Prostaglandin E₂ inhibits human lung fibroblast chemotaxis through disparate actions on different E-prostanoid receptors

Extracellular stimulation of lung fibroblasts with arachidonic acid increases interleukin 11 expression through p38 and ERK signaling

Interleukin-11 (IL-11) is a pleiotropic cytokine that regulates proliferation and motility of cancer cells. Fibroblasts reside in the cancer microenvironment and are the primary source of IL-11. Activated fibroblasts, including cancer-associated fibroblasts that produce IL-11, contribute to the development and progression of cancer, and induce fibrosis associated with cancer. Changes in fatty acid composition or its metabolites, and an increase in free fatty acids have been observed in cancer. The effect of deregulated fatty acids on the development and progression of cancer is not fully understood yet. In the present study, we investigated the effects of fatty acids on mRNA expression and secretion of IL-11 in lung fibroblasts. Among the eight fatty acids added exogenously, arachidonic acid (AA) increased mRNA expression and secretion of IL-11 in lung fibroblasts in a dose-dependent manner. AA-induced upregulation of IL-11 was dependent on the activation of the p38 or ERK MAPK signaling pathways. Furthermore, prostaglandin E2, associated with elevated cyclooxygenase-2 expression, participated in the upregulation of IL-11 via its specific receptor in an autocrine/paracrine manner. These results suggest that AA may mediate IL-11 upregulation in lung fibroblasts in the cancer microenvironment, accompanied by unbalanced fatty acid composition.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Lipids - two sides of the same coin in lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is characterized by progressive extracellular matrix deposition in the lung parenchyma leading to the destruction of lung structure, respiratory failure and premature death. Recent studies revealed that the pathogenesis of IPF is associated with alterations in the synthesis and the activity of lipids, lipid regulating proteins and cell membrane lipid transporters and receptors in different lung cells. Furthermore, deregulated lipid metabolism was found to contribute to the profibrotic phenotypes of lung fibroblasts and alveolar epithelial cells. Consequently, several pharmacological agents, targeting lipids, lipid mediators, and lipoprotein receptors, was successfully tested in the animal models of lung fibrosis and entered early phase clinical trials. In this review, we highlight new therapeutic options to counteract disturbed lipid hemostasis in the maladaptive lung remodeling.

Matrix Remodeling in Pulmonary Fibrosis and Emphysema

Pulmonary fibrosis and emphysema are chronic lung diseases characterized by a progressive decline in lung function, resulting in significant morbidity and mortality. A hallmark of these diseases is recurrent or persistent alveolar epithelial injury, typically caused by common environmental exposures such as cigarette smoke. We propose that critical determinants of the outcome of the injury-repair processes that result in fibrosis versus emphysema are mesenchymal cell fate and associated extracellular matrix dynamics. In this review, we explore the concept that regulation of mesenchymal cells under the influence of soluble factors, in particular transforming growth factor-β1, and the extracellular matrix determine the divergent tissue remodeling responses seen in pulmonary fibrosis and emphysema.

Structural features of subtype-selective EP receptor modulators

Prostaglandin E2 is a potent endogenous molecule that binds to four different G-protein-coupled receptors: EP1-4. Each of these receptors is a valuable drug target, with distinct tissue localisation and signalling pathways. We review the structural features of EP modulators required for subtype-selective activity, as well as the structural requirements for improved pharmacokinetic parameters. Novel EP receptor subtype selective agonists and antagonists appear to be valuable drug candidates in the therapy of many pathophysiological states, including ulcerative colitis, glaucoma, bone healing, B cell lymphoma, neurological diseases, among others, which have been studied in vitro, in vivo and in early phase clinical trials.

Prostaglandin E₂ possesses different potencies in inducing Vascular Endothelial Growth Factor and Interleukin-8 production in COPD human lung fibroblasts

We studied the role of PGE2, its biosynthetic enzymes and its receptors, in regulating the functions of lung fibroblasts through the production of Vascular Endothelial Growth Factor (VEGF) and Interleukin-8 (IL-8) in COPD subjects. Lung fibroblasts from Control (C) (n=6), Smoker (HS) (n=6) and COPD patients (n=8) were cultured, and basal PGE2, VEGF, and IL-8 measured in supernatants by ELISA. COX-1/COX-2 and EP receptors expression were assessed by western blot and by RT-PCR. Release of VEGF and IL-8 by human fetal lung fibroblasts (HFL-1; lung, diploid, human) was evaluated under different conditions. PGE2, VEGF, and IL-8 levels, COX-2, EP2, and EP4 protein expression and mRNA were increased in COPD when compared to Controls. Low concentrations of synthetic PGE2 increased the release of VEGF in HFL-1, but higher concentrations were needed to induce the release of IL-8. This effect was mimicked by an EP2 agonist and modulated by an EP4 antagonist. In the airways of COPD subjects, fibroblast-derived PGE2 may regulate angiogenesis and inflammation through the production of VEGF and IL-8 respectively, suggesting that the increase in expression of COX-2, EP2 and EP4 observed in COPD fibroblasts may contribute to steering the role of PGE2 from homeostatic to pro-inflammatory.

