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

Are secondary bacterial pneumonia mortalities increased because of insufficient pro-resolving mediators?

Respiratory viral infections, including respiratory syncytial virus (RSV), parainfluenza viruses and type A and B influenza viruses, can have severe outcomes. Bacterial infections frequently follow viral infections, and influenza or other viral epidemics periodically have higher mortalities from secondary bacterial pneumonias. Most secondary bacterial infections can cause lung immunosuppression by fatty acid mediators which activate cellular receptors to manipulate neutrophils, macrophages, natural killer cells, dendritic cells and other lung immune cells. Bacterial infections induce synthesis of inflammatory mediators including prostaglandins and leukotrienes, then eventually also special pro-resolving mediators, including lipoxins, resolvins, protectins and maresins, which normally resolve inflammation and immunosuppression. Concurrent viral and secondary bacterial infections are more dangerous, because viral infections can cause inflammation and immunosuppression before the secondary bacterial infections worsen inflammation and immunosuppression. Plausibly, the higher mortalities of secondary bacterial pneumonias are caused by the overwhelming inflammation and immunosuppression, which the special pro-resolving mediators might not resolve.

Spinster homolog 2/S1P signaling ameliorates macrophage inflammatory response to bacterial infections by balancing PGE2 production

BACKGROUND

Mitochondria play a crucial role in shaping the macrophage inflammatory response during bacterial infections. Spinster homolog 2 (Spns2), responsible for sphingosine-1-phosphate (S1P) secretion, acts as a key regulator of mitochondrial dynamics in macrophages. However, the link between Spns2/S1P signaling and mitochondrial functions remains unclear.

METHODS

Peritoneal macrophages were isolated from both wild-type and Spns2 knockout rats, followed by non-targeted metabolomics and RNA sequencing analysis to identify the potential mediators through which Spns2/S1P signaling influences the mitochondrial functions in macrophages. Various agonists and antagonists were used to modulate the activation of Spns2/S1P signaling and its downstream pathways, with the underlying mechanisms elucidated through western blotting. Mitochondrial functions were assessed using flow cytometry and oxygen consumption assays, as well as morphological analysis. The impact on inflammatory response was validated through both in vitro and in vivo sepsis models, with the specific role of macrophage-expressed Spns2 in sepsis evaluated using Spns2flox/floxLyz2-Cre mice. Additionally, the regulation of mitochondrial functions by Spns2/S1P signaling was confirmed using THP-1 cells, a human monocyte-derived macrophage model.

RESULTS

In this study, we unveil prostaglandin E2 (PGE2) as a pivotal mediator involved in Spns2/S1P-mitochondrial communication. Spns2/S1P signaling suppresses PGE2 production to support malate-aspartate shuttle activity. Conversely, excessive PGE2 resulting from Spns2 deficiency impairs mitochondrial respiration, leading to intracellular lactate accumulation and increased reactive oxygen species (ROS) generation through E-type prostanoid receptor 4 activation. The overactive lactate-ROS axis contributes to the early-phase hyperinflammation during infections. Prolonged exposure to elevated PGE2 due to Spns2 deficiency culminates in subsequent immunosuppression, underscoring the dual roles of PGE2 in inflammation throughout infections. The regulation of PGE2 production by Spns2/S1P signaling appears to depend on the coordinated activation of multiple S1P receptors rather than any single one.

CONCLUSIONS

These findings emphasize PGE2 as a key effector of Spns2/S1P signaling on mitochondrial dynamics in macrophages, elucidating the mechanisms through which Spns2/S1P signaling balances both early hyperinflammation and subsequent immunosuppression during bacterial infections.

Automatic substantia nigra segmentation with Swin-Unet in susceptibility- and T2-weighted imaging: application to Parkinson disease diagnosis

Background

Accurately distinguishing between Parkinson disease (PD) and healthy controls (HCs) through reliable imaging method is crucial for appropriate therapeutic intervention. However, PD diagnosis is hindered by the subjective nature of the evaluation. We aimed to develop an automatic deep-learning method that can segment the substantia nigra areas on susceptibility-weighted imaging (SWI) and T2-weighted imaging (T2WI) and further differentiate patients with PD from HCs using a machine learning algorithm.

