Hypoxia-inducible factor-dependent induction of myeloid-derived netrin-1 attenuates natural killer cell infiltration during endotoxin-induced lung injury.

Sepsis and sepsis-associated lung inflammation significantly contribute to the morbidity and mortality of critical illness. Here, we examined the hypothesis that neuronal guidance proteins could orchestrate inflammatory events during endotoxin-induced lung injury. Through a targeted array, we identified netrin-1 as the top upregulated neuronal guidance protein in macrophages treated with lipopolysaccharide (LPS). Furthermore, we found that netrin-1 is highly enriched in infiltrating myeloid cells, particularly in macrophages during LPS-induced lung injury. Transcriptional studies implicate hypoxia-inducible factor HIF-1α in the transcriptional induction of netrin-1 during LPS treatment. Subsequently, the deletion of netrin-1 in the myeloid compartment (Ntn1loxp/loxp LysM Cre) resulted in exaggerated mortality and lung inflammation. Surprisingly, further studies revealed enhanced natural killer cells (NK cells) infiltration in Ntn1loxp/loxp LysM Cre mice, and neutralization of NK cell chemoattractant chemokine (C-C motif) ligand 2 (CCL2) reversed the exaggerated lung inflammation. Together, these studies provide functional insight into myeloid cell-derived netrin-1 in controlling lung inflammation through the modulation of CCL2-dependent infiltration of NK cells.