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

Systemic EP4 receptor agonist and Arginase-1 therapy in a murine model of chronic asthma and influenza virus-induced asthma exacerbation

BACKGROUND AND PURPOSE

Myeloid-derived suppressor cells (MDSCs) play important roles in the pathogenesis of asthma. Recent studies demonstrate that their function can be modulated by different pharmacological approaches. In this study, we focussed on the effects of systemically administered prostaglandin EP4 receptor agonist L-902,688 and pegylated human Arginase-1 on MDSCs in a murine model of chronic asthma and asthma exacerbation.

EXPERIMENTAL APPROACH

BALB/c mice were challenged with house dust mite (HDM) over a period of 5 weeks, establishing a chronic asthma phenotype. To induce asthma exacerbation, mice were infected with Influenza Virus H1N1 A/Puerto Rico/8/1934. In vivo lung function, lung inflammatory features, number and suppressive activity of MDSCs, number of different T cell subsets in lung and spleen and viral titer in the bronchoalveolar lavage fluid (BALF) were assessed.

KEY RESULTS

In asthmatic mice, treatment with the EP4 receptor agonist or Arginase-1 significantly reduced the number of eosinophils in the BALF. Both treatments improved lung function and ameliorated airway hyperresponsiveness (AHR) in asthma exacerbation. The number and suppressive activity of MDSCs in the lung were increased by virus-induced asthma exacerbation.

CONCLUSION AND IMPLICATIONS

We found beneficial effects of systemic EP4 receptor agonist and Arginase-1 therapy in a murine model of chronic asthma and influenza virus-induced asthma exacerbation. Our findings highlight the potential efficacy of EP4 receptor agonists, Arginase-1, and MDSCs, as novel therapeutic approaches in asthma and asthma exacerbation.

The Emerging Therapeutic Role of Prostaglandin E2 Signaling in Pulmonary Hypertension

Mild-to-moderate pulmonary hypertension (PH) is a common complication of chronic obstructive pulmonary disease (COPD). It is characterized by narrowing and thickening of the pulmonary arteries, resulting in increased pulmonary vascular resistance (PVR) and ultimately leading to right ventricular dysfunction. Pulmonary vascular remodeling in COPD is the main reason for the increase of pulmonary artery pressure (PAP). The pathogenesis of PH in COPD is complex and multifactorial, involving chronic inflammation, hypoxia, and oxidative stress. To date, prostacyclin and its analogues are widely used to prevent PH progression in clinical. These drugs have potent anti-proliferative, anti-inflammatory, and stimulating endothelial regeneration properties, bringing therapeutic benefits to the slowing, stabilization, and even some reversal of vascular remodeling. As another well-known and extensively researched prostaglandins, prostaglandin E2 (PGE2) and its downstream signaling have been found to play an important role in various biological processes. Emerging evidence has revealed that PGE2 and its receptors (i.e., EP1-4) are involved in the regulation of pulmonary vascular homeostasis and remodeling. This review focuses on the research progress of the PGE2 signaling pathway in PH and discusses the possibility of treating PH based on the PGE2 signaling pathway.

Prorelaxant E-type Prostanoid Receptors Functionally Partition to Different Procontractile Receptors in Airway Smooth Muscle

Prostaglandin E2 imparts diverse physiological effects on multiple airway cells through its actions on four distinct E-type prostanoid (EP) receptor subtypes (EP1-EP4). Gs-coupled EP2 and EP4 receptors are expressed on airway smooth muscle (ASM), yet their capacity to regulate the ASM contractile state remains subject to debate. We used EP2 and EP4 subtype-specific agonists (ONO-259 and ONO-329, respectively) in cell- and tissue-based models of human ASM contraction-magnetic twisting cytometry (MTC), and precision-cut lung slices (PCLSs), respectively-to study the EP2 and EP4 regulation of ASM contraction and signaling under conditions of histamine or methacholine (MCh) stimulation. ONO-329 was superior (<0.05) to ONO-259 in relaxing MCh-contracted PCLSs (log half maximal effective concentration [logEC50]: 4.9 × 10-7 vs. 2.2 × 10-6; maximal bronchodilation ± SE, 35 ± 2% vs. 15 ± 2%). However, ONO-259 and ONO-329 were similarly efficacious in relaxing histamine-contracted PCLSs. Similar differential effects were observed in MTC studies. Signaling analyses revealed only modest differences in ONO-329- and ONO-259-induced phosphorylation of the protein kinase A substrates VASP and HSP20, with concomitant stimulation with MCh or histamine. Conversely, ONO-259 failed to inhibit MCh-induced phosphorylation of the regulatory myosin light chain (pMLC20) and the F-actin/G-actin ratio (F/G-actin ratio) while effectively inhibiting their induction by histamine. ONO-329 was effective in reversing induced pMLC20 and the F/G-actin ratio with both MCh and histamine. Thus, the contractile-agonist-dependent differential effects are not explained by changes in the global levels of phosphorylated protein kinase A substrates but are reflected in the regulation of pMLC20 (cross-bridge cycling) and F/G-actin ratio (actin cytoskeleton integrity, force transmission), implicating a role for compartmentalized signaling involving muscarinic, histamine, and EP receptor subtypes.