Methods

Magnetic resonance imaging (MRI) data from 83 patients with PD and 83 age- and sex-matched HCs were obtained on the same 3.0-T MRI scanner. A deep learning method with Swin-Unet was developed to segment volumes of interest (VOIs) on SWI and then map the VOIs on SWI to the corresponding T2WI; features were then extracted from the VOIs on SWI and T2WI. Three machine learning models were developed and compared to differentiate those with PD from HCs.

Results

Swin-Unet achieved a better Dice coefficient than did U-Net in SWI segmentation (0.832 vs. 0.712). Machine learning models outperformed visual analysis (P>0.05), and logistic regression (LR) achieved the best performance [area under the curve (AUC) ≥0.819] and the most stable (relative standard deviations in AUC ≤0.05). The test results showed that the AUC of the LR model based on SWI segmentation was 0.894 while that of the LR model based on T2WI segmentation was 0.876. There was no significant difference in VOIs based on manual labeling or automatic segmentation across T2WI, SWI, or a combination of the two (P>0.05). The AUCs of the LR model based on automatic segmentation were close to those of the model based on manual labeling (P>0.05).

Conclusions

Our approach could provide a powerful and useful method for automatically and rapidly diagnosing PD in the clinic with only T2WI.

Roles of prostaglandins in immunosuppression

Prostaglandins (PGs) play a crucial and multifaceted role in various physiological processes such as intercellular signaling, inflammation regulation, neurotransmission, vasodilation, vasoconstriction, and reproductive functions. The diversity and biological significance of these effects are contingent upon the specific types or subtypes of PGs, with each PG playing a crucial role in distinct physiological and pathological processes. Particularly within the immune system, PGs are essential in modulating the function of immune cells and the magnitude and orientation of immune responses. Hence, a comprehensive comprehension of the functions PG signaling pathways in immunosuppressive regulation holds substantial clinical relevance for disease prevention and treatment strategies. The manuscript provides a review of recent developments in PG signaling in immunosuppressive regulation. Furthermore, the potential clinical applications of PGs in immunosuppression are also discussed. While research into the immunosuppressive effects of PGs required further exploration, targeted therapies against their immunosuppressive pathways might open new avenues for disease prevention and treatment.

Oxylipin profiling for clinical research: Current status and future perspectives

Oxylipins are potent lipid mediators with increasing interest in clinical research. They are usually measured in systemic circulation and can provide a wealth of information regarding key biological processes such as inflammation, vascular tone, or blood coagulation. Although procedures still require harmonization to generate comparable oxylipin datasets, performing comprehensive profiling of circulating oxylipins in large studies is feasible and no longer restricted by technical barriers. However, it is essential to improve and facilitate the biological interpretation of complex oxylipin profiles to truly leverage their potential in clinical research. This requires regular updating of our knowledge about the metabolism and the mode of action of oxylipins, and consideration of all factors that may influence circulating oxylipin profiles independently of the studied disease or condition. This review aims to provide the readers with updated and necessary information regarding oxylipin metabolism, their different forms in systemic circulation, the current limitations in deducing oxylipin cellular effects from in vitro bioactivity studies, the biological and technical confounding factors needed to consider for a proper interpretation of oxylipin profiles.

PGE2 binding to EP2 promotes ureteral stone expulsion by relaxing ureter via the cAMP-PKA pathway

BACKGROUND

This study investigated the relaxation effect of PGE2 on the ureter and its role in promoting calculi expulsion following calculi development.

METHODS

By using immunofluorescence and Western blot, we were able to locate EP receptors in the ureter. In vitro experiments assessed the impact of PGE2, receptor antagonists, and agonists on ureteral relaxation rate. We constructed a model of ureteral calculi with flowable resin and collected ureteral tissue from postoperative side of the ureter after obstruction surgery. Western blot analysis was used to determine the protein expression levels of EP receptors and the PGE2 terminal synthase mPGES-1. Additionally, PGE2 was added to smooth muscle cells to observe downstream cAMP and PKA changes.

RESULTS

The expression of EP2 and EP4 proteins in ureteral smooth muscle was verified by Western blot analysis. According to immunofluorescence, EP2 was primarily found on the cell membrane, while EP4 was found in the nucleus. In vitro, PGE2 induced concentration-dependent ureteral relaxation. Maximum diastolic rate was 70.94 ± 4.57% at a concentration of 30µM. EP2 antagonists hindered this effect, while EP4 antagonists did not. Obstructed ureters exhibited elevated mPGES-1 and EP2 protein expression (P < 0.01). Smooth muscle cells treated with PGE2 displayed increased cAMP and phosphorylated PKA.

