Functionally similar genes exhibit comparable/similar time-course expression kinetics in the UV-induced photoaged mouse model

Skin photoaging induced by ultraviolet (UV) irradiation contributes to the formation of thick and coarse wrinkles. Humans are exposed to UV light throughout their lives. Therefore, it is crucial to determine the time-sequential effects of UV on the skin. In this study, we irradiated the mouse back skin with UV light for eight weeks and observed the changes in gene expressions via microarray analysis every week. There were more downregulated genes (514) than upregulated genes (123). The downregulated genes had more functional diversity than the upregulated genes. Additionally, the number of downregulated genes did not increase in a time-dependent manner. Instead, time-dependent kinetic patterns were observed. Interestingly, each kinetic cluster harbored functionally enriched gene sets. Since collagen changes in the dermis are considered to be a major cause of photoaging, we hypothesized that other gene sets contributing to photoaging would exhibit kinetics similar to those of the collagen-regulatory genes identified in this study. Accordingly, co-expression network analysis was conducted using 11 well-known collagen-regulatory seed genes to predict genes with similar kinetics. We ranked all downregulated genes from 1 to 504 based on their expression levels, and the top 50 genes were suggested to be involved in the photoaging process. Additionally, to validate and support our identified top 50 gene lists, we demonstrated that the genes (FN1, CCDC80, PRELP, and TGFBR3) we discovered are downregulated by UV irradiation in cultured human fibroblasts, leading to decreased collagen levels, which is indicative of photoaging processes. Overall, this study demonstrated the time-sequential genetic changes in chronically UV-irradiated skin and proposed 50 genes that are involved in the mechanisms of photoaging.

Melia azedarach extract stimulates melanogenesis through increase of tyrosinase-related protein 1 expression in B16F10 mouse melanoma cells

Melia azedarach (MA) has been used in folk medicine in Asia for the treatment of several diseases. Several constituents from MA possess anti-herpetic, anti-angiogenic and anticancer properties. The aim of the present study was to investigate the effect of a 70% ethanol extract of MA on melanogenesis and the underlying mechanisms involved. A B16F10 mouse melanoma cell line was used in our experiments. Treatment of B16F10 cells with the MA extract (10, 20 and 40 µg/ml) increased melanin content in a concentration-dependent manner without cytotoxicity at 24 h. Further experiments indicated that the MA extract (20 µg/ml) increased melanin content as early as at 4 h after treatment. Additionally, although the MA extract did not affect intracellular tyrosinase activity and the protein levels of tyrosinase and tyrosinase-related protein-2 (TRP-2) at 2 and 4 h after treatment, the MA extract increased TRP-1 protein expression at both time points. However, no significant effect of the MA extract treatment on TRP-1 mRNA level at the time points measured was observed. In conclusion, the results from the present study demonstrate that the MA extract increases melanogenesis through the upregulation of TRP-1 protein expression by post-transcriptional control in B16F10 cells and suggest that the MA extract can be viewed as a rapid inducer of melanogenesis, thus rendering it a potential treatment for hypopigmentation diseases including vitiligo.

Ardisia crenata extract stimulates melanogenesis in B16F10 melanoma cells through inhibiting ERK1/2 and Akt activation

Melanin protects the skin against ultraviolet radiation by scattering incoming light and absorbing diverse free radicals. Agents that increase melanin synthesis in melanocytes may reduce the risk of photodamage and skin cancer. The present study investigated the effect of a methanol extract of Ardisia crenata (AC) on melanogenesis in B16F10 cells. Treatment of cultured B16F10 cells with AC extract (10, 20 and 40 µg/ml) stimulated an increase in melanin levels in a concentration-dependent manner, without cytotoxicity. Tyrosinase is key in the regulation of melanin production, thus the effect of AC extract on tyrosinase activity and protein expression was analyzed. AC extract was observed to significantly increase tyrosinase activity and protein expression in B16F10 cells. Furthermore, AC extract was found to markedly increase the protein expression of microphthalmia-associated transcription factor, which is an important transcription factor involved in tyrosinase gene expression. In addition, AC extract (40 µg/ml) was observed to suppress the activation of extracellular signal-regulated kinase (ERK) and Akt, which negatively regulate melanin synthesis in B16F10 cells. In conclusion, to the best of our knowledge, the present study is the first to show that a methanol extract of AC stimulates melanogenesis by increasing tyrosinase expression via the inhibition of ERK and Akt. Thus, methanol extract of AC may be a potential treatment for hypopigmentation diseases and may be a candidate for skin-tanning cosmetic products.

[6]-Shogaol inhibits melanogenesis in B16 mouse melanoma cells through activation of the ERK pathway

AIM

To investigate the effect of [6]-shogaol, an active ingredient in ginger, on melanogenesis and the underlying mechanisms.

METHODS

B16F10 mouse melanoma cells were tested. Cell viability was determined with the MTT assay. Melanin content and tyrosinase activity were analyzed with a spectrophotometer. The protein expression of tyrosinase and microphthalmia associated transcription factor (MITF), as well as phosphorylated or total ERK1/2 and Akt were measured using Western blot.

RESULTS

Treatment of the cells with [6]-shogaol (1, 5, 10 μmol/L) reduced the melanin content in a concentration-dependent manner. [6]-Shogaol (5 and 10 μmol/L) significantly decreased the intracellular tyrosinase activity, and markedly suppressed the expression levels of tyrosinase and MITF proteins in the cells. Furthermore, [6]-shogaol (10 μmol/L) activated ERK, which was known to negatively regulate melanin synthesis in these cells. Pretreatment with the specific ERK pathway inhibitor PD98059 (20 μmol/L) greatly attenuated the inhibition of melanin synthesis by [6]-shogaol (10 μmol/L).

CONCLUSION

The results demonstrate that [6]-shogaol inhibits melanogenesis in B16F10 mouse melanoma cells via activating the ERK pathway.