Two-pore potassium channel TREK-1 (K2P2.1) regulates NLRP3 inflammasome activity in macrophages.

Because of the importance of potassium efflux in inflammasome activation, we investigated the role of the two-pore potassium (K2P) channel TREK-1 in macrophage inflammasome activity. Using primary alveolar macrophages (AMs) and bone marrow-derived macrophages (BMDMs) from wild-type (wt) and TREK-1-/- mice, we measured responses to inflammasome priming [using lipopolysaccharide (LPS)] and activation (LPS + ATP). We measured IL-1ß, caspase-1, and NLRP3 via ELISA and Western blot. A membrane-permeable potassium indicator was used to measure potassium efflux during ATP exposure, and a fluorescence-based assay was used to assess changes in membrane potential. Inflammasome activation induced by LPS + ATP increased IL-1ß secretion in wt AMs, whereas activation was significantly reduced in TREK-1-/- AMs. Priming of BMDMs using LPS was not affected by either genetic deficiency or pharmacological inhibition of TREK-1 with Spadin. Cleavage of caspase-1 following LPS + ATP treatment was significantly reduced in TREK-1-/- BMDMs. The intracellular potassium concentration in LPS-primed wt BMDMs was significantly lower compared with TREK-1-/- BMDMs or wt BMDMs treated with Spadin. Conversely, activation of TREK-1 with BL1249 caused a decrease in intracellular potassium in wt BMDMs. Treatment of LPS-primed BMDMs with ATP caused a rapid reduction in intracellular potassium levels, with the largest change observed in TREK-1-/- BMDMs. Intracellular K+ changes were associated with changes in the plasma membrane potential (Em), as evidenced by a more depolarized Em in TREK-1-/- BMDMs compared with wt, and Em hyperpolarization upon TREK-1 channel opening with BL1249. These results suggest that TREK-1 is an important regulator of NLRP3 inflammasome activation in macrophages.NEW & NOTEWORTHY Because of the importance of potassium efflux in inflammasome activation, we investigated the role of the two-pore potassium (K2P) channel TREK-1 in macrophage inflammasome activity. Using primary alveolar macrophages and bone marrow-derived macrophages from wild-type and TREK-1-/- mice, we measured responses to inflammasome priming (using LPS) and activation (LPS + ATP). Our results suggest that TREK-1 is an important regulator of NLRP3 inflammasome activation in macrophages.

Apoptosis signal-regulating kinase-1 promotes inflammasome priming in macrophages.

We previously showed that mice deficient in apoptosis signal-regulating kinase-1 (ASK1) were partially protected against ventilator-induced lung injury. Because ASK1 can promote both cell death and inflammation, we hypothesized that ASK1 activation regulates inflammasome-mediated inflammation. Mice deficient in ASK1 expression (ASK1-/-) exhibited significantly less inflammation and lung injury (as measured by neutrophil infiltration, IL-6, and IL-1ß) in response to treatment with inhaled lipopolysaccharide (LPS) compared with wild-type (WT) mice. To determine whether this proinflammatory response was mediated by ASK1, we investigated inflammasome-mediated responses to LPS in primary macrophages and bone marrow-derived macrophages (BMDMs) from WT and ASK1-/- mice, as well as the mouse alveolar macrophage cell line MH-S. Cells were treated with LPS alone for priming or LPS followed by ATP for activation. When macrophages were stimulated with LPS followed by ATP to activate the inflammasome, we found a significant increase in secreted IL-1ß from WT cells compared with ASK1-deficient cells. LPS priming stimulated an increase in NOD-like receptor 3 (NLRP3) and pro-IL-1ß in WT BMDMs, but expression of NLRP3 was significantly decreased in ASK1-/- BMDMs. Subsequent ATP treatment stimulated an increase in cleaved caspase-1 and IL-1ß in WT BMDMs compared with ASK1-/- BMDMs. Similarly, treatment of MH-S cells with LPS + ATP caused an increase in both cleaved caspase-1 and IL-1ß that was diminished by the ASK-1 inhibitor NQDI1. These results demonstrate, for the first time, that ASK1 promotes inflammasome priming.