Sphingosine 1-phosphate is a novel inhibitor of T-cell proliferation

Rewiring Endothelial Sphingolipid Metabolism to Favor S1P Over Ceramide Protects From Coronary Atherosclerosis

BACKGROUND

Growing evidence correlated changes in bioactive sphingolipids, particularly S1P (sphingosine-1-phosphate) and ceramides, with coronary artery diseases. Furthermore, specific plasma ceramide species can predict major cardiovascular events. Dysfunction of the endothelium lining lesion-prone areas plays a pivotal role in atherosclerosis. Yet, how sphingolipid metabolism and signaling change and contribute to endothelial dysfunction and atherosclerosis remain poorly understood.

METHODS

We used an established model of coronary atherosclerosis in mice, combined with sphingolipidomics, RNA-sequencing, flow cytometry, and immunostaining to investigate the contribution of sphingolipid metabolism and signaling to endothelial cell (EC) activation and dysfunction.

RESULTS

We demonstrated that hemodynamic stress induced an early metabolic rewiring towards endothelial sphingolipid de novo biosynthesis, favoring S1P signaling over ceramides as a protective response. This finding is a paradigm shift from the current belief that ceramide accrual contributes to endothelial dysfunction. The enzyme SPT (serine palmitoyltransferase) commences de novo biosynthesis of sphingolipids and is inhibited by NOGO-B (reticulon-4B), an ER membrane protein. Here, we showed that NOGO-B is upregulated by hemodynamic stress in myocardial EC of ApoE-/- mice and is expressed in the endothelium lining coronary lesions in mice and humans. We demonstrated that mice lacking NOGO-B specifically in EC (Nogo-A/BECKOApoE-/-) were resistant to coronary atherosclerosis development and progression, and mortality. Fibrous cap thickness was significantly increased in Nogo-A/BECKOApoE-/- mice and correlated with reduced necrotic core and macrophage infiltration. Mechanistically, the deletion of NOGO-B in EC sustained the rewiring of sphingolipid metabolism towards S1P, imparting an atheroprotective endothelial transcriptional signature.

CONCLUSIONS

These data demonstrated that hemodynamic stress induced a protective rewiring of sphingolipid metabolism, favoring S1P over ceramide. NOGO-B deletion sustained the rewiring of sphingolipid metabolism toward S1P protecting EC from activation under hemodynamic stress and refraining coronary atherosclerosis. These findings also set forth the foundation for sphingolipid-based therapeutics to limit atheroprogression.

Sphingosine 1-phosphate signaling during infection and immunity

Sphingolipids are essential components of all eukaryotic membranes. The bioactive sphingolipid molecule, Sphingosine 1-Phosphate (S1P), regulates various important biological functions. This review aims to provide a comprehensive overview of the role of S1P signaling pathway in various immune cell functions under different pathophysiological conditions including bacterial and viral infections, autoimmune disorders, inflammation, and cancer. We covered the aspects of S1P pathways in NOD/TLR pathways, bacterial and viral infections, autoimmune disorders, and tumor immunology. This implies that targeting S1P signaling can be used as a strategy to block these pathologies. Our current understanding of targeting various components of S1P signaling for therapeutic purposes and the present status of S1P pathway inhibitors or modulators in disease conditions where the host immune system plays a pivotal role is the primary focus of this review.

The Role of Sphingolipids and Sphingosine-1-phosphate-Sphingosine-1-phosphate-receptor Signaling in Psoriasis

Psoriasis is a long-lasting skin condition characterized by redness and thick silver scales on the skin's surface. It involves various skin cells, including keratinocytes, dendritic cells, T lymphocytes, and neutrophils. The treatments for psoriasis range from topical to systemic therapies, but they only alleviate the symptoms and do not provide a fundamental cure. Moreover, systemic treatments have the disadvantage of suppressing the entire body's immune system. Therefore, a new treatment strategy with minimal impact on the immune system is required. Recent studies have shown that sphingolipid metabolites, particularly ceramide and sphingosine-1-phosphate (S1P), play a significant role in psoriasis. Specific S1P-S1P-receptor (S1PR) signaling pathways have been identified as crucial to psoriasis inflammation. Based on these findings, S1PR modulators have been investigated and have been found to improve psoriasis inflammation. This review will discuss the metabolic pathways of sphingolipids, the individual functions of these metabolites, and their potential as a new therapeutic approach to psoriasis.

