Degree of Ultraviolet-Induced Tortuosity of Elastic Fibers in Rat Skin Is Age Dependent

To elucidate differential effects of ultraviolet (UV) exposure on three-dimensional networks of elastic fibers during maturation of rat skin, Sprague-Dawley rat hind limbs were irradiated with suberythemal doses of UV light (UVB, 130 mJ/cm2, or UVA, 27 J/cm2) in three different time courses of exposure: 3–9 weeks old, 9–15 weeks old, and 3–15 weeks old. Three-dimensional arrangement with special reference to linearity of elastic fibers was quantified by image analysis using a scanning electron microscope after a combination of intravascular resin injection and selective digestion technique using formic acid. Among the three irradiation groups, the group irradiated with UVB or UVA between 3 and 15 weeks old (UVB, three times per week; UVA, five times per week) elicited the most marked decrease in the linearity of elastic fibers. Despite the same irradiation period, there was a significant difference in the decreased linearity between the two irradiation groups of 3–9 and 9–15 weeks old, with the former irradiation group exhibiting greater loss of linearity than the latter irradiation group. The magnitude of the decreased linearity was greater in the UVB-exposed groups than in the UVA-exposed group. These findings indicate that the three-dimensional linearity of elastic fibers is more susceptible to disruption by UV exposures during the growth period than that after the growth period

Epostatic connections between microphthalmia-associated trancecription factor and endothelin signaling in Waardenburg syndrome and other pigmentary disorders

Division of Stem Cell Medicin

Melanocyte Activation Mechanisms and Rational Therapeutic Treatments of Solar Lentigos

To characterize the pathobiology of solar lentigos (SLs), analyses by semiquantitative RT-PCR, Western blotting, and immunohistochemistry revealed the upregulated expression of endothelin (EDN)-1/endothelin B receptors (EDNBRs), stem cell factor (SCF)/c-KIT, and tumor necrosis factor (TNF)α in the lesional epidermis, which contrasted with the downregulated expression of interleukin (IL) 1α. These findings strongly support the hypothesis that previous repeated UVB exposure triggers keratinocytes to continuously produce TNFα. TNFα then stimulates the secretion of EDNs and the production of SCF in an autocrine fashion, leading to the continuous melanogenic activation of neighboring melanocytes, which causes SLs. A clinical study of 36 patients with SLs for six months treated with an M. Chamomilla extract with a potent ability to abrogate the EDN1-induced increase in DNA synthesis and melanization of human melanocytes in culture revealed a significant improvement in pigment scores and color differences expressed as L values. Another clinical study using a tyrosinase inhibitor L-ascorbate-2-phosphate 3 Na (ASP) demonstrated that L values of test lotion (6% APS)-treated skin significantly increased in SLs and in non-lesional skin with a significantly higher ΔL value in SLs when compared with non-lesional skin. The sum of these findings strongly suggests that combined topical treatment with EDN signaling blockers and tyrosinase inhibitors is a desirable therapeutic choice for SLs

Functional Analysis of Tyrosinase Isozymes of Cultured Malignant Melanoma Cells During the Recovery Period Following Interrupted Melanogenesis Induced by Glycosylation Inhibitors

Multiple forms of tyrosinase, T1, T2, T3, have been shown to differ with respect to carbohydrate moieties of these isozymes. We demonstrated that, in cultured B-16 melanoma cells, melanization can be completely interrupted by glycosylation inhibitors, such as glucosamine and tunicamycin, and that these inhibitors cause a selective loss of membrane-bound T3. It is further found that inhibition of melanization induced by glucosamine occurs even in the presence of protease inhibitors, such as phenylmethylsulfonyl fluoride and leupeptin, and that melanization inhibition is reversible upon removal of the inhibitor. In this report we have also examined the process of development and recovery of the tyrosinase isozymes in cells in which the interruption of melanogenesis has been released by the removal of these glycosylation inhibitors. The recovery process, which occurs during the period after interrupted melanogenesis and is a process of remelanization, has been biochemically followed. Tyrosinases obtained from the deoxycholate-solubilized large-granule fraction of these melanoma cells have been analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Immediately after removal (0 h recovery) of the glycosylation inhibitor, loss of melanization and T3 is accompanied by T1 heterogeneity which is visualized as two electrophoretically distinct species, T1' and T1″. At this time, T1' and T1″ do not have a concanavalin A affinitive carbohydrate moiety but do possess in vitro dopa reactivity. When recovery of melanization begins visibly 24 h later, T3 is reformed with disappearance of T1 heterogeneity. By 48 h, the previous normal level of melanization is almost attained

Biological Mechanisms Underlying the Ultraviolet Radiation-Induced Formation of Skin Wrinkling and Sagging I: Reduced Skin Elasticity, Highly Associated with Enhanced Dermal Elastase Activity, Triggers Wrinkling and Sagging

The repetitive exposure of skin to ultraviolet B (UVB) preferentially elicits wrinkling while ultraviolet A (UVA) predominantly elicits sagging. In chronically UVB or UVA-exposed rat skin there is a similar tortuous deformation of elastic fibers together with decreased skin elasticity, whose magnitudes are greater in UVB-exposed skin than in UVA-exposed skin. Comparison of skin elasticity with the activity of matrix metalloproteinases (MMPs) in the dermis of ovariectomized rats after UVB or UVA irradiation demonstrates that skin elasticity is more significantly decreased in ovariectomized rats than in sham-operated rats, which is accompanied by a reciprocal increase in elastase activity but not in the activities of collagenases I or IV. Clinical studies using animal skin and human facial skin demonstrated that topical treatment with a specific inhibitor or an inhibitory extract of skin fibroblast-derived elastase distinctly attenuates UVB and sunlight-induced formation of wrinkling. Our results strongly indicated that the upregulated activity of skin fibroblast-derived elastase plays a pivotal role in wrinkling and/or sagging of the skin via the impairment of elastic fiber configuration and the subsequent loss of skin elasticity