MECHANICS AND DEFORMATION RESPONSES OF LUNG CELLS

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DESCRIPTION (Applicant's abstract): There is overwhelming evidence that large lung deformations trigger edema and inflammation. This evidence has generated an intense debate about the choice of ventilator settings for patients with injured lungs and has fueled research on the mechanisms of ventilator-induced lung injury (VILI). The number of mechanisms and the complex interplay between them complicate analyses of experiments on whole lungs. For this reason, we propose to test our principal hypothesis (that deformation represents a pro-inflammatory stimulus for epithelial and endothelial lung cells) in whole organ as well as in reduced systems. In studies detailed under Aim 1, we will define the relationships between substratum deformation and the inflammatory signaling responses of alveolar epithelial and pulmonary capillary endothelial cells in culture. We postulate that cyclic deformation of sufficient amplitude up-regulates production and release of inflammatory mediators and consider calcium oscillations accompanying intermittent non-lethal plasma membrane stress failure events to be a possible signal transduction mechanism. Aim 2 is to underscore the biologic relevance of the cell culture work by testing in a rat model of VILI whether alveolar epithelial cells express mediators of inflammation and whether this expression requires input from alveolar macrophages. Aims 3 and 4 are to dissect the responsible mechanisms by characterizing the effects of substratum strain on cell shape and the mechanical interactions between cytoskeleton and plasma membrane. We postulate (1) that deformed cells minimize plasma membrane stress by inserting lipid molecules from intracellular stores and (2) that plasma membrane stress and the probability of stress failure vary with cytoskeletal stiffness. The recognition and transduction of deforming stresses is a rapidly expanding area of research. Much of its focus has been on membrane channel physiology and the regulation of lipid and protein mediators. The signal itself (the change in cell shape and the associated stress-distribution), the interactions between the cytoskeleton and the plasma membrane, and the implications of these interactions for plasma membrane stress failure have in comparison received little attention. This is the gap in knowledge that we intend to fill.