Sphingosine 1-Phosphate Receptor 1 Signaling in Mammalian Cells

S1P/S1PR1 signaling is involved in the development of nociceptive pain

Background

Pain is a complex perception involving unpleasant somatosensory and emotional experiences. However, the underlying mechanisms that mediate its different components remain unclear. Sphingosine-1-phosphate (S1P), a metabolite of sphingomyelin and a potent lipid mediator, initiates signaling via G protein-coupled receptors (S1PRs) on cell surfaces. It serves as a second messenger in cellular processes such as proliferation and apoptosis. Nevertheless, the neuropharmacology of sphingolipid signaling in pain conditions within the central nervous system remains largely unexplored and controversial.

Methods

Chronic nociceptive pain models were induced in vivo by intraplantar injection of 20 μL complete Freund's adjuvant (CFA) into the left hind paws. We assessed S1P and S1PR1 expression in the spinal cords of CFA model mice. Functional antagonists of S1PR1 or S1PR1-specific siRNA were administered daily following CFA model establishment. Paw withdrawal response frequency (PWF) and paw withdrawal latency (PWL) were measured to evaluate mechanical allodynia and thermal hyperalgesia, respectively. RT-PCR assessed interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α levels. Western blotting and immunofluorescence were used to analyze glial fibrillary acidic protein (GFAP), ionized calcium-binding adapter molecule (Iba1), STAT3, ERK, and p38 MAPK protein expression.

Results

In the chronic nociceptive pain model induced by CFA, S1P and S1PR1 expression levels were significantly elevated, leading to activation of spinal cord glial cells. S1PR1 activation also promoted MMP2-mediated cleavage of mature IL-1β. Additionally, S1PR1 activation upregulated phosphorylation of STAT3, ERK, and p38 MAPK in glial cells, profoundly impacting downstream signaling pathways and contributing to chronic nociceptive pain.

Conclusion

The S1P/S1PR1 axis plays a pivotal role in the cellular and molecular mechanisms underlying nociceptive pain. This signaling pathway modulates glial cell activation and the expression of pain-related genes (STAT3, ERK, p38 MAPK) and inflammatory factors in the spinal dorsal horn. These findings underscore the potential of targeting the S1P system for developing novel analgesic therapies.

Design, synthesis, and biological evaluation of multiple F-18 S1PR1 radiotracers in rodent and nonhuman primate

Here we report our design and synthesis of 28 new fluorine-containing compounds as potential F-18 radiotracers for CNS imaging of sphingosine-1-phosphate receptor 1 (S1PR1), and determination of their in vitro binding potency and selectivity toward S1PR1 over other S1PR subtypes. Nine potent and selective compounds, 7c&d, 9a&c, 12b, 15b, and 18a-c with IC50 values ranging from 0.6-12.3 nM for S1PR1 and weak binding toward S1PR2, 3, 4, and 5, were further 18F-radiolabeled to produce [18F]7c&d, [18F]9a&c, [18F]12b, [18F]15b, and [18F]18a-c. Multi-step F-18 radiochemistry procedures were investigated for radiosynthesis of [18F]7c&d and [18F]9a&c, and the presumed intermediates were synthesized and authenticated by analytic HPLC. We then performed nonhuman primate (NHP) PET brain imaging studies for eight radiotracers: [18F]7c&d, [18F]9a, [18F]12b, [18F]15b, and [18F]18a-c. Three radiotracers, [18F]7c, [18F]7d, and [18F]15b, had high NHP brain uptake with standardized uptake values (SUVs) at 2 h post-injection of 2.42, 2.84, and 2.00, respectively, and good brain retention. Our ex vivo biodistribution study in rats confirmed [18F]7d had a high brain uptake with no in vivo defluorination. Radiometabolic analysis of [18F]7c and [18F]7d in rat plasma and brain samples found that [18F]7c has a more favorable metabolic profile than [18F]7d. However, the trend of increased brain uptake precludes [18F]7c as a suitable PET radiotracer for imaging S1PR1 in the brain. Further structural optmization is warranted to identify a highly S1PR1-specific radiotracer with rapid brain uptake kinetics.

A Lifelike guided journey through the pathophysiology of pulmonary hypertension-from measured metabolites to the mechanism of action of drugs

Introduction

Pulmonary hypertension (PH) is a pathological condition that affects approximately 1% of the population. The prognosis for many patients is poor, even after treatment. Our knowledge about the pathophysiological mechanisms that cause or are involved in the progression of PH is incomplete. Additionally, the mechanism of action of many drugs used to treat pulmonary hypertension, including sotatercept, requires elucidation.

Methods

Using our graph-powered knowledge mining software Lifelike in combination with a very small patient metabolite data set, we demonstrate how we derive detailed mechanistic hypotheses on the mechanisms of PH pathophysiology and clinical drugs.

Results

In PH patients, the concentration of hypoxanthine, 12(S)-HETE, glutamic acid, and sphingosine 1 phosphate is significantly higher, while the concentration of L-arginine and L-histidine is lower than in healthy controls. Using the graph-based data analysis, gene ontology, and semantic association capabilities of Lifelike, led us to connect the differentially expressed metabolites with G-protein signaling and SRC. Then, we associated SRC with IL6 signaling. Subsequently, we found associations that connect SRC, and IL6 to activin and BMP signaling. Lastly, we analyzed the mechanisms of action of several existing and novel pharmacological treatments for PH. Lifelike elucidated the interplay between G-protein, IL6, activin, and BMP signaling. Those pathways regulate hallmark pathophysiological processes of PH, including vasoconstriction, endothelial barrier function, cell proliferation, and apoptosis.

Discussion

The results highlight the importance of SRC, ERK1, AKT, and MLC activity in PH. The molecular pathways affected by existing and novel treatments for PH also converge on these molecules. Importantly, sotatercept affects SRC, ERK1, AKT, and MLC simultaneously. The present study shows the power of mining knowledge graphs using Lifelike's diverse set of data analytics functionalities for developing knowledge-driven hypotheses on PH pathophysiological and drug mechanisms and their interactions. We believe that Lifelike and our presented approach will be valuable for future mechanistic studies of PH, other diseases, and drugs.

Non-coding RNAs in diabetic peripheral neuropathy: their role and mechanisms underlying their effects

Diabetic peripheral neuropathy (DPN) is a complication of diabetes with a high rate of disability. However, current clinical treatments for DPN are suboptimal. Non-coding RNAs (ncRNAs) are a type of RNAs that are not translated into proteins. NcRNAs perform functions that regulate epigenetic modifications, transcriptional or post-transcriptional regulators of proteins, and thus participate in the physiological and pathological processes of the body. NcRNAs play a role in the progress of DPN by affecting the processes of inflammation, oxidative stress, cellular autophagy or apoptosis. Therefore, ncRNAs treatment is regarded as a promising therapeutic approach for DPN. In addition, since some ncRNAs present stably in the blood of DPN patients, they are considered as potential biomarkers that contribute to early clinical diagnosis. In this paper, we review the studies on the role of ncRNAs in DPN in the last decade, and discuss the mechanisms of ncRNAs, aiming to provide a reference for the future research on the treatment and early diagnosis of DPN.

