Summary The NLRP3 inflammasome is a multi-protein cytoplasmic complex functioning as a pattern recognition receptor that has emerged as a key regulator of sterile inflammation and cell death. Upon activation, NLRP3 assembles a complex comprised of the adaptor protein apoptosis- associated speck-like protein (ASC) and the serine protease caspase-1. This protease cleaves and activates inflammasome target cytokines, mainly IL-1?. Caspase 1 activation can also initiates a distinct form of programmed cell death, called pyroptosis, that allows the release of active NLRP3 inflammasome particles to the extracellular space While focused on the investigation of the specific contribution of NLRP3 inflammasome activation and the downstream mechanisms involved in the development of liver fibrosis, we have made the following key observations: 1) Persistent global NLRP3 inflammasome activation results in spontaneous liver fibrosis; 2) Two important consequences of persistent global NLRP3 activation in the liver include hepatocyte pyroptotic cell death and HSC activation; 3) In murine models and patients with NASH, caspase 1 activity is increased in circulation; and 4) Blocking IL-1 signaling during persistent NLRP3 activation rescues mice from inflammatory changes, but not from HSC activation and fibrosis. These data are remarkable because they identify new molecular pathways of liver fibrosis and provide a window for discovery of novel therapies. Based on these preliminary data we propose the CENTRAL HYPOTHESIS that cell- and time-specific NLRP3 inflammasome activation is a central mechanism that triggers liver fibrogenesis and fibrosis, while pyroptosis and extracellular inflammasomes are key events leading to amplification and perpetuation of NLRP3 inflammasome activity. To investigate this hypothesis our proposal has following SPECIFIC AIMS. FIRST we will establish how NLRP3 inflammasome activation modulates HSC phenotype, fibrogenesis and induces liver fibrosis. SECOND we will determine the role of pyroptosis and extracellular NRLP3 Inflammasome as a mechanism of amplification and perpetuation of inflammasome driven fibrogenesis and liver fibrosis. To address these central issues, we have put together a Multi-PI investigative team including a Pioneered Scientist in Inflammasome Biology, and Experts in Cell Death, Fibrosis and Liver Pathology. The results of these studies will uncover crucial aspects of NLRP3 Inflammasome biology and contribution to liver pathology and may lead to novel therapeutic strategies for treatment of various liver conditions associated with NLRP3 Inflammasome activation.