Prostaglandin E2 enhances interleukin-8 production via EP4 receptor in human pulmonary microvascular endothelial cells

Eicosanoids Signals in SARS-CoV-2 Infection: A Foe or Friend

SARS-CoV-2 mediated infection instigated a scary pandemic state since 2019. They created havoc comprising death, imbalanced social structures, and a wrecked global economy. During infection, the inflammation and associated cytokine storm generate a critical pathological situation in the human body, especially in the lungs. By the passage of time of infection, inflammatory disorders, and multiple organ damage happen which might lead to death, if not treated properly. Until now, many pathological parameters have been used to understand the progress of the severity of COVID-19 but with limited success. Bioactive lipid mediators have the potential of initiating and resolving inflammation in any disease. The connection between lipid storm and inflammatory states of SARS-CoV-2 infection has surfaced and got importance to understand and mitigate the pathological states of COVID-19. As the role of eicosanoids in COVID-19 infection is not well defined, available information regarding this issue has been accumulated to address the possible network of eicosanoids related to the initiation of inflammation, promotion of cytokine storm, and resolution of inflammation, and highlight possible strategies for treatment and drug discovery related to SARS-CoV-2 infection in this study. Understanding the involvement of eicosanoids in exploration of cellular events provoked by SARS-CoV-2 infection has been summarized as an important factor to deescalate any upcoming catastrophe imposed by the lethal variants of this micro-monster. Additionally, this study also recognized the eicosanoid based drug discovery, treatment, and strategies for managing the severity of SARS-COV-2 infection.

The calcineurin-NFATc pathway modulates the lipid mediators in BAL fluid extracellular vesicles, thereby regulating microvascular endothelial cell barrier function

Extracellular vesicles mediate intercellular communication by transporting biologically active macromolecules. Our prior studies have demonstrated that the nuclear factor of activated T cell cytoplasmic member 3 (NFATc3) is activated in mouse pulmonary macrophages in response to lipopolysaccharide (LPS). Inhibition of NFATc3 activation by a novel cell-permeable calcineurin peptide inhibitor CNI103 mitigated the development of acute lung injury (ALI) in LPS-treated mice. Although pro-inflammatory lipid mediators are known contributors to lung inflammation and injury, it remains unclear whether the calcineurin-NFATc pathway regulates extracellular vesicle (EV) lipid content and if this content contributes to ALI pathogenesis. In this study, EVs from mouse bronchoalveolar lavage fluid (BALF) were analyzed for their lipid mediators by liquid chromatography in conjunction with mass spectrometry (LC-MS/MS). Our data demonstrate that EVs from LPS-treated mice contained significantly higher levels of arachidonic acid (AA) metabolites, which were found in low levels by prior treatment with CNI103. The catalytic activity of lung tissue cytoplasmic phospholipase A2 (cPLA2) increased during ALI, correlating with an increased amount of arachidonic acid (AA) in the EVs. Furthermore, ALI is associated with increased expression of cPLA2, cyclooxygenase 2 (COX2), and lipoxygenases (5-LOX, 12-LOX, and 15-LOX) in lung tissue, and pretreatment with CNI103 inhibited the catalytic activity of cPLA2 and the expression of cPLA2, COX, and LOX transcripts. Furthermore, co-culture of mouse pulmonary microvascular endothelial cell (PMVEC) monolayer and NFAT-luciferase reporter macrophages with BALF EVs from LPS-treated mice increased the pulmonary microvascular endothelial cell (PMVEC) monolayer barrier permeability and luciferase activity in macrophages. However, EVs from CNI103-treated mice had no negative impact on PMVEC monolayer barrier integrity. In summary, BALF EVs from LPS-treated mice carry biologically active NFATc-dependent, AA-derived lipids that play a role in regulating PMVEC monolayer barrier function.

The role of PGE2 and EP receptors on lung's immune and structural cells; possibilities for future asthma therapy

Asthma is the most common airway chronic disease with treatments aimed mainly to control the symptoms. Adrenergic receptor agonists, corticosteroids and anti-leukotrienes have been used for decades, and the development of more targeted asthma treatments, known as biological therapies, were only recently established. However, due to the complexity of asthma and the limited efficacy as well as the side effects of available treatments, there is an urgent need for a new generation of asthma therapies. The anti-inflammatory and bronchodilatory effects of prostaglandin E2 in asthma are promising, yet complicated by undesirable side effects, such as cough and airway irritation. In this review, we summarize the most important literature on the role of all four E prostanoid (EP) receptors on the lung's immune and structural cells to further dissect the relevance of EP2/EP4 receptors as potential targets for future asthma therapy.

