Modulation of microphthalmia-associated transcription factor gene expression alters skin pigmentation

The microphthalmia-associated transcription factor is implicated in melanocyte development and in the regulation of melanogenesis. Microphthalmia-associated transcription factor is thought to bind to the M-box promoter elements of tyrosinase, tyrosinase-related protein-1 and dopachrome tautomerase/tyrosinase-related protein-2 and transactivate these genes, resulting in increased pigmentation. Using a luciferase reporter construct driven by the microphthalmia-associated transcription factor promoter, we identified agents that modulate microphthalmia-associated transcription factor promoter activity. Changes in endogenous microphthalmia-associated transcription factor expression levels upon treatment with these agents were confirmed using northern and western blots, and their pigmentary modulating activities were demonstrated. Ultraviolet B irradiation and traditional Chinese medicine-1, a natural extract used in traditional Chinese medicine, upregulated microphthalmia-associated transcription factor gene expression and enhanced tyrosinase activity in vitro. Dihydrolipoic acid, lipoic acid, and resveratrol reduced microphthalmia-associated transcription factor and tyrosinase promoter activities. These agents also inhibited the forskolin- and ultraviolet B-stimulated promoter activities of these genes and significantly reduced tyrosinase activity in melanocyte cultures, resulting in depigmentation. Overexpressed microphthalmia-associated transcription factor was capable of rescuing the repressive effects of these compounds on the cotransfected tyrosinase promoter. Dark-skinned Yucatan swine treated with these agents showed visible skin lightening, which was confirmed histologically, whereas ultraviolet B-induced tanning of light-skinned swine was inhibited using these agents. Our findings suggest that modulation of microphthalmia-associated transcription factor expression can alter skin pigmentation and further confirm the central role of microphthalmia-associated transcription factor in melanogenesis.

Soymilk reduces hair growth and hair follicle dimensions

We have recently shown that soybean-derived serine protease inhibitors and soybean extracts alter skin pigmentation, suggesting that soymilk could be used as a natural alternative to skin lightening. The present studies were initiated to examine the possible effect of STI, BBI and soymilk on hair pigmentation. Interestingly, these agents were found to affect not only hair pigmentation, but also the rate of hair growth, the dimensions of the hair follicle and hair shaft, and the appearance of the hair. The studies presented here provide first evidence, at the morphological and histological level, that soymilk and the soybean-derived serine protease inhibitors could be used as effective agents for hair care and management. These agents could reduce the rate of hair growth, decrease hair shaft dimensions and alter the pattern of melanogenic gene expression.

Protease-activated receptor 2, a receptor involved in melanosome transfer, is upregulated in human skin by ultraviolet irradiation

Previous studies have shown that the protease-activated receptor 2 is involved in skin pigmentation through increased phagocytosis of melanosomes by keratinocytes. Ultraviolet irradiation is a potent stimulus for melanosome transfer. We show that protease-activated receptor 2 expression in human skin is upregulated by ultraviolet irradiation. Subjects with skin type I, II, or III were exposed to two or three minimal erythema doses of irradiation from a solar simulator. Biopsies were taken from nonexposed and irradiated skin 24 and 96 h after irradiation and protease-activated receptor 2 expression was detected using immunohistochemical staining. In nonirradiated skin, protease-activated receptor 2 expression was confined to keratinocytes in the lower one-third of the epidermis. After ultraviolet irradiation protease-activated receptor 2 expression was observed in keratinocytes in the upper two-thirds of the epidermis or the entire epidermis at both time points studied. Subjects with skin type I showed delayed upregulation of protease-activated receptor 2 expression, however, compared with subjects with skin types II and III. Irradiated cultured human keratinocytes showed upregulation in protease-activated receptor 2 expression as determined by immunofluorescence microscopy and Western blotting. Cell culture supernatants from irradiated keratinocytes also exhibited a dose-dependent increase in protease-activated receptor-2 cleavage activity. These results suggest an important role for protease-activated receptor-2 in pigmentation in vivo. Differences in protease-activated receptor 2 regulation in type I skin compared with skin types II and III suggest a potential mechanism for differences in tanning in subjects with different skin types.

The protease-activated receptor-2 upregulates keratinocyte phagocytosis

The protease-activated receptor-2 (PAR-2) belongs to the family of seven transmembrane domain receptors, which are activated by the specific enzymatic cleavage of their extracellular amino termini. Synthetic peptides corresponding to the tethered ligand domain (SLIGRL in mouse, SLIGKV in human) can activate PAR-2 without the need for receptor cleavage. PAR-2 activation is involved in cell growth, differentiation and inflammatory processes, and was shown to affect melanin and melanosome ingestion by human keratinocytes. Data presented here suggest that PAR-2 activation may regulate human keratinocyte phagocytosis. PAR-2 activation by trypsin, SLIGRL or SLIGKV increased the ability of keratinocytes to ingest fluorescently labeled microspheres or E. coli K-12 bioparticles. This PAR-2 mediated increase in keratinocyte phagocytic capability correlated with an increase in actin polymerization and *-actinin reorganization, cell surface morphological changes and increased soluble protease activity. Moreover, addition of serine protease inhibitors downmodulated both the constitutive and the PAR-2 mediated increases in phagocytosis, suggesting that serine proteases mediate this functional activity in keratinocytes. PAR-2 involvement in keratinocyte phagocytosis is a novel function for this receptor.