The prostaglandin receptor EP4 suppresses colitis, mucosal damage and CD4 cell activation in the gut

Uterine prostaglandin DP receptor induced upon implantation contributes to decidualization together with EP4 receptor

To investigate the yet-unknown roles of prostaglandins (PGs) in the uterus, we analyzed the expression of various PG receptors in the uterus. We found that three types of Gs-coupled PG receptors, DP, EP2, and EP4 were expressed in luminal epithelial cells from the peri-implantation period to late pregnancy. DP expression was also induced in stromal cells within the mesometrial region, whereas EP4 was expressed in stromal cells within the anti-mesometrial region during the peri-implantation period. The timing of DP induction after embryo attachment correlated well with that of cyclooxygenase-2 (COX-2); however, COX-2-expressing stromal cells were located in the vicinity of the embryo, whereas DP-expressing stromal cells surrounded these cells on the mesometrial side. Specific [3H]PGD2-binding activity was detected in the decidua of uteri, with PGD2 synthesis comparable to that of PGE2 detected in the uteri during the peri-implantation period. Administration of the COX-2-specific inhibitor celecoxib caused adverse effects on decidualization, as demonstrated by the attenuated weight of the implantation sites, which was recovered by the simultaneous administration of a DP agonist. Such a rescuing effect of the DP agonist was mimicked by an EP4 agonist, but not an EP2 agonist. Whereas the importance of DP signaling was shown pharmacologically, DP/EP2 double deficiency did not affect implantation and decidualization, suggesting the contribution of EP4 to these processes. Indeed, administration of an EP4 antagonist substantially affected decidualization in DP/EP2-deficient mice. These results suggest that COX-2-derived PGD2 and PGE2 contribute to decidualization via a coordinated pathway of DP and EP4 receptors.

Ileal Crohn's Disease Exhibits Reduced Activity of Phospholipase C-β3-Dependent Wnt/β-Catenin Signaling Pathway

Crohn's disease is a chronic, debilitating, inflammatory bowel disease. Here, we report a critical role of phospholipase C-β3 (PLC-β3) in intestinal homeostasis. In PLC-β3-deficient mice, exposure to oral dextran sodium sulfate induced lethality and severe inflammation in the small intestine. The lethality was due to PLC-β3 deficiency in multiple non-hematopoietic cell types. PLC-β3 deficiency resulted in reduced Wnt/β-catenin signaling, which is essential for homeostasis and the regeneration of the intestinal epithelium. PLC-β3 regulated the Wnt/β-catenin pathway in small intestinal epithelial cells (IECs) at transcriptional, epigenetic, and, potentially, protein-protein interaction levels. PLC-β3-deficient IECs were unable to respond to stimulation by R-spondin 1, an enhancer of Wnt/β-catenin signaling. Reduced expression of PLC-β3 and its signature genes was found in biopsies of patients with ileal Crohn's disease. PLC-β regulation of Wnt signaling was evolutionally conserved in Drosophila. Our data indicate that a reduction in PLC-β3-mediated Wnt/β-catenin signaling contributes to the pathogenesis of ileal Crohn's disease.

PGE2 inhibits TIL expansion by disrupting IL-2 signalling and mitochondrial function

Expansion of antigen-experienced CD8+ T cells is critical for the success of tumour-infiltrating lymphocyte (TIL)-adoptive cell therapy (ACT) in patients with cancer1. Interleukin-2 (IL-2) acts as a key regulator of CD8+ cytotoxic T lymphocyte functions by promoting expansion and cytotoxic capability2,3. Therefore, it is essential to comprehend mechanistic barriers to IL-2 sensing in the tumour microenvironment to implement strategies to reinvigorate IL-2 responsiveness and T cell antitumour responses. Here we report that prostaglandin E2 (PGE2), a known negative regulator of immune response in the tumour microenvironment4,5, is present at high concentrations in tumour tissue from patients and leads to impaired IL-2 sensing in human CD8+ TILs via the PGE2 receptors EP2 and EP4. Mechanistically, PGE2 inhibits IL-2 sensing in TILs by downregulating the IL-2Rγc chain, resulting in defective assembly of IL-2Rβ-IL2Rγc membrane dimers. This results in impaired IL-2-mTOR adaptation and PGC1α transcriptional repression, causing oxidative stress and ferroptotic cell death in tumour-reactive TILs. Inhibition of PGE2 signalling to EP2 and EP4 during TIL expansion for ACT resulted in increased IL-2 sensing, leading to enhanced proliferation of tumour-reactive TILs and enhanced tumour control once the cells were transferred in vivo. Our study reveals fundamental features that underlie impairment of human TILs mediated by PGE2 in the tumour microenvironment. These findings have therapeutic implications for cancer immunotherapy and cell therapy, and enable the development of targeted strategies to enhance IL-2 sensing and amplify the IL-2 response in TILs, thereby promoting the expansion of effector T cells with enhanced therapeutic potential.

Revisiting prostaglandin E2: A promising therapeutic target for osteoarthritis

Osteoarthritis (OA) is a complex disease characterized by cartilage degeneration and persistent pain. Prostaglandin E2 (PGE2) plays a significant role in OA inflammation and pain. Recent studies have revealed the significant role of PGE2-mediated skeletal interoception in the progression of OA, providing new insights into the pathogenesis and treatment of OA. This aspect also deserves special attention in this review. Additionally, PGE2 is directly involved in pathologic processes including aberrant subchondral bone remodeling, cartilage degeneration, and synovial inflammation. Therefore, celecoxib, a commonly used drug to alleviate inflammatory pain through inhibiting PGE2, serves not only as an analgesic for OA but also as a potential disease-modifying drug. This review provides a comprehensive overview of the discovery history, synthesis and release pathways, and common physiological roles of PGE2. We discuss the roles of PGE2 and celecoxib in OA and pain from skeletal interoception and multiple perspectives. The purpose of this review is to highlight PGE2-mediated skeletal interoception and refresh our understanding of celecoxib in the pathogenesis and treatment of OA.

Bacterial indole-3-lactic acid affects epithelium-macrophage crosstalk to regulate intestinal homeostasis

Tryptophan and its derivatives perform a variety of biological functions; however, the role and specific mechanism of many tryptophan derivatives in intestinal inflammation remain largely unclear. Here, we identified that an Escherichia coli strain (Ec-TMU) isolated from the feces of tinidazole-treated individuals, and indole-3-lactic acid (ILA) in its supernatant, decreased the susceptibility of mice to dextran sulfate sodium-induced colitis. Ec-TMU and ILA contribute to the relief of colitis by inhibiting the production of epithelial CCL2/7, thereby reducing the accumulation of inflammatory macrophages in vitro and in vivo. Mechanistically, ILA downregulates glycolysis, NF-κB, and HIF signaling pathways via the aryl hydrocarbon receptor, resulting in decreased CCL2/7 production in epithelial cells. Clinical evidence suggests that the fecal ILA level is negatively correlated with the progression indicator of inflammatory bowel diseases. These results demonstrate that ILA has the potential to regulate intestinal homeostasis by modulating epithelium-macrophage interactions.

