Regulatory Effect of the HMGB1-TLR4 Signaling Pathway in Pulmonary Ischemia/Reperfusion

Abstract Background Pulmonary ischemia/reperfusion (I/R) injury derived from hemorrhagic shock-resuscitation is a significant cause of death in trauma patients. However, effective preventive interventions in early trauma resuscitation are lacking. Aims To investigate the critical role of the HMGB1-TLR4 pathway in the early inflammatory response after ischemia-reperfusion lung injury, and its specific regulatory mechanisms and the types of downstream cytokines regulated by this pathway. Methods In this study, to determine the molecular mechanism underlying pulmonary I/R injury and identify effective therapeutic targets to reduce the incidence and mortality, the expression of the HMGB1-TLR4 pathway in a pulmonary I/R injury model, its correlation with downstream inflammatory factors, and the effects of HMGB1-neutralizing antibodies on inflammation were evaluated. Results IL-6 and TNF-α levels in the three mouse models showed a rapid increase， IL-1β, IL-6, and TNF-α were upregulated in alveolar macrophages after LPS stimulation，TNF-α and HMGB1 were upregulated in TLR4+/+ cells and peaked at 48 h but was not upregulated in TLR4-/- cells. Western blot assays revealed that in TLR4+/+ cells, TLR4 was upregulated after stimulation by LPS and was rapidly downregulated after treatment with the HMGB1-neutralizing antibody. In contrast, TLR4-/- cells did not respond to LPS stimulation, and the HMGB1-neutralizing antibody did not significantly alter the TLR4 concentration. Conclusions HMGB1-TLR4 pathway plays an important role in the regulation of inflammation in pulmonary I/R injury. Furthermore, HMGB1 upregulated downstream inflammatory factors via TLR4. HMGB1-neutralizing antibodies had a protective effect against lung injury by downregulating the inflammatory response.