Sphingosine-1-phosphate receptor 1/5 selective agonist alleviates ocular vascular pathologies.

Ocular abnormal angiogenesis and edema are featured in several ocular diseases. S1P signaling via S1P1 likely is part of the negative feedback mechanism necessary to maintain vascular health. In this study, we conducted pharmacological experiments to determine whether ASP4058, a sphingosine 1-phosphate receptor 1/5 (S1P1/5) agonist, is useful in abnormal vascular pathology in the eye. First, human retinal microvascular endothelial cells (HRMECs) were examined using vascular endothelial growth factor (VEGF)-induced cell proliferation and hyperpermeability. ASP4058 showed high affinity and inhibited VEGF-induced proliferation and hyperpermeability of HRMECs. Furthermore, S1P1 expression and localization changes were examined in the murine laser-induced choroidal neovascularization (CNV) model, a mouse model of exudative age-related macular degeneration, and the efficacy of ASP4058 was verified. In the CNV model mice, S1P1 tended to decrease in expression immediately after laser irradiation and colocalized with endothelial cells and Müller glial cells. Oral administration of ASP4058 also suppressed vascular hyperpermeability and CNV, and the effect was comparable to that of the intravitreal administration of aflibercept, an anti-VEGF drug. Next, efficacy was also examined in a retinal vein occlusion (RVO) model in which retinal vascular permeability was increased. ASP4058 dose-dependently suppressed the intraretinal edema. In addition, it suppressed the expansion of the perfusion area observed in the RVO model. ASP4058 also suppressed the production of VEGF in the eye. Collectively, ASP4058 can be a potential therapeutic agent that normalizes abnormal vascular pathology, such as age-related macular degeneration and RVO, through its direct action on endothelial cells.

Pharmacological sphingosine-1 phosphate receptor 1 targeting in cigarette smoke-induced emphysema in mice.

Primarily caused by chronic cigarette smoking (CS), emphysema is characterized by loss of alveolar cells comprising lung units involved in gas exchange and inflammation that culminate in airspace enlargement. Dysregulation of sphingolipid metabolism with increases of ceramide relative to sphingosine-1 phosphate (S1P) signaling has been shown to cause lung cell apoptosis and is emerging as a potential therapeutic target in emphysema. We sought to determine the impact of augmenting S1P signaling via S1P receptor 1 (S1P1) in a mouse model of CS-induced emphysema. DBA2 mice were exposed to CS for 4 or 6 mo and treated with pharmacological agonists of S1P1: phosphonated FTY720 (FTY720-1S and 2S analogs; 0.01-1.0 mg/kg) or GSK183303A (10 mg/kg). Pharmacological S1P1 agonists ameliorated CS-induced lung parenchymal apoptosis and airspace enlargement as well as loss of body weight. S1P1 agonists had modest inhibitory effects on CS-induced airspace inflammation and lung functional changes measured by Flexivent, improving lung tissue resistance. S1P1 abundance was reduced in chronic CS-conditions and remained decreased after CS-cessation or treatment with FTY720-1S. These results support an important role for S1P-S1P1 axis in maintaining the structural integrity of alveoli during chronic CS exposure and suggest that increasing both S1P1 signaling and abundance may be beneficial to counteract the effects of chronic CS exposure.

Structural insights into sphingosine-1-phosphate receptor activation.

As a critical sphingolipid metabolite, sphingosine-1-phosphate (S1P) plays an essential role in immune and vascular systems. There are five S1P receptors, designated as S1PR1 to S1PR5, encoded in the human genome, and their activities are governed by endogenous S1P, lipid-like S1P mimics, or nonlipid-like therapeutic molecules. Among S1PRs, S1PR1 stands out due to its nonredundant functions, such as the egress of T and B cells from the thymus and secondary lymphoid tissues, making it a potential therapeutic target. However, the structural basis of S1PR1 activation and regulation by various agonists remains unclear. Here, we report four atomic resolution cryo-electron microscopy (cryo-EM) structures of Gi-coupled human S1PR1 complexes: bound to endogenous agonist d18:1 S1P, benchmark lipid-like S1P mimic phosphorylated Fingolimod [(S)-FTY720-P], or nonlipid-like therapeutic molecule CBP-307 in two binding modes. Our results revealed the similarities and differences of activation of S1PR1 through distinct ligands binding to the amphiphilic orthosteric pocket. We also proposed a two-step "shallow to deep" transition process of CBP-307 for S1PR1 activation. Both binding modes of CBP-307 could activate S1PR1, but from shallow to deep transition may trigger the rotation of the N-terminal helix of Gαi and further stabilize the complex by increasing the Gαi interaction with the cell membrane. We combine with extensive biochemical analysis and molecular dynamic simulations to suggest key steps of S1P binding and receptor activation. The above results decipher the common feature of the S1PR1 agonist recognition and activation mechanism and will firmly promote the development of therapeutics targeting S1PRs.