Prostaglandin E2 and myocarditis; friend or foe?

This review article summarizes the role of prostaglandin E2 (PGE2) and its receptors (EP1-EP4) as it relates to the inflammatory cardiomyopathy, myocarditis. During the COVID-19 pandemic, the onset of myocarditis in a subset of patients prompted a debate on the use of nonsteroidal anti-inflammatory drugs (NSAIDs), like ibuprofen, which act to inhibit the actions of prostaglandins. This review aims to further understanding of the role of PGE2 in the pathogenesis or protection of the myocardium in myocarditis. Inflammatory cardiomyopathies encompass a broad spectrum of disorders, all characterized by cardiac inflammation. Therefore, for the purpose of this review, the authors have placed particular emphasis on etiologies of myocarditis where effects of PGE2 have been documented.

G protein-coupled receptors: A target for microbial metabolites and a mechanistic link to microbiome-immune-brain interactions

Human-microorganism interactions play a key role in human health. However, the underlying molecular mechanisms remain poorly understood. Small-molecules that offer a functional readout of microbe-microbe-human relationship are of great interest for deeper understanding of the inter-kingdom crosstalk at the molecular level. Recent studies have demonstrated that small-molecules from gut microbiota act as ligands for specific human G protein-coupled receptors (GPCRs) and modulate a range of human physiological functions, offering a mechanistic insight into the microbe-human interaction. To this end, we focused on analysis of bacterial metabolites that are currently recognized to bind to GPCRs and are found to activate the known downstream signaling pathways. We further mapped the distribution of these molecules across the public mass spectrometry-based metabolomics data, to identify the presence of these molecules across body sites and their association with health status. By combining this with RNA-Seq expression and spatial localization of GPCRs from a public human protein atlas database, we inferred the most predominant GPCR-mediated microbial metabolite-human cell interactions regulating gut-immune-brain axis. Furthermore, by evaluating the intestinal absorption properties and blood-brain barrier permeability of the small-molecules we elucidated their molecular interactions with specific human cell receptors, particularly expressed on human intestinal epithelial cells, immune cells and the nervous system that are shown to hold much promise for clinical translational potential. Furthermore, we provide an overview of an open-source resource for simultaneous interrogation of bioactive molecules across the druggable human GPCRome, a useful framework for integration of microbiome and metabolite cataloging with mechanistic studies for an improved understanding of gut microbiota-immune-brain molecular interactions and their potential therapeutic use.

The Role of Lipids in the Regulation of Immune Responses

Lipid metabolism plays a major role in the regulation of the immune system. Exogenous (dietary and microbial-derived) and endogenous (non-microbial-derived) lipids play a direct role in regulating immune cell activation, differentiation and expansion, and inflammatory phenotypes. Understanding the complexities of lipid-immune interactions may have important implications for human health, as certain lipids or immune pathways may be beneficial in circumstances of acute infection yet detrimental in chronic inflammatory diseases. Further, there are key differences in the lipid effects between specific immune cell types and location (e.g., gut mucosal vs. systemic immune cells), suggesting that the immunomodulatory properties of lipids may be tissue-compartment-specific, although the direct effect of dietary lipids on the mucosal immune system warrants further investigation. Importantly, there is recent evidence to suggest that lipid-immune interactions are dependent on sex, metabolic status, and the gut microbiome in preclinical models. While the lipid-immune relationship has not been adequately established in/translated to humans, research is warranted to evaluate the differences in lipid-immune interactions across individuals and whether the optimization of lipid-immune interactions requires precision nutrition approaches to mitigate or manage disease. In this review, we discuss the mechanisms by which lipids regulate immune responses and the influence of dietary lipids on these processes, highlighting compelling areas for future research.

The severity of NEC is ameliorated by prostaglandin E2 through regulating intestinal microcirculation

Prostaglandin E2 (PGE2) is implicated in intestinal inflammation and intestinal blood flow regulation with a paradoxical effect on the pathogenesis of necrotizing enterocolitis (NEC), which is not yet well understood. In the current study, we found that PGE2, EP4, and COX-2 varied at different distances from the most damaged area in the terminal ileum obtained from human infants with NEC. PGE2 administration alleviated the phenotype of experimental NEC and the intestinal microvascular features in experimental NEC, but this phenomenon was inhibited by eNOS depletion, suggesting that PGE2 promoted intestinal microcirculatory perfusion through eNOS. Furthermore, PGE2 administration increased the VEGF content in MIMECs under TNFα stress and promoted MIMEC proliferation. This response to PGE2 was involved in eNOS phosphorylation and nitric oxide (NO) production and was blocked by the EP4 antagonist in vitro, suggesting that targeting the PGE2-EP4-eNOS axis might be a potential clinical and therapeutic strategy for NEC treatment. The study is reported in accordance with ARRIVE guidelines ( https://arriveguidelines.org ).

Modulation of immunity by the secreted phospholipase A2 family

Among the phospholipase A2 (PLA2 ) superfamily, which typically catalyzes the sn-2 hydrolysis of phospholipids to yield fatty acids and lysophospholipids, the secreted PLA2 (sPLA2 ) family contains 11 isoforms in mammals. Individual sPLA2 s have unique enzymatic specificity toward fatty acids and polar heads of phospholipid substrates and display distinct tissue/cellular distributions, suggesting their distinct physiological functions. Recent studies using knockout and/or transgenic mice for a full set of sPLA2 s have revealed their roles in modulation of immunity and related disorders. Application of mass spectrometric lipidomics to these mice has enabled to identify target substrates and products of individual sPLA2 s in given tissue microenvironments. sPLA2 s hydrolyze not only phospholipids in the plasma membrane of activated, damaged or dying mammalian cells, but also extracellular phospholipids such as those in extracellular vesicles, microbe membranes, lipoproteins, surfactants, and dietary phospholipids, thereby exacerbating or ameliorating various diseases. The actions of sPLA2 s are dependent on, or independent of, the generation of fatty acid- or lysophospholipid-derived lipid mediators according to the pathophysiological contexts. In this review, we make an overview of our current understanding of the roles of individual sPLA2 s in various immune responses and associated diseases.

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.

The Effects of a High-Fat Diet on Inflammatory Bowel Disease

The interactions among diet, intestinal immunity, and microbiota are complex and play contradictory roles in inflammatory bowel disease (IBD). An increasing number of studies has shed light on this field. The intestinal immune balance is disrupted by a high-fat diet (HFD) in several ways, such as impairing the intestinal barrier, influencing immune cells, and altering the gut microbiota. In contrast, a rational diet is thought to maintain intestinal immunity by regulating gut microbiota. In this review, we emphasize the crucial contributions made by an HFD to the gut immune system and microbiota.

Studies in Zebrafish and Rat Models Support Dual Blockade of EP2 and EP4 (Prostaglandin E2 Receptors Type 2 and 4) for Renoprotection in Glomerular Hyperfiltration and Albuminuria

BACKGROUND

Glomerular hyperfiltration (GH) is an important mechanism in the development of albuminuria in hypertension. Upregulation of COX2 (cyclooxygenase 2) and prostaglandin E₂ (PGE₂) was linked to podocyte damage in GH. We explored the potential renoprotective effects of either separate or combined pharmacological blockade of EP2 (PGE₂ receptor type 2) and EP4 (PGE₂ receptor type 4) in GH.