Inhibitory effect of prostaglandin E(2) on the migration of nasal fibroblasts

BACKGROUND

Fibroblast migration is crucial for normal wound repair after sinonasal surgery. Prostaglandin E2 (PGE2) is a potent inhibitor of fibroblast functions including chemotaxis, proliferation, and matrix production. The purpose of this study was to determine whether PGE2 affects the migration of nasal fibroblasts and to investigate the mechanism of action of PGE2 on nasal fibroblasts.

METHODS

Primary cultures of nasal fibroblasts were established from inferior turbinate samples. Fibroblast migration was evaluated with scratch assays. Reverse-transcription polymerase chain reaction was performed for E prostanoid (EP) 1, EP2, EP3, and EP4 receptors. EP receptor-selective agonists and antagonists were used to evaluate receptor functions. Stimulatory G (Gs) proteins were activated to evaluate mechanisms. Intracellular cyclic adenosine monophosphate (cAMP) levels were measured by ELISA, and fibroblast cytoskeletal structures were visualized with immunocytochemistry.

RESULTS

PGE2 significantly reduced the migration of nasal fibroblasts. Agonists selective for the EP2 and EP4 receptors significantly reduced the nasal fibroblast migration. Antagonists of the EP2 and EP4 receptors inhibited the effect of PGE2 on nasal fibroblast migration. Activation of Gs protein and adenyl cyclase reduced nasal fibroblast migration.

CONCLUSION

PGE2 inhibited the migration of nasal fibroblasts via the EP2 and EP4 receptors, and this inhibition was mediated by cAMP elevation. Targeting specific EP receptors could offer therapeutic opportunities for conditions such as delayed wound healing after nasal surgery.

Effect of culture conditions on microRNA expression in primary adult control and COPD lung fibroblasts in vitro

In vitro cell cultures, including lung fibroblasts, have been used to identify microRNAs (miRNAs) associated with chronic obstructive pulmonary disease (COPD) pathogenesis. However, culture conditions may affect miRNA expression. We examined whether miRNA expression in primary adult lung fibroblasts varies with cell density or passage in vitro and whether culture conditions confound the identification of altered miRNA expression in COPD lung fibroblasts. Primary adult control and COPD lung fibroblasts were cultured until passage 3 or 8, after which cells were further cultured for 3 or 7 d (low vs. high density). Then, cells at low density were cultured with serum-free media, and those at high density were cultured with serum-free media in the absence or presence of interleukin-1β (IL-1β) and tumor necrosis factor alpha (TNF-α) for 24 h. RNA was extracted to perform miRNA microarray from which 1.25-fold differential expression and 10% false discovery rate were applied to identify "invariant" and "variant" miRNA for the various culture conditions. Of the 2226 miRNAs evaluated, 39.0% for cell density, 40.7% for cell passage, and 29.4% for both conditions were identified as "invariant" miRNAs. Furthermore, 38.1% of the evaluated miRNAs were "invariant" for cell passage with IL-1β and TNF-α. Differentially expressed miRNAs between control and COPD lung fibroblasts were identified with and without IL-1β and TNF-α, and of these, 32 out of the 34 top-ranked miRNAs exceeded the differences due to culture conditions. Thus, culture conditions may affect miRNA expression of adult human lung fibroblasts. Nevertheless, in vitro cultures can be used to assess differential miRNA expression in COPD lung fibroblasts.

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.