Sphingosine-1-phosphate receptor 1 agonist SEW2871 alters membrane properties of late-firing somatostatin expressing neurons in the central lateral amygdala.

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide spectrum of biological processes including apoptosis, immune response and inflammation. Here, we sought to understand how S1P signaling affects neuronal excitability in the central amygdala (CeA), which is a brain region associated with fear learning, aversive memory, and the affective dimension of pain. Because the G-protein coupled S1P receptor 1 (S1PR1) has been shown to be the primary mediator of S1P signaling, we utilized S1PR1 agonist SEW2871 and S1PR1 antagonist NIBR to determine a potential role of S1PR1 in altering the cellular physiology of neurons in the lateral division of the CeA (CeL) that share the neuronal lineage marker somatostatin (Sst). CeL-Sst neurons play a critical role in expression of conditioned fear and pain modulation. Here we used transgenic breeding strategies to identify fluorescently labeled CeL-Sst neurons for electrophysiological recordings. Using principal component analysis, we identified two primary subtypes of Sst neurons within the CeL in both male and female mice. We denoted the two types regular-firing (type A) and late-firing (type B) CeL-Sst neurons. In response to SEW2871 application, Type A neurons exhibited increased input resistance, while type B neurons displayed a depolarized resting membrane potential and voltage threshold, increased current threshold, and decreased voltage height. NIBR application had no effect on CeL Sst neurons, indicating the absence of tonic S1P-induced S1PR1. Our findings reveal subtypes of Sst neurons within the CeL that are uniquely affected by S1PR1 activation, which may have implications for how S1P alters supraspinal circuits.

Exploring lipophilic compounds that induce BDNF secretion in astrocytes beyond the BBB using a new multi-cultured human in vitro BBB model.

Brain-derived neurotrophic factor (BDNF) cannot cross the blood-brain barrier (BBB) when administered peripherally, which hinders its therapeutic potential. We utilized an in vitro BBB model-a tri-culture of a human endothelial cell line, a pericyte cell line, and an astrocyte cell line-to study the effect of twenty candidate lipophilic compounds on stimulating BDNF secretion in pericytes and astrocytes. The prostaglandin E2 receptor 4 agonist and sphingosine-1-phosphate receptor 5 agonist facilitated secretion of BDNF in the astrocyte, but did not decrease the transendothelial electrical resistance. These compounds may be promising agents for neurodegenerative and neuroinflammatory diseases.

Structures of signaling complexes of lipid receptors S1PR1 and S1PR5 reveal mechanisms of activation and drug recognition.

Sphingosine-1-phosphate (S1P) is an important bioactive lipid molecule in cell membrane metabolism and binds to G protein-coupled S1P receptors (S1PRs) to regulate embryonic development, physiological homeostasis, and pathogenic processes in various organs. S1PRs are lipid-sensing receptors and are therapeutic targets for drug development, including potential treatment of COVID-19. Herein, we present five cryo-electron microscopy structures of S1PRs bound to diverse drug agonists and the heterotrimeric Gi protein. Our structural and functional assays demonstrate the different binding modes of chemically distinct agonists of S1PRs, reveal the mechanical switch that activates these receptors, and provide a framework for understanding ligand selectivity and G protein coupling.

Enhanced CXCR4 Expression of Human CD8Low T Lymphocytes Is Driven by S1P4.

