Sphingosine-1-phosphate receptors and innate immunity

Effects and action mechanism of gonadotropins on ovarian follicular cells: A novel role of Sphingosine-1-Phosphate (S1P). A review

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) control antral follicular growth by regulating several processes, such as the synthesis of hormones and signaling molecules, proliferation, survival, apoptosis, luteinization, and ovulation. To exert these effects, gonadotropins bind to their respective Gs protein-coupled receptors, activating the protein kinase A (PKA) pathway or recruiting Gq proteins to activate protein kinase C (PKC) signaling. Although the action mechanism of FSH and LH is clear, recently, it has been shown that both gonadotropins promote the synthesis of sphingosine-1-phosphate (S1P) in granulosa and theca cells through the activation of sphingosine kinase 1. Moreover, the inhibition of SPHKs reduces S1P synthesis, cell viability, and the proliferation of follicular cells in response to gonadotropins, and the addition of S1P to the culture medium increases the proliferation of granulosa and theca cells without apparent effects on sexual steroid synthesis. Therefore, we consider that S1P is a crucial signaling molecule that complements the canonical gonadotropin pathway to promote the proliferation and viability of granulosa and theca cells.

Metabolomics reveals altered metabolites in cirrhotic patients with severe portal hypertension in Tibetan population

Background

Portal hypertension (PHT) presents a challenging issue of liver cirrhosis. This study aims to identify novel biomarkers for severe PHT (SPHT) and explore the pathophysiological mechanisms underlying PHT progression.

Methods

Twenty-three Tibetan cirrhotic patients who underwent hepatic venous pressure gradient (HVPG) measurement were included. Eleven patients had an HVPG between 5 mmHg and 15 mmHg (MPHT), while 12 had an HVPG ≥16 mmHg (SPHT). Peripheral sera were analyzed using liquid chromatograph-mass spectrometer for metabolomic assessment. An additional 14 patients were recruited for validation of metabolites.

Results

Seven hundred forty-five metabolites were detected and significant differences in metabolomics between MPHT and SPHT patients were observed. Employing a threshold of p < 0.05 and a variable importance in projection score >1, 153 differential metabolites were identified. A significant number of these metabolites were lipids and lipid-like molecules. Pisumionoside and N-decanoylglycine (N-DG) exhibited the highest area under the curve (AUC) values (0.947 and 0.9091, respectively). Additional differential metabolites with AUC >0.8 included 6-(4-ethyl-2-methoxyphenoxy)-3,4,5-trihydroxyoxane-2-carboxylic acid, sphinganine 1-phosphate, 4-hydroxytriazolam, 4,5-dihydroorotic acid, 6-hydroxy-1H-indole-3-acetamide, 7alpha-(thiomethyl)spironolactone, 6-deoxohomodolichosterone, glutaminylisoleucine, taurocholic acid 3-sulfate, and Phe Ser. Enzyme-linked immunosorbent assay further confirmed elevated levels of sphinganine 1-phosphate, N-DG, and serotonin in SPHT patients. Significant disruptions in linoleic acid, amino acid, sphingolipid metabolisms, and the citrate cycle were observed in SPHT patients.

Conclusion

Pisumionoside and N-DG are identified as promising biomarkers for SPHT. The progression of PHT may be associated with disturbances in lipid, linoleic acid, and amino acid metabolisms, as well as alterations in the citrate cycle.

The Effect of Etrasimod on Fecal Calprotectin and High-sensitivity C-reactive Protein: Results From the ELEVATE UC Clinical Program

BACKGROUND

Biomarkers offer potential alternatives to endoscopies in monitoring ulcerative colitis (UC) progression and therapeutic response. This post hoc analysis of the ELEVATE UC clinical program assessed potential predictive values of fecal calprotectin (fCAL) and high-sensitivity C-reactive protein (hsCRP) as biomarkers and associated responses to etrasimod, an oral, once-daily, selective sphingosine 1-phosphate (S1P)1,4,5 receptor modulator for the treatment of moderately to severely active UC, in 2 phase 3 clinical trials.

METHODS

In ELEVATE UC 52 and ELEVATE UC 12, patients were randomized 2:1 to 2 mg of etrasimod once daily or placebo for 52 or 12 weeks, respectively. Fecal calprotectin/hsCRP differences between responders and nonresponders for efficacy end points (clinical remission, clinical response, endoscopic improvement-histologic remission [EIHR]) were assessed by Wilcoxon P-values. Sensitivity and specificity were presented as receiver operating characteristics (ROC) curves with area under the curve (AUC).

RESULTS

In ELEVATE UC 52 and ELEVATE UC 12, 289 and 238 patients received etrasimod and 144 and 116 received placebo, respectively. Baseline fCAL/hsCRP concentrations were generally balanced. Both trials had lower week-12 median fCAL levels in week-12 responders vs nonresponders receiving etrasimod for clinical remission, clinical response, and EIHR (all P < .001), with similar trends for hsCRP levels (all P < .01). For etrasimod, AUCs for fCAL/hsCRP and EIHR were 0.85/0.74 (week 12; ELEVATE UC 52), 0.83/0.69 (week 52; ELEVATE UC 52), and 0.80/0.65 (week 12; ELEVATE UC 12).

CONCLUSIONS

Fecal calprotectin/hsCRP levels decreased with etrasimod treatment; ROC analyses indicated a prognostic correlation between fCAL changes during induction and short-/long-term treatment response.

Extracellular α-synuclein impairs sphingosine 1-phosphate receptor type 3 (S1PR3)-regulated lysosomal delivery of cathepsin D in HeLa cells

α-Synuclein (α-Syn)-positive intracellular fibrillar protein deposits, known as Lewy bodies, are thought to be involved in the pathogenesis of Parkinson's disease (PD). Although recent lines of evidence suggested that extracellular α-Syn secreted from pathogenic neurons contributes to the propagation of PD pathology, the precise mechanism of action remains unclear. We have reported that extracellular α-Syn caused sphingosine 1-phosphate (S1P) receptor type 1 (S1PR1) uncoupled from Gi and inhibited downstream G-protein signaling in SH-SY5Y cells, although its patho/physiological role remains to be clarified. Here we show that extracellular α-Syn caused S1P receptor type 3 (S1PR3) uncoupled from G protein in HeLa cells. Further studies indicated that α-Syn treatment reduced cathepsin D activity while enhancing the secretion of immature pro-cathepsin D into cell culture medium, suggesting that lysosomal delivery of cathepsin D was disturbed. Actually, extracellular α-Syn attenuated the retrograde trafficking of insulin-like growth factor-II/mannose 6-phosphate (IGF-II/M6P) receptor, which is under the regulation of S1PR3. These findings shed light on the understanding of dissemination of the PD pathology, that is, the mechanism underlying how extracellular α-Syn secreted from pathogenic cells causes lysosomal dysfunction of the neighboring healthy cells, leading to propagation of the disease.

The emerging roles of sphingosine 1-phosphate and SphK1 in cancer resistance: a promising therapeutic target

Cancer chemoresistance is a problematic dilemma that significantly restrains numerous cancer management protocols. It can promote cancer recurrence, spreading of cancer, and finally, mortality. Accordingly, enhancing the responsiveness of cancer cells towards chemotherapies could be a vital approach to overcoming cancer chemoresistance. Tumour cells express a high level of sphingosine kinase-1 (SphK1), which acts as a protooncogenic factor and is responsible for the synthesis of sphingosine-1 phosphate (S1P). S1P is released through a Human ATP-binding cassette (ABC) transporter to interact with other phosphosphingolipids components in the interstitial fluid in the tumor microenvironment (TME), provoking communication, progression, invasion, and tumor metastasis. Also, S1P is associated with several impacts, including anti-apoptotic behavior, metastasis, mesenchymal transition (EMT), angiogenesis, and chemotherapy resistance. Recent reports addressed high levels of S1P in several carcinomas, including ovarian, prostate, colorectal, breast, and HCC. Therefore, targeting the S1P/SphK signaling pathway is an emerging therapeutic approach to efficiently attenuate chemoresistance. In this review, we comprehensively discussed S1P functions, metabolism, transport, and signaling. Also, through a bioinformatic framework, we pointed out the alterations of SphK1 gene expression within different cancers with their impact on patient survival, and we demonstrated the protein-protein network of SphK1, elaborating its sparse roles. Furthermore, we made emphasis on different machineries of cancer resistance and the tight link with S1P. We evaluated all publicly available SphK1 inhibitors and their inhibition activity using molecular docking and how SphK1 inhibitors reduce the production of S1P and might reduce chemoresistance, an approach that might be vital in the course of cancer treatment and prognosis.

