Contribution of particle-induced lysosome membrane permeabilization to NLRP3 inflammasome activation and mitochondrial ROS production

Nickel oxide nanoparticles (NiONPs) can trigger reactive oxygen species (ROS) production and NLRP3 inflammasome activation in macrophages as key steps in promoting lung inflammation. However, the impact of NiONP-induced lysosome membrane permeabilization (LMP) on mitochondrial ROS (mtROS) production and NLRP3 inflammasome activation is unknown. Murine ex vivo alveolar macrophages (mexAM) were exposed to NiONPs or crystalline silica (cSiO2) as a positive control particle. Imipramine was used to inhibit LMP before measuring mtROS and NLRP3 inflammasome activation and MitoTEMPO was used to block mtROS before measuring LMP and NLRP3 inflammasome activation. The ability of phagocytosed NiONPs to leach Ni2+ and stimulate ROS production was also assessed. Exposure to either particle resulted in LMP, mtROS production, and NLRP3 inflammasome activation with cSiO2 causing greater effects than NiONPs. LMP was rate-limiting in cSiO2-induced NLRP3 inflammasome activation and mtROS production, which further activated the inflammasome. Similar to cSiO2, NiONP-induced LMP was rate-limiting in NLRP3 inflammasome activation. In contrast to cSiO2, NiONP-induced mtROS was detected whether or not LMP was inhibited. Furthermore, NiONP-derived Ni2+ ions were present in the cytosol whether or not LMP occurred, and Ni2+ release was proportional to measured mtROS production and hydroxyl radical formation. The inability of MitoTEMPO to block the effects of Ni2+ ions on mtROS production suggested an alternative unclear mechanism was involved. This study demonstrates that LMP serves as a pivotal upstream trigger of NLRP3 inflammasome activation and potentially ROS production in response to cSiO2 and NiONPs - underscoring the crucial role of lysosomes in particle-induced inflammation.