Host-derived extracellular vesicles in inflammatory caspase activation

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Inflammasome related caspases such as caspase-1, caspase-4, and caspase-11 are a subset of the caspase family specialized in executing a lytic form of cell death and IL-1 cytokine-based inflammatory response. The activation of these inflammatory caspases is strongly coupled to innate immune detection of infections and cellular perturbations via canonical and noncanonical inflammasomes. Inflammasomes are multiprotein complexes in the cytosol assembled in response to wide variety of pathogen-associated molecular patterns (PAMPs) including nucleic acids, toxins, flagellin, and cell wall components and endogenous danger signals (danger- associated molecular patterns, or DAMPs) such as ATP and uric acid crystals. The assembly of inflammasome complex leads to the autoproteolytic activation of inflammatory caspases. Enzymatically active versions of inflammatory caspases activate a pore forming protein called gasdermin D, which lyses the cells via plasma membrane perforation. Active caspase-1 also cleaves the inflammatory cytokines pro-IL-1β and pro-IL-18 into their active forms. Inflammatory caspases are important for initiating the inflammatory response against a wide variety of pathogens including bacteria and viruses. Inflammatory caspases also play crucial roles in sepsis, a major life-threatening condition associated with infections. Extracellular vesicles (EVs) are membrane-bound structures abundantly released by our living cells into the extracellular space. EVs are packaged with proteins, lipids, and RNAs, and EVs have emerged as a crucial mode of inter-cellular transfer of all three cargoes. EV-cargoes are functional and modulate the physiology of the recipient cells. However, the role of EVs in the inflammasome signaling is poorly understood. This proposal seeks to comprehensively address this critical knowledge gap in three specific aims. Aim 1 will characterize the impact of host-derived EVs on inflammatory caspase activation by PAMPs. Aims 2 and 3 will demonstrate the molecular and cellular mechanisms by which the host-derived EVs regulate PAMP-activation of inflammatory caspases. In summary, this proposal will reveal a new role for host-derived EVs in inflammasome responses in the context of host defense with great implications for human infectious diseases and sepsis.