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

Abstract

BackgroundArsenic (As) is an environmental pollutant that induces numerous pathological effects, including neurodevelopmental disorders.Objectives and MethodsWe evaluated the role of the LKB1–AMPK pathway in As-induced developmental neurotoxicity using Neuro-2a (N2a) neuroblastoma cells as a model of developing neurons.ResultsThe addition of low concentrations of As (≤ 5 μM) during differentiation caused an inhibitory effect on the neurite outgrowth in N2a cells in the absence of cell death. Activation of adenosine 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 overexpression of a constitutively active AMPK-α1 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 translocation 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.ConclusionsReduced 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.

Taurine resumed neuronal differentiation in arsenite-treated N2a cells through reducing oxidative stress, endoplasmic reticulum stress, and mitochondrial dysfunction

“…Indeed, oxidative stress not only altered intracellular The letters a-c mean the significant difference with p < 0.05 among each group signaling and led to arrest of neuronal differentiation, but also impaired mitochondrial function and mtDNA integrity (Wang et al 2010a(Wang et al , b, 2011. In addition, oxidative products would also abnormally modified structure of cytoskeleton such as nitrosylation and result in conformational changes of cytoskeleton (Fan et al 2010).…”

“…Next day, N2a cells were co-treated with or without different concentrations of As (0, 0.5, 2.5, 5 μM) and 25 mM taurine in a 6-well plate for 48 h. After the experimental period, cells were washed by PBS and fixed in icecold methanol for 15 min at −20 °C. To make a clear image and cell morphology, cells were then stained by 0.5 % crystal violet solution for 30 min at 25 °C (Wang et al 2010a). After that, cells were washed by PBS twice and pictured using inverted microscope at magnification 200×.…”

“…Abnormal changes of morphology of neuronal structure and axons were also found in another 1 3 study (R´ros et al 2009). Recent study revealed that As exposure interrupted neuronal differentiation in N2a cells (Wang et al 2010a). Epidemiological study also reported impaired cognitive performance in Mexican school children who exposed to As (Rosado et al 2007).…”

“…These pathological signs are also considered as major contributors to neurological disease. Indeed, As interrupted neuronal differentiation by inducing oxidative stress in N2A cells (Wang et al 2010a). On the other hand, As inhibited metabolism-related enzymes such as pyruvate dehydrogenase via attacking with their thiol groups and altered balance of cellular energy (Samikkannu et al 2003).…”

Role of Environmental Chemical Insult in Neuronal Cell Death and Cytoskeleton Damage

“…31,32) Cytoskeletal alteration has been considered a major histopathologic hallmark of neurodegenerative disease. For example, abnormal accumulations of neurofilaments in the cell body and proximal axons are major pathologic features of ALS.…”