Tributyltin inhibits autophagy by decreasing lysosomal acidity in SH-SY5Y cells

Tributyltin activates the Keap1-Nrf2 pathway via a macroautophagy-independent reduction in Keap1

Tributyltin (TBT) is an environmental chemical, which was used as an antifouling agent for ships. Although its use has been banned, it is still persistently present in ocean sediments. Although TBT reportedly causes various toxicity in mammals, few studies on the mechanisms of biological response against TBT toxicity exist. The well-established Keap1-Nrf2 pathway is activated as a cytoprotective mechanism under stressful conditions. The relationship between TBT and the Keap1-Nrf2 pathway remains unclear. In the present study, we evaluated the effect of TBT on the Keap1-Nrf2 pathway. TBT reduced Keap1 protein expression in Neuro2a cells, a mouse neuroblastoma cell line, after 6 hr without altering mRNA expression levels. TBT also promoted the nuclear translocation of Nrf2, a transcription factor for antioxidant proteins, after 12 hr and augmented the expression of heme oxygenase 1, a downstream protein of Nrf2. Furthermore, TBT decreased Keap1 levels in mouse embryonic fibroblast (MEF) cells, with the knockout of Atg5, which is essential for macroautophagy, as well as in wild-type MEF cells. These results suggest that TBT activates the Keap1-Nrf2 pathway via the reduction in the Keap1 protein level in a macroautophagy-independent manner. The Keap1-Nrf2 pathway is activated by conformational changes in Keap1 induced by reactive oxygen species or electrophiles. Furthermore, any unutilized Keap1 protein is degraded by macroautophagy. Understanding the novel mechanism governing the macroautophagy-independent reduction in Keap1 by TBT may provide insights into the unresolved biological response mechanism against TBT toxicity and the activation mechanism of the Keap1-Nrf2 pathway.

Lysosomal dysfunction is associated with NLRP3 inflammasome activation in chronic unpredictable mild stress-induced depressive mice

NLRP3 inflammasome pathway-mediated inflammatory response is closely associated with depression. Increasing attention has been recently paid to the links between autophagy and depression, however, the relationship between autophagy and NLRP3 inflammasome in depressive behavior remain poorly understood. In the present study, the potential roles of autophagy-lysosome pathway in NLRP3 inflammasome regulation were investigated both in vivo (chronic unpredictable mild stress (CUMS)-induced depressive mouse model) and in vitro (LPS-induced cellular model) model. It demonstrated that CUMS induces depressive-like behaviors in mice, accompanied by increased expression of NLRP3 inflammasome and inflammatory responses. Meanwhile, it promoted the autophagosome marker LC3 and autophagic adaptor protein p62 accumulation, accompanied by the decrease of lysosomal cathepsins B and D expression in the prefrontal cortex of mice. Notably, a significant colocalization of NLRP3 and LC3 in CUMS mice by immunofluorescence co-staining were observed. For the in vitro study, disrupting the lysosomal function with Baf A1 significantly increased the LPS-induced NLRP3 inflammasome accumulation and pro-inflammatory factors (IL-1β and IL-18) production in BV2 cells. Collectively, our results suggested that the autophagic process is related to NLRP3 inflammasome activation, and dysfunctional lysosome in autophagy-lysosomal pathway may retard NLRP3 inflammasome degradation, facilitating the production of pro-inflammatory factors, thereby contributing to depressive behavior in CUMS mice.