Lipopolysaccharide-induced lung injury: role of P2X7 receptor

P2X7 receptor antagonist A-438079 alleviates oxidative stress of lung in LPS-induced septic rats

Sepsis is a deadly systemic inflammatory response of the body against infection resulting in immune response, cell differentiation and organ damage. Endotoxemia is one of the causes of sepsis-related acute respiratory distress and respiratory burst is an important generator of oxidants. Inflammation may be aggravated by overexpression of ATP-gated purinergic receptors (i.e., P2X7R) following cell damage. We aimed to evaluate the effects of P2X7R antagonist A-438079 on lung oxidative status and the receptor expression in endotoxemia of sepsis. Rats were subjected to sepsis by E. coli lipopolysaccharide (LPS) and treated with 15 mg/kg A-438079. The increase in circulatory IL-1β and IL-8 concentrations in LPS group confirmed the systemic inflammatory response to endotoxemia compared with Control groups (p < 0.001). Besides, there was an increase in P2X7R expression in lung tissue after LPS administration. Compared with Control groups, there were significant increases in the values of malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) (p < 0.001), and myeloperoxidase (MPO) (p < 0.05) in lung tissue of LPS group. P2X7R expression in lung and IL-1β level in blood did not increase in LPS + A-438079 group. A-438079 decreased the lung levels of MDA, GSH, CAT and SOD (p < 0.001), and MPO (p < 0.01) in septic rats. As a result, administration of pathogen-associated LPS led to increased P2X7R expression into lung tissue and elevated lipid peroxidation product MDA with regard to oxidative damage. The P2X7R antagonist A-438079 alleviated the oxidative stress of lung with a balance of tissue oxidant/antioxidant factors in experimental sepsis in rats.

Therapeutic potential of P2X7 purinergic receptor modulation in the main organs affected by the COVID-19 cytokine storm

Defined by the World Health Organization as a global public health pandemic, coronavirus 2019 (COVID-19) has a global impact and the death of thousands of people. The "severe acute respiratory syndrome coronavirus 2" virus (SARS-CoV-2) is the etiologic agent of this disease, which uses the angiotensin-converting enzyme receptor 2 (ACE2) to infect the body, so any organ that expresses the gene ACE2 is a possible target for the new coronavirus. In addition, in severe cases of COVID-19, a cytokine storm occurs, which triggers widespread systemic inflammation due to the uncontrolled release of proinflammatory cytokines. In this perspective, the modulation of purinergic receptors are highlighted in the literature as a possible therapy, considering its application in other viral infections and systemic inflammation. Therefore, the objective of this review is to gather information on the modulation of the P2X7 receptor in the main organs directly affected by the virus and by the cytokine storm: heart, brain, lung, liver and kidneys. Thus, demonstrating possible therapies for reducing inflammation, as well as reducing the level of morbidity and mortality of COVID-19.

CaMK4 Promotes Acute Lung Injury Through NLRP3 Inflammasome Activation in Type II Alveolar Epithelial Cell

Background

Type II alveolar epithelial cell (AEC II), in addition to its roles in maintaining lung homeostasis, takes an active role in inflammatory response during acute lung injury (ALI). Ca2+/calmodulin-dependent protein kinase IV (CaMK4) activated by Ca2+/calmodulin signaling, has been implicated in immune responses. This study was to investigate the roles of CaMK4 in the development of ALI and the underlying mechanisms.

Methods

CaMK4 inhibitor KN-93 was used to investigate the effects of CaMK4 on NLRP3 inflammasome activation. The effects of KN-93 on disease development of lipopolysaccharide (LPS)-induced ALI were also evaluated. The role of CaMK4 on NLRP3 inflammasome activation was explored in human AEC II cell line A549 using KN-93 or CaMK4 siRNA. NLRP3 inflammasome activation was measured by histology immunofluorescence and Western blot. IL-1β and IL-18 were measured by ELISA.

Results

Phosphorylation of CaMK4 and the expression of NLRP3 and Caspase-1 p20 were increased in the lungs of LPS-induced ALI mice, which was suppressed by KN-93 as measured by Western blot. Further, the activation of NLRP3 inflammasome was detected in AEC II from patients with acute respiratory distress syndrome (ARDS) and LPS-induced ALI mice. In vitro, inhibition or silencing CaMK4 in AEC II significantly inhibited NLRP3 inflammasome activation, resulting in reduced IL-1β production. The inhibition of NLRP3 inflammasome and decreased IL-1β/IL-18 production by KN-93 led to reduced inflammatory infiltration and ameliorated lung injury in LPS-induced ALI mice.

Conclusion

CaMK4 controls the activation of NLRP3 inflammasome in AEC II during LPS-induced ALI. CaMK4 inhibition could be a novel therapeutic approach for the treatment of ALI.

Purinergic receptor ligands: the cytokine storm attenuators, potential therapeutic agents for the treatment of COVID-19

The coronavirus disease-19 (COVID-19), at first, was reported in Wuhan, China, and then rapidly became pandemic throughout the world. Cytokine storm syndrome (CSS) in COVID-19 patients is associated with high levels of cytokines and chemokines that cause multiple organ failure, systemic inflammation, and hemodynamic instabilities. Acute respiratory distress syndrome (ARDS), a common complication of COVID-19, is a consequence of cytokine storm. In this regard, several drugs have been being investigated to suppress this inflammatory condition. Purinergic signaling receptors comprising of P1 adenosine and P2 purinoceptors play a critical role in inflammation. Therefore, activation or inhibition of some subtypes of these kinds of receptors is most likely to be beneficial to attenuate cytokine storm. This article summarizes suggested therapeutic drugs with potential anti-inflammatory effects through purinergic receptors.

The P2X7 purinergic receptor in intervertebral disc degeneration

Mechanisms involved in the development of intervertebral disc (IVD) degeneration are only partially known, thus making the implementation of effective therapies very difficult. In this study, we investigated P2X7 purinergic receptor (P2X7R), NLRP3 inflammasome, and interleukin (IL)-1β expression in IVD specimens at different stages of disease progression, and during the in vitro dedifferentiation process of the primary cells derived thereof. We found that P2X7R, NLRP3, and IL-1β expression was higher in the IVD samples at a more advanced stage of degeneration and in the expanded IVD cells in culture which partially recapitulated the in vivo degeneration process. In IVD cells, the P2X7R showed a striking nuclear localization, while NLRP3 was mainly cytoplasmic. Stimulation with the semiselective P2X7R agonist benzoyl ATP together with lipopolysaccharide treatment triggered P2X7R transfer to the cytoplasm and P2X7R/NLRP3 colocalization. Taken together, these findings support pathophysiological evidence that the degenerated disc is a highly inflamed microenvironment and highlight the P2X7R/NLRP3 axis as a suitable therapeutic target. The immunohistochemical analysis and the assessment of subcellular localization revealed a substantial expression of P2X7R also in normal disc tissue. This gives us the opportunity to contribute to the few studies performed in natively expressed human P2X7R so far, and to understand the possible physiological ATP-mediated P2X7R homeostasis signaling. Therefore, collectively, our findings may offer a new perspective and pave the way for the exploration of a role of P2X7R-mediated purinergic signaling in IVD metabolism that goes beyond its involvement in inflammation.

