Adaptation of lung epithelial cells subjected to chronic cyclic strain

Background: Breathing movements cause cyclic mechanical strain of the lung tissue, in particular of the alveolar epithelium.Since this is a physiological process, it also suggests a certain capacity of alveolar epithelial cells (AEC) to adapt to this stress situation. Therefore, we studied cell signaling pathways and the gene expression profile in various AEC lines. Methods: Adherent human AEC (A549 as principal cell line and four others) were subjected to cyclic strain (16% surface distension at 0.2 Hz) for up to 24 h in a self-constructed strain chamber. Activation of general signaling pathways was estimated by immunoblot (phosphorylation of signaling molecules), electron spin resonance spectroscopy (generation of reactive oxygen species (ROS)), gene microarray and qPCR technique (gene expression). Results: Microarray analyses revealed many differences in the gene expression but at very moderate levels. In all, 25 genes were moderately down-regulated (0.86-fold ±0.06) and 26 genes were up-regulated (1.18-fold ±0.10) in A549 and the others. Strain-regulated genes often code for transcription factors, such as E2F4 and SRF, which was confirmed by qPCR analyses. In accordance with this observation, we identified an immediate increase in selected signaling molecules (active p42/p44, active PKB/Akt and ROS but not active JNK/SAPK) but with time their increase normalized relatively fast. Conclusion: Fast normalization of cell signaling pathways and moderate changes in the gene expression profile suggests an effective adaptation of lung cells to chronic mechanical stress.