Spontaneous formation of neutrophil extracellular traps is associated with autophagy

Neutrophils release neutrophil extracellular traps (NETs), via NETosis, as a defense mechanism against pathogens. Neutrophils can release NETs spontaneously; however, the mechanisms underlying spontaneous NETosis remain unclear. Neutrophils isolated from healthy donors were tested for NET formation and autophagy at 1, 6, 12, and 24 h after incubation. Autophagy response was evaluated in response to various autophagy inducers and inhibitors. The relationship between autophagy and NETosis was detected in vivo using an ovalbumin-induced mouse model of asthma. We found that the increase in the proportion of spontaneous NETosis was time-dependent. The number of autophagy-positive cells also increased over time and LC3B protein played an integral role in NET formation. Trehalose (an inducer of mTOR-independent autophagy) treatment significantly increased NET formation, whereas rapamycin (an mTOR-dependent autophagy inducer) did not increase NET release by neutrophils. Compared with the control group, 3-methyladenine (an autophagy sequestration inhibitor) and hydroxychloroquine sulfate (autophagosome-lysosome fusion inhibitor) treatments significantly reduced the percentage of NET-positive cells. In vivo studies on ovalbumin-induced asthma lung sections revealed NETs and LC3B and citH3 proteins were found to co-localize with DNA. Our findings suggest that autophagy plays a crucial role in aging-related spontaneous NETosis.