Eupalinolide B attenuates lipopolysaccharide-induced acute lung injury through inhibition of NF-κB and MAPKs signaling by targeting TAK1 protein

Acute lung injury (ALI) is a life-threatening disease characterized by severe inflammatory response, which has no pharmacological therapy in clinic. In this study, we found that eupalinolide B (EB), a sesquiterpene lactone isolated from Eupatorium lindleyanum, significantly ameliorated lipopolysaccharide (LPS)-induced ALI in mice, which manifests as reduction in lung injury score, activity of myeloperoxidase, and release of cytokines interleukin (IL)-1β, IL-6, tumor necrosis factor-α (TNF-α), and monocyte chemoattractant protein-1 (MCP-1). In RAW264.7 murine macrophages, EB effectively inhibited LPS-induced production of nitric oxide (NO) and prostaglandin E2 (PGE₂) by down-regulating the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX2), respectively. Mechanistically, EB not only blocked LPS-induced phosphorylation of inhibitor of nuclear factor kappa B kinase-α/β (IKKα/β), phosphorylation and degradation of inhibitor of nuclear factor-kappa B alpha (IκBα), and phosphorylation and nuclear translocation of nuclear factor-kappa B (NF-κB) P65, but also suppressed LPS-induced phosphorylation of mitogen-activated protein kinases (MAPKs) in vitro or in vivo. Through cellular thermal shift assay and western blotting, EB was demonstrated to target and inactivate transforming growth factor β activated kinase-1 (TAK1), which is an important upstream kinase for the activation of NF-κB and MAPKs pathways. Additionally, EB-mediated actions were markedly abolished by dithiothreitol in LPS-exposed RAW264.7 cells, suggesting a crucial role of the α,γ-unsaturated lactone for the anti-inflammatory activity of EB. In conclusion, our findings showed that EB could effectively alleviate ALI in mice, and attenuate inflammatory response by inhibiting the activation of TAK1, and TAK1-mediated activation of NF-κB and MAPKs cascades.

Therapeutic potential of ginger against COVID-19: Is there enough evidence?

In addition to the respiratory system, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) strikes other systems, including the digestive, circulatory, urogenital, and even the central nervous system, as its receptor angiotensin-converting enzyme 2 (ACE2) is expressed in various organs, such as lungs, intestine, heart, esophagus, kidneys, bladder, testis, liver, and brain. Different mechanisms, in particular, massive virus replication, extensive apoptosis and necrosis of the lung-related epithelial and endothelial cells, vascular leakage, hyper-inflammatory responses, overproduction of pro-inflammatory mediators, cytokine storm, oxidative stress, downregulation of ACE2, and impairment of the renin-angiotensin system contribute to the COVID-19 pathogenesis. Currently, COVID-19 is a global pandemic with no specific anti-viral treatment. The favorable capabilities of the ginger were indicated in patients suffering from osteoarthritis, neurodegenerative disorders, rheumatoid arthritis, type 2 diabetes, respiratory distress, liver diseases and primary dysmenorrheal. Ginger or its compounds exhibited strong anti-inflammatory and anti-oxidative influences in numerous animal models. This review provides evidence regarding the potential effects of ginger against SARS-CoV-2 infection and highlights its antiviral, anti-inflammatory, antioxidative, and immunomodulatory impacts in an attempt to consider this plant as an alternative therapeutic agent for COVID-19 treatment.