CONCLUSIONS

PGE2 binding to EP2 induces ureteral relaxation through the cAMP-PKA pathway. This will provide a new theoretical basis for the development of new therapeutic approaches for the use of PGE2 in the treatment of ureteral stones.

Metabolite-sensing GPCRs in rheumatoid arthritis

Persistent inflammation in damaged joints results in metabolic dysregulation of the synovial microenvironment, causing pathogenic alteration of cell activity in rheumatoid arthritis (RA). Recently, the role of metabolite and metabolite-sensing G protein-coupled receptors (GPCRs) in the RA-related inflammatory immune response (IIR) has become a focus of research attention. These GPCRs participate in the progression of RA by modulating immune cell activation, migration, and inflammatory responses. Here, we discuss recent evidence implicating metabolic dysregulation in RA pathogenesis, focusing on the connection between RA-related IIR and GPCR signals originating from the synovial joint and gut. Furthermore, we discuss future directions for targeting metabolite-sensing GPCRs for therapeutic benefit, emphasizing the importance of identifying endogenous ligands and investigating the various transduction mechanisms involved.

GRK2 inhibits Flt-1+ macrophage infiltration and its proangiogenic properties in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease with a complex etiology. Monocyte-derived macrophages (MDMs) infiltration are associated with RA severity. We have reported the deletion of G-protein-coupled receptor kinase 2 (GRK2) reprograms macrophages toward an anti-inflammatory phenotype by recovering G-protein-coupled receptor signaling. However, as more GRK2-interacting proteins were discovered, the GRK2 interactome mechanisms in RA have been understudied. Thus, in the collagen-induced arthritis mouse model, we performed genetic GRK2 deletion using GRK2f/fLyz2-Cre+/- mice. Synovial inflammation and M1 polarization were improved in GRK2f/fLyz2-Cre+/- mice. Supporting experiments with RNA-seq and dual-luciferase reporter assays identified peroxisome proliferator-activated receptor γ (PPARγ) as a new GRK2-interacting protein. We further confirmed that fms-related tyrosine kinase 1 (Flt-1), which promoted macrophage migration to induce angiogenesis, was inhibited by GRK2-PPARγ signaling. Mechanistically, excess GRK2 membrane recruitment in CIA MDMs reduced the activation of PPARγ ligand-binding domain and enhanced Flt-1 transcription. Furthermore, the treatment of mice with GRK2 activity inhibitor resulted in significantly diminished CIA pathology, Flt-1+ macrophages induced-synovial inflammation, and angiogenesis. Altogether, we anticipate to facilitate the elucidation of previously unappreciated details of GRK2-specific intracellular signaling. Targeting GRK2 activity is a viable strategy to inhibit MDMs infiltration, affording a distinct way to control joint inflammation and angiogenesis of RA.

Comprehensive insights into the multifaceted roles of the transient receptor potential vanilloid 1 channel in the digestive system

The transient receptor potential vanilloid (TRPV) channel, a family of calcium transporters comprising six distinct members (TRPV1-6), takes on a paramount role in maintaining intracellular Ca2+ homeostasis in mammalian cells. Notably, TRPV1, among its counterparts, has emerged as the subject of extensive scrutiny, owing to its pervasive presence in diverse cellular, tissue, and organ settings. This ubiquitous distribution underscores its fundamental involvement in the genesis of pain, making it a central focus in pain-related research. However, recent investigations have unveiled that TRPV1's functional significance transcends the realm of pain modulation, extending its influence to encompass a wide spectrum of physiological and pathological processes. The ambit of TRPV1's influence encompasses not only pain responses but also embraces the intricate domains of nervous system disorders, cancer metastasis, as well as afflictions pertaining to the skin and heart. Moreover, compelling evidence now demonstrates that TRPV1 also wields substantial sway in the domain of digestive diseases, further highlighting its versatility and far-reaching impact on human health. Therefore, this comprehensive review endeavors to delve into the multifaceted roles played by TRPV1 in the various organs constituting the digestive system.