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.

Eicosanoid receptors as therapeutic targets for asthma

Eicosanoids comprise a group of oxidation products of arachidonic and 5,8,11,14,17-eicosapentaenoic acids formed by oxygenases and downstream enzymes. The two major pathways for eicosanoid formation are initiated by the actions of 5-lipoxygenase (5-LO), leading to leukotrienes (LTs) and 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and cyclooxygenase (COX), leading to prostaglandins (PGs) and thromboxane (TX). A third group (specialized pro-resolving mediators; SPMs), including lipoxin A4 (LXA4) and resolvins (Rvs), are formed by the combined actions of different oxygenases. The actions of the above eicosanoids are mediated by approximately 20 G protein-coupled receptors, resulting in a variety of both detrimental and beneficial effects on airway smooth muscle and inflammatory cells that are strongly implicated in asthma pathophysiology. Drugs targeting proinflammatory eicosanoid receptors, including CysLT1, the receptor for LTD4 (montelukast) and TP, the receptor for TXA2 (seratrodast) are currently in use, whereas antagonists of a number of other receptors, including DP2 (PGD2), BLT1 (LTB4), and OXE (5-oxo-ETE) are under investigation. Agonists targeting anti-inflammatory/pro-resolving eicosanoid receptors such as EP2/4 (PGE2), IP (PGI2), ALX/FPR2 (LXA4), and Chemerin1 (RvE1/2) are also being examined. This review summarizes the contributions of eicosanoid receptors to the pathophysiology of asthma and the potential therapeutic benefits of drugs that target these receptors. Because of the multifactorial nature of asthma and the diverse pathways affected by eicosanoid receptors, it will be important to identify subgroups of asthmatics that are likely to respond to any given therapy.

Myeloid-Derived Suppressor Cells Dampen Airway Inflammation Through Prostaglandin E2 Receptor 4

Emerging evidence suggests a mechanistic role for myeloid-derived suppressor cells (MDSCs) in lung diseases like asthma. Previously, we showed that adoptive transfer of MDSCs dampens lung inflammation in murine models of asthma through cyclooxygenase-2 and arginase-1 pathways. Here, we further dissected this mechanism by studying the role and therapeutic relevance of the downstream mediator prostaglandin E2 receptor 4 (EP4) in a murine model of asthma. We adoptively transferred MDSCs generated using an EP4 agonist in a murine model of asthma and studied the consequences on airway inflammation. Furthermore, pegylated human arginase-1 was used to model MDSC effector activities. We demonstrate that the selective EP4 agonist L-902,688 increased the number and suppressive activity of MDSCs through arginase-1 and nitric oxide synthase-2. These results showed that adoptive transfer of EP4-primed MDSCs, EP4 agonism alone or arginase-1 administration ameliorated lung inflammatory responses and histopathological changes in asthmatic mice. Collectively, our results provide evidence that MDSCs dampen airway inflammation in murine asthma through a mechanism involving EP4.

The Biology of Prostaglandins and Their Role as a Target for Allergic Airway Disease Therapy

Prostaglandins (PGs) are a family of lipid compounds that are derived from arachidonic acid via the cyclooxygenase pathway, and consist of PGD₂, PGI₂, PGE₂, PGF₂, and thromboxane B₂. PGs signal through G-protein coupled receptors, and individual PGs affect allergic inflammation through different mechanisms according to the receptors with which they are associated. In this review article, we have focused on the metabolism of the cyclooxygenase pathway, and the distinct biological effect of each PG type on various cell types involved in allergic airway diseases, including asthma, allergic rhinitis, nasal polyposis, and aspirin-exacerbated respiratory disease.

Bronchodilation induced by PGE2 is impaired in Group III pulmonary hypertension

BACKGROUND AND PURPOSE

In patients with pulmonary hypertension (PH) associated with lung disease and/or hypoxia (Group III), decreased pulmonary vascular tone and tissue hypoxia is therapeutically beneficial. PGE₂ and PGI₂ induce potent relaxation of human bronchi from non-PH (control) patients via EP₄ and IP receptors, respectively. However, the effects of PGE₂ /PGI₂ and their mimetics on human bronchi from PH patients are unknown. Here, we have compared relaxant effects of several PGI₂ -mimetics approved for treating PH Group I with several PGE₂ -mimetics, in bronchial preparations derived from PH Group III and control patients.