Role of arachidonic cascade in COVID-19 infection: A review

The World Health Organization has described the 2019 Coronavirus disease caused by an influenza-like virus called SARS-CoV-2 as a pandemic. Millions of people worldwide are already infected by this virus, and severe infection causes hyper inflammation, thus disrupting lung function, exacerbating breath difficulties, and death. Various inflammatory mediators bio-synthesized through the arachidonic acid pathway play roles in developing cytokine storms, injuring virus-infected cells. Since pro-inflammatory eicosanoids, including prostaglandins, and leukotrienes, are key brokers for physiological processes such as inflammation, fever, allergy, and pain but, their function in COVID-19 is not well defined. This study addresses eicosanoid's crucial role through the arachidonic pathway in inflammatory cascading and recommends using bioactive lipids, NSAIDs, steroids, cell phospholipase A2 (cPLA2) inhibitors, and specialized pro-resolving mediators (SPMs) to treat COVID-19 disease. The role of soluble epoxide hydrolase inhibitors (SEHIs) in promoting the activity of epoxyeicosatrienoic acids (EETs) and 17-hydroxide-docosahexaenoic acid (17-HDHA) is also discussed. Additional research that assesses the eicosanoid profile in COVID-19 patients or preclinical models generates novel insights into coronavirus-host interaction and inflammation regulation.

Non-steroidal anti-inflammatory drugs, prostaglandins, and COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of the novel coronavirus disease 2019 (COVID-19), a highly pathogenic and sometimes fatal respiratory disease responsible for the current 2020 global pandemic. Presently, there remains no effective vaccine or efficient treatment strategies against COVID-19. Non-steroidal anti-inflammatory drugs (NSAIDs) are medicines very widely used to alleviate fever, pain, and inflammation (common symptoms of COVID-19 patients) through effectively blocking production of prostaglandins (PGs) via inhibition of cyclooxyganase enzymes. PGs can exert either proinflammatory or anti-inflammatory effects depending on the inflammatory scenario. In this review, we survey the potential roles that NSAIDs and PGs may play during SARS-CoV-2 infection and the development and progression of COVID-19. LINKED ARTICLES: This article is part of a themed issue on The Pharmacology of COVID-19. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.21/issuetoc.

What about COVID-19 and arachidonic acid pathway?

Background and objective

COVID-19 is a highly contagious viral disease. In this study, we tried to define and discuss all the findings on the potential association between arachidonic acid (AA) pathway and COVID-19 pathophysiology.

Methods

A literature search across PubMed, Scopus, Embase, and Cochrane database was conducted. A total of 25 studies were identified.

Results

The data elucidated that COX-2 and prostaglandins (PGs), particularly PGE₂, have pro-inflammatory action in COVID-19 pathophysiology. Arachidonic acid can act as endogenous antiviral compound. A deficiency in AA can make humans more susceptible to COVID-19. Targeting these pro-inflammatory mediators may help in decreasing the mortality and morbidity rate in COVID-19 patients.

Conclusions

PGE₂ levels and other PGs levels should be measured in patients with COVID-19. Lowering the PGE₂ levels through inhibition of human microsomal prostaglandin E synthase-1 (mPGES-1) can enhance the host immune response against COVID-19. In addition, the hybrid compounds, such as COX-2 inhibitors/TP antagonists, can be an innovative treatment to control the overall balance between AA mediators in patients with COVID-19.

Anti-Inflammatory Properties of Chemical Probes in Human Whole Blood: Focus on Prostaglandin E2 Production

We screened 57 chemical probes, high-quality tool compounds, and relevant clinically used drugs to investigate their effect on pro-inflammatory prostaglandin E2 (PGE2) production and interleukin-8 (IL-8) secretion in human whole blood. Freshly drawn blood from healthy volunteers and patients with systemic lupus erythematosus (SLE) or dermatomyositis was incubated with compounds at 0.1 or 1 µM and treated with lipopolysaccharide (LPS, 10 µg/ml) to induce a pro-inflammatory condition. Plasma was collected after 24 h for lipid profiling using liquid chromatography tandem mass spectrometry (LC-MS/MS) and IL-8 quantification using enzyme-linked immunosorbent assay (ELISA). Each compound was tested in at least four donors at one concentration based on prior knowledge of binding affinities and in vitro activity. Our screening suggested that PD0325901 (MEK-1/2 inhibitor), trametinib (MEK-1/2 inhibitor), and selumetinib (MEK-1 inhibitor) decreased while tofacitinib (JAK inhibitor) increased PGE2 production. These findings were validated by concentration-response experiment in two donors. Moreover, the tested MEK inhibitors decreased thromboxane B2 (TXB2) production and IL-8 secretion. We also investigated the lysophophatidylcholine (LPC) profile in plasma from treated whole blood as these lipids are potentially important mediators in inflammation, and we did not observe any changes in LPC profiles. Collectively, we deployed a semi-high throughput and robust methodology to investigate anti-inflammatory properties of new chemical probes.

