Bovine DDX3X Restrains Bovine SP110c-Mediated Activation of Inflammasome in Macrophages

Abstract

Simple Summary

As a crucial component of the innate immune system, inflammasomes are activated by cellular infection or stress, which leads to the secretion of proinflammatory cytokines IL-1β and IL-18. In order to avert harmful inflammatory responses and maintain immune homeostasis, the precise control mechanisms of inflammasome activation need to be further defined. Previously, researchers have characterized the bovine SP110c isoform (bSP110c) as a new trigger of inflammasome activation in macrophages stimulated with bacterial lipopolysaccharide; however, the exact molecular mechanism for negative regulation of bSP110c-induced inflammasome remains unknown. In this study, the researchers demonstrated that bovine DDX3X is a novel bSP110c binding protein that restricts the bSP110c-mediated inflammatory response through the negative regulation of the NLRP3 inflammasome. These findings support a new cooperative mechanism between bSP110c and bovine DDX3X to balance inflammasome activation and advance our understanding of the function of the SP110c protein in the bovine innate immune system.

Abstract

The inflammasome is a vital part of the host’s innate immunity activated by cellular infection or stress. Our previous research identified the bovine SP110c isoform (bSP110c) as a novel activator of the inflammasome that promoted the secretion of proinflammatory cytokines IL-1β and IL-18 in macrophages infected with Listeria monocytogenes or stimulated with lipopolysaccharide (LPS). However, the exact molecular mechanism for inhibiting bSP110c-induced inflammasome activation requires further clarification. Here, the researchers identified bovine DDX3X (bDDX3X) as an NLRP3-associated protein and an inhibitor of the bSP110c-induced inflammasome in the human THP1 macrophage cell line. Immunoprecipitation showed that bDDX3X interacted with the bSP110c CARD domain via its helicase domain. The co-expression of bSP110c and bDDX3X in THP1 macrophages significantly prevented the bSP110c-induced activation of inflammasomes. In addition, both bDDX3X and bSP110c interacted with bovine NLRP3 (bNLRP3), and bDDX3X enhanced the interaction between bSP110c and bNLRP3. The expression of bDDX3X in nigericin-stimulated THP1 macrophages significantly suppressed NLRP3 inflammasome activation, ASC speck formation, and pyroptosis. These findings demonstrate that bDDX3X negatively regulates the bSP110c-mediated inflammatory response by restricting the activation of the NLRP3 inflammasome. This discovery unveils a novel regulatory mechanism involving bDDX3X and bSP110c in coordinating inflammasome activation and subsequent cell-fate decisions in LPS-treated macrophages and, in turn, constitutes a step forward toward the implementation of marker-assisted selection in breeding programs aimed at utilizing cattle’s immune defenses.