Carbon monoxide negatively regulates NLRP3 inflammasome activation in macrophages

Abstract

Inflammasomes are cytosolic protein complexes that promote the cleavage of caspase-1, which leads to the maturation and secretion of proinflammatory cytokines, including interleukin-1β (IL-1β) and IL-18. Among the known inflammasomes, the nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3 (NLRP3)-dependent inflammasome is critically involved in the pathogenesis of various acute or chronic inflammatory diseases. Carbon monoxide (CO), a gaseous molecule physiologically produced in cells and tissues during heme catabolism, can act as an anti-inflammatory molecule and a potent negative regulator of Toll-like receptor signaling pathways. To date, the role of CO in inflammasome-mediated immune responses has not been fully investigated. Here, we demonstrated that CO inhibited caspase-1 activation and the secretion of IL-1β and IL-18 in response to lipopolysaccharide (LPS) and ATP treatment in bone marrow-derived macrophages. CO also inhibited IL-18 secretion in response to LPS and nigericin treatment, another NLRP3 inflammasome activation model. In contrast, CO did not suppress IL-18 secretion in response to LPS and poly(dA:dT), an absent in melanoma 2 (AIM2)-mediated inflammasome model. LPS and ATP stimulation induced the formation of complexes between NLRP3 and apoptosis-associated speck-like protein, or NLRP3 and caspase-1. CO treatment inhibited these molecular interactions that were induced by LPS and ATP. Furthermore, CO inhibited mitochondrial ROS generation and the decrease of mitochondrial membrane potential induced by LPS and ATP in macrophages. We also observed that the inhibitory effect of CO on the translocation of mitochondrial DNA into the cytosol was associated with suppression of cytokine secretion. Our results suggest that CO negatively regulates NLRP3 inflammasome activation by preventing mitochondrial dysfunction.

Targeting heme oxygenase-1 and carbon monoxide for therapeutic modulation of inflammation

“…In addition, CO inhibited mitochondrial depolarization induced by LPS and ATP in macrophages. 191 These results suggest that CO negatively regulates NLRP3 inflammasome activation in part by preventing mitochondrial dysfunction. 191 Application of the CO donor compound CORM-2 downregulated caspase-1 activation and IL-1β maturation and secretion in the context of ER-stress induced inflammation.…”

“…191 CO also inhibited IL-18 secretion in response to LPS and nigericin, an alternate NLRP3 inflammasome activator. LPS and ATP stimulation induced the formation of complexes between NLRP3 and ASC, or NLRP3 and caspase-1.…”

Molecular mechanisms regulating NLRP3 inflammasome activation

“…It has been found that CO inhibits the generation of mitochondrial ROS, mitochondrial membrane potential, and the cytosolic translocation of mitochondrial DNA in macrophages in response to LPS and ATP. 121 The adaptor protein caspase recruitment domain-containing protein 8 (CARD8) interacts with NLRP3 and inhibits IL-1b secretion during NLRP3 inflammasome activation. However, CARD8 is unable to bind to mutant NLRP3 associated with cryopyrin-associated periodic syndrome (CAPS), suggesting that it is relevant to the pathogenesis of CAPS.…”

Mitochondria in lung disease

“…While there has been considerable advancement in the development of mitochondria-targeted small molecule antioxidants (3) and alternative approaches to targeting mROS (133)(134)(135)(136)(137) appear promising, such mROS-targeted therapeutic approaches must be used with caution. mROS behave as a cytoprotective agent that leaves cells less susceptible to sub- …”