The need for paradigm shift: prognostic significance and implications of standard therapy-related systemic immunosuppression in glioblastoma for immunotherapy and oncolytic virotherapy

Despite significant advances in our knowledge regarding the genetics and molecular biology of gliomas over the past two decades and hundreds of clinical trials, no effective therapeutic approach has been identified for adult patients with newly diagnosed glioblastoma, and overall survival remains dismal. Great hopes are now placed on combination immunotherapy. In clinical trials, immunotherapeutics are generally tested after standard therapy (radiation, temozolomide, and steroid dexamethasone) or concurrently with temozolomide and/or steroids. Only a minor subset of patients with progressive/recurrent glioblastoma have benefited from immunotherapies. In this review, we comprehensively discuss standard therapy-related systemic immunosuppression and lymphopenia, their prognostic significance, and the implications for immunotherapy/oncolytic virotherapy. The effectiveness of immunotherapy and oncolytic virotherapy (viro-immunotherapy) critically depends on the activity of the host immune cells. The absolute counts, ratios, and functional states of different circulating and tumor-infiltrating immune cell subsets determine the net immune fitness of patients with cancer and may have various effects on tumor progression, therapeutic response, and survival outcomes. Although different immunosuppressive mechanisms operate in patients with glioblastoma/gliomas at presentation, the immunological competence of patients may be significantly compromised by standard therapy, exacerbating tumor-related systemic immunosuppression. Standard therapy affects diverse immune cell subsets, including dendritic, CD4+, CD8+, natural killer (NK), NKT, macrophage, neutrophil, and myeloid-derived suppressor cell (MDSC). Systemic immunosuppression and lymphopenia limit the immune system's ability to target glioblastoma. Changes in the standard therapy are required to increase the success of immunotherapies. Steroid use, high neutrophil-to-lymphocyte ratio (NLR), and low post-treatment total lymphocyte count (TLC) are significant prognostic factors for shorter survival in patients with glioblastoma in retrospective studies; however, these clinically relevant variables are rarely reported and correlated with response and survival in immunotherapy studies (e.g., immune checkpoint inhibitors, vaccines, and oncolytic viruses). Our analysis should help in the development of a more rational clinical trial design and decision-making regarding the treatment to potentially improve the efficacy of immunotherapy or oncolytic virotherapy.

A decade of USFDA-approved small molecules as anti-inflammatory agents: Recent trends and Commentaries on the "industrial" perspective

Inflammation is the human body's defence process against various pathogens, toxic substances, irradiation, and physically injured cells that have been damaged. Inflammation is characterized by swelling, pain, redness, heat, as well as diminished tissue function. Multiple important inflammatory markers determine the prognosis of inflammatory processes, which include likes of pro-inflammatory cytokines which are controlled by nuclear factor kappa-B (NF-kB), mitogen-activated protein kinase (MAPK), Janus kinase signal transducer and activator of transcription (JAK-STAT) pathway, all of which are activated in response to the stimulation of specific receptors. Besides these, the cyclooxygenase (COX) enzyme family also plays a significant role in inflammation. The current review is kept forth to compile a summary of small molecules-based drugs approved by the USFDA during the study period of 2013-2023. A thorough discussion has also been made to focus on biologics, macromolecules, and small chemical entities approved during this study period and their greener synthetic routes with a brief discussion on the chemical spacing parameters of anti-inflammatory drugs. The compilation is expected to assist the medicinal chemist and the scientist actively engaged in drug discovery and development of anti-inflammatory agents from newer perspectives during the current years.

S1PR2 inhibition mitigates cognitive deficit in diabetic mice by modulating microglial activation via Akt-p53-TIGAR pathway

Cognitive deficit is one of the challenging complications of type 2 diabetes. Sphingosine 1- phosphate receptors (S1PRs) have been implicated in various neurodegenerative and metabolic disorders. The association of S1PRs and cognition in type 2 diabetes remains elusive. Microglia-mediated neuronal damage could be the thread propagating cognitive deficit. The effects of S1PR2 inhibition on cognition in high-fat diet and streptozotocin-induced diabetic mice were examined in this work. We further assessed microglial activation and putative microglial polarisation routes. Cognitive function loss was observed after four months of diabetes induction in Type 2 diabetes animal model. JTE013, an S1PR2 inhibitor, was used to assess neuroprotection against cognitive decline and neuroinflammation in vitro and in vivo diabetes model. JTE013 (10 mg/kg) improved synaptic plasticity by upregulating psd95 and synaptophysin while reducing cognitive decline and neuroinflammation. It further enhanced anti-inflammatory microglia in the hippocampus and prefrontal cortex (PFC), as evidenced by increased Arg-1, CD206, and YM-1 levels and decreased iNOS, CD16, and MHCII levels. TIGAR, TP53-induced glycolysis and apoptosis regulator, might facilitate the anti-inflammatory microglial phenotype by promoting oxidative phosphorylation and decreasing apoptosis. However, since p53 is a TIGAR suppressor, inhibiting p53 could be beneficial. S1PR2 inhibition increased p-Akt and TIGAR levels and reduced the levels of p53 in the PFC and hippocampus of type 2 diabetic mice, thereby decreasing apoptosis. In vitro, palmitate was used to imitate sphingolipid dysregulation in BV2 cells, followed by conditioned media exposure to Neuro2A cells. JTE013 rescued the palmitate-induced neuronal apoptosis by promoting the anti-inflammatory microglia. In the present study, we demonstrate that the inhibition of S1PR2 improves cognitive function and skews microglia toward anti-inflammatory phenotype in type 2 diabetic mice, thereby promising to be a potential therapy for neuroinflammation.

Targeting Farnesoid X Receptor in Tumor and the Tumor Microenvironment: Implication for Therapy

The farnesoid-X receptor (FXR), a member of the nuclear hormone receptor superfamily, can be activated by bile acids (BAs). BAs binding to FXR activates BA signaling which is important for maintaining BA homeostasis. FXR is differentially expressed in human organs and exists in immune cells. The dysregulation of FXR is associated with a wide range of diseases including metabolic disorders, inflammatory diseases, immune disorders, and malignant neoplasm. Recent studies have demonstrated that FXR influences tumor cell progression and development through regulating oncogenic and tumor-suppressive pathways, and, moreover, it affects the tumor microenvironment (TME) by modulating TME components. These characteristics provide a new perspective on the FXR-targeted therapeutic strategy in cancer. In this review, we have summarized the recent research data on the functions of FXR in solid tumors and its influence on the TME, and discussed the mechanisms underlying the distinct function of FXR in various types of tumors. Additionally, the impacts on the TME by other BA receptors such as takeda G protein-coupled receptor 5 (TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and muscarinic receptors (CHRM2 and CHRM3), have been depicted. Finally, the effects of FXR agonists/antagonists in a combination therapy with PD1/PD-L1 immune checkpoint inhibitors and other anti-cancer drugs have been addressed.

The Implication of Sphingolipids in Viral Infections

Sphingolipids are involved in cell signaling and metabolic pathways, and their metabolites play a critical role in host defense against intracellular pathogens. Here, we review the known mechanisms of sphingolipids in viral infections and discuss the potential implication of the study of sphingolipid metabolism in vaccine and therapeutic development.

Sphingosine 1-Phosphate Lyase in the Developing and Injured Nervous System: a Dichotomy?

Sphingosine 1-phosphate lyase (SPL) is the terminal enzyme that controls the degradation of the bioactive lipid sphingosine 1-phosphate (S1P) within an interconnected sphingolipid metabolic network. The unique metabolic position of SPL in maintaining S1P levels implies SPL could be an emerging new therapeutic target. Over the past decade, an evolving effort has been made to unravel the role of SPL in the nervous system; however, to what extent SPL influences the developing and mature nervous system through altering S1P biosynthesis remains opaque. While congenital SPL deletion is associated with deficits in the developing nervous system, the loss of SPL activity in adults appears to be neuroprotective in acquired neurological disorders. The controversial findings concerning SPL's role in the nervous system are further constrained by the current genetic and pharmacological tools. This review attempts to focus on the multi-faceted nature of SPL function in the mammalian nervous systems, implying its dichotomy in the developing and adult central nervous system (CNS). This article also highlights SPL is emerging as a therapeutic molecule that can be selectively targeted to modulate S1P for the treatment of acquired neurodegenerative diseases, raising new questions for future investigation. The development of cell-specific inducible conditional SPL mutants and selective pharmacological tools will allow the precise understanding of SPL's function in the adult CNS, which will aid the development of a new strategy focusing on S1P-based therapies for neuroprotection.

