Actions Of Sphingosine-1-phosphate Research Articles

Targeting Sphingosine-1-Phosphate Signaling in Breast Cancer.

In recent years, newly emerging therapies, such as immune checkpoint inhibitors and antibody-drug conjugates, have further improved outcomes for breast cancer patients. However, recurrent and metastatic breast cancer often eventually develops resistance to these drugs, and cure is still rare. As such, the development of new therapies for refractory breast cancer that differ from conventional mechanisms of action is necessary. Sphingosine-1-phosphate (S1P) is a key molecule with a variety of bioactive activities, including involvement in cancer cell proliferation, invasion, and metastasis. S1P also contributes to the formation of the cancer microenvironment by inducing surrounding vascular- and lymph-angiogenesis and regulating the immune system. In this article, we outline the basic mechanism of action of S1P, summarize previous findings on the function of S1P in cancer cells and the cancer microenvironment, and discuss the clinical significance of S1P in breast cancer and the therapeutic potential of targeting S1P signaling.

Sphingosine kinase 1 is involved in triglyceride breakdown by maintaining lysosomal integrity in brown adipocytes

Sphingosine 1-phosphate (S1P) has been implicated in brown adipose tissue (BAT) formation and energy consumption; however, the mechanistic role of sphingolipids, including S1P, in BAT remains unclear. Here, we showed that, in mice, BAT activation by cold exposure upregulated mRNA and protein expression of the S1P-synthesizing enzyme sphingosine kinase 1 (SphK1) and S1P production in BAT. Treatment of wild-type brown adipocytes with exogenous S1P or S1P receptor subtype-selective agonists stimulated triglyceride (TG) breakdown only marginally, compared with noradrenaline. However, genetic deletion of Sphk1 resulted in hypothermia and diminished body weight loss upon cold exposure, suggesting that SphK1 is involved in thermogenesis through mechanisms different from receptor-mediated, extracellular action of S1P. In BAT of wild-type mice, SphK1 was localized largely in the lysosomes of brown adipocytes. In the brown adipocytes of Sphk1−/− mice, the number of lysosomes was reduced and lysosomal function, including proteolytic activity, acid esterase activity, and motility, was impaired. Concordantly, nuclear translocation of transcription factor EB, a master transcriptional regulator of lysosome biogenesis, was reduced, leading to decreased mRNA expression of the lysosome-related genes in Sphk1−/− BAT. Moreover, BAT of Sphk1−/− mice showed greater TG accumulation with dominant larger lipid droplets in brown adipocytes. Inhibition of lysosomes with chloroquine resulted in a less extent of triglyceride accumulation in Sphk1−/− brown adipocytes compared with wild-type brown adipocytes, suggesting a reduced lysosome-mediated TG breakdown in Sphk1−/− mice. Our results indicate a novel role of SphK1 in lysosomal integrity, which is required for TG breakdown and thermogenesis in BAT.

Sphingosine 1-Phosphate Activates S1PR3 to Induce a Proinflammatory Phenotype in Human Myometrial Cells.

One of the common mechanisms responsible for obstetric complications, affecting millions of women every year, is abnormal uterine contractility. Despite the critical importance of this process for women's health, the mechanisms of uterine contraction regulation remain poorly understood. The initiation of uterine smooth muscle (myometrial) contraction is an inflammatory process, accompanied by upregulation of proinflammatory genes and cytokine release. In this study, we show that sphingolipid metabolism is activated during human labor and that sphingosine 1-phosphate (S1P), the main bioactive sphingolipid, may modify the myometrial proinflammatory phenotype. Our data in both primary and immortalized human myometrial cells show that exogenous S1P induces a proinflammatory gene signature and upregulates the expression of known inflammatory markers of parturition, such as IL8 and COX2. Using expression of IL8 as a readout for S1P activity in myometrial cells, we established that these S1P effects are mediated through the activation of S1P receptor 3 (S1PR3) and downstream activation of ERK1/2 pathways. Inhibition of S1PR3 in human myometrial cells attenuates upregulation of IL8, COX2, and JUNB both at the mRNA and protein levels. Furthermore, activation of S1PR3 with a receptor-specific agonist recapitulated the effects seen after treatment with exogenous S1P. Collectively, these results suggest a signaling pathway activated by S1P in human myometrium during parturition and propose new targets for development of novel therapeutics to alter uterine contractility during management of preterm labor or labor dystocia.