1-Phosphate receptor agonists: A promising therapeutic avenue for ischemia-reperfusion injury management

Ischemia-reperfusion injury (IRI) - a complex pathological condition occurring when blood supply is abruptly restored to ischemic tissues, leading to further tissue damage - poses a significant clinical challenge. Sphingosine-1-phosphate receptors (S1PRs), a specialized set of G-protein-coupled receptors comprising five subtypes (S1PR1 to S1PR5), are prominently present in various cell membranes, including those of lymphocytes, cardiac myocytes, and endothelial cells. Increasing evidence highlights the potential of targeting S1PRs for IRI therapeutic intervention. Notably, preconditioning and postconditioning strategies involving S1PR agonists like FTY720 have demonstrated efficacy in mitigating IRI. As the synthesis of a diverse array of S1PR agonists continues, with FTY720 being a prime example, the body of experimental evidence advocating for their role in IRI treatment is expanding. Despite this progress, comprehensive reviews delineating the therapeutic landscape of S1PR agonists in IRI remain limited. This review aspires to meticulously elucidate the protective roles and mechanisms of S1PR agonists in preventing and managing IRI affecting various organs, including the heart, kidney, liver, lungs, intestines, and brain, to foster novel pharmacological approaches in clinical settings.

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.

High-Density Lipoproteins at the Interface between the NLRP3 Inflammasome and Myocardial Infarction

Despite significant therapeutic advancements, morbidity and mortality following myocardial infarction (MI) remain unacceptably high. This clinical challenge is primarily attributed to two significant factors: delayed reperfusion and the myocardial injury resulting from coronary reperfusion. Following reperfusion, there is a rapid intracellular pH shift, disruption of ionic balance, heightened oxidative stress, increased activity of proteolytic enzymes, initiation of inflammatory responses, and activation of several cell death pathways, encompassing apoptosis, necroptosis, and pyroptosis. The inflammatory cell death or pyroptosis encompasses the activation of the intracellular multiprotein complex known as the NLRP3 inflammasome. High-density lipoproteins (HDL) are endogenous particles whose components can either promote or mitigate the activation of the NLRP3 inflammasome. In this comprehensive review, we explore the role of inflammasome activation in the context of MI and provide a detailed analysis of how HDL can modulate this process.

Anti-inflammatory Effects of Siponimod in a Mouse Model of Excitotoxicity-Induced Retinal Injury

Glaucoma is a leading cause of permanent blindness worldwide and is characterized by neurodegeneration linked to progressive retinal ganglion cell (RGC) death, axonal damage, and neuroinflammation. Glutamate excitotoxicity mediated through N-methyl-D-aspartate (NMDA) receptors plays a crucial role in glaucomatous RGC loss. Sphingosine 1-phosphate receptors (S1PRs) are important mediators of neurodegeneration and neuroinflammation in the brain and the retina. Siponimod is an immunomodulatory drug for multiple sclerosis and is a selective modulator of S1PR subtypes 1 and 5 and has been shown to have beneficial effects on the central nervous system (CNS) in degenerative conditions. Our previous study showed that mice administered orally with siponimod protected inner retinal structure and function against acute NMDA excitotoxicity. To elucidate the molecular mechanisms behind these protective effects, we investigated the inflammatory pathways affected by siponimod treatment in NMDA excitotoxicity model. NMDA excitotoxicity resulted in the activation of glial cells coupled with upregulation of the inflammatory NF-kB pathway and increased expression of TNFα, IL1-β, and IL-6. Siponimod treatment significantly reduced glial activation and suppressed the pro-inflammatory pathways. Furthermore, NMDA-induced activation of NLRP3 inflammasome and upregulation of neurotoxic inducible nitric oxide synthase (iNOS) were significantly diminished with siponimod treatment. Our data demonstrated that siponimod induces anti-inflammatory effects via suppression of glial activation and inflammatory singling pathways that could protect the retina against acute excitotoxicity conditions. These findings provide insights into the anti-inflammatory effects of siponimod in the CNS and suggest a potential therapeutic strategy for neuroinflammatory conditions.

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.

A genome-wide in vivo CRISPR screen identifies essential regulators of T cell migration to the CNS in a multiple sclerosis model

Multiple sclerosis (MS) involves the infiltration of autoreactive T cells into the CNS, yet we lack a comprehensive understanding of the signaling pathways that regulate this process. Here, we conducted a genome-wide in vivo CRISPR screen in a rat MS model and identified 5 essential brakes and 18 essential facilitators of T cell migration to the CNS. While the transcription factor ETS1 limits entry to the CNS by controlling T cell responsiveness, three functional modules, centered around the adhesion molecule α4-integrin, the chemokine receptor CXCR3 and the GRK2 kinase, are required for CNS migration of autoreactive CD4+ T cells. Single-cell analysis of T cells from individuals with MS confirmed that the expression of these essential regulators correlates with the propensity of CD4+ T cells to reach the CNS. Our data thus reveal key regulators of the fundamental step in the induction of MS lesions.

Therapeutic Plasma Exchange and Multiple Sclerosis Dysregulations: Focus on the Removal of Pathogenic Circulatory Factors and Altering Nerve Growth Factor and Sphingosine-1-Phosphate Plasma Levels

Multiple sclerosis (MS) is predominantly an immune-mediated disease of the central nervous system (CNS) of unknown etiology with a possible genetic predisposition and effect of certain environmental factors. It is generally accepted that the disease begins with an autoimmune inflammatory reaction targeting oligodendrocytes followed by a rapid depletion of their regenerative capacity with subsequent permanent neurodegenerative changes and disability. Recent research highlights the central role of B lymphocytes and the corresponding IgG and IgM autoantibodies in newly forming MS lesions. Thus, their removal along with the modulation of certain bioactive molecules to improve neuroprotection using therapeutic plasma exchange (TPE) becomes of utmost importance. Recently, it has been proposed to determine the levels and precise effects of both beneficial and harmful components in the serum of MS patients undergoing TPE to serve as markers for appropriate TPE protocols. In this review we discuss some relevant examples, focusing on the removal of pathogenic circulating factors and altering the plasma levels of nerve growth factor and sphingosine-1-phosphate by TPE. Altered plasma levels of the reviewed molecular compounds in response to TPE reflect a successful reduction of the pro-inflammatory burden at the expense of an increase in anti-inflammatory potential in the circulatory and CNS compartments.

Comparative expression analysis of water buffalo (Bubalus bubalis) to identify genes associated with economically important traits

The milk, meat, skins, and draft power of domestic water buffalo (Bubalus bubalis) provide substantial contributions to the global agricultural economy. The world's water buffalo population is primarily found in Asia, and the buffalo supports more people per capita than any other livestock species. For evaluating the workflow, output rate, and completeness of transcriptome assemblies within and between reference-free (RF) de novo transcriptome and reference-based (RB) datasets, abundant bioinformatics studies have been carried out to date. However, comprehensive documentation of the degree of consistency and variability of the data produced by comparing gene expression levels using these two separate techniques is lacking. In the present study, we assessed the variations in the number of differentially expressed genes (DEGs) attained with RF and RB approaches. In light of this, we conducted a study to identify, annotate, and analyze the genes associated with four economically important traits of buffalo, viz., milk volume, age at first calving, post-partum cyclicity, and feed conversion efficiency. A total of 14,201 and 279 DEGs were identified in RF and RB assemblies. Gene ontology (GO) terms associated with the identified genes were allocated to traits under study. Identified genes improve the knowledge of the underlying mechanism of trait expression in water buffalo which may support improved breeding plans for higher productivity. The empirical findings of this study using RNA-seq data-based assembly may improve the understanding of genetic diversity in relation to buffalo productivity and provide important contributions to answer biological issues regarding the transcriptome of non-model organisms.

