Fas-deficient mice have impaired alveolar neutrophil recruitment and decreased expression of anti-KC autoantibody:KC complexes in a model of acute lung injury

The bioactivity of soluble Fas ligand is modulated by key amino acids of its stalk region

We have previously reported that the 26-amino acid N-terminus stalk region of soluble Fas ligand (sFasL), which is separate from its binding site, is required for its biological function. Here we investigate the mechanisms that link the structure of the sFasL stalk region with its function. Using site-directed mutagenesis we cloned a mutant form of sFasL in which all the charged amino acids of the stalk region were changed to neutral alanines (mut-sFasL). We used the Fas-sensitive Jurkat T-cell line and mouse and human alveolar epithelial cells to test the bioactivity of sFasL complexes, using caspase-3 activity and Annexin-V externalization as readouts. Finally, we tested the effects of mut-sFasL on lipopolysaccharide-induced lung injury in mice. We found that mutation of all the 8 charged amino acids of the stalk region into the non-charged amino acid alanine (mut-sFasL) resulted in reduced apoptotic activity compared to wild type sFasL (WT-sFasL). The mut-sFasL attenuated WT-sFasL function on the Fas-sensitive human T-cell line Jurkat and on primary human small airway epithelial cells. The inhibitory mechanism was associated with the formation of complexes of mut-sFasL with the WT protein. Intratracheal administration of the mut-sFasL to mice 24 hours after intratracheal Escherichia coli lipopolysaccharide resulted in attenuation of the inflammatory response 24 hours later. Therefore, the stalk region of sFasL has a critical role on bioactivity, and changes in the structure of the stalk region can result in mutant variants that interfere with the wild type protein function in vitro and in vivo.

Penehyclidine hydrochloride exerts protective effects in rats with acute lung injury via the Fas/FasL signaling pathway

Acute lung injury (ALI) is a critical syndrome that is associated with high morbidity and mortality rates. The activation of the Fas/Fas ligand (FasL) signaling pathway may be an important pathophysiological mechanism during ALI development. Penehyclidine hydrochloride (PHC) has been revealed to exhibit anti-apoptotic properties and may attenuate the observed systemic inflammatory response. The present study was performed to elucidate the molecular mechanism of PHC in the regulation of the Fas/FasL signaling pathway in rats with ALI. An ALI rat model was constructed by inducing blunt chest trauma and hemorrhagic shock (T/HS), with PHC administration prior to or following T/HS. At 6 h following T/HS, blood samples and lung tissues were collected. Western blotting, arterial blood gas analysis, ELISA, hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining and biochemical indicator analysis were performed to determine the degree of lung injury and the key signaling pathways associated with lung damage. The results indicated that the administration of PHC following T/HS effectively attenuates lung injury by improving pulmonary oxygenation, decreasing histopathological damage, decreasing polymorphonuclear neutrophil count and decreasing Fas, FasL, caspase-8, caspase-3, tumor necrosis factor-α, interleukin (IL)-6 and IL-1β expression. The results indicated that PHC exhibits anti-apoptotic functions and exerts protective effects in ALI rats induced by T/HS, which may be attributed to the inhibition of the Fas/FasL signaling pathway.

Fas activation alters tight junction proteins in acute lung injury

Background:The acute respiratory distress syndrome (ARDS) is characterized by protein-rich oedema in the alveolar spaces, a feature in which Fas-mediated apoptosis of the alveolar epithelium has been involved. Objective:To determine whether Fas activation increases protein permeability by mechanisms involving disruption of the paracellular tight junction (TJ) proteins in the pulmonary alveoli. Methods: Protein permeability and the expression of TJ proteins were assessed in vivo in wild-type and Fas-deficient lpr mice 16 hours after the intratracheal instillation of recombinant human soluble Fas ligand (rh-sFasL), and at different time points in vitro in human pulmonary alveolar epithelial cells (HPAEpiC) exposed to rh-sFasL Results:Activation of the Fas pathway increased protein permeability in mouse lungs and altered the expression of the TJ proteins occludin and zonula occludens-1 in the alveolar-capillary membrane in vivo and in human alveolar epithelial cell monolayers in vitro. Blockade of caspase-3, but not inhibition of tyrosine kinase dependent pathways, prevented the alterations in TJ protein expression and permeability induced by the Fas/FasL system in human alveolar cell monolayers in vitro. We also observed that both the Fas-induced increase of protein permeability and disruption of TJ proteins occurred before cell death could be detected in the cell monolayers in vitro. Conclusion:Targeting caspase pathways could prevent the disruption of TJs and reduce the formation of lung oedema in the early stages of ARDS.

Aquaporin 5 increases keratinocyte-derived chemokine expression and NF-κB activity through ERK activation

Aquaporin-5 (AQP5) is a water-selective channel protein that is expressed in submucosal glands and alveolar epithelial cells in the lungs. Recent studies have revealed that AQPs regulate not only water metabolism, but also some cellular functions such as cell growth and migration. Here, we report the role of AQP5 in inflammatory responses. In MLE-12 cells, knockdown of AQP5 using siRNA (10-50 nM) attenuated TNF-α-induced expression of keratinocyte chemoattractant (KC) mRNA and protein. Conversely, in NIH-3T3 cells, overexpression of AQP5 increased KC expression, NF-κB activation, and ERK phosphorylation. The AQP5-induced increase of KC expression was diminished by treatment with ERK inhibitors. Taken together, we propose a new function of AQP5 as an inflammatory signal potentiator, which may be mediated by increased activation of ERK and NF-κB.