Adenosine and ATPγS protect against bacterial pneumonia-induced acute lung injury

Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, disrupts the alveolar-capillary barrier, triggering pulmonary vascular leak thus inducing acute lung injury (ALI). Extracellular purines, adenosine and ATP, protected against ALI induced by purified LPS. In this study, we investigated whether these purines can impact vascular injury in more clinically-relevant E.coli (non-sterile LPS) murine ALI model. Mice were inoculated with live E. coli intratracheally (i.t.) with or without adenosine or a non-hydrolyzable ATP analog, adenosine 5'-(γ-thio)-triphosphate (ATPγS) added intravenously (i.v.). After 24 h of E. coli treatment, we found that injections of either adenosine or ATPγS 15 min prior or adenosine 3 h after E.coli insult significantly attenuated the E.coli-mediated increase in inflammatory responses. Furthermore, adenosine prevented weight loss, tachycardia, and compromised lung function in E. coli-exposed mice. Accordingly, treatment with adenosine or ATPγS increased oxygen saturation and reduced histopathological signs of lung injury in mice exposed to E. coli. Lastly, lung-targeting gene delivery of adenosine or ATPγS downstream effector, myosin phosphatase, significantly attenuated the E. coli-induced compromise of lung function. Collectively, our study has demonstrated that adenosine or ATPγS mitigates E. coli-induced ALI in mice and may be useful as an adjuvant therapy in future pre-clinical studies.

Purinergic signaling in infectious diseases of the central nervous system

The incidence of infectious diseases affecting the central nervous system (CNS) has been increasing over the last several years. Among the reasons for the expansion of these diseases and the appearance of new neuropathogens are globalization, global warming, and the increased proximity between humans and wild animals due to human activities such as deforestation. Neurotropism affecting normal brain function is shared by organisms such as viruses, bacteria, fungi, and parasites. Neuroinfections caused by these agents activate immune responses, inducing neuroinflammation, excitotoxicity, and neurodegeneration. Purinergic signaling is an evolutionarily conserved signaling pathway associated with these neuropathologies. During neuroinfections, host cells release ATP as an extracellular danger signal with pro-inflammatory activities. ATP is metabolized to its derivatives by ectonucleotidases such as CD39 and CD73; ATP and its metabolites modulate neuronal and immune mechanisms through P1 and P2 purinergic receptors that are involved in pathophysiological mechanisms of neuroinfections. In this review we discuss the beneficial or deleterious effects of various components of the purinergic signaling pathway in infectious diseases that affect the CNS, including human immunodeficiency virus (HIV-1) infection, herpes simplex virus type 1 (HSV-1) infection, bacterial meningitis, sepsis, cryptococcosis, toxoplasmosis, and malaria. We also provide a description of this signaling pathway in emerging viral infections with neurological implications such as Zika and SARS-CoV-2.

Protective effects of P2X7R antagonist in sepsis-induced acute lung injury in mice via regulation of circ_0001679 and circ_0001212 and downstream Pln, Cdh2, and Nprl3 expression

BACKGROUND

Sepsis induces pulmonary P2X₇ receptor (P2X₇ R) expression and P2X₇ R-knockout reduced lung inflammation in mice. The present study investigated the expression of circular RNA (circRNA) and mRNA in sepsis-induced acute lung injury (ALI) treated with a P2X₇ R antagonist.

METHODS

Sepsis was induced by tracheal administration of lipopolysaccharide (LPS), and the mice were then divided into two groups: without [sepsis + dimethyl sulfoxide (DMSO)] or with P2X₇ R antagonist treatment (sepsis + P2X₇ A). Sham mice were administrated sterile normal saline. Serum levels of interleukin (IL)-1β and tumor necrosis factor (TNF)-α, pathological changes, cell apoptosis and P2X₇ R expression in lung were assessed, followed by RNA sequencing (RNA-seq) and bioinformatics analyses. A quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) was used to validate circRNAs and mRNAs.

RESULTS

Compared to the sham group, LPS-induced sepsis produced obvious pathological changes in lung tissue, as well as increased apoptotic lung cells, serum TNF-α and IL-1β levels, and P2X₇ R expression; P2X₇ R antagonism significantly ameliorated these changes. RNA-seq identified many dysregulated circRNAs and mRNAs during sepsis, whereas this changed with P2X₇ R antagonism. RT-qPCR confirmed that Mus musculus (mmu)_circ_0001679, mmu_circ_0001212, phospholamban (Pln), cadherin-2 (Cdh2) and nitrogen permease regulator 3-like (Nprl3) expression were significantly increased in the sepsis + DMSO group compared to that in the sham group but were decreased in the sepsis + P2X₇ A group compared to that in the sepsis + DMSO group. The circRNA-microRNA-mRNA coexpression network indicated that mmu_circ_0001679 may regulate Nprl3 and that mmu_circ_0001212 may similarly regulate Pln, Cdh2 and Nprl3 as a competing endogenous RNA.

CONCLUSIONS

P2X₇ R antagonism attenuates sepsis-induced ALI by inhibiting dysregulated expression of circRNA (circ_0001679, circ_0001212) and mRNA (Pln, Cdh2 and Nprl3).

The potential involvement of P2X7 receptor in COVID-19 pathogenesis: A new therapeutic target?

Coronavirus disease 2019 (COVID‐19) pathogenesis remains under investigation. Growing evidence indicates the establishment of a hyperinflammatory response, characterized by sustained production of cytokines, such as IL‐1β. The release and maturation of this cytokine are dependent on the activation of a catalytic multiprotein complex, known as “inflammasome”. The most investigated is the NLRP3 inflammasome, which can be activated by various stimuli, such as the recognition of extracellular ATP by the P2X7 receptor. Based on the recent literature, we present evidence that supports the idea that the P2X7R/NLRP3 axis may be involved in the immune dysregulation caused by the SARS‐CoV‐2 infection.

Silencing of long non-coding RNA MEG3 alleviates lipopolysaccharide-induced acute lung injury by acting as a molecular sponge of microRNA-7b to modulate NLRP3

We aimed to elucidate the roles of the long non-coding RNA (lncRNA) maternally expressed gene 3 (MEG3)/microRNA-7b (miR-7b)/NLR pyrin domain containing 3 (NLRP3) axis in lipopolysaccharide (LPS)-induced acute lung injury (ALI). Mouse alveolar macrophage NR8383 and mice were administrated with LPS to establish ALI models in vitro and in vivo. NLRP3 was silenced while miR-7b was overexpressed in LPS-induced NR8383 cell model of ALI. The interleukin-18 (IL-18) and IL-1β, as well as caspase-1, tumor necrosis factor-α (TNF-α) and IL-6 protein levels were assayed. To further investigate the underlying mechanisms of NLRP3 in ALI, lncRNA MEG3 was silenced and miR-7b was overexpressed in LPS-induced NR8383 cell model of ALI, after which in vivo experiments were performed for further verification. NLRP3 was highly expressed in LPS-induced NR8383 cell model of ALI. Silencing NLRP3 or overexpressing miR-7b inhibited IL-18 and IL-1β, as well as caspase-1, TNF-α and IL-6. LncRNA MEG3 could sponge miR-7b, and lncRNA MEG3 silencing or miR-7b overexpression downregulates NLRP3 expression, thus reducing IL-18 and IL-1β, as well as caspase-1, TNF-α and IL-6 levels. The in vivo experiments further confirmed the aforementioned findings. Silencing lncRNA MEG3 augments miR-7b binding to NLRP3 and downregulates NLRP3 expression, which ultimately improves LPS-induced ALI.

Deletion of P2X7 Receptor Decreases Basal Glutathione Level by Changing Glutamate-Glutamine Cycle and Neutral Amino Acid Transporters

Glutathione (GSH) is an endogenous tripeptide antioxidant that consists of glutamate-cysteine-glycine. GSH content is limited by the availability of glutamate and cysteine. Furthermore, glutamine is involved in the regulation of GSH synthesis via the glutamate–glutamine cycle. P2X7 receptor (P2X7R) is one of the cation-permeable ATP ligand-gated ion channels, which is involved in neuronal excitability, neuroinflammation and astroglial functions. In addition, P2X7R activation decreases glutamate uptake and glutamine synthase (GS) expression/activity. In the present study, we found that P2X7R deletion decreased the basal GSH level without altering GSH synthetic enzyme expressions in the mouse hippocampus. P2X7R deletion also increased expressions of GS and ASCT2 (a glutamine:cysteine exchanger), but diminished the efficacy of N-acetylcysteine (NAC, a GSH precursor) in the GSH level. SIN-1 (500 μM, a generator nitric oxide, superoxide and peroxynitrite), which facilitates the cystine–cysteine shuttle mediated by xCT (a glutamate/cystein:cystine/NAC antiporter), did not affect basal GSH concentration in WT and P2X7R knockout (KO) mice. However, SIN-1 effectively reduced the efficacy of NAC in GSH synthesis in WT mice, but not in P2X7R KO mice. Therefore, our findings indicate that P2X7R may be involved in the maintenance of basal GSH levels by regulating the glutamate–glutamine cycle and neutral amino acid transports under physiological conditions, which may be the defense mechanism against oxidative stress during P2X7R activation.