Factor VIIa releases phosphatidylserine-enriched extracellular vesicles from endothelial cells by activating acid sphingomyelinase

BACKGROUND

Our recent studies showed that activated factor (F) VII (FVIIa) releases extracellular vesicles (EVs) from the endothelium. FVIIa-released EVs were found to be enriched with phosphatidylserine (PS) and contribute to the hemostatic effect of FVIIa in thrombocytopenia and hemophilia.

OBJECTIVE

To investigate mechanisms by which FVIIa induces EV biogenesis and enriches EVs with PS.

METHODS

FVIIa activation of acid sphingomyelinase (aSMase) was evaluated by its translocation to the cell surface. The role of aSMase in the biogenesis of FVIIa-induced EVs and their enrichment with PS was investigated using specific siRNAs and inhibitors of aSMase and its downstream metabolites. Wild-type and aSMase-/- mice were injected with a control vehicle or FVIIa. EVs released into circulation were quantified by nanoparticle tracking analysis. EVs hemostatic potential was assessed in a murine thrombocytopenia model.

RESULTS

FVIIa activation of aSMase is responsible for both the externalization of PS and the release of EVs in endothelial cells. FVIIa-induced aSMase activation led to ceramide generation and de novo expression of transmembrane protein 16F. Inhibitors of ceramidases, sphingosine kinase, or sphingosine-1-phosphate receptor modulator blocked FVIIa-induced expression of transmembrane protein 16F and PS externalization without interfering with FVIIa release of EVs. In vivo, FVIIa release of EVs was markedly impaired in aSMase-/- mice compared with wild-type mice. Administration of a low dose of FVIIa, sufficient to induce EVs release, corrected bleeding associated with thrombocytopenia in wild-type mice but not in aSMase-/- mice.

CONCLUSION

Our study identifies a novel mechanism by which FVIIa induces PS externalization and releases PS-enriched EVs.

The Role of Sphingosine-1-Phosphate Receptor 2 in Mouse Retina Light Responses

The bioactive sphingolipid sphingosine-1-phosphate (S1P) acts as a ligand for a family of G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways. However, their specific roles in the neural retina remain unclear. We previously showed that S1P receptor subtype 2 (S1PR2) is expressed in murine retinas, primarily in photoreceptors and bipolar cells, and its expression is altered by retinal stress. This study aims to elucidate the role of S1PR2 in the mouse retina. We examined light responses by electroretinography (ERG), structural differences by optical coherence tomography (OCT), and protein levels by immunohistochemistry (IHC) in wild-type (WT) and S1PR2 knockout (KO) mice at various ages between 3 and 6 months. We found that a- and b-wave responses significantly increased at flash intensities between 400~2000 and 4~2000 cd.s/m2, respectively, in S1PR2 KO mice relative to those of WT controls at baseline. S1PR2 KO mice also exhibited significantly increased retinal nerve fiber layer (RNFL) and outer plexiform layer (OPL) thickness by OCT relative to the WT. Finally, in S1PR2 KO mice, we observed differential labeling of synaptic markers by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (RT-qPCR). These results suggest a specific involvement of S1PR2 in the structure and synaptic organization of the retina and a potential role in light-mediated functioning of the retina.

S1P/S1PR signaling pathway advancements in autoimmune diseases

Sphingosine-1-phosphate (S1P) is a versatile sphingolipid that is generated through the phosphorylation of sphingosine by sphingosine kinase (SPHK). S1P exerts its functional effects by binding to the G protein-coupled S1P receptor (S1PR). This lipid mediator plays a pivotal role in various cellular activities. The S1P/S1PR signaling pathway is implicated in the pathogenesis of immune-mediated diseases, significantly contributing to the functioning of the immune system. It plays a crucial role in diverse physiological and pathophysiological processes, including cell survival, proliferation, migration, immune cell recruitment, synthesis of inflammatory mediators, and the formation of lymphatic and blood vessels. However, the full extent of the involvement of this signaling pathway in the development of autoimmune diseases remains to be fully elucidated. Therefore, this study aims to comprehensively review recent research on the S1P/S1PR axis in diseases related to autoimmunity.

Receptor-dependent effects of sphingosine-1-phosphate (S1P) in COVID-19: the black side of the moon

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection leads to hyper-inflammation and amplified immune response in severe cases that may progress to cytokine storm and multi-organ injuries like acute respiratory distress syndrome and acute lung injury. In addition to pro-inflammatory cytokines, different mediators are involved in SARS-CoV-2 pathogenesis and infection, such as sphingosine-1-phosphate (S1P). S1P is a bioactive lipid found at a high level in plasma, and it is synthesized from sphingomyelin by the action of sphingosine kinase. It is involved in inflammation, immunity, angiogenesis, vascular permeability, and lymphocyte trafficking through G-protein coupled S1P receptors. Reduction of the circulating S1P level correlates with COVID-19 severity. S1P binding to sphingosine-1-phosphate receptor 1 (S1PR1) elicits endothelial protection and anti-inflammatory effects during SARS-CoV-2 infection, by limiting excessive INF-α response and hindering mitogen-activated protein kinase and nuclear factor kappa B action. However, binding to S1PR2 opposes the effect of S1PR1 with vascular inflammation, endothelial permeability, and dysfunction as the concomitant outcome. This binding also promotes nod-like receptor pyrin 3 (NLRP3) inflammasome activation, causing liver inflammation and fibrogenesis. Thus, higher expression of macrophage S1PR2 contributes to the activation of the NLRP3 inflammasome and the release of pro-inflammatory cytokines. In conclusion, S1PR1 agonists and S1PR2 antagonists might effectively manage COVID-19 and its severe effects. Further studies are recommended to elucidate the potential conflict in the effects of S1P in COVID-19.

Transcriptional suppression of sphingolipid catabolism controls pathogen resistance in C. elegans

Sphingolipids are required for diverse biological functions and are degraded by specific catabolic enzymes. However, the mechanisms that regulate sphingolipid catabolism are not known. Here we characterize a transcriptional axis that regulates sphingolipid breakdown to control resistance against bacterial infection. From an RNAi screen for transcriptional regulators of pathogen resistance in the nematode C. elegans, we identified the nuclear hormone receptor nhr-66, a ligand-gated transcription factor homologous to human hepatocyte nuclear factor 4. Tandem chromatin immunoprecipitation-sequencing and RNA sequencing experiments revealed that NHR-66 is a transcriptional repressor, which directly targets sphingolipid catabolism genes. Transcriptional de-repression of two sphingolipid catabolic enzymes in nhr-66 loss-of-function mutants drives the breakdown of sphingolipids, which enhances host susceptibility to infection with the bacterial pathogen Pseudomonas aeruginosa. These data define transcriptional control of sphingolipid catabolism in the regulation of cellular sphingolipids, a process that is necessary for pathogen resistance.

The role of sphingosine-1-phosphate receptor 2 in mouse retina light responses

The bioactive sphingolipid sphingosine-1-phosphate (S1P) acts as a ligand for a family of G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways. However, their specific roles in the neural retina remain unclear. We previously showed that S1P receptor subtype 2 (S1PR2) is expressed in murine retinas, primarily in photoreceptors and bipolar cells, and its expression is altered by retinal stress. This study aims to elucidate the role of S1PR2 in the mouse retina. We examined light responses by electroretinography (ERG), structural differences by optical coherence tomography (OCT), and protein levels by immunohistochemistry (IHC) in wild-type (WT) and S1PR2 knockout (KO) mice at various ages between 3 and 6 months. We found that a- and b-wave responses significantly increased at flash intensities between 400∼2000 and 4∼2,000 cd.s/m 2 respectively, in S1PR2 KO mice relative to those of WT controls at baseline. S1PR2 KO mice also exhibited significantly increased retinal nerve fiber layer (RNFL) and outer plexiform layer (OPL) thickness by OCT relative to the WT. Finally, in S1PR2 KO mice, we observed differential labeling of synaptic markers by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (RT-qPCR). These results suggest a specific involvement of S1PR2 in the structure and synaptic organization of the retina and a potential role in light-mediated functioning of the retina.

A Preliminary Study of Pharmacokinetics and Pharmacodynamics of Oral Fingolimod in Dogs

BACKGROUND/AIM

Fingolimod is a sphingosine-1-phosphate receptor modulator that prevents lymphocytes egress from lymphoid organs. It has been used as a disease-modifying drug for human multiple sclerosis and has shown better therapeutic effects than other conventional therapies. Therefore, this study was performed to obtain preclinical data of fingolimod in dogs.

