Inhibition of neurite outgrowth and alteration of cytoskeletal gene expression by sodium arsenite

Arsenic compounds that are often found in drinking water increase the risk of developmental brain disorders. In this study, we performed live imaging analyses of Neuro-2a cells expressing SCAT3, a caspase-3 cleavage peptide sequence linking two fluorescent proteins; enhanced cyan fluorescence protein (ECFP) and Venus, to determine whether sodium arsenite (NaAsO2; 0, 1, 5, or 10 mu M) affects both neurite outgrowth and/or induces apoptosis with the same doses and in the same cell cultures. We observed that the area ratio of neurite to cell body in SCAT3-expressing cells was significantly reduced by 5 and 10 mu M NaAsO2, but not by 1 mu M, although the emission ratio of ECFP to Venus, an endpoint of caspase-3 activity, was not changed. However, cytological assay using apoptotic and necrotic markers resulted in that apoptosis, but not necrosis, was significantly induced in Neuro-2a cells when NaAsO2 exposure continued after the significant effects of NaAsO2 on neurite outgrowth were found by live imaging. These results suggested that neurite outgrowth was suppressed by NaAsO2 prior to NaAsO2-induced apoptosis. Next, we examined the effects of NaAsO2 on cytoskeletal gene expression in Neuro-2a cells. NaAsO2 increased the mRNA levels of the light and medium subunits of neurofilament and decreased the mRNA levels of tau and tubulin in a dose-dependent manner; no significant effect was found in the mRNA levels of the heavy subunit of neurofilament, microtubule-associated protein 2, or actin. The changes in cytoskeletal gene expression are likely responsible for the inhibitory effects of NaAsO2 on neurite outgrowth. (C) 2012 Elsevier Inc. All rights reserved.