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The present study was investigated that astaxanthin improves stem cell potency via an increase in the proliferation of neural progenitor cells (NPCs). Treatment of astaxanthin (1, 5, and 10 ng/ml) for 3 days significantly increased the proliferation of NPCs. Especially, 10 ng/ml astaxanthin applied for 3 days showed the highest proliferation of NPCs. A clonogenic (CFU) assay was also performed to estimate the proliferation efficiency of the astaxanthin-treated NPCs. In CFU assay, 10 ng/ml astaxanthin-treated NPCs had an approximately 2-fold increase in colony formation. To identify the possible activated signaling molecules involved in active cell proliferation occurring after astaxanthin treatment, the total protein levels of several proliferation-related proteins and expression levels of proliferation-related transcription factors were assessed in NPCs by Western blot analysis and RT-PCR. In Western blot analysis, astaxanthin induced significant activation of PI3K and its downstream mediators, p-Rac, p-c-Raf, p-MEK, p-ERK, p-Akt, p-mTOR, and p-Stat3 in a time dependent manner. The results of RT-PCR analysis showed upregulation of proliferation-related transcription factors (Rex1, CDK1, and CDK2) and stemness genes (OCT4, SOX2, Nanog, and KLF4). To estimate the relevance of PI3K and MEK signaling
pathways in cell growth of astaxanthin–treated NPCs, inhibition assays were performed with LY294002 (10 mM, a specific inhibitor of PI3K) and PD98059 (10 mM, a specific inhibitor of MEK). These results clearly showed that astaxanthin induces the proliferation of NPCs via the activation of PI3K and MEK signaling pathways and improves stem cell potency via stemness acting signals, including OCT4, SOX2, Nanog, and KLF4.