Abstract 1312: Pro-survival lipid metabolism activates intracellular complement signaling to induce inflammasome-mediated tumor metastasis

Abstract Tumor metastasis remains one of the major causes of cancer-related deaths in patients with solid tumors. Mechanisms by which metabolic alterations regarding pro-survival lipid signaling activation in inducing cancer cell migration and metastasis are largely unknown. Here, we demonstrate that sphingosine 1-phosphate (S1P) metabolism activates endogenous complement signaling for inducing tumor metastasis via inducing inflammasome-mediated pro-inflammation. Our studies using molecular, pharmacologic, and genetic tools showed that activation of S1P and S1P receptor 1 (S1P/S1PR1) induces tumor metastasis via enhanced intracellular complement signaling by the regulation of the C3-PPIL1 complex and subsequent inflammasome activation in cancer cells and in vivo xenograft-derived tumors. Citation Format: Alhaji H. Janneh, Besim Ogretmen. Pro-survival lipid metabolism activates intracellular complement signaling to induce inflammasome-mediated tumor metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1312.

The role of endogenous Smad7 in regulating macrophage phenotype following myocardial infarction.

Smad7 restrains TGF-β responses, and has been suggested to exert both pro- and anti-inflammatory actions that may involve effects on macrophages. Myocardial infarction triggers a macrophage-driven inflammatory response that not only plays a central role in cardiac repair, but also contributes to adverse remodeling and fibrosis. We hypothesized that macrophage Smad7 expression may regulate inflammation and fibrosis in the infarcted heart through suppression of TGF-β responses, or via TGF-independent actions. In a mouse model of myocardial infarction, infiltration with Smad7+ macrophages peaked 7days after coronary occlusion. Myeloid cell-specific Smad7loss in mice had no effects on homeostatic functions and did not affect baseline macrophage gene expression. RNA-seq predicted that Smad7may promote TREM1-mediated inflammation in infarct macrophages. However, these alterations in the transcriptional profile of macrophages were associated with a modest and transient reduction in infarct myofibroblast infiltration, and did not affect dysfunction, chamber dilation, scar remodeling, collagen deposition, and macrophage recruitment. In vitro, RNA-seq and PCR arrays showed that TGF-β has profound effects on macrophage profile, attenuating pro-inflammatory cytokine/chemokine expression, modulating synthesis of matrix remodeling genes, inducing genes associated with sphingosine-1 phosphate activation and integrin signaling, and inhibiting cholesterol biosynthesis genes. However, Smad7loss did not significantly affect TGF-β-mediated macrophage responses, modulating synthesis of only a small fraction of TGF-β-induced genes, including Itga5, Olfml3, and Fabp7. Our findings suggest a limited role for macrophage Smad7 in regulation of post-infarction inflammation and repair, and demonstrate that the anti-inflammatory effects of TGF-β in macrophages are not restrained by endogenous Smad7 induction.

Pro‐survival lipid metabolism activates intracellular complement signaling to induce inflammasome‐mediated tumor metastasis

Tumor metastasis remains one of the major causes of cancer‐related deaths in patients with solid tumors. Mechanisms by which metabolic alterations regarding pro‐survival lipid signaling activation in inducing cancer cell migration and metastasis are largely unknown. Here, we demonstrate that sphingosine 1‐phosphate (S1P) metabolism activates endogenous complement signaling for inducing tumor metastasis via inducing inflammasome‐mediated pro‐inflammation. Our studies using molecular, pharmacologic, and genetic tools showed that activation of S1P and S1P receptor 1 (S1P/S1PR1) induces tumor metastasis via enhanced intracellular complement signaling by the regulation of the C3‐PPIL1 complex and subsequent inflammasome activation in cancer cells and in vivo xenograft‐derived tumors.