EXPERIMENTAL APPROACH

Relaxation of bronchial muscle was assessed in samples isolated from control and PH Group III patients. Expression of prostanoid receptors was analysed by western blot and real-time PCR, and endogenous PGE₂ , PGI₂ , and cAMP levels were determined by ELISA.

KEY RESULTS

Maximal relaxations induced by different EP₄ receptor agonists (PGE₂ , L-902688, and ONO-AE1-329) were decreased in human bronchi from PH patients, compared with controls. However, maximal relaxations produced by PGI₂ -mimetics (iloprost, treprostinil, and beraprost) were similar for both groups of patients. Both EP₄ and IP receptor protein and mRNA expressions were significantly lower in human bronchi from PH patients. cAMP levels significantly correlated with PGI₂ but not with PGE₂ levels.

CONCLUSION AND IMPLICATIONS

The PGI₂ -mimetics retained maximal bronchodilation in PH Group III patients, whereas bronchodilation induced by EP₄ receptor agonists was decreased. Restoration of EP₄ receptor expression in airways of PH Group III patients with respiratory diseases could bring additional therapeutic benefit.

Cooperativity of E-prostanoid receptor subtypes in regulating signaling and growth inhibition in human airway smooth muscle

Prostaglandin E2 (PGE₂) is produced in the airway during allergic lung inflammation and both promotes and inhibits features of asthma pathology. These mixed effects relate to 4 E-prostanoid (EP) receptor subtypes (EP1, 2, 3 and 4) expressed at different levels on different resident and infiltrating airway cells. Although studies have asserted both EP2 and EP4 expression in human airway smooth muscle (HASM), a recent study asserted EP4 to be the functionally dominant EP subtype in HASM. Herein, we employ recently-developed subtype-selective ligands to investigate singular or combined EP2 and EP4 receptor activation in regulating HASM signaling and proliferation. The subtype specificity of ONO-AE1-259-01 (EP2 agonist) and ONO-AE1-329 (EP4 agonist) was first demonstrated in human embryonic kidney 293 cells stably expressing different EP receptor subtypes. EP receptor knockdown and subtype-selective antagonists demonstrated EP2 and EP4 receptor responsiveness in HASM cells to the specific ONO compounds, whereas PGE₂ appeared to preferentially signal via the EP4 receptor. Both singular EP2 and EP4 receptor agonists inhibited HASM proliferation, and combined EP2 and EP4 receptor agonism exhibited positive cooperativity in both chronic G_s-mediated signaling and inhibiting HASM proliferation. These findings suggest both EP2 and EP4 are functionally important in HASM, and their combined targeting optimally inhibits airway smooth muscle proliferation.-Michael, J. V. Gavrila, A., Nayak, A. P., Pera, T., Liberato, J. R., Polischak, S. R., Shah, S. D., Deshpande, D. A., Penn, R. B. Cooperativity of E-prostanoid receptor subtypes in regulating signaling and growth inhibition in human airway smooth muscle.

Cyclic stretch enhances reorientation and differentiation of 3-D culture model of human airway smooth muscle

Activation of airway smooth muscle (ASM) cells plays a central role in the pathophysiology of asthma. Because ASM is an important therapeutic target in asthma, it is beneficial to develop bioengineered ASM models available for assessing physiological and biophysical properties of ASM cells. In the physiological condition in vivo, ASM cells are surrounded by extracellular matrix (ECM) and exposed to mechanical stresses such as cyclic stretch. We utilized a 3-D culture model of human ASM cells embedded in type-I collagen gel. We further examined the effects of cyclic mechanical stretch, which mimics tidal breathing, on cell orientation and expression of contractile proteins of ASM cells within the 3-D gel. ASM cells in type-I collagen exhibited a tissue-like structure with actin stress fiber formation and intracellular Ca²⁺ mobilization in response to methacholine. Uniaxial cyclic stretching enhanced alignment of nuclei and actin stress fibers of ASM cells. Moreover, expression of mRNAs for contractile proteins such as α-smooth muscle actin, calponin, myosin heavy chain 11, and transgelin of stretched ASM cells was significantly higher than that under the static condition. Our findings suggest that mechanical force and interaction with ECM affects development of the ASM tissue-like construct and differentiation to the contractile phenotype in a 3-D culture model.

