Autophagy and apoptosis are the major types of cell death in pesticide-induced neurotoxicity, and autophagy is known to play a role in cell protection by inhibiting apoptosis. In this study, we characterized the relationship between autophagy and apoptosis in diquat (DQ)-induced cell death and explored a novel pharmacotherapeutic approach involving autophagy regulation to prevent DQ neurotoxicity. DQ was cytotoxic to PC12 cells in a concentration-dependent manner, as shown by decreased cell viability and decreased dopamine (DA) levels. DQ-induced apoptosis was found in PC12 cells, as demonstrated by activation of caspase-3 and -9 and by nuclear condensation. By monitoring expression of microtubule-associated protein 1A/1B light chain 3B (LC3-II) and p62, DQ was found to induce autophagy. Exposure of PC12 cells to DQ led to the production of reactive oxygen species (ROS), and N-acetyl-cysteine (NAC) antioxidant effectively blocked both apoptosis and autophagy. Interestingly, DQ in PC12 cells showed increased p53 and NF-κB in a time-dependent manner; furthermore, pifithrin-α (PFT-α), a p53 inhibitor, downregulates the cytotoxicity of DQ, as shown by decreased LC3-II and cleaved caspase-3. SN50, an NF-κB inhibitor, results in diminished LC3-II, cleaved caspase-3, and p53. DQ induces mitogen-activated protein kinase (MAPK) signaling including ERK, JNK, and p38, which inhibit regulated apoptosis and autophagic cell death by controlling mTOR signaling. In addition, modulation of DQ-induced apoptosis in response to autophagy regulation was investigated. Pretreatment with rapamycin, an autophagy inducer, significantly enhanced the viability of DQ-exposed cells by alleviating DQ-induced apoptosis. Conversely, cell pretreatment with 3-methyladenine (3MA), an autophagy inhibitor increased DQ toxicity. Our results suggest that DQ-induced cytotoxicity is modified by autophagy regulation. Pharmacologic induction of autophagy may be a useful treatment strategy in neurodegenerative disorders.
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This study contains parts of Aeri Park’s master dissertation at Graduate school of Biomedical Science & Engineering, Hanyang University. This work was supported by the Korea Science and Engineering Foundation (2017R1A5A2015395) through the Medical Research Center at Hanyang University College of Medicine, Republic of Korea, and by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science, and Technology (2015R1D1A1A01059531).
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Conflict of interest
The authors have no conflicts of interest to declare.
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