The relationship between sphingosine-1-phosphate receptor 2 and epidermal growth factor in migration and invasion of oral squamous cell carcinoma

Sphingosine-1-phosphate (S1P) is a lipid mediator and its binding to the S1P receptor 2 (S1PR2) is reported to regulate cytoskeletal organization. Epidermal growth factor (EGF) has been shown to induce migration and invasion in tumour cells. Since binding of S1P to S1PR2 and EGF to the EGF receptors exhibit some overlapping functionality, this study aimed to determine whether S1PR2 was involved in EGF-induced migration and invasion of oral squamous cell carcinoma (OSCC) lines and to identify any potential crosstalk between the two pathways. Migration was investigated using the scratch wound assay while invasion was studied using the transwell invasion and multicellular tumour spheroid (MCTS) assays. Activity of Rac1, a RhoGTPase, was measured using G-LISA (small GTPase activation assays) while S1P production was indirectly measured via the expression of sphingosine kinase (Sphk). S1PR2 inhibition with 10 µM JTE013 reduced EGF-induced migration, invasion and Rac1 activity, however, stimulation of S1PR2 with 10 µM CYM5478 did not enhance the effect of EGF on migration, invasion or Rac1 activity. The data demonstrated a crosstalk between EGF/EGFR and S1P/S1PR2 pathways at the metabolic level. S1PR2 was not involved in EGF production, but EGF promoted S1P production through the upregulation of Sphk1. In conclusion, OSCC lines could not migrate and invade without S1PR2 regulation, even with EGF stimulation. EGF also activated S1PR2 by stimulating S1P production via Sphk1. The potential for S1PR2 to control cellular motility may lead to promising treatments for OSCC patients and potentially prevent or reduce metastasis.

Visualizing Sphingosine-1-Phosphate Receptor 1(S1P1) Signaling During Central Nervous System De- and Remyelination

Multiple sclerosis (MS) is an inflammatory-demyelinating disease of the central nervous system (CNS) mediated by aberrant auto-reactive immune responses. The current immune-modulatory therapies are unable to protect and repair immune-mediated neural tissue damage. One of the therapeutic targets in MS is the sphingosine-1-phosphate (S1P) pathway which signals via sphingosine-1-phosphate receptors 1-5 (S1P1-5). S1P receptors are expressed predominantly on immune and CNS cells. Considering the potential neuroprotective properties of S1P signaling, we utilized S1P1-GFP (Green fluorescent protein) reporter mice in the cuprizone-induced demyelination model to investigate in vivo S1P - S1P1 signaling in the CNS. We observed S1P1 signaling in a subset of neural stem cells in the subventricular zone (SVZ) during demyelination. During remyelination, S1P1 signaling is expressed in oligodendrocyte progenitor cells in the SVZ and mature oligodendrocytes in the medial corpus callosum (MCC). In the cuprizone model, we did not observe S1P1 signaling in neurons and astrocytes. We also observed β-arrestin-dependent S1P1 signaling in lymphocytes during demyelination and CNS inflammation. Our findings reveal β-arrestin-dependent S1P1 signaling in oligodendrocyte lineage cells implying a role of S1P1 signaling in remyelination.

Dexmedetomidine alleviates oxidative stress and mitochondrial dysfunction in diabetic peripheral neuropathy via the microRNA-34a/SIRT2/S1PR1 axis

OBJECTIVE

Dexmedetomidine (Dex) is a highly selective α₂-adrenoceptor agonist with sedative, analgesic, sympatholytic, and hemodynamic-stabilizing properties, which plays a neuroprotective role in diabetic peripheral neuropathy (DPN) and diabetes-induced nerve damage. However, the related molecular mechanisms are not fully understood. Therefore, our study explored the mechanism of Dex in DPN using rat and RSC96 cell models.

METHODS

Sciatic nerve sections were observed under an optical microscope and the ultrastructure of the sciatic nerves was observed under a transmission electron microscope. Oxidative stress was assessed by detecting MDA, SOD, GSH-Px, and ROS levels. The motor nerve conduction velocity (MNCV), mechanical withdrawal threshold (MWT), and thermal withdrawal latency (TWL) of rats were measured. Cell viability, apoptosis, and the changes in the expression of related genes and proteins were examined. Furthermore, the relationship between microRNA (miR)-34a and SIRT2 or SIRT2 and S1PR1 was analyzed.

RESULTS

Dex reversed DPN-induced decreases in MNCV, MWT, and TWL. Dex alleviated oxidative stress, mitochondrial damage, and apoptosis in both the rat and RSC96 cell models of DPN. Mechanistically, miR-34a negatively targeted SIRT2, and SIRT2 inhibited S1PR1 transcription. The overexpression of miR-34a or S1PR1 or the inhibition of SIRT2 counteracted the neuroprotective effects of Dex in DPN in vivo and in vitro.

CONCLUSION

Dex alleviates oxidative stress and mitochondrial dysfunction associated with DPN by downregulating miR-34a to regulate the SIRT2/S1PR1 axis.

Etrasimod for the treatment of ulcerative colitis

Sphingosine-1-phosphate (S1P) and its receptor (S1PR) are involved in the pathogenesis of multiple immune-mediated inflammatory disorders, including inflammatory bowel disease. The use of S1PR modulators represents a new therapeutic option for ulcerative colitis patients. Etrasimod is an oral selective S1PR1, S1PR4 and S1PR5 modulator that inhibits the trafficking of lymphocytes from the lymph nodes into the blood. Recently, etrasimod has demonstrated efficacy in the phase II OASIS study and its open-label extension for the treatment of ulcerative colitis patients. This article reviews the mechanism of action of etrasimod and summarizes the available clinical efficacy and safety data regarding etrasimod, which is a promising drug in the treatment of patients with moderate to severe ulcerative colitis.

S1PR1 signaling attenuates apoptosis of retinal ganglion cells via modulation of cJun/Bim cascade and Bad phosphorylation in a mouse model of glaucoma

Glaucoma is a complex neurodegenerative disease characterized by optic nerve damage and apoptotic retinal ganglion cell (RGC) death, and is the leading cause of irreversible blindness worldwide. Among the sphingosine 1-phosphate receptors (S1PRs) family, S1PR1 is a highly expressed subtype in the central nervous system and has gained rapid attention as an important mediator of pathophysiological processes in the brain and the retina. Our recent study showed that mice treated orally with siponimod drug exerted neuroprotection via modulation of neuronal S1PR1 in experimental glaucoma. This study identified the molecular signaling pathway modulated by S1PR1 activation with siponimod treatment in RGCs in glaucomatous injury. We investigated the critical neuroprotective signaling pathway in vivo using mice deleted for S1PR1 in RGCs. Our results showed marked upregulation of the apoptotic pathway was associated with decreased Akt and Erk1/2 activation levels in the retina in glaucoma conditions. Activation of S1PR1 with siponimod treatment significantly increased neuroprotective Akt and Erk1/2 activation and attenuated the apoptotic signaling via suppression of c-Jun/Bim cascade and by increasing Bad phosphorylation. Conversely, deletion of S1PR1 in RGCs significantly increased the apoptotic cells in the ganglion cell layer in glaucoma and diminished the neuroprotective effects of siponimod treatment on Akt/Erk1/2 activation, c-Jun/Bim cascade, and Bad phosphorylation. Our data demonstrated that activation of S1PR1 in RGCs induces crucial neuroprotective signaling that suppresses the proapoptotic c-Jun/Bim cascade and increases antiapoptotic Bad phosphorylation. Our findings suggest that S1PR1 is a potential therapeutic target for neuroprotection of RGCs in glaucoma.