MicroRNA-638 inhibits human airway smooth muscle cell proliferation and migration through targeting cyclin D1 and NOR1

Abnormal airway smooth muscle cell (ASMC) proliferation and migration contribute significantly to increased ASM mass associated with asthma. MicroRNA (miR)-638 is a primate-specific miRNA that plays important roles in development, DNA damage repair, hematopoiesis, and tumorigenesis. Although it is highly expressed in ASMCs, its function in ASM remodeling remains unknown. In the current study, we found that in response to various mitogenic stimuli, including platelet-derived growth factor-two B chains (PDGF-BB), transforming growth factor β1, and fetal bovine serum, the expression of miR-638, as determined by quantitative real-time polymerase chain reaction (qRT-PCR), was significantly downregulated in the proliferative human ASMCs. Both gain- and loss-of-function studies were performed to study the role of miR-638 in ASMC proliferation and migration. We found that adenovirus-mediated miR-638 overexpression markedly inhibits ASMC proliferation and migration, while ablation of miR-638 by anti-miR-638 markedly increases cell proliferation and migration, as determined by WST-8 proliferation and scratch wound assays. Dual-luciferase reporter assay, qRT-PCR, and immunoblot analysis were used to investigate the effects of miR-638 on the expression of the downstream target genes in ASMCs. Our results demonstrated that miR-638 overexpression significantly reduced the expression of downstream target cyclin D1 and NOR1, both of which have been shown to be essential for cell proliferation and migration. Together, our study provides the first in vitro evidence highlighting the antiproliferative and antimigratory roles of miR-638 in human ASMC remodeling and suggests that targeted overexpression of miR-638 in ASMCs may provide a novel therapeutic strategy for preventing ASM hyperplasia associated with asthma.

Expression of E-prostanoid receptors in nasal polyp tissues of smoking and nonsmoking patients with chronic rhinosinusitis

Background

Different inflammatory reactions have been observed in the polyp tissues of nonsmokers and smokers with chronic rhinosinusitis (CRS). E-prostanoid (EP) receptors play a role in the inflammatory processes. Cigarette smoke (CS) exposure regulates EP-receptor expression levels promoting inflammatory mediator release from various inflammatory cells. In this study, we characterize the EP-receptor expression profiles in the polyps of nonsmoking and smoking CRS patients to explore the possible role of CS in the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP).

Methods

Polyp biopsies were obtained from 28 non-smoking and 21 smoking CRSwNP patients. Histopathological characteristics were observed under a light microscope. The prostaglandin E₂ (PGE₂), TNF-α, and IL-8 contents in polyp tissues were detected using enzyme-linked immunosorbent assay. Immunostaining was used to locate EP receptors in polyps. Messenger RNA and protein expression of EP receptors were examined using quantitative real-time polymerase chain reaction and Western blot, respectively.

Results

More severe inflammatory reactions occurred in polyp tissues of smoking CRSwNP patients. The PGE₂, TNF-α, and IL-8 in tissue homogenate levels were significantly higher in smoking CRSwNP patients than those in nonsmoking CRSwNP patients. Moreover, the distribution of each EP receptor subtype was similar in both groups. Compared with the EP-receptor expression in nonsmokers, messenger RNA and protein of EP2 and EP4 receptor were significantly down-expressed in smoking patients, but EP1 and EP3 receptors did not show significant differences.

Conclusion

CS exposure downregulates the expression levels of EP2 and EP4 receptors and stimulates the production of PGE₂ and the proinflammatory cytokine IL-8 and TNF-α in polyp tissues of CRS patients. The down-expressed EP2 and EP4 receptors might be associated with severe inflammatory reactions in smoking CRSwNP patients.

Matrix stiffness regulates migration of human lung fibroblasts

In patients with pulmonary diseases such as idiopathic pulmonary fibrosis and severe acute respiratory distress syndrome, progressive pulmonary fibrosis is caused by dysregulated wound healing via activation of fibroblasts after lung inflammation or severe damage. Migration of fibroblasts toward the fibrotic lesions plays an important role in pulmonary fibrosis. Fibrotic tissue in the lung is much stiffer than normal lung tissue. Emerging evidence supports the hypothesis that the stiffness of the matrix is not only a consequence of fibrosis, but also can induce fibroblast activation. Nevertheless, the effects of substrate rigidity on migration of lung fibroblasts have not been fully elucidated. We evaluated the effects of substrate stiffness on the morphology, α-smooth muscle actin (α-SMA) expression, and cell migration of primary human lung fibroblasts by using polyacrylamide hydrogels with stiffnesses ranging from 1 to 50 kPa. Cell motility was assessed by platelet-derived growth factor (PDGF)-induced chemotaxis and random walk migration assays. As the stiffness of substrates increased, fibroblasts became spindle-shaped and spread. Expression of α-SMA proteins was higher on the stiffer substrates (25 kPa gel and plastic dishes) than on the soft 2 kPa gel. Both PDGF-induced chemotaxis and random walk migration of fibroblasts precultured on stiff substrates (25 kPa gel and plastic dishes) were significantly higher than those of cells precultured on 2 kPa gel. Transfection of the fibroblasts with short interfering RNA for α-SMA inhibited cell migration. These findings suggest that fibroblast activation induced by a stiff matrix is involved in mechanisms of the pathophysiology of pulmonary fibrosis.

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.

