Background: Depletion of macrophages, neutrophils, or lymphocytes confers only partial protection against experimental lung reperfusion injury, suggesting that inflammatory responses in other cell types contribute to tissue injury. Endothelial cell activation has previously been shown to be critical to the development of ischemia-reperfusion injury in other vascular beds. Furthermore, cyclosporine (CSA) reduces in vivo lung reperfusion injury through attenuated secretion of proinflammatory mediators. These studies determined whether pulmonary artery endothelial cells (PAEC), subjected to hypoxia and reoxygenation, promote inflammation and whether CSA afforded any modulation of that response.
Methods: Isolated rat PAEC were subjected in vitro to 2 hours hypoxia followed by up to 4 hours reoxygenation. Cells were pretreated with CSA or a cremaphor vehicle. Differences in activation of signaling kinases and transcription factors were assessed, as was cytokine-chemokine protein secretion.
Results: There was significant signaling kinase (extracellular signal regulated kinase [ERK 1/2]) activation by 15 minutes reoxygenation, which was temporally associated with marked activation of the transcription factors nuclear factor kappa B (NFkappaB) and early growth response one (EGR-1). At 4 hours reoxygenation there were significant increases in chemokine protein secretion. The CSA decreased ERK 1/2 phosphorylation and significantly attenuated transcription factor transactivation at 15 minutes reoxygenation. The CSA was found to be selective in reducing cytokine-chemokine elaboration at 4 hours reoxygenation.
Conclusions: Hypoxia-reoxygenation induces ERK 1/2 phosphorylation, as well as transactivation of the transcription factors NFkappaB and EGR-1 in PAEC. Cyclosporine selectively reduces proinflammatory mediator secretion, likely by transcriptional regulation through NFkappaB and EGR-1. This is the first demonstration of ERK 1/2 inhibition afforded by CSA.