LncRNA ANRIL-mediated miR-181b-5p/S1PR1 axis is involved in the progression of uremic cardiomyopathy through activating T cells

This study aimed to explore the regulatory role of lncRNA ANRIL/miR-181b-5p/S1PR1 in UC. UC mouse model was established by 5/6th nephrectomy. We detected body weight, serum levels of renal function and inflammatory factors (biochemical analyzer/ELISA), and cardiac parameters (echocardiography). HE and Masson staining showed the pathological changes and fibrosis in myocardial and nephridial tissues. The expression of ANRIL, miR-181b-5p, and S1PR1 were detected by qRT-PCR or Western blot/immunofluorescence. T cells activation was analyzed by Flow cytometry. ANRIL/S1PR1 were up-regulated and miR-181b-5p was down-regulated in UC mice. ANRIL silencing up-regulated miR-181b-5p and down-regulated S1PR1 (a target of miR-181b-5p). ANRIL silencing increased the body weight, recovered renal function [decreased blood urea nitrogen (BUN) and serum creatinine (Scr)] and cardiac function [decreased left ventricular end-diastolic diameter (LVEDD), LV end-systolic diameter (LVESD), LV systolic anterior wall thickness (LVAWS), LV end-diastolic anterior wall thickness (LVAWD), myocardial performance index (MPI), and isovolumic relaxation time (IVRT); increased LV ejection fraction (LVEF), LVEF/MPI, fractional shortening (FS), and E- and A-waves (E/A)], inhibited the inflammation [decreased interferon (IFN)-γ, interleukin (IL)-2, IL-10, and tumor necrosis factor (TNF)-α], and relieved pathological injuries and fibrosis. ANRIL silencing also recovered the viability and inhibited the inflammation of activated T cells in vitro, and inhibited T cell activation in UC mice in vivo. In addition, miR-181b-5p overexpression exhibited same effects with ANRIL silencing in UC. ANRIL silencing inhibited T cell activation through regulating miR-181b-5p/S1PR1, contributing to the remission of UC.

Sphingosine-1-phosphate receptor modulators in stroke treatment

Sphingosine-1-phosphate (S1P) is a bioactive lysophospholipid that can influence a broad range of biological processes through its binding to five distinct G protein-coupled receptors. S1P receptor modulators are a new group of immunosuppressive agents currently used in the immunotherapy of multiple sclerosis. Inflammation following stroke may exacerbate injury. Given that S1P signaling is linked to multiple immune processes, therapies targeting the S1P axis may be suitable for treating stroke. In this review, we outline S1P metabolism and S1P receptors, discuss the mechanisms of action of S1P receptor modulators in lymphocyte migration and their direct action on cells of the central nervous system, and provide a concise summary of the efficacy of S1P receptor modulators in animal studies and clinical trials on treatments for stroke.

Sphingosine-1-Phosphate (S1P) and S1P Signaling Pathway Modulators, from Current Insights to Future Perspectives

Sphingosine-1-phosphate (S1P) and S1P receptors (S1PR) are bioactive lipid molecules that are ubiquitously expressed in the human body and play an important role in the immune system. S1P-S1PR signaling has been well characterized in immune trafficking and activation in both innate and adaptive immune systems. Despite this knowledge, the full scope in the pathogenesis of autoimmune disorders is not well characterized yet. From the discovery of fingolimod, the first S1P modulator, until siponimod, the new molecule recently approved for the treatment of secondary progressive multiple sclerosis (SPMS), there has been a great advance in understanding the S1P functions and their involvement in immune diseases, including multiple sclerosis (MS). Modulation on S1P is an interesting target for the treatment of various autoimmune disorders. Improved understanding of the mechanism of action of fingolimod has allowed the development of the more selective second-generation S1PR modulators. Subtype 1 of the S1PR (S1PR1) is expressed on the cell surface of lymphocytes, which are known to play a major role in MS pathogenesis. The understanding of S1PR1’s role facilitated the development of pharmacological strategies directed to this target, and theoretically reduced the safety concerns derived from the use of fingolimod. A great advance in the MS treatment was achieved in March 2019 when the Food and Drug Association (FDA) approved Siponimod, for both active secondary progressive MS and relapsing–remitting MS. Siponimod became the first oral disease modifying therapy (DMT) specifically approved for active forms of secondary progressive MS. Additionally, for the treatment of relapsing forms of MS, ozanimod was approved by FDA in March 2020. Currently, there are ongoing trials focused on other new-generation S1PR1 modulators. This review approaches the fundamental aspects of the sphingosine phosphate modulators and their main similarities and differences.

A critical review of ozanimod for the treatment of adults with moderately to severely active ulcerative colitis

INTRODUCTION

Ozanimod is a sphingosine-1-phosphate (S1P) modulator that inhibits lymphocyte trafficking from lymph nodes to the circulation. It is approved by the US Food and Drug Administration (FDA) for the treatment of relapsing multiple sclerosis and most recently for the management of moderate-severe ulcerative colitis (UC).

AREAS COVERED

Here we review the status of drugs approved for moderate-severe UC, the unmet needs in the management of UC, proposed mechanisms of action of S1P modulators, clinical data regarding ozanimod in UC, and emerging S1P modulators being evaluated in inflammatory bowel disease.

EXPERT OPINION

Ozanimod is superior to placebo in inducing and maintaining clinical and endoscopic remission in UC. Adverse events include transient asymptomatic bradycardia, first-degree atrioventricular blocks, transient asymptomatic hepatotoxicity, macular edema in patients with preexisting risk factors, and increased risk of nasopharyngitis. Ozanimod is contraindicated in patients with clinically significant cardiovascular diseases, type II second-, or third-degree atrioventricular blocks, and females of childbearing age who do not use contraception. Ozanimod is the first S1P modulator to be approved for UC, offering a new therapeutic class option for patients. It has the advantages of being convenient with a once-daily oral administration, non-immunogenic, and overall safe when used in patients without contraindications.

Sphingosine-1 phosphate receptor 1 contributes to central sensitization in recurrent nitroglycerin-induced chronic migraine model

BACKGROUND

Central sensitization is an important pathophysiological mechanism of chronic migraine (CM), and microglia activation in trigeminocervical complex (TCC) contributes to the development of central sensitization. Emerging evidence implicates that blocking sphingosine-1-phosphate receptor 1 (S1PR1) can relieve the development of chronic pain and inhibit the activation of microglia. However, it is unclear whether S1PR1 is involved in the central sensitization of CM. Therefore, the purpose of this study is to explore the role of S1PR1 and its downstream signal transducers and activators of transcription 3 (STAT3) signaling pathway in the CM, mainly in inflammation.