Expression profiles of prostaglandin E2 receptor subtypes in aspirin tolerant adult Chinese with chronic rhinosinusitis

BACKGROUND

Several studies have indicated that prostaglandin E2 and E-prostanoid (EP) receptors play a role in the pathogenesis of chronic rhinosinusitis (CRS) in white populations. However, until now there was no report about EP receptor expression and its role in the pathophysiology of CRS in Chinese patients.

OBJECTIVE

To investigate the expression profiles of EP receptors, including EP1, EP2, EP3, and EP4 receptors in different Chinese patients with CRS with aspirin tolerance.

METHODS

Nasal biopsy specimens were obtained from 12 controls, 12 patients with CRS without nasal polyps (CRSsNP), 12 with eosinophilic CRS with nasal polyps (CRSwNP), and 16 with noneosinophilic CRSwNP. Histopathologic characteristics were observed under a light microscope. Immunostaining was used to examine tissue localization of EP receptors. Messenger RNA and protein expression of EP receptors were examined by means of quantitative RT-polymerase chain reaction and Western blot, respectively.

RESULTS

Different types of CRS presented different histopathologic hallmarks. EP receptors were expressed mainly on epithelium, glands, and infiltrating inflammatory cells in nasal tissue. In controls, patients with CRSsNP, and those with noneosinophilic CRSwNP, EP4 mRNA levels were higher than EP1, EP2, and EP3 receptors. EP2 was downexpressed, and EP1 was upexpressed in patients with eosinophilic CRSwNP. When comparing EP receptor expression among different groups, Messenger RNA and protein of EP1 receptor were significantly enhanced in eosinophilic CRSwNP, but EP2, EP3, and EP4 receptors did not show significant differences.

CONCLUSION

EP receptor expressions present different features in healthy subjects and patients with CRS. The upregulated EP1 receptor in eosinophilic CRSwNP might be associated with excessive infiltrations of eosinophils and other inflammatory cells. The accurate role of the four EP receptors in the pathogenesis of different CRS remains to be further explored.

The activation of M3 mAChR in airway epithelial cells promotes IL-8 and TGF-β1 secretion and airway smooth muscle cell migration

BACKGROUND

Muscarinic acetylcholine receptors (mAChRs) have been identified in airway epithelium, and epithelium-derived chemokines can initiate the migration of airway smooth muscle (ASM) cells. However, the mAChRs that are expressed in airway epithelium and the mechanism underlying the regulation of ASM cell migration are not clear. The aim of this study was to test whether the effects of the epithelium-derived chemokines on ASM cell migration could be modulated by mAChRs.

METHOD

Human epithelial cells (A549 cells) were stimulated with cigarette smoke extract (CSE) or the mAChRs agonist carbachol. IL-8 and TGF-β1 production were measured by ELISA, and human ASM cell migration was measured using the transwell migration assay and scratch assay. The mRNA levels of the mAChRs subtypes and the acetylcholine concentrations were measured using RT-PCR and LC-MS/MS, respectively.

RESULTS

ASM cell migration toward CSE-stimulated A549 cells was markedly reduced by Ac-RRWWCR-NH2 (IL-8 inhibitor) and SB431542 (TGF-β1 inhibitor). CSE-induced ASM cell migration was also suppressed by the mAChRs antagonist tiotropium. Interestingly, carbachol-stimulated A549 cells also induced ASM cell migration; this migration event was suppressed by tiotropium, Ac-RRWWCR-NH2 and SB431542. In addition, the effects of CSE on ASM cell migration were significantly and cooperatively enhanced by carbachol compared to CSE alone. Carbachol-induced ASM cell migration was reduced by selective inhibitors of PI3K/Akt (LY294002) and p38 (SB203580), suggesting that it occurred through p38 and Akt phosphorylation, which was inhibited by the M3 mAChR antagonist 4-DAMP.

CONCLUSIONS

These findings indicate that M3 mAChR may be important therapeutic target for obstructive airway diseases, as it regulates the effects of the epithelial-derived chemokines on ASM cell migration, which results in lung remodeling.

Real-time imaging of ATP release induced by mechanical stretch in human airway smooth muscle cells

Airway smooth muscle (ASM) cells within the airway walls are continually exposed to mechanical stimuli, and exhibit various functions in response to these mechanical stresses. ATP acts as an extracellular mediator in the airway. Moreover, extracellular ATP is considered to play an important role in the pathophysiology of asthma and chronic obstructive pulmonary disease. However, it is not known whether ASM cells are cellular sources of ATP secretion in the airway. We therefore investigated whether mechanical stretch induces ATP release from ASM cells. Mechanical stretch was applied to primary human ASM cells cultured on a silicone chamber coated with type I collagen using a stretching apparatus. Concentrations of ATP in cell culture supernatants measured by luciferin-luciferase bioluminescence were significantly elevated by cyclic stretch (12 and 20% strain). We further visualized the stretch-induced ATP release from the cells in real time using a luminescence imaging system, while acquiring differential interference contrast cell images with infrared optics. Immediately after a single uniaxial stretch for 1 second, strong ATP signals were produced by a certain population of cells and spread to surrounding spaces. The cyclic stretch-induced ATP release was significantly reduced by inhibitors of Ca(2+)-dependent vesicular exocytosis, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester, monensin, N-ethylmaleimide, and bafilomycin. In contrast, the stretch-induced ATP release was not inhibited by a hemichannel blocker, carbenoxolone, or blockade of transient receptor potential vanilloid 4 by short interfering RNA transfection or ruthenium red. These findings reveal a novel property of ASM cells: mechanically induced ATP release may be a cellular source of ATP in the airway.