Although the human immune response to cancer is naturally potent, it can be severely disrupted as a result of an immunosuppressive tumor microenvironment. Infiltrating regulatory T lymphocytes contribute to this immunosuppression by inhibiting proliferation of cytotoxic CD8+ T lymphocytes, which are key to an effective anti-cancer immune response. Other important contributory factors are thought to include metabolic stress caused by the local nutrient deprivation common to many solid tumors. Interleukin-33 (IL-33), an alarmin released in reaction to cell damage, and sphingosine-1-phosphate (S1P) are known to control cell positioning and differentiation of T lymphocytes. In an in vitro model of nutrient deprivation, we investigated the influence of IL-33 and S1P receptor 4 (S1P4) on the differentiation and migration of human CD8+ T lymphocytes. Serum starvation of CD8+ T lymphocytes induced a subset of CD8Low and IL-33 receptor-positive (ST2L+) cells characterized by enhanced expression of the regulatory T cell markers CD38 and CD39. Both S1P1 and S1P4 were transcriptionally regulated after stimulation with IL-33. Moreover, expression of the chemokine receptor CXCR4 was increased in CD8+ T lymphocytes treated with the selective S1P4 receptor agonist CYM50308. We conclude that nutrient deprivation promotes CD8Low T lymphocytes, contributing to an immunosuppressive microenvironment and a poor anti-cancer immune response by limiting cytotoxic effector functions. Our results suggest that S1P4 signaling modulation may be a promising target for anti-CXCR4 cancer immunotherapy.

Ponesimod: First Approval.

Ponesimod (PONVORY™) is an orally administered selective sphingosine-1-phosphate (S1P) receptor 1 (S1P1) agonist being developed by the Janssen Pharmaceutical Companies of Johnson & Johnson for the treatment of multiple sclerosis (MS). Based on the results of the phase III OPTIMUM trial, ponesimod was recently approved in the USA for the treatment of relapsing forms of MS and has received a positive CHMP opinion in the EU for this indication. This article summarizes the milestones in the development of ponesimod leading to this first US approval.

Effects of S1PR2 antagonist on blood pressure and angiogenesis imbalance in preeclampsia rats.

Preeclampsia (PE), a hypertensive multisystem disorder, can lead to increased maternal and fetal mortality and morbidity. Sphingosine­1­phosphate (S1P) plays various roles, depending on the cell type, by binding to S1P receptors (S1PR). The present study evaluated the changes of S1PRs and investigated the potential role of S1PRs in pregnancy­induced hypertension. PE rats were established by reduced uterine perfusion pressure. The involvement of S1PR2 was evaluated using JTE­013, a specific S1PR2 antagonist, in PE rats. After the treatment, inflammatory cytokines were evaluated using enzyme linked immunosorbent assay, and the expression of vascular endothelial growth factor (VEGF), inducible nitric oxide synthase (iNOS) activation and endothelial nitric oxide synthase (eNOS) were evaluated by reverse transcription­quantitative PCR and western blotting. Results showed that S1PR2, but not S1PR1 and S1PR3, was significantly increased in the serum and placenta tissues of PE rats. Notably, JTE­013 significantly decreased blood pressure, attenuated infiltration of inflammatory cells and decreased inflammation, as indicated by the decreased expression of inflammatory cytokines, including tumor necrosis factor­α, interleukin­1ß (IL­1ß) and IL­6, in placental tissues. Mechanistic studies demonstrated that JTE­013 significantly increased the expression of VEGF and decreased the expression of fms­like tyrosine kinase 1 in placental tissue. Furthermore, JTE­013 prevented iNOS activation and increased eNOS in placental tissue. In summary, the present study demonstrated that S1PR2 contributed to hypertension and angiogenesis imbalance in PE rats.

Activating Sphingosine-1-phospahte signaling in endothelial cells increases myosin light chain phosphorylation to decrease endothelial permeability thereby inhibiting cancer metastasis.

