The inflammatory response provides an absolutely essential host defense mechanism that, if perturbed, can itself cause a large number of human diseases. Collectively, innate immune responses integrate a number of genome-encoded sensor proteins to combat threats such as pathogens and endogenous damage. Selected throughout multicellular evolution, these proteins recognize patterns of pathogen-specific molecules, such as bacterial flagellin and lipopolysaccharide, with remarkable sensitivity and selectivity. Following detection, host cells launch coordinated defensive measures through innate immune signaling pathways. In one such pathway, cytosolic sensor proteins assemble supramolecular signaling complexes called canonical inflammasomes to active the zymogen pro-caspase-1. Subsequent downstream signaling leads to cytokine release and pyroptosis, an inflammatory form of cell death consisting of cell lysis, alerting phagocytic cells to the site of infection or damage. While imperative to the inflammatory response, aberrant gain-of-function mutations in sensor proteins can cause constitutive pyroptosis that leads to human diseases such as inflammatory bowel disease, cardiovascular disease, gout, and other rare autoinflammatory disorders. Moreover, inhibiting the inflammasome pathway is a therapeutic strategy for preventing lethal septic shock. Despite its therapeutic potential, many mechanistic details underlying the activation of inflammasomes remain unknown. Herein, I propose to elucidate the molecular mechanisms underlying the activation and regulation of two inflammasome sensor proteins, NLRP1 and CARD8, by the prolyl peptidase DPP9. DPP9 directly binds both NLRP1 and CARD8, and pharmacological inhibition of DPP9 results in either NLRP1 or CARD8 activation dependent on cell type. DPP9, however, may not act on NLRP1 or CARD8 as substrate; therefore, the mechanism by which DPP9 mediates NLRP1 and CARD8 inhibition remains poorly understood, but might involve scaffolding a repressive complex and/or its catalytic activity.
I aim to interrogate this system through a combination of structural, biochemical, and cellular approaches. Completion of these independent aims will significantly advance our understanding of innate immunity and expedite treatments that improve human health.
Innate immunity protects against threats such as damage and pathogens, but when immunity goes awry, autoimmune disorders can develop. This project aims to uncover the mechanisms of two important proteins in innate immunity called CARD8 and NLRP1, which are dysregulated in a number of human diseases.