Stretch-activated signaling pathways responsible for early response gene expression in fetal lung epithelial cells

High-tidal volume ventilation has been shown to increase the expression of several inflammation-associated genes prior to overt physiologic lung injury. Herein, using an in vitro stretch system, we investigated the mechanotransduction pathways involved in ventilation-induced expression of these early response genes (i.e., early growth response gene (Egr)1, heat-shock protein (HSP)70, and the pro-inflammatory cytokines interleukin (IL)-1 beta, IL-6, and MIP-2). Mechanical stretch of fetal lung epithelial cells activated various signaling pathways, resulting in transient or progressive increases in gene expression of the early response genes. The transient increase in Egr1 and IL-6 expression was mediated via p44/42 mitogen-activated protein kinase (p44/42 MAPK), while nuclear factor-kappaB (NF-kappa B) was responsible for the sustained and progressive increase in expression of HSP70 and MIP-2. Blockage of Egr-1 expression did not affect the upregulation of IL-6, HSP70, MIP-2, and itself by stretch. Inhibition of calcium mobilization abolished stretch-induced p44/42 MAPK activation and NF-kappa B nuclear translocation as well as increased expression of all early response genes. Similar results were obtained with an inhibitor of Ras. These results suggest that mechanical stretch of fetal lung epithelial cells evokes a complex network of signaling molecules, which diverge downstream to regulate the temporal expression of a unique set of early response genes, but upstream converge at calcium. Thus, calcium mobilization may be a point of hierarchical integration of mechanotransduction in lung epithelial cells.