Targeting the metastatic process to prevent disease dissemination in cancer remains challenging. One step in the metastatic cascade involves cancer cells transiting through the vascular endothelium after inflammation has increased the permeability of this cellular layer. Reducing inflammation-mediated gaps in the vascular endothelium could potentially be used to retard metastasis. This study describes the development of a novel ASR396-containing nanoparticle designed to activate the Sphingosine-1-Phosphate Receptor 1 (S1PR1) in order to tighten the junctions between the endothelial cells lining the vascular endothelium thereby inhibiting metastasis. ASR396 was derived from the S1PR1 agonist SEW2871 through chemical modification enabling the new compound to be loaded into a nanoliposome. ASR396 retained S1PR1 binding activity and the nanoliposomal formulation (nanoASR396) made it systemically bioavailable upon intravenous injection. Studies conducted in microvessels demonstrated that nanoASR396 significantly attenuated inflammatory mediator-induced permeability increase through the S1PR1 activation. Similarly, nanoASR396 inhibited gap formation mediated by inflammatory agents on an endothelial cell monolayer by decreasing levels of phosphorylated myosin light chain protein thereby inhibiting cellular contractility. In animal models, nanoASR396 inhibited lung metastasis by up to 80%, indicating its potential for retarding melanoma metastasis. Thus, a novel bioavailable nanoparticle-based S1PR1 agonist has been developed to negate the effects of inflammatory mediators on the vascular endothelium in order to reduce the metastatic dissemination of cancer cells.

S1PR3-G12-biased agonist ALESIA targets cancer metabolism and promotes glucose starvation.

Metabolic activities are altered in cancer cells compared with those in normal cells, and the cancer-specific pathway becomes a potential therapeutic target. Higher cellular glucose consumption, which leads to lower glucose levels, is a hallmark of cancer cells. In an objective screening for chemicals that induce cell death under low-glucose conditions, we discovered a compound, denoted as ALESIA (Anticancer Ligand Enhancing Starvation-induced Apoptosis). By our shedding assay of transforming growth factor α in HEK293A cells, ALESIA was determined to act as a sphingosine-1-phosphate receptor 3-G12-biased agonist that promotes nitric oxide production and oxidative stress. The oxidative stress triggered by ALESIA resulted in the exhaustion of glucose, cellular NADPH deficiency, and then cancer cell death. Intraperitoneal administration of ALESIA improved the survival of mice with peritoneally disseminated rhabdomyosarcoma, indicating its potential as a new type of anticancer drug for glucose starvation therapy.

Protective effect of the sphingosine-1 phosphate receptor agonist siponimod on disrupted blood brain barrier function.

Sphingosine 1 phosphate (S1P) is a bioactive sphingolipid that exerts several functions in physiological and pathological conditions. The modulation of one of its receptors, S1P1, plays an important role in the egress of lymphocytes from lymph nodes and is a useful target in multiple sclerosis (MS) treatment. A new drug, siponimod (BAF-312) has been recently approved for the treatment of secondary progressive MS and has affinity for two S1P receptors, S1P1 and S1P5. The two receptors are expressed by endothelial cells that, as components of the blood-brain barrier (BBB), prevent the access of solutes and lymphocytes into the central nervous system, function often compromised in MS. Using an in vitro BBB model exposed to inflammatory cytokines (TNFα and IFNγ, 5 UI and 10 UI respectively), we evaluated the effects of BAF-312 (100 nM) on expression and function of endothelial tight junctional proteins (Zo-1 and claudin-5), regulation of transendothelial electrical resistance (TEER) and permeability to FITC-conjugated dextran. Zo-1 expression, as well as TEER values, were promptly recovered (24 h) when both S1P1 and S1P5 were activated by BAF-312. In contrast, at this time point, activation of S1P5 with the selective agonist UC-42-WP04 (300 nM) or with BAF-312, under blockade of S1P1 with the selective antagonist NIBR-0213 (1 µM), resulted in recovery of expression and localization of claudin-5 and reduction of TNFα/INFγ-induced expression of metalloproteinase 9. Only after a prolonged BAF-312 exposure (48 h), S1P1 was involved through activation of the PI3K/Akt pathway. The PI3K inhibitor LY294002 (10 µM) prevented in fact the effects of BAF-312 on all the parameters examined. In conclusion, BAF-312, by modulating both S1P1 and S1P5, may strengthen BBB properties, thus providing additional effects in the treatment of MS.

Preventive and Therapeutic Efficacy of ONO-4641, a Selective Agonist for Sphingosine 1-Phosphate Receptor 1 and 5, in Preclinical Models of Type 1 Diabetes Mellitus.

