C22-Ceramide Derived from Marine Microalgae Emiliania huxleyi Induces Melanosomal Autophagy via JNK/c-Jun Signaling Pathway in Mouse B16 Melanoma Cells

Melanosomes are specialized membrane-bound organelles within which melanin is synthesized and stored. The levels of melanin can be effectively reduced by inhibiting melanin synthesis or promoting melanosome degradation via autophagy. Ceramide, a central molecule in sphingolipid metabolism, has been widely implicated in the regulation of autophagy. Few researchers have addressed the potential effects of ceramide analogs on suppressing melanin synthesis. However, whether ceramide can induce melanosome autophagy and the potential autophagy-dependent mechanism underlying this phenomenon remain unknown. Here, an active compound from the marine microalgae Emiliania huxleyi extract was firstly isolated and identified as a long-chain C22-ceramide (C22-Cer). In vitro results of mouse B16 melanoma cell experiments showed that treatment with 2-5 mu mol/L C22-Cer significantly suppressed the increase of alpha-MSH-induced melanin levels and tyrosinase activity without cytotoxicity. C22-Cer induced typical hallmarks of autophagy such as accumulation of autophagosomes, enhanced autophagic flux and microtubule-associated protein light chain 3, LC3-II expression, and p62 degradation through activating c-Jun N-terminal kinase (JNK) directly. Furthermore, C22-Cer activated JNK-Bcl-2 signaling, dissociated the Beclin1/Bcl-2 complex, and induced melanosome autophagy without affecting the expression of MITF. Besides, the Ca2+ influx induced by treatment with C22-Cer further increased the substantial accumulation of autophagosomes. Together, we found a novel marine-derived compound, C22-Cer, targeting JNK pathway and Ca2+ signaling to induce melanosome autophagy and suppress melanin accumulation in B16 cells. This study implicates that C22-Cer might be a potential therapeutic mediator against skin pigmentation in mammals.