MATERIALS AND METHODS

Nine laboratory Beagle dogs were used and randomized into three groups for pharmacokinetics (PK) and pharmacodynamics (PD). The dogs were administered once with a low-dose (0.01 mg/kg, n=3), medium-dose (0.05 mg/kg, n=3), and high-dose (0.1 mg/kg, n=3) of fingolimod, orally. Samples were collected serially at predetermined time points, and whole blood fingolimod concentrations were measured using high-performance liquid chromatography-mass spectrometry. Differential counts of leukocytes over time were determined to identify immune cells' response to fingolimod.

RESULTS

Regarding PK, the concentration of fingolimod in the blood increased in a dose-dependent manner, but it was not proportional. Regarding PD, the number of lymphocytes significantly decreased compared to baseline in all dose groups (low-dose, p=0.0002; medium-dose, p<0.0001; high-dose, p=0.0012). Eosinophils were significantly reduced in low- (p=0.0006) and medium- (p=0.0006) doses, and neutrophils were also significantly reduced in medium-(p=0.0345) and high- (p=0.0016) doses.

CONCLUSION

This study provides the basis for future clinical applications of fingolimod in dogs with immune-mediated diseases, such as meningoencephalitis of unknown etiology.

Immune System and Brain/Intestinal Barrier Functions in Psychiatric Diseases: Is Sphingosine-1-Phosphate at the Helm?

Over the past few decades, extensive research has shed light on immune alterations and the significance of dysfunctional biological barriers in psychiatric disorders. The leaky gut phenomenon, intimately linked to the integrity of both brain and intestinal barriers, may play a crucial role in the origin of peripheral and central inflammation in these pathologies. Sphingosine-1-phosphate (S1P) is a bioactive lipid that regulates both the immune response and the permeability of biological barriers. Notably, S1P-based drugs, such as fingolimod and ozanimod, have received approval for treating multiple sclerosis, an autoimmune disease of the central nervous system (CNS), and ulcerative colitis, an inflammatory condition of the colon, respectively. Although the precise mechanisms of action are still under investigation, the effectiveness of S1P-based drugs in treating these pathologies sparks a debate on extending their use in psychiatry. This comprehensive review aims to delve into the molecular mechanisms through which S1P modulates the immune system and brain/intestinal barrier functions. Furthermore, it will specifically focus on psychiatric diseases, with the primary objective of uncovering the potential of innovative therapies based on S1P signaling.

Platelet-derived factors dysregulate placental sphingosine-1-phosphate receptor 2 in human trophoblasts

RESEARCH QUESTION

Sphingosine-1-phosphate (S1P) is an essential and bioactive sphingolipid with various functions, which acts through five different G-protein-coupled receptors (S1PR1-5). What is the localization of S1PR1-S1PR3 in the human placenta and what is the effect of different flow rates, various oxygen concentrations and platelet-derived factors on the expression profile of S1PR in trophoblasts?

DESIGN

Expression dynamics of placental S1PR1-S1PR3 were determined in human first trimester (n = 10), pre-term (n = 9) and term (n = 10) cases. Furthermore, the study investigated the expression of these receptors in different primary cell types isolated from human placenta, verified the findings with publicly available single-cell RNA-Seq data from first trimester and immunostaining of human first trimester and term placentas. The study also tested whether the placental S1PR subtypes are dysregulated in differentiated BeWo cells under different flow rates, different oxygen concentrations or in the presence of platelet-derived factors.

RESULTS

Quantitative polymerase chain reaction revealed that S1PR2 is the predominant placental S1PR in the first trimester and reduces towards term (P < 0.0001). S1PR1 and S1PR3 increased from first trimester towards term (P < 0.0001). S1PR1 was localized in endothelial cells, whereas S1PR2 and S1PR3 were predominantly found in villous trophoblasts. Furthermore, S1PR2 was found to be significantly down-regulated in BeWo cells when co-incubated with platelet-derived factors (P = 0.0055).

CONCLUSION

This study suggests that the placental S1PR repertoire is differentially expressed across gestation. S1PR2 expression in villous trophoblasts is negatively influenced by platelet-derived factors, which could contribute to down-regulation of placental S1PR2 over time of gestation as platelet presence and activation in the intervillous space increases from the middle of the first trimester onwards.

New therapeutic concepts against ischemia-reperfusion injury in organ transplantation

INTRODUCTION

Ischemia-reperfusion injury (IRI) involves a positive amplification feedback loop that stimulates innate immune-driven tissue damage associated with organ procurement from deceased donors and during transplantation surgery. As our appreciation of its basic immune mechanisms has improved in recent years, translating putative biomarkers into therapeutic interventions in clinical transplantation remains challenging.

AREAS COVERED

This review presents advances in translational/clinical studies targeting immune responses to reactive oxygen species in IRI-stressed solid organ transplants, especially livers. Here we focus on novel concepts to rejuvenate suboptimal donor organs and improve transplant function using pharmacologic and machine perfusion (MP) strategies. Cellular damage induced by cold ischemia/warm reperfusion and the latest mechanistic insights into the microenvironment's role that leads to reperfusion-induced sterile inflammation is critically discussed.

EXPERT OPINION

Efforts to improve clinical outcomes and increase the donor organ pool will depend on improving donor management and our better appreciation of the complex mechanisms encompassing organ IRI that govern the innate-adaptive immune interface triggered in the peritransplant period and subsequent allo-Ag challenge. Computational techniques and deep machine learning incorporating the vast cellular and molecular mechanisms will predict which peri-transplant signals and immune interactions are essential for improving access to the long-term function of life-saving transplants.

S1P/S1PR1 axis promotes macrophage M1 polarization through NLRP3 inflammasome activation in Lupus nephritis

Lupus nephritis (LN) is a common complication of systemic lupus erythematosus (SLE) as well as the leading cause of mortality in patients. Previous studies revealed that S1P level is elevated in plasma samples of SLE patients and murine lupus models. FTY720, targeting S1P receptors, exhibited therapeutic effects in improving the nephritis symptoms of lupus mouse models. However, few studies have discussed the potential relevance of S1P/S1PR to the pathogenesis of LN. Macrophages have been shown to be an important causative agent of renal inflammation, while the pro-inflammatory M1-type promotes kidney injury and inflammation during LN. Importantly, macrophages express various S1P receptors, and how they respond to S1P in the setting of LN remains unclear. Therefore, we examined the level of S1P in the lupus MRL/lpr mice and explored the ensuing interaction of macrophages and S1P. We found that S1P level was elevated in the MRL/lpr mice with a subsequent enhancement of the S1PR1 expression, and blocking S1PR1 by FTY720, the nephritis symptoms of MRL/lpr mice were improved. Mechanistically, we demonstrated that elevated S1P level increase the M1-type macrophage accumulation. And the in-vitro studies proved that S1P/S1PR1 was involved in the promotion of macrophage polarization towards M1 type through activation of NLRP3 inflammasome. These findings confer a novel role to macrophage S1PR1 and provide a new perspective for targeting S1P during LN.

FTY720 in immuno-regenerative and wound healing technologies for muscle, epithelial and bone regeneration

In 2010, the FDA approved the administration of FTY720, S1P lipid mediator, as a therapy to treat relapsing forms of multiple sclerosis. FTY720 was found to sequester pro-inflammatory lymphocytes within the lymph node, preventing them from causing injury to the central nervous system due to inflammation. Studies harnessing the anti-inflammatory properties of FTY720 as a pro-regenerative strategy in wound healing of muscle, bone and mucosal injuries are currently being performed. This in-depth review discusses the current regenerative impact of FTY720 due to its anti-inflammatory effect stratified into an assessment of wound regeneration in the muscular, skeletal, and epithelial systems. The regenerative effect of FTY720 in vivo was characterized in three animal models, with differing delivery mechanisms emerging in the last 20 years. In these studies, local delivery of FTY720 was found to increase pro-regenerative immune cell phenotypes (neutrophils, macrophages, monocytes), vascularization, cell proliferation and collagen deposition. Delivery of FTY720 to a localized wound environment demonstrated increased bone, muscle, and mucosal regeneration through changes in gene and cytokine production primarily by controlling the local immune cell phenotypes. These changes in gene and cytokine production reduced the inflammatory component of wound healing and increased the migration of pro-regenerative cells (neutrophils and macrophages) to the wound site. The application of FTY720 delivery using a biomaterial has demonstrated the ability of local delivery of FTY720 to promote local wound healing leveraging an immunomodulatory mechanism.

