Tris (1, 3-dichloro-2-propyl) phosphate induces apoptosis and autophagy in SH-SY5Y cells: Involvement of ROS-mediated AMPK/mTOR/ULK1 pathways

Tris (1, 3-dichloro-2-propyl) phosphate (TDCIPP), an extensively used organophosphorus flame retardant, is frequently detected in the environment and biota. Recent studies have shown that TDCIPP has neurotoxic effects. We hypothesized that the neurotoxicity might occur via the induction of the apoptosis and autophagy pathways. In the present study, we investigated TDCIPP-induced apoptotic death and autophagy in SH-SY5Y cells. Treatment with TDCIPP induced increased reactive oxygen species (ROS) generation and cell apoptosis, as well as autophagy. The autophagy inhibitor 3-methyladenine (3-MA) markedly decreased the expression of the autophagy marker beclin-1, microtubule-associated protein light chain 3-II (LC3II), p62/sequestosome 1 (SQSTM1) degradation, and promoted apoptosis. Conversely, the autophagy inducer rapamycin (Rapa) alleviated TDCIPP-induced apoptosis and markedly increased the expression of the autophagy markers. Pretreatment with N-acetyl cysteine (NAC) eliminated the increased ROS generation, resulting in increased cell viability. For further examination of the signaling pathways involved in TDCIPP-induced autophagy, compound C, a pharmacological inhibitor of adenosine monophosphate activated protein kinase (AMPK) was used. Western blotting showed that compound C markedly reduced the expression of phospho-AMPK (p-AMPK) and phospho-Unc-51-like kinase 1 (p-ULK1), increased phospho-mammalian target of rapamycin (p-mTOR) expression, and decreased beclin-1 and LC3II expression. These results suggested that the AMPK/mTOR/ULK1 signaling pathway was involved in TDCIPP-induced autophagy. The antioxidant NAC antagonized TDCIPP-induced activation of AMPK and autophagy. Taken together, our findings provide the first evidence that TDCIPP promotes apoptosis and autophagy simultaneously and that this process involves the ROS-mediated AMPK/mTOR/ULK1 pathways. Lastly, the induction of autophagy is a protective mechanism against TDCIPP-induced apoptosis.

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S2767 3-Methyladenine (3-MA) 3-Methyladenine (3-MA, NSC 66389) is a selective PI3K inhibitor for Vps34 and PI3Kγ with IC50 of 25 μM and 60 μM in HeLa cells; blocks class I PI3K consistently, whereas suppression of class III PI3K is transient, and also blocks autophagosome formation. 3-Methyladenine (3-MA) is successfully used to suppress mitophagy. Solutions of 3-MA are best fresh-prepared by heating. (688) (6)

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