Polychlorinated Biphenyl Quinone Induces Caspase 1-Mediated Pyroptosis through Induction of Pro-inflammatory HMGB1-TLR4-NLRP3-GSDMD Signal Axis.

Polychlorinated biphenyls (PCBs) are one of the most refractory environmental pollutants. Because of their ubiquitous existence in the biological systems (including human body), it is important to investigate their toxic behavior. Our previous findings demonstrated that a high reactive metabolite of PCB, namely PCB29-pQ, causes several programmed cell death (PCD) such as intrinsic/extrinsic apoptosis and autophagic cell death. The mechanistic study suggested the toxic actions of PCB29-pQ is largely related to its reactive oxygen species (ROS)-generation ability. Pyroptosis is a caspase 1-mediated pro-inflammatory PCD, which was discovered recently. The aim of this study is to seek the linkage between pyroptosis and PCB29-pQ exposures. We first confirmed that PCB29-pQ stimulates Hela cells to produce excess amounts of ROS. Then we found PCB29-pQ activates NOD-like receptor pyrin domain-containing 3 (NLRP3) inflammasome that mediates caspase 1 activation. The activated caspase 1 (cleaved caspase 1) promotes gasdermin D (GSDMD) cleavage and translocation, which facilitates the release of intracellular inflammatory substances by forming membrane hole, ultimately leading cells to pyroptosis. PCB29-pQ-induced high-mobility group box 1 (HMGB1) release and subsequent binding to its receptors [toll-like receptor 2 (TLR2), TLR4, TLR9, and receptor for advanced glycation end products (RAGE)] are essential for the activation of NLRP3 inflammasome. The current study revealed pyroptosis as a new death mode induced by PCB29-pQ, which enriched the understanding of PCBs-induced toxicity and helped to prevent the toxic effects of residual PCBs in the environment.