Prostaglandin E2 switches from a stimulator to an inhibitor of cell migration after epithelial-to-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is critical for embryonic development, and this process is recapitulated in adults during wound healing, tissue regeneration, fibrosis and cancer progression. Cell migration is believed to play a key role in both normal wound repair and in abnormal tissue remodeling. Prostaglandin E2 (PGE2) inhibits fibroblast chemotaxis, but stimulates chemotaxis in airway epithelial cells. The current study was designed to explore the role of PGE2 and its four receptors on airway epithelial cell migration following EMT using both the Boyden blindwell chamber chemotaxis assay and the wound closure assay. EMT in human bronchial epithelial cells (HBECs) was induced by TGF-β1 and a mixture of cytokines (IL-1β, TNF-α, and IFN-γ). PGE2 and selective agonists for all four EP receptors stimulated chemotaxis and wound closure in HBECs. Following EMT, the EP1 and EP3 agonists were without effect, while the EP2 and EP4 agonists inhibited chemotaxis as did PGE2. The effects of the EP2 and EP4 receptors on HBEC and EMT cell migration were further confirmed by blocking the expected signaling pathways. Taken together, these results demonstrate that PGE2 switches from a stimulator to an inhibitor of cell migration following EMT of airway epithelial cells and that this inhibition is mediated by an altered effect of EP2 and EP4 signaling and an apparent loss of the stimulatory effects of EP1 and EP3. Change in the PGE2 modulation of chemotaxis may play a role in repair following injury.

Ca2+ influx and ATP release mediated by mechanical stretch in human lung fibroblasts

One cause of progressive pulmonary fibrosis is dysregulated wound healing after lung inflammation or damage in patients with idiopathic pulmonary fibrosis and severe acute respiratory distress syndrome. The mechanical forces are considered to regulate pulmonary fibrosis via activation of lung fibroblasts. In this study, the effects of mechanical stretch on the intracellular Ca(2+) concentration ([Ca(2+)]i) and ATP release were investigated in primary human lung fibroblasts. Uniaxial stretch (10-30% in strain) was applied to fibroblasts cultured in a silicone chamber coated with type I collagen using a stretching apparatus. Following stretching and subsequent unloading, [Ca(2+)]i transiently increased in a strain-dependent manner. Hypotonic stress, which causes plasma membrane stretching, also transiently increased the [Ca(2+)]i. The stretch-induced [Ca(2+)]i elevation was attenuated in Ca(2+)-free solution. In contrast, the increase of [Ca(2+)]i by a 20% stretch was not inhibited by the inhibitor of stretch-activated channels GsMTx-4, Gd(3+), ruthenium red, or cytochalasin D. Cyclic stretching induced significant ATP releases from fibroblasts. However, the stretch-induced [Ca(2+)]i elevation was not inhibited by ATP diphosphohydrolase apyrase or a purinergic receptor antagonist suramin. Taken together, mechanical stretch induces Ca(2+) influx independently of conventional stretch-sensitive ion channels, the actin cytoskeleton, and released ATP.

Prostaglandin E2 receptors in asthma and in chronic rhinosinusitis/nasal polyps with and without aspirin hypersensitivity

Chronic rhinosinusitis with nasal polyps (CRSwNP) and asthma frequently coexist and are always present in patients with aspirin exacerbated respiratory disease (AERD). Although the pathogenic mechanisms of this condition are still unknown, AERD may be due, at least in part, to an imbalance in eicosanoid metabolism (increased production of cysteinyl leukotrienes (CysLTs) and reduced biosynthesis of prostaglandin (PG) E2), possibly increasing and perpetuating the process of inflammation. PGE2 results from the metabolism of arachidonic acid (AA) by cyclooxygenase (COX) enzymes, and seems to play a central role in homeostasis maintenance and inflammatory response modulation in airways. Therefore, the abnormal regulation of PGE2 could contribute to the exacerbated processes observed in AERD. PGE2 exerts its actions through four G-protein-coupled receptors designated E-prostanoid (EP) receptors EP1, EP2, EP3, and EP4. Altered PGE2 production as well as differential EP receptor expression has been reported in both upper and lower airways of patients with AERD. Since the heterogeneity of these receptors is the key for the multiple biological effects of PGE2 this review focuses on the studies available to elucidate the importance of these receptors in inflammatory airway diseases.