The oxylipin analog CS585 prevents platelet activation and thrombosis through activation of the prostacyclin receptor

Cardiovascular disease remains the primary cause of morbidity and mortality globally. Platelet activation is critical for maintaining hemostasis and preventing the leakage of blood cells from the vessel. There has been a paucity in the development of new drugs to target platelet reactivity. Recently, the oxylipin 12(S)-hydroxy-eicosatrienoic acid (12-HETrE), which is produced in platelets, was shown to limit platelet reactivity by activating the prostacyclin receptor. Here, we demonstrated the synthesis of a novel analog of 12-HETrE, known as CS585. Human blood and mouse models of hemostasis and thrombosis were assessed for the ability of CS585 to attenuate platelet activation and thrombosis without increasing the risk of bleeding. Human platelet activation was assessed using aggregometry, flow cytometry, western blot analysis, total thrombus formation analysis system, microfluidic perfusion chamber, and thromboelastography. Hemostasis, thrombosis, and bleeding assays were performed in mice. CS585 was shown to potently target the prostacyclin receptor on the human platelet, resulting in a highly selective and effective mechanism for the prevention of platelet activation. Furthermore, CS585 was shown to inhibit platelet function in human whole blood ex vivo, prevent thrombosis in both small and large vessels in mouse models, and exhibit long-lasting prevention of clot formation. Finally, CS585 was not observed to perturb coagulation or increase the risk of bleeding in the mouse model. Hence, CS585 represents a new validated target for the treatment of thrombotic diseases without the risk of bleeding or off-target activation observed with other prostaglandin receptor agonists.

Single hormone or synthetic agonist induces Gs/Gi coupling selectivity of EP receptors via distinct binding modes and propagating paths

To accomplish concerted physiological reactions, nature has diversified functions of a single hormone at at least two primary levels: 1) Different receptors recognize the same hormone, and 2) different cellular effectors couple to the same hormone-receptor pair [R.P. Xiao, Sci STKE 2001, re15 (2001); L. Hein, J. D. Altman, B.K. Kobilka, Nature 402, 181-184 (1999); Y. Daaka, L. M. Luttrell, R. J. Lefkowitz, Nature 390, 88-91 (1997)]. Not only these questions lie in the heart of hormone actions and receptor signaling but also dissecting mechanisms underlying these questions could offer therapeutic routes for refractory diseases, such as kidney injury (KI) or X-linked nephrogenic diabetes insipidus (NDI). Here, we identified that Gs-biased signaling, but not Gi activation downstream of EP4, showed beneficial effects for both KI and NDI treatments. Notably, by solving Cryo-electron microscope (cryo-EM) structures of EP3-Gi, EP4-Gs, and EP4-Gi in complex with endogenous prostaglandin E2 (PGE2)or two synthetic agonists and comparing with PGE2-EP2-Gs structures, we found that unique primary sequences of prostaglandin E2 receptor (EP) receptors and distinct conformational states of the EP4 ligand pocket govern the Gs/Gi transducer coupling selectivity through different structural propagation paths, especially via TM6 and TM7, to generate selective cytoplasmic structural features. In particular, the orientation of the PGE2 ω-chain and two distinct pockets encompassing agonist L902688 of EP4 were differentiated by their Gs/Gi coupling ability. Further, we identified common and distinct features of cytoplasmic side of EP receptors for Gs/Gi coupling and provide a structural basis for selective and biased agonist design of EP4 with therapeutic potential.

DHA, RvD1, RvD5, and MaR1 reduce human coronary arteries contractions induced by PGE2

In patients with coronary artery disease (CAD), plasma levels of pro-inflammatory lipid mediators such as PGE₂ and TxA₂ are increased. They could increase vascular contraction while EPA and DHA could reduce it. Studies have been mostly conducted on animal vessels. Therefore, the aim of the study was to investigate if EPA, DHA, and DHA-derived metabolites: RvD1, RvD5 and MaR1 can modulate contraction of human coronary arteries (HCA) induced by PGE₂ or TxA₂ stable analogue (U46619). DHA and EPA relaxed HCA pre-contracted with PGE₂. 18 h-incubation with DHA but not EPA reduced the PGE₂-induced contractions. Pre-incubation with RvD1, RvD5 and MaR1 reduced the PGE₂-induced contractions. Indomethacin did not significantly modify the PGE₂ responses. L-NOARG (inhibitor of nitric oxide synthase), reduced only the PGE₂-induced contractions in RvD1-treated rings. Finally, FPR2/ALX, GPR32 and LGR6 receptors are detected in HCA by immunofluorescence. Our results indicate that DHA and its metabolites could be beneficial for HCA blood flow and could be a therapeutic perspective for patients with CAD.

