title: Neurotrophic action of 5-hydroxylated polymethoxyflavones: 5-demethylnobiletin and gardenin A stimulate neuritogenesis in PC12 cells.
abstract: Polymethoxyflavones (PMFs) exhibit a broad spectrum of biological properties, including anticancer, antiatherogenic, and neuroprotective effects. The aim of this study is to investigate the neurotrophic effects of 5-demethylnobiletin, a hydroxylated PMF found in citrus plants, and gardenin A, a synthetic PMF analogue, on neurite outgrowth and neuronal differentiation in PC12 cells. The results of this study showed that 5-demethylnobiletin and gardenin A (10-20 μM) potently induce neurite outgrowth in PC12 cells, accompanied by the expression of neuronal differentiation and synapse formation marker proteins, growth-associated protein-43 (GAP-43), and synaptophysin. We observed that the addition of K252a, a TrKA antagonist, significantly inhibited NGF-induced neurite outgrowth in PC12 cells, but 5-demethylnobiletin- or gardenin A-induced neurite outgrowth was not affected. Treatment with 5-demethylnobiletin and gardenin A markedly induced the phosphorylation of both cyclic AMP response element-binding protein (CREB) and CRE-mediated transcription, which was suppressed through the administration of the inhibitor 2-naphthol AS-E phosphate (KG-501) or using CREB siRNA. Furthermore, our results showed that MAPK/ERK kinase 1/2 (MEK1/2), protein kinase A (PKA), and protein kinase C (PKC) inhibitors blocked the CRE transcription activity and neurite outgrowth induced through 5-demethylnobiletin or gardenin A. Consistently, increased ERK phosphorylation and PKA and PKC activities were observed in PC12 cells treated with 5-demethylnobiletin or gardenin A. These results reveal for the first time that 5-demethylnobiletin and gardenin A promote neuritogenesis through the activation of MAPK/ERK-, PKC-, and PKA-dependent, but not TrkA-dependent, CREB signaling pathways in PC12 cells.
authors.affiliation: Department of Molecular Biology and Human Genetics, Tzu Chi University , Hualien 970, Taiwan.
authors.forename: Szu-Ping
authors.initials: SP
authors.lastname: Chiu
authors.forename: Ming-Jiuan
authors.initials: MJ
authors.lastname: Wu
authors.forename: Pei-Yi
authors.initials: PY
authors.lastname: Chen
authors.forename: Yi-Ru
authors.initials: YR
authors.lastname: Ho
authors.forename: Mi-Hsueh
authors.initials: MH
authors.lastname: Tai
authors.forename: Chi-Tang
authors.initials: CT
authors.lastname: Ho
authors.forename: Jui-Hung
authors.initials: JH
authors.lastname: Yen
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002957:Citrus / Q000737:chemistry; D047309:Flavones / Q000378:metabolism* / Q000494:pharmacology*; D005638:Fruit / Q000737:chemistry; D005786:Gene Expression Regulation / Q000187:drug effects; D020935:MAP Kinase Signaling System / Q000187:drug effects; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D016501:Neurites / Q000187:drug effects* / Q000378:metabolism; D055495:Neurogenesis / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D018697:Nootropic Agents / Q000494:pharmacology*; D016716:PC12 Cells; D051381:Rats
chemical_list: D015415:Biomarkers; D047309:Flavones; D009419:Nerve Tissue Proteins; D018697:Nootropic Agents; C000589472:gardenin A; C509545:5-O-demethylnobiletin