Potential of a sphingosine 1-phosphate receptor antagonist and sphingosine kinase inhibitors as targets for multiple myeloma treatment.

Sphingosine 1-phosphate (S1P) is a bioactive lipid involved in cancer progression through its binding to S1P receptors (S1PRs). However, the association between multiple myeloma (MM) and S1P is unclear. The current study aimed to investigate the potential anti-cancer effects of fingolimod and sphingosine kinase (SK) inhibitors in myeloma cells and the effects of S1P-induced chemoresistance and neovascularization on MM cell proliferation. MM cell lines were treated with the S1PR1 antagonist fingolimod and the SK inhibitors ABC294640 and SK1-I, after which cell proliferation was measured. Protein expression was also assessed under each condition using immunoblotting. Serum S1P levels in patients with MM, monoclonal gammopathy of undetermined significance and healthy volunteers were assessed. Human umbilical vessel cells (HUVECs) were co-cultured with anti-S1P agents to assess the effect on cell migration. All treatments suppressed myeloma cell proliferation and caspase-3-mediated apoptosis by suppressing S1P activity. These findings suggest that S1P activation is associated with proliferation and survival for MM cells. S1P attenuated the proteosome inhibitor (PI) effect, while the anti-S1P agents recovered the effect. In addition, S1P promoted the migration and proliferation of HUVECs, whereas the S1P inhibitors reduced the influence of S1P. This study highlights the therapeutic potential of anti-S1P agents for MM treatment. Inhibition of S1P function may overcome resistance to PI developed by myeloma cells and inhibit the changes to the bone marrow microenvironment via neovascularization.

To Be or Not to Be: The Divergent Action and Metabolism of Sphingosine-1 Phosphate in Pancreatic Beta-Cells in Response to Cytokines and Fatty Acids.

Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid with multiple functions conveyed by the activation of cell surface receptors and/or intracellular mediators. A growing body of evidence indicates its important role in pancreatic insulin-secreting beta-cells that are necessary for maintenance of glucose homeostasis. The dysfunction and/or death of beta-cells lead to diabetes development. Diabetes is a serious public health burden with incidence growing rapidly in recent decades. The two major types of diabetes are the autoimmune-mediated type 1 diabetes (T1DM) and the metabolic stress-related type 2 diabetes (T2DM). Despite many differences in the development, both types of diabetes are characterized by chronic hyperglycemia and inflammation. The inflammatory component of diabetes remains under-characterized. Recent years have brought new insights into the possible mechanism involved in the increased inflammatory response, suggesting that environmental factors such as a westernized diet may participate in this process. Dietary lipids, particularly palmitate, are substrates for the biosynthesis of bioactive sphingolipids. Disturbed serum sphingolipid profiles were observed in both T1DM and T2DM patients. Many polymorphisms were identified in genes encoding enzymes of the sphingolipid pathway, including sphingosine kinase 2 (SK2), the S1P generating enzyme which is highly expressed in beta-cells. Proinflammatory cytokines and free fatty acids have been shown to modulate the expression and activity of S1P-generating and S1P-catabolizing enzymes. In this review, the similarities and differences in the action of extracellular and intracellular S1P in beta-cells exposed to cytokines or free fatty acids will be identified and the outlook for future research will be discussed.

Sphingosine-1-phosphate and Sphingosine-1-phosphate receptors in the cardiovascular system: pharmacology and clinical implications.