P2Y12 Receptor Antagonist Clopidogrel Attenuates Lung Inflammation Triggered by Silica Particles

Silicosis is an occupational lung disease caused by inhalation of silica particles. It is characterized by intense lung inflammation, with progressive and irreversible fibrosis, leading to impaired lung function. Purinergic signaling modulates silica-induced lung inflammation and fibrosis through P2X7 receptor. In the present study, we investigate the role of P2Y12, the G-protein-coupled subfamily prototype of P2 receptor class in silicosis. To that end, BALB/c mice received an intratracheal injection of PBS or silica particles (20 mg), without or with P2Y12 receptor blockade by clopidogrel (20 mg/kg body weight by gavage every 48 h) - groups CTRL, SIL, and SIL + Clopi, respectively. After 14 days, lung mechanics were determined by the end-inflation occlusion method. Lung histology was analyzed, and lung parenchyma production of nitric oxide and cytokines (IL-1β, IL-6, TNF-α, and TGF-β) were determined. Silica injection reduced animal survival and increased all lung mechanical parameters in relation to CTRL, followed by diffuse lung parenchyma inflammation, increased neutrophil infiltration, collagen deposition and increased pro-inflammatory and pro-fibrogenic cytokine secretion, as well as increased nitrite production. Clopidogrel treatment prevented silica-induced changes in lung function, and significantly reduced lung inflammation, fibrosis, as well as cytokine and nitrite production. These data suggest that inhibition of P2Y12 signaling improves silica-induced lung inflammation, preventing lung functional changes and mortality. Our results corroborate previous observations of silica-induced lung changes and expand the understanding of purinergic signaling in this process.

P2X7 Receptor Indirectly Regulates the JAM-A Protein Content via Modulation of GSK-3β

The alveolar epithelial cells represent an important part of the alveolar barrier, which is maintained by tight junction proteins, particularly JAM-A, occludin, and claudin-18, which regulate paracellular permeability. In this study, we report on a strong increase in epithelial JAM-A expression in P2X7 receptor knockout mice when compared to the wildtype. Precision-cut lung slices of wildtype and knockout lungs and immortal epithelial lung E10 cells were treated with bleomycin, the P2X7 receptor inhibitor oxATP, and the agonist BzATP, respectively, to evaluate early changes in JAM-A expression. Biochemical and immunohistochemical data showed evidence for P2X7 receptor-dependent JAM-A expression in vitro. Inhibition of the P2X7 receptor using oxATP increased JAM-A, whereas activation of the receptor decreased the JAM-A protein level. In order to examine the role of GSK-3β in the expression of JAM-A in alveolar epithelial cells, we used lithium chloride for GSK-3β inhibiting experiments, which showed a modulating effect on bleomycin-induced alterations in JAM-A levels. Our data suggest that an increased constitutive JAM-A protein level in P2X7 receptor knockout mice may have a protective effect against bleomycin-induced lung injury. Bleomycin-treated precision-cut lung slices from P2X7 receptor knockout mice responded with a lower increase in mRNA expression of JAM-A than bleomycin-treated precision-cut lung slices from wildtype mice.

Alveolar-Capillary Membrane-Related Pulmonary Cells as a Target in Endotoxin-Induced Acute Lung Injury

The main function of the lungs is oxygen transport from the atmosphere into the blood circulation, while it is necessary to keep the pulmonary tissue relatively free of pathogens. This is a difficult task because the respiratory system is constantly exposed to harmful substances entering the lungs by inhalation or via the blood stream. Individual types of lung cells are equipped with the mechanisms that maintain pulmonary homeostasis. Because of the clinical significance of acute respiratory distress syndrome (ARDS) the article refers to the physiological role of alveolar epithelial cells type I and II, endothelial cells, alveolar macrophages, and fibroblasts. However, all these cells can be damaged by lipopolysaccharide (LPS) which can reach the airspaces as the major component of the outer membrane of Gram-negative bacteria, and lead to local and systemic inflammation and toxicity. We also highlight a negative effect of LPS on lung cells related to alveolar-capillary barrier and their response to LPS exposure. Additionally, we describe the molecular mechanism of LPS signal transduction pathway in lung cells.

Extracellular ATP is a danger signal activating P2X7 receptor in a LPS mediated inflammation (ARDS/ALI)

Acute respiratory distress syndrome (ARDS) is a life-threating lung condition resulting from a direct and indirect injury to the lungs [1, 2]. Pathophysiologically it is characterized by an acute alveolar damage, an increased permeability of the microvascular-barrier, leading to protein-rich pulmonary edema and subsequent impairment of arterial oxygenation and respiratory failure [1]. This study examined the role of extracellular ATP in recruiting inflammatory cells to the lung after induction of acute lung injury with lipopolysaccharide (LPS). However, the precise mechanism is poorly understood. Our objective was to investigate the functional role of the P2X7 receptor in the pathogenesis of acute respiratory distress syndrome (ARDS/ acute lung injury (ALI)) in vitro and in vivo. We show that intratracheally applied LPS causes an acute accumulation of ATP in the BALF (bronchoalveolar lavage) and lungs of mice. Prophylactic and therapeutic inhibition of P2X7R signalling by a specific antagonist and knock-out experiments was able to ameliorate the inflammatory response demonstrated by reduced ATP-levels, number of neutrophils and concentration of pro-inflammatory cytokine levels in the BALF. Experiments with chimeric mice showed that P2X7R expression on immune cells was responsible for the observed effect. Consistently, the inflammatory response is diminished only by a cell-type specific knockdown of P2X7 receptor on non-stationary immune cells. Since the results of BALF from patients with acute ARDS or pneumonia simulated the in vivo data after LPS exposure, the P2X7 receptor may be a new therapeutic target for treatment in acute respiratory distress syndrome (ARDS/ALI).

The potential of P2X7 receptors as a therapeutic target, including inflammation and tumour progression

Seven P2X ion channel nucleotide receptor subtypes have been cloned and characterised. P2X7 receptors (P2X7R) are unusual in that there are extra amino acids in the intracellular C terminus. Low concentrations of ATP open cation channels sometimes leading to cell proliferation, whereas high concentrations of ATP open large pores that release inflammatory cytokines and can lead to apoptotic cell death. Since many diseases involve inflammation and immune responses, and the P2X7R regulates inflammation, there has been recent interest in the pathophysiological roles of P2X7R and the potential of P2X7R antagonists to treat a variety of diseases. These include neurodegenerative diseases, psychiatric disorders, epilepsy and a number of diseases of peripheral organs, including the cardiovascular, airways, kidney, liver, bladder, skin and musculoskeletal. The potential of P2X7R drugs to treat tumour progression is discussed.