METHODS

We conducted in vivo studies in a transgenic zebrafish model (Tg[fabp10a:gc-EGFP]) suitable for analysis of glomerular filtration barrier function and a genetic rat model with GH, albuminuria, and upregulation of PGE₂. Similar pharmacological interventions and primary outcome analysis on albuminuria phenotype development were conducted in both model systems.

RESULTS

Stimulation of zebrafish embryos with PGE₂ induced an albuminuria-like phenotype, thus mimicking the suggested PGE₂ effects on glomerular filtration barrier dysfunction. Both separate and combined blockade of EP2 and EP4 reduced albuminuria phenotypes in zebrafish and rat models. A significant correlation between albuminuria and podocyte damage in electron microscopy imaging was identified in the rat model. Dual blockade of both receptors showed a pronounced synergistic suppression of albuminuria. Importantly, this occurred without changes in arterial blood pressure, glomerular filtration rate, or tissue oxygenation in magnetic resonance imaging, while RNA sequencing analysis implicated a potential role of circadian clock genes.

CONCLUSIONS

Our findings confirm a role of PGE₂ in the development of albuminuria in GH and support the renoprotective potential of combined pharmacological blockade of EP2 and EP4 receptors. These data support further translational research to explore this therapeutic option and a possible role of circadian clock genes.

A mouse model to test the anti-inflammatory effect of facultative anaerobes on dextran sulfate sodium-induced colitis

The role of facultative anaerobic bacteria in colitis remains to be elucidated. We have adapted a mouse model to explore the effect of individual facultative anaerobic bacteria on colitis, focusing on adapting a cocktail of antibiotics and multiple instillations by gavage. Weight, disease activity index, colon length, and histological score are used to assess the severity of colitis. We also describe anaerobic processing protocols of preparing facultative anaerobes. For complete details on the use and execution of this protocol, please refer to Li et al. (2022).1.

Small molecule inhibitors of 15-PGDH exploit a physiologic induced-fit closing system

15-prostaglandin dehydrogenase (15-PGDH) is a negative regulator of tissue stem cells that acts via enzymatic activity of oxidizing and degrading PGE2, and related eicosanoids, that support stem cells during tissue repair. Indeed, inhibiting 15-PGDH markedly accelerates tissue repair in multiple organs. Here we have used cryo-electron microscopy to solve the solution structure of native 15-PGDH and of 15-PGDH individually complexed with two distinct chemical inhibitors. These structures identify key 15-PGDH residues that mediate binding to both classes of inhibitors. Moreover, we identify a dynamic 15-PGDH lid domain that closes around the inhibitors, and that is likely fundamental to the physiologic 15-PGDH enzymatic mechanism. We furthermore identify two key residues, F185 and Y217, that act as hinges to regulate lid closing, and which both inhibitors exploit to capture the lid in the closed conformation, thus explaining their sub-nanomolar binding affinities. These findings provide the basis for further development of 15-PGDH targeted drugs as therapeutics for regenerative medicine.

Role of cyclooxygenase pathways in bowel fibrotic remodelling in a murine model of experimental colitis

OBJECTIVE

Gut fibrosis occurs under chronic inflammation. This study examined the effects of different cyclooxygenase (COX) inhibitors on fibrosis in the inflamed colon.

METHODS

Colitis was induced by 2,4-dinitrobenzenesulfonic acid (DNBS) in albino male Sprague-Dawley rats. After 6, 12 and 18 days, macroscopic and microscopic damage, collagen and elastic fibre content were examined. At day 6, pro-fibrotic factors (collagen I and III, hydroxyproline, fibronectin, matrix metalloproteinase-2 and -9), transforming growth factor-beta (TGF-β) signalling [TGF-β, Ras homolog gene family member A (RhoA), phosphorylated small mother against decapentaplegic (pSMAD)-2 and -6] and peristalsis were assessed, and the effects of indomethacin, SC-560 or celecoxib were tested.

KEY FINDINGS

Six days after DNBS administration, significant histopathological signs of fibrotic remodelling were observed in rats. At day 6, pro-fibrotic factors were up-regulated and colonic peristalsis was altered. COX inhibitors reversed the histochemical, molecular and functional changes in the fibrotic colon. COX inhibition reduced TGF-β expression, SMAD2 phosphorylation and RhoA, and increased SMAD6 expression.

CONCLUSIONS

Colonic fibrosis is associated with altered bowel motility and induction of profibrotic factors driven by TGF-β signalling. COX-1 and COX-2 inhibition counteracts this fibrotic remodelling by the modulation of TGF-β/SMAD signalling, mainly via SMAD6 induction and reduction in SMAD2 phosphorylation.

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.

Orally Bioavailable Quinoxaline Inhibitors of 15-Prostaglandin Dehydrogenase (15-PGDH) Promote Tissue Repair and Regeneration

15-Prostaglandin dehydrogenase (15-PGDH) regulates the concentration of prostaglandin E2 in vivo. Inhibitors of 15-PGDH elevate PGE2 levels and promote tissue repair and regeneration. Here, we describe a novel class of quinoxaline amides that show potent inhibition of 15-PGDH, good oral bioavailability, and protective activity in mouse models of ulcerative colitis and recovery from bone marrow transplantation.

The epoxy fatty acid pathway enhances cAMP in mammalian cells through multiple mechanisms

The cellular mechanism by which epoxy fatty acids (EpFA) improves disease status is not well characterized. Previous studies suggest the involvement of cellular receptors and cyclic AMP (cAMP). Herein, the action of EpFAs derived from linoleic acid (LA), arachidonic acid (ARA), and docosahexaenoic acid on cAMP levels was studied in multiple cell types to elucidate relationships between EpFAs, receptors and cells' origin. cAMP levels were enhanced in HEK293 and LLC-PK1 cells by EpFAs from LA and ARA. Using selective antagonists, the EpFA effects on cAMP levels appear dependent on the prostaglandin E2 receptor 2 (EP2) but not 4 (EP4). Human coronary artery smooth muscle cells responded similarly to the EpFAs. However, we were not able to show the involvement of any of the receptors tested in this cell type. The results pinpointed distinct cell lines and receptor subtypes that natively respond to EpFA.

