TLR4/MD-2 complex promotes transfusion-related acute lung injury pathogenesis through the activation of the AP-1 and NF-κB signaling pathways

Background: Transfusion-related acute lung injury (TRALI) is a severe complication of blood transfusion, but its molecular mechanisms remain poorly understood. This study aimed to investigate the role of Toll-like Receptor 4 (TLR4) and its downstream signaling cascade in the pathogenesis of TRALI.

Methods: Lipopolysaccharide (LPS)-treated PAEC cells and BALB/c mice were used as a model of TRALI. Relative mRNA expression was evaluated via quantitative RT-PCR. Protein abundance in cells/tissues and Cell Culture supernatant/serum was detected using western blot and ELISA, respectively. Lung tissue injury was evaluated by hematoxylin and eosin staining, and protein expression in lung tissues was analyzed by immunohistochemistry.

Results: Expressions of TLR2, TLR4 and myeloid differentiation 2 (MD-2) were significantly elevated in the cellular TRALI model and accompanied by an increase in c-Jun, c-Fos, and P65 phosphorylation and increased expression and secretion of IL-1β, IL-6, IL-8, and TNF-α. The TLR4 Inhibitor TAK-242 or MD-2 siRNAs effectively suppressed the molecular alterations induced by LPS in the cellular TRALI model. TAK-242 significantly reduced mortality and lung tissue injury in the TRALI mouse model, decreased TLR2, TLR4 and MD-2 expression, inhibited c-Jun, c-Fos, and p65 phosphorylation, and downregulated IL-1β, IL-6, IL-8, and TNF-α expression.

Conclusions: In this animal model of TRALI, the highly expressed TLR4/MD-2 complex promotes the pathogenesis of TRALI through the activation of the activator protein-1(AP-1) and nuclear factor-κB (NF-κB) signaling pathways and the release of inflammatory mediators. One limitation is the positive study in rodent model but not in humans.