Modulating sphingosine 1-phosphate receptor signaling skews intrahepatic leukocytes and attenuates murine nonalcoholic steatohepatitis

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid associated with nonalcoholic steatohepatitis (NASH). Immune cell-driven inflammation is a key determinant of NASH progression. Macrophages, monocytes, NK cells, T cells, NKT cells, and B cells variably express S1P receptors from a repertoire of 5 receptors termed S1P1 - S1P5. We have previously demonstrated that non-specific S1P receptor antagonism ameliorates NASH and attenuates hepatic macrophage accumulation. However, the effect of S1P receptor antagonism on additional immune cell populations in NASH remains unknown. We hypothesized that S1P receptor specific modulation may ameliorate NASH by altering leukocyte recruitment. A murine NASH model was established by dietary feeding of C57BL/6 male mice with a diet high in fructose, saturated fat, and cholesterol (FFC) for 24 weeks. In the last 4 weeks of dietary feeding, the mice received the S1P1,4,5 modulator Etrasimod or the S1P1 modulator Amiselimod, daily by oral gavage. Liver injury and inflammation were determined by histological and gene expression analyses. Intrahepatic leukocyte populations were analyzed by flow cytometry, immunohistochemistry, and mRNA expression. Alanine aminotransferase, a sensitive circulating marker for liver injury, was reduced in response to Etrasimod and Amiselimod treatment. Liver histology showed a reduction in inflammatory foci in Etrasimod-treated mice. Etrasimod treatment substantially altered the intrahepatic leukocyte populations through a reduction in the frequency of T cells, B cells, and NKT cells and a proportional increase in CD11b+ myeloid cells, polymorphonuclear cells, and double negative T cells in FFC-fed and control standard chow diet (CD)-fed mice. In contrast, FFC-fed Amiselimod-treated mice showed no changes in the frequencies of intrahepatic leukocytes. Consistent with the improvement in liver injury and inflammation, hepatic macrophage accumulation and the gene expression of proinflammatory markers such as Lgals3 and Mcp-1 were decreased in Etrasimod-treated FFC-fed mice. Etrasimod treated mouse livers demonstrated an increase in non-inflammatory (Marco) and lipid associated (Trem2) macrophage markers. Thus, S1P1,4,5 modulation by Etrasimod is more effective than S1P1 antagonism by Amiselimod, at the dose tested, in ameliorating NASH, likely due to the alteration of leukocyte trafficking and recruitment. Etrasimod treatment results in a substantial attenuation of liver injury and inflammation in murine NASH.

Sphingosine Kinases Promote Ebola Virus Infection and Can Be Targeted to Inhibit Filoviruses, Coronaviruses, and Arenaviruses Using Late Endocytic Trafficking to Enter Cells

Entry of enveloped viruses in host cells requires the fusion of viral and host cell membranes, a process that is facilitated by viral fusion proteins protruding from the viral envelope. These viral fusion proteins need to be triggered by host factors, and for some viruses, this event occurs inside endosomes and/or lysosomes. Consequently, these 'late-penetrating viruses' must be internalized and delivered to entry-conducive intracellular vesicles. Because endocytosis and vesicular trafficking are tightly regulated cellular processes, late-penetrating viruses also depend on specific host proteins for efficient delivery to the site of fusion, suggesting that these could be targeted for antiviral therapy. In this study, we investigated a role for sphingosine kinases (SKs) in viral entry and found that chemical inhibition of sphingosine kinase 1 (SK1) and/or SK2 and knockdown of SK1/2 inhibited entry of Ebola virus (EBOV) into host cells. Mechanistically, inhibition of SK1/2 prevented EBOV from reaching late-endosomes and lysosomes that contain the EBOV receptor, Niemann Pick C1 (NPC1). Furthermore, we present evidence that suggests that the trafficking defect caused by SK1/2 inhibition occurs independently of sphingosine-1-phosphate (S1P) signaling through cell-surface S1P receptors. Lastly, we found that chemical inhibition of SK1/2 prevents entry of other late-penetrating viruses, including arenaviruses and coronaviruses, and inhibits infection by replication-competent EBOV and SARS-CoV-2 in Huh7.5 cells. In sum, our results highlight an important role played by SK1/2 in endocytic trafficking, which can be targeted to inhibit entry of late-penetrating viruses and could serve as a starting point for the development of broad-spectrum antiviral therapeutics.

Single-tailed heterocyclic carboxamide lipids for macrophage immune-modulation

The discovery of new immune-modulating biomaterials is of significant value to immuno-engineering and therapy development. Here, we discovered that single-tailed heterocyclic carboxamide lipids preferentially modulated macrophages - but not dendritic cells - by interfering with sphingosine-1-phosphate-related pathways, consequently increasing interferon alpha expression. We further performed extensive downstream correlation analysis and determined key factors in physicochemical properties likely to modulate pro-inflammatory and anti-inflammatory immune responses. These properties will be useful for the rational design of the next generation of cell type-specific immune-modulating lipids.

S1PR1 modulators in multiple sclerosis: Efficacy, safety, comparison, and chemical structure insights

Multiple sclerosis (MS) is a neurological disease that leads to severe physical and cognitive disabilities. Drugs used in the treatment of MS vary from small synthetic molecules to large macromolecules such as antibodies. Sphingosine 1-phosphate receptor modulators are frequently used for the treatment of MS. These medicines prevent the egress of lymphocytes from secondary lymphoid organs leading to immune system suppression. Currently, four S1PR modulators are on the market and several potential drug candidates are in clinical trials for the treatment of MS. These compounds differ in chemical structure, adverse effects, and efficacy points of view. The current article reviews the latest studies on S1PR1 modulators and compares them with other MS drugs in terms of efficacy, tolerability, and safety. A special focus was dedicated to discussing the structure-activity relationships of these compounds and performing a three-dimensional quantitative structure-activity relationship (3D-QSAR) analysis to gain better insight into the ligand-receptor interaction mode.

Etrasimod as induction and maintenance therapy for ulcerative colitis (ELEVATE): two randomised, double-blind, placebo-controlled, phase 3 studies

BACKGROUND

Etrasimod, a once-daily, oral, sphingosine 1-phosphate (S1P) receptor modulator that selectively activates S1P receptor subtypes 1, 4, and 5, with no detectable activity on S1P_2,3, is in development for the treatment of immune-mediated diseases, including ulcerative colitis. In these two phase 3 trials, we aimed to evaluate the safety and efficacy of etrasimod in adult patients with moderately to severely active ulcerative colitis.

METHODS

In two independent randomised, multicentre, double-blind, placebo-controlled, phase 3 trials, ELEVATE UC 52 and ELEVATE UC 12, adults with active moderate-to-severe ulcerative colitis and an inadequate or loss of response or intolerance to at least one approved ulcerative colitis therapy were randomly assigned (2:1) to once-daily oral etrasimod 2 mg or placebo. Patients in ELEVATE UC 52 were enrolled from 315 centres in 40 countries. Patients in ELEVATE UC 12 were enrolled from 407 centres in 37 countries. Randomisation was stratified by previous exposure to biologicals or Janus kinase inhibitor therapy (yes vs no), baseline corticosteroid use (yes vs no), and baseline disease activity (modified Mayo score [MMS]; 4-6 vs 7-9). ELEVATE UC 52 comprised a 12-week induction period followed by a 40-week maintenance period with a treat-through design. ELEVATE UC 12 independently assessed induction at week 12. The primary efficacy endpoints were the proportion of patients with clinical remission at weeks 12 and 52 in ELEVATE UC 52 and week 12 in ELEVATE UC 12. Safety was evaluated in both trials. ELEVATE UC 52 and ELEVATE UC 12 were registered with ClinicalTrials.gov, NCT03945188 and NCT03996369, respectively.

FINDINGS

Patients in ELEVATE UC 52 were enrolled between June 13, 2019, and Jan 28, 2021. Patients in ELEVATE UC 12 were enrolled between Sept 15, 2020, and Aug 12, 2021. ELEVATE UC 52 and ELEVATE UC 12 screened 821 patients and 606 patients, respectively, with 433 and 354 subsequently undergoing random assignment. The full analysis set of ELEVATE UC 52 comprised 289 patients assigned to etrasimod and 144 to placebo. In ELEVATE UC 12, 238 patients were assigned to etrasimod and 116 to placebo. In ELEVATE UC 52, a significantly greater proportion of patients in the etrasimod group achieved clinical remission compared with patients in the placebo group at completion of the 12-week induction period (74 [27%] of 274 patients vs ten [7%] of 135 patients; p<0·0001) and at week 52 (88 [32%] of 274 patients vs nine [7%] of 135 patients; p<0·0001). In ELEVATE UC 12, 55 (25%) of 222 patients in the etrasimod group had clinical remission compared with 17 (15%) of 112 patients in the placebo group at the end of the 12-week induction period (p=0·026). Adverse events were reported in 206 (71%) of 289 patients in the etrasimod group and 81 (56%) of 144 patients in the placebo group in ELEVATE UC 52 and 112 (47%) of 238 patients in the etrasimod group and 54 (47%) of 116 patients in the placebo group in ELEVATE UC 12. No deaths or malignancies were reported.

