PAR1, a therapeutic target for remote lung injury associated with hind limb ischemia/reperfusion: ERK5/KLF2-dependent lung capillary barrier preservation.

Protease-activated receptor 1 (PAR1) is expressed in pneumocytes and endothelial cells of the alveolar barrier. Its activation by thrombin disrupts the barrier integrity dynamics and induces lung injury in in vitro and in vivo paradigms. Nonetheless, the role of PAR1, as a therapeutic target, in hind limb ischemia/reperfusion (I/R)-mediated remote lung injury has been unclear. Therefore, this study aimed to determine the potential benefit of PAR1 blockade using the selective antagonist SCH79797 in distant lung dysfunction following hind limb I/R injury with special emphasis on the extracellular signal-regulated kinase 5 (ERK5)/Krüppel-like factor 2 (KLF2) axis. Rats were subdivided into control, bilateral hind limb I/R, SCH79797, and SCH79797+BIX02189 (ERK5 inhibitor) groups. PAR1 blockade, ERK5-dependently, alleviated alveolar barrier disruption as evidenced by reductions in both pulmonary systemic leakage of surfactant protein-D and lung fluid accumulation with increase in pulmonary claudin 5, vascular endothelial cadherin, and connexin 37 levels. Such improvements are downstream targets of the ERK5/KLF2-mediated sphingosine-1-phosphate receptor 1 (S1PR1) upregulated expression and pS536-nuclear factor-κB (NF-κB) p65 inhibition. SCH79797 effectively impedes the evoked inflammatory response and oxidative burst by suppressing vascular endothelial growth factor, tumor necrosis factor-α, lipid peroxidation, and neutrophil infiltration while boosting the glutathione antioxidant defense. Accordingly, PAR1 could be a therapeutic target, where its blockade mitigated pulmonary-endothelial barrier disruption via mutual S1PR1 enhancement and NF-κB p65 inhibition following ERK5/KLF2 activation.