Cigarette smoke-induced necroptosis and DAMP release trigger neutrophilic airway inflammation in mice.

Recent data indicate a role for airway epithelial necroptosis, a regulated form of necrosis, and the associated release of damage-associated molecular patterns (DAMPs) in the development of chronic obstructive pulmonary disease (COPD). DAMPs can activate pattern recognition receptors (PRRs), triggering innate immune responses. We hypothesized that cigarette smoke (CS)-induced epithelial necroptosis and DAMP release initiate airway inflammation in COPD. Human bronchial epithelial BEAS-2B cells were exposed to cigarette smoke extract (CSE), and necrotic cell death (membrane integrity by propidium iodide staining) and DAMP release (i.e., double-stranded DNA, high-mobility group box 1, heat shock protein 70, mitochondrial DNA, ATP) were analyzed. Subsequently, BEAS-2B cells were exposed to DAMP-containing supernatant of CS-induced necrotic cells, and the release of proinflammatory mediators [C-X-C motif ligand 8 (CXCL-8), IL-6] was evaluated. Furthermore, mice were exposed to CS in the presence and absence of the necroptosis inhibitor necrostatin-1, and levels of DAMPs and inflammatory cell numbers were determined in bronchoalveolar lavage fluid. CSE induced a significant increase in the percentage of necrotic cells and DAMP release in BEAS-2B cells. Stimulation of BEAS-2B cells with supernatant of CS-induced necrotic cells induced a significant increase in the release of CXCL8 and IL-6, in a myeloid differentiation primary response gene 88-dependent fashion. In mice, exposure of CS increased the levels of DAMPs and numbers of neutrophils in bronchoalveolar lavage fluid, which was statistically reduced upon treatment with necrostatin-1. Together, we showed that CS exposure induces necrosis of bronchial epithelial cells and subsequent DAMP release in vitro, inducing the production of proinflammatory cytokines. In vivo, CS exposure induces neutrophilic airway inflammation that is sensitive to necroptosis inhibition.

Cigarette smoke-induced damage-associated molecular pattern release from necrotic neutrophils triggers proinflammatory mediator release.

Cigarette smoking, the major causative factor for the development of chronic obstructive pulmonary disease, is associated with neutrophilic airway inflammation. Cigarette smoke (CS) exposure can induce a switch from apoptotic to necrotic cell death in airway epithelium. Therefore, we hypothesized that CS promotes neutrophil necrosis with subsequent release of damage-associated molecular patterns (DAMPs), including high mobility group box 1 (HMGB1), alarming the innate immune system. We studied the effect of smoking two cigarettes on sputum neutrophils in healthy individuals and of 5-day CS or air exposure on neutrophil counts, myeloperoxidase, and HMGB1 levels in bronchoalveolar lavage fluid of BALB/c mice. In human peripheral blood neutrophils, mitochondrial membrane potential, apoptosis/necrosis markers, caspase activity, and DAMP release were studied after CS exposure. Finally, we assessed the effect of neutrophil-derived supernatants on the release of chemoattractant CXCL8 in normal human bronchial epithelial cells. Cigarette smoking caused a significant decrease in sputum neutrophil numbers after 3 hours. In mice, neutrophil counts were significantly increased 16 hours after repeated CS exposure but reduced 2 hours after an additional exposure. In vitro, CS induced necrotic neutrophil cell death, as indicated by mitochondrial dysfunction, inhibition of apoptosis, and DAMP release. Supernatants from CS-treated neutrophils significantly increased the release of CXCL8 in normal human bronchial epithelial cells. Together, these observations show, for the first time, that CS exposure induces neutrophil necrosis, leading to DAMP release, which may amplify CS-induced airway inflammation by promoting airway epithelial proinflammatory responses.

Glucocorticoids induce the production of the chemoattractant CCL20 in airway epithelium.

Th17-mediated neutrophilic airway inflammation has been implicated in decreased response to glucocorticoids in asthma. We aimed to investigate the effect of glucocorticoids on the airway epithelial release of the neutrophilic and Th17-cell chemoattractant CCL20. We studied CCL20 and CXCL8 sputum levels in asthmatic subjects using inhaled glucocorticoids or not, and the effect of budesonide on CCL20 and CXCL8 production in primary bronchial epithelial cells. The mechanism behind the effect of budesonide-induced CCL20 production was studied in 16HBE14o- cells using inhibitors for the glucocorticoid receptor, intracellular pathways and metalloproteases. We observed higher levels of CCL20, but not CXCL8, in the sputum of asthmatics who used inhaled glucocorticoids. CCL20 levels correlated with inhaled glucocorticoid dose and sputum neutrophils. Budesonide increased tumour necrosis factor (TNF)-α-induced CCL20 by primary bronchial epithelium, while CXCL8 was suppressed. In 16HBE14o- cells, similar effects were observed at the CCL20 protein and mRNA levels, indicating transcriptional regulation. Although TNF-α-induced CCL20 release was dependent on the ERK, p38 and STAT3 pathways, the increase by budesonide was not. Inhibition of glucocorticoid receptor or ADAM17 abrogated the budesonide-induced increase in CCL20 levels. We show that glucocorticoids enhance CCL20 production by bronchial epithelium, which may constitute a novel mechanism in Th17-mediated glucocorticoid-insensitive inflammation in asthma.