Evaluation of the NOD-like receptor protein 3 (NLRP3) inflammasome pathway in human myelomonocytic THP1 cells
Guzova, Julia Alexandrovna
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Activation of the NOD-like receptor protein 3 (NLRP3) inflammasome complex causes the processing and release of mature IL-1β, with mitochondria playing key roles in its assembly. An orally active NLRP3 inflammasome inhibitor would be a significant advance in therapy for IL-1β-driven diseases. To overcome both, the variability among primary immune cells and the limitations of genetic manipulation of differentiated human or murine macrophages, we developed a simplified, reliable and relevant cell-based model for studying the NLRP3 inflammasome using the undifferentiated human myelomonocytic cell line THP1. We established that undifferentiated THP1 cells are fully competent for activation of the NLRP3 inflammasome and production of IL-1β, without differentiation into macrophages. CP-456,773 is a potent and selective inhibitor of the NLRP3 inflammasome, and it is an analogue of glyburide, a sulfonylurea receptor (SUR) inhibitor. Despite the extensive experimental use of CP-456,773, its molecular target remains unknown. Here we tested the hypothesis that mitochondrial ABCb7 or ABCb10 could be the pharmacologic targets of CP-456,773. We optimized a viral shRNA transduction method for genetic manipulations in THP1 cells and generated ABCb7 and ABCb10 knockdown (KD) THP1 cells. We demonstrate that NLRP3 inflammasome activation and CP-456,773 pharmacology are not altered in ABCb7- or ABCb10-deficient THP1 cells. For ABCb10, we confirmed these results using CRISPR/CAS9-mediated ABCb10 knockout (KO) THP1 sub-lines. In studies of mitochondrial fitness, we found that a previously observed reduction in oxygen consumption rate (OCR) following nigericin treatment was completely blocked in NLRP3 KO cells. Our data demonstrating that CP-456,773 rescues the NLRP3-dependent nigericin-induced decline in OCR and protects undifferentiated THP1 cells from nigericin-induced pyroptosis are consistent with the possibility that the NLRP3 protein itself may be the molecular target of CP-456,773. Moreover, we showed that ABCb10 KO THP1 cells exhibit increased rates of basal ATP production and glycolysis, suggesting an important role for ABCb10 in mitochondrial metabolism. Finally, RNA-Seq analysis of ABCb7 and ABCb10 KD in undifferentiated THP1 cells indicate new functions for these proteins, including cell communication and migration, apoptosis and cell adhesion. Overall, our findings demonstrate that undifferentiated THP1 cells are an ideal system in which to study the NLRP3 inflammasome.