ONO-4641, 1-({6-[(2-methoxy-4-propylbenzyl)oxy]-1-methyl-3,4-dihydronaphthalen-2-yl}methyl)azetidine-3-carboxylic acid (ceralifimod), is a second-generation sphingosine 1-phosphate receptor agonist selective for sphingosine 1-phosphate receptors 1 and 5, and has clinical effects in multiple sclerosis. The objective of the present study was to explore other potential indications for ONO-4641 based on its immunomodulatory effects. ONO-4641 was tested in non-obese diabetic (NOD) mice, an animal model of spontaneous type 1 diabetes mellitus, an autoimmune disease with unmet medical needs. ONO-4641 at a dose of 0.1 mg/kg prevented the onset of diabetes mellitus in NOD mice. Furthermore, ONO-4641 at doses of 0.03 and 0.1 mg/kg decreased diabetic prevalence in NOD mice after the onset of diabetes mellitus in a dose-dependent manner. Histopathological analysis demonstrated that insulin-positive areas in the islets of mice administered 0.03 and 0.1 mg/kg ONO-4641 showed a tendency of high values although they were not significantly different from the Control group, which was treated with vehicle. These observations suggest ONO-4641 may delay the onset and progression of type 1 diabetes mellitus.

Fingolimod inhibits glutamate release through activation of S1P1 receptors and the G protein ßγ subunit-dependent pathway in rat cerebrocortical nerve terminals.

Fingolimod, a sphingosine-1-phosphate (S1P) receptor modulator approved for treating multiple sclerosis, is reported to prevent excitotoxic insult. Because excessive glutamate release is a major cause of neuronal damage in various neurological disorders, the effect of fingolimod on glutamate release in rat cerebrocortical nerve terminals (synaptosomes) was investigated in the current study. Fingolimod decreased 4-aminopyridine (4-AP)-stimulated glutamate release and calcium concentration elevation. Fingolimod-mediated inhibition of 4-AP-induced glutamate release was dependent on extracellular calcium, persisted in the presence of the glutamate transporter inhibitor DL-TBOA or intracellular Ca2+-releasing inhibitors dantrolene and CGP37157, and was prevented by blocking vesicular transporters or N- and P/Q-type channels. Western blot and immunocytochemical analysis revealed the presence of S1P1 receptor proteins in presynaptic terminals. Fingolimod-mediated inhibition of 4-AP-induced glutamate release was also abolished by the sphingosine kinase inhibitor DMS, selective S1P1 receptor antagonist W146, Gi/o protein inhibitor pertussis toxin, and G protein ßγ subunit inhibitor gallein; however, it was unaffected by the adenylyl cyclase inhibitor SQ22536, protein kinase A inhibitor H89, and phospholipase C inhibitor U73122. These data indicate that fingolimod decreases glutamate release from rat cerebrocortical synaptosomes by suppressing N- and P/Q-type Ca2+ channel activity; additionally, the activation of presynaptic S1P1 receptors and the G protein ßγ subunit participates in achieving the effect.

Novel compounds with dual S1P receptor agonist and histamine H3 receptor antagonist activities act protective in a mouse model of multiple sclerosis.

The sphingosine 1-phosphate (S1P) receptor 1 (S1P1) has emerged as a therapeutic target for the treatment of multiple sclerosis (MS). Fingolimod (FTY720) is the first functional antagonist of S1P1 that has been approved for oral treatment of MS. Previously, we have developed novel butterfly derivatives of FTY720 that acted similar to FTY720 in reducing disease symptoms in a mouse model of experimental autoimmune encephalomyelitis (EAE). In this study, we have synthesized a piperidine derivative of the oxazolo-oxazole compounds, denoted ST-1505, and its ring-opened analogue ST-1478, and characterised their in-vitro and in-vivo functions. Notably, the 3-piperidinopropyloxy moiety resembles a structural motif of pitolisant, a drug with histamine H3R antagonistic/inverse agonist activity approved for the treatment of narcolepsy. Both novel compounds exerted H3R affinities, and in addition, ST-1505 was characterised as a dual S1P1+3 agonist, whereas ST-1478 was a dual S1P1+5 agonist. Both multitargeting compounds were also active in mice and reduced the lymphocyte numbers as well as diminished disease symptoms in the mouse model of MS. The effect of ST-1478 was dependent on SK-2 activity suggesting that it is a prodrug like FTY720, but with a more selective S1P receptor activation profile, whereas ST-1505 is a fully active drug even in the absence of SK-2. In summary, these data suggest that the well soluble piperidine derivatives ST-1505 and ST-1478 hold promise as novel drugs for the treatment of MS and other autoimmune or inflammatory diseases, and by their H3R antagonist potency, they might additionally improve cognitive impairment during disease.