Role of the Purinergic Receptor P2XR4 After Blunt Chest Trauma in Cigarette Smoke-Exposed Mice

Both acute and chronic lung injury are associated with up-regulation of the pulmonary expression of the purinergic receptors P2XR4 and P2XR7. Genetic deletion or blockade of P2XR7 attenuated pulmonary hyperinflammation, but simultaneous P2XR4 up-regulation compensated for P2XR7 deletion. Therefore, we tested the hypothesis whether genetic P2XR4 deletion would attenuate the pulmonary inflammatory response and thereby improve organ function after blunt chest trauma in mice with and without pretraumatic cigarette smoke (CS) exposure.After 3 weeks to 4 weeks of exposure to CS, anesthetized wildtype or P2XR4 mice (n = 32) underwent a blast wave-induced blunt chest trauma followed by 4 h of lung-protective mechanical ventilation, fluid resuscitation, and noradrenaline support to maintain mean arterial pressure >55 mm Hg. Hemodynamics, lung mechanics, gas exchange, and acid-base status were measured together with blood and tissue cytokine and chemokine concentrations, heme oxygenase-1, B-cell lymphoma-extra large (Bcl-xL), endogenous nuclear factor-κB inhibitor (IκBα) expression, nitrotyrosine formation, purinergic receptor expression, and histological scoring.Despite a significant increase in the histopathology score in both CS-exposed groups, neither CS exposure nor P2XR4 deletion had any significant effect on post-traumatic pulmonary function and inflammatory response. However, P2XR4 deletion was associated with attenuated impairment of glucose homeostasis and acid-base-status after CS exposure and chest trauma.In conclusion, genetic P2XR4 deletion failed to attenuate the acute post-traumatic pulmonary inflammatory response. The improved glucose homeostasis and acid-base-status after CS exposure in the P2XR4 group was possibly due to less alveolar hypoxia-induced right ventricular remodeling resulting in preserved liver metabolic capacity.

The P2X7 Receptor in Inflammatory Diseases: Angel or Demon?

Under physiological conditions, adenosine triphosphate (ATP) is present at low levels in the extracellular milieu, being massively released by stressed or dying cells. Once outside the cells, ATP and related nucleotides/nucleoside generated by ectonucleotidases mediate a high evolutionary conserved signaling system: the purinergic signaling, which is involved in a variety of pathological conditions, including inflammatory diseases. Extracellular ATP has been considered an endogenous adjuvant that can initiate inflammation by acting as a danger signal through the activation of purinergic type 2 receptors-P2 receptors (P2Y G-protein coupled receptors and P2X ligand-gated ion channels). Among the P2 receptors, the P2X7 receptor is the most extensively studied from an immunological perspective, being involved in both innate and adaptive immune responses. P2X7 receptor activation induces large-scale ATP release via its intrinsic ability to form a membrane pore or in association with pannexin hemichannels, boosting purinergic signaling. ATP acting via P2X7 receptor is the second signal to the inflammasome activation, inducing both maturation and release of pro-inflammatory cytokines, such as IL-1β and IL-18, and the production of reactive nitrogen and oxygen species. Furthermore, the P2X7 receptor is involved in caspases activation, as well as in apoptosis induction. During adaptive immune response, P2X7 receptor modulates the balance between the generation of T helper type 17 (Th17) and T regulatory (Treg) lymphocytes. Therefore, this receptor is involved in several inflammatory pathological conditions. In infectious diseases and cancer, P2X7 receptor can have different and contrasting effects, being an angel or a demon depending on its level of activation, cell studied, type of pathogen, and severity of infection. In neuroinflammatory and neurodegenerative diseases, P2X7 upregulation and function appears to contribute to disease progression. In this review, we deeply discuss P2X7 receptor dual function and its pharmacological modulation in the context of different pathologies, and we also highlight the P2X7 receptor as a potential target to treat inflammatory related diseases.

P2X7R: independent modulation of aquaporin 5 expression in CdCl2-injured alveolar epithelial cells

The expression of aquaporin 5 in alveolar epithelial type I cells under conditions of cadmium-induced injury has not yet been discovered. We investigated the effect of the P2X7R agonist BzATP under this condition, since P2X7R is involved in altered regulation of aquaporin 5 in pulmonary fibrosis. CdCl₂/TGF-β1 treatment of lung epithelial MLE-12 cells was leading to increasing P2X7R, and aquaporin 5 protein levels. The aquaporin 5 expression was P2X7R-independent in MLE-12 cells under cadmium, as was shown in blocking experiments with oxATP. Further, the expression of both proteins increased after 24 h CdCl₂/TGF-β1 treatment of precision-cut lung slices, but decreased after 72 h. Using immunohistochemistry, the activation of the P2X7R with the agonist BzATP modulated the aquaporin 5 immunoreactivity in the alveolar epithelium of precision-cut lung slices from wild-type but not from P2X7R knockout mice. Similarly, aquaporin 5 protein was reduced in BzATP-treated immortal lung epithelial E10 cells. Surprisingly, untreated alveolar epithelial type II cells of P2X7R knockouts exhibited a pronounced apical immunoreactivity in addition to the remaining alveolar epithelial type I cells. BzATP exposure did not alter this distribution pattern, but increased the number of apoptotic alveolar epithelial type II cells in wild-type lung slices.

Lung Diseases

Inflammasomes are large innate cytoplasmic complexes that play a major role in promoting inflammation in the lung in response to a range of environmental and infectious stimuli. Inflammasomes are critical for driving acute innate immune responses that resolve infection and maintain tissue homeostasis. However, dysregulated or excessive inflammasome activation can be detrimental. Here, we discuss the plethora of recent data from clinical studies and small animal disease models that implicate excessive inflammasome responses in the pathogenesis of a number of acute and chronic respiratory inflammatory diseases. Understanding of the role of inflammasomes in lung disease is of great therapeutic interest.

Inhibition of inflammasome activation improves lung acute injury induced by carrageenan in a mouse model of pleurisy

The inflammasome NLRP3 is a molecular pathway activated by a wide range of cellular insults to elicit innate immune defenses through the activation of caspase-1 and the maturation of proinflammatory cytokines, such as IL-1β and IL-18. The expression of NRLP3 is abnormally elevated in numerous human inflammatory diseases, including pulmonary diseases. An injection of carrageenan (CAR) into the pleural cavity triggered an acute inflammatory response, leading to tissue damage, inflammatory exudates, leukocyte infiltration, and increased myeloperoxidase activity. The aim of this study was to assess the effect of the inflammasome blocking agents BAY 11-7082 (30 mg/kg, i.p.) and Brilliant Blue G (BBG) (45.5 mg/kg, i.p.) in a mouse model of CAR-induced pleurisy. Treatment with BAY 11-7082 or BBG 1 h after CAR injection attenuated pulmonary membrane thickening and polymorphonuclear leukocyte infiltration, reduced NF-κB translocation in the nucleus, and inhibited the assembly of the NRLP3/ASC/caspase-1 complex. Treatment with BAY 11-7082 or BBG also down-regulated iNOS, nitrotyrosine, and poly-ADP-ribosyl polymerase expression and inhibited CAR-induced apoptosis. Our results demonstrate that treatment with inflammasome-blocking agents can significantly reduce the development of acute CAR-induced lung injury.-Fusco, R. Gugliandolo, E., Biundo, F., Campolo, M., Di Paola, R., Cuzzocrea, S. Inhibition of inflammasome activation improves lung acute injury induced by carrageenan in a mouse model of pleurisy.

Role of P2X7R in the development and progression of pulmonary hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a devastating disease that lacks sufficient treatment. Studies have shown that the Nod-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome contributes to PAH pathogenesis, but the role of the upstream molecular P2X₇ receptor (P2X₇R) has remained unexplored. We investigated the role of P2X7R in the pathogenesis of PAH.

METHODS AND RESULTS

PH was induced by a single subcutaneous injection of monocrotaline (MCT) (60 mg/kg) on left pneumonectomised Sprague-Dawley rats, as validated by significant increases in pulmonary artery pressure and vessel wall thickness. Marked P2X₇R was detected by predominant PA immunostaining in lungs from PH rats. Western blot revealed a significant increase in the protein levels of P2X₇R as well as NLRP3 and caspase-1 in the diseased lung tissue compared with normal tissue. The rats received A-740003 (a selective P2X₇ receptor antagonist, 30 mg/kg) daily starting from 1 week before or 2 weeks after MCT injection. Consequently, A-740003 reversed the NLRP3 inflammasome upregulation, significantly decreased the mean right ventricular (RV) pressure and RV hypertrophy, and reversed pulmonary arterial remodelling 4 weeks after MCT injection, as both a pretreatment and rescue intervention. Notably, A-740003 significantly reduced macrophage and pro-inflammatory cytokine levels, as measured via bronchoalveolar lavage. The recruitment of macrophages as well as collagen fibre deposition in the perivascular areas were also reduced, as confirmed by histological staining.