METHODS

Chronic intermittent intraperitoneal injection of nitroglycerin (NTG) established a mouse model of CM. First, we observed the changes and subcellular localization of S1PR1 in the trigeminocervical complex (TCC). Then, W146, a S1PR1 antagonist; SEW2871, a S1PR1 agonist; AG490, a STAT3 inhibitor were applied by intraperitoneal injection to investigate the related molecular mechanism. The changes in the number of microglia and the expression of calcitonin gene-related peptide (CGRP) and c-fos in the TCC site were explored by immunofluorescence. In addition, we studied the effect of S1PR1 inhibitors on STAT3 in lipopolysaccharide-treated BV-2 microglia.

RESULTS

Our results showed that the expression of S1PR1 was increased after NTG injection and S1PR1 was colocalized with in neurons and glial cells in the TCC. The S1PR1 antagonist W146 alleviated NTG-induced hyperalgesia and suppressed the upregulation of CGRP, c-fos and pSTAT3 in the TCC. Importantly, blocking S1PR1 reduced activation of microglia. In addition, we found that inhibiting STAT3 signal also attenuated NTG-induced basal mechanical and thermal hyperalgesia.

CONCLUSIONS

Our results indicate that inhibiting S1PR1 signal could alleviate central sensitization and inhibit microglia activity caused by chronic NTG administration via STAT3 signal pathway, which provide a new clue for the clinical treatment of CM.

The Two Sides of Siponimod: Evidence for Brain and Immune Mechanisms in Multiple Sclerosis

Siponimod is a selective sphingosine 1-phosphate receptor subtype 1 (S1P₁) and 5 (S1P₅) modulator approved in the United States and the European Union as an oral treatment for adults with relapsing forms of multiple sclerosis (RMS), including active secondary progressive multiple sclerosis (SPMS). Preclinical and clinical studies provide support for a dual mechanism of action of siponimod, targeting peripherally mediated inflammation and exerting direct central effects. As an S1P₁ receptor modulator, siponimod reduces lymphocyte egress from lymph nodes, thus inhibiting their migration from the periphery to the central nervous system. As a result of its peripheral immunomodulatory effects, siponimod reduces both magnetic resonance imaging (MRI) lesion (gadolinium-enhancing and new/enlarging T2 hyperintense) and relapse activity compared with placebo. Independent of these effects, siponimod can penetrate the blood-brain barrier and, by binding to S1P₁ and S1P₅ receptors on a variety of brain cells, including astrocytes, oligodendrocytes, neurons, and microglia, exert effects to modulate neural inflammation and neurodegeneration. Clinical data in patients with SPMS have shown that, compared with placebo, siponimod treatment is associated with reductions in levels of neurofilament light chain (a marker of neuroaxonal damage) and thalamic and cortical gray matter atrophy, with smaller reductions in MRI magnetization transfer ratio and reduced confirmed disability progression. This review examines the preclinical and clinical data supporting the dual mechanism of action of siponimod in RMS.

Sphingolipids in Hematopoiesis: Exploring Their Role in Lineage Commitment

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

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).

Targeting the SphK-S1P-SIPR Pathway as a Potential Therapeutic Approach for COVID-19

The world is currently experiencing the worst health pandemic since the Spanish flu in 1918-the COVID-19 pandemic-caused by the coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This pandemic is the world's third wake-up call this century. In 2003 and 2012, the world experienced two major coronavirus outbreaks, SARS-CoV-1 and Middle East Respiratory syndrome coronavirus (MERS-CoV), causing major respiratory tract infections. At present, there is neither a vaccine nor a cure for COVID-19. The severe COVID-19 symptoms of hyperinflammation, catastrophic damage to the vascular endothelium, thrombotic complications, septic shock, brain damage, acute disseminated encephalomyelitis (ADEM), and acute neurological and psychiatric complications are unprecedented. Many COVID-19 deaths result from the aftermath of hyperinflammatory complications, also referred to as the "cytokine storm syndrome", endotheliitus and blood clotting, all with the potential to cause multiorgan dysfunction. The sphingolipid rheostat plays integral roles in viral replication, activation/modulation of the immune response, and importantly in maintaining vasculature integrity, with sphingosine 1 phosphate (S1P) and its cognate receptors (SIPRs: G-protein-coupled receptors) being key factors in vascular protection against endotheliitus. Hence, modulation of sphingosine kinase (SphK), S1P, and the S1P receptor pathway may provide significant beneficial effects towards counteracting the life-threatening, acute, and chronic complications associated with SARS-CoV-2 infection. This review provides a comprehensive overview of SARS-CoV-2 infection and disease, prospective vaccines, and current treatments. We then discuss the evidence supporting the targeting of SphK/S1P and S1P receptors in the repertoire of COVID-19 therapies to control viral replication and alleviate the known and emerging acute and chronic symptoms of COVID-19. Three clinical trials using FDA-approved sphingolipid-based drugs being repurposed and evaluated to help in alleviating COVID-19 symptoms are discussed.

The wonderful and masterful G protein-coupled receptor (GPCR): A focus on signaling mechanisms and the neuroendocrine control of fertility

Human GnRH deficiency, both clinically and genetically, is a heterogeneous disorder comprising of congenital GnRH deficiency with anosmia (Kallmann syndrome), or with normal olfaction [normosmic idiopathic hypogonadotropic hypogonadism (IHH)], and adult-onset hypogonadotropic hypogonadism. Our understanding of the neural mechanisms underlying GnRH secretion and GnRH signaling continues to increase at a rapid rate and strikingly, the heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) continue to emerge as essential players in these processes. GPCRs were once viewed as binary on-off switches, where in the "on" state they are bound to their Gα protein, but now we understand that view is overly simplistic and does not adequately characterize GPCRs. Instead, GPCRs have emerged as masterful signaling molecules exploiting different physical conformational states of itself to elicit an array of downstream signaling events via their G proteins and the β-arrestins. The "one receptor-multiple signaling conformations" model is likely an evolved strategy that can be used to our advantage as researchers have shown that targeting specific receptor conformations via biased ligands is proving to be a powerful tool in the effective treatment of human diseases. Can biased ligands be used to selectively modulate signaling by GPCR regulators of the neuroendocrine axis in the treatment of IHH? As discussed in this review, the grand possibility exists. However, while we are still very far from developing these treatments, this exciting likelihood can happen through a much greater mechanistic understanding of how GPCRs signal within the cell.

Post-translational modifications of S1PR1 and endothelial barrier regulation

Sphingosine-1-phosphate receptor-1 (S1PR1), a G-protein coupled receptor that is expressed in endothelium and activated upon ligation by the bioactive lipid sphingosine-1-phosphate (S1P), is an important vascular-barrier protective mechanism at the level of adherens junctions (AJ). Loss of endothelial barrier function is a central factor in the pathogenesis of various inflammatory conditions characterized by protein-rich lung edema formation, such as acute respiratory distress syndrome (ARDS). While several S1PR1 agonists are available, the challenge of arresting the progression of protein-rich edema formation remains to be met. In this review, we discuss the role of S1PRs, especially S1PR1, in regulating endothelial barrier function. We review recent findings showing that replenishment of the pool of cell-surface S1PR1 may be crucial to the effectiveness of S1P in repairing the endothelial barrier. In this context, we discuss the S1P generating machinery and mechanisms that regulate S1PR1 at the cell surface and their impact on endothelial barrier function.

