Role of ASM/Cer/TXNIP signaling module in the NLRP3 inflammasome activation

Abstract

Background: The NOD-Like Receptor Protein 3 (NLRP3) inflammasome is a crucial component of an array of inflammatory conditions. It functions by boosting the secretion of pro-inflammatory cytokines: interleukin-1β (IL-1β) and interleukin-18 (IL-18). Previous studies have established the vital role of the acid sphingomyelinase (ASM)/ceramide (Cer) pathway in the functional outcome of cells, with a particular emphasis on the inflammatory processes. This study aimed to explore the effects and associated underlying mechanism of Cer-induced NLRP3 inflammasome activation.Methods: Lipopolysaccharide (LPS)/adenosine triphosphate (ATP)-induced NLRP3 inflammasome activation in J774A.1 cells was used as an in vitro inflammatory model. Western blotting and Real-time PCR (RT-PCR) were used to detect the protein and mRNA levels, respectively. IL-1β and IL-18 levels were evaluated using ELISA kits. ASM assay kit and immunofluorescence were used to detect ASM activity and Cer content.Results: Imipramine, a well-known inhibitor of ASM, significantly inhibited ASM activity and inhibited Cer accumulation, which indicated ASM activation. Besides, it also suppressed the LPS/ATP-induced expression of proteins and mRNA: thioredoxin interacting protein (TXNIP), NLRP3, caspase-1, IL-1β and IL-18. Interestingly verapamil, a TXNIP inhibitor, suppressed LPS/ATP-induced TXNIP/NLRP3 inflammasome activation; however, it did not affect LPS/ATP-induced ASM activation and ceramide production. Further analysis showed that the exogenous C2-Cer treated J774A.1 cells induced the overexpression of TXNIP, NLRP3, caspase-1, IL-1β and IL-18. Besides, TXNIP siRNA or verapamil inhibited C2-Cer-induced TXNIP overexpression and NLRP3 inflammasome activation.Conclusion: This study demonstrated the involvement of the ASM/Cer/TXNIP signaling pathway in NLRP3 inflammasome activation.