Inflammasomes are intracellular danger-sensing protein complexes that are important for host protection. They initiate inflammation by controlling the activity of the proinflammatory cytokine interleukin-1β (IL-1β). Unlike most other cytokines, IL-1β is produced and retained in the cytoplasm in an inactive pro-form. Inflammasome-dependent maturation of proIL-1β is mediated by the common component of all inflammasomes, the protease caspase-1. Caspase-1 also controls the secretion of IL-1β, but the mechanism and route of secretion are unknown. We have recently demonstrated that the ability of caspase-1 to control IL-1β secretion is not dependent on its protease activity, but rather on a scaffold or adapter function of caspase-1. Furthermore, we and others could show that caspase-1 can control the secretion of non-substrates like IL-1α. These insights provide us with new and potentially revealing means to investigate the downstream effector functions of caspase-1, including the route and mechanism of IL-1 secretion. We will develop new tools to study the process of IL-1 secretion by microscopy and the novel mode-of-action of caspase-1 through the generation of transgenic models.
Despite the important role of IL-1 in host defence against infection, dysregulated inflammasome activation and IL-1 production has a causal role in a number of acquired and hereditary auto-inflammatory conditions. These include particle-induced sterile inflammation (as is seen in gout and asbestosis), hereditary periodic fever syndromes, and metabolic diseases like diabetes and atherosclerosis. Currently, recombinant proteins that block the IL-1 receptor or deplete secreted IL-1 are used to treat IL-1-dependent diseases. These are costly treatments, and are also therapeutically cumbersome since they are not orally available. We hope that a better understanding of caspase-1-mediated secretion of IL-1 will unveil mechanisms that may serve as targets for future therapies for these diseases.
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