Microcystin‐LR‐Caused ROS generation involved in p38 activation and tau hyperphosphorylation in neuroendocrine (PC12) cells

Microcystin‐LR (MC‐LR), a potent specific hepatotoxin produced by cyanobacteria, has recently been reported to show neurotoxicity. Our previous study demonstrated that MC‐LR caused the reorganization of cytoskeleton architectures and hyperphosphorylation of the cytoskeletal‐associated proteins tau and HSP27 in neuroendocrine PC12 cell line by direct PP2A inhibition and indirect p38 mitogen‐activated protein kinase (MAPK) activation. It has been shown that oxidative stress is extensively associated with MC‐LR toxicity, mainly resulting from an excessive production of reactive oxygen species (ROS). However, the mechanisms by which ROS mediates the cytotoxic action of MC‐LR are unclear. In the present study, we investigated whether ROS might play a critical role in MC‐LR‐induced hyperphosphorylation of microtubule‐associated protein tau and the activation of the MAPKs in PC12 cell line. The results showed that MC‐LR had time‐ and concentration‐dependent effects on ROS generation, p38‐MAPK activation and tau phosphorylation. The time‐course studies indicated similar biphasic changes in ROS generation and tau hyperphosphorylation, which started to increase within 1 h and reached the maximum level at 3 h followed by a decrease after prolonged treatment. Furthermore, pretreatment with the antioxidants, N‐acetylcysteine and vitamin C, significantly decreased MC‐LR‐induced ROS generation and effectively attenuated p38‐MAPK activation as well as tau hyperphosphorylation. Taken together, these findings suggest that ROS generation triggered by MC‐LR is a key intracellular event that contributes to an induction of p38‐MAPK activation and tau phosphorylation, and that blockade of this ROS‐mediated redox‐sensitive signal cascades may attenuate the toxic effects of MC‐LR. © 2013 Wiley Periodicals, Inc. Environ Toxicol 30: 366–374, 2015.