Arsenic Inhibits Neurite Outgrowth by Inhibiting the LKB1-AMPK Signaling Pathway

BACKGROUND: Arsenic (As) is an environmental pollutant that induces numerous pathological effects, including neurodevelopmental disorders. OBJECTIVES AND METHODS: We evaluated the role of the LKB1-AMPK pathway in As-induced developmental neuro-toxicity using Neuro-2a (N2a) neuroblastoma cells as a model of developing neurons. RESULTS: The addition of low concentrations of As (<= 5 mu M) during differentiation caused an inhibitory effect on the neurite outgrowth in N2a cells in the absence of cell death. Activation of adeno-sine monophosphate-activated kinase (AMPK) induced by retinoic acid in differentiating cells was blocked by As. Pretreatment with the AMPK-specific activator 5-aminoimidazole-4-carboxamide riboside or over-expression of a constitutively active AMPK-a1 plasmid reversed As-induced inhibition of neurite outgrowth. The activation of LKB1 (serine/threonine kinase 11), a major AMPK kinase, was also suppressed by As by inhibiting both the phosphorylation and the trans-location of LKB1 from nucleus to cytoplasm. Antioxidants, such as N-acetyl cysteine and superoxide dismutase, but not catalase, protected against As-induced inactivation of the LKB1-AMPK pathway and reversed the inhibitory effect of As on neurite outgrowth. CONCLUSIONS: Reduced neurite outgrowth induced by As results from deficient activation of AMPK as a consequence of a lack of activation of LKB1. Oxidative stress induced by As, especially excessive superoxide, plays a critical role in blocking the LKB1-AMPK pathway. Our studies provide insight into the mechanisms underlying As-induced developmental neurotoxicity, which is important for designing a new strategy for protecting children against this neurotoxic substance.