Lipopolysaccharide/adenosine triphosphate induces IL-1β and IL-18 secretion through the NLRP3 inflammasome in RAW264.7 murine macrophage cells

Abstract

The NOD-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome plays pivotal roles in inflammation and autoimmunity. The NLRP3 inflammasome is activated in response to various signals, including pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs). However, its role in inflammation remains unclear. In this study, we used lipopolysaccharide (LPS) and adenosine triphosphate (ATP) to simulate an inflammatory environment as the testing model. We found that the exposure of RAW264.7 cells to LPS/ATP triggered the activation of caspase-1 (P<0.01) and the cleavage of interleukin (IL)-1β (P<0.01), as well as the release of other cytokines, such as IL-18 (P<0.01) and IL-33 (P<0.01). Extracellular potas ?sium chloride at a high concentration (150 mM) abrogated the secretion of IL-1β and IL-18 (P<0.01), but did not reduce the processing of IL-33 (P>0.05). In addition, the silencing of NLRP3 with small interfering RNA (siRNA) suppressed the generation of proinflammatory cytokines, such as IL-1β (P<0.01), IL-18 (P<0.01), but not IL-33 (P>0.05), along with the decreased mRNA and protein expression of NLRP3 and caspase-1 (P<0.05). However, extracellular potassium at a high concentration and NLRP3 siRNA did not affect the level of apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC; P>0.05). Our results suggest that the NLRP3/ASC/caspase-1 axis participates in the regulation of pro-imflammatory cytokine secretion in RAW264.7 cells, particularly the generation of IL-1β and IL-18.