Controlling Inflammation Improves Aging Skeletal Muscle Health

Chronic inflammation is associated with a decline in aging skeletal muscle health. Inflammation also seems to interfere with the beneficial skeletal muscle adaptations conferred by exercise training in older individuals. We hypothesize that the cyclooxygenase pathway is partially responsible for this negative inflammatory influence on aging skeletal muscle health and plasticity.

E-prostanoid 3 receptor deficiency on myeloid cells protects against ischemic acute kidney injury via breaking the auto-amplification loop of necroinflammation

Necroinflammation plays an important role in disease settings such as acute kidney injury (AKI). We and others have elucidated that prostaglandins, which are critically involved in inflammation, may activate E-prostanoid 3 receptor (EP3) at low concentrations. However, how EP3 blockade interacts with regulated cell death and affects AKI remains unknown. In this study, AKI was induced by ischemia-reperfusion (30 minutes/24 hours) in Ep3 knockout (Ep3-/-), bone marrow chimeric, myeloid conditional EP3 knockout and corresponding control mice. The production of prostaglandins E2 and I2 was markedly increased after ischemia-reperfusion, and either abrogation or antagonism of EP3 ameliorated the injury. EP3 deficiency curbed inflammatory cytokine release, neutrophil infiltration and serum high-mobility group box 1 levels, but additional TLR4 inhibition with TAK-242 did not offer further protection against the injury and inflammation. The protection of Ep3-/- was predominantly mediated by suppressing Mixed Lineage Kinase domain-Like-dependent necroptosis, resulting from the inhibition of cytokine generation and the switching of cell death modality from necroptosis to apoptosis through caspase-8 up-regulation, in part due to the restraint of IL-6/JAK2/STAT3 signaling. EP3 deficiency failed to further alleviate the injury when necroptosis was inhibited. Ep3-/- in bone marrow-derived cells, particularly that in myeloid cells, protected kidneys to the same extent as that of global EP3 deletion. Thus, our results demonstrate that EP3 deficiency especially that on myeloid cells, ameliorates ischemic AKI via curbing inflammation and breaking the auto-amplification loop of necroinflammation. Hence, EP3 may be a promising target for the prevention and/or treatment of AKI.

The biological actions of prostanoids in adipose tissue in physiological and pathophysiological conditions

Adipose tissue has been established as an endocrine organ that plays an important role in maintaining metabolic homeostasis. Adipose tissue releases several bioactive molecules called adipokines. Inflammation, dysregulation of adipokine synthesis, and secretion are observed in obesity and related diseases and cause adipose tissue dysfunction. Prostanoids, belonging to the eicosanoid family of lipid mediators, can be synthesized in adipose tissue and play a critical role in adipose tissue biology. In this review, we summarized the current knowledge regarding the interaction of prostanoids with adipokines, the expression of prostanoid receptors, and prostanoid synthase enzymes in adipose tissues in health and disease. Furthermore, the involvement of prostanoids in the physiological function or dysfunction of adipose tissue including inflammation, lipolysis, adipogenesis, thermogenesis, browning of adipocytes, and vascular tone regulation was also discussed by examining studies using pharmacological approaches or genetically modified animals for prostanoid receptors/synthase enzymes. Overall, the present review provides a perspective on the evidence from literature regarding the biological effects of prostanoids in adipose tissue. Among prostanoids, prostaglandin E2 (PGE₂) is prominent in regards to its substantial role in both adipose tissue physiology and pathophysiology. Targeting prostanoids may serve as a potential therapeutic strategy for preventing or treating obesity and related diseases.

Structural insights into the G protein selectivity revealed by the human EP3-Gi signaling complex

Prostaglandin receptors have been implicated in a wide range of functions, including inflammation, immune response, reproduction, and cancer. Our group has previously determined the crystal structure of the active-like EP3 bound to its endogenous agonist, prostaglandin E₂. Here, we present the single-particle cryoelectron microscopy (cryo-EM) structure of the human EP3-G_i signaling complex at a resolution of 3.4 Å. The structure reveals the binding mode of G_i to EP3 and the structural changes induced in EP3 by G_i binding. In addition, we compare the structure of the EP3-G_i complex with other subtypes of prostaglandin receptors (EP2 and EP4) bound to G_s that have been previously reported and examine the differences in amino acid composition at the receptor-G protein interface. Mutational analysis reveals that the selectivity of the G protein depends on specific amino acid residues in the second intracellular loop and TM5.