The role of Sphingolipids in myelination and myelin stability and their involvement in childhood and adult demyelinating disorders

Multiple sclerosis (MS) represents the most common demyelinating disease affecting the central nervous system (CNS) in adults as well as in children. Furthermore, in children, in addition to acquired diseases such as MS, genetically inherited diseases significantly contribute to the incidence of demyelinating disorders. Some genetic defects lead to sphingolipid alterations that are able to elicit neurological symptoms. Sphingolipids are essential for brain development, and their aberrant functionality may thus contribute to demyelinating diseases such as MS. In particular, sphingolipidoses caused by deficits of sphingolipid-metabolizing enzymes, are often associated with demyelination. Sphingolipids are not only structural molecules but also bioactive molecules involved in the regulation of cellular events such as development of the nervous system, myelination and maintenance of myelin stability. Changes in the sphingolipid metabolism deeply affect plasma membrane organization. Thus, changes in myelin sphingolipid composition might crucially contribute to the phenotype of diseases characterized by demyelinalization. Here, we review key features of several sphingolipids such as ceramide/dihydroceramide, sphingosine/dihydrosphingosine, glucosylceramide and, galactosylceramide which act in myelin formation during rat brain development and in human brain demyelination during the pathogenesis of MS, suggesting that this knowledge could be useful in identifying targets for possible therapies.

Discovery of fingolimod based on the chemical modification of a natural product from the fungus, Isaria sinclairii

Fingolimod is a first-in-class of sphingosine-1-phosphate (S1P) receptor modulator and is widely used a therapeutic drug for multiple sclerosis (MS), autoimmune disease in the central nervous system. About 25 year ago, a natural product, myriocin was isolated from culture broths of the fungus Isaria sinclairii. Myriocin, a rather complex amino acid having three successive asymmetric centers, was found to show a potent immunosuppressive activity in vitro; however, it induced a strong toxicity in vivo. To find out a less toxic immunosuppressive candidate, the chemical structure of myriocin was simplified to a nonchiral symmetric 2-substituted-2-aminoproane-1,3-diol framework. Finally, a highly potent immunosuppressant, fingolimod was found by the extensive chemical modification and pharmacological evaluation using skin allograft model in vivo. Throughout the analyses of the mechanism action of fingolimod, it is revealed that S1P receptor 1 (S1P₁) plays an essential role in lymphocyte circulation and that the molecular target of fingolimod is S1P₁. Phosphorylated fingolimod acts as a "functional" antagonist at S1P₁, modulates lymphocyte circulation, and shows a potent immunosuppressive activity. Fingolimod significantly reduced the relapse rate of MS in the clinical studies and has been approved as a new therapeutic drug for MS in more than 80 countries.

Mitochondrial sphingosine-1-phosphate lyase is essential for phosphatidylethanolamine synthesis and survival of Trypanosoma brucei

Sphingosine-1-phosphate is a signaling molecule involved in the control of cell migration, differentiation, survival and other physiological processes. This sphingolipid metabolite can be degraded by the action of sphingosine-1-phosphate lyase (SPL) to form hexadecenal and ethanolamine phosphate. The importance of SPL-mediated ethanolamine phosphate formation has been characterized in only few cell types. We show that in the protozoan parasite Trypanosoma brucei, expression of TbSpl is essential for cell survival. Ablation of TbSpl expression increased sphingosine-1-phosphate levels and reduced de novo formation and steady-state levels of the glycerophospholipid phosphatidylethanolamine (PE). Growth of TbSpl-depleted parasites could be in part rescued by ethanolamine supplementation to the growth medium, indicating that the main function of TbSpl is to provide ethanolamine phosphate for PE synthesis. In contrast to most cell types analyzed, where SPL localizes to the endoplasmic reticulum, we found by high-resolution microscopy that TbSpl is a mitochondrial protein. In spite of its mitochondrial localization, TbSpl depletion had no apparent effect on mitochondrial morphology but resulted in aggregation of acidocalcisomes. Our results link mitochondria to sphingolipid metabolism and suggest possible roles for PE in acidocalcisome function.

S1PR1 as a Novel Promising Therapeutic Target in Cancer Therapy

Sphingosine-1-phosphate (S1P) can regulate several physiological and pathological processes. S1P signaling via its cell surface receptor S1PR1 has been shown to enhance tumorigenesis and stimulate growth, expansion, angiogenesis, metastasis, and survival of cancer cells. S1PR1-mediated tumorigenesis is supported and amplified by activation of downstream effectors including STAT3, interleukin-6, and NF-κB networks. S1PR1 signaling can also trigger various other signaling pathways involved in carcinogenesis including activation of PI3K/AKT, MAPK/ERK1/2, Rac, and PKC/Ca, as well as suppression of cyclic adenosine monophosphate (cAMP). It also induces immunological tolerance in the tumor microenvironment, while the immunosuppressive function of S1PR1 can also lead to the generation of pre-metastatic niches. Some tumor cells upregulate S1PR1 signaling pathways, which leads to drug resistant cancer cells, mainly through activation of STAT3. This signaling pathway is also implicated in some inflammatory conditions leading to the instigation of inflammation-driven cancers. Furthermore, it can also increase survival via induction of anti-apoptotic pathways, for instance, in breast cancer cells. Therefore, S1PR1 and its signaling pathways can be considered as potential anti-tumor therapeutic targets, alone or in combination therapies. Given the oncogenic nature of S1PR1 and its distribution in a variety of cancer cell types along with its targeting advantages over other molecules of this family, S1PR1 should be considered a favorable target in therapeutic approaches to cancer. This review describes the role of S1PR1 in cancer development and progression, specifically addressing breast cancer, glioma, and hematopoietic malignancies. We also discuss the potential use of S1P signaling modulators as therapeutic targets in cancer therapy.

Significance of sphingosine-1-phosphate in cardiovascular physiology and pathology

Sphingosine-1-phosphate (S1P) is a signaling lipid, synthetized by sphingosine kinases (SPHK1 and SPHK2), that affects cardiovascular function in various ways. S1P signaling is complex, particularly since its molecular action is reliant on the differential expression of its receptors (S1PR1, S1PR2, S1PR3, S1PR4, S1PR5) within various tissues. Significance of this sphingolipid is manifested early in vertebrate development as certain defects in S1P signaling result in embryonic lethality due to defective vasculo- or cardiogenesis. Similar in the mature organism, S1P orchestrates both physiological and pathological processes occurring in the heart and vasculature of higher eukaryotes. S1P regulates cell fate, vascular tone, endothelial function and integrity as well as lymphocyte trafficking, thus disbalance in its production and signaling has been linked with development of such pathologies as arterial hypertension, atherosclerosis, endothelial dysfunction and aberrant angiogenesis. Number of signaling mechanisms are critical - from endothelial nitric oxide synthase through STAT3, MAPK and Akt pathways to HDL particles involved in redox and inflammatory balance. Moreover, S1P controls both acute cardiac responses (cardiac inotropy and chronotropy), as well as chronic processes (such as apoptosis and hypertrophy), hence numerous studies demonstrate significance of S1P in the pathogenesis of hypertrophic/fibrotic heart disease, myocardial infarction and heart failure. This review presents current knowledge concerning the role of S1P in the cardiovascular system, as well as potential therapeutic approaches to target S1P signaling in cardiovascular diseases.

Determinants of Serum- and Plasma Sphingosine-1-Phosphate Concentrations in a Healthy Study Group

Introduction  To correctly interpret plasma- or serum-sphingosine-1-phosphate (S1P) concentrations measured in clinical studies it is critical to understand all major determinants in healthy controls.

