AUTOPHAGY MEDIATES INTERLEUKIN-1 BETA EXPORTATION FROM HUMAN NEUTROPHILS

TREVANI, ANALIA; KEITELMAN, IRENE; SABBIONE, FLORENCIA; JANCIC, CAROLINA; IULA, LEONARDO

Boston

Congreso; The 12th World Congress on Inflammation; 2015

Inflammation Research Association

Introduction: Interleukin-1b (IL-1b) is a pro-inflammatory cytokine synthesized in the cytoplasm as a precursor, pro-IL-1b, which has to be proteolytically processed to acquire biological activity. We have previously demonstrated that human neutrophil IL-1b processing is dependent of caspase-1 and elastase and/or proteinase-3. The release of IL-1b 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-1b secretion in other myeloid cells; with studies indicating either that autophagy targets IL-1b 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-1b secretion. Methods and results: We found that autophagy inhibitors like 3-methyadenine markedly reduced IL-1b 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 releasefollows the canonical ER-Golgi pathway. In neutrophil-differentiated PLB985 cells, siRNA knockdown of ATG5, an essential component of the autophagic pathway, abolished IL-1b secretion. In agreement with these findings, stimulation of autophagy by cell starvation promoted IL-1b secretion induced by both agonists. At 4 h poststimulation with LPS+ ATP, intracellular IL-1b showed a vesicular distribution co-localizing with LC3B, a marker of autophagy vesicles, by confocal microscopy. Furthermore, neutrophil starvation increased IL-1b and LC3B colocalization. Conclusion: Taken together, our studies reveal that autophagy is part of the pathway involved in IL-1b exportation from human PMN.