INTERPRETATION

Etrasimod was effective and well tolerated as an induction and maintenance therapy in patients with moderately to severely active ulcerative colitis. Etrasimod is a treatment option with a unique combination of attributes that might address the persistent unmet needs of patients with ulcerative colitis.

FUNDING

Arena Pharmaceuticals.

Neutrophil CEACAM1 determines susceptibility to NETosis by regulating the S1PR2/S1PR3 axis in liver transplantation

Neutrophils, the largest innate immune cell population in humans, are the primary proinflammatory sentinel in the ischemia-reperfusion injury (IRI) mechanism in orthotopic liver transplantation (OLT). Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1, CC1, or CD66a) is essential in neutrophil activation and serves as a checkpoint regulator of innate immune-driven IRI cascade in OLT. Although CC1 alternative splicing generates two functionally distinct short and long cytoplasmic isoforms, their role in neutrophil activation remains unknown. Here, we undertook molecular and functional studies to interrogate the significance of neutrophil CC1 signaling in mouse and human OLT recipients. In the experimental arm, we employed a mouse OLT model to document that ablation of recipient-derived neutrophil CC1-long (CC1-L) isotype aggravated hepatic IRI by promoting neutrophil extracellular traps (NETs). Notably, by regulating the S1P-S1PR2/S1PR3 axis, neutrophil CC1-L determined susceptibility to NET formation via autophagy signaling. In the clinical arm, liver grafts from 55 transplant patients selectively enriched for neutrophil CC1-L showed relative resistance to ischemia-reperfusion (IR) stress/tissue damage, improved hepatocellular function, and clinical outcomes. In conclusion, despite neutrophils being considered a principal villain in peritransplant tissue injury, their CC1-L isoform may serve as a regulator of IR stress resistance/NETosis in human and mouse OLT recipients.

Sphingosine-1-Phosphate Recruits Macrophages and Microglia and Induces a Pro-Tumorigenic Phenotype That Favors Glioma Progression

Glioblastoma is the most aggressive brain tumor in adults. Treatment failure is predominantly caused by its high invasiveness and its ability to induce a supportive microenvironment. As part of this, a major role for tumor-associated macrophages/microglia (TAMs) in glioblastoma development was recognized. Phospholipids are important players in various fundamental biological processes, including tumor-stroma crosstalk, and the bioactive lipid sphingosine-1-phosphate (S1P) has been linked to glioblastoma cell proliferation, invasion, and survival. Despite the urgent need for better therapeutic approaches, novel strategies targeting sphingolipids in glioblastoma are still poorly explored. Here, we showed that higher amounts of S1P secreted by glioma cells are responsible for an active recruitment of TAMs, mediated by S1P receptor (S1PR) signaling through the modulation of Rac1/RhoA. This resulted in increased infiltration of TAMs in the tumor, which, in turn, triggered their pro-tumorigenic phenotype through the inhibition of NFkB-mediated inflammation. Gene set enrichment analyses showed that such an anti-inflammatory microenvironment correlated with shorter survival of glioblastoma patients. Inhibition of S1P restored a pro-inflammatory phenotype in TAMs and resulted in increased survival of tumor-bearing mice. Taken together, our results establish a crucial role for S1P in fine-tuning the crosstalk between glioma and infiltrating TAMs, thus pointing to the S1P-S1PR axis as an attractive target for glioma treatment.

Prolonged hypernutrition impairs TREM2-dependent efferocytosis to license chronic liver inflammation and NASH development

Obesity-induced chronic liver inflammation is a hallmark of nonalcoholic steatohepatitis (NASH)-an aggressive form of nonalcoholic fatty liver disease. However, it remains unclear how such a low-grade, yet persistent, inflammation is sustained in the liver. Here, we show that the macrophage phagocytic receptor TREM2, induced by hepatocyte-derived sphingosine-1-phosphate, was required for efferocytosis of lipid-laden apoptotic hepatocytes and thereby maintained liver immune homeostasis. However, prolonged hypernutrition led to the production of proinflammatory cytokines TNF and IL-1β in the liver to induce TREM2 shedding through ADAM17-dependent proteolytic cleavage. Loss of TREM2 resulted in aberrant accumulation of dying hepatocytes, thereby further augmenting proinflammatory cytokine production. This ultimately precipitated a vicious cycle that licensed chronic inflammation to drive simple steatosis transition to NASH. Therefore, impaired macrophage efferocytosis is a previously unrecognized key pathogenic event that enables chronic liver inflammation in obesity. Blocking TREM2 cleavage to restore efferocytosis may represent an effective strategy to treat NASH.

An endogenous inhibitor of angiogenesis downregulated by hypoxia in human aortic valve stenosis promotes disease pathogenesis

Aortic valve stenosis is the most common valve disease in the western world. Central to the pathogenesis of this disease is the growth of new blood vessels (angiogenesis) within the aortic valve allowing infiltration of immune cells and development of intra-valve inflammation. Identifying the cellular mediators involved in this angiogenesis is important as this may reveal new therapeutic targets which could ultimately prevent the progression of aortic valve stenosis. Aortic valves from patients undergoing surgery for aortic valve replacement or dilation of the aortic arch were examined both ex vivo and in vitro. We now demonstrate that the anti-angiogenic protein, soluble fms-like tyrosine kinase 1 (sFlt1), a non-signalling soluble receptor for vascular endothelial growth factor, is constitutively expressed in non-diseased valves. sFlt-1 expression was, however, significantly reduced in aortic valve tissue from patients with aortic valve stenosis while protein markers of hypoxia were simultaneously increased. Exposure of primary-cultured valve interstitial cells to hypoxia resulted in a decrease in the expression of sFlt-1. We further reveal using a bioassay that siRNA knock-down of sFlt1 in valve interstitial cells directly results in a pro-angiogenic environment. Finally, incubation of aortic valves with sphingosine 1-phosphate, a bioactive lipid-mediator, increased sFlt-1 expression and inhibited angiogenesis within valve tissue. In conclusion, this study demonstrates that sFlt1 expression is directly correlated with angiogenesis in aortic valves and the observed decrease in sFlt-1 expression in aortic valve stenosis could increase valve inflammation, promoting disease progression. This could be a viable therapeutic target in treating this disease.

Differential Upregulation and Functional Activity of S1PR1 in Human Peripheral Blood Basophils of Atopic Patients

Basophils are key effector cells in atopic diseases, and the signaling sphingolipid Sphigosine-1-phosphate (S1P) is emerging as an important mediator in these conditions. The possible interaction of S1P and basophils and the resulting biological effects have not yet been studied. We hypothesize that S1P influences the function of basophils in atopy and aim to elucidate the modes of interaction. S1P receptor (S1PR) expression in human peripheral blood basophils from atopic and non-atopic patients was assessed through qRT-PCR and flow cytometry analysis. Functional effects of S1P were assessed through a basophil activation test (BAT), calcium flux, apoptosis, and chemotaxis assays. Immunofluorescence staining was performed to visualize intracellular S1P. Human basophils express S1PR1, S1PR2, S1PR3, and S1PR4 on the mRNA level. 0.1 µM S1P have anti-apoptotic, while 10 µM exhibits apoptotic effects on basophils. Basophils from atopic patients show less chemotactic activity in response to S1P than those from healthy donors. Protein expression of S1PR1 is downregulated in atopic patients, and basophils in lesional AD skin possess intracellular S1P. These findings suggest that the interaction of S1P and basophils might be an important factor in the pathophysiology of atopy.