Neuroprotective Effects of Danshen Chuanxiongqin Injection Against Ischemic Stroke: Metabolomic Insights by UHPLC-Q-Orbitrap HRMS Analysis

The incidence of cerebral ischemic stroke characterized by high mortality is increasing every year. Danshen Chuanxiongqin Injection (DSCXQ), a traditional Chinese medicine (TCM) preparation, is often applied to treat cerebral apoplexy and its related sequelae. However, there is a lack of systematic research on how DSCXQ mediates its protective effects against cerebral ischemia stroke. Metabolomic analysis based on UHPLC-Q-Orbitrap HRMS was employed to explore the potential mechanisms of DSCXQ on ischemic stroke induced by transient middle cerebral artery occlusion (MCAO). Pattern analysis and metabolomic profiling, combined by multivariate analysis disclosed that 55 differential metabolites were identified between Sham group and Model group, involving sphingolipid metabolism, glycerophospholipid metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, primary bile acid biosynthesis, pantothenate and CoA synthesis and valine, leucine and isoleucine biosynthesis pathways. DSCXQ could reverse brain metabolic deviations in stroke by significantly upregulating the levels of L-tryptophan, Lyso (18:0/0:0), LPC (18:2), Indole-3-methyl acetate, and downregulating the levels of sphinganine 1-phosphate, L-threonic acid, glutaconic acid and N6,N6,N6-Trimethyl-L-lysine. In our study, we focused on the neuroprotective effects of DSCXQ against neuroinflammatory responses and neuronal apoptosis on a stroke model based on sphingolipid metabolism. The expressions of Sphk1, S1PR1, CD62P, Bcl-2, Bax, and cleaved Caspase-3 in brain tissue were evaluated. The neurological deficit, cerebral infarct size and behavioral abnormality were estimated. Results showed that DSCXQ intervention significantly reduced cerebral infarct size, ameliorated behavioral abnormality, inhibited the expression of Sphk1, S1PR1, CD62P, Bax, Cleaved Caspase-3, while increased the level of Bcl-2, and prevented neuronal apoptosis. The limitations are that our study mainly focused on the verification of sphingolipid metabolism pathway in stroke, and while other metabolic pathways left unverified. Our study indicates that SphK1-SIP axis may potentiate neuroinflammatory responses and mediate brain damage through neuronal apoptosis, and DSCXQ could suppress the activity of SphK1-SIP axis to protect brain tissue in cerebral ischemia. In conclusion, this study facilitates our understanding of metabolic changes in ischemia stroke and the underlying mechanisms related to the clinical application of DSCXQ.

The Role of Innate and Adaptive Immune Cells in Skeletal Muscle Regeneration

Skeletal muscle regeneration is highly dependent on the inflammatory response. A wide variety of innate and adaptive immune cells orchestrate the complex process of muscle repair. This review provides information about the various types of immune cells and biomolecules that have been shown to mediate muscle regeneration following injury and degenerative diseases. Recently developed cell and drug-based immunomodulatory strategies are highlighted. An improved understanding of the immune response to injured and diseased skeletal muscle will be essential for the development of therapeutic strategies.

Beta-Arrestins and Receptor Signaling in the Vascular Endothelium

The vascular endothelium is the innermost layer of blood vessels and is a key regulator of vascular tone. Endothelial function is controlled by receptor signaling through G protein-coupled receptors, receptor tyrosine kinases and receptor serine-threonine kinases. The β-arrestins, multifunctional adapter proteins, have the potential to regulate all of these receptor families, although it is unclear as to whether they serve to integrate signaling across all of these different axes. Notably, the β-arrestins have been shown to regulate signaling by a number of receptors important in endothelial function, such as chemokine receptors and receptors for vasoactive substances such as angiotensin II, endothelin-1 and prostaglandins. β-arrestin-mediated signaling pathways have been shown to play central roles in pathways that control vasodilation, cell proliferation, migration, and immune function. At this time, the physiological impact of this signaling has not been studied in detail, but a deeper understanding of it could lead to the development of novel therapies for the treatment of vascular disease.

Maternal exposure to soy diet reduces atheroma in hyperlipidemic F1 offspring mice by promoting macrophage and T cell anti-inflammatory responses

BACKGROUND AND AIMS

Maternal hypercholesterolemia has been implicated in earlier onset of atherosclerotic lesions in neonatal offspring. In this study, we investigated whether maternal exposure to soy protein isolate (SPI) diet attenuated the progression of atherosclerosis in F1 offspring.

METHOD

Pregnant apolipoprotein E knockout (Apoe^-/-) female mice were fed SPI diet until postnatal day 21 (PND21) of the offspring (SPI-offspring). SPI-offspring were switched at PND21 to casein (CAS) diet until PND140. Mice fed CAS throughout their lifetime (gestation to adulthood) were used as controls (CAS-offspring).

RESULTS

Atherosclerotic lesions in the aortic sinuses were reduced in SPI-offspring compared with CAS-offspring. Total serum cholesterol levels in CAS-offspring or dams were comparable to levels in their SPI-counterparts, suggesting that alternative mechanisms contributed to the athero-protective effect of maternal SPI diet. Aortic VCAM-1, MCP-1, and TNF-α mRNA and protein expression, and expression of macrophage pro-inflammatory cytokines was reduced in SPI-offspring. Interestingly, CD4⁺ T cells from SPI-offspring showed reduced IFN-γ expression (Th1), while the expression of IL-10 (Th2/Treg), and IL-13 (Th2) was increased. DNA methylation analyses revealed that anti-inflammatory T cell-associated Gata3 and Il13 promoter regions were hypomethylated in SPI-offspring. These findings suggest that anti-inflammatory macrophage and T cell response may have contributed to the athero-protective effect in SPI-offspring.