PGE2 stimulates COX-2 expression via EP2/4 receptors and acts in synergy with IL-1β in human follicular dendritic cell-like cells

PGE2 is the major lipid mediator of inflammation produced by multiple cell types including follicular dendritic cells (FDCs) of the lymphoid tissue. We have investigated the immunoregulatory function of PGE2 and its production mechanism using FDC-like cells isolated from human tonsil. Our recent observation of COX-2-inducing effect of PGE2 prompted us to identify the responsible receptor in this study. Pharmacologic approaches were adopted and Western blotting was utilized to measure protein expression levels. Agonists selective for EP2 and EP4 significantly stimulated COX-2 expression, while antagonists for these receptors prevented PGE2 from triggering COX-2 induction. The combined addition of EP2 and EP4 antagonists resulted in further inhibition of PGE2. In contrast, EP1 and EP3 antagonists failed to exhibit the inhibitory effect on PGE2-induced COX-2 expression. Since PGE2 achieves COX-2 induction by repressing Akt activation in FDC-like cells, we confirmed EP2 and EP4 being the targets of PGE2 by examining the effects of E-prostanoid (EP) agonists and antagonists on the level of Akt phosphorylation. After the identification of PGE2 receptor, we examined the effect of PGE2 on IL-1β-induced COX-2 expression. PGE2 and IL-1β brought about a synergistic induction of COX-2 expression. Taken together, this study implies the impact of the combined role of eicosanoids and cytokines in inflammatory milieu.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.

The EP1/EP3 receptor agonist 17-pt-PGE2 acts as an EP4 receptor agonist on endothelial barrier function and in a model of LPS-induced pulmonary inflammation

Endothelial dysfunction is a hallmark of inflammatory conditions. We recently demonstrated that prostaglandin (PG)E₂ enhances the resistance of pulmonary endothelium in vitro and counteracts lipopolysaccharide (LPS)-induced pulmonary inflammation in vivo via EP4 receptors. The aim of this study was to investigate the role of the EP1/EP3 receptor agonist 17-phenyl-trinor-(pt)-PGE₂ on acute lung inflammation in a mouse model. In LPS-induced pulmonary inflammation in mice, 17-pt-PGE₂ reduced neutrophil infiltration and inhibited vascular leakage. These effects were unaltered by an EP1 antagonist, but reversed by EP4 receptor antagonists. 17-pt-PGE₂ increased the resistance of pulmonary microvascular endothelial cells and prevented thrombin-induced disruption of endothelial junctions. Again, these effects were not mediated via EP1 or EP3 but through activation of the EP4 receptor, as demonstrated by the lack of effect of more selective EP1 and EP3 receptor agonists, prevention of these effects by EP4 antagonists and EP4 receptor knock-down by siRNA. In contrast, the aggregation enhancing effect of 17-pt-PGE₂ in human platelets was mediated via EP3 receptors. Our results demonstrate that 17-pt-PGE₂ enhances the endothelial barrier in vitro on pulmonary microvascular endothelial cells, and accordingly ameliorates the recruitment of neutrophils, via EP4 receptors in vivo. This suggests a beneficial effect of 17-pt-PGE₂ on pulmonary inflammatory diseases.

A Randomized Placebo Controlled Trial of Ibuprofen for Respiratory Syncytial Virus Infection in a Bovine Model

Background

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis and hospital admission in infants. An analogous disease occurs in cattle and costs US agriculture a billion dollars a year. RSV causes much of its morbidity indirectly via adverse effects of the host response to the virus. RSV is accompanied by elevated prostaglandin E₂ (PGE₂) which is followed by neutrophil led inflammation in the lung. Ibuprofen is a prototypical non-steroidal anti-inflammatory drug that decreases PGE₂ levels by inhibiting cyclooxygenase.

Hypotheses

We hypothesized that treatment of RSV with ibuprofen would decrease PGE₂ levels, modulate the immune response, decrease clinical illness, and decrease the histopathological lung changes in a bovine model of RSV. We further hypothesized that viral replication would be unaffected.