Maturation and specialization of group 2 innate lymphoid cells through the lung-gut axis

Innate lymphoid cells (ILC) are abundant in mucosal tissues. They serve critical functions in anti-pathogen response and tissue homeostasis. However, the heterogenous composition of ILCs in mucosal sites and their various maturation trajectories are less well known. In this study, we characterize ILC types and functions from both the lung and the small intestine, and identify their tissue-specific markers. We find that ILC2s residing in the lung express CCR2, whereas intestinal ILC2s express CCR4. Through the use of CCR2 and CCR4 reporter mice, we show that ILC2s undergo translocation via the lung-gut axis upon IL-33 treatment. This trajectory of ILC2s is also observed at the postnatal stage. Allergen-induced activation of lung ILC2s affects the homeostasis of gut ILC2s. Together, our findings implicate that ILCs display tissue-specific features in both the lung and gut, and ILC2s mature along the lung-gut axis in particular homeostatic and inflammatory conditions.

The Crosstalk between FcεRI and Sphingosine Signaling in Allergic Inflammation

Sphingolipid molecules have recently attracted attention as signaling molecules in allergic inflammation diseases. Sphingosine-1-phosphate (S1P) is synthesized by two isoforms of sphingosine kinases (SPHK 1 and SPHK2) and is known to be involved in various cellular processes. S1P levels reportedly increase in allergic inflammatory diseases, such as asthma and anaphylaxis. FcεRI signaling is necessary for allergic inflammation as it can activate the SPHKs and increase the S1P level; once S1P is secreted, it can bind to the S1P receptors (S1PRs). The role of S1P signaling in various allergic diseases is discussed. Increased levels of S1P are positively associated with asthma and anaphylaxis. S1P can either induce or suppress allergic skin diseases in a context-dependent manner. The crosstalk between FcεRI and S1P/SPHK/S1PRs is discussed. The roles of the microRNAs that regulate the expression of the components of S1P signaling in allergic inflammatory diseases are also discussed. Various reports suggest the role of S1P in FcεRI-mediated mast cell (MC) activation. Thus, S1P/SPHK/S1PRs signaling can be the target for developing anti-allergy drugs.

Platelet-Derived S1P and Its Relevance for the Communication with Immune Cells in Multiple Human Diseases

Sphingosine-1-phosphate (S1P) is a versatile signaling lipid involved in the regulation of numerous cellular processes. S1P regulates cellular proliferation, migration, and apoptosis as well as the function of immune cells. S1P is generated from sphingosine (Sph), which derives from the ceramide metabolism. In particular, high concentrations of S1P are present in the blood. This originates mainly from erythrocytes, endothelial cells (ECs), and platelets. While erythrocytes function as a storage pool for circulating S1P, platelets can rapidly generate S1P de novo, store it in large quantities, and release it when the platelet is activated. Platelets can thus provide S1P in a short time when needed or in the case of an injury with subsequent platelet activation and thereby regulate local cellular responses. In addition, platelet-dependently generated and released S1P may also influence long-term immune cell functions in various disease processes, such as inflammation-driven vascular diseases. In this review, the metabolism and release of platelet S1P are presented, and the autocrine versus paracrine functions of platelet-derived S1P and its relevance in various disease processes are discussed. New pharmacological approaches that target the auto- or paracrine effects of S1P may be therapeutically helpful in the future for pathological processes involving S1P.

Multi-omic comparative analysis of COVID-19 and bacterial sepsis-induced ARDS

BACKGROUND

Acute respiratory distress syndrome (ARDS), a life-threatening condition characterized by hypoxemia and poor lung compliance, is associated with high mortality. ARDS induced by COVID-19 has similar clinical presentations and pathological manifestations as non-COVID-19 ARDS. However, COVID-19 ARDS is associated with a more protracted inflammatory respiratory failure compared to traditional ARDS. Therefore, a comprehensive molecular comparison of ARDS of different etiologies groups may pave the way for more specific clinical interventions.

METHODS AND FINDINGS

In this study, we compared COVID-19 ARDS (n = 43) and bacterial sepsis-induced (non-COVID-19) ARDS (n = 24) using multi-omic plasma profiles covering 663 metabolites, 1,051 lipids, and 266 proteins. To address both between- and within- ARDS group variabilities we followed two approaches. First, we identified 706 molecules differently abundant between the two ARDS etiologies, revealing more than 40 biological processes differently regulated between the two groups. From these processes, we assembled a cascade of therapeutically relevant pathways downstream of sphingosine metabolism. The analysis suggests a possible overactivation of arginine metabolism involved in long-term sequelae of ARDS and highlights the potential of JAK inhibitors to improve outcomes in bacterial sepsis-induced ARDS. The second part of our study involved the comparison of the two ARDS groups with respect to clinical manifestations. Using a data-driven multi-omic network, we identified signatures of acute kidney injury (AKI) and thrombocytosis within each ARDS group. The AKI-associated network implicated mitochondrial dysregulation which might lead to post-ARDS renal-sequalae. The thrombocytosis-associated network hinted at a synergy between prothrombotic processes, namely IL-17, MAPK, TNF signaling pathways, and cell adhesion molecules. Thus, we speculate that combination therapy targeting two or more of these processes may ameliorate thrombocytosis-mediated hypercoagulation.

CONCLUSION

We present a first comprehensive molecular characterization of differences between two ARDS etiologies-COVID-19 and bacterial sepsis. Further investigation into the identified pathways will lead to a better understanding of the pathophysiological processes, potentially enabling novel therapeutic interventions.

Multi-omic comparative analysis of COVID-19 and bacterial sepsis-induced ARDS

Background

Acute respiratory distress syndrome (ARDS), a life-threatening condition characterized by hypoxemia and poor lung compliance, is associated with high mortality. ARDS induced by COVID-19 has similar clinical presentations and pathological manifestations as non-COVID-19 ARDS. However, COVID-19 ARDS is associated with a more protracted inflammatory respiratory failure compared to traditional ARDS. Therefore, a comprehensive molecular comparison of ARDS of different etiologies groups may pave the way for more specific clinical interventions.

Methods and Findings

In this study, we compared COVID-19 ARDS (n=43) and bacterial sepsis-induced (non-COVID-19) ARDS (n=24) using multi-omic plasma profiles covering 663 metabolites, 1,051 lipids, and 266 proteins. To address both between- and within-ARDS group variabilities we followed two approaches. First, we identified 706 molecules differently abundant between the two ARDS etiologies, revealing more than 40 biological processes differently regulated between the two groups. From these processes, we assembled a cascade of therapeutically relevant pathways downstream of sphingosine metabolism. The analysis suggests a possible overactivation of arginine metabolism involved in long-term sequelae of ARDS and highlights the potential of JAK inhibitors to improve outcomes in bacterial sepsis-induced ARDS. The second part of our study involved the comparison of the two ARDS groups with respect to clinical manifestations. Using a data-driven multi-omic network, we identified signatures of acute kidney injury (AKI) and thrombocytosis within each ARDS group. The AKI-associated network implicated mitochondrial dysregulation which might lead to post-ARDS renal-sequalae. The thrombocytosis-associated network hinted at a synergy between prothrombotic processes, namely IL-17, MAPK, TNF signaling pathways, and cell adhesion molecules. Thus, we speculate that combination therapy targeting two or more of these processes may ameliorate thrombocytosis-mediated hypercoagulation.

Conclusion

We present a first comprehensive molecular characterization of differences between two ARDS etiologies - COVID-19 and bacterial sepsis. Further investigation into the identified pathways will lead to a better understanding of the pathophysiological processes, potentially enabling novel therapeutic interventions.

Sphingosine 1-phosphate modulation and immune cell trafficking in inflammatory bowel disease

Immune cell trafficking is a critical element of the intestinal immune response, both in homeostasis and in pathological conditions associated with inflammatory bowel disease (IBD). This process involves adhesion molecules, chemoattractants and receptors expressed on immune cell surfaces, blood vessels and stromal intestinal tissue as well as signalling pathways, including those modulated by sphingosine 1-phosphate (S1P). The complex biological processes of leukocyte recruitment, activation, adhesion and migration have been targeted by various monoclonal antibodies (vedolizumab, etrolizumab, ontamalimab). Promising preclinical and clinical data with several oral S1P modulators suggest that inhibition of lymphocyte egress from the lymph nodes to the bloodstream might be a safe and efficacious alternative mechanism for reducing inflammation in immune-mediated disorders, including Crohn's disease and ulcerative colitis. Although various questions remain, including the potential positioning of S1P modulators in treatment algorithms and their long-term safety, this novel class of compounds holds great promise. This Review summarizes the critical mediators and mechanisms involved in immune cell trafficking in IBD and the available evidence for efficacy, safety and pharmacokinetics of S1P receptor modulators in IBD and other immune-mediated disorders. Further, it discusses potential future approaches to incorporate S1P modulators into the treatment of IBD.