Prostanoid Signaling in Cancers: Expression and Regulation Patterns of Enzymes and Receptors

Cancer-associated disturbance of prostanoid signaling provides an aberrant accumulation of prostanoids. This signaling consists of 19 target genes, encoding metabolic enzymes and G-protein-coupled receptors, and prostanoids (prostacyclin, thromboxane, and prostaglandins E2, F2α, D2, H2). The study addresses the systems biology analysis of target genes in 24 solid tumors using a data mining pipeline. We analyzed differential expression patterns of genes and proteins, promoter methylation status as well as tissue-specific master regulators and microRNAs. Tumor types were clustered into several groups according to gene expression patterns. Target genes were characterized as low mutated in tumors, with the exception of melanoma. We found at least six ubiquitin ligases and eight protein kinases that post-translationally modified the most connected proteins PTGES3 and PTGIS. Models of regulation of PTGIS and PTGIR gene expression in lung and uterine cancers were suggested. For the first time, we found associations between the patient’s overall survival rates with nine multigene transcriptomics signatures in eight tumors. Expression patterns of each of the six target genes have predictive value with respect to cytostatic therapy response. One of the consequences of the study is an assumption of prostanoid-dependent (or independent) tumor phenotypes. Thus, pharmacologic targeting the prostanoid signaling could be a probable additional anticancer strategy.

Roles of EP Receptors in the Regulation of Fluid Balance and Blood Pressure

Prostaglandin E2 (PGE2) is an important prostanoid expressing throughout the kidney and cardiovascular system. Despite the diverse effects on fluid metabolism and blood pressure, PGE2 is implicated in sustaining volume and hemodynamics homeostasis. PGE2 works through four distinct E-prostanoid (EP) receptors which are G protein-coupled receptors. To date, pharmacological specific antagonists and agonists of all four subtypes of EP receptors and genetic targeting knockout mice for each subtype have helped in uncoupling the diverse functions of PGE2 and discriminating the respective characteristics of each receptor. In this review, we summarized the functions of individual EP receptor subtypes in the renal and blood vessels and the molecular mechanism of PGE2-induced fluid metabolism and blood pressure homeostasis.

Prostaglandin signaling in ciliogenesis and development

Prostaglandin (PG) signaling regulates a wide variety of physiological and pathological processes, including body temperature, cardiovascular homeostasis, reproduction, and inflammation. Recent studies have revealed that PGs play pivotal roles in embryo development, ciliogenesis, and organ formation. Prostaglandin E2 (PGE2) and its receptor EP4 modulate ciliogenesis by increasing the anterograde intraflagellar transport. Many G-protein-coupled receptors (GPCRs) including EP4 are localized in cilia for modulating cAMP signaling under various conditions. During development, PGE2 signaling regulates embryogenesis, hepatocyte differentiation, hematopoiesis, and kidney formation. Prostaglandins are also essential for skeletal muscle repair. This review outlines recent advances in understanding the functions and mechanisms of prostaglandin signaling in ciliogenesis, embryo development, and organ formation.

Comparative study on the effect of aspirin, TP receptor antagonist and TxA2 synthase inhibitor on the vascular tone of human saphenous vein and internal mammary artery

AIMS

Thromboxane (TxA₂) is synthesized from arachidonic acid (AA) via thromboxane synthase (TxS) enzyme and induces vasoconstriction via TP receptor. Our aim is to compare the effects of aspirin, TxS inhibitor and TP receptor antagonist on vascular reactivity of bypass grafts (saphenous vein and internal mammary artery).

MAIN METHODS

Using isolated organ bath, saphenous vein and internal mammary artery preparations were incubated with TP receptor antagonist, TxS inhibitor, aspirin, IP or EP4 receptor antagonist. Then prostaglandin (PG)E₂, PGF_2α, phenylephrine and AA were administered in concentration-dependent manner. The expression of prostanoid receptor and PGI₂ synthase (PGIS) enzyme was determined by Western Blot.