CONCLUSIONS

P2X₇R contributes to the pathogenesis of PH, probably in association with activation of the NLRP3 inflammasome. Blockade of P2X7R might be applied as a novel therapeutic approach for the treatment of PAH.

Repression of acetaminophen-induced hepatotoxicity by a combination of celastrol and brilliant blue G

The sterile inflammatory response is an eminent contributor to acetaminophen (APAP)-hepatotoxicity in humans. Recent advances unraveled an axial role of the NLRP3-inflammasome in APAP-post injury inflammation. Nevertheless, the role of signaling events preceded the NLRP3-inflammasome activation, like the transcription factor NF-κB and the purinergic receptor P2X7, is still unclear and needs further elucidation. Here, we investigated the pharmacological inhibition of these upstream signaling molecules by celastrol and brilliant blue G (BBG) (separately or simultaneously) in APAP-hepatotoxicity in mice. The results indicated that both celastrol and BBG pretreatments, especially when combined together, curbed APAP-induced hepatocellular injury (ALT, AST and LDH) and death (necrosis and apoptosis). The underlying mechanisms of protection of such combination against APAP-challenge were attributed to their efficient cooperation in: i) preventing the consumption of hepatic antioxidants (reduced glutathione and superoxide dismutase); ii) limiting the overproduction of lipid peroxidation aldehydes (malondialdehyde and 4-hydroxynonenal) and total nitrate/nitrite products; iii) attenuating the inflammatory cells accumulation in the liver, as evidenced by reducing the number of F4/80 positive cells/field in immunostaining and myeloperoxidase activity; iv) reversing the dysregulation in production of pro-inflammatory (TNF-α, IL-17A and IL-23) and anti-inflammatory (IL-10) cytokines; and v) enhancing the reparative capacity of injured hepatocytes, as demonstrated by increasing the percentage of PCNA positive hepatocytes per field of immunostaining. In conclusion, this murine study elicits a potential clinical applicability and therapeutic utility of celastrol and BBG combination in human cases of APAP-overdose hepatotoxicity.

P2X1, P2X4, and P2X7 Receptor Knock Out Mice Expose Differential Outcome of Sepsis Induced by α-Haemolysin Producing Escherichia coli

α-haemolysin (HlyA)-producing Escherichia coli commonly inflict severe urinary tract infections, including pyelonephritis, which comprises substantial risk for sepsis. In vitro, the cytolytic effect of HlyA is mainly mediated by ATP release through the HlyA pore and subsequent P2X₁/P2X₇ receptor activation. This amplification of the lytic process is not unique to HlyA but is observed by many other pore-forming proteins including complement-induced haemolysis. Since free hemoglobin in the blood is known to be associated with a worse outcome in sepsis one could speculate that inhibition of P2X receptors would ameliorate the course of sepsis. Surprisingly, this study demonstrates that [Formula: see text] and [Formula: see text] mice are exceedingly sensitive to sepsis with uropathogenic E. coli. These mice have markedly lower survival, higher cytokine levels and activated intravascular coagulation. Quite the reverse is seen in [Formula: see text] mice, which had markedly lower cytokine levels and less coagulation activation compared to controls after exposure to uropathogenic E. coli. The high cytokine levels in the [Formula: see text] mouse are unexpected, since P2X₇ is implicated in caspase-1-dependent IL-1β production. Here, we demonstrate that IL-1β production during sepsis with uropathogenic E. coli is mediated by caspase-8, since caspase-8 and RIPK3 double knock out mice show substantially lower cytokine during sepsis and increased survival after injection of TNFα. These data support that P2X₇ and P2X₄ receptor activation has a protective effect during severe E. coli infection.

Inflammatory early events associated to the role of P2X7 receptor in acute murine toxoplasmosis

Activation of the purinergic P2X7 receptor by extracellular ATP (eATP) potentiates proinflammatory responses during infections by intracellular pathogens. Extracellular ATP triggers an antimicrobial response in macrophages infected with Toxoplasma gondii in vitro, suggesting that purinergic signaling may stimulate host defense mechanisms against toxoplasmosis. Here, we provide in vivo evidence in support of this hypothesis, by showing that P2X7^-/- mice are more susceptible than P2X7^+/+ mice to acute infection by the RH strain of T. gondii, and that this phenomenon is associated with a deficient proinflammatory response. Four days post-infection, peritoneal washes from infected P2X7^-/- mice had no or little increase in the levels of the proinflammatory cytokines IL-12, IL-1β, IFN-γ, and TNF-α, whose levels increased markedly in samples from infected P2X7^+/+ mice. Infected P2X7^-/- mice displayed an increase in organ weight and histological alterations in some of the 'shock organs' in toxoplasmosis - the liver, spleen and mesenteric lymph nodes. The liver of infected P2X7^-/- mice had smaller granulomas, but increased parasite load/granuloma. Our results confirm that the P2X7 receptor is involved in containing T. gondii spread in vivo, by stimulating inflammation.

Low level laser therapy reduces acute lung inflammation without impairing lung function

Acute lung injury is a condition characterized by exacerbate inflammatory reaction in distal airways and lung dysfunction. Here we investigate the treatment of acute lung injury (ALI) by low level laser therapy (LLLT), an effective therapy used for the treatment of patients with inflammatory disorders or traumatic injuries, due to its ability to reduce inflammation and promote tissue regeneration. However, studies in internal viscera remains unclear. C57BL/6 mice were treated with intratracheal lipopolysaccharide (LPS) (5 mg/kg) or phosphate buffer saline (PBS). Six hours after instillation, two groups were irradiated with laser at 660 nm and radiant exposure of 10 J/cm² . Intratracheal LPS inoculation induced a marked increase in the number of inflammatory cells in perivascular and alveolar spaces. There was also an increase in the expression and secretion of cytokines (TNF-α, IL-1β, IL-6,) and chemokine (MCP-1). The LLLT application induced a significant decrease in both inflammatory cells influx and inflammatory mediators secretion. These effects did not affect lung mechanical properties, since no change was observed in tissue resistance or elastance. In conclusion LLLT is able to reduce inflammatory reaction in lungs exposed to LPS without affecting the pulmonary function and recovery.

Involvement of matrix metalloproteinases (MMPs) and inflammasome pathway in molecular mechanisms of fibrosis

Fibrosis is a basic connective tissue lesion defined by the increase in the fibrillar extracellular matrix (ECM) components in tissue or organ. Matrix metalloproteinases (MMPs) are a major group of proteases known to regulate the turn-over of ECM and so they are suggested to be important in tissue remodelling observed during fibrogenic process associated with chronic inflammation. Tissue remodelling is the result of an imbalance in the equilibrium of the normal processes of synthesis and degradation of ECM components markedly controlled by the MMPs/TIMP imbalance. We previously showed an association of the differences in collagen deposition in the lungs of bleomycin-treated mice with a reduced molar pro-MMP-9/TIMP-1 ratio. Using the carbon tetrachloride (CCl₄) preclinical model of liver fibrosis in mice, we observed a significant increase in collagen deposition with increased expression and release of tissue inhibitors of metalloproteinase (TIMP)-1 both at 24 h and 3 weeks later. This suggests an early altered regulation of matrix turnover involved in the development of fibrosis. We also demonstrated an activation of NLRP3-inflammasome pathway associated with the IL-1R/MyD88 signalling in the development of experimental fibrosis both in lung and liver. This was also associated with an increased expression of purinergic receptors mainly P2X₇. Finally, these observations emphasize those effective therapies for these disorders must be given early in the natural history of the disease, prior to the development of tissue remodelling and fibrosis.

