Intracellular ATP Decrease Mediates NLRP3 Inflammasome Activation upon Nigericin and Crystal Stimulation

Abstract

Activation of the nucleotide-binding oligomerization domain–like receptor family, pyrin domain–containing 3 (NLRP3) inflammasome initiates an inflammatory response, which is associated with host defense against pathogens and the progression of chronic inflammatory diseases such as gout and atherosclerosis. The NLRP3 inflammasome mediates caspase-1 activation and subsequent IL-1β processing in response to various stimuli, including extracellular ATP, although the roles of intracellular ATP (iATP) in NLRP3 activation remain unclear. In this study, we found that in activated macrophages artificial reduction of iATP by 2-deoxyglucose, a glycolysis inhibitor, caused mitochondrial membrane depolarization, leading to IL-1β secretion via NLRP3 and caspase-1 activation. Additionally, the NLRP3 activators nigericin and monosodium urate crystals lowered iATP through K+- and Ca2+-mediated mitochondrial dysfunction, suggesting a feedback loop between iATP loss and lowering of mitochondrial membrane potential. These results demonstrate the fundamental roles of iATP in the maintenance of mitochondrial function and regulation of IL-1β secretion, and they suggest that maintenance of the intracellular ATP pools could be a strategy for countering NLRP3-mediated inflammation.

Hexokinase Is an Innate Immune Receptor for the Detection of Bacterial Peptidoglycan

“…It competes with glucose in the glycolytic pathway. When we treated primed BMDMs with 2-DG, we observed dose-dependent induction of IL-1β by ELISA (Figure 6D), as well as cleaved IL-1β p17 and caspase-1 p10 in the supernatant (Figure 6E), as has recently been reported by others (Nomura et al, 2015). However, 2-DG does not function as an inhibitor of hexokinase like NAG or G6P.…”

When Hexokinase Gets that NAG-ing Feeling…

“…Also NLRP3 inflammasome activation was not due to loss of mitochondrial integrity, as mitochondrial membrane potential was maintained following PGN administration. Interestingly, this effect is distinct from a previous study that found 2-DG reduced mitochondrial membrane potential in macrophages (Nomura et al, 2015). Another mechanism could be mitochondrial DNA (mtDNA) release, as increased mtDNA was evident in the cytosol in response to PGN.…”

“…Although previously observed (Nomura et al, 2015), this result contrasts with studies demonstrating that blocking glycolysis with 2-DG can inhibit IL-1β activation (O’Neill and Pearce, 2016; Tannahill et al, 2013). It is conceivable that differences in stimulation conditions, 2-DG concentration, level of cell death, or the timing of hexokinase inhibition could explain these differential effects.…”

Role of Uric Acid Metabolism-Related Inflammation in the Pathogenesis of Metabolic Syndrome Components Such as Atherosclerosis and Nonalcoholic Steatohepatitis

“…Other studies have indicated the application of MUC to raise intracellular ROS levels. However, the relationship between intracellular K + level changes and ROS generation remains unknown, and future studies are expected to resolve this issue [27, 28]. Elevation of intracellular ROS mediates the detachment of thioredoxin-interacting protein (TXNIP) from thioredoxin and enables TXNIP to associate with NLRP3, leading to NLRP3 inflammasome activation [29, 30].…”