Airway smooth muscle in asthma: linking contraction and mechanotransduction to disease pathogenesis and remodelling

Asthma is an obstructive airway disease, with a heterogeneous and multifactorial pathogenesis. Although generally considered to be a disease principally driven by chronic inflammation, it is becoming increasingly recognised that the immune component of the pathology poorly correlates with the clinical symptoms of asthma, thus highlighting a potentially central role for non-immune cells. In this context airway smooth muscle (ASM) may be a key player, as it comprises a significant proportion of the airway wall and is the ultimate effector of acute airway narrowing. Historically, the contribution of ASM to asthma pathogenesis has been contentious, yet emerging evidence suggests that ASM contractile activation imparts chronic effects that extend well beyond the temporary effects of bronchoconstriction. In this review article we describe the effects that ASM contraction, in combination with cellular mechanotransduction and novel contraction-inflammation synergies, contribute to asthma pathogenesis. Specific emphasis will be placed on the effects that ASM contraction exerts on the mechanical properties of the airway wall, as well as novel mechanisms by which ASM contraction may contribute to more established features of asthma such as airway wall remodelling.

CXCL1 inhibits airway smooth muscle cell migration through the decoy receptor Duffy antigen receptor for chemokines

Airway smooth muscle cell (ASMC) migration is an important mechanism postulated to play a role in airway remodeling in asthma. CXCL1 chemokine has been linked to tissue growth and metastasis. In this study, we present a detailed examination of the inhibitory effect of CXCL1 on human primary ASMC migration and the role of the decoy receptor, Duffy AgR for chemokines (DARC), in this inhibition. Western blots and pathway inhibitors showed that this phenomenon was mediated by activation of the ERK-1/2 MAPK pathway, but not p38 MAPK or PI3K, suggesting a biased selection in the signaling mechanism. Despite being known as a nonsignaling receptor, small interference RNA knockdown of DARC showed that ERK-1/2 MAPK activation was significantly dependent on DARC functionality, which, in turn, was dependent on the presence of heat shock protein 90 subunit α. Interestingly, DARC- or heat shock protein 90 subunit α-deficient ASMCs responded to CXCL1 stimulation by enhancing p38 MAPK activation and ASMC migration through the CXCR2 receptor. In conclusion, we demonstrated DARC's ability to facilitate CXCL1 inhibition of ASMC migration through modulation of the ERK-1/2 MAPK-signaling pathway.

FAM3A promotes vascular smooth muscle cell proliferation and migration and exacerbates neointima formation in rat artery after balloon injury

The biological function of FAM3A, the first member of family with sequence similarity 3 (FAM3) gene family, remains largely unknown. This study aimed to determine its role in the proliferation and migration of vascular smooth muscle cells (VSMCs). Immunohistochemical staining revealed that FAM3A protein is expressed in the tunica media of rodent arteries, and its expression is reduced with an increase in prostaglandin E receptor 2 (EP2) expression after injury. In vitro, FAM3A overexpression promotes proliferation and migration of VSMCs, whereas FAM3A silencing inhibits these processes. In vivo, FAM3A overexpression results in exaggerated neointima formation of rat carotid artery after balloon injury. FAM3A activates Akt in a PI3K-dependent manner. In contrast, FAM3A induces ERK1/2 activation independent of PI3K. FAM3A protein is subcellularly located in mitochondria, where it affects ATP production and release. Activation of EP2 represses FAM3A expression, leading to impaired ATP production and release in VSMCs. FAM3A-induced activation of Akt and ERK1/2 pathways, proliferation and migration of VSMCs are inhibited by P2 receptor antagonist suramin. Furthermore, inhibition or knockdown of P2Y1 receptor inihibits FAM3A-induced proliferation and migration of VSMCs. In conclusion, FAM3A promotes proliferation and migration of VSMCs via P2Y1 receptor-mediated activation of Akt and ERK1/2 pathways. In injured vessels, FAM3A was repressed by upregulated EP2 expression, leading to the attenuation of ATP-P2Y1 receptor signaling, which is beneficial for preventing excessive proliferation and migration of VSMCs.

