State Key Laboratory of Quality Research in Chinese Medicine, Macau University of Science and Technology, Macau, China.
Department of Applied Biology Chemical Technology, The Hong Kong Polytechnic University, Hong Kong SAR, China.
Phytomedicine. 2019 Jul;60:153008. doi: 10.1016/j.phymed.2019.153008. Epub 2019 Jul 1.
Melanogenesis is a physiological process of melanin production in response to UV exposure, which is modulated through multi-signaling pathways including cAMP/PKA, Wnt/β-catenin and MAPK signaling cascades.
HYPOTHESIS/PURPOSE: The present study aims to investigate the molecular mechanism of hyperpigmentation induced by Gynostemma pentaphyllum saponins.
STUDY DESIGN/METHODS: In this study, we investigated the melanogenic effects of triterpenoid saponins of Gynostemma pentaphyllum (GpS), a medicinal plant. Two mouse melanogenic cell lines B16 and B16F10 were employed for the current study.
The results showed that non-toxic doses of GpS markedly increased melanin formation in both B16 and B16F10 cells. Western blot analysis showed that GpS treatment significantly up-regulated the expression levels of the key melanogenic proteins, including tyrosinase (TYR), microphthalmia-associated transcription factor (MITF), TRP-1 and TRP-2 in a dose-dependent manner. The phospho-CREB, which is the downstream target of PKA is also elevated upon GpS treatment. We further observed that H89, a PKA inhibitor, attenuated the GpS induced tyrosinase activity, melanin content, the expression of phospho-CREB. In addition to the cAMP/PKA signaling pathway, GpS treatment also up-regulated the β-catenin of the Wnt signaling pathway which is involved in the transcriptional activation of MITF in melanogensis. We further demonstrated that treatment with GpS markedly enhance mRNA expression of MITF, along with the downstream target molecules, TYR, TRP-1 and TRP-2. Knock-down MITF with siMITF inhibited the expression of MITF mRNA by 63%, and the melanin content was reduced 70% in the siMITF-transfected cells compared to untransfected or scramble siRNA control cells.
These findings demonstrated strong melanogenic activities of GpS, and the MITF is essential for the melanogenesis stimulated by GpS.
黑色素生成是一种生理过程，即黑色素在受到紫外线照射时的产生，这一过程通过包括 cAMP/PKA、Wnt/β-catenin 和 MAPK 信号级联在内的多种信号通路进行调节。
假设/目的：本研究旨在探讨绞股蓝皂苷诱导皮肤色素沉着的分子机制。
研究设计/方法：在这项研究中，我们研究了药用植物绞股蓝中的三萜皂苷对黑色素生成的影响。本研究采用了两种小鼠黑色素细胞系 B16 和 B16F10。
结果表明，非毒性剂量的绞股蓝皂苷显著增加了 B16 和 B16F10 细胞中的黑色素形成。Western blot 分析表明，绞股蓝皂苷处理以剂量依赖性方式显著上调了关键黑色素生成蛋白的表达水平，包括酪氨酸酶（TYR）、小眼畸形相关转录因子（MITF）、TRP-1 和 TRP-2。PKA 的下游靶标磷酸化 CREB 的水平也随着绞股蓝皂苷处理而升高。我们进一步观察到，PKA 抑制剂 H89 减弱了绞股蓝皂苷诱导的酪氨酸酶活性、黑色素含量和磷酸化 CREB 的表达。除了 cAMP/PKA 信号通路外，绞股蓝皂苷处理还上调了 Wnt 信号通路中的β-catenin，该通路参与了黑色素生成过程中 MITF 的转录激活。我们进一步证明，绞股蓝皂苷处理显著增强了 MITF 的 mRNA 表达，以及下游靶分子 TYR、TRP-1 和 TRP-2。用 siMITF 敲低 MITF 后，未转染或转染 scramble siRNA 对照细胞中的 MITF mRNA 表达降低了 63%，黑色素含量降低了 70%。
这些发现表明绞股蓝皂苷具有很强的黑色素生成活性，MITF 是绞股蓝皂苷刺激黑色素生成所必需的。