Quantitative phosphoproteomic analysis of signaling downstream of the prostaglandin e2/g-protein coupled receptor in human synovial fibroblasts: potential antifibrotic networks

The Prostaglandin E2 (PGE2) signaling mechanism within fibroblasts is of growing interest as it has been shown to prevent numerous fibrotic features of fibroblast activation with limited evidence of downstream pathways. To understand the mechanisms of fibroblasts producing tremendous amounts of PGE2 with autocrine effects, we apply a strategy of combining a wide-screening of PGE2-induced kinases with quantitative phosphoproteomics. Our large-scale proteomic approach identified a PKA signal transmitted through phosphorylation of its substrates harboring the R(R/X)X(S*/T*) motif. We documented 115 substrates, of which 72 had 89 sites with a 2.5-fold phosphorylation difference in PGE2-treated cells than in untreated cells, where approximately half of such sites were defined as being novel. They were compiled by networking software to focus on highlighted activities and to associate them with a functional readout of fibroblasts. The substrates were associated with a variety of cellular functions including cytoskeletal structures (migration/motility), regulators of G-protein coupled receptor function, protein kinases, and transcriptional/translational regulators. For the first time, we extended the PGE2 pathway into an elaborate network of interconnecting phosphoproteins, providing vital information to a once restricted signalosome. These data provide new insights into eicosanoid-initiated cell signaling with regards to the regulation of fibroblast activation and the identification of new targets for evidenced-based pharmacotherapy against fibrosis.

Phosphodiesterase-4 inhibition augments human lung fibroblast vascular endothelial growth factor production induced by prostaglandin E2

Lung fibroblasts are believed to be a major source of vascular endothelial growth factor (VEGF), which supports the survival of lung endothelial cells and modulates the maintenance of the pulmonary microvasculature. VEGF has been related to the pathogenesis of lung diseases, including chronic obstructive pulmonary disease (COPD). Prostaglandin E2 (PGE2) stimulates VEGF production from lung fibroblasts via the E-prostanoid (EP)-2 receptor. The EP2 signaling pathway uses cyclic adenosine monophosphate (cAMP) as a second messenger, and cAMP is degraded by phosphodiesterases (PDEs). This study investigates whether phosphodiesterase inhibition modulates the human lung fibroblast VEGF production induced by PGE2. Human fetal lung fibroblasts were cultured with PGE2 and PDE inhibitors. The PDE4 inhibitors roflumilast, roflumilast N-oxide, and rolipram with PGE2 increased VEGF release, as quantified in supernatant media by ELISA. In contrast, PDE3, PDE5, and PDE7 inhibitors did not affect VEGF release. Roflumilast increased VEGF release with either an EP2 or an EP4 agonist. Roflumilast augmented the cytosolic cAMP levels induced by PGE2 and VEGF release with other agents that use the cAMP signaling pathway. Roflumilast-augmented VEGF release was completely inhibited by a protein kinase A (PKA) inhibitor. Roflumilast with PGE2 increased VEGF mRNA levels, and the blockade of mRNA synthesis inhibited the augmented VEGF release. The stimulatory effect of roflumilast on VEGF release was replicated using primary healthy and COPD lung fibroblasts. These findings demonstrate that PDE4 inhibition can modulate human lung fibroblast VEGF release by PGE2 acting through the EP2 and EP4 receptor-cAMP/PKA signaling pathway. Through this action, PDE4 inhibitors such as roflumilast could contribute to the survival of lung endothelial cells.

TGF-β1 downregulates COX-2 expression leading to decrease of PGE2 production in human lung cancer A549 cells, which is involved in fibrotic response to TGF-β1

Transforming growth factor-ß1 (TGF-β1) is a multifunctional cytokine that is involved in various pathophysiological processes, including cancer progression and fibrotic disorders. Here, we show that treatment with TGF-β1 (5 ng/mL) induced downregulation of cyclooxygenase-2 (COX-2), leading to reduced synthesis of prostaglandin E2 (PGE2), in human lung cancer A549 cells. Treatment of cells with specific inhibitors of COX-2 or PGE2 receptor resulted in growth inhibition, indicating that the COX-2/PGE2 pathway contributes to proliferation in an autocrine manner. TGF-β1 treatment induced growth inhibition, which was attenuated by exogenous PGE2. TGF-β1 is also a potent inducer of epithelial mesenchymal transition (EMT), a phenotype change in which epithelial cells differentiate into fibroblastoid cells. Supplementation with PGE2 or PGE2 receptor EP4 agonist PGE1-alcohol, as compared with EP1/3 agonist sulprostone, inhibited TGF-β1-induced expression of fibronectin and collagen I (extracellular matrix components). Exogenous PGE2 or PGE2 receptor agonists also suppressed actin remodeling induced by TGF-β1. These results suggest that PGE2 has an anti-fibrotic effect. We conclude that TGF-β1-induced downregulation of COX-2/PGE2 signaling is involved in facilitation of fibrotic EMT response in A549 cells.