Efficacy of the sphingosine-1-phosphate receptor agonist fingolimod in animal models of stroke: an updated meta-analysis.

Objective: Neuroinflammation is a central part of cerebral ischemia/reperfusion injury. The novel immune suppressant, fingolimod, is a promising candidate to ameliorate stroke-induced damage. Fingolimod is efficacious in experimental ischemic models, but a rigorous meta-analysis is lacking that considers how different experiment variables affect outcomes.Methods: We conducted a systematic literature review of fingolimod in stroke models, with the aim of rigorously evaluating fingolimod's effects on reducing infarct volume improving neurological outcomes. Seventeen variables were evaluated as covariates for the source of heterogeneity, and effect sizes were combined by using normalized mean difference meta-analysis to evaluate efficacy. Study quality was evaluated by the CAMARADES ten-item checklist, and publication bias was evaluated by funnel plots and Egger's tests.Results: About 123 unduplicated articles were identified in the literature research. Of these papers, 118 articles were excluded after reading titles and abstracts. Another 17 articles were selected in this study. Study quality was moderate (median = 6; interquartile range = 4), and publication bias was statistically insignificant. fingolimod reduced infarct volume by 30.4% (95% CI 22.4%-38.3%; n = 24; I2 = 90.0%; p < 0.0001) and consistently enhanced neurobehavioral outcome by 34.2% (95% CI 23.1%-45.2%; n = 14; I2 = 76.5%; p < 0.0001). No single factors accounted for heterogeneity.Conclusions: Our rigorous statistical evaluation confirmed the neuroprotective properties of fingolimod. New data can be used in designing future clinical trials.

Ponesimod suppresses hepatitis B virus infection by inhibiting endosome maturation.

The discovery of novel antivirals to treat hepatitis B virus (HBV) infection is urgently needed, as the currently available drugs mainly target viral proteins at replication step, whereas host factors also play significant roles in HBV infection. Although numerous studies have reported candidate drugs for HBV treatment, there remains a need to find a new drug that may target other steps of the HBV life cycle. In this study, by drug screening of a 533 G-protein-coupled receptors (GPCRs)-associated compound library, we identified ponesimod, a selective agonist of sphingosine-1-phosphate receptor 1 (S1P1), as a drug candidate for the suppression of HBV infection. However, the anti-HBV effect of ponesimod is independent of S1P1 and other sphingosine-1-phosphate receptors (S1PRs). Treatment with ponesimod at an early step of infection but not at a post-entry step significantly reduced the HBV relaxed circular DNA (rcDNA) level in a dose-dependent manner. Ponesimod treatment did not inhibit attachment, binding, or internalization of HBV particles via endocytosis through an interaction with sodium taurocholate cotransporting polypeptide (NTCP) or epidermal growth factor receptor (EGFR). Importantly, during the transportation of HBV particles to the nucleus, co-localization of HBV with early endosomes but not with late endosomes and lysosomes was induced by the treatment with ponesimod, suggesting that ponesimod interferes with the conversion of early endosomes to late endosomes without significant damage to cellular growth. Conclusion: Ponesimod is a promising anti-HBV drug targeting the endosome maturation of HBV. This finding can be applied to the development of novel antivirals that target the trafficking pathway of HBV particles.

Endothelial S1P1 Signaling Counteracts Infarct Expansion in Ischemic Stroke.