Sphingosine-1-phosphate (S1P) is a lipid that binds and activates five distinct receptor subtypes, S1P1, S1P2, S1P3, S1P4, S1P5, widely expressed in different cells, tissues and organs. In the cardiovascular system these receptors have been extensively studied, but no drug acting on them has been approved so far for treating cardiovascular diseases. In contrast, a number of S1P receptor agonists are approved as immunomodulators, mainly for multiple sclerosis, because of their action on lymphocyte trafficking. This chapter summarizes the available information on S1P receptors in the cardiovascular system and discusses their potential for treating cardiovascular conditions and/or their role on the clinical pharmacology of drugs so far approved for non-cardiovascular conditions. Basic research has recently produced data useful to understand the molecular pharmacology of S1P and S1P receptors, regarding biased agonism, S1P storage, release and vehiculation and chaperoning by lipoproteins, paracrine actions, intracellular non-receptorial S1P actions. On the other hand, the approval of fingolimod and newer generation S1P receptor ligands as immunomodulators, provides information on a number of clinical observations on the impact of these drugs on cardiovascular system which need to be integrated with preclinical data. S1P receptors are potential targets for prevention and treatment of major cardiovascular conditions, including hypertension, myocardial infarction, heart failure and stroke.

Uncovering the 'sphinx' of sphingosine 1-phosphate signalling: from cellular events to organ morphogenesis.

ABSTRACTSphingosine 1‐phosphate (S1P) is a bioactive sphingolipid metabolite, functioning as a signalling molecule in diverse cellular processes. Over the past few decades, studies of S1P signalling have revealed that the physiological activity of S1P largely depends on S1P metabolizing enzymes, transporters and receptors on the plasma membrane, as well as on the intracellular proteins that S1P binds directly to. In addition to its roles in cancer signalling, immunity and inflammation, a large body of evidence has identified a close link of S1P signalling with organ morphogenesis. Here we discuss the vital role of S1P signalling in orchestrating various cellular events during organ morphogenesis through analysing each component along the extracellular and intracellular S1P signalling axes. For each component, we review advances in our understanding of S1P signalling and function from the upstream regulators to the downstream effectors and from cellular behaviours to tissue organization, primarily in the context of morphogenetic mechanisms. S1P‐mediated vesicular trafficking is also discussed as a function independent of its signalling function. A picture emerges that reveals a multifaceted role of S1P‐dependent pathways in the development and maintenance of organ structure and function.

Lysophosphatidate Promotes Sphingosine 1-Phosphate Metabolism and Signaling: Implications for Breast Cancer and Doxorubicin Resistance.

Lysophosphatidate (LPA) and sphingosine 1-phosphate (S1P) promote vasculogenesis, angiogenesis, and wound healing by activating a plethora of overlapping signaling pathways that stimulate mitogenesis, cell survival, and migration. As such, maladaptive signaling by LPA and S1P have major effects in increasing tumor progression and producing poor patient outcomes after chemotherapy and radiotherapy. Many signaling actions of S1P and LPA are not redundant; each are vital in normal physiology and their metabolisms differ. In the present work, we studied how LPA signaling impacts S1P metabolism and signaling in MDA-MB-231 and MCF-7 breast cancer cells. LPA increased sphingosine kinase-1 (SphK1) synthesis and rapidly activated cytosolic SphK1 through association with membranes. Blocking phospholipase D activity attenuated the LPA-induced activation of SphK1 and the synthesis of ABCC1 and ABCG2 transporters that secrete S1P from cells. This effect was magnified in doxorubicin-resistant MCF-7 cells. LPA also facilitated S1P signaling by increasing mRNA expression for S1P1 receptors. Doxorubicin-resistant MCF-7 cells had increased S1P2 and S1P3 receptor expression and show increased LPA-induced SphK1 activation, increased expression of ABCC1, ABCG2 and greater S1P secretion. Thus, LPA itself and LPA-induced S1P signaling counteract doxorubicin-induced death of MCF-7 cells. We conclude from the present and previous studies that LPA promotes S1P metabolism and signaling to coordinately increase tumor growth and metastasis and decrease the effectiveness of chemotherapy and radiotherapy for breast cancer treatment.

