Autophagy mediates Interleukin-1 beta exportation from human neutrophils.

TREVANI AS; KEITELMAN I; SABBIONE F; JANCIC C; IULA L

Boston

Congreso; 12th World Congress on Inflammation; 2015

Introduction: Interleukin-1β (IL-1β) is a pro-inflammatory cytokine synthesized in the cytoplasm as a precursor, pro-IL-1β, which has to be proteolytically processed to acquire biological activity. We have previously demonstrated that human neutrophil IL-1β processing is dependent of caspase-1 and elastase and/or proteinase-3. The release of IL-1β does not follow the conventional ER-Golgi route of secretion, being secreted by poorly-defined non-conventional secretory pathways among which autophagy has been proposed to be involved. However, controversial findings have been reported regarding the role of autophagy in controlling IL-1 secretion in other myeloid cells; with studies indicating either that autophagy targets IL-1 for degradation or that it is involved in its unconventional secretion. Here we tested the hypothesis that an unconventional autophagy mechanism is required for neutrophil IL-1β secretion. Methods and results: We found that autophagy inhibitors like 3-methyadenine markedly reduced IL-1β secretion induced by 5 h stimulation of human neutrophils with LPS or LPS+ATP evaluated by ELISA, without affecting cell viability. By contrast, these inhibitors did not modulate IL-8 secretion, a cytokine whose release follows the canonical ER-Golgi pathway. In neutrophil-differentiated PLB985 cells, siRNA knockdown of ATG5, an essential component of the autophagic pathway, abolished IL-1 secretion. In agreement with these findings, stimulation of autophagy by cell starvation promoted IL-1β secretion induced by both agonists. At 4 h post-stimulation with LPS+ATP, intracellular IL-1β showed a vesicular distribution co-localizing with LC3B, a marker of autophagy vesicles, by confocal microscopy. Furthermore, neutrophil starvation increased IL-1 and LC3B colocalization. Conclusion: Taken together, our studies reveal that autophagy is part of the pathway involved in IL-1β exportation from human PMN.