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

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.

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.

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.

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.