Enterobacter ludwigii protects DSS-induced colitis through choline-mediated immune tolerance

Commensal intestinal bacteria play key roles in regulating host immune tolerance; however, bacterial strains and related metabolites directly involved in this regulation are largely unknown. Here, using a mouse model of dextran sulfate sodium (DSS)-induced colitis combined with different antibiotic treatment, Enterobacter ludwigii, abundant in microbiota of mice treated with metronidazole, is screened out to have prophylactic and therapeutic effects on DSS-induced colitis with or without the presence of complex intestinal bacteria. E. ludwigii is found to induce CD103⁺DC and regulatory T (Treg)-mediated immune tolerance for colitis remission using in vitro and in vivo experiments. Moreover, choline, one metabolite of E. ludwigii, is identified to increase dendritic cells' (DCs) immune tolerance to promote Treg differentiation. E. ludwigii is found to induce DCs' immune tolerance ability for Treg differentiation through choline and α7nAChR-mediated retinoic acid (RA) and transforming growth factor beta (TGF-β) upregulation, resulting in protecting mice against DSS-induced colitis. This study suggests potential therapeutic approaches for inflammatory bowel diseases (IBDs).

Inflammation Modulating Activity of the Hydroethanol Stem Bark Extract of Bombax costatum in Murine Models

Bombax costatum (Bombacaceae) is traditionally used as a decoction of the leaves, stem, and root to treat headaches, fever, and oedema that may be associated with inflammatory conditions. Thus, the aim of this study was to evaluate the effect of 70%^v/_v ethanolic extract of the stem bark of Bombax costatum on acute and chronic inflammation. The effect of Bombax costatum extract (10, 50, 100 mg kg^-1, p.o) was studied in prostaglandin E₂-induced paw oedema in Sprague-Dawley rats (n = 5). Subsequently, the effect of the extract on clonidine and haloperidol-induced catalepsy was also investigated in ICR mice (n = 5). Finally, the ability of the extract to inhibit chronic inflammation was studied using a rat adjuvant-induced arthritis model. Pre-emptive and therapeutic administration of the extract at all doses significantly suppressed the formation of oedema following prostaglandin E ₂ administration. As a measure of indirect antihistaminic effect, treatment with the extract suppressed clonidine-induced catalepsy but not haloperidol-induced catalepsy. Moreover, Bombax costatum extract significantly inhibited joint inflammation and damage following injection of complete Freund's adjuvant. Treatment with the extract also inhibited the onset of polyarthritis; thus, suppressing the systemic spread of joint inflammation from ipsilateral limbs to contralateral limbs. In conclusion, the hydroethanol extract of the stem bark of Bombax costatum inhibits both acute and chronic inflammation.

Network-based response module comprised of gene expression biomarkers predicts response to infliximab at treatment initiation in ulcerative colitis

This cross-cohort study aimed to (1) determine a network-based molecular signature that predicts the likelihood of inadequate response to the tumor necrosis factor-ɑ inhibitor (TNFi) therapy, infliximab, in ulcerative colitis (UC) patients, and (2) address biomarker irreproducibility across different cohort studies. Whole-transcriptome microarray data were derived from biopsies of affected colon tissue from 2 cohorts of infliximab-treated UC patients (training N = 24 and validation N = 22). Response was defined as endoscopic and histologic healing at 4-6 weeks and 8 weeks, respectively. From the training cohort, genes with RNA expression that significantly correlated with clinical response outcomes were mapped onto the Human Interactome network map of protein-protein interactions to identify a largest connected component (LCC) of proteins indicative of infliximab response status in UC. Expression levels of transcripts within the LCC were fed into a probabilistic neural network model to generate a classifier that predicts inadequate response to infliximab. A classifier predictive of inadequate response to infliximab was generated and tested in a cross-cohort, blinded fashion; the AUC was 0.83 and inadequate response was predicted with a 100% positive predictive value and 64% sensitivity. Genes separately identified from the 2 cohorts that correlated with response to infliximab appeared distinct but mapped onto the same network region of the Human Interactome, reflecting a common underlying biology of response among UC patients. Cross-cohort validation of a classifier predictive of infliximab response status in UC patients indicates that a molecular signature of non-response to TNFi therapies is present in patients' baseline gene expression data. The goal is to develop a diagnostic test that predicts which patients will have an inadequate response to targeted therapies and define new targets and pathways for therapeutic development.

Associations of serum long-chain fatty acids with multiple organ involvement in patients with sarcoidosis

Background

Fatty acids have diverse immunomodulatory functions and the potential to be associated with inflammatory responses in sarcoidosis.

Methods

The serum levels of multiple long-chain fatty acids (LCFAs) were compared between 63 patients with sarcoidosis and 38 healthy controls. The associations of LCFAs with clinical outcomes of sarcoidosis were also evaluated.

Results

The patients with sarcoidosis had significantly lower levels of n-3 poly-unsaturated fatty acids (PUFAs) (p < 0.001) and n-6 PUFAs (p < 0.001) than the healthy controls. However, there were no significant differences in the levels of saturated fatty acids (SFAs) and mono-unsaturated fatty acids (MUFAs) between the two groups. On multivariate logistic analysis, lower levels of n-3 PUFAs, n-6 PUFAs, and n-3/n-6 ratio were predictive of sarcoidosis. Among the patients with sarcoidosis, those with multiple organ involvement had significantly lower levels of n-3 PUFAs and n-3/n-6 ratio than those with single organ involvement. There were no significant differences in the levels of n-6 PUFAs, SFAs, and MUFAs between the patients with multiple and single organ involvement. On multivariate logistic analysis, lower levels of SFAs and n-3/n-6 ratio were predictive of multiple organ involvement. The levels of LCFAs had no significant association with radiographic stage or spontaneous remission.

Conclusions

Assessment of LCFA profiles may be useful for the diagnosis of sarcoidosis and evaluation of the disease activity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-022-02084-x.

Phytochemicals from medicinal plants from African forests with potentials in rheumatoid arthritis management

OBJECTIVES

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by inflammation, pain, and cartilage and bone damage. There is currently no cure for RA. It is however managed using nonsteroidal anti-inflammatory drugs, corticosteroids and disease-modifying anti-rheumatic drugs, often with severe side effects. Hidden within Africa's lush vegetation are plants with diverse medicinal properties including anti-RA potentials. This paper reviews the scientific literature for medicinal plants, growing in Africa, with reported anti-RA activities and identifies the most abundant phytochemicals deserving research attention. A search of relevant published scientific literature, using the major search engines, such as Pubmed/Medline, Scopus, Google Scholar, etc. was conducted to identify medicinal plants, growing in Africa, with anti-RA potentials.

KEY FINDINGS

Twenty plants belonging to 17 families were identified. The plants are rich in phytochemicals, predominantly quercetin, rutin, catechin, kaempferol, etc., known to affect some pathways relevant in RA initiation and progression, and therefore useful in its management.

