Determinants of plasma membrane wounding by deforming stress

Abstract

Once excess liquid gains access to air spaces of an injured lung, the act of breathing creates and destroys foam and thereby contributes to the wounding of epithelial cells by interfacial stress. Since cells are not elastic continua, but rather complex network structures composed of solid as well as liquid elements, we hypothesize that plasma membrane (PM) wounding is preceded by a phase separation, which results in blebbing. We postulate that interventions such as a hypertonic treatment increase adhesive PM-cytoskeletal (CSK) interactions, thereby preventing blebbing as well as PM wounds. We formed PM tethers in alveolar epithelial cells and fibroblasts and measured their retractive force as readout of PM-CSK adhesive interactions using optical tweezers. A 50-mOsm increase in media osmolarity consistently increased the tether retractive force in epithelial cells but lowered it in fibroblasts. The osmo-response was abolished by pretreatment with latrunculin, cytochalasin D, and calcium chelation. Epithelial cells and fibroblasts were exposed to interfacial stress in a microchannel, and the fraction of wounded cells were measured. Interventions that increased PM-CSK adhesive interactions prevented blebbing and were cytoprotective regardless of cell type. Finally, we exposed ex vivo perfused rat lungs to injurious mechanical ventilation and showed that hypertonic conditioning reduced the number of wounded subpleural alveolus resident cells to baseline levels. Our observations support the hypothesis that PM-CSK adhesive interactions are important determinants of the cellular response to deforming stress and pave the way for preclinical efficacy trials of hypertonic treatment in experimental models of acute lung injury. alveolar epithelial cell; acute lung injury; interfacial stress; osmotic response; cytoprotection THE SYNDROME OF ventilator-induced lung injury (VILI) contributes to the morbidity and mortality of critically ill patients (25). The clinical manifestations of the syndrome are indistinguishable from those of all-cause acute lung injury and at their core reflect a mechanotransduction event, i.e., the effects of deforming stress on cell and tissue injury, remodeling, and repair. The complex topographical distributions of lung mechanical properties, and hence of parenchymal stress and strain together with the numerous and nuanced injury manifestations, make it very difficult to establish mechanistic cause and effect relationships on the scale of interest, e.g., that of individual cells. Our research, therefore, focuses on a very specific mechanotransduction event, namely physical stress-related epithelial cell wounding and repair, which we believe contributes to the pathogenesis VILI.In the current study, we present a body of work in which we have explored the effects of hypertonic exposure on cell wounding in experimental models ranging from individual cells to rodent VILI preparations. The experiments were not designed to test the preclinical efficacy of an intervention, but rather to explore a cell bio...

Interfacial stress affects rat alveolar type II cell signaling and gene expression

“…This hypothesis, however, remains elusive as long as vital lung microscopy, employing sophisticated techniques, will allow it to be proven or disproven (41,66). In contrast to this hypothesis, experiments provided evidence that interfacial stress is a determinant of cell wounding in pathophysiological settings, e.g., in surfactant-compromised lungs or as a consequence of alveolar edema (9,48).…”

Early subclinical increase in pulmonary water content in athletes performing sustained heavy exercise at sea level: ultrasound lung comet-tail evidence

“…Alveolar cells, an element of the blood-gas barrier, also have a critical role in determining the homeostatic balance of pulmonary interstitial fluids during stress. Because alveolar cells are not elastic, Oeckler et al (31) showed that plasma membrane-cytoskeletal adhesive interactions are important determinants of the cellular response to deforming stress. Caveolar endocytic response to transient actin remodeling following deformation of plasma membrane increases cell permeability in both alveolar (15,49) and endothelial cells (26) in a dose-dependent manner.…”

Influence of airway wall compliance on epithelial cell injury and adhesion during interfacial flows

“…Using a similar rigid airway model, Yalcin et al (48) demonstrated that the degree of cell injury during cyclic airway closure/reopening is inversely proportional to airway diameter, and that changes in the cell's cytoskeletal structure can be used to mitigate cell injury during reopening (47). Similarly, Oeckler et al (35) demonstrated that hypertonic treatment reduces cell injury by increasing plasma membrane-cytoskeleton adhesive interactions. Although these results indicate that altering cell mechanics represents a novel way to reduce atelectrauma, the in vitro models used in these studies do not take into consideration the compliant nature of lung tissue.…”