Sphingosine‐1‐Phosphate Contributes to TLR9‐Induced TNF‐α Release in Lung Tumor Cells

Sphingosine-1-phosphate (S1P) is a membrane-derived bioactive phospholipid involved in many lung physiological and pathological processes. Higher levels of S1P have been registered in a broad range of respiratory diseases, including inflammatory disorders and cancer. The aim of our study was to understand the role of the S1P in healthy versus tumor cells after Toll-Like Receptors (TLRs) activation, well-known modulators of sphingolipid metabolism. We found that S1P was involved in TLR9-induced TNF-α release in that the inhibition of both ceramidase and sphingosine kinase I/II (SPHK I/II) significantly reduced the levels of TNF-α after TLR9 triggering in lung adenocarcinoma cells. These results were not observed in healthy fibroblasts, implying that this pathway was mainly involved in pathological conditions. Moreover, the activation of TLR4 by means of LPS did not have similar effects as in the case of CpG-stimulated TLR9. Importantly, the activation of TLR9 induced S1P generation and allowed it to interact on the outside receptors S1P1 and S1P3 via the efflux through its membrane transporter SPNS2. Indeed, both the blockade of S1P3 and the transporter SPNS2 significantly reduced the activity of S1P on TNF-α release from lung adenocarcinoma cells. To note, although CpG induced higher levels of TNF-α than exogenous S1P, we found that TLR9 stimulation was involved in S1P synthesis. In conclusion, our study identified a novel inflammatory pathway in that TLR9 increases a pro-inflammatory cytokine, such as TNF-α, via the induction of a ceramide/S1P imbalance in favor of S1P. Therefore, these data will shed more light on the role of the higher levels of S1P during inflammatory conditions.

Sphingosine-1-Phosphate Contributes to TLR9-Induced TNF-α Release in Lung Tumor Cells.

Sphingosine-1-phosphate (S1P) is a membrane-derived bioactive phospholipid involved in many lung physiological and pathological processes. Higher levels of S1P have been registered in a broad range of respiratory diseases, including inflammatory disorders and cancer. The aim of our study was to understand the role of S1P in healthy versus tumor cells after Toll-Like Receptors (TLRs) activation, well-known modulators of sphingolipid metabolism. Lung adenocarcinoma cells and non-pathological human fibroblasts were stimulated with unmethylated Cytosine phosphate Guanosine (CpG), the TLR9 ligand, and S1P-dependent TNF-α release was evaluated by means of ELISA. Immunofluorescence and LC-MS/MS analysis were performed to evaluate/quantify S1P generation following TLR9 activation. We found that S1P was involved in TLR9-induced TNF-α release in that the inhibition of both ceramidase and sphingosine kinase I/II (SPHK I/II) significantly reduced the levels of TNF-α after TLR9 triggering in lung adenocarcinoma cells. These results were not observed in healthy fibroblasts, implying that this pathway was mainly involved in pathological conditions. Moreover, the activation of TLR4 by means of LPS did not have similar effects as in the case of CpG-stimulated TLR9. Importantly, the activation of TLR9 induced S1P generation and allowed it to interact on the outside membrane receptor S1P1 and S1P3 via the efflux through its membrane transporter SPNS2. Indeed, both the blockade of S1P3 and the transporter SPNS2 significantly reduced the activity of S1P on TNF-α release from lung adenocarcinoma cells. Our study identifies a novel inflammatory pathway in that TLR9 increases the pro-inflammatory cytokine release, such as TNF-α, via the induction of a ceramide/S1P imbalance in favor of S1P, adding a novel puzzle piece in TLR9-orchestrated inflammatory pathway and shedding more light on the role of the higher levels of S1P during inflammatory conditions.

Sphingosine 1-Phosphate in Malaria Pathogenesis and Its Implication in Therapeutic Opportunities.

