Objective To explore the role and mechanism of plasminogen activator inhibitor-1 (PAI-1) in lipopolysaccharide (LPS)-induced injury of alveolar epithelial type Ⅱ cells (AEC Ⅱ).

Methods The expression of intracellular and extracellular PAI-1 was measured by Western blotting and ELISA after LPS treatment of AEC Ⅱ. The effects of PAI-1 on neutrophil viability and chemotaxis were examined using PAI-1 recombinant protein and PAI-039 (an inhibitor of PAI-1) by CCK8 and Transwell assays. Pro-inflammatory factors including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), myeloperoxidase (MPO), matrix metalloproteinase-1 (MMP-1) and platelet/endothelial cell adhesion molecule (PECAM) were detected as well as phosphorylation of STAT3 Tyr705 and Ser727 at AEC Ⅱ. The extent of cell damage of AEC Ⅱ after LPS challenge with or without JAK inhibitor was observed using Trypan blue staining.

Results LPS significantly promoted the death of AEC Ⅱ and announced the expression and release of PAI-1 (P < 0.01). Moreover, PAI-1 recombinant protein inhibited the death of neutrophils, promoted their migration with IL-6 releasing (P < 0.001), and increased the phosphorylation level of STAT3 Tyr305 in AEC Ⅱ. When PAI-039 and AZD1480 were used to inhibit the expression of PAI-1 and activation of JAK, respectively, the phosphorylation level of STAT3 was suppressed, and LPS-induced AEC Ⅱ injury alleviated.

Conclusion PAI-1 recruits neutrophils to release large amounts of IL-6 and increases JAK-mediated phosphorylation level at the STAT3 Tyr705 site to promote LPS-induced AECⅡ injury.