Activation of TLR4 by the endotoxin LPS is a critical event in the pathogenesis of Gram-negative sepsis. Caveolin-1, the signaling protein associated with caveolae, is implicated in regulating the lung inflammatory response to LPS; however, the mechanism is not understood. Here we investigated the role of caveolin-1 in regulating TLR4 signaling in endothelial cells. We observed that LPS interaction with CD14 in endothelial cells induced Src-dependent caveolin-1 phosphorylation at Tyr 14. Using TLR4-MD2-CD14 transfected HEK-293 cell line and caveolin-1-deficient (cav-1−/−) mouse lung microvascular endothelial cells, we demonstrated that caveolin-1 phosphorylation at Tyr14 following LPS exposure induced caveolin-1 and TLR4 interaction and thereby TLR4 activation of MyD88, leading to NF-κB activation and generation of proinflammatory cytokines. Exogenous expression of phosphorylation-deficient Y14F caveolin-1 mutant in cav-1−/− mouse pulmonary vasculature rendered the mice resistant to LPS compared to reintroduction of wild type caveolin-1. Thus, caveolin-1 Y14 phosphorylation was required for the interaction with TLR4 and activation of TLR4-MyD88 signaling and sepsis-induced lung inflammation. Inhibiting caveolin-1 Tyr14 phosphorylation and resultant inactivation of TLR4 signaling in pulmonary vascular endothelial cells represents a novel strategy for preventing sepsis-induced lung inflammation and injury.

No abstract

in pulmonary macrophages mediates lung inflammatory injury via NLRP3 inflammasome activation during mechanical ventilation. Am J Physiol Lung Cell Mol Physiol 307: L173-L185, 2014. First published May 16, 2014 doi:10.1152/ajplung.00083.2014.-The inflammatory response is a primary mechanism in the pathogenesis of ventilator-induced lung injury. Autophagy is an essential, homeostatic process by which cells break down their own components. We explored the role of autophagy in the mechanisms of mechanical ventilation-induced lung inflammatory injury. Mice were subjected to low (7 ml/kg) or high (28 ml/kg) tidal volume ventilation for 2 h. Bone marrow-derived macrophages transfected with a scrambled or autophagy-related protein 5 small interfering RNA were administered to alveolar macrophage-depleted mice via a jugular venous cannula 30 min before the start of the ventilation protocol. In some experiments, mice were ventilated in the absence and presence of autophagy inhibitors 3-methyladenine (15 mg/kg ip) or trichostatin A (1 mg/kg ip). Mechanical ventilation with a high tidal volume caused rapid (within minutes) activation of autophagy in the lung. Conventional transmission electron microscopic examination of lung sections showed that mechanical ventilation-induced autophagy activation mainly occurred in lung macrophages. Autophagy activation in the lungs during mechanical ventilation was dramatically attenuated in alveolar macrophage-depleted mice. Selective silencing of autophagyrelated protein 5 in lung macrophages abolished mechanical ventilation-induced nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) inflammasome activation and lung inflammatory injury. Pharmacological inhibition of autophagy also significantly attenuated the inflammatory responses caused by lung hyperinflation. The activation of autophagy in macrophages mediates early lung inflammation during mechanical ventilation via NLRP3 inflammasome signaling. Inhibition of autophagy activation in lung macrophages may therefore provide a novel and promising strategy for the prevention and treatment of ventilator-induced lung injury. lung injury; autophagy; mechanical ventilation; inflammasome; macrophage MECHANICAL VENTILATION not only saves the lives of patients with respiratory failure but also initiates and exacerbates lung injury known as ventilator-induced lung injury (VILI), which in turn contributes to patient morbidity and mortality (11). VILI is characterized by an influx of inflammatory cells, increased pulmonary vascular permeability, and endothelial and epithelial cell death. The release of proinflammatory cytokines by lung cells in response to mechanical stretch is a crucial event for initiation and/or potentiation of VILI and may cause systemic inflammatory response and multiple system organ failure (4,22,35). The alveolar macrophages (AMs) (5, 7, 26), neutrophils (42), alveolar epithelium (35), and endothelium (10) are all involved in the production of proinflammatory cytokines during mechanical ...

No abstract