Methods

We performed a randomized placebo controlled trial of ibuprofen in 16 outbred Holstein calves that we infected with RSV. We measured clinical scores, cyclooxygenase, lipoxygenase and endocannabinoid products in plasma and mediastinal lymph nodes and interleukin (Il)-4, Il-13, Il-17 and interferon-γ in mediastinal lymph nodes. RSV shedding was measured daily and nasal Il-6, Il-8 and Il-17 every other day. The calves were necropsied on Day 10 post inoculation and histology performed.

Results

One calf in the ibuprofen group required euthanasia on Day 8 of infection for respiratory distress. Clinical scores (p<0.01) and weight gain (p = 0.08) seemed better in the ibuprofen group. Ibuprofen decreased cyclooxygenase, lipoxygenase, and cytochrome P450 products, and increased monoacylglycerols in lung lymph nodes. Ibuprofen modulated the immune response as measured by narrowed range of observed Il-13, Il-17 and IFN-γ gene expression in mediastinal lymph nodes. Lung histology was not different between groups, and viral shedding was increased in calves randomized to ibuprofen.

Conclusions

Ibuprofen decreased PGE₂, modulated the immune response, and improved clinical outcomes. However lung histopathology was not affected and viral shedding was increased.

Novel regulators of endothelial barrier function

Endothelial barrier function is an essential and tightly regulated process that ensures proper compartmentalization of the vascular and interstitial space, while allowing for the diffusive exchange of small molecules and the controlled trafficking of macromolecules and immune cells. Failure to control endothelial barrier integrity results in excessive leakage of fluid and proteins from the vasculature that can rapidly become fatal in scenarios such as sepsis or the acute respiratory distress syndrome. Here, we highlight recent advances in our understanding on the regulation of endothelial permeability, with a specific focus on the endothelial glycocalyx and endothelial scaffolds, regulatory intracellular signaling cascades, as well as triggers and mediators that either disrupt or enhance endothelial barrier integrity, and provide our perspective as to areas of seeming controversy and knowledge gaps, respectively.

The Multifaceted Roles Neutrophils Play in the Tumor Microenvironment

Neutrophils are myeloid cells that constitute 50-70 % of all white blood cells in the human circulation. Traditionally, neutrophils are viewed as the first line of defense against infections and as a major component of the inflammatory process. In addition, accumulating evidence suggest that neutrophils may also play a key role in multiple aspects of cancer biology. The possible involvement of neutrophils in cancer prevention and promotion was already suggested more than half a century ago, however, despite being the major component of the immune system, their contribution has often been overshadowed by other immune components such as lymphocytes and macrophages. Neutrophils seem to have conflicting functions in cancer and can be classified into anti-tumor (N1) and pro-tumor (N2) sub-populations. The aim of this review is to discuss the varying nature of neutrophil function in the cancer microenvironment with a specific emphasis on the mechanisms that regulate neutrophil mobilization, recruitment and activation.

Prostaglandin E2 Induces IL-6 and IL-8 Production by the EP Receptors/Akt/NF-κB Pathways in Nasal Polyp-Derived Fibroblasts

Purpose

Interleukin 6 (IL-6) and IL-8 participate in the pathogenesis of chronic rhinosinusitis with nasal polyps, and their levels are increased by prostaglandin E2 (PGE2) in different cell types. The purposes of this study were to determine whether PGE2 has any effect on the increase in the levels of IL-6 and IL-8 in nasal polyp-derived fibroblasts (NPDFs) and subsequently investigate the possible mechanism of this effect.

Methods

Different concentrations of PGE2 were used to stimulate NPDFs at different time intervals. NPDFs were treated with agonists and antagonists of E prostanoid (EP) receptors. To determine the signaling pathway for the expression of PGE2-induced IL-6 and IL-8, PGE2 was treated with Akt and NF-κB inhibitors in NPDFs. Reverse transcription-polymerase chain reaction for IL-6 and IL-8 mRNAs was performed. IL-6 and IL-8 levels were measured byenzyme-linked immunosorbent assay (ELISA). The activation of Akt and NF-κB was evaluated by western blot analysis.

Results

PGE2 significantly increased the mRNA and protein expression levels of IL-6 and IL-8 in NPDFs. The EP2 and EP4 agonists and antagonists induced and inhibited IL-6 expression. However, the EP4 agonist and antagonist were only observed to induce and inhibit IL-8 expression level. The Akt and NF-κB inhibitors significantly blocked PGE2-induced expression of IL-6 and IL-8.