RATIONALE: Cerebrovascular function is critical for brain health, and endogenous vascular protective pathways may provide therapeutic targets for neurological disorders. S1P (Sphingosine 1-phosphate) signaling coordinates vascular functions in other organs, and S1P1 (S1P receptor-1) modulators including fingolimod show promise for the treatment of ischemic and hemorrhagic stroke. However, S1P1 also coordinates lymphocyte trafficking, and lymphocytes are currently viewed as the principal therapeutic target for S1P1 modulation in stroke. OBJECTIVE: To address roles and mechanisms of engagement of endothelial cell S1P1 in the naive and ischemic brain and its potential as a target for cerebrovascular therapy. METHODS AND RESULTS: Using spatial modulation of S1P provision and signaling, we demonstrate a critical vascular protective role for endothelial S1P1 in the mouse brain. With an S1P1 signaling reporter, we reveal that abluminal polarization shields S1P1 from circulating endogenous and synthetic ligands after maturation of the blood-neural barrier, restricting homeostatic signaling to a subset of arteriolar endothelial cells. S1P1 signaling sustains hallmark endothelial functions in the naive brain and expands during ischemia by engagement of cell-autonomous S1P provision. Disrupting this pathway by endothelial cell-selective deficiency in S1P production, export, or the S1P1 receptor substantially exacerbates brain injury in permanent and transient models of ischemic stroke. By contrast, profound lymphopenia induced by loss of lymphocyte S1P1 provides modest protection only in the context of reperfusion. In the ischemic brain, endothelial cell S1P1 supports blood-brain barrier function, microvascular patency, and the rerouting of blood to hypoperfused brain tissue through collateral anastomoses. Boosting these functions by supplemental pharmacological engagement of the endothelial receptor pool with a blood-brain barrier penetrating S1P1-selective agonist can further reduce cortical infarct expansion in a therapeutically relevant time frame and independent of reperfusion. CONCLUSIONS: This study provides genetic evidence to support a pivotal role for the endothelium in maintaining perfusion and microvascular patency in the ischemic penumbra that is coordinated by S1P signaling and can be harnessed for neuroprotection with blood-brain barrier-penetrating S1P1 agonists.

MYPT1 O-GlcNAc modification regulates sphingosine-1-phosphate mediated contraction.

Many intracellular proteins are modified by N-acetylglucosamine, a post-translational modification termed O-GlcNAc. This modification is found on serine and threonine side chains and has the potential to regulate signaling pathways through interplay with phosphorylation. Here, we discover and characterize one such example. We find that O-GlcNAc levels control the sensitivity of fibroblasts to actin contraction induced by the signaling lipid sphingosine-1-phosphate (S1P), culminating in the phosphorylation of myosin light chain (MLC) and cellular contraction. Specifically, O-GlcNAc modification of the phosphatase subunit MYPT1 inhibits this pathway by blocking MYPT1 phosphorylation, maintaining its activity and causing the dephosphorylation of MLC. Finally, we demonstrate that O-GlcNAc levels alter the sensitivity of primary human dermal fibroblasts in a collagen-matrix model of wound healing. Our findings have important implications for the role of O-GlcNAc in fibroblast motility and differentiation, particularly in diabetic wound healing.

Sphingosine 1-phosphate Receptor Modulator Therapy for Multiple Sclerosis: Differential Downstream Receptor Signalling and Clinical Profile Effects.

Lysophospholipids are a class of bioactive lipid molecules that produce their effects through various G protein-coupled receptors (GPCRs). Sphingosine 1-phosphate (S1P) is perhaps the most studied lysophospholipid and has a role in a wide range of physiological and pathophysiological events, via signalling through five distinct GPCR subtypes, S1PR1 to S1PR5. Previous and continuing investigation of the S1P pathway has led to the approval of three S1PR modulators, fingolimod, siponimod and ozanimod, as medicines for patients with multiple sclerosis (MS), as well as the identification of new S1PR modulators currently in clinical development, including ponesimod and etrasimod. S1PR modulators have complex effects on S1PRs, in some cases acting both as traditional agonists as well as agonists that produce functional antagonism. S1PR subtype specificity influences their downstream effects, including aspects of their benefit:risk profile. Some S1PR modulators are prodrugs, which require metabolic modification such as phosphorylation via sphingosine kinases, resulting in different pharmacokinetics and bioavailability, contrasting with others that are direct modulators of the receptors. The complex interplay of these characteristics dictates the clinical profile of S1PR modulators. This review focuses on the S1P pathway, the characteristics and S1PR binding profiles of S1PR modulators, the mechanisms of action of S1PR modulators with regard to immune cell trafficking and neuroprotection in MS, together with a summary of the clinical effectiveness of the S1PR modulators that are approved or in late-stage development for patients with MS. Sphingosine 1-phosphate receptor modulator therapy for multiple sclerosis: differential downstream receptor signalling and clinical profile effects (MP4 65540 kb).