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.

Transforming growth factor Beta 1 stimulates profibrotic activities of luteal fibroblasts in cows

Luteolysis is characterized by angioregression, luteal cell apoptosis, and remodeling of the extracellular matrix characterized by deposition of collagen 1. Transforming growth factor beta 1 (TGFB1) is a potent mediator of wound healing and fibrotic processes through stimulation of the synthesis of extracellular matrix components. We hypothesized that TGFB1 stimulates profibrotic activities of luteal fibroblasts. We examined the actions of TGFB1 on luteal fibroblast proliferation, extracellular matrix production, floating gel contraction, and chemotaxis. Fibroblasts were isolated from the bovine corpus luteum. Western blot analysis showed that luteal fibroblasts expressed collagen 1 and prolyl 4-hydroxylase but did not express markers of endothelial or steroidogenic cells. Treatment of fibroblasts with TGFB1 stimulated the phosphorylation of SMAD2 and SMAD3. [³H]thymidine incorporation studies showed that TGFB1 caused concentration-dependent reductions in DNA synthesis in luteal fibroblasts and significantly (P < 0.05) reduced the proliferative effect of FGF2 and fetal calf serum. However, TGFB1 did not reduce the viability of luteal fibroblasts. Treatment of luteal fibroblasts with TGFB1 induced the expression of laminin, collagen 1, and matrix metalloproteinase 1 as determined by Western blot analysis and gelatin zymography of conditioned medium. TGFB1 increased the chemotaxis of luteal fibroblasts toward fibronectin in a transwell system. Furthermore, TGFB1 increased the fibroblast-mediated contraction of floating bovine collagen 1 gels. These results suggest that TGFB1 contributes to the structural regression of the corpus luteum by stimulating luteal fibroblasts to remodel and contract the extracellular matrix.

Attenuation of inhibitory prostaglandin E2 signaling in human lung fibroblasts is mediated by phosphodiesterase 4

The etiology of chronic obstructive pulmonary disease (COPD) is complex and involves an aberrant inflammatory response. Prostaglandin (PG)E2 is elevated in COPD, is a key modulator of lung fibroblast functions, and may influence COPD progression. Most studies evaluating the effects of PGE2 on lung fibroblasts have used acute exposures. The current study evaluated whether longer-term exposure would induce attenuation of PGE2 signaling as part of an autoregulatory pathway. Human fetal lung fibroblasts were pretreated with PGE2 for 24 hours, and migration and cAMP accumulation in response to acute stimulation with PGE2 were assessed. Fibroblasts from adults with and without COPD were pretreated, and migration was assessed. PGE2 pretreatment attenuated subsequent PGE2-mediated inhibition of chemotaxis and cAMP stimulation. This attenuation was predominantly due to an increase in phosphodiesterase (PDE)4-mediated degradation of cAMP rather than to decreased activation of PGE2 receptors (receptor desensitization). Albuterol- and iloprost-mediated signaling were also attenuated after PGE2 pretreatment, suggesting that activation of PDE4 was able to broadly modulate multiple cAMP-coupled pathways. Lung fibroblasts from adult control subjects pretreated with PGE2 also developed attenuation of PGE2-mediated inhibition of chemotaxis. In contrast, fibroblasts obtained from patients with COPD maintained inhibitory PGE2 signaling after PGE2 pretreatment. These data identify a PDE4-mediated attenuation of PGE2 inhibitory signaling in normal fibroblasts that appears to be altered in COPD fibroblasts. These alterations may contribute to COPD pathogenesis and could provide novel therapeutic targets.

Contrary effects of sphingosine-1-phosphate on expression of α-smooth muscle actin in transforming growth factor β1-stimulated lung fibroblasts