Conclusions

PGE2 increases IL-6 expression via EP2 and EP4 receptors, and IL-8 expression via the EP4 receptor in NPDFs. It also activates the Akt and NF-κB signal pathways for the production of IL-6 and IL-8 in NPDFs. These results suggest that signaling pathway for IL-6 and IL-8 expression induced by PGE2 might be a useful therapeutic target for the treatment of nasal polyposis.

NOD2 triggers PGE2 synthesis leading to IL-8 activation in Staphylococcus aureus-infected human conjunctival epithelial cells

We previously showed that Staphylococcus aureus and Pseudomonas aeruginosa stimulate IL-8 expression in human conjunctival epithelial cells through different signal transduction pathways. As in some cell types both the bacteria may induce the release of prostaglandin E2 (PGE2) and PGE2 may affect the expression of IL-8, we aimed at investigating whether in human conjunctival cells infected with S. aureus or P. aeruginosa the activation of IL-8 transcription was mediated by PGE2 and which were the underlying molecular mechanisms. We found that S. aureus, but not P. aeruginosa, triggered IL-8 activation by increasing COX-2 expression and PGE2 levels in a time-dependent manner. Overexpression of nucleotide-binding oligomerization domain-2 (NOD2) resulted to be essential in the enhancement of IL-8 induced by S. aureus. It dramatically activated c-jun NH2-terminal kinase (JNK) pathway which in turn led to COX2 upregulation and ultimately to IL-8 transcription. The full understanding of the S. aureus-induced biochemical processes in human conjunctival epithelium will bring new insight to the knowledge of the molecular mechanisms involved in conjunctiva bacterial infections and develop novel treatment aiming at phlogosis modulation.

Beneficial role of vitamin D3 in the prevention of certain respiratory diseases

There is evidence of aberrations in the vitamin D-endocrine system in subjects with respiratory diseases. Vitamin D deficiency is highly prevalent in patients with respiratory diseases, and patients who receive vitamin D have significantly larger improvements in inspiratory muscle strength and maximal oxygen uptake. Studies have provided an opportunity to determine which proteins link vitamin D to respiratory pathology, including the major histocompatibility complex class II molecules, vitamin D receptor, vitamin D-binding protein, chromosome P450, Toll-like receptors, poly(ADP-ribose) polymerase-1, and the reduced form of nicotinamide adenine dinucleotide phosphate. Vitamin D also exerts its effect on respiratory diseases through cell signaling mechanisms, including matrix metalloproteinases, mitogen-activated protein kinase pathways, the Wnt/β-catenin signaling pathway, prostaglandins, reactive oxygen species, and nitric oxide synthase. In conclusion, vitamin D plays a significant role in respiratory diseases. The best form of vitamin D for use in the treatment of respiratory diseases is calcitriol because it is the active metabolite of vitamin D3 and modulates inflammatory cytokine expression. Further investigation of calcitriol in respiratory diseases is needed.

Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction

In this review we summarize recent major advances in our understanding on the molecular mechanisms, mediators, and biomarkers of acute lung injury (ALI) and alveolar-capillary barrier dysfunction, highlighting the role of immune cells, inflammatory and noninflammatory signaling events, mechanical noxae, and the affected cellular and molecular entities and functions. Furthermore, we address novel aspects of resolution and repair of ALI, as well as putative candidates for treatment of ALI, including pharmacological and cellular therapeutic means.

Role of hypoxia-inducible factor 1, α subunit and cAMP-response element binding protein 1 in synergistic release of interleukin 8 by prostaglandin E2 and nickel in lung fibroblasts

