Proinflammatory response of alveolar type II pneumocytes to in vitro hypoxia and reoxygenation

Type II pneumocytes (T2P) are integral in preserving the integrity of the alveolar space by modulating the fluid composition surrounding the alveolar epithelium. There is also mounting evidence supporting their contribution to the development of acute inflammatory lung injury subsequent to oxidative stress. This study characterized the response of T2P to in vitro hypoxia and reoxygenation (H&R). Rat T2P from a cultured cell line (RLE-6TN) were rendered hypoxic for 2 h, and reoxygenated for up to 6 h. Activation of signaling kinases, the nuclear translocation of proinflammatory transcription factors, and quantification of secreted cytokine and chemokine protein content were assessed. Type II pneumocytes expressed activated extracellular signal regulated kinase (ERK) 1/2 maximally at 15 min of reoxygenation. C-jun n-terminal kinase (JNK) and p38 activation was minimal at all time points studied. The nuclear translocation of nuclear factor kappa B (NFkappaB) and activator protein (AP)-1 were dramatic after 15 min of reoxygenation. There was a significant increase in the protein secretion of CINC (p = 0.03), IL-1beta (p = 0.02), and monocyte chemoattractant protein-1 (p < 0.001) at 6 h of reoxygenation. Type II pneumocytes respond directly to H&R. ERK 1/2 activity peaks at 15 min of reoxygenation, and correlates temporally with the nuclear translocation of NFkappaB and AP-1. These signaling cascades likely promote the elaboration of proinflammatory mediators.