KEY FINDINGS

TP receptor antagonist inhibited the contraction induced by PGE₂, PGF_2α, and AA but not that induced by phenylephrine in both types of vessels. Aspirin increased phenylephrine-induced contraction only in internal mammary artery and decreased AA-induced contraction in saphenous vein. TxS inhibitor decreased both PGE₂ and AA-induced contraction in both types of vessels. This decrease was reversed by co-incubation of TxS inhibitor and IP/EP4 receptor antagonists. The expressions of EP3 receptor and PGIS enzyme were greater in internal mammary artery compared to saphenous vein while IP and TP receptors expressed at similar levels.

SIGNIFICANCE

TP receptor antagonist and TxS inhibitor are more effective to reduce contraction induced by different spasmogens in comparison to aspirin. Our results suggest that TP receptor antagonist and TxS inhibitor might have an advantage over aspirin due to their preventive effect on increased vascular reactivity observed in post-operative period of coronary artery bypass grafting.

Redressing the interactions between stem cells and immune system in tissue regeneration

Skeletal muscle has an extraordinary regenerative capacity reflecting the rapid activation and effective differentiation of muscle stem cells (MuSCs). In the course of muscle regeneration, MuSCs are reprogrammed by immune cells. In turn, MuSCs confer immune cells anti-inflammatory properties to resolve inflammation and facilitate tissue repair. Indeed, MuSCs can exert therapeutic effects on various degenerative and inflammatory disorders based on their immunoregulatory ability, including effects primed by interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). At the molecular level, the tryptophan metabolites, kynurenine or kynurenic acid, produced by indoleamine 2,3-dioxygenase (IDO), augment the expression of TNF-stimulated gene 6 (TSG6) through the activation of the aryl hydrocarbon receptor (AHR). In addition, insulin growth factor 2 (IGF2) produced by MuSCs can endow maturing macrophages oxidative phosphorylation (OXPHOS)-dependent anti-inflammatory functions. Herein, we summarize the current understanding of the immunomodulatory characteristics of MuSCs and the issues related to their potential applications in pathological conditions, including COVID-19.

Oral administration of E-type prostanoid (EP) 1 receptor antagonist suppresses carcinogenesis and development of prostate cancer via upregulation of apoptosis in an animal model

Prostaglandin E2 plays an important role in carcinogenesis and malignant potential of prostate cancer (PC) cells by binding to its specific receptors, E-type prostanoid (EP) receptors. However, anti-carcinogenic effects of the EP receptor antagonist are unclear. In this study, we used a mouse model of PC. The mice were provided standard feed (control) or feed containing the EP1 receptor antagonist and were sacrificed at 10, 15, 30, and 52 weeks of age. Apoptosis was evaluated by immunohistochemical analysis using a cleaved caspase-3 assay. The incidence of cancer in the experimental group was significantly lower than that in the control group at 15, 30, and 52 weeks of age. The percentage of poorly differentiated PC cells was significantly lower in the experimental group than in the control group at 30 and 52 weeks of age. The percentage of apoptotic cells in the experimental group was significantly higher than that in the control group at 15, 30, and 52 weeks of age. These findings indicate that feeding with the addition of EP1 receptor antagonist delayed PC progression via the upregulation of apoptosis. We suggest that the EP1 receptor antagonist may be a novel chemopreventive agent for PC.

Absence of prostacyclin greatly relieves cyclophosphamide-induced cystitis and bladder pain in mice

Cyclophosphamide (CP) has been widely used in the treatment of various malignancies and autoimmune diseases, but acrolein, a byproduct of CP, causes severe hemorrhagic cystitis as the major side effect of CP. On the other hand, a large amount of prostacyclin (PGI₂ ) is produced in bladder tissues, and PGI₂ has been shown to play a critical role in bladder homeostasis. PGI₂ is biosynthesized from prostaglandin (PG) H₂ , the common precursor of PGs, by PGI₂ synthase (PTGIS) and is known to also be involved in inflammatory responses. However, little is known about the roles of PTGIS-derived PGI₂ in bladder inflammation including CP-induced hemorrhagic cystitis. Using both genetic and pharmacological approaches, we here revealed that PTGIS-derived PGI₂ -IP (PGI₂ receptor) signaling exacerbated CP-induced bladder inflammatory reactions. Ptgis deficiency attenuated CP-induced vascular permeability and chemokine-mediated neutrophil migration into bladder tissues and then suppressed hemorrhagic cystitis. Treatment with RO1138452, an IP selective antagonist, also suppressed CP-induced cystitis. We further found that cystitis-related nociceptive behavior was also relieved in both Ptgis^-/- mice and RO1138452-treated mice. Our findings may provide new drug targets for bladder inflammation and inflammatory pain in CP-induced hemorrhagic cystitis.

