Morus alba L. root decreases melanin synthesis via sphingosine-1-phosphate signaling in B16F10 cells

Morus alba L. has long been used for beauty in many Asian countries and regions, including anti-aging and hyperpigmentation.This study aimed at the inhibitory effect of Morus alba L. root on melanogenesis in B16F10 melanoma cells and the mechanism involved.This study evaluated the anti-melanogenic effect of Morus alba L. root extract (MAR) on B16F10 melanoma cells by assessing cell viability, melanin accumulation, cellular tyrosinase activity, intra/inter-cellular S1P levels, cellular S1P-related metabolic enzyme activity, and western blot analysis. In addition, the potential S1P lyase (S1PL) inhibitory constituents in MAR were identified by LC-MS/MS.Without affecting the viability of B16F10 melanoma cells, MAR inhibited intracellular tyrosinase activity in a dose-dependent manner, thereby reducing the accumulation of melanin. MAR also downregulated the expression level of MITF via activating the ERK signaling pathway. Furthermore, MAR increased the intra/inter-cellular S1P by inhibiting S1PL. Several compounds with inhibitory S1PL activity have been identified in MAR, such as mulberroside A and oxyresveratrol.The anti-melanogenic effects of MAR mainly involve promoting MITF degradation mediated via S1P-S1PR3-ERK signaling through increasing cellular S1P levels by inhibiting S1PL activity.