Deletion of P2X7 attenuates hyperoxia-induced acute lung injury via inflammasome suppression

Increasing evidence shows that hyperoxia is a serious complication of oxygen therapy in acutely ill patients that causes excessive production of free radicals leading to hyperoxia-induced acute lung injury (HALI). Our previous studies have shown that P2X7 receptor activation is required for inflammasome activation during HALI. However, the role of P2X7 in HALI is unclear. The main aim of this study was to determine the effect of P2X7 receptor gene deletion on HALI. Wild-type (WT) and P2X7 knockout (P2X7 KO) mice were exposed to 100% O2 for 72 h. P2X7 KO mice treated with hyperoxia had enhanced survival in 100% O2 compared with the WT mice. Hyperoxia-induced recruitment of inflammatory cells and elevation of IL-1β, TNF-α, monocyte chemoattractant protein-1, and IL-6 levels were attenuated in P2X7 KO mice. P2X7 deletion decreased lung edema and alveolar protein content, which are associated with enhanced alveolar fluid clearance. In addition, activation of the inflammasome was suppressed in P2X7-deficient alveolar macrophages and was associated with suppression of IL-1β release. Furthermore, P2X7-deficient alveolar macrophage in type II alveolar epithelial cells (AECs) coculture model abolished protein permeability across mouse type II AEC monolayers. Deletion of P2X7 does not lead to a decrease in epithelial sodium channel expression in cocultures of alveolar macrophages and type II AECs. Taken together, these findings show that deletion of P2X7 is a protective factor and therapeutic target for the amelioration of hyperoxia-induced lung injury.

P2X7 receptor knockout prevents streptozotocin-induced type 1 diabetes in mice

Type 1 diabetes (T1D) is caused by autoimmune destruction of islet of Langerhans β-cells. P2X7 receptors (P2X7R) modulate proinflammatory immune responses by binding extracellular ATP, a classic 'danger signal'. Here, we evaluated whether the P2X7R has a role in T1D development. P2X7(-/-) mice are resistant to TD1 induction by streptozotocin (STZ) treatment, with no increase in blood glucose, decrease in insulin-positive cells, and pancreatic islet reduction, compared to WT (C57BL/6) mice. Also, the levels of proinflammatory mediators (IL-1β, IFN-γ and NO) did not increase after STZ treatment in P2X7(-/-) animals, with reduced infiltration of CD4(+), CD8(+), B220(+), CD11b(+) and CD11c(+) cells in the pancreatic lymph nodes. Treatment with a P2X7 antagonist mimicked the effect of P2X7 knockout, preventing STZ-induced diabetes. Our results show that the absence of the P2X7R provides resistance in the induction of diabetes in this model, and suggest that therapy targeting the P2X7R may be useful against clinical T1D.

Blunt Chest Trauma in Mice after Cigarette Smoke-Exposure: Effects of Mechanical Ventilation with 100% O2

Cigarette smoking (CS) aggravates post-traumatic acute lung injury and increases ventilator-induced lung injury due to more severe tissue inflammation and apoptosis. Hyper-inflammation after chest trauma is due to the physical damage, the drop in alveolar PO₂, and the consecutive hypoxemia and tissue hypoxia. Therefore, we tested the hypotheses that 1) CS exposure prior to blunt chest trauma causes more severe post-traumatic inflammation and thereby aggravates lung injury, and that 2) hyperoxia may attenuate this effect. Immediately after blast wave-induced blunt chest trauma, mice (n=32) with or without 3-4 weeks of CS exposure underwent 4 hours of pressure-controlled, thoraco-pulmonary compliance-titrated, lung-protective mechanical ventilation with air or 100 % O₂. Hemodynamics, lung mechanics, gas exchange, and acid-base status were measured together with blood and tissue cytokine and chemokine concentrations, heme oxygenase-1 (HO-1), activated caspase-3, and hypoxia-inducible factor 1-α (HIF-1α) expression, nuclear factor-κB (NF-κB) activation, nitrotyrosine formation, purinergic receptor 2X₄ (P2XR₄) and 2X₇ (P2XR₇) expression, and histological scoring. CS exposure prior to chest trauma lead to higher pulmonary compliance and lower PaO₂ and Horovitz-index, associated with increased tissue IL-18 and blood MCP-1 concentrations, a 2-4-fold higher inflammatory cell infiltration, and more pronounced alveolar membrane thickening. This effect coincided with increased activated caspase-3, nitrotyrosine, P2XR₄, and P2XR₇ expression, NF-κB activation, and reduced HIF-1α expression. Hyperoxia did not further affect lung mechanics, gas exchange, pulmonary and systemic cytokine and chemokine concentrations, or histological scoring, except for some patchy alveolar edema in CS exposed mice. However, hyperoxia attenuated tissue HIF-1α, nitrotyrosine, P2XR₇, and P2XR₄ expression, while it increased HO-1 formation in CS exposed mice. Overall, CS exposure aggravated post-traumatic inflammation, nitrosative stress and thereby organ dysfunction and injury; short-term, lung-protective, hyperoxic mechanical ventilation have no major beneficial effect despite attenuation of nitrosative stress, possibly due to compensation of by regional alveolar hypoxia and/or consecutive hypoxemia, resulting in down-regulation of HIF-1α expression.

Blockage of P2X7 attenuates acute lung injury in mice by inhibiting NLRP3 inflammasome

NLRP3 inflammasome is engaged in the inflammatory response during acute lung injury (ALI). Purinergic receptor P2X7 has been reported to be upstream of NLRP3 activation. However, the therapeutic implication of P2X7 in ALI remains to be explored. The present study used lipopolysaccharide (LPS)-induced mouse model to investigate the therapeutic potential of P2X7 blockage in ALI. Our results showed that P2X7/NLRP3 inflammasome pathway was significantly upregulated in the lungs of ALI mice as compared with control mice. P2X7 antagonist A438079 suppressed NLRP3/ASC/caspase 1 activation, production of IL-1β, IL-17A and IFN-γ and neutrophil infiltration but not the production of IL-10, resulting in a significant amelioration of lung injury. Moreover, blockage of P2X7 significantly inhibited NLRP3 inflammasome activation and IL-1β production in bone marrow derived macrophages. Similar results were obtained using another P2X7 inhibitor brilliant blue G (BBG) in vivo. Thus, pharmacological blockage of P2X7/NLRP3 pathway can be considered as a potential therapeutic strategy in patients with ALI.

Lipopolysaccharide Induces Alveolar Macrophage Necrosis via CD14 and the P2X7 Receptor Leading to Interleukin-1α Release

Acute lung injury (ALI) remains a serious health issue with little improvement in our understanding of the pathophysiology and therapeutic approaches. We investigated the mechanism that lipopolysaccharide (LPS) induces early neutrophil recruitment to lungs and increases pulmonary vascular permeability during ALI. Intratracheal LPS induced release of pro-interleukin-1α (IL-1α) from necrotic alveolar macrophages (AM), which activated endothelial cells (EC) to induce vascular leakage via loss of vascular endothelial (VE)-cadherin. LPS triggered the AM purinergic receptor P2X7(R) to induce Ca(2+) influx and ATP depletion, which led to necrosis. P2X7R deficiency significantly reduced necrotic death of AM and release of pro-IL-1α into the lung. CD14 was required for LPS binding to P2X7R, as CD14 neutralization significantly diminished LPS induced necrotic death of AM and pro-IL-1α release. These results demonstrate a key role for pro-IL-1α from necrotic alveolar macrophages in LPS-mediated ALI, as a critical initiator of increased vascular permeability and early neutrophil infiltration.

The P2X7 Receptor Contributes to the Development of the Exacerbated Inflammatory Response Associated with Sepsis

BACKGROUND

Sepsis is associated with high mortality rates in intensive care units worldwide and represents a systemic inflammatory response to infection. P2X7 is an ionotropic purine receptor with known proinflammatory activity. Here, we investigated the role of the P2X7 receptor in sepsis induced by cecal ligation and puncture (CLP).

