. This suggests that there is an overall reduction in the natural hydration potential as Japanese facial epidermis ages.〈section xml:id="abs1-6"〉〈title type="main"〉The immune system – epidermal CD1a-positive cellsEpidermal dendritic cells, mainly Langerhans cells, control the skin immune system. These cells are CD1a positive (CD1a+). Immunostaining showed a major population of highly dendritic cells throughout the epidermis of all the Japanese skin samples. It also showed that the areas most exposed to sunlight (cheeks, forehead and nose) had significantly more CD1a+ cells than less exposed areas (upper eyelid) (〈link href="#f2-7"〉Fig. 2a). This confirms previous findings on the wrinkling of area of Caucasian facial skin after chronic exposure to UV light [11]. The number of CD1a+ cells in less exposed areas of skin increased significantly with donor age (〈link href="#f2-7"〉Fig. 2b). This shows that chronological aging and exposure to sunlight give rise to an epidermis which cellular immune homeostasis is perturbed.〈figure xml:id="f2-7"〉2〈mediaResource alt="image" href="urn:x-wiley:01425463:ICS254_7_7:ICS_254_f2-7"/〉Immunostaining for CD1a in Japanese facial skin: numbers of CD1a-positive (CD1a+) epidermal cells per mm of dermal–epidermal junction (DEJ) in skin exposed to sunlight and skin from protected areas (a), and sun-protected area of facial skin from subjects of different ages (b).〈section xml:id="abs1-7"〉〈title type="main"〉The pigmentation system – melanocytes and melanin depositsPigmentation is part of the protective system developed by the skin epidermis, but unwanted pigmentation is one of the first signs of aging and has a major social impact. The pigmentation of the facial skin of Japanese women increases with age, and spots develop, particularly on the cheeks [12]. We found a significantly greater density of melanocytes in the epidermis of older donors in both sun-exposed and protected areas. But there were significantly fewer melanocytes in the areas exposed to sunlight than in protected areas. As expected, there were greater deposits of melanin in keratinocytes in the regions exposed to sunlight. This suggests that older donors had a pool of highly active melanocytes in areas of skin exposed to sunlight, with a high rate of melanin transfer to keratinocytes and/or reduced keratinoc
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Archives of Biochemistry and Biophysics 260 (1988), S. 153-160 
    ISSN: 0003-9861
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Archives of Biochemistry and Biophysics 260 (1988), S. 146-152 
    ISSN: 0003-9861
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0375-9474
    Keywords: Nuclear reactions
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2946-2948 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate optical response from a side-injection light-controlled bistable laser diode buried with semi-insulating InP using hydride vapor phase epitaxy. The buried surface around both the 〈110〉 and 〈−110〉 oriented mesas is flat. The bistable operation is obtained by applying control voltage to the saturable absorption region. After optimization of the device parameters, we obtained error-free operation at a bit rate as high as 2.5 Gbit/s. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Crystal Growth 130 (1993), S. 21-28 
    ISSN: 0022-0248
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Crystal Growth 130 (1993), S. 29-36 
    ISSN: 0022-0248
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0022-2313
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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