The role of TREM-2 in regulating MSU-mediated NLRP3 inflammasome activation

• Main Authors: Ying-Chieh Tsai, 蔡瑩潔
• Other Authors: Nien-Jung Chen
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/p9uvwy

碩士 === 國立陽明大學 === 微生物及免疫學研究所 === 107 === The NLRP3 inflammasome is a protein complex that can be activated by widely recognizing intracellular foreign pathogens or damage-associated molecular pattern. Monosodium urate (MSU) crystals can trigger myeloid cells infiltration and initiate phagocytosis, then increase intracellular reactive oxygen species (ROS) production to activate NLRP3 inflammasome and interleukin(IL)-1β production, resulting in joint inflammation. Our laboratory previously found that triggering receptor expressed on myeloid cells-2 (TREM-2) may play a role in mediating MSU-triggered myeloid cells activation and downstream NLRP3 inflammasome process. We found that there were more soluble TREM-2 levels were observed in the serum of acute gout patients compared with healthy controls. Moreover, the interaction between human TREM-2 and MSU crystals was also examined by a modified TREM-2/Fc pull-down assay. TREM-2 had been reported for its special functions of phagocytes such as regulating phagocytosis. Spleen tyrosine kinase (SYK), a downstream molecule of TREM-2, affects protein kinase C-δ (PKC-δ) activation. Here, we speculate that TREM-2 may affect Syk / PKC-δ-mediated phagocytosis to promote NLRP3 inflammasome activation in response to MSU stimulation. We investigated the regulatory mechanism mediated by TREM-2 in the process of MSU-induced inflammation. In TREM-2 deficient dendritic cells, weak phagocytic capacity, lower inflammasome activity and less IL-1β secretion were observed in comparison to control cells. We also proved that TREM-2 was involved in the process of regulating ROS production and NLRP3 inflammasome assembly. To further confirm our findings, we used the phagocytosis inhibitor to confirm that the phagocytosis of MSU by dendritic cells and the production of ROS are regulated by TREM-2. We further used PKC-δ inhibitor and observed that TREM-2 regulated inflammasome activity through targeting the PKC-δ activation, phagocytosis, and ROS production. Finally, we established a mice air pouch model for evaluating the in vivo immune response to MSU stimulation. The data showed that the number of total cells and the levels of IL-1β in air pouch exudates were increased after MSU stimulation for 24 hours, and TREM-2 deficient cells had less total cell numbers and IL-1β production compare to WT cells. We also found that the mRNA expression levels of TREM-1ヽIL-1β and NLRP3 in the synovial tissue were increased after MSU stimulation for 24 hours. Taken together, our results suggested that TREM-2 regulates NLRP3 inflammasome activity through the Syk-, PKCδ-, and phagocytosis-dependent NADPH oxidase activation signaling pathway.