SUMMARY

Targeted research is needed to unlock the potentials of medicinal plants by developing easy-to-use technologies for preparing medicines from them. Research attention should focus on how best to exploit the major phytochemicals identified in this review for the development of anti-RA 'green pharmaceuticals'.

m6A demethylase ALKBH5 is required for antibacterial innate defense by intrinsic motivation of neutrophil migration

Neutrophil migration into the site of infection is necessary for antibacterial innate defense, whereas impaired neutrophil migration may result in excessive inflammation and even sepsis. The neutrophil migration directed by extracellular signals such as chemokines has been extensively studied, yet the intrinsic mechanism for determining neutrophil ability to migrate needs further investigation. N⁶-methyladenosine (m⁶A) RNA modification is important in immunity and inflammation, and our preliminary data indicate downregulation of RNA m⁶A demethylase alkB homolog 5 (ALKBH5) in neutrophils during bacterial infection. Whether m⁶A modification and ALKBH5 might intrinsically modulate neutrophil innate response remain unknown. Here we report that ALKBH5 is required for antibacterial innate defense by enhancing intrinsic ability of neutrophil migration. We found that deficiency of ALKBH5 increased mortality of mice with polymicrobial sepsis induced by cecal ligation and puncture (CLP), and Alkbh5-deficient CLP mice exhibited higher bacterial burden and massive proinflammatory cytokine production in the peritoneal cavity and blood because of less neutrophil migration. Alkbh5-deficient neutrophils had lower CXCR2 expression, thus exhibiting impaired migration toward chemokine CXCL2. Mechanistically, ALKBH5-mediated m⁶A demethylation empowered neutrophils with high migration capability through altering the RNA decay, consequently regulating protein expression of its targets, neutrophil migration-related molecules, including increased expression of neutrophil migration-promoting CXCR2 and NLRP12, but decreased expression of neutrophil migration-suppressive PTGER4, TNC, and WNK1. Our findings reveal a previously unknown role of ALKBH5 in imprinting migration-promoting transcriptome signatures in neutrophils and intrinsically promoting neutrophil migration for antibacterial defense, highlighting the potential application of targeting neutrophil m⁶A modification in controlling bacterial infections.

The EP3 and EP4 Receptor Subtypes both Mediate the Fever-producing Effects of Prostaglandin E2 in the Rostral Ventromedial Preoptic Area of the Hypothalamus in Rats

This study aimed to re-examine the receptor subtype that mediates the fever-producing effects of prostaglandin E₂ (PGE₂) in the rostral ventromedial preoptic area (rvmPOA) of the hypothalamus. Among the four subtypes of PGE₂ receptors (EP₁, EP₂, EP₃, and EP₄), EP₃ receptor is crucially involved in the febrile effects of PGE₂. However, it is possible for other subtypes of PGE₂ receptor to contribute in the central mechanism of fever generation. Accordingly, effects of microinjection of PGE₂ receptor subtype-specific agonists or antagonists were examined at the locus where a microinjection of a small amount (420 fmol) of PGE₂ elicited prompt increases in the O₂ consumption rate (VO₂), heart rate, and colonic temperature (T_c) in the rvmPOA of urethane-chloralose-anesthetized rats. The EP₃ agonist sulprostone mimicked, whereas its antagonist L-798,106 reduced, the febrile effects of PGE₂ microinjected into the same site. Similarly, the EP₄ agonist rivenprost mimicked, whereas its antagonist ONO-AE3-208 reduced, the effects of PGE₂ microinjected into the same site. In contrast, microinjection of the EP₁ agonist iloprost induced a very small increase in VO₂ but did not have significant influences on the heart rate and T_c, whereas its antagonist, AH6809, did not affect the PGE₂-induced responses. Microinjection of the EP₂ agonist butaprost had no effects on the VO₂, heart rate, and T_c. The results suggest that the EP₃ and EP₄ receptor subtypes are both involved in the fever generated by PGE₂ in the rvmPOA.

Down-regulation of the expression of cyclooxygenase-2 and prostaglandin E2 by interleukin-4 is mediated via a reduction in the expression of prostanoid EP4 receptors in HCA-7 human colon cancer cells

Chronic inflammatory bowel disease (IBD), which is characterized by prolonged inflammation of the gastrointestinal tract is associated with an increased risk of colorectal cancer. Recent studies revealed that the pathology of IBD is caused by hyperactivated immune responses mediated by differentiated CD4⁺ naïve helper T cells, such as Th1 and Th17 cells, but not Th2 cells. The human E-type prostanoid 4 (EP4) receptor and its pathways have also been implicated in and/or associated with the early developmental stages of colorectal cancer along with increases in the levels of prostaglandin E₂ (PGE₂) and cyclooxygenase-2 (COX-2), the hallmarks of colorectal carcinogenesis. In the present study, using an in silico analysis and pharmacological experiments, we demonstrated that interleukin (IL)-4, a signature cytokine of Th2 cells, down-regulated the expression of COX-2 and PGE₂ in the human colon cancer cell line, HCA-7. This result may be attributed to a reduction in the expression of prostanoid EP4 receptors through the induction of hypoxia inducible factor-1α via the interleukin-4 receptor-stimulated activation of signal transducer and activator of transcription 6. However, another major Th2 cytokine IL-13 had no effect on the expression of COX-2 or prostanoid EP4 receptors in HCA-7 cells. Therefore, instead of the hyperactivation of Th1/Th17 cells, the deactivation/down-regulation of Th2 cells followed by a decrease in the production of IL-4 in IBD may play a role in the cancerous transformation of cells, at least in prostanoid EP4 receptor-overactivated tumorigenesis.

Macrophage control of Crohn's disease

The intestinal tract is the body's largest mucosal surface and permanently exposed to microbial and environmental signals. Maintaining a healthy intestine requires the presence of sentinel grounds keeper cells, capable of controlling immunity and tissue homeostasis through specialized functions. Intestinal macrophages are such cells and important players in steady-state functions and during acute and chronic inflammation. Crohn's disease, a chronic inflammatory condition of the intestinal tract is proposed to be the consequence of an altered immune system through microbial and environmental stimulation. This hypothesis suggests an involvement of macrophages in the regulation of this pathology. Within this chapter, we will discuss intestinal macrophage development and highlight data suggesting their implication in chronic intestinal pathologies like Crohn's disease.

Glomerular Biomechanical Stress and Lipid Mediators during Cellular Changes Leading to Chronic Kidney Disease

Hyperfiltration is an important underlying cause of glomerular dysfunction associated with several systemic and intrinsic glomerular conditions leading to chronic kidney disease (CKD). These include obesity, diabetes, hypertension, focal segmental glomerulosclerosis (FSGS), congenital abnormalities and reduced renal mass (low nephron number). Hyperfiltration-associated biomechanical forces directly impact the cell membrane, generating tensile and fluid flow shear stresses in multiple segments of the nephron. Ongoing research suggests these biomechanical forces as the initial mediators of hyperfiltration-induced deterioration of podocyte structure and function leading to their detachment and irreplaceable loss from the glomerular filtration barrier. Membrane lipid-derived polyunsaturated fatty acids (PUFA) and their metabolites are potent transducers of biomechanical stress from the cell surface to intracellular compartments. Omega-6 and ω-3 long-chain PUFA from membrane phospholipids generate many versatile and autacoid oxylipins that modulate pro-inflammatory as well as anti-inflammatory autocrine and paracrine signaling. We advance the idea that lipid signaling molecules, related enzymes, metabolites and receptors are not just mediators of cellular stress but also potential targets for developing novel interventions. With the growing emphasis on lifestyle changes for wellness, dietary fatty acids are potential adjunct-therapeutics to minimize/treat hyperfiltration-induced progressive glomerular damage and CKD.

Pain killers: the interplay between nonsteroidal anti-inflammatory drugs and Clostridioides difficile infection

Clostridioides difficile is one of the leading causes of nosocomial infections worldwide. Increases in incidence, severity, and healthcare cost associated with C. difficile infection (CDI) have made this pathogen an urgent public health threat worldwide. The factors shaping the evolving epidemiology of CDI and impacting clinical outcomes of infection are not well understood, but involve tripartite interactions between the host, microbiota, and C. difficile. In addition to this, emerging data suggests an underappreciated role for environmental factors, such as diet and pharmaceutical drugs, in CDI. In this review, we discuss the role of nonsteroidal anti-inflammatory drugs (NSAIDs) and eicosanoids in CDI.

Group 3 innate lymphoid cells produce the growth factor HB-EGF to protect the intestine from TNF-mediated inflammation

Tumor necrosis factor (TNF) drives chronic inflammation and cell death in the intestine, and blocking TNF is a therapeutic approach in inflammatory bowel disease (IBD). Despite this knowledge, the pathways that protect the intestine from TNF are incompletely understood. Here we demonstrate that group 3 innate lymphoid cells (ILC3s) protect the intestinal epithelium from TNF-induced cell death. This occurs independent of interleukin-22 (IL-22), and we identify that ILC3s are a dominant source of heparin-binding epidermal growth factor-like growth factor (HB-EGF). ILC3s produce HB-EGF in response to prostaglandin E2 (PGE2) and engagement of the EP2 receptor. Mice lacking ILC3-derived HB-EGF exhibit increased susceptibility to TNF-mediated epithelial cell death and experimental intestinal inflammation. Finally, human ILC3s produce HB-EGF and are reduced from the inflamed intestine. These results define an essential role for ILC3-derived HB-EGF in protecting the intestine from TNF and indicate that disruption of this pathway contributes to IBD.

Human Oral Epithelial Cells Suppress T Cell Function via Prostaglandin E2 Secretion

The oral mucosa is constantly exposed to a plethora of stimuli including food antigens, commensal microbiota and pathogens, requiring distinct immune responses. We previously reported that human oral epithelial cells (OECs) suppress immune responses to bacteria, using H413 and TR146 OEC lines and primary OECs in co-culture with dendritic cells (DCs) and T cells (OEC-conditioned cells). OECs reduced DCs expression of CD80/CD86 and IL-12/TNFα release and impaired T cell activation. Here, we further evaluated the immunosuppression by these OECs and investigated the underlying mechanisms. OEC-conditioned DCs did not induce CD4 T cell polarization towards Treg, judging by the absence of FoxP3 expression. OECs also repressed T-bet/IFNγ expression in CD4 and CD8 T cells activated by DCs or anti-CD3/CD28 antibodies. This inhibition depended on OEC:T cell ratio and IFNγ repression occurred at the transcriptional level. Time-lapse experiments showed that OECs inhibited early steps of T cell activation, consistent with OECs inability to suppress T cells stimulated with PMA/ionomycin. Blocking CD40/CD40L, CD58/CD2 and PD-L1/PD-1 interactions with specific antibodies did not disrupt T cell suppression by OECs. However, preventing prostaglandin E2 (PGE2) synthesis or blocking PGE2 binding to the cognate EP2/EP4 receptors, restored IFNγ and TNFα production in OEC-conditioned T cells. Finally, treating OECs with poly(I:C), which simulates viral infections, limited T cell suppression. Overall, these results point to an inherent ability of OECs to suppress immune responses, which can nonetheless be eluded when OECs are under direct assault.

Acid increases PGE2 in the duodenal mucosa in rats

Attention has recently been paid to the duodenum as the pathophysiologic center of functional dyspepsia. However, the precise mechanisms of symptom generation remain unknown. We here investigated the effect of acid on duodenal prostaglandin E₂ and localization of prostaglandin E₂ related receptors. Sprague–Dawley rats were used for this study. Hydrochloric acid was administered in the duodenum, then prostaglandin E₂ levels in the duodenum were measured using the ELISA. The expression and localization of prostaglandin receptors (EP1–4) and the mRNAs of prostaglandin synthases were investigated using in situ hybridization histochemistry in duodenal tissue. After acid perfusion, prostaglandin E₂ levels in the duodenum significantly increased. EP3 was expressed mainly at the myenteric plexus in the duodenal mucosa, and EP4 at both the epithelial surface and myenteric plexus. Contrary, EP2 was sparsely distributed in the villi and EP1 were not clearly seen on in situ hybridization histochemistry. Prostaglandin-synthetic enzymes were also distributed in the duodenal mucosa. The prostaglandin E₂ levels in the duodenum increased after acidification. Prostaglandin E₂ receptors and prostaglandin E₂-producing enzymes were both observed in rat duodenum. These observations suggest that duodenal prostaglandin E₂ possibly play a role in the symptom generation of functional dyspepsia.

Prostaglandin E2 increases the expression of cyclooxygenase-2 in cultured rat microglia

Prostaglandin E₂ (PGE₂) plays pivotal roles in controlling microglial activation with the EP₂ receptor, a PGE₂ receptor subtype. Activated microglia are often reported to increase cyclooxygenase (COX)-2 expression, followed by PGE₂ production, but it is unclear whether extracellular PGE₂ is involved in microglial PGE₂ synthesis. In the present study, we report that PGE₂ increases COX-2 protein in microglia. In a culture system, PGE₂ at 10^-6 M for 3 h increased COX-2 and microsomal PGE synthase (mPGES)-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cytosolic PGE synthase (cPGES) in microglia. PGE₂ at 10^-6 M for 3 h also increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. An EP₂ agonist, ONO-AE1-259-01, also increased COX-2 and mPGES-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cPGES, whereas an EP₁ agonist, ONO-DI-004, an EP₃ agonist, ONO-AE-248, and an EP₄ agonist, ONO-AE1-329, had no effect. Similar to PGE₂, ONO-AE1-259-01 increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. In addition, the effects of PGE₂ were inhibited by an EP₂ antagonist, PF-04418948, but not by an EP₁ antagonist, ONO-8713, an EP₃ antagonist, ONO-AE3-240, or an EP₄ antagonist, ONO-AE3-208, at 10^-6 M. On the other hand, lipopolysaccharide (LPS) increased PGE₂ production, but the LPS-induced PGE₂ production was not affected by ONO-8713, PF-04418948, ONO-AE3-240, or ONO-AE3-208. These results indicate that PGE₂ increases COX-2 protein in microglia through the EP₂ receptor supporting the idea that extracellular PGE₂ has a triggering aspect for microglial activation.

The role of fatty acids in Crohn's disease pathophysiology - An overview

Crohn's disease (CD) is an inflammatory bowel disease (IBD) which is characterized by chronic and relapsing inflammation of the gastrointestinal (GI) tract. The etiology of CD is unknown, but factors such as epithelial barrier dysfunction, immune system imbalance, microbiota dysbiosis and environmental influences are thought to be involved in its pathogenesis. Recent studies have shown that short chain fatty acids (SCFAs) and long chain fatty acids (LCFAs) play a vital role in pathophysiology and development of CD by various mechanisms affecting pro- and anti-inflammatory mediators, and maintaining the intestinal homeostasis and regulation of gene expression. SCFAs and LCFAs activate signaling cascades that control immune functions through interaction with cell surface free fatty acid receptors (FFARs), i.e. FFAR1, FFAR2, FFAR3, and FFAR4. This review highlights the role of fatty acids in maintenance of intestinal and immune homeostasis and supports the supplementation of fatty acids as a promising adjunctive treatment for CD.

Systems approach reveals distinct and shared signaling networks of the four PGE2 receptors in T cells

[Figure: see text].

Epithelial wound healing in inflammatory bowel diseases: the next therapeutic frontier

Patients with one of the many chronic inflammatory disorders broadly classified as inflammatory bowel disease (IBD) now have a diverse set of immunomodulatory therapies at their disposal. Despite these recent medical advances, complete sustained remission of disease remains elusive for most patients. The full healing of the damaged intestinal mucosa is the primary goal of all therapies. Achieving this requires not just a reduction of the aberrant immunological response, but also wound healing of the epithelium. No currently approved therapy directly targets the epithelium. Epithelial repair is compromised in IBD and normally facilitates re-establishment of the homeostatic barrier between the host and the microbiome. In this review, we summarize the evidence that epithelial wound healing represents an important yet underdeveloped therapeutic modality for IBD. We highlight 3 general approaches that are promising for developing a new class of epithelium-targeted therapies: epithelial stem cells, cytokines, and microbiome engineering. We also provide a frank discussion of some of the challenges that must be overcome for epithelial repair to be therapeutically leveraged. A concerted approach by the field to develop new therapies targeting epithelial wound healing will offer patients a game-changing, complementary class of medications and could dramatically improve outcomes.

E-type prostanoid receptor 4 drives resolution of intestinal inflammation by blocking epithelial necroptosis

Inflammatory bowel diseases present with elevated levels of intestinal epithelial cell (IEC) death, which compromises the gut barrier, activating immune cells and triggering more IEC death. The endogenous signals that prevent IEC death and break this vicious cycle, allowing resolution of intestinal inflammation, remain largely unknown. Here we show that prostaglandin E2 signalling via the E-type prostanoid receptor 4 (EP4) on IECs represses epithelial necroptosis and induces resolution of colitis. We found that EP4 expression correlates with an improved IBD outcome and that EP4 activation induces a transcriptional signature consistent with resolution of intestinal inflammation. We further show that dysregulated necroptosis prevents resolution, and EP4 agonism suppresses necroptosis in human and mouse IECs. Mechanistically, EP4 signalling on IECs converges on receptor-interacting protein kinase 1 to suppress tumour necrosis factor-induced activation and membrane translocation of the necroptosis effector mixed-lineage kinase domain-like pseudokinase. In summary, our study indicates that EP4 promotes the resolution of colitis by suppressing IEC necroptosis.

Deep learning for discovering pathological continuum of crypts and evaluating therapeutic effects: An implication for in vivo preclinical study

Applying deep learning to the field of preclinical in vivo studies is a new and exciting prospect with the potential to unlock decades worth of underutilized data. As a proof of concept, we performed a feasibility study on a colitis model treated with Sulfasalazine, a drug used in therapeutic care of inflammatory bowel disease. We aimed to evaluate the colonic mucosa improvement associated with the recovery response of the crypts, a complex histologic structure reflecting tissue homeostasis and repair in response to inflammation. Our approach requires robust image segmentation of objects of interest from whole slide images, a composite low dimensional representation of the typical or novel morphological variants of the segmented objects, and exploration of image features of significance towards biology and treatment efficacy. Both interpretable features (eg. counts, area, distance and angle) as well as statistical texture features calculated using Gray Level Co-Occurance Matrices (GLCMs), are shown to have significance in analysis. Ultimately, this analytic framework of supervised image segmentation, unsupervised learning, and feature analysis can be generally applied to preclinical data. We hope our report will inspire more efforts to utilize deep learning in preclinical in vivo studies and ultimately make the field more innovative and efficient.

Intersecting Mechanisms of Hypoxia and Prostaglandin E2-Mediated Inflammation in the Comparative Biology of Oral Squamous Cell Carcinoma

The importance of inflammation in the pathogenesis of cancer was first proposed by Rudolph Virchow over 150 years ago, and our understanding of its significance has grown over decades of biomedical research. The arachidonic acid pathway of inflammation, including cyclooxygenase (COX) enzymes, PGE2 synthase enzymes, prostaglandin E2 (PGE2) and PGE2 receptors has been extensively studied and has been associated with different diseases and different types of cancers, including oral squamous cell carcinoma (OSCC). In addition to inflammation in the tumour microenvironment, low oxygen levels (hypoxia) within tumours have also been shown to contribute to tumour progression. Understandably, most of our OSCC knowledge comes from study of this aggressive cancer in human patients and in experimental rodent models. However, domestic animals develop OSCC spontaneously and this is an important, and difficult to treat, form of cancer in veterinary medicine. The primary goal of this review article is to explore the available evidence regarding interaction between hypoxia and the arachidonic acid pathway of inflammation during malignant behaviour of OSCC. Overlapping mechanisms in hypoxia and inflammation can contribute to tumour growth, angiogenesis, and, importantly, resistance to therapy. The benefits and controversies of anti-inflammatory and anti-angiogenic therapies for human and animal OSCC patients will be discussed, including conventional pharmaceutical agents as well as natural products.

Inhibitory effects of a selective prostaglandin E2 receptor antagonist RQ-15986 on inflammation-related colon tumorigenesis in APC-mutant rats

Prostaglandin E2 receptor EP4 is involved in inflammation and related tumorigenesis in the colorectum. This study aimed to investigate the chemopreventive ability of RQ-15986, a selective EP4 antagonist, in colitis-related colorectal tumorigenesis. Male Kyoto APC delta rats, which have APC mutations, were treated with azoxymethane and dextran sulfate sodium and subsequently administered RQ-15986 for eight weeks. At the end of the experiment, the development of colorectal tumor was significantly inhibited in the RQ-15986-treated group. The cell proliferation of the crypts and tumors in the colorectum was decreased following RQ-15986 treatment. RQ-15986 also suppressed the expression of pro-inflammatory cytokines, including tumor necrosis factor-α, interleukin-6, interleukin-18, and monocyte chemotactic protein-1, in the colon mucosa. In addition, the expression levels of indoleamine 2,3-dioxygenase, which is involved in immune tolerance, were decreased in the colorectal epithelium and tumors of the RQ-15986-treated group. These findings indicate that RQ-15986 inhibits colitis-associated colorectal tumorigenesis by attenuating inflammation, suppressing cell proliferation, and modulating the expression of indoleamine 2,3-dioxygenase. Targeting prostaglandin E2/EP4 signaling might be a useful strategy for chemoprevention of inflammation-related colorectal cancer.

Role of PGE2 in colonic motility: PGE2 attenuates spontaneous contractions of circular smooth muscle via EP4 receptors in the rat colon

Colonic motor activity is important for the formation and propulsion of feces. The production of prostaglandins (PGs) in colonic tissue is considered to play a critical role in the generation and regulation of colonic motility. In this study, we investigated the inhibitory effects of PGE2 and selective agonists of four EP receptors on the spontaneous phasic contractions, called 'giant contractions' (GCs), of mucosa-free circular smooth muscle strips from the rat middle colon. Neural blockade with tetrodotoxin (TTX) increased the frequency and amplitude of the GCs by about twofold. However, inhibiting PG production with piroxicam reduced the GC frequency in the presence of TTX, but did not affect the GC amplitude. In the presence of both TTX and piroxicam, exogenous PGE2 and each EP receptor agonist were cumulatively added to the tissue bath. In this setting, PGE2, the EP2 agonist ONO-AE1-259, and the EP4 agonist ONO-AE1-329, but not the EP1 agonist ONO-AE-DI-004 or the EP3 agonist ONO-AE-248, concentration-dependently reduced the GC frequency and amplitude. The PGE2-induced inhibition of GC frequency and amplitude was inhibited by the EP4 antagonist ONO-AE3-208, but not by the EP1/2 antagonist AH6809. Immunohistochemistry revealed the EP2 and EP4 receptors were localized in perinuclear sites in circular smooth muscle cells. EP2 immunoreactivity was also located in GFAP-immunoreactive enteroglia, whereas EP4 immunoreactivity was also located in HU (embryonic lethal, abnormal vision [ELAV] protein; a marker of all myenteric neurons)-immunoreactive myenteric nerve cell bodies. These results suggest that the PGs produced in the colonic tissue inhibit the GC frequency and amplitude of circular muscle in the rat middle colon, and is mediated by EP4 receptors expressed in the smooth muscle cells.

Prostaglandin E2 promotes intestinal inflammation via inhibiting microbiota-dependent regulatory T cells

The gut microbiota fundamentally regulates intestinal homeostasis and disease partially through mechanisms that involve modulation of regulatory T cells (Tregs), yet how the microbiota-Treg cross-talk is physiologically controlled is incompletely defined. Here, we report that prostaglandin E2 (PGE2), a well-known mediator of inflammation, inhibits mucosal Tregs in a manner depending on the gut microbiota. PGE2 through its receptor EP4 diminishes Treg-favorable commensal microbiota. Transfer of the gut microbiota that was modified by PGE2-EP4 signaling modulates mucosal Treg responses and exacerbates intestinal inflammation. Mechanistically, PGE2-modified microbiota regulates intestinal mononuclear phagocytes and type I interferon signaling. Depletion of mononuclear phagocytes or deficiency of type I interferon receptor diminishes PGE2-dependent Treg inhibition. Together, our findings provide emergent evidence that PGE2-mediated disruption of microbiota-Treg communication fosters intestinal inflammation.

Prostaglandin E2 receptors and their role in gastrointestinal motility - Potential therapeutic targets

Prostaglandin E2 (PGE2) is found throughout the gastrointestinal tract in a diverse variety of functions and roles. The recent discovery of four PGE2 receptor subtypes in intestinal muscle layers as well as in the enteric plexus has led to much interest in the study of their roles in gut motility. Gut dysmotility has been implicated in functional disease processes including irritable bowel syndrome (IBS) and slow transit constipation, and lubiprostone, a PGE2 derivative, has recently been licensed to treat both conditions. The diversity of actions of PGE2 in the intestinal tract is attributed to its differing effects on its downstream receptor types, as well as their varied distribution in the gut, in both health and disease. This review aims to identify the role and distribution of PGE2 receptors in the intestinal tract, and aims to elucidate their distinct role in gut motor function, with a specific focus on functional intestinal pathologies.

Macrophage ATP citrate lyase deficiency stabilizes atherosclerotic plaques

Macrophages represent a major immune cell population in atherosclerotic plaques and play central role in the progression of this lipid-driven chronic inflammatory disease. Targeting immunometabolism is proposed as a strategy to revert aberrant macrophage activation to improve disease outcome. Here, we show ATP citrate lyase (Acly) to be activated in inflammatory macrophages and human atherosclerotic plaques. We demonstrate that myeloid Acly deficiency induces a stable plaque phenotype characterized by increased collagen deposition and fibrous cap thickness, along with a smaller necrotic core. In-depth functional, lipidomic, and transcriptional characterization indicate deregulated fatty acid and cholesterol biosynthesis and reduced liver X receptor activation within the macrophages in vitro. This results in macrophages that are more prone to undergo apoptosis, whilst maintaining their capacity to phagocytose apoptotic cells. Together, our results indicate that targeting macrophage metabolism improves atherosclerosis outcome and we reveal Acly as a promising therapeutic target to stabilize atherosclerotic plaques.

Bioactive lipids in inflammatory bowel diseases - From pathophysiological alterations to therapeutic opportunities

Inflammatory bowel diseases (IBDs), such as Crohn's disease and ulcerative colitis, are lifelong diseases that remain challenging to treat. IBDs are characterized by alterations in intestinal barrier function and dysregulation of the innate and adaptive immunity. An increasing number of lipids are found to be important regulators of inflammation and immunity as well as gut physiology. Therefore, the study of lipid mediators in IBDs is expected to improve our understanding of disease pathogenesis and lead to novel therapeutic opportunities. Here, through selected examples - such as fatty acids, specialized proresolving mediators, lysophospholipids, endocannabinoids, and oxysterols - we discuss how lipid signaling is involved in IBD physiopathology and how modulating lipid signaling pathways could affect IBDs.

EP4 receptor as a novel promising therapeutic target in colon cancer

The most prevalent malignancy that can occur in the gastrointestinal tract is colon cancer. The current treatment options for colon cancer patients include chemotherapy, surgery, radiotherapy, immunotherapy, and targeted therapy. Although the chance of curing the disease in the early stages is high, there is no cure for almost all patients with advanced and metastatic disease. It has been found that over-activation of cyclooxygenase 2 (COX-2), followed by the production of prostaglandin E2 (PGE2) in patients with colon cancer are significantly increased. The tumorigenic function of COX-2 is mainly due to its role in the production of PGE2. PGE2, as a main generated prostanoid, has an essential role in growth and survival of colon cancer cell's. PGE2 exerts various effects in colon cancer cells including enhanced expansion, angiogenesis, survival, invasion, and migration. The signaling of PGE2 via the EP4 receptor has been shown to induce colon tumorigenesis. Moreover, the expression levels of the EP4 receptor significantly affect tumor growth and development. Overexpression of EP4 by various mechanisms increases survival and tumor vasculature in colon cancer cells. It seems that the pathway starting with COX2, continuing with PGE2, and ending with EP4 can promote the spread and growth of colon cancer. Therefore, targeting the COX-2/PGE2/EP4 axis can be considered as a worthy therapeutic approach to treat colon cancer. In this review, we have examined the role and different mechanisms that the EP4 receptor is involved in the development of colon cancer.