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P2X7 Receptor and Caspase 1 Activation Are Central to Airway Inflammation Observed after Exposure to Tobacco Smoke

Chronic Obstructive Pulmonary Disease (COPD) is a cigarette smoke (CS)-driven inflammatory airway disease with an increasing global prevalence. Currently there is no effective medication to stop the relentless progression of this disease. It has recently been shown that an activator of the P2X7/inflammasome pathway, ATP, and the resultant products (IL-1β/IL-18) are increased in COPD patients. The aim of this study was to determine whether activation of the P2X7/caspase 1 pathway has a functional role in CS-induced airway inflammation. Mice were exposed to CS twice a day to induce COPD-like inflammation and the role of the P2X7 receptor was investigated. We have demonstrated that CS-induced neutrophilia in a pre-clinical model is temporally associated with markers of inflammasome activation, (increased caspase 1 activity and release of IL-1β/IL-18) in the lungs. A selective P2X7 receptor antagonist and mice genetically modified so that the P2X7 receptors were non-functional attenuated caspase 1 activation, IL-1β release and airway neutrophilia. Furthermore, we demonstrated that the role of this pathway was not restricted to early stages of disease development by showing increased caspase 1 activation in lungs from a more chronic exposure to CS and from patients with COPD. This translational data suggests the P2X7/Inflammasome pathway plays an ongoing role in disease pathogenesis. These results advocate the critical role of the P2X7/caspase 1 axis in CS-induced inflammation, highlighting this as a possible therapeutic target in combating COPD.

The role of the NLRP3 Inflammasome in the pathogenesis of airway disease

The incidences of respiratory diseases like asthma and Chronic Obstructive Pulmonary Disease (COPD) are increasing dramatically. Significantly, there are currently no treatments that can slow or prevent the relentless progression of COPD; and a sub-population of asthmatics are resistant to available therapies. What is more, currently prescribed medication has only minimal effect on the symptoms suffered in these patient groups. There is therefore an urgent need to develop effective drugs to treat these diseases. Whilst asthma and COPD are thought to be distinct diseases, it is currently believed that the pathogenesis of both is driven by the chronic inflammation present in the airways of these patients. It is thus hypothesised that if the inflammation could be attenuated, disease development would be slowed and symptoms reduced. It is therefore paramount to determine the pathways driving/propagating the inflammation. Recently there has been a growing body of evidence to suggest that the multimeric protein complex known as the Inflammasome may play key roles in the inflammation observed in respiratory diseases. The aim of this review is to discuss the role of the NLRP3 Inflammasome, and its associated inflammatory mediators (IL-1β and IL-18), in the pathogenesis of asthma and COPD.

Role of the Inflammasome-Caspase1/11-IL-1/18 Axis in Cigarette Smoke Driven Airway Inflammation: An Insight into the Pathogenesis of COPD

Background Chronic Obstructive Pulmonary Disease (COPD) is an inflammatory airway disease often associated with cigarette smoke (CS) exposure. The disease is increasing in global prevalence and there is no effective therapy. A major step forward would be to understand the disease pathogenesis. The ATP-P2X7 pathway plays a dominant role in murine models of CS induced airway inflammation, and markers of activation of this axis are upregulated in patients with COPD. This strongly suggests that the axis could be important in the pathogenesis of COPD. The aim of this study was to perform a detailed characterisation of the signalling pathway components involved in the CS-driven, P2X7 dependent airway inflammation. Methods We used a murine model system, bioassays and a range of genetically modified mice to better understand this complex signalling pathway. Results The inflammasome-associated proteins NALP3 and ASC, but not IPAF and AIM2, are required for CS-induced IL-1β/IL-18 release, but not IL-1α. This was associated with a partial decrease in lung tissue caspase 1 activity and BALF neutrophilia. Mice missing caspase 1/11 or caspase 11 had markedly attenuated levels of all three cytokines and neutrophilia. Finally the mechanism by which these inflammatory proteins are involved in the CS-induced neutrophilia appeared to be via the induction of proteins involved in neutrophil transmigration e.g. E-Selectin. Conclusion This data indicates a key role for the P2X7-NALP3/ASC-caspase1/11-IL-1β/IL-18 axis in CS induced airway inflammation, highlighting this pathway as a possible therapeutic target for the treatment of COPD.

Role of transient receptor potential and pannexin channels in cigarette smoke-triggered ATP release in the lung

Background COPD is an inflammatory disease usually associated with cigarette smoking (CS) with an increasing global prevalence and no effective medication. Extracellular ATP is increased in the COPD affected lung and may play a key role in driving CS-induced airway inflammation, but the mechanism involved in ATP release has eluded researchers. Recently, the transient receptor potential (TRP) and pannexin-1 channels have been suggested to play a role in other experimental paradigms. Thus, the aim of this work is to investigate if these channels are involved in CS-induced ATP release in the lung. Methods Primary human cells were exposed to CS and extracellular ATP levels measured. Mice were exposed to mainstream CS and airway inflammation assessed. TRPV1/4 mRNA expression was assessed in human lung parenchyma. Results CS exposure caused a dose-related increase in ATP from primary airway bronchial epithelial cells. This was attenuated by blockers of TRPV1, TRPV4 and pannexin-1 channels. Parallel data was obtained using murine acute CS-driven model systems. Finally, TRPV1/4 mRNA expression was increased in lung tissue samples from patients with COPD. Conclusions Extracellular ATP is increased in the COPD affected lung and may play a key role in driving disease pathophysiology. These experiments uncover a novel mechanism which may be responsible for CS-induced ATP release. These findings highlight novel targets that could lead to the development of medicine to treat this devastating disease.

