Toll-Like Receptor 4 Mediates Lung Ischemia-Reperfusion Injury

Background: We have previously reported that nuclear factor (NF)-κB activation and inflammatory cytokine expression were involved in the development of lung ischemia-reperfusion injury (LIRI). Because Toll-like receptor 4 (TLR4) activates NF-κB-dependent transcription of inflammatory cytokine genes during myocardial ischemia-reperfusion injury, we examined whether absence of TLR4 in TLR4-deficient mice protects against LIRI. Methods: Left lungs of wild-type (C57BL/6J) mice or TLR4-null (TLR4^-/-) mice were made ischemic for 60 minutes and then reperfused for 180 minutes. Response to injury was quantified by tissue myeloperoxidase activity, vascular permeability ([¹²⁵I]-bovine serum albumin extravasation), and leukocyte and inflammatory mediator accumulation in bronchoalveolar lavage expression. Lung homogenates were also analyzed for activation of mitogen-activated protein kinases and nuclear translocation of the transcription factors NF-κB and activator protein-1. Results: After LIRI, lungs from TLR4^-/- mice demonstrated a 52.4% reduction in vascular permeability (p = 0.001), a 52.6% reduction in lung myeloperoxidase activity (p = 0.006), and a marked reduction in bronchoalveolar lavage leukocyte accumulation when compared with lungs from wild-type mice. The TLR4^-/- mice lungs, subjected to LIRI, also demonstrated marked reductions in amounts of several proinflammatory cytokines/chemokines in bronchoalveolar lavage samples. Phosporylation of c-Jun NH₂-terminal kinase, and activation of NF-κB and activator protein-1 were also significantly reduced in homogenates of lungs from TLR4^-/- mice injured by ischemia and reperfusion (p < 0.05). Conclusions: These data suggest that TLR4 plays a role in LIRI. Thus, TLR4 may be a potential therapeutic target to minimize ischemic-reperfusion-induced tissue damage and organ dysfunction.