Sphingosine 1-Phosphate (S1P) is a bioactive lipid intermediate in the sphingolipid metabolism, which exist in two pools, intracellular and extracellular, and each pool has a different function. The circulating extracellular pool, specifically the plasma S1P is shown to be important in regulating various physiological processes related to malaria pathogenesis in recent years. Although blood cells (red blood cells and platelets), vascular endothelial cells and hepatocytes are considered as the important sources of plasma S1P, their extent of contribution is still debated. The red blood cells (RBCs) and platelets serve as a major repository of intracellular S1P due to lack, or low activity of S1P degrading enzymes, however, contribution of platelets toward maintaining plasma S1P is shown negligible under normal condition. Substantial evidences suggest platelets loss during falciparum infection as a contributing factor for severe malaria. However, platelets function as a source for plasma S1P in malaria needs to be examined experimentally. RBC being the preferential site for parasite seclusion, and having the ability of trans-cellular S1P transportation to EC upon tight cell-cell contact, might play critical role in differential S1P distribution and parasite growth. In the present review, we have summarized the significance of both the S1P pools in the context of malaria, and how the RBC content of S1P can be channelized in better ways for its possible implication in therapeutic opportunities to control malaria.

Responsiveness of sphingosine phosphate lyase insufficiency syndrome to vitamin B6 cofactor supplementation.

Sphingosine-1-phosphate (S1P) lyase is a vitamin B6-dependent enzyme that degrades sphingosine-1-phosphate in the final step of sphingolipid metabolism. In 2017, a new inherited disorder was described caused by mutations in SGPL1, which encodes sphingosine phosphate lyase (SPL). This condition is referred to as SPL insufficiency syndrome (SPLIS) or alternatively as nephrotic syndrome type 14 (NPHS14). Patients with SPLIS exhibit lymphopenia, nephrosis, adrenal insufficiency, and/or neurological defects. No targeted therapy for SPLIS has been reported. Vitamin B6 supplementation has therapeutic activity in some genetic diseases involving B6-dependent enzymes, a finding ascribed largely to the vitamin's chaperone function. We investigated whether B6 supplementation might have activity in SPLIS patients. We retrospectively monitored responses of disease biomarkers in patients supplemented with B6 and measured SPL activity and sphingolipids in B6-treated patient-derived fibroblasts. In two patients, disease biomarkers responded to B6 supplementation. S1P abundance and activity levels increased and sphingolipids decreased in response to B6. One responsive patient is homozygous for an SPL R222Q variant present in almost 30% of SPLIS patients. Molecular modeling suggests the variant distorts the dimer interface which could be overcome by cofactor supplementation. We demonstrate the first potential targeted therapy for SPLIS and suggest that 30% of SPLIS patients might respond to cofactor supplementation.

Apolipoprotein‐M bound sphingosine‐1 phosphate enhances heparan sulfate expression and endothelial nitric oxide synthase phosphorylation in cultured endothelial cells