METHODS

Wild-type (WT) and P2X7KO (P2X7 null) mice were subjected to CLP and their survival was monitored for 7 days. Blood, peritoneal wash and lungs were collected 24 h after CLP and used to measure bacterial load, immune cell infiltration, nitric oxide (NO), cytokine levels, and peritoneal cell death and to assess lung injury.

RESULTS

P2X7KO mice showed significantly increased survival 7 days after CLP (30% compared to 60% in WT animals) accompanied by an overall attenuated inflammatory response, with decreased cell recruitment to the peritoneum, no or limited increases in the levels of NO and proinflammatory cytokines (IL-1β, IL-6, IL-12, IL-17, and IL-4), reduced peritoneal cell apoptosis, and less pronounced lung infiltration and morphological changes.

CONCLUSIONS

Our data show the P2X7 receptor is required for the development of the inflammatory response associated with sepsis and support the notion that P2X7 receptor is a valid therapeutic target against inflammatory diseases.

Involvement of purinergic receptors and NOD-like receptor-family protein 3-inflammasome pathway in the adenosine triphosphate-induced cytokine release from macrophages

Adenosine triphosphate (ATP) has been described as a danger signal activating the NOD-like receptor-family protein 3 (NLRP3)-inflammasome leading to the pro-inflammatory cytokine, interleukin (IL)-1β, release in the lung. The NLRP3-inflammasome pathway has been previously described to be involved in experimental collagen deposition and the development of pulmonary fibrosis. The aim of the present study was to investigate the role of the NLRP3 inflammasome pathway and P2X7 purinergic receptor in the activation of human macrophages in vitro by ATP. We showed that adenosine 5'-[γ-thio]triphosphate tetralithium salt (ATPγS) and 2',3'-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (BzATP), two stable analogs of ATP, are able to potentiate the release of IL-1β from human monocyte-derived macrophages induced by low concentration of lipopolysaccharide (LPS). However, in the same conditions no increase in IL-1α and IL-6 was observed. Immunochemistry has shown that human macrophages natively express NLRP3 and purinergic P2X7 receptors (P2X7 R). NLRP3 and IL-1β mRNA expression were induced from LPS-primed macrophages, but also after 5-h treatment of BzATP as analysed by reverse transcription quantitative polymerase chain reaction. However, other inflammasome pathways (NLRP1, NLRP2, NLRC4, NLRP6 and AIM2) and P2X7 R were not induced by BzATP. We observed that P2X7 R antagonists, A-438079 and A-740003, were able to reduce the release of IL-1β, but not of IL-1α and IL-6 from macrophages stimulated by ATPγS or BzATP. The present results showed the involvement of the P2X7 R-NLRP3 inflammasome pathway in the secretion of IL-1β from ATP-stimulated human macrophages, and suggest that P2X7 R were not involved in IL-1α and IL-6 release. This study also points out that repression of the P2X7 R represents a novel potential therapeutic approach to control fibrosis in lung injury.

Decreased inflammatory responses of human lung epithelial cells after ethanol exposure are mimicked by ethyl pyruvate

Background and Purpose. Leukocyte migration into alveolar space plays a critical role in pulmonary inflammation resulting in lung injury. Acute ethanol (EtOH) exposure exerts anti-inflammatory effects. The clinical use of EtOH is critical due to its side effects. Here, we compared effects of EtOH and ethyl pyruvate (EtP) on neutrophil adhesion and activation of cultured alveolar epithelial cells (A549). Experimental Approach. Time course and dose-dependent release of interleukin- (IL-) 6 and IL-8 from A549 were measured after pretreatment of A549 with EtP (2.5–10 mM), sodium pyruvate (NaP, 10 mM), or EtOH (85–170 mM), and subsequent lipopolysaccharide or IL-1beta stimulation. Neutrophil adhesion to pretreated and stimulated A549 monolayers and CD54 surface expression were determined. Key Results. Treating A549 with EtOH or EtP reduced substantially the cytokine-induced release of IL-8 and IL-6. EtOH and EtP (but not NaP) reduced the adhesion of neutrophils to monolayers in a dose- and time-dependent fashion. CD54 expression on A549 decreased after EtOH or EtP treatment before IL-1beta stimulation. Conclusions and Implications. EtP reduces secretory and adhesive potential of lung epithelial cells under inflammatory conditions. These findings suggest EtP as a potential treatment alternative that mimics the anti-inflammatory effects of EtOH in early inflammatory response in lungs.

P2X7 receptor modulates inflammatory and functional pulmonary changes induced by silica

Silicosis is an occupational lung disease, characterized by irreversible and progressive fibrosis. Silica exposure leads to intense lung inflammation, reactive oxygen production, and extracellular ATP (eATP) release by macrophages. The P2X7 purinergic receptor is thought to be an important immunomodulator that responds to eATP in sites of inflammation and tissue damage. The present study investigates the role of P2X7 receptor in a murine model of silicosis. To that end wild-type (C57BL/6) and P2X7 receptor knockout mice received intratracheal injection of saline or silica particles. After 14 days, changes in lung mechanics were determined by the end-inflation occlusion method. Bronchoalveolar lavage and flow cytometry analyzes were performed. Lungs were harvested for histological and immunochemistry analysis of fibers content, inflammatory infiltration, apoptosis, as well as cytokine and oxidative stress expression. Silica particle effects on lung alveolar macrophages and fibroblasts were also evaluated in cell line cultures. Phagocytosis assay was performed in peritoneal macrophages. Silica exposure increased lung mechanical parameters in wild-type but not in P2X7 knockout mice. Inflammatory cell infiltration and collagen deposition in lung parenchyma, apoptosis, TGF-β and NF-κB activation, as well as nitric oxide, reactive oxygen species (ROS) and IL-1β secretion were higher in wild-type than knockout silica-exposed mice. In vitro studies suggested that P2X7 receptor participates in silica particle phagocytosis, IL-1β secretion, as well as reactive oxygen species and nitric oxide production. In conclusion, our data showed a significant role for P2X7 receptor in silica-induced lung changes, modulating lung inflammatory, fibrotic, and functional changes.

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

Background

The 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.

Methods

Mice 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.

Results

BALF 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.

Conclusions

TLR4 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.

Pulmonary infection with hypervirulent Mycobacteria reveals a crucial role for the P2X7 receptor in aggressive forms of tuberculosis

The purinergic P2X7 receptor (P2X7R) is a sensor of extracellular ATP, a damage-associated molecule that is released from necrotic cells and that induces pro-inflammatory cytokine production and cell death. To investigate whether the innate immune response to damage signals could contribute to the development of pulmonary necrotic lesions in severe forms of tuberculosis, disease progression was examined in C57BL/6 and P2X7R^−/− mice that were intratracheally infected with highly virulent mycobacterial strains (Mycobacterium tuberculosis strain 1471 of the Beijing genotype family and Mycobacterium bovis strain MP287/03). The low-dose infection of C57BL/6 mice with bacteria of these strains caused the rapid development of extensive granulomatous pneumonia with necrotic areas, intense bacillus dissemination and anticipated animal death. In contrast, in P2X7R^−/− mice, the lung pathology presented with moderate infiltrates of mononuclear leukocytes without visible signs of necrosis; the disease attenuation was accompanied by a delay in mortality. In vitro, the hypervirulent mycobacteria grew rapidly inside macrophages and induced death by a P2X7R-dependent mechanism that facilitated the release of bacilli. Furthermore, these bacteria were resistant to the protective mechanisms elicited in macrophages following extracellular ATP stimulation. Based on this study, we propose that the rapid intracellular growth of hypervirulent mycobacteria results in massive macrophage damage. The ATP released by damaged cells engages P2X7R and accelerates the necrotic death of infected macrophages and the release of bacilli. This vicious cycle exacerbates pneumonia and lung necrosis by promoting widespread cell destruction and bacillus dissemination. These findings suggest the use of drugs that have been designed to inhibit the P2X7R as a new therapeutic approach to treat the aggressive forms of tuberculosis.