Transforming growth factor-β1 (TGFβ1) plays a pivotal role in fibrosis in various organs including the lung. Following pulmonary injury, TGFβ1 stimulates conversion of fibroblasts to myofibroblasts that are mainly characterized by up-regulation of α-smooth muscle actin (αSMA) expression, and the resulting excess production of extracellular matrix proteins causes fibrosis with loss of alveolar function. The present study was undertaken to define the role of the sphingosine-1-phosphate (S1P) pathway in TGFβ1-induced expression of αSMA in human fetal lung fibroblasts, HFL1 cells. Analysis of mRNA revealed the existence of S1P(1), S1P(2), and S1P(3) receptor mRNAs. Treatment with TGFβ1 increased sphingosine kinase (SphK) activity and S1P(3) receptor mRNA at 24h after stimulation, and pharmacological data showed the involvement of sphingomyelinase, SphK, and S1P(3) receptor in the TGFβ1-induced up-regulation of αSMA with and without serum. Treatment with pertussis toxin and S1P(1) receptor antagonist W146 enhanced αSMA expression by TGFβ1/serum, and S1P decreased and increased αSMA levels with and without serum, respectively. TGFβ1 increased cyclooxygenase-2 expression in a manner dependent on serum and the sphingomyelinase/SphK pathway, and the response was decreased by pertussis toxin. Prostaglandin E(2), formed by TGFβ1/serum stimulation, decreased the TGFβ1-induced expression of αSMA via EP prostanoid receptor. These data suggest that S1P formed by TGFβ1 stimulation has diverse effects on the expression of αSMA, inhibition via the S1P(1) receptor-mediated and serum-dependent expression of cyclooxygenase-2 and the resulting formation of prostaglandin E(2), and stimulation via the S1P(3) receptor in a serum-independent manner.

Intestinal ellagitannin metabolites ameliorate cytokine-induced inflammation and associated molecular markers in human colon fibroblasts

Pomegranate ellagitannins (ETs) are transformed in the gut to ellagic acid (EA) and its microbiota metabolites, urolithin A (Uro-A) and urolithin B (Uro-B). These compounds exert anti-inflammatory effects in vitro and in vivo. The aim of this study was to investigate the effects of Uro-A, Uro-B, and EA on colon fibroblasts, cells that play a key role in intestinal inflammation. CCD18-Co colon fibroblasts were exposed to a mixture of Uro-A, Uro-B, and EA, at concentrations comparable to those found in the colon (40 μM Uro-A, 5 μM Uro-B, 1 μM EA), both in the presence or in the absence of IL-1β (1 ng/mL) or TNF-α (50 ng/mL), and the effects on fibroblast migration and monocyte adhesion were determined. The levels of several growth factors and adhesion cytokines were also measured. The mixture of metabolites significantly inhibited colon fibroblast migration (∼70%) and monocyte adhesion to fibroblasts (∼50%). These effects were concomitant with a significant down-regulation of the levels of PGE(2), PAI-1, and IL-8, as well as other key regulators of cell migration and adhesion. Of the three metabolites tested, Uro-A exhibited the most significant anti-inflammatory effects. The results show that a combination of the ET metabolites found in colon, urolithins and EA, at concentrations achievable in the intestine after the consumption of pomegranate, was able to moderately improve the inflammatory response of colon fibroblasts and suggest that consumption of ET-containing foods has potential beneficial effects on gut inflammatory diseases.

Prostaglandin E2 stimulates the production of vascular endothelial growth factor through the E-prostanoid-2 receptor in cultured human lung fibroblasts

Fibroblasts are the major mesenchymal cells present within the interstitium of the lung and are a major source of vascular endothelial growth factor (VEGF), which modulates the maintenance of pulmonary microvasculature. Prostaglandin E(2) (PGE(2)) acts on a set of E-prostanoid (EP) receptors that activate multiple signal transduction pathways leading to downstream responses. We investigated the modulation by PGE(2) of VEGF release by human lung fibroblasts. Human lung fibroblasts were cultured until reaching 90% confluence in tissue culture plates, after which the culture media were changed to serum-free Dulbecco's modified Eagle's medium, with or without PGE(2), and with specific agonists or antagonists for each EP receptor. After 2 days, culture media were assayed for VEGF by ELISA. The results demonstrated that PGE(2) and the EP2 agonist ONO-AE1-259-01 significantly stimulated the release of VEGF in a concentration-dependent manner. Agonists for other EP receptors did not stimulate the release of VEGF. The stimulatory effect of PGE(2) was blocked by the EP2 antagonist AH6809, but was not blocked by antagonists for other EP receptors. The protein kinase-A (PKA) inhibitor KT-5720 also blocked the stimulatory effect of PGE(2). The increased release of VEGF induced by PGE(2) was accompanied by a transient increase in the concentration of VEGF mRNA. These findings demonstrate that PGE(2) can modulate the release of VEGF by human lung fibroblasts through its actions in the EP2 receptor/PKA pathway. This activity may contribute to the maintenance of pulmonary microvasculature in the alveolar wall.