Comparative study of coronary artery bypass graft materials: reduced contraction and ADMA levels in internal mammary artery versus saphenous vein

BACKGROUND

Vasospasm and atherosclerosis due to low endothelial capacity are the most important causes of coronary artery bypass graft failure observed in internal mammary artery (IMA) and saphenous vein (SV). Vasospasm can be mimicked in in vitro studies by inducing vasoconstriction of graft materials. In the present study, we aimed to compare the vascular contraction induced by several spasmogens including prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2α), phenylephrine (PE), leukotriene C4 (LTC4), LTD4, potassium chloride (KCl), and arachidonic acid between IMA and SV preparations. Furthermore, endothelial capacity, nitrite and asymmetric dimethylarginine (ADMA) levels were compared between two grafts.

METHODS

By using organ bath, contractile responses induced by different spasmogens were compared between IMA and SV preparations derived from patients underwent coronary artery bypass surgery (n=35). The endothelial capacity was determined by acetylcholine (ACh) -induced relaxation in PE-precontracted vessels. Nitrite and ADMA levels were measured in organ culture supernatant of IMA and SV preparations.

RESULTS

Contractile responses induced by PGE2, PGF2α, PE, LTC4, LTD4, KCl and arachidonic acid were significantly lower in IMA preparations versus SV preparations. ACh-induced relaxation was significantly more prominent in IMA than SV preparations. Nitrite levels were greater and ADMA levels were lower in IMA versus SV preparations.

CONCLUSIONS

IMA has reduced capacity to constrict to several vasoconstrictor agents. Furthermore, IMA has greater endothelial capacity associated with higher nitrite levels and lower ADMA levels. Our results support the greater patency rate observed in IMA versus SV preparations.

EP2 Antagonists (2011-2021): A Decade's Journey from Discovery to Therapeutics

In the wake of health disasters associated with the chronic use of cyclooxygenase-2 (COX-2) inhibitor drugs, it has been widely proposed that modulation of downstream prostanoid synthases or receptors might provide more specificity than simply shutting down the entire COX cascade for anti-inflammatory benefits. The pathogenic actions of COX-2 have long been thought attributable to the prostaglandin E2 (PGE2) signaling through its Gαs-coupled EP2 receptor subtype; however, the truly selective EP2 antagonists did not emerge until 2011. These small molecules provide game-changing tools to better understand the EP2 receptor in inflammation-associated conditions. Their applications in preclinical models also reshape our knowledge of PGE2/EP2 signaling as a node of inflammation in health and disease. As we celebrate the 10-year anniversary of this breakthrough, the exploration of their potential as drug candidates for next-generation anti-inflammatory therapies has just begun. The first decade of EP2 antagonists passes, while their future looks brighter than ever.

Prostaglandin D2 strengthens human endothelial barrier by activation of E-type receptor 4

Life-threatening inflammatory conditions such as acute respiratory distress syndrome or sepsis often go hand in hand with severe vascular leakage. During inflammation, endothelial cell integrity and intact barrier function are crucial to limit leukocyte and plasma extravasation. Prostaglandin D₂ (PGD₂) is a potent inflammatory lipid mediator with vasoactive properties. Previous studies suggest that PGD₂ is involved in the regulation of endothelial barrier function; however, it is unclear whether this is also true for primary human pulmonary microvascular endothelial cells. Furthermore, as PGD₂ is a highly promiscuous ligand, we set out to determine which receptors are important in human pulmonary endothelial cells. In the current study, we found that PGD₂ and the DP1 agonist BW245c potently strengthened pulmonary and dermal microvascular endothelial cell barrier function and protected against thrombin-induced barrier disruption. Yet surprisingly, these effects were mediated only to a negligible extent via DP1 receptor activation. In contrast, we observed that the EP4 receptor was most important and mediated the barrier enhancement by PGD₂ and BW245c. Stimulation with PGE₂ or PGD₂ reduced AKT phosphorylation which could be reversed by prior blockade of EP4 receptors. These data demonstrate a novel mechanism by which PGD₂ may modulate inflammation and emphasizes the role of EP4 receptors in human endothelial cell function.