Prostaglandin E2 alters Wnt-dependent migration and proliferation in neuroectodermal stem cells: implications for autism spectrum disorders

Prostaglandin E2 (PGE₂) is a natural lipid-derived molecule that is involved in important physiological functions. Abnormal PGE₂ signalling has been associated with pathologies of the nervous system. Previous studies provide evidence for the interaction of PGE₂ and canonical Wnt signalling pathways in non-neuronal cells. Since the Wnt pathway is crucial in the development and organization of the brain, the main goal of this study is to determine whether collaboration between these pathways exists in neuronal cell types. We report that PGE₂ interacts with canonical Wnt signalling through PKA and PI-3K in neuroectodermal (NE-4C) stem cells. We used time-lapse microscopy to determine that PGE₂ increases the final distance from origin, path length travelled, and the average speed of migration in Wnt-activated cells. Furthermore, PGE₂ alters distinct cellular phenotypes that are characteristic of Wnt-induced NE-4C cells, which corresponds to the modified splitting behaviour of the cells. We also found that in Wnt-induced cells the level of β-catenin protein was increased and the expression levels of Wnt-target genes (Ctnnb1, Ptgs2, Ccnd1, Mmp9) was significantly upregulated in response to PGE₂ treatment. This confirms that PGE₂ activated the canonical Wnt signalling pathway. Furthermore, the upregulated genes have been previously associated with ASD. Our findings show, for the first time, evidence for cross-talk between PGE₂ and Wnt signalling in neuronal cells, where PKA and PI-3K might act as mediators between the two pathways. Given the importance of PGE₂ and Wnt signalling in prenatal development of the nervous system, our study provides insight into how interaction between these two pathways may influence neurodevelopment.

Therapeutic implications of the prostaglandin pathway in Alzheimer's disease

An important pathologic hallmark of Alzheimer's disease (AD) is neuroinflammation, a process characterized in AD by disproportionate activation of cells (microglia and astrocytes, primarily) of the non-specific innate immune system within the CNS. While inflammation itself is not intrinsically detrimental, a delicate balance of pro- and anti-inflammatory signals must be maintained to ensure that long-term exaggerated responses do not damage the brain over time. Non-steroidal anti-inflammatory drugs (NSAIDs) represent a broad class of powerful therapeutics that temper inflammation by inhibiting cyclooxygenase-mediated signaling pathways including prostaglandins, which are the principal mediators of CNS neuroinflammation. While historically used to treat discrete or systemic inflammatory conditions, epidemiologic evidence suggests that protracted NSAID use may delay AD onset, as well as decrease disease severity and rate of progression. Unfortunately, clinical trials with NSAIDs have thus far yielded disappointing results, including premature discontinuation of a large-scale prevention trial due to unexpected cardiovascular side effects. Here we review the literature and make the argument that more targeted exploitation of downstream prostaglandin signaling pathways may offer significant therapeutic benefits for AD while minimizing adverse side effects. Directed strategies such as these may ultimately help to delay the deleterious consequences of brain aging and might someday lead to new therapies for AD and other chronic neurodegenerative diseases.

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.

Cyclooxygenase-2-derived prostaglandin E₂ promotes injury-induced vascular neointimal hyperplasia through the E-prostanoid 3 receptor

RATIONALE

Vascular smooth muscle cell (VSMC) migration and proliferation are the hallmarks of restenosis pathogenesis after angioplasty. Cyclooxygenase (COX)-derived prostaglandin (PG) E₂ is implicated in the vascular remodeling response to injury. However, its precise molecular role remains unknown.

OBJECTIVE

This study investigates the impact of COX-2-derived PGE₂ on neointima formation after injury.

METHODS AND RESULTS

Vascular remodeling was induced by wire injury in femoral arteries of mice. Both neointima formation and the restenosis ratio were diminished in COX-2 knockout mice as compared with controls, whereas these parameters were enhanced in COX-1>COX-2 mice, in which COX-1 is governed by COX-2 regulatory elements. PG profile analysis revealed that the reduced PGE₂ by COX-2 deficiency, but not PGI2, could be rescued by COX-1 replacement, indicating COX-2-derived PGE₂ enhanced neointima formation. Through multiple approaches, the EP3 receptor was identified to mediate the VSMC migration response to various stimuli. Disruption of EP3 impaired VSMC polarity for directional migration by decreasing small GTPase activity and restricted vascular neointimal hyperplasia, whereas overexpression of EP3α and EP3β aggravated neointima formation. Inhibition or deletion of EP3α/β, a Gαi protein-coupled receptor, activated the cAMP/protein kinase A pathway and decreased activation of RhoA in VSMCs. PGE₂ could stimulate phosphatidylinositol 3-kinase/Akt/glycogen synthase kinase3β signaling in VSMCs through Gβγ subunits on EP3α/β activation. Ablation of EP3 suppressed phosphatidylinositol 3-kinase signaling and reduced GTPase activity in VSMCs and altered cell polarity and directional migration.

CONCLUSIONS

COX-2-derived PGE₂ facilitated the neointimal hyperplasia response to injury through EP3α/β-mediated cAMP/protein kinase A and phosphatidylinositol 3-kinase pathways, indicating EP3 inhibition may be a promising therapeutic strategy for percutaneous transluminal coronary angioplasty.