Lipid Ligands and Allergenic LTPs: Redefining the Paradigm of the Protein-Centered Vision in Allergy

Lipid Transfer Proteins (LTPs) have been described as one of the most prevalent and cross-reactive allergen families in the general population. They are widely distributed among the plant kingdom, as well as in different plant organs ranging from pollen to fruits. Thus, they can initiate allergic reactions with very different outcomes, such as asthma and food allergy. Several mouse models have been developed to unravel the mechanisms that lead LTPs to promote such strong sensitization patterns. Interestingly, the union of certain ligands can strengthen the allergenic capacity of LTPs, suggesting that not only is the protein relevant in the sensitization process, but also the ligands that LTPs carry in their cavity. In fact, different LTPs with pro-allergenic capacity have been shown to transport similar ligands, thus positioning lipids in a central role during the first stages of the allergic response. Here, we offer the latest advances in the use of experimental animals to study the topic, remarking differences among them and providing future researchers a tool to choose the most suitable model to achieve their goals. Also, recent results derived from metabolomic studies in humans are included, highlighting how allergic diseases alter the lipidic metabolism toward a pathogenic state in the individual. Altogether, this review offers a comprehensive body of work that sums up the background evidence supporting the role of lipids as modulators of allergic diseases. Studying the role of lipids during allergic sensitization might broaden our understanding of the molecular events leading to tolerance breakdown in the epithelium, thus helping us to understand how allergy is initiated and established in the individuals.

The Role of Sphingolipids in Allergic Disorders

Allergy is defined as a complex chronic inflammatory condition in which genetic and environmental factors are implicated. Sphingolipids are involved in multiple biological functions, from cell membrane components to critical signaling molecules. To date, sphingolipids have been studied in different human pathologies such as neurological disorders, cancer, autoimmunity, and infections. Sphingolipid metabolites, in particular, ceramide and sphingosine-1-phosphate (S1P), regulate a diverse range of cellular processes that are important in immunity and inflammation. Moreover, variations in the sphingolipid concentrations have been strongly associated with allergic diseases. This review will focus on the role of sphingolipids in the development of allergic sensitization and allergic inflammation through the activation of immune cells resident in tissues, as well as their role in barrier remodeling and anaphylaxis. The knowledge gained in this emerging field will help to develop new therapeutic options for allergic disorders.

Drug treatment strategies for eosinophilic esophagitis in adults

INTRODUCTION

Eosinophilic esophagitis (EoE) is a clinical and pathological disorder, characterized by symptoms of esophageal dysfunction, and eosinophil-predominant inflammation restricted to the esophagus. Treatment outcomes include symptomatic remission, histological and endoscopic normalization and improving quality of life. Besides dietary modifications and endoscopic dilation, drugs available are swallowed topical corticosteroids (STCs) with reduced bioavailability and proton pump inhibitors (PPI).

AREAS COVERED

Herein, the authors review the current treatment strategies for EoE in adults, providing the reader with their expert perspectives. The authors give discussion to the value of PPIs as a first-line therapy for EoE, in addition to the use of STCs. The current development of new formulations of STCs targeting the esophagus and novel therapies aimed at blocking molecular pathways are also discussed. Finally, the authors briefly look at the value of monoclonal antibodies targeting IL-5RA, IL-13, IL-4 or Siglec8, and oral S1PR agonists to the treatment of EoE.

EXPERT OPINION

Viscose formulations of STC designed to coat the esophagus and new effervescent orodispersible tablets provide increased effectiveness at low doses. Investigational therapies that target several Th2-associated diseases seem useful in EoE. Comparative effectiveness and cost-utility analyses will help to position them in a complex therapeutic scenario.

Review article: the sphingosine 1 phosphate/sphingosine 1 phosphate receptor axis - a unique therapeutic target in inflammatory bowel disease

BACKGROUND

Ozanimod, a high selective sphingosine 1 phosphate (S1P) receptor (S1PR) 1/5 modulator was approved by the Food and Drug Administration for the treatment of adult patients with moderately to severely active ulcerative colitis. Additional S1PR modulators are being tested in clinical development programmes for both ulcerative colitis and Crohn's disease.

AIM

To provide an overview of advances in understanding S1PRs biology and summarise preclinical and clinical investigations of S1P receptor modulators in chronic inflammatory disease with special emphasis on inflammatory bowel diseases (IBD).

METHODS

We performed a narrative review using PubMed and ClinicalTrials.gov.

RESULTS

Through S1PRs, S1P regulates multiple cellular processes, including proliferation, migration, survival, and vascular barrier integrity. The S1PRs function of regulating lymphocyte trafficking is well known, but new functions of S1PRs expand our knowledge of S1PRs biology. Several S1PR modulators are in clinical development for both ulcerative colitis and Crohn's disease and have shown promise in phase II and III studies with ozanimod now being approved for ulcerative colitis.

CONCLUSIONS

S1P receptor modulators constitute a novel, promising, safe, and convenient strategy for the treatment of IBD.

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.

Targeting Chronic Inflammation of the Digestive System in Cancer Prevention: Modulators of the Bioactive Sphingolipid Sphingosine-1-Phosphate Pathway

Incidence of gastrointestinal (GI) cancers is increasing, and late-stage diagnosis makes these cancers difficult to treat. Chronic and low-grade inflammation are recognized risks for most GI cancers. The GI mucosal immune system maintains healthy homeostasis and signalling molecules made from saturated fats, bioactive sphingolipids, play essential roles in healthy GI immunity. Sphingosine-1-phosphate (S1P), a bioactive sphingolipid, is a key mediator in a balanced GI immune response. Disruption in the S1P pathway underlies systemic chronic metabolic inflammatory disorders, including diabetes and GI cancers, providing a strong rationale for using modulators of the S1P pathway to treat pathological inflammation. Here, we discuss the effects of bioactive sphingolipids in immune homeostasis with a focus on S1P in chronic low-grade inflammation associated with increased risk of GI carcinogenesis. Contemporary information on S1P signalling involvement in cancers of the digestive system, from top to bottom, is reviewed. Further, we discuss the use of novel S1P receptor modulators currently in clinical trials and their potential as first-line drugs in the clinic for chronic inflammatory diseases. Recently, ozanimod (Zeposia^TM) and etrasimod have been approved for clinical use to treat ulcerative colitis and eosinophilic oesophagitis, respectively, which may have longer term benefits in reducing risk of GI cancers.

Sphingosine Kinase 1 Plays an Important Role in Atorvastatin-Mediated Anti-Inflammatory Effect against Acute Lung Injury

Atorvastatin is a 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) inhibitor and inhibits cholesterol synthesis. Recently, atorvastatin also showed anti-inflammatory effect in acute lung injury, ameliorating pulmonary gas-blood exchanging function. Sphingosine kinase 1 plays a central role in endothelial (EC) cytoskeleton rearrangement and EC barrier integrity regulation. In this study, the role of sphingosine kinase 1 in atorvastatin anti-inflammatory effect against acute lung injury was investigated. Both wild-type (WT) and SphK1^-/- mice were challenged with high tidal volume ventilation (40 ml/kg body weight, 65 breathing/min, 4 hours). The acute lung injury was evaluated and the mechanisms were explored. In WT mice, atorvastatin treatment significantly decreased acute lung injury responding to high tidal volume ventilation (HT), including protein, cellular infiltration, and cytokine releasing; comparing to WT mice, SphK1^-/- mice showed significantly worsen pulmonary injuries on HT model. Moreover, the atorvastatin-mediated anti-inflammatory effect was diminished in SphK1^-/- mice. To further confirm the role of SphK1 in VILI, we then compared the inflammatory response of endothelial cells that were isolated from WT and SphK1^-/- mice to cyclic stretching. Similarly, atorvastatin significantly decreased cytokine generation from WT EC responding to cyclic stretching. Atorvastatin also significantly preserved endothelial junction integrity in WT EC against thrombin challenge. However, the inhibitory effect of atorvastatin on cytokine generation induced by cyclic stretching was abolished on SphK1^-/- mice EC. The endothelial junction integrity effects of atorvastatin also diminished on SphK1^-/- mouse EC. Signal analysis indicated that atorvastatin inhibited JNK activation induced by cyclic stretch. SphK1 knockout also blocked atorvastatin-mediated VE-cadherin junction enhancement. In summary, by inhibition of MAPK activity and maintenance of EC junction homeostasis, SphK1 plays a critical role in atorvastatin-mediated anti-inflammatory effects in both cellular and in vivo model. This study also offers an insight into mechanical stress-mediated acute lung injury and potential therapy in the future.