Numerous epidemiological studies have linked exposure to particulate matter (PM) air pollution with acute respiratory infection and chronic respiratory and cardiovascular diseases. We have previously shown that soluble nickel (Ni), a common component of PM, alters the release of CXC chemokines from cultured human lung fibroblasts (HLF) in response to microbial stimuli via a pathway dependent on disrupted prostaglandin (PG)E2 signaling. The current study sought to identify the molecular events underlying Ni-induced alterations in PGE2 signaling and its effects on IL-8 production. PGE2 synergistically enhances Ni-induced IL-8 release from HLF in a concentration-dependent manner. The effects of PGE2 were mimicked by butaprost and PGE1-alcohol and inhibited with antagonists AH6809 and L-161,982, indicating PGE2 signals via PGE2 receptors 2 and 4. PGE2 and forskolin stimulated cAMP, but it was only in the presence of Ni-induced hypoxia-inducible factor 1, α subunit (HIF1A) that these agents stimulated IL-8 release. The Ni-induced HIF1A DNA binding was enhanced by PGE2 and mediated, in part, by activation of p38 MAPK. Negation of cAMP-response element binding protein 1 or HIF1A using short interfering RNA blocked the synergistic interactions between Ni and PGE2. The results of the current study provide novel information on the ability of atmospheric hypoxia-mimetic metals to disrupt the release of immune-modulating chemokines by HLF in response to PGE2. Moreover, in the presence of HIF1A, cAMP-mediated signaling pathways may be altered to exacerbate inflammatory-like processes in lung tissue, imparting a susceptibility of PM-exposed populations to adverse respiratory health effects.

E-type prostanoid receptor 4 (EP4) in disease and therapy

The large variety of biological functions governed by prostaglandin (PG) E2 is mediated by signaling through four distinct E-type prostanoid (EP) receptors. The availability of mouse strains with genetic ablation of each EP receptor subtype and the development of selective EP agonists and antagonists have tremendously advanced our understanding of PGE2 as a physiologically and clinically relevant mediator. Moreover, studies using disease models revealed numerous conditions in which distinct EP receptors might be exploited therapeutically. In this context, the EP4 receptor is currently emerging as most versatile and promising among PGE2 receptors. Anti-inflammatory, anti-thrombotic and vasoprotective effects have been proposed for the EP4 receptor, along with its recently described unfavorable tumor-promoting and pro-angiogenic roles. A possible explanation for the diverse biological functions of EP4 might be the multiple signaling pathways switched on upon EP4 activation. The present review attempts to summarize the EP4 receptor-triggered signaling modules and the possible therapeutic applications of EP4-selective agonists and antagonists.

Netrin-1 regulates the inflammatory response of neutrophils and macrophages, and suppresses ischemic acute kidney injury by inhibiting COX-2-mediated PGE2 production

Netrin-1 regulates inflammation but the mechanism by which this occurs is unknown. Here we explore the role of netrin-1 in regulating the production of the prostanoid metabolite PGE2 from neutrophils in in vitro and in vivo disease models. Ischemia reperfusion in wild-type and RAG-1 knockout mice induced severe kidney injury that was associated with a large increase in neutrophil infiltration and COX-2 expression in the infiltrating leukocytes. Administration of netrin-1 suppressed COX-2 expression, PGE2 and thromboxane production, and neutrophil infiltration into the kidney. This was associated with reduced apoptosis, inflammatory cytokine and chemokine expression, and improved kidney function. Treatment with the PGE2 receptor EP4 agonist enhanced neutrophil infiltration and renal injury which was not inhibited by netrin-1. Consistent with in vivo data, both LPS and IFNγ-induced inflammatory cytokine production in macrophages and IL-17-induced IFNγ production in neutrophils were suppressed by netrin-1 in vitro by suppression of COX-2 expression. Moreover, netrin-1 regulates COX-2 expression at the transcriptional level through the regulation of NFκB activation. Thus, netrin-1 regulates the inflammatory response of neutrophils and macrophages through suppression of COX-2 mediated PGE2 production. This could be a potential drug for treating many inflammatory immune disorders.

cAMP regulation of airway smooth muscle function

Agonists activating β(2)-adrenoceptors (β(2)ARs) on airway smooth muscle (ASM) are the drug of choice for rescue from acute bronchoconstriction in patients with both asthma and chronic obstructive pulmonary disease (COPD). Moreover, the use of long-acting β-agonists combined with inhaled corticosteroids constitutes an important maintenance therapy for these diseases. β-Agonists are effective bronchodilators due primarily to their ability to antagonize ASM contraction. The presumed cellular mechanism of action involves the generation of intracellular cAMP, which in turn can activate the effector molecules cAMP-dependent protein kinase (PKA) and Epac. Other agents such as prostaglandin E(2) and phosphodiesterase inhibitors that also increase intracellular cAMP levels in ASM, can also antagonize ASM contraction, and inhibit other ASM functions including proliferation and migration. Therefore, β(2)ARs and cAMP are key players in combating the pathophysiology of airway narrowing and remodeling. However, limitations of β-agonist therapy due to drug tachyphylaxis related to β(2)AR desensitization, and recent findings regarding the manner in which β(2)ARs and cAMP signal, have raised new and interesting questions about these well-studied molecules. In this review we discuss current concepts regarding β(2)ARs and cAMP in the regulation of ASM cell functions and their therapeutic roles in asthma and COPD.

