Elucidating the functional mechanism of NLRP3 inflammasome activation

Innate immunity is an absolutely essential host defense mechanism that, if perturbed, can itself cause a large number of human diseases. Among innate immune defense mechanisms, inflammasomes are cytosolic supramolecular complexes that recruit and activate inflammatory caspases, in particular caspase-1, to mediate proteolytic maturation of proinflammatory cytokines in the IL-1 family, and induce the rapid inflammatory form of cell death known as pyroptosis. Cytokine release and pyroptosis both signal danger to the rest of the immune system and pyroptosis kills infected or damaged cells to curtail the spread of the disease. NLRP3 is the inflammasome sensor that has caught the attention of the field and is emerging to be a general sensor of membrane damage and cellular stress, induced by pathogens and endogenous danger signals such as bacterial toxin nigericin, extracellular ATP, uric acid crystals, cholesterol crystals, hyaluronan and amyloid-β fibrils. Uric acid crystal-induced inflammasome activation is causal to severe joint inflammation in gout, and other stimuli could contribute to cardiovascular and neurodegenerative diseases. NLRP3 has a tripartite organization with an N- terminal effector domain known as PYD, a central nucleotide-binding ATPase domain (NBD, also known as NACHT) and a C-terminal LRR domain. Upon activation, NLRP3 recruits the adaptor ASC through PYD-PYD interactions and ASC further recruits caspase-1 through CARD-CARD interactions to induce proximity-promoted caspase dimerization and activation. Despite the great academic and clinical interest on NLRP3, the molecular pathway and mechanism for NLRP3 activation remain unclear, likely due to the complicated conformational transitions and intracellular trafficking that are just beginning to be elucidated. In this application, we propose to elucidate the functional mechanism of NLRP3 inflammasome activation by investigating the conformational transitions and intracellular trafficking.