Methods  Serum- and plasma-S1P from 174 healthy blood donors was measured by liquid chromatography-tandem mass spectrometry and correlated to clinical laboratory data. Selected plasma samples, 10 with high and 10 with low S1P concentrations, were fractionated into very low-density lipoprotein (VLDL)-, low density lipoprotein (LDL)-, high density lipoprotein (HDL)-, and lipoprotein-free fractions. S1P was then measured in each fraction to determine its distribution.

Results  The mean S1P concentration in serum (1.04 ± 0.24 nmol/mL) was found 39% higher compared with plasma (0.75 ± 0.16 nmol/mL) and overall was not different between men and women. Only when stratified for age and gender, older women were found to exhibit higher circulatory S1P levels than men. In plasma, S1P levels correlate to red blood cell (RBC) counts but not to platelet counts. Conversely, serum-S1P correlates to platelet counts but not to RBC counts. In addition, eosinophil counts are strongly associated with serum-S1P concentrations. Both serum- and plasma-S1P correlate to total cholesterol but not to HDL-C. The distribution of S1P between VLDL-, LDL-, HDL-, and lipoprotein-free fractions is independent of total plasma-S1P concentrations. S1P concentrations in HDL but not in LDL are highly variable.

Conclusion  These data indicate S1P concentrations in plasma and serum to be differentially associated with cell counts and S1P carrier proteins. Besides platelets, eosinophil counts are identified as a novel determinant for serum-S1P concentrations further suggesting a role for S1P in eosinophil pathologies.

Sphingosine 1-Phosphate Receptor 2 Induces Otoprotective Responses to Cisplatin Treatment

Ototoxicity is a major adverse effect of platinum-based chemotherapeutics and currently, there remains a lack of United States Food and Drug Administration-approved therapies to prevent or treat this problem. In our study, we examined the role of the sphingosine 1-phosphate receptor 2 (S1P₂) in attenuating cisplatin-induced ototoxicity in several different animal models and cell lines. We found that ototoxicity in S1P₂ knockout mice is dependent on reactive oxygen species (ROS) production and that S1P₂ receptor activation with a specific agonist, CYM-5478, significantly attenuates cisplatin-induced defects, including hair cell degeneration in zebrafish and prolonged auditory brainstem response latency in rats. We also evaluated the cytoprotective effect of CYM-5478 across different cell lines and showed that CYM-5478 protects neural-derived cell lines but not breast cancer cells against cisplatin toxicity. We show that this selective protection of CYM-5478 is due to its differential effects on key regulators of apoptosis between neural cells and breast cancer cells. Overall, our study suggests that targeting the S1P₂ receptor represents a promising therapeutic approach for the treatment of cisplatin-induced ototoxicity in cancer patients.

Sphingolipids in Alzheimer's disease, how can we target them?

Altered levels of sphingolipids and their metabolites in the brain, and the related downstream effects on neuronal homeostasis and the immune system, provide a framework for understanding mechanisms in neurodegenerative disorders and for developing new intervention strategies. In this review we will discuss: the metabolites of sphingolipids that function as second messengers; and functional aberrations of the pathway resulting in Alzheimer's disease (AD) pathophysiology. Focusing on the central product of the sphingolipid pathway ceramide, we describ approaches to pharmacologically decrease ceramide levels in the brain and we argue on how the sphingolipid pathway may represent a new framework for developing novel intervention strategies in AD. We also highlight the possible use of clinical and non-clinical drugs to modulate the sphingolipid pathway and sphingolipid-related biological cascades.

Long noncoding RNAs APOA1-AS, IFNG-AS1, RMRP and their related biomolecules in Egyptian patients with relapsing-remitting multiple sclerosis: Relation to disease activity and patient disability

Lately, long noncoding (lnc) RNAs are increasingly appreciated for their involvement in multiple sclerosis (MS). In inflammation and autoimmunity, a role of apoprotein A1 (ApoA1), mediated by sphingosine 1-phosphate receptors (S1PRs), was reported. However, the epigenetic mechanisms regulating these biomolecules and their role in MS remains elusive. This case control study investigated the role of ApoA1, sphingosine kinase 1 and 2 (SPHK1 & 2), S1PR1 & 5, interferon-γ (IFN-γ) and interleukin 17 (IL17) in MS, beside three lncRNA: APOA1-AS, IFNG-AS1, and RMRP. Expression of SPHKs, S1PRs, and lncRNAs were measured in 72 relapsing-remitting MS patients (37 during relapse and 35 in remission) and 28 controls. Plasma levels of ApoA1, IFN-γ and IL17 were determined. The impact of these parameters on MS activity, relapse rate and patient disability was assessed. APOA1-AS, IFNG-AS1, SPHK1 & 2, and S1PR5 were upregulated in RRMS patients. Differences in ApoA1, SPHK2, and IL17 were observed between relapse and remission. Importantly, ApoA1, SPHK2, and IL17 were related to activity, while S1PR1 and IFN-γ were linked to disability, though, only IFN-γ was associated with relapse rate. Finally, an excellent diagnostic power of IFN-γ, IL17, SPHK1 and APOA1-AS was demonstrated, whereas SPHK2 showed promising prognostic power in predicting relapses.

Lipid-Binding Proteins in Brain Health and Disease

A proper lipid management is paramount for a healthy brain. Lipid homeostasis alterations are known to be causative or risk factors for many neurodegenerative diseases, or key elements in the recovery from nervous system injuries of different etiology. In addition to lipid biogenesis and catabolism, non-enzymatic lipid-binding proteins play an important role in brain function and maintenance through aging. Among these types of lipoproteins, apolipoprotein E has received much attention due to the relationship of particular alleles of its gene with the risk and progression of Alzheimer's disease. However, other lipid-binding proteins whose role in lipid homeostasis and control are less known need to be brought to the attention of both researchers and clinicians. The aim of this review is to cover the knowledge of lipid-managing proteins in the brain, with particular attention to new candidates to be relevant for brain function and health.

New Routes in GPCR/β-Arrestin-Driven Signaling in Cancer Progression and Metastasis

Tumor cells acquire invasive and metastatic behavior by sensing changes in the localization and activation of signaling pathways, which in turn determine changes in actin cytoskeleton. The core-scaffold machinery associated to β-arrestin (β-arr) is a key mechanism of G-protein coupled receptors (GPCR) to achieve spatiotemporal specificity of different signaling complexes driving cancer progression. Within different cellular contexts, the scaffold proteins β-arr1 or β-arr2 may now be considered organizers of protein interaction networks involved in tumor development and metastatic dissemination. Studies have uncovered the importance of the β-arr engagement with a growing number of receptors, signaling molecules, cytoskeleton regulators, epigenetic modifiers, and transcription factors in GPCR-driven tumor promoting pathways. In many of these molecular complexes, β-arrs might provide a physical link to active dynamic cytoskeleton, permitting cancer cells to adapt and modify the tumor microenvironment to promote the metastatic spread. Given the complexity and the multidirectional β-arr-driven signaling in cancer cells, therapeutic targeting of specific GPCR/β-arr molecular mechanisms is an important avenue to explore when considering future new therapeutic options. The focus of this review is to integrate the most recent developments and exciting findings of how highly connected components of β-arr-guided molecular connections to other pathways allow precise control over multiple signaling pathways in tumor progression, revealing ways of therapeutically targeting the convergent signals in patients.

