TLR4 activation primes human macrophages for non-canonical caspase-4 inflammasome-induced extracellular vesicle secretion

Human macrophages secrete extracellular vesicles loaded with numerous immunoregulatory proteins. Here we employed high throughput quantitative proteomics to characterize the modulation of vesicle-mediated protein secretion during non-canonical caspase-4/5-dependent inflammasome activation. We show that human macrophages activate robust caspase-4- dependent extracellular vesicle secretion upon transfection of LPS, and this process is also partially dependent on NLRP-3 and caspase-5. Similar effect occurs with delivery of the LPS with E. coli-derived outer membrane vesicles. Moreover, sensitization of the macrophages through TLR4 prior to LPS transfection dramatically augments the EV-mediated protein secretion. Our data demonstrate that this process differs significantly from ATP-induced vesiculation, and is dependent on autocrine interferon signal associated with TLR4 activation. TLR4 activation preceding the non-canonical inflammasome activation significantly enhances vesicle-mediated secretion of inflammasome components caspase-1, ASC and lytic cell death effectors GSDMD, MLKL and NINJ1, suggesting that inflammatory EV transfer may exert paracrine effects in recipient cells. Moreover, using bioinformatic methods, we identify 15-deoxy-delta-12,14-prostaglandin J2 and parthenolide as inhibitors of caspase-4-mediated inflammation and vesicle secretion, indicating potential new therapeutic potential of these anti-inflammatory drugs.