Sphingosine‐1 phosphate (S1P) is blood borne bioactive sphingolipid metabolite that has protective properties against microvascular leakage under inflammatory conditions and also can promote endothelial NO production. Previous investigations suggest that functions are mediated by S1P receptor‐1 (S1pr1) but are also limited by action of S1P on other S1P receptors. Apolipoprotein‐M (ApoM), which has been shown to act as a carrier of S1P, may help target S1P to S1pr1, producing biased S1pr1 signaling. In the current study, we hypothesized that combination of ApoM will improve the ability of S1P to enhance 1) endothelial barrier function, and 2) phosphorylation of eNOS on its activation site. We used confluent monolayers of human umbilical vein endothelial cells (HUVEC) to model the endothelial barrier. Transendothelial electrical resistance (TER), determined by electric cell‐substrate impedance sensing, served as an indicator of barrier function. Because endothelial glycocalyx health is related to barrier function, we also determined the degree of heparan sulfate expression on the cell surface, visualized by immunofluorescence microscopy of fixed, non‐permeabilized HUVEC. Western blotting was used to measure eNOS phosphorylation on its activation site (S1177). These endpoints were evaluated in control cells and cells that were treated with ApoM (0.5 μM), S1P (1 μM), or the combination of both. The results show that the addition of ApoM‐bound S1P to HUVEC significantly increased and sustained the increase in TER of the HUVEC monolayers compared to the vehicle and S1P alone. ApoM‐bound S1P also increased heparan sulfate expression on the plasma membrane and elicited enhanced phosphorylation of eNOS on S1177 compared to either ApoM or S1P alone. Collectively, the findings support that ApoM enhances the ability of S1P to promote endothelial barrier function, surface heparan sulfate expression, and activation of eNOS. These findings suggest high potential for using ApoM‐bound S1P as a therapeutic target for ameliorating endothelial dysfunction.Support or Funding InformationThis work was supported by NIH R01GM120774 and American Heart Association 18UFEL33960365. Tabitha E. Norton and Taylor E. Collignon contributed equally to this work.

Investigation of sphingosin-1-phosphate-triggered matriptase activation using a rat primary hepatocyte model.

Sphingosine-1-phosphate (S1P) has been reported as a matriptase activator. The aim of this study was to reveal if S1P can influence hepcidin production. Furthermore, we investigated how S1P can affect the viability and the redox status of primary hepatocytes. Rat primary hepatocytes were cultivated for 72 h and were treated with 50, 200, 1000 ng/ml S1P. Cell-free supernatants were collected every 24 h. Cell viability was tested by a colorimetric method using tetrazolium compound (MTS). The hepcidin levels in the cell-free supernatants were examined with hepcidin sandwich ELISA to determine the effect of S1P on the hepcidin-modulating ability of matriptase. In order to estimate the extent of S1P-generated oxidative stress, extracellular H2O2 measurements were performed by the use of fluorescent dye. Based on the findings, S1P treatment did not cause cell death for 72 h at concentrations up to 1000 ng/ml. S1P did not influence the extracellular H2O2 production for 72 h. The hepcidin levels were significantly suppressed in hepatocytes exposed to S1P treatment. Further studies would be needed to explore the exact mechanism of action of S1P.

Sphingosine Kinase 2 Potentiates Amyloid Deposition but Protects against Hippocampal Volume Loss and Demyelination in a Mouse Model of Alzheimer's Disease.

Sphingosine 1-phosphate (S1P) is a potent vasculoprotective and neuroprotective signaling lipid, synthesized primarily by sphingosine kinase 2 (SK2) in the brain. We have reported pronounced loss of S1P and SK2 activity early in Alzheimer's disease (AD) pathogenesis, and an inverse correlation between hippocampal S1P levels and age in females, leading us to speculate that loss of S1P is a sensitizing influence for AD. Paradoxically, SK2 was reported to mediate amyloid β (Aβ) formation from amyloid precursor protein (APP) in vitro To determine whether loss of S1P sensitizes to Aβ-mediated neurodegeneration, we investigated whether SK2 deficiency worsens pathology and memory in male J20 (PDGFB-APPSwInd) mice. SK2 deficiency greatly reduced Aβ content in J20 mice, associated with significant improvements in epileptiform activity and cross-frequency coupling measured by hippocampal electroencephalography. However, several key measures of APPSwInd-dependent neurodegeneration were enhanced on the SK2-null background, despite reduced Aβ burden. These included hippocampal volume loss, oligodendrocyte attrition and myelin loss, and impaired performance in Y-maze and social novelty memory tests. Inhibition of the endosomal cholesterol exporter NPC1 greatly reduced sphingosine phosphorylation in glial cells, linking loss of SK2 activity and S1P in AD to perturbed endosomal lipid metabolism. Our findings establish SK2 as an important endogenous regulator of both APP processing to Aβ, and oligodendrocyte survival, in vivo These results urge greater consideration of the roles played by oligodendrocyte dysfunction and altered membrane lipid metabolic flux as drivers of neurodegeneration in AD.SIGNIFICANCE STATEMENT Genetic, neuropathological, and functional studies implicate both Aβ and altered lipid metabolism and/or signaling as key pathogenic drivers of Alzheimer's disease. In this study, we first demonstrate that the enzyme SK2, which generates the signaling lipid S1P, is required for Aβ formation from APP in vivo Second, we establish a new role for SK2 in the protection of oligodendrocytes and myelin. Loss of SK2 sensitizes to Aβ-mediated neurodegeneration by attenuating oligodendrocyte survival and promoting hippocampal atrophy, despite reduced Aβ burden. Our findings support a model in which Aβ-independent sensitizing influences such as loss of neuroprotective S1P are more important drivers of neurodegeneration than gross Aβ concentration or plaque density.