Novel oral-targeted therapies for mucosal healing in ulcerative colitis

Ulcerative colitis (UC), a chronic, relapsing, remitting disease of the colon and rectum, is characterized by inflammatory ulceration of the mucosa. Current UC therapy relies on controlling acute episodes and preventing relapse. To predict modifications in the natural course of UC, mucosal healing (MH) has emerged as a major treatment goal. Endoscopic evaluation is considered the gold standard for assessing MH, which can be achieved by conventional drugs and biologics in many, but not all, patients. Consequently, interest is focusing on the development of new substances for UC therapy, and new oral agents are in the pipeline. This review will focus on the ability of newly developed oral drugs to induce and maintain MH in UC patients.

Sphingolipids in adipose tissue: What's tipping the scale?

Adipose tissue lies at the heart of obesity, mediating its many effects upon the rest of the body, with its unique capacity to expand and regenerate, throughout the lifespan of the organism. Adipose is appreciated as an endocrine organ, with its myriad adipokines that elicit both physiological and pathological outcomes. Sphingolipids, bioactive signaling molecules, affect many aspects of obesity and the metabolic syndrome. While sphingolipids are appreciated in the context of these diseases in other tissues, there are many discoveries yet to be uncovered in the adipose tissue. This review focuses on the effects of sphingolipids on various aspects of adipose function and dysfunction. The processes of adipogenesis, metabolism and thermogenesis, in addition to inflammation and insulin resistance are intimately linked to sphingolipids as discussed below.

β-Arrestin Based Receptor Signaling Paradigms: Potential Therapeutic Targets for Complex Age-Related Disorders

G protein coupled receptors (GPCRs) were first characterized as signal transducers that elicit downstream effects through modulation of guanine (G) nucleotide-binding proteins. The pharmacotherapeutic exploitation of this signaling paradigm has created a drug-based field covering nearly 50% of the current pharmacopeia. Since the groundbreaking discoveries of the late 1990s to the present day, it is now clear however that GPCRs can also generate productive signaling cascades through the modulation of β-arrestin functionality. β-Arrestins were first thought to only regulate receptor desensitization and internalization - exemplified by the action of visual arrestin with respect to rhodopsin desensitization. Nearly 20 years ago, it was found that rather than controlling GPCR signal termination, productive β-arrestin dependent GPCR signaling paradigms were highly dependent on multi-protein complex formation and generated long-lasting cellular effects, in contrast to G protein signaling which is transient and functions through soluble second messenger systems. β-Arrestin signaling was then first shown to activate mitogen activated protein kinase signaling in a G protein-independent manner and eventually initiate protein transcription - thus controlling expression patterns of downstream proteins. While the possibility of developing β-arrestin biased or functionally selective ligands is now being investigated, no additional research has been performed on its possible contextual specificity in treating age-related disorders. The ability of β-arrestin-dependent signaling to control complex and multidimensional protein expression patterns makes this therapeutic strategy feasible, as treating complex age-related disorders will likely require therapeutics that can exert network-level efficacy profiles. It is our understanding that therapeutically targeting G protein-independent effectors such as β-arrestin will aid in the development of precision medicines with tailored efficacy profiles for disease/age-specific contextualities.

'Crystal' Clear? Lysophospholipid Receptor Structure Insights and Controversies

Lysophospholipids (LPLs), particularly sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA), are bioactive lipid modulators of cellular homeostasis and pathology. The discovery and characterization of five S1P- and six LPA-specific G protein-coupled receptors (GPCRs), S1P1-5 and LPA1-6, have expanded their known involvement in all mammalian physiological systems. Resolution of the S1P1, LPA1, and LPA6 crystal structures has fueled the growing interest in these receptors and their ligands as targets for pharmacological manipulation. In this review, we have attempted to provide an integrated overview of the three crystallized LPL GPCRs with biochemical and physiological structure-function data. Finally, we provide a novel discussion of how chaperones for LPLs may be considered when extrapolating crystallographic and computational data toward understanding actual biological interactions and phenotypes.

Sphingosine-1-phosphate receptors and innate immunity

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

ENPP2 protects cardiomyocytes from erastin-induced ferroptosis

Ferroptosis is an iron- and oxidative-dependent form of regulated cell death and may play important roles in maintaining myocardium homeostasis and pathology of cardiovascular diseases. Currently, the regulatory roles of lipid signals in regulating cardiomyocytes ferroptosis has not been explored. In this study, we show that ENPP2, as a lipid kinase involved in lipid metabolism, protects against erastin-induced ferroptosis in cardiomyocytes. The classical ferroptosis inducer erastin remarkably inhibits the growth which could be rescued by the small molecule Fer-1 in H9c2 cells. Adenovirus mediated ENPP2 overexpression modestly promotes migration and proliferation and significantly inhibits erastin-induced ferroptosis of H9c2 cells. ENPP2 overexpression leads to increase the LPA level in supernatant of H9c2 cells. H9c2 cells express the LPAR1, LPAR3, LPAR4 and LPAR5 receptors. The supernatant of ENPP2 transduced cardiomyocytes could protects the cells from erastin-induced ferroptosis of H9c2 cells. Furthermore, we observed that ENPP2 overexpression regulates ferroptosis-associated gene GPX4, ACSL4 and NRF2 expression and modulates MAPK and AKT signal in H9c2 cells. Collectively, these findings demonstrated that ENPP2/LPA protects cardiomyocytes from erastin-induced ferroptosis through modulating GPX4, ACSL4 and NRF2 expression and enhancing AKT survival signal.

Alkaline ceramidase 2 is essential for the homeostasis of plasma sphingoid bases and their phosphates

Sphingosine-1-phosphate (S1P) plays important roles in cardiovascular development and immunity. S1P is abundant in plasma because erythrocytes-the major source of S1P-lack any S1P-degrading activity; however, much remains unclear about the source of the plasma S1P precursor, sphingosine (SPH), derived mainly from the hydrolysis of ceramides by the action of ceramidases that are encoded by 5 distinct genes, acid ceramidase 1 ( ASAH1)/ Asah1, ASAH2/ Asah2, alkaline ceramidase 1 ( ACER1)/ Acer1, ACER2/ Acer2, and ACER3/ Acer3, in humans/mice. Previous studies have reported that knocking out Asah1 or Asah2 failed to reduce plasma SPH and S1P levels in mice. In this study, we show that knocking out Acer1 or Acer3 also failed to reduce the blood levels of SPH or S1P in mice. In contrast, knocking out Acer2 from either whole-body or the hematopoietic lineage markedly decreased the blood levels of SPH and S1P in mice. Of interest, knocking out Acer2 from whole-body or the hematopoietic lineage also markedly decreased the levels of dihydrosphingosine (dhSPH) and dihydrosphingosine-1-phosphate (dhS1P) in blood. Taken together, these results suggest that ACER2 plays a key role in the maintenance of high plasma levels of sphingoid base-1-phosphates-S1P and dhS1P-by controlling the generation of sphingoid bases-SPH and dhSPH-in hematopoietic cells.-Li, F., Xu, R., Low, B. E., Lin, C.-L., Garcia-Barros, M., Schrandt, J., Mileva, I., Snider, A., Luo, C. K., Jiang, X.-C., Li, M.-S., Hannun, Y. A., Obeid, L. M., Wiles, M. V., Mao, C. Alkaline ceramidase 2 is essential for the homeostasis of plasma sphingoid bases and their phosphates.