A translocator protein 18 kDa ligand, Ro5-4864, inhibits ATP-induced NLRP3 inflammasome activation

Ro5-4864 and PK11195, prototypical synthetic ligands of translocator protein 18 kDa (TSPO), have shown anti-inflammatory effects in several models of inflammatory diseases; however, their biochemical mechanisms remain poorly understood. Nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome activation as a part of the innate immune system, has been implicated in a variety of inflammatory diseases. Here, we demonstrate for the first time that TSPO ligands, especially Ro5-4864, potently suppressed ATP-induced NLRP3 inflammasome activation in THP-1 and BMDM cells. Detailed action mechanism was further investigated in THP-1 cells. Ro5-4864 efficiently attenuated NLRP3 translocation to mitochondria, inflammasome assembly/oligomerization, activation of caspase-1, and subsequent secretion of the mature forms of interleukin-1β and -18. Ro5-4864 also reduced the production of mitochondrial superoxide and preserved the mitochondrial membrane potential in ATP-treated cells, suggesting that Ro5-4864 may act on mitochondria or more upstream targets in NLRP3 inflammasome signaling. We also observed the distinct effects of the TSPO ligands between THP-1 monocytes and macrophages, which suggested different NLRP3 inflammasome signaling depending on cell type. Collectively, our novel findings demonstrate that Ro5-4864 effectively inhibited ATP-induced NLRP3 inflammasome activation through the prevention of mitochondrial perturbation. Our results indicate Ro5-4864 as a promising candidate for the treatment of NLRP3 inflammasome-related diseases.