Fig. 2

Second signal of NLRP3 inflammasome activation. A Perturbation of ion homeostasis perturbation. Membrane damage induced by Mycobacterium tuberculosis and TLR4 activation triggered by ornithine lead to K⁺ efflux. In addition, Ca²⁺ influx through the mechanosensitive channel PIEZO is converted into K⁺ efflux via KCNN4, thereby promoting NLRP3 inflammasome activation following stimulation with LPS and Yoda1. K⁺ efflux is further facilitated by various ion channels, including Kv1.3, KCa3.1, and TREK-1, ultimately contributing to NLRP3 activation. HBV activates the NLRP3 inflammasome through both K⁺ efflux and Na⁺ influx. Moreover, extracellular histones induce Ca²⁺ influx and recruit TWIK2 to the plasma membrane, resulting in K⁺ efflux through the TWIK2 channel. Extracellular ATP, released via pannexin-1 channels, binds to P2X7 receptors, leading to both Ca²⁺ influx and K⁺ efflux. Subsequently, K⁺ efflux promotes Cl⁻ efflux through CLIC1 and CLIC4, further contributing to NLRP3 inflammasome activation. Additionally, Ca²⁺ influx via TRPM2 induces mtROS production, providing an additional activation signal. VRAC activation, ATP release, and subsequent P2YR activation also participate in this process. Together, these ionic fluxes converge to promote NLRP3 inflammasome activation. B Perturbation of mitochondrial homeostasis. Extracellular mtDNA, SFTSV, forchlorfenuron, and aristolochic acid I have been shown to induce mitochondrial dysfunction. Gasdermin processing is essential for the release of mtDNA into the cytosol. Imiquimod inhibits mitochondrial complex I of the ETC and NQO2, leading to the production of mtROS. In contrast, PCr, generated through ETC activity, helps maintain intracellular ATP levels. ROS generated via FADDosome induction, along with ox-mtDNA produced through the TLR4–CMPK2 signaling axis, translocate to the cytosol through the mPTP and VDAC, where they trigger NLRP3 inflammasome activation. Furthermore, cardiolipin interacts with NLRP3 to promote inflammasome assembly. The recruitment of pro-IL-1α to mitochondrial cardiolipin impairs mitophagy and further enhances NLRP3 inflammasome activation during LPS stimulation. C Perturbation of lysosomal homeostasis. Various stimuli—including imatinib, masitinib, LL-37, LLME, LPC, Candida albicans, H-ferritin, nicotine, particulate matter and crystals, carbon nanotubes, and lecithinase from Clostridium perfringens—induce lysosomal damage. This damage leads to the release of cathepsins into the cytosol, which subsequently triggers K⁺ efflux and activates the NLRP3 inflammasome. ATP adenosine triphosphate, Casp8 caspase-8, CLIC chloride intracellular channels, CMPK2 cytidine monophosphate kinase 2, ER endoplasmic reticulum, ETC electron transport chain, FADD fas-associated death domain, GSDMD gasdermin D, GSDME gasdermin E, HBV hepatitis B virus, H-ferritin, heavy chain-ferritin, IP3R2 inositol 1,4,5-trisphosphate receptor type 2, KCNN4 potassium–calcium-activated channel subfamily N member 4, LLME Leu-Leu-O-methyl ester, LPC lysophosphatidylcholine, LPS lipopolysaccharide, mPTP mitochondrial permeability transition pore, mtDNA mitochondrial DNA, N- N terminal, NQO2 quinone oxidoreductase 2, ox-mtDNA oxidized-mitochondrial DNA, PCr phosphocreatine, ROS reactive oxygen species, RTK receptor tyrosine kinase, SFTSV severe fever with thrombocytopenia syndrome virus, TLR4 toll-like receptor 4, TRPM2 transient receptor potential melastatin 2, VDAC voltage-dependent anion channel, VRAC volume-regulated anion channel