Role of PGE2 in asthma and nonasthmatic eosinophilic bronchitis

Eosinophilic bronchitis is a common cause of chronic cough, which like asthma is characterized by sputum eosinophilia, but unlike asthma there is no variable airflow obstruction or airway hyperresponsiveness. Several studies suggest that prostaglandins may play an important role in orchestrating interactions between different cells in several inflammatory diseases such as asthma. PGE₂ is important because of the multiplicity of its effects on immune response in respiratory diseases; however, respiratory system appears to be unique in that PGE₂ has beneficial effects. We described that the difference in airway function observed in patients with eosinophilic bronchitis and asthma could be due to differences in PGE₂ production. PGE₂ present in induced sputum supernatant from NAEB patients decreases BSMC proliferation, probably due to simultaneous stimulation of EP2 and EP4 receptors with inhibitory activity. This protective effect of PGE₂ may not only be the result of a direct action exerted on airway smooth-muscle proliferation but may also be attributable to the other anti-inflammatory actions.

IL-4 induces differentiation of human embryonic stem cells into fibrogenic fibroblast-like cells

BACKGROUND

Fibroblast heterogeneity is recognized, and fibroblasts from diseased tissues, including those of asthmatic subjects, have functional phenotypes that differ from normal tissue. However, progenitor-progeny relationships and the factors that control fibroblast differentiation are poorly defined.

OBJECTIVE

We sought to determine whether IL-4 could alter the functional phenotype of fibroblasts during their differentiation from stem/progenitor cells.

METHODS

Using a 3-dimensional collagen gel system, we obtained embryoid bodies derived from human embryonic stem cells and recovered spindle-shaped cells consistent with fibroblasts that had differentiated in the presence or absence of IL-4.

RESULTS

IL-4-induced fibroblast-like cells were more active in contraction of collagen gels, migration, and production of fibronectin than control (without IL-4) cells. IL-4-induced cells demonstrated less expression of miR-155, which modulated contraction, migration, and fibronectin production. These differences persisted in culture without further addition of IL-4, suggesting the differentiated phenotype might be a permanent alteration.

CONCLUSION

The current study demonstrates that IL-4 induces differentiation of stem/precursor cells into fibroblast-like cells that demonstrate a more fibrogenic phenotype, which is due to reduced expression of miR-155. These findings provide a novel mechanism for the persistent abnormalities in IL-4-related diseases and a novel target to regulate tissue remodeling by fibroblasts.

Prostaglandin E2 differentially modulates human platelet function through the prostanoid EP2 and EP3 receptors

Activated human platelets synthesize prostaglandin (PG) E(2), although at lower rate than thromboxane A(2). PGE(2) acts through different receptors (EP1-4), but its role in human platelet function remains poorly characterized compared with thromboxane. We studied the effect of PGE(2) and its analogs on in vitro human platelet function and platelet and megakaryocyte EP expression. Platelets preincubated with PGE(2) or its analogs were stimulated with agonists and studied by optical aggregometry. Intraplatelet calcium mobilization was investigated by the stopped flow method; platelet vasodilator-stimulated phosphoprotein (VASP), P-selectin, and microaggregates were investigated by flow cytometry. PGE(2) at nanomolar concentrations dose-dependently increased the slope (velocity) of the secondary phase of ADP-induced platelet aggregation (EC(50), 25.6 ± 6 nM; E(max) of 100 ± 19% increase versus vehicle-treated), without affecting final maximal aggregation. PGE(2) stabilized reversible aggregation induced by low ADP concentrations (EC(50), 37.7 ± 9 nM). The EP3 agonists, 11-deoxy-16,16-dimethyl PGE(2) (11d-16dm PGE(2)) and sulprostone enhanced the secondary wave of ADP-induced aggregation, with EC(50) of 48.6 ± 10 nM (E(max), 252 ± 51%) and 5 ± 2 nM (E(max), 300 ± 35%), respectively. The EP2 agonist butaprost inhibited ADP-induced secondary phase slopes (IC(50), 40 ± 20 nM). EP4 stimulation had minor inhibitory effects. 11d-16dm PGE(2) alone raised intraplatelet Ca(2+) and enhanced ADP-induced Ca(2+) increase. 11d-16dm PGE(2) and 17-phenyltrinor PGE(2) (EP3 > EP1 agonist) at nanomolar concentrations counteracted PGE(1)-induced VASP phosphorylation and induced platelet microaggregates and P-selectin expression. EP1, EP2, EP3, and EP4 were expressed on human platelets and megakaryocytes. PGE(2) through different EPs finely modulates human platelet responsiveness. These findings should inform the rational selection of novel antithrombotic strategies based on EP modulation.