CONCLUSIONS

Our findings demonstrate that gestational and lactational soy diet exposure inhibits susceptibility to atherosclerotic lesion formation by promoting anti-inflammatory responses by macrophages and T cells.

Mfsd2a and Spns2 are essential for sphingosine-1-phosphate transport in the formation and maintenance of the blood-brain barrier

To maintain brain homeostasis, a unique interface known as the blood-brain barrier (BBB) is formed between the blood circulation and the central nervous system (CNS). Major facilitator superfamily domain-containing 2a (Mfsd2a) is a specific marker of the BBB. However, the mechanism by which Mfsd2a influences the BBB is poorly understood. In this study, we demonstrated that Mfsd2a is essential for sphingosine-1-phosphate (S1P) export from endothelial cells in the brain. We found that Mfsd2a and Spinster homolog 2 (Spns2) form a protein complex to ensure the efficient transport of S1P. Furthermore, the S1P-rich microenvironment in the extracellular matrix (ECM) in the vascular endothelium dominates the formation and maintenance of the BBB. We demonstrated that different concentrations of S1P have different effects on BBB integrity. These findings help to unravel the mechanism by which S1P regulates BBB and also provide previously unidentified insights into the delivery of neurological drugs in the CNS.

S1P Signaling in the Tumor Microenvironment

Sphingosine-1-phosphate (S1P), together with other phosphosphingolipids, has been found to regulate complex cellular function in the tumor microenvironment (TME) where it acts as a signaling molecule that participates in cell-cell communication. S1P, through intracellular and extracellular signaling, was found to promote tumor growth, angiogenesis, chemoresistance, and metastasis; it also regulates anticancer immune response, modulates inflammation, and promotes angiogenesis. Interestingly, cancer cells are capable of releasing S1P and thus modifying the behavior of the TME components in a way that contributes to tumor growth and progression. Therefore, S1P is considered an important therapeutic target, and several anticancer therapies targeting S1P signaling are being developed and tested in clinics.

S1PR5 regulates NK cell responses in preventing graft-versus-host disease while preserving graft-versus-tumour activity in a murine allogeneic haematopoietic stem cell transplantation model

Graft-versus-host disease (GVHD) remains a major complication following allogeneic haematopoietic stem cell transplantation (allo-HSCT) leading to high transplant-related mortality. Natural killer (NK) cells have been found to mitigate GVHD without attenuating the graft-versus-tumour (GVT) activity in the murine model of haematopoietic stem cell transplantation. Sphingosine-1-phosphate receptor 5 (S1PR5) is a very important chemokine receptor on NK cells that governs NK cell distribution in vivo and trafficking at lesion sites. Our preliminary studies showed that the incidence of GVHD was negatively correlated with S1PR5 expression in the NK cells of patients after allo-HSCT. In the present study, we found that S1PR5 deficiency in murine NK cells blocked the migration of NK cells from the bone marrow to the GVHD target organs and attenuated the inhibitory effects on the alloreactive T cells, especially CD3⁺ CD8⁺ T cells, which may be the reason why the loss of S1PR5 in NK cells could aggravate GVHD in recipient mice. Furthermore, we also demonstrated that the absence of S1PR5 expression in NK cells did not interfere with the antitumour effects of NK cells and T cells in vivo. Taken together, our data indicate that S1PR5 plays an essential role in balancing GVHD and GVT activity.

Loss of Neurological Disease HSAN-I-Associated Gene SPTLC2 Impairs CD8+ T Cell Responses to Infection by Inhibiting T Cell Metabolic Fitness

Patients with the neurological disorder HSAN-I suffer frequent infections, attributed to a lack of pain sensation and failure to seek care for minor injuries. Whether protective CD8⁺ T cells are affected in HSAN-I patients remains unknown. Here, we report that HSAN-I-associated mutations in serine palmitoyltransferase subunit SPTLC2 dampened human T cell responses. Antigen stimulation and inflammation induced SPTLC2 expression, and murine T-cell-specific ablation of Sptlc2 impaired antiviral-T-cell expansion and effector function. Sptlc2 deficiency reduced sphingolipid biosynthetic flux and led to prolonged activation of the mechanistic target of rapamycin complex 1 (mTORC1), endoplasmic reticulum (ER) stress, and CD8⁺ T cell death. Protective CD8⁺ T cell responses in HSAN-I patient PBMCs and Sptlc2-deficient mice were restored by supplementing with sphingolipids and pharmacologically inhibiting ER stress-induced cell death. Therefore, SPTLC2 underpins protective immunity by translating extracellular stimuli into intracellular anabolic signals and antagonizes ER stress to promote T cell metabolic fitness.

The role of dihydrosphingolipids in disease

Dihydrosphingolipids refer to sphingolipids early in the biosynthetic pathway that do not contain a C4-trans-double bond in the sphingoid backbone: 3-ketosphinganine (3-ketoSph), dihydrosphingosine (dhSph), dihydrosