EDG6, a novel G-protein-coupled receptor related to receptors for bioactive lysophospholipids, is specifically expressed in lymphoid tissue

The role of sphingosine-1-phosphate in the development and progression of Parkinson's disease

Parkinson's disease (PD) could be viewed as a proteinopathy caused by changes in lipids, whereby modifications in lipid metabolism may lead to protein alterations, such as the accumulation of alpha-synuclein (α-syn), ultimately resulting in neurodegeneration. Although the loss of dopaminergic neurons in the substantia nigra is the major clinical manifestation of PD, the etiology of it is largely unknown. Increasing evidence has highlighted the important role of lipids in the pathophysiology of PD. Sphingosine-1-phosphate (S1P), a signaling lipid, has been suggested to have a potential association with the advancement and worsening of PD. Therefore, better understanding the mechanisms and regulatory proteins is of high interest. Most interestingly, S1P appears to be an important target to offers a new strategy for the diagnosis and treatment of PD. In this review, we first introduce the basic situation of S1P structure, function and regulation, with a special focus on the several pathways. We then briefly describe the regulation of S1P signaling pathway on cells and make a special focused on the cell growth, proliferation and apoptosis, etc. Finally, we discuss the function of S1P as potential therapeutic target to improve the clinical symptoms of PD, and even prevent the progression of the PD. In the context of PD, the functions of S1P modulators have been extensively elucidated. In conclusion, S1P modulators represent a novel and promising therapeutic principle and therapeutic method for PD. However, more research is required before these drugs can be considered as a standard treatment option for PD.

Keep a Little Fire Burning-The Delicate Balance of Targeting Sphingosine-1-Phosphate in Cancer Immunity

The sphingolipid sphingosine-1-phosphate (S1P) promotes tumor development through a variety of mechanisms including promoting proliferation, survival, and migration of cancer cells. Moreover, S1P emerged as an important regulator of tumor microenvironmental cell function by modulating, among other mechanisms, tumor angiogenesis. Therefore, S1P was proposed as a target for anti-tumor therapy. The clinical success of current cancer immunotherapy suggests that future anti-tumor therapy needs to consider its impact on the tumor-associated immune system. Hereby, S1P may have divergent effects. On the one hand, S1P gradients control leukocyte trafficking throughout the body, which is clinically exploited to suppress auto-immune reactions. On the other hand, S1P promotes pro-tumor activation of a diverse range of immune cells. In this review, we summarize the current literature describing the role of S1P in tumor-associated immunity, and we discuss strategies for how to target S1P for anti-tumor therapy without causing immune paralysis.

Loss of E-Cadherin Leads to Druggable Vulnerabilities in Sphingolipid Metabolism and Vesicle Trafficking

Simple Summary

Germline loss of the CDH1 gene is the primary genetic basis for hereditary diffuse gastric cancer, a disease resulting in elevated risk of both diffuse gastric cancer and lobular breast cancer. Current preventative treatment consists of prophylactic total gastrectomy, a therapy with several associated long-term morbidities. To address the lack of targeted molecular therapies for hereditary diffuse gastric cancer, we have utilized a synthetic lethal approach to identify candidate compounds that can specifically kill CDH1-null cells. Inhibitors of sphingolipid metabolism and vesicle trafficking pathways were identified as promising candidate compounds in a cell line model of CDH1 loss, then further validated in murine-derived organoid models of hereditary diffuse gastric cancer. With further research, these findings may lead to the development of novel chemoprevention strategies for the treatment of hereditary diffuse gastric cancer.

Abstract

Germline inactivating variants of CDH1 are causative of hereditary diffuse gastric cancer (HDGC), a cancer syndrome characterized by an increased risk of both diffuse gastric cancer and lobular breast cancer. Because loss of function mutations are difficult to target therapeutically, we have taken a synthetic lethal approach to identify targetable vulnerabilities in CDH1-null cells. We have previously observed that CDH1-null MCF10A cells exhibit a reduced rate of endocytosis relative to wildtype MCF10A cells. To determine whether this deficiency is associated with wider vulnerabilities in vesicle trafficking, we screened isogenic MCF10A cell lines with known inhibitors of autophagy, endocytosis, and sphingolipid metabolism. Relative to wildtype MCF10A cells, CDH1^−/− MCF10A cells showed significantly greater sensitivity to several drugs targeting these processes, including the autophagy inhibitor chloroquine, the endocytosis inhibitors chlorpromazine and PP1, and the sphingosine kinase 1 inhibitor PF-543. Synthetic lethality was confirmed in both gastric and mammary organoid models of CDH1 loss, derived from CD44-Cre/Cdh1^fl/fl/tdTomato mice. Collectively, these results suggest that both sphingolipid metabolism and vesicle trafficking represent previously unrecognised druggable vulnerabilities in CDH1-null cells and may lead to the development of new therapies for HDGC.

Novel functions of S1P in chronic itchy and inflammatory skin diseases

S1P is a pleotropic sphingolipid signalling molecule that acts through binding to five high-affinity G-protein coupled receptors. S1P-signaling affects cell fate in a multitude of ways, e.g. influencing cell differentiation, proliferation, and apoptosis, as well as playing an important role in immune cell trafficking. Though many effects of S1P-signaling in the human body have been discovered, the full range of functions is yet to be understood. For inflammatory skin diseases such as atopic dermatitis and psoriasis, evidence is emerging that dysfunction and imbalance of the S1P-axis is a contributing factor. Multiple studies investigating the efficacy of S1PR modulators in alleviating the severity and symptoms of skin conditions in various animal models and human clinical trials have shown promising results and validated the interest in the S1P-axis as a potential therapeutic target. Even though the involvement of S1P-signalling in inflammatory skin diseases still requires further clarification, the implications of the recent findings may prompt expansion of research to additional skin conditions and more S1P-axis modulatory pharmaceuticals.

Sphingolipids in Hematopoiesis: Exploring Their Role in Lineage Commitment

Sphingolipids, associated enzymes, and the sphingolipid pathway are implicated in complex, multifaceted roles impacting several cell functions, such as cellular homeostasis, apoptosis, cell differentiation, and more through intrinsic and autocrine/paracrine mechanisms. Given this broad range of functions, it comes as no surprise that a large body of evidence points to important functions of sphingolipids in hematopoiesis. As the understanding of the processes that regulate hematopoiesis and of the specific characteristics that define each type of hematopoietic cells is being continuously refined, the understanding of the roles of sphingolipid metabolism in hematopoietic lineage commitment is also evolving. Recent findings indicate that sphingolipid alterations can modulate lineage commitment from stem cells all the way to megakaryocytic, erythroid, myeloid, and lymphoid cells. For instance, recent evidence points to the ability of de novo sphingolipids to regulate the stemness of hematopoietic stem cells while a substantial body of literature implicates various sphingolipids in specialized terminal differentiation, such as thrombopoiesis. This review provides a comprehensive discussion focused on the mechanisms that link sphingolipids to the commitment of hematopoietic cells to the different lineages, also highlighting yet to be resolved questions.

Physiological and pathological functions of sphingolipids in pregnancy

Signaling by the bioactive sphingolipid, sphingosine 1-phosphate (S1P), and its precursors are emerging areas in pregnancy research. S1P and ceramide levels increase towards end of gestation, suggesting a physiological role in parturition. However, high levels of circulating S1P and ceramide are correlated with pregnancy disorders such as preeclampsia, gestational diabetes mellitus and intrauterine growth restriction. Expression of placental and decidual enzymes that metabolize S1P and S1P receptors are also dysregulated during pregnancy complications. In this review, we provide an in-depth examination of the signaling mechanism of S1P and ceramide in various reproductive tissues during gestation. These factors determine implantation and early pregnancy success by modulating corpus luteum function from progesterone production to luteolysis through to apoptosis. We also highlight the role of S1P through receptor signaling in inducing decidualization and angiogenesis in the decidua, as well as regulating extravillous trophoblast migration to anchor the placenta into the uterine wall. Recent advances on the role of the S1P:ceramide rheostat in controlling the fate of villous trophoblasts and the role of S1P as a negative regulator of trophoblast syncytialization to a multinucleated placental barrier are discussed. This review also explores the role of S1P in anti-inflammatory and pro-inflammatory signaling, its role as a vasoconstrictor, and the effects of S1P metabolizing enzymes and receptors in pregnancy.

Sphingosine-1-phosphate receptor 3 signaling

Sphingosine-1-phosphate (S1P) is a bioactive lipid which regulates a series of physiological and pathological processes via binding to five S1P receptors (S1PR1-5). Although S1PR1-3 are widely expressed, the study of S1PRs, however, mainly addressed S1PR1 and S1PR2, and few studies focus on S1PR3-5. In recent years, a growing number of studies have shown that S1PR3 plays an important role in cell proliferation, differentiation, apoptosis, and migration, but its function is still controversial. This is the first comprehensive review paper about the role of S1PR3 signaling in cardiovascular function, tissue fibrosis, cancer, immune response, and neurological function. In addition, existing S1PR3 agonists and antagonists are listed at the end of the article, and we also put forward our opinion on the dispute of S1PR3 function.

Suppressive Effect of CYM50358 S1P4 Antagonist on Mast Cell Degranulation and Allergic Asthma in Mice

Levels of sphingosine 1-phosphate (S1P), an intercellular signaling molecule, reportedly increase in the bronchoalveolar lavage fluids of patients with asthma. Although the type 4 S1P receptor, S1P₄ has been detected in mast cells, its functions have been poorly investigated in an allergic asthma model in vivo. S1P₄ functions were evaluated following treatment of CYM50358, a selective antagonist of S1P₄, in an ovalbumin-induced allergic asthma model, and antigen-induced degranulation of mast cells. CYM50358 inhibited antigen-induced degranulation in RBL-2H3 mast cells. Eosinophil accumulation and an increase of Th2 cytokine levels were measured in the bronchoalveolar lavage fluid and via the inflammation of the lungs in ovalbumin-induced allergic asthma mice. CYM50358 administration before ovalbumin sensitization and before the antigen challenge strongly inhibited the increase of eosinophils and lymphocytes in the bronchoalveolar lavage fluid. CYM50358 administration inhibited the increase of IL-4 cytokines and serum IgE levels. Histological studies revealed that CYM50358 reduced inflammatory scores and PAS (periodic acid–Schiff)-stained cells in the lungs. The pro-allergic functions of S1P₄ were elucidated using in vitro mast cells and in vivo ovalbumin-induced allergic asthma model experiments. These results suggest that S1P₄ antagonist CYM50358 may have therapeutic potential in the treatment of allergic asthma.

Sphingosine-1-Phosphate Metabolism and Signaling in Kidney Diseases

In the past few decades, sphingolipids and sphingolipid metabolites have gained attention because of their essential role in the pathogenesis and progression of kidney diseases. Studies in models of experimental and clinical nephropathies have described accumulation of sphingolipids and sphingolipid metabolites, and it has become clear that the intracellular sphingolipid composition of renal cells is an important determinant of renal function. Proper function of the glomerular filtration barrier depends heavily on the integrity of lipid rafts, which include sphingolipids as key components. In addition to contributing to the structural integrity of membranes, sphingolipid metabolites, such as sphingosine-1-phosphate (S1P), play important roles as second messengers regulating biologic processes, such as cell growth, differentiation, migration, and apoptosis. This review will focus on the role of S1P in renal cells and how aberrant extracellular and intracellular S1P signaling contributes to the pathogenesis and progression of kidney diseases.

Spinster homolog 2 in cancers, its functions and mechanisms

Spinster homolog 2 (SPNS2) is a multi-transmembrane transporter, widely located in the cell membrane and organelle membranes. It transports sphingosine-1-phosphate (S1P) into the extracellular space and the circulatory system, thus alters the concentration and the distribution of S1P, sphingosine-1-phosphate receptor (S1PRs) and S1P related enzymes, meaning that it exerts its functions via S1P signaling pathways. Studies also show that ectopic SPNS2 mediates parts of the physiological process of the cells. As of now, SPNS2 has been reported to participate in physiological processes such as angiogenesis, embryonic development, immune response and metabolisms. It is also associated with the transformation from inflammation to cancer as well as the proliferation and metastasis of cancer cells. In this review, we summarize the functions and the mechanisms of SPNS2 in the pathogenesis of cancer to provide new insights for the diagnosis and the treatments of cancer.

Emerging roles of lysophospholipids in health and disease

Lipids are abundant and play essential roles in human health and disease. The main functions of lipids are building blocks for membrane biogenesis. However, lipids are also metabolized to produce signaling molecules. Here, we discuss the emerging roles of circulating lysophospholipids. These lysophospholipids consist of lysoglycerophospholipids and lysosphingolipids. They are both present in cells at low concentration, but their concentrations in extracellular fluids are significantly higher. The biological functions of some of these lysophospholipids have been recently revealed. Remarkably, some of the lysophospholipids play pivotal signaling roles as well as being precursors for membrane biogenesis. Revealing how circulating lysophospholipids are produced, released, transported, and utilized in multi-organ systems is critical to understand their functions. The discovery of enzymes, carriers, transporters, and membrane receptors for these lysophospholipids has shed light on their physiological significance. In this review, we summarize the biological roles of these lysophospholipids via discussing about the proteins regulating their functions. We also discuss about their potential impacts to human health and diseases.

Druggable Lipid GPCRs: Past, Present, and Prospects

G protein-coupled receptors (GPCRs) have seven transmembrane spanning domains and comprise the largest superfamily with ~800 receptors in humans. GPCRs are attractive targets for drug discovery because they transduce intracellular signaling in response to endogenous ligands via heterotrimeric G proteins or arrestins, resulting in a wide variety of physiological and pathophysiological responses. The endogenous ligands for GPCRs are highly chemically diverse and include ions, biogenic amines, nucleotides, peptides, and lipids. In this review, we follow the KonMari method to better understand druggable lipid GPCRs. First, we have a comprehensive tidying up of lipid GPCRs including receptors for prostanoids, leukotrienes, specialized pro-resolving mediators (SPMs), lysophospholipids, sphingosine 1-phosphate (S1P), cannabinoids, platelet-activating factor (PAF), free fatty acids (FFAs), and sterols. This tidying up consolidates 46 lipid GPCRs and declutters several perplexing lipid GPCRs. Then, we further tidy up the lipid GPCR-directed drugs from the literature and databases, which identified 24 clinical drugs targeting 16 unique lipid GPCRs available in the market and 44 drugs under evaluation in more than 100 clinical trials as of 2019. Finally, we introduce drug designs for GPCRs that spark joy, such as positive or negative allosteric modulators (PAM or NAM), biased agonism, functional antagonism like fingolimod, and monoclonal antibodies (MAbs). These strategic drug designs may increase the efficacy and specificity of drugs and reduce side effects. Technological advances will help to discover more endogenous lipid ligands from the vast number of remaining orphan GPCRs and will also lead to the development novel lipid GPCR drugs to treat various diseases.

Lipid Signaling in Ocular Neovascularization

Vasculogenesis and angiogenesis play a crucial role in embryonic development. Pathological neovascularization in ocular tissues can lead to vision-threatening vascular diseases, including proliferative diabetic retinopathy, retinal vein occlusion, retinopathy of prematurity, choroidal neovascularization, and corneal neovascularization. Neovascularization involves various cellular processes and signaling pathways and is regulated by angiogenic factors such as vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF). Modulating these circuits may represent a promising strategy to treat ocular neovascular diseases. Lipid mediators derived from membrane lipids are abundantly present in most tissues and exert a wide range of biological functions by regulating various signaling pathways. In particular, glycerophospholipids, sphingolipids, and polyunsaturated fatty acids exert potent pro-angiogenic or anti-angiogenic effects, according to the findings of numerous preclinical and clinical studies. In this review, we summarize the current knowledge regarding the regulation of ocular neovascularization by lipid mediators and their metabolites. A better understanding of the effects of lipid signaling in neovascularization may provide novel therapeutic strategies to treat ocular neovascular diseases and other human disorders.

Potential sphingosine-1-phosphate-related therapeutic targets in the treatment of cerebral ischemia reperfusion injury

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that regulates lymphocyte trafficking, glial cell activation, vasoconstriction, endothelial barrier function, and neuronal death pathways in the brain. Research has increasingly implicated S1P in the pathology of cerebral ischemia reperfusion (IR) injury. As a high-affinity agonist of S1P receptor, fingolimod exhibits excellent neuroprotective effects against ischemic challenge both in vivo and in vitro. By summarizing recent progress on how S1P participates in the development of brain IR injury, this review identifies potential therapeutic targets for the treatment of brain IR injury.

Characterizing Sphingosine Kinases and Sphingosine 1-Phosphate Receptors in the Mammalian Eye and Retina

Sphingosine 1-phosphate (S1P) signaling regulates numerous biological processes including neurogenesis, inflammation and neovascularization. However, little is known about the role of S1P signaling in the eye. In this study, we characterize two sphingosine kinases (SPHK1 and SPHK2), which phosphorylate sphingosine to S1P, and three S1P receptors (S1PR1, S1PR2 and S1PR3) in mouse and rat eyes. We evaluated sphingosine kinase and S1P receptor gene expression at the mRNA level in various rat tissues and rat retinas exposed to light-damage, whole mouse eyes, specific eye structures, and in developing retinas. Furthermore, we determined the localization of sphingosine kinases and S1P receptors in whole rat eyes by immunohistochemistry. Our results unveiled unique expression profiles for both sphingosine kinases and each receptor in ocular tissues. Furthermore, these kinases and S1P receptors are expressed in mammalian retinal cells and the expression of SPHK1, S1PR2 and S1PR3 increased immediately after light damage, which suggests a function in apoptosis and/or light stress responses in the eye. These findings have numerous implications for understanding the role of S1P signaling in the mechanisms of ocular diseases such as retinal inflammatory and degenerative diseases, neovascular eye diseases, glaucoma and corneal diseases.

Bioactive lysolipids in cancer and angiogenesis

While normal angiogenesis is critical for development and tissue growth, pathological angiogenesis is important for the growth and spread of cancers by supplying nutrients and oxygen as well as providing a conduit for distant metastasis. The interaction among extracellular matrix molecules, tumor cells, endothelial cells, fibroblasts, and immune cells is critical in pathological angiogenesis, in which various angiogenic growth factors, chemokines, and lipid mediators produced from these cells as well as hypoxic microenvironment promote angiogenesis by regulating expression and/or activity of various related genes. Sphingosine 1-phosphate and lysophosphatidic acid, bioactive lipid mediators which act via specific G protein-coupled receptors, play critical roles in angiogenesis. In addition, other lipid mediators including prostaglandin E₂, lipoxin, and resolvins are produced in a stimulus-dependent manner and have pro- or anti-angiogenic effects, presumably through their specific GPCRs. Dysregulated lipid mediator signaling pathways are observed in the contxt of some tumors. This review will focus on LPA and S1P, two bioactive lipid mediators in their regulation of angiogenesis and cell migration that are critical for tumor growth and spread.

S1P₄ Regulates Passive Systemic Anaphylaxis in Mice but Is Dispensable for Canonical IgE-Mediated Responses in Mast Cells

Mast cells are key players in the development of inflammatory allergic reactions. Cross-linking of the high-affinity receptor for IgE (FcεRI) on mast cells leads to the generation and secretion of the sphingolipid mediator, sphingosine-1-phosphate (S1P) which is able, in turn, to transactivate its receptors on mast cells. Previous reports have identified the expression of two of the five receptors for S1P on mast cells, S1P₁ and S1P₂, with functions in FcεRI-mediated chemotaxis and degranulation, respectively. Here, we show that cultured mouse mast cells also express abundant message for S1P₄. Genetic deletion of S1pr4 did not affect the differentiation of bone marrow progenitors into mast cells or the proliferation of mast cells in culture. A comprehensive characterization of IgE-mediated responses in S1P₄-deficient bone marrow-derived and peritoneal mouse mast cells indicated that this receptor is dispensable for mast cell degranulation, cytokine/chemokine production and FcεRI-mediated chemotaxis in vitro. However, interleukin-33 (IL-33)-mediated enhancement of IgE-induced degranulation was reduced in S1P₄-deficient peritoneal mast cells, revealing a potential negative regulatory role for S1P₄ in an IL-33-rich environment. Surprisingly, genetic deletion of S1pr4 resulted in exacerbation of passive systemic anaphylaxis to IgE/anti-IgE in mice, a phenotype likely related to mast cell-extrinsic influences, such as the high circulating levels of IgE in these mice which increases FcεRI expression and consequently the extent of the response to FcεRI engagement. Thus, we provide evidence that S1P₄ modulates anaphylaxis in an unexpected manner that does not involve regulation of mast cell responsiveness to IgE stimulation.

Sphingosine-1-phosphate receptors and innate immunity

Sphingosine-1-phosphate (S1P) is a signalling lipid that regulates many cellular processes in mammals. One well-studied role of S1P signalling is to modulate T-cell trafficking, which has a major impact on adaptive immunity. Compounds that target S1P signalling pathways are of interest for immune system modulation. Recent studies suggest that S1P signalling regulates many more cell types and processes than previously appreciated. This review will summarise current understanding of S1P signalling, focusing on recent novel findings in the roles of S1P receptors in innate immunity.

Testosterone regulates the expression and functional activity of sphingosine-1-phosphate receptors in the rat corpus cavernosum

The bioactive lipid sphingosine‐1‐phosphate (S1P) regulates smooth muscle (SM) contractility predominantly via three G protein‐coupled receptors. The S1P1 receptor is associated with nitric oxide (NO)‐mediated SM relaxation, while S1P2 & S1P3 receptors are linked to SM contraction via activation of the Rho‐kinase pathway. This study is to determine testosterone (T) modulating the expression and functional activity of S1P receptors in corpus cavernosum (CC). Adult male Sprague‐Dawley rats were randomly divided into three groups: sham‐operated controls, surgical castration and T supplemented group. Serum S1P levels were detected by high‐performance liquid chromatography. The expression of S1P1‐3 receptors and sphingosine kinases was detected by real‐time RT‐PCR. In vitro organ bath contractility and in vivo intracavernous pressure (ICP) measurement were also performed. T deprivation significantly decreased ICP rise. Meanwhile, surgical castration induced a significant increase in serum S1P level and the expression of S1P2‐3 receptors by twofold (P < 0.05) but a decrease in the expression of S1P1 receptor. Castration also augmented exogenous phenylephrine (PE), S1P, S1P1,3 receptor agonist FTY720‐P contractility and S1P2‐specific antagonist JTE013 relaxation effect. T supplemented could restore the aforementioned changes. We provide novel data that castration increased serum S1P concentration and up‐regulated the expression of S1P2‐3 receptors in CC. Consistently, agonizing S1P receptors induced CCSM contraction and antagonizing mediated relaxation were augmented. This provides the first clear evidence that S1P system dysregulation may contribute to hypogonadism‐related erectile dysfunction (ED), and S1P receptors may be expected as a potential target for treating ED.

Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors

Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.

Sphingosine kinase 1/sphingosine-1-phosphate (S1P)/S1P receptor axis is involved in ovarian cancer angiogenesis

Sphingosine kinase (SphK)/sphingosine-1-phosphate (S1P)/S1P receptor (S1PR) signaling pathway has been implicated in a variety of pathological processes of ovarian cancer. However, the function of this axis in ovarian cancer angiogenesis remains incompletely defined. Here we provided the first evidence that SphK1/S1P/S1PR_1/3 pathway played key roles in ovarian cancer angiogenesis. The expression level of SphK1, but not SphK2, was closely correlated with the microvascular density (MVD) of ovarian cancer tissue. In vitro, the angiogenic potential and angiogenic factor secretion of ovarian cancer cells could be attenuated by SphK1, but not SphK2, blockage and were restored by the addition of S1P. Moreover, in these cells, we found S1P stimulation induced the angiogenic factor secretion via S1PR₁ and S1PR₃, but not S1PR₂. Furthermore, inhibition of S1PR_1/3, but not S1PR₂, attenuated the angiogenic potential and angiogenic factor secretion of the cells. in vivo, blockage of SphK or S1PR_1/3 could attenuate ovarian cancer angiogenesis and inhibit angiogenic factor expression in mouse models. Collectively, the current study showed a novel role of SphK1/S1P/S1PR_1/3 axis within the ovarian cancer, suggesting a new target to block ovarian cancer angiogenesis.

Beyond Immune Cell Migration: The Emerging Role of the Sphingosine-1-phosphate Receptor S1PR4 as a Modulator of Innate Immune Cell Activation

The sphingolipid sphingosine-1-phosphate (S1P) emerges as an important regulator of immunity, mainly by signaling through a family of five specific G protein-coupled receptors (S1PR1–5). While S1P signaling generally has the potential to affect not only trafficking but also differentiation, activation, and survival of a diverse range of immune cells, the specific outcome depends on the S1P receptor repertoire expressed on a given cell. Among the S1PRs, S1PR4 is specifically abundant in immune cells, suggesting a major role of the S1P/S1PR4 axis in immunity. Recent studies indeed highlight its role in activation of immune cells, differentiation, and, potentially, trafficking. In this review, we summarize the emerging data that support a major role of S1PR4 in modulating immunity in humans and mice and discuss therapeutic implications.

Sphingosine 1-Phosphate Receptors: Do They Have a Therapeutic Potential in Cardiac Fibrosis?

Sphingosine 1-phosphate (S1P) is a bioactive lipid that is characterized by a peculiar mechanism of action. In fact, S1P, which is produced inside the cell, can act as an intracellular mediator, whereas after its export outside the cell, it can act as ligand of specific G-protein coupled receptors, which were initially named endothelial differentiation gene (Edg) and eventually renamed sphingosine 1-phosphate receptors (S1PRs). Among the five S1PR subtypes, S1PR1, S1PR2 and S1PR3 isoforms show broad tissue gene expression, while S1PR4 is primarily expressed in immune system cells, and S1PR5 is expressed in the central nervous system. There is accumulating evidence for the important role of S1P as a mediator of many processes, such as angiogenesis, carcinogenesis and immunity, and, ultimately, fibrosis. After a tissue injury, the imbalance between the production of extracellular matrix (ECM) and its degradation, which occurs due to chronic inflammatory conditions, leads to an accumulation of ECM and, consequential, organ dysfunction. In these pathological conditions, many factors have been described to act as pro- and anti-fibrotic agents, including S1P. This bioactive lipid exhibits both pro- and anti-fibrotic effects, depending on its site of action. In this review, after a brief description of sphingolipid metabolism and signaling, we emphasize the involvement of the S1P/S1PR axis and the downstream signaling pathways in the development of fibrosis. The current knowledge of the therapeutic potential of S1PR subtype modulators in the treatment of the cardiac functions and fibrinogenesis are also examined.

Clinical pharmacology, efficacy, and safety aspects of sphingosine-1-phosphate receptor modulators

INTRODUCTION

Sphingosine-1-phosphate (S1P) receptor modulators, of which one has received marketing approval and several others are in clinical development, display promising potential in the treatment of a spectrum of autoimmune diseases.

AREAS COVERED

Administration of S1P1 receptor modulators leads to functional receptor antagonism triggering sustained inhibition of the egress of lymphocytes from lymphoid organs. First-dose administration is associated with transient cardiovascular effects. We compiled and discussed available pharmacokinetic, pharmacodynamic, and safety data of selective and non-selective S1P receptor modulators that were investigated in recent years.

EXPERT OPINION

The safety profile of S1P receptor modulators is considered better than other classes of immunomodulators and was further improved by the development of up-titration regimens to mitigate first-dose effects. S1P receptor modulators display similar pharmacodynamic effects but have very different pharmacokinetic profiles. Drugs with a rapid elimination are of interest in case of opportunistic infections or pregnancy, whereas the need of re-initiation of up-titration in case of treatment interruption can present a challenge.

S1PR4 Signaling Attenuates ILT 7 Internalization To Limit IFN-α Production by Human Plasmacytoid Dendritic Cells

Plasmacytoid dendritic cells (pDCs) produce large amounts of type I IFN in response to TLR7/9 ligands. This conveys antiviral effects, activates other immune cells (NK cells, conventional DCs, B, and T cells), and causes the induction and expansion of a strong inflammatory response. pDCs are key players in various type I IFN-driven autoimmune diseases such as systemic lupus erythematosus or psoriasis, but pDCs are also involved in (anti-)tumor immunity. The sphingolipid sphingosine-1-phosphate (S1P) signals through five G-protein-coupled receptors (S1PR1-5) to regulate, among other activities, immune cell migration and activation. The present study shows that S1P stimulation of human, primary pDCs substantially decreases IFN-α production after TLR7/9 activation with different types of CpG oligodeoxynucleotides or tick-borne encephalitis vaccine, which occurred in an S1PR4-dependent manner. Mechanistically, S1PR4 activation preserves the surface expression of the human pDC-specific inhibitory receptor Ig-like transcript 7. We provide novel information that Ig-like transcript 7 is rapidly internalized upon receptor-mediated endocytosis of TLR7/9 ligands to allow high IFN-α production. This is antagonized by S1PR4 signaling, thus decreasing TLR-induced IFN-α secretion. At a functional level, attenuated IFN-α production failed to alter Ag-driven T cell proliferation in pDC-dependent T cell activation assays, but shifted cytokine production of T cells from a Th1 (IFN-γ) to a regulatory (IL-10) profile. In conclusion, S1PR4 agonists block human pDC activation and may therefore be a promising tool to restrict pathogenic IFN-α production.

Comprehensive analysis of sphingosine-1-phosphate receptor mutants during zebrafish embryogenesis

The lipid mediator sphingosine-1-phosphate (S1P) regulates various physiological and pathological phenomena such as angiogenesis and oncogenesis. Secreted S1P associates with the G-protein-coupled S1P receptors (S1PRs), leading to the activation of downstream signaling molecules. In mammals, five S1prs have been identified and the genetic disruption of a single S1pr1 gene causes vascular defects. In zebrafish, seven s1prs have been isolated. We found that individual s1prs showed unique expression patterns with some overlapping expression domains during early embryogenesis. We generated all s1pr single-mutant zebrafish by introducing premature stop codons in their coding regions using transcription activator-like effector nucleases and analyzed their phenotypes during early embryogenesis. Zygotic s1pr1, s1pr3a, s1pr3b, s1pr4, s1pr5a and s1pr5b mutants showed no developmental defects and grew into adults, whereas zygotic s1pr2 mutant showed embryonic lethality with a cardiac defect, showing quite distinct embryonic phenotypes for individual S1pr mutants between zebrafish and mouse. We further generated maternal-zygotic s1pr1, s1pr3a, s1pr3b, s1pr4, s1pr5a and s1pr5b mutants and found that these maternal-zygotic mutants also showed no obvious developmental defects, presumably suggesting the redundant functions of the S1P receptor-mediated signaling in zebrafish.

CFTR and sphingolipids mediate hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) optimizes pulmonary ventilation-perfusion matching in regional hypoxia, but promotes pulmonary hypertension in global hypoxia. Ventilation-perfusion mismatch is a major cause of hypoxemia in cystic fibrosis. We hypothesized that cystic fibrosis transmembrane conductance regulator (CFTR) may be critical in HPV, potentially by modulating the response to sphingolipids as mediators of HPV. HPV and ventilation-perfusion mismatch were analyzed in isolated mouse lungs or in vivo. Ca(2+) mobilization and transient receptor potential canonical 6 (TRPC6) translocation were studied in human pulmonary (PASMCs) or coronary (CASMCs) artery smooth muscle cells. CFTR inhibition or deficiency diminished HPV and aggravated ventilation-perfusion mismatch. In PASMCs, hypoxia caused CFTR to interact with TRPC6, whereas CFTR inhibition attenuated hypoxia-induced TRPC6 translocation to caveolae and Ca(2+) mobilization. Ca(2+) mobilization by sphingosine-1-phosphate (S1P) was also attenuated by CFTR inhibition in PASMCs, but amplified in CASMCs. Inhibition of neutral sphingomyelinase (nSMase) blocked HPV, whereas exogenous nSMase caused TRPC6 translocation and vasoconstriction that were blocked by CFTR inhibition. nSMase- and hypoxia-induced vasoconstriction, yet not TRPC6 translocation, were blocked by inhibition or deficiency of sphingosine kinase 1 (SphK1) or antagonism of S1P receptors 2 and 4 (S1P2/4). S1P and nSMase had synergistic effects on pulmonary vasoconstriction that involved TRPC6, phospholipase C, and rho kinase. Our findings demonstrate a central role of CFTR and sphingolipids in HPV. Upon hypoxia, nSMase triggers TRPC6 translocation, which requires its interaction with CFTR. Concomitant SphK1-dependent formation of S1P and activation of S1P2/4 result in phospholipase C-mediated TRPC6 and rho kinase activation, which conjointly trigger vasoconstriction.

An update on the biology of sphingosine 1-phosphate receptors

Sphingosine 1-phosphate (S1P) is a membrane-derived lysophospholipid that acts primarily as an ex-tracellular signaling molecule. Signals initiated by S1P are transduced by five G protein-coupled receptors, named S1P1-5 Cellular and temporal expression of the S1P receptors (S1PRs) determine their specific roles in various organ systems, but they are particularly critical for regulation of the cardiovascular, immune, and nervous systems, with the most well-known contributions of S1PR signaling being modulation of vascular barrier function, vascular tone, and regulation of lymphocyte trafficking. However, our knowledge of S1PR biology is rapidly increasing as they become attractive therapeutic targets in several diseases, such as chronic inflammatory pathologies, autoimmunity, and cancer. Understanding how the S1PRs regulate interactions between biological systems will allow for greater efficacy in this novel therapeutic strategy as well as characterization of complex physiological networks. Because of the rapidly expanding body of research, this review will focus on the most recent advances in S1PRs.

Systemic distribution, subcellular localization and differential expression of sphingosine-1-phosphate receptors in benign and malignant human tissues

AIMS

Five sphingosine-1-phosphate receptors (S1PR): S1PR1, S1PR2, S1PR3, S1PR4 and S1PR5 (S1PR1-5) have been shown to be involved in the proliferation and progression of various cancers. However, none of the S1PRs have been systemically investigated. In this study, we performed immunohistochemistry (IHC) for S1PR1-S1PR5 on different tissues, in order to simultaneously determine the systemic distribution, subcellular localization and expression level of all five S1PRs.

METHODS

We constructed tissue microarrays (TMAs) from 384 formalin-fixed paraffin-embedded (FFPE) blocks containing 183 benign and 201 malignant tissues from 34 human organs/systems. Then we performed IHC for all five S1PRs simultaneously on these TMA slides. The distribution, subcellular localization and expression of each S1PR were determined for each tissue. The data in benign and malignant tissues from the same organ/tissue were then compared using the Student's t-test. In order to reconfirm the subcellular localization of each S1PR as determined by IHC, immunocytochemistry (ICC) was performed on several malignant cell lines.

RESULTS

We found that all five S1PRs are widely distributed in multiple human organs/systems. All S1PRs are expressed in both the cytoplasm and nucleus, except S1PR3, whose IHC signals are only seen in the nucleus. Interestingly, the S1PRs are rarely expressed on cellular membranes. Each S1PR is unique in its organ distribution, subcellular localization and expression level in benign and malignant tissues. Among the five S1PRs, S1PR5 has the highest expression level (in either the nucleus or cytoplasm), with S1PR1, 3, 2 and 4 following in descending order. Strong nuclear expression was seen for S1PR1, S1PR3 and S1PR5, whereas S1PR2 and S1PR4 show only weak staining. Four organs/tissues (adrenal gland, liver, brain and colon) show significant differences in IHC scores for the multiple S1PRs (nuclear and/or cytoplasmic), nine (stomach, lymphoid tissues, lung, ovary, cervix, pancreas, skin, soft tissues and uterus) show differences for only one S1PR (cytoplasmic or nuclear), and twenty three organs/tissues show no significant difference in IHC scores for any S1PR (cytoplasmic or nuclear) between benign and malignant changes.

CONCLUSION

This is the first study to evaluate the expression level of all S1PRs in benign and malignant tissues from multiple human organs. This study provides data regarding the systemic distribution, subcellular localization and differences in expression of all five S1PRs in benign and malignant changes for each organ/tissue.

Second generation S1P pathway modulators: research strategies and clinical developments

Multiple Sclerosis (MS) is a chronic autoimmune disorder affecting the central nervous system (CNS) through demyelination and neurodegeneration. Until recently, major therapeutic treatments have relied on agents requiring injection delivery. In September 2010, fingolimod/FTY720 (Gilenya, Novartis) was approved as the first oral treatment for relapsing forms of MS. Fingolimod causes down-modulation of S1P1 receptors on lymphocytes which prevents the invasion of autoaggressive T cells into the CNS. In astrocytes, down-modulation of S1P1 by the drug reduces astrogliosis, a hallmark of MS, thereby allowing restoration of productive astrocyte communication with other neural cells and the blood brain barrier. Animal data further suggest that the drug directly supports the recovery of nerve conduction and remyelination. In human MS, such mechanisms may explain the significant decrease in the number of inflammatory markers on brain magnetic resonance imaging in recent clinical trials, and the reduction of brain atrophy by the drug. Fingolimod binds to 4 of the 5 known S1P receptor subtypes, and significant efforts were made over the past 5 years to develop next generation S1P receptor modulators and determine the minimal receptor selectivity needed for maximal therapeutic efficacy in MS patients. Other approaches considered were competitive antagonists of the S1P1 receptor, inhibitors of the S1P lyase to prevent S1P degradation, and anti-S1P antibodies. Below we discuss the current status of the field, and the functional properties of the most advanced compounds. This article is part of a Special Issue entitled New Frontiers in Sphingolipid Biology.

Discovery, design and synthesis of a selective S1P(3) receptor allosteric agonist

Potent and selective S1P3 receptor (S1P3-R) agonists may represent important proof-of-principle tools used to clarify the receptor biological function and assess the therapeutic potential of the S1P3-R in cardiovascular, inflammatory and pulmonary diseases. N,N-Dicyclohexyl-5-propylisoxazole-3-carboxamide was identified by a high-throughput screening of MLSMR library as a promising S1P3-R agonist. Rational chemical modifications of the hit allowed the identification of N,N-dicyclohexyl-5-cyclopropylisoxazole-3-carboxamide, a S1P3-R agonist endowed with submicromolar activity and exquisite selectivity over the remaining S1P1,2,4,5-R family members. A combination of ligand competition, site-directed mutagenesis and molecular modeling studies showed that the N,N-dicyclohexyl-5-cyclopropylisoxazole-3-carboxamide is an allosteric agonist and binds to the S1P3-R in a manner that does not disrupt the S1P3-R-S1P binding. The lead molecule herein disclosed constitutes a valuable pharmacological tool to explore the molecular basis of the receptor function, and provides the bases for further rational design of more potent and drug-like S1P3-R allosteric agonists.

Promoter methylation patterns in Richter syndrome affect stem-cell maintenance and cell cycle regulation and differ from de novo diffuse large B-cell lymphoma

In a fraction of patients, chronic lymphocytic leukaemia (CLL) can transform to Richter syndrome (RS), usually a diffuse large B-cell lymphoma (DLBCL). We studied genome-wide promoter DNA methylation in RS and clonally related CLL-phases of transformed patients, alongside de novo DLBCL (of non-germinal centre B type), untransformed-CLL and normal B-cells. The greatest differences in global DNA methylation levels were observed between RS and DLBCL, indicating that these two diseases, although histologically similar, are epigenetically distinct. RS was more highly methylated for genes involved in cell cycle regulation. When RS was compared to the preceding CLL-phase and with untransformed-CLL, RS presented a higher degree of methylation for genes possessing the H3K27me3 mark and PRC2 targets, as well as for gene targets of TP53 and RB1. Comparison of the methylation levels of individual genes revealed that OSM, a stem cell regulatory gene, exhibited significantly higher methylation levels in RS compared to CLL-phases. Its transcriptional repression by DNA methylation was confirmed by 5-aza-2'deoxycytidine treatment of DLBCL cells, determining an increased OSM expression. Our results showed that methylation patterns in RS are largely different from de novo DLBCL. Stem cell-related genes and cell cycle regulation genes are targets of DNA methylation in RS.

Sphingosine-1-phosphate receptor 2

Sphingosine-1-phosphate (S1P) is a potent bioactive sphingolipid involved in cell proliferation, angiogenesis, inflammation and malignant transformation among other functions. S1P acts either directly on intracellular targets or activates G protein-coupled receptors, specifically five S1P receptors (S1PRs). The identified S1PRs differ in cellular and tissue distribution, and each is coupled to specific G proteins, which mediate unique functions. Here, we describe functional characteristics of all five receptors, emphasizing S1PR2, which is critical in the immune, nervous, metabolic, cardiovascular, musculoskeletal, and renal systems. This review also describes the role of this receptor in tumor growth and metastasis and suggests potential therapeutic avenues that exploit S1PR2.

The role of sphingosine-1-phosphate in breast cancer tumor-induced lymphangiogenesis

Sphingosine-1-phosphate (S1P) is a potent sphingolipid metabolite that regulates a number of biological processes critical for cancer. S1P produced inside cancer cells is exported and exerts its extracellular functions by binding to its specific receptors in an autocrine, paracrine, and/or endocrine manner, which is known as inside-out signaling. S1P is also known to exert its intracellular functions especially in the inflammatory process, but its relevance to cancer biology remains to be elucidated. Recently, there have been growing interests in the role of S1P in breast cancer progression, including angiogenesis and lymphangiogenesis. Our group demonstrated that activation of sphingosine kinase 1, the enzyme that catalyzes the phosphorylation of sphingosine to S1P, is a key step of this process. In this review, we will cover our current knowledge on the role of S1P signaling pathway in breast cancer progression with an emphasis on its role in tumor-induced lymphangiogenesis.

Sphingosine 1-phosphate receptor signaling regulates proper embryonic vascular patterning

Sphingosine 1-phosphate (S1P) binds G-protein-coupled receptors (S1P(1-5)) to regulate a multitude of physiological effects, especially those in the vascular and immune systems. S1P receptors in the vascular system have been characterized primarily in mammals. Here, we report that the S1P receptors and metabolic enzymes are conserved in the genome of zebrafish Danio rerio. Bioinformatic analysis identified seven S1P receptor-like sequences in the zebrafish genome, including duplicated orthologs of receptors 3 and 5. Sphingolipidomic analysis detected erythrocyte and plasma S1P as well as high plasma ceramides and sphingosine. Morpholino-mediated knockdown of s1pr1 causes global and pericardial edema, loss of blood circulation, and vascular defects characterized by both reduced vascularization in intersegmental vessels, decreased proliferation of intersegmental and axial vessels, and hypersprouting in the caudal vein plexus. The s1pr2 gene was previously characterized as a regulator of cell migration and heart development, but its role in angiogenesis is not known. However, when expression of both s1pr1 and s1pr2 is suppressed, severely reduced vascular development of the intersegmental vessels was observed with doses of the s1pr1 morpholino that alone did not cause any discernible vascular defects, suggesting that s1pr1 and s1pr2 function cooperatively to regulate vascular development in zebrafish. Similarly, the S1P transporter, spns2, also cooperated with s1pr1. We propose that extracellular S1P acts through vascular S1P receptors to regulate vascular development.