Cigarette Smoke Induced Airway Inflammation Is Independent of NF-κB Signalling

Rationale COPD is an inflammatory lung disease largely associated with exposure to cigarette smoke (CS). The mechanism by which CS leads to the pathogenesis of COPD is currently unclear; it is known however that many of the inflammatory mediators present in the COPD lung can be produced via the actions of the transcription factor Nuclear Factor-kappaB (NF-κB) and its upstream signalling kinase, Inhibitor of κB kinase-2 (IKK-2). Therefore the NF-κB/IKK-2 signalling pathway may represent a therapeutic target to attenuate the inflammation associated with COPD. Aim To use a range of assays, genetically modified animals and pharmacological tools to determine the role of NF-κB in CS-induced airway inflammation. Methods NF-κB pathway activation was measured in pre-clinical models of CS-induced airway inflammation and in human lung tissue from COPD patients. This data was complemented by employing mice missing a functional NF-κB pathway in specific cell types (epithelial and myeloid cells) and with systemic inhibitors of IKK-2. Results We showed in an airway inflammation model known to be NF-κB-dependent that the NF-κB pathway activity assays and modulators were functional in the mouse lung. Then, using the same methods, we demonstrated that the NF-κB pathway appears not to play an important role in the inflammation observed after exposure to CS. Furthermore, assaying human lung tissue revealed that in the clinical samples there was also no increase in NF-κB pathway activation in the COPD lung, suggesting that our pre-clinical data is translational to human disease. Conclusions In this study we present compelling evidence that the IKK-2/NF-κB signalling pathway does not play a prominent role in the inflammatory response to CS exposure and that this pathway may not be important in COPD pathogenesis.

Respiratory infections cause the release of extracellular vesicles: implications in exacerbation of asthma/COPD.

Background Infection-related exacerbations of respiratory diseases are a major health concern; thus understanding the mechanisms driving them is of paramount importance. Despite distinct inflammatory profiles and pathological differences, asthma and COPD share a common clinical facet: raised airway ATP levels. Furthermore, evidence is growing to suggest that infective agents can cause the release of extracellular vesicle (EVs) in vitro and in bodily fluids. ATP can evoke the P2X7/caspase 1 dependent release of IL-1β/IL-18 from EVs; these cytokines are associated with neutrophilia and are increased during exacerbations. Thus we hypothesized that respiratory infections causes the release of EVs in the airway and that the raised ATP levels, present in respiratory disease, triggers the release of IL-1β/IL-18, neutrophilia and subsequent disease exacerbations. Methods To begin to test this hypothesis we utilised human cell-based assays, ex vivo murine BALF, in vivo pre-clinical models and human samples to test this hypothesis. Results Data showed that in a murine model of COPD, known to have increased airway ATP levels, infective challenge causes exacerbated inflammation. Using cell-based systems, murine models and samples collected from challenged healthy subjects, we showed that infection can trigger the release of EVs. When exposed to ATP the EVs release IL-1β/IL-18 via a P2X7/caspase-dependent mechanism. Furthermore ATP challenge can cause a P2X7 dependent increase in LPS-driven neutrophilia. Conclusions This preliminary data suggests a possible mechanism for how infections could exacerbate respiratory diseases and may highlight a possible signalling pathway for drug discovery efforts in this area.

Cigarette Smoke Exposure as a Model of Inflammation Associated with COPD

Chronic obstructive pulmonary disease (COPD) is characterized by progressive airflow limitation resulting from inflammation‐driven pathologies in the lungs that are a consequence of smoking over many years. Given that the disease is increasing globally, understanding the mechanism by which cigarette smoke (CS) causes lung inflammation and exploiting that knowledge to develop effective treatments is urgently required. Animal models of CS exposure are commonly used to examine the inflammatory processes that may be involved in the development of COPD. The protocols described in this unit detail the development of preclinical models of CS‐driven lung inflammation. These systems can be utilized to investigate the role of various biological pathways in CS‐mediated inflammation and to assess the efficacy of new therapeutic strategies for treating COPD. Curr. Protoc. Pharmacol. 60:14.24.1‐14.24.18.

TLR4 activation induces IL-1β release via an IPAF dependent but caspase 1/11/8 independent pathway in the lung

BackgroundThe IL-1 family of cytokines is known to play an important role in inflammation therefore understanding the mechanism by which they are produced is paramount. Despite the recent plethora of publications dedicated to the study of these cytokines, the mechanism by which they are produced in the airway following endotoxin, Lipopolysaccharide (LPS), exposure is currently unclear. The aim was to determine the mechanism by which the IL-1 cytokines are produced after LPS inhaled challenge.MethodsMice were challenged with aerosolised LPS, and lung tissue and bronchiolar lavage fluid (BALF) collected. Targets were measured at the mRNA and protein level; caspase activity was determined using specific assays.ResultsBALF IL-1b/IL-18, but not IL-1a, was dependent on Ice Protease-Activating Factor (IPAF), and to a lesser extent Apoptosis-associated Speck-like protein containing a CARD (ASC). Interestingly, although we measured an increase in mRNA expression for caspase 1 and 11, we could not detect an increase in lung enzyme activity or a role for them in IL-1a/b production. Further investigations showed that whilst we could detect an increase in caspase 8 activity at later points in the time course (during resolution of inflammation), it appeared to play no role in the production of IL-1 cytokines in this model system.ConclusionsTLR4 activation increases levels of BALF IL-1b/IL-18 via an IPAF dependent and caspase 1/11/8 independent pathway. Furthermore, it would appear that the presence of IL-1a in the BALF is independent of these pathways. This novel data sheds light on innate signalling pathways in the lung that control the production of these key inflammatory cytokines.