Nearly 9 million new cases of tuberculosis and 1.3 million deaths are reported yearly worldwide. Most individuals infected with tubercle bacilli remain asymptomatic; however, some develop active tuberculosis due to the reactivation of latent infections. Progressive primary tuberculosis is an alternative form of the disease that mostly affects children and immunocompromised individuals. Extensive pneumonia, pulmonary necrosis and bacillus dissemination characterize some of the aggressive forms of tuberculosis. To investigate the molecular mechanisms that underlie severe disease progression, we used experimental models of relatively resistant C57BL/6 mice that were infected with highly virulent strains of Mycobacterium tuberculosis or Mycobacterium bovis. Two hypervirulent strains (Mtb strain 1471 and Mbv strain MP287/03) induced extensive pulmonary inflammation and necrosis in mice and promoted bacillus dissemination and animal death. We hypothesized that the innate immune response to endogenous damage signals from necrotic cells could aggravate the disease. We focused our study on the purinergic P2X7 receptor (P2X7R), a sensor of ATP that is released from necrotic cells and that induces pro-inflammatory cytokine production and cell death. Our data provide new insights into the pathogenesis of severe tuberculosis by showing that mice that lack P2X7R have attenuated disease with substantially reduced bacillus dissemination and lung inflammation without evidence of necrosis.

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.

Wnt3a mitigates acute lung injury by reducing P2X7 receptor-mediated alveolar epithelial type I cell death

Acute lung injury (ALI) is characterized by pulmonary endothelial and epithelial cell damage, and loss of the alveolar–capillary barrier. We have previously shown that P2X7 receptor (P2X7R), a cell death receptor, is specifically expressed in alveolar epithelial type I cells (AEC I). In this study, we hypothesized that P2X7R-mediated purinergic signaling and its interaction with Wnt/β-catenin signaling contributes to AEC I death. We examined the effect of P2X7R agonist 2′-3′-O-(4-benzoylbenzoyl)-ATP (BzATP) and Wnt agonist Wnt3a on AEC I death in vitro and in vivo. We also assessed the therapeutic potential of Wnt3a in a clinically relevant ALI model of intratracheal lipopolysaccharide (LPS) exposure in ventilated mice. We found that the activation of P2X7R by BzATP caused the death of AEC I by suppressing Wnt/β-catenin signaling through stimulating glycogen synthase kinase-3β (GSK-3β) and proteasome. On the other hand, the activation of Wnt/β-catenin signaling by Wnt3a, GSK-3β inhibitor, or proteasome inhibitor blocked the P2X7R-mediated cell death. More importantly, Wnt3a attenuated the AEC I damage caused by intratracheal instillation of BzATP in rats or LPS in ventilated mice. Our results suggest that Wnt3a overrides the effect of P2X7R on the Wnt/β-catenin signaling to prevent the AEC I death and restrict the severity of ALI.

Role of P2X purinoceptor 7 in neurogenic pulmonary edema after subarachnoid hemorrhage in rats

Introduction

Neurogenic pulmonary edema (NPE) is an acute and serious complication after subarachnoid hemorrhage (SAH) with high mortality. The present study aimed to test the therapeutic potential of brilliant blue G (BBG), a selective P2X purinoceptor 7 (P2X7R) antagonist, on NPE in a rat SAH model.

Methods

SAH was induced by endovascular perforation. 86 Sprague-Dawley rats were randomly divided into sham, vehicle-, or BBG-treatment groups. Mortality, body weight, SAH grading, neurological deficits, NPE clinical symptoms, and pulmonary index were measured at 24 hours following SAH. Western blot, gelatin zymography, lung histopathology, and immunofluorescence staining were performed in the left lung lobe to explore the underlying mechanisms at 24 hours post-surgery.

Results

The incidence of clinical symptoms was correlated with pulmonary index. P2X7R and the marker of alveolar type I epithelial cells (the mucin-type glycoprotein T1-α) immunoreactivities were generally co-localized. BBG administration decreased mature interleukin-1β, myeloperoxidase, and matrix metallopeptidase-9 activation, but increased tight junction proteins, such as ZO-1 and occludin, which ameliorated pulmonary edema via anti-inflammation and improved neurological deficits.

Conclusion

P2X7R inhibition prevented NPE after SAH by attenuating inflammation. Thus, BBG is a potential therapeutic application for NPE after SAH and warrants further research.

Effect of TRIF on permeability and apoptosis in bovine microvascular endothelial cells exposed to lipopolysaccharide

Bovine respiratory disease complex (BRDC) can be caused by several Gram negative bacteria. Lung endothelial cells may be damaged by the release of lipopolysaccharide (LPS) from these organisms. Toll-like receptor (TLR-4) signaling pathways include the myeloid differentiation primary response gene 88 (MyD88) and the Toll/interleukin (IL)-1 receptor (TIR) domain-containing adapter-inducing interferon-β (TRIF) pathways. The aim of this study was to determine which of these pathways is responsible for permeability changes, apoptosis and cytokine production in bovine lung microvascular cells exposed to LPS. Bovine lung endothelial cells were treated with a peptide to inhibit MyD88 signaling or small interfering RNA (siRNA) to inhibit TRIF signaling. Effects were measured using trans-well endothelial electrical resistance to determine cell monolayer permeability, annexin staining to estimate apoptosis and real-time PCR to measure levels of expression of IL-1β and tumor necrosis factor (TNF)-α mRNA. Inhibition of TRIF signaling reduced permeability changes and apoptosis in endothelial cells exposed to LPS. In contrast, MyD88 inhibition reduced expression of IL-1β and TNF-α mRNA in LPS treated cells, but had no effect on permeability. It was concluded that TRIF signaling in LPS-stimulated lung endothelial cells results in permeability changes and apoptosis.

Adenosine-5'-triphosphate (ATP) protects mice against bacterial infection by activation of the NLRP3 inflammasome

It has been established that Adenosine-5'-triphosphate (ATP) can activate the NLRP3 inflammasome. However, the physiological effect of extracellular ATP on NLRP3 inflammasome activation has not yet been investigated. In the present study, we found that ATP was indeed released during bacterial infection. By using a murine peritonitis model, we also found that ATP promotes the fight against bacterial infection in mice. ATP induced the secretion of IL-1β and chemokines by murine bone marrow-derived macrophages in vitro. Furthermore, the intraperitoneal injection of ATP elevated the levels of IL-1β and chemokines in the mouse peritoneal lavage. Neutrophils were rapidly recruited to the peritoneum after ATP injection. In addition, the effects on cytokine and chemokine secretion and neutrophil recruitment were markedly attenuated by the pre-administration of the caspase-1 inhibitor Ac-YVAD-cho. Ac-YVAD-cho also significantly attenuated the protective effect of ATP against bacterial infection. In the present study, we demonstrated a protective role for ATP during bacterial infection and this effect was related to NLRP3 inflammasome activation. Together, these results suggest a role for ATP in initiating the immune response in hosts suffering from infections.

Role of extracellular nucleotides in the immune response against intracellular bacteria and protozoan parasites

Extracellular nucleotides are danger signals involved in recognition and control of intracellular pathogens. They are an important component of the innate immune response against intracellular pathogens, inducing the recruitment of inflammatory cells, stimulating secretion of cytokines, and producing inflammatory mediators such as reactive oxygen species (ROS) and nitric oxide (NO). In the case of extracellular ATP, some of the immune responses are mediated through activation of the NLRP3 inflammasome and secretion of the cytokine, interleukin-1β (IL-1β), through a mechanism dependent on ligation of the P2X7 receptor. Here we review the role of extracellular nucleotides as sensors of intracellular bacteria and protozoan parasites, and discuss how these pathogens manipulate purinergic signaling to diminish the immune response against infection.