S1P(4) receptor mediates S1P-induced vasoconstriction in normotensive and hypertensive rat lungs

This study aimed to identify receptors mediating sphingosine-1-phosphate (S1P)-induced vasoconstriction in the normotensive and chronic hypoxia-induced hypertensive rat pulmonary circulation. In isolated perfused lungs from normoxic rats, infusion of S1P caused a sustained vasoconstriction, which was not reduced by combinational pretreatment with the dual S1P_{1 and 3} receptor antagonist VPC23019 and the S1P₂ receptor antagonist JTE013. The S1P₄ receptor agonists phytosphingosine-1-phospate and VPC23153, but not the dual S1P_{1 and 3} receptor agonist VPC24191, caused dose-dependent vasoconstrictions. In hypertensive lungs from chronically hypoxic rats, the vasoconstrictor responses to S1P and VPC23153 were markedly enhanced. The S1P₄ receptor agonist VPC 23153 caused contraction of isolated pulmonary but not of renal or mesenteric arteries from chronically hypoxic rats. S1P₄ receptor protein as well as mRNA were detected in both normotensive and hypertensive pulmonary arteries. In contrast to what has been reported in the systemic circulation and mouse lung, our findings raise the possibility that S1P₄ receptor plays a significant role in S1P-induced vasoconstriction in the normotensive and hypertensive rat pulmonary circulation.

Sphingosine-1-phosphate inhibits H2O2-induced granulosa cell apoptosis via the PI3K/Akt signaling pathway

OBJECTIVE

To investigate the protective effect of sphingosine-1-phosphate (S1P) against H(2)O(2)-induced apoptosis in human granulosa cell cultures with freshly harvested granulosa cells.

DESIGN

Experimental study.

SETTING

Academic medical center for reproductive medicine.

PATIENT(S)

Cultures of primary granulosa cells isolated from women undergoing in vitro fertilization (IVF).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Cell apoptosis and Western blot analysis of signaling pathway proteins.

RESULT(S)

We found that S1P (1 and 10 mM) statistically significantly decreased granulosa cell apoptosis after H(2)O(2) treatment. The decreased cell apoptosis induced by S1P was abolished after treatment with VPC23019, an inhibitor of S1P1 and S1P3 receptors, W146, an inhibitor of S1P1 receptors, and CAY10444, an inhibitor of S1P3 receptors. A Western blot analysis revealed that the level of phospho-Akt increased and peaked at 10 minutes after 10 mM S1P exposure.

CONCLUSION(S)

Treatment with S1P can inhibit the apoptosis of granulosa cells in response to oxidative stress induced by H(2)O(2). The protective effect of S1P is mediated by activating the PI3K/Akt pathway, and the antiapoptotic effect of S1P is mainly mediated through the S1P1 and S1P3 receptor.

G protein-coupled receptors as therapeutic targets for multiple sclerosis

G protein-coupled receptors (GPCRs) mediate most of our physiological responses to hormones, neurotransmitters and environmental stimulants. They are considered as the most successful therapeutic targets for a broad spectrum of diseases. Multiple sclerosis (MS) is an inflammatory disease that is characterized by immune-mediated demyelination and degeneration of the central nervous system (CNS). It is the leading cause of non-traumatic disability in young adults. Great progress has been made over the past few decades in understanding the pathogenesis of MS. Numerous data from animal and clinical studies indicate that many GPCRs are critically involved in various aspects of MS pathogenesis, including antigen presentation, cytokine production, T-cell differentiation, T-cell proliferation, T-cell invasion, etc. In this review, we summarize the recent findings regarding the expression or functional changes of GPCRs in MS patients or animal models, and the influences of GPCRs on disease severity upon genetic or pharmacological manipulations. Hopefully some of these findings will lead to the development of novel therapies for MS in the near future.

Extracellular and intracellular sphingosine-1-phosphate in cancer

Sphingosine-1-phosphate (S1P) was first described as a signaling molecule over 20 years ago. Since then, great strides have been made to reveal its vital roles in vastly different cellular and disease processes. Initially, S1P was considered nothing more than the terminal point of sphingolipid metabolism; however, over the past two decades, a large number of reports have helped unveil its full potential as an important regulatory, bioactive sphingolipid metabolite. S1P has a plethora of physiological functions, due in part to its many sites of actions and its different pools, which are both intra- and extracellular. S1P plays pivotal roles in many physiological processes, including the regulation of cell growth, migration, autophagy, angiogenesis, and survival, and thus, not surprisingly, S1P has been linked to cancer. In this review, we will summarize the vast body of knowledge, highlighting the connection between S1P and cancer. We will also suggest new avenues for future research.

Insights into the pharmacological relevance of lysophospholipid receptors

The discovery of lysophospholipid (LP) 7-transmembrane, G protein-coupled receptors (GPCRs) that began in the 1990s, together with research into the functional roles of the major LPs known as lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P), have opened new research avenues into their biological processes and mechanisms. Major examples of LP signalling effects include embryogenesis, nervous system development, vascular development, uterine implantation, immune cell trafficking, and inflammatory reactions. LP signalling also influences the pathophysiology of many diseases including cancer, autoimmune and inflammatory diseases, which indicate that LP receptors may be attractive targets for pharmacological therapies. A key example of such a therapeutic agent is the S1P receptor modulator FTY720, which upon phosphorylation and continued drug exposure, acts as an S1P receptor functional antagonist. This compound (also known as fingolimod or Gilenya) has recently been approved by the FDA for the treatment of relapsing forms of multiple sclerosis. Continued basic and translational research on LP signalling should provide novel insights into both basic biological mechanisms, as well as novel therapeutic approaches to combat a range of human diseases.

Discovery, design and synthesis of novel potent and selective sphingosine-1-phosphate 4 receptor (S1P₄-R) agonists

High affinity and selective small molecule agonists of the S1P(4) receptor (S1P(4)-R) may have significant therapeutic utility in diverse disease areas including autoimmune diseases, viral infections and thrombocytopenia. A high-throughput screening (HTS) of the Molecular Libraries-Small Molecule Repository library identified 3-(2-(2,4-dichlorophenoxy)ethoxy)-6-methyl-2-nitropyridine as a moderately potent and selective S1P(4)-R hit agonist. Design, synthesis and systematic structure-activity relationships study of the HTS-derived hit led to the development of novel potent S1P(4)-R agonists exquisitely selective over the remaining S1P(1-3,5)-Rs family members. Remarkably, the molecules herein reported provide novel pharmacological tools to decipher the biological function and assess the therapeutic utility of the S1P(4)-R.