Sphingosine-1-phosphate signaling: A novel target for simultaneous adjuvant treatment of triple negative breast cancer and chemotherapy-induced neuropathic pain.

Triple-negative breast cancer (TNBC) is very aggressive with high metastatic and mortality rates and unfortunately, except for chemotherapy, there are few therapeutic options. The bioactive sphingolipid metabolite sphingosine-1-phosphate (S1P) regulates numerous processes important for cancer progression, metastasis, and neuropathic pain. The pro-drug FTY720 (fingolimod, Gilenya) used to treat multiple sclerosis is phosphorylated in the body to a S1P mimic that binds to S1PRs, except S1PR2, and also acts as a functional antagonist of S1PR1. This review highlights current findings showing that FTY720 has multiple anti-cancer activities and simultaneously prevents formation and actions of S1P. Moreover, in mouse breast cancer models, treatment with FTY720 reduces tumor growth, metastasis, and enhances sensitivity of advanced and hormonal refractory breast cancer and TNBC to conventional therapies. We discuss recent studies demonstrating that neuropathic pain induced by the chemotherapeutic bortezomib is also greatly reduced by administration of clinically relevant doses of FTY720, likely by targeting S1PR1 on astrocytes. FTY720 also shows promising anticancer potential in pre-clinical studies and is FDA approved, thus we suggest in this review that further studies are needed to pave the way for fast-tracking approval of FTY720/fingolimod for enhancing chemotherapy effectiveness and reduction of painful neuropathies.

Molecular Mechanism of S1P Binding and Activation of the S1P1 Receptor.

Sphingosine-1-phosphate (S1P) is a lipidic mediator in mammals that functions either as a second messenger or as a ligand. In the latter case, it is transported by its HDL-associated apoM carrier and circulated in blood where it binds to specific S1P receptors on cell membranes and induces downstream reactions. Although S1P signaling pathways are essential for many biological processes, they are poorly understood at the molecular level. Here, the solved crystal structures of the S1P1 receptor were used to evaluate molecular dynamics (MD) simulations to generate greater detailed molecular insights into the mechanism of S1P signaling. The MD simulations provided observations at the coarse-grained and atomic levels indicating that S1P may access the receptor binding pocket directly from solvents. Lifting of the bulky N-terminal cap region of the receptor precedes initial S1P binding. Glu1213.29 guides S1P penetration, and together with Arg2927.34 is responsible for the stabilization of S1P in the binding pocket, which is consistent with experimental predictions. The complete binding of S1P is followed by receptor activation, wherein Trp2696.48 moves toward the transmembrane helix (TM) 7, resulting in the formation of an enhanced hydrogen bond network in the lower region of TM7. The distance between TM3 and TM6 is subsequently increased, resulting in the opening of the intracellular binding pocket that enables G protein binding. Further analysis of the force distribution network in the receptor yielded a detailed molecular understanding of the signal transmission network that is activated upon agonist binding.