Differential regulation of airway smooth muscle cell migration by E-prostanoid receptor subtypes

Migration of airway smooth muscle (ASM) cells plays an important role in the pathophysiology of airway hyperresponsiveness and remodeling in asthma. It has been reported that prostaglandin (PG)E2 inhibits migration of ASM cells. Although PGE2 regulates cellular functions via binding to distinct prostanoid EP receptors, the role of EP receptor subtypes in mechanisms underlying cell migration has not been fully elucidated. We investigated the role of EP receptors in the inhibitory effects of PGE2 on the migration of human ASM cells. Migration induced by platelet-derived growth factor (PDGF)-BB (10 ng/ml, 6 h) was assessed by a chemotaxis chamber assay. PDGF-BB-induced cell migration was inhibited by PGE2, the specific EP2 agonist ONO-AE1-259-01, the specific EP4 agonist ONO-AE1-329, and cAMP-mobilizing agents. The inhibition of cell migration by PGE2 was significantly reversed by a blockade of EP2 and EP4 receptors using antagonists or transfection with siRNAs. Moreover, PGE2, the EP2 agonist, and the EP4 agonist significantly increased phosphorylation of small heat shock protein 20, one of the protein substrates for protein kinase A (PKA), with depolymerization of actin. In contrast, the EP3 agonist ONO-AE-248 significantly promoted baseline cell migration without affecting PDGF-BB-induced cell migration. In summary, activation of EP2 and EP4 receptors and subsequent activation of the cAMP/PKA pathway are the main mechanisms of inhibition of ASM cell migration by PGE2. HSP20 phosphorylation by PKA is possibly involved in this mechanism. Conversely, EP3 is potent in promoting cell migration. EP receptor subtypes may be novel therapeutic target molecules in airway remodeling and asthma.

STIM1 regulates platelet-derived growth factor-induced migration and Ca2+ influx in human airway smooth muscle cells

It is suggested that migration of airway smooth muscle (ASM) cells plays an important role in the pathogenesis of airway remodeling in asthma. Increases in intracellular Ca(2+) concentrations ([Ca(2+)](i)) regulate most ASM cell functions related to asthma, such as contraction and proliferation. Recently, STIM1 was identified as a sarcoplasmic reticulum (SR) Ca(2+) sensor that activates Orai1, the Ca(2+) channel responsible for store-operated Ca(2+) entry (SOCE). We investigated the role of STIM1 in [Ca(2+)](i) and cell migration induced by platelet-derived growth factor (PDGF)-BB in human ASM cells. Cell migration was assessed by a chemotaxis chamber assay. Human ASM cells express STIM1, STIM2, and Orai1 mRNAs. SOCE activated by thapsigargin, an inhibitor of SR Ca(2+)-ATPase, was significantly blocked by STIM1 siRNA and Orai1 siRNA but not by STIM2 siRNA. PDGF-BB induced a transient increase in [Ca(2+)](i) followed by sustained [Ca(2+)](i) elevation. Sustained increases in [Ca(2+)](i) due to PDGF-BB were significantly inhibited by a Ca(2+) chelating agent EGTA or by siRNA for STIM1 or Orai1. The numbers of migrating cells were significantly increased by PDGF-BB treatment for 6 h. Knockdown of STIM1 and Orai1 by siRNA transfection inhibited PDGF-induced cell migration. Similarly, EGTA significantly inhibited PDGF-induced cell migration. In contrast, transfection with siRNA for STIM2 did not inhibit the sustained elevation of [Ca(2+)](i) or cell migration induced by PDGF-BB. These results demonstrate that STIM1 and Orai1 are essential for PDGF-induced cell migration and Ca(2+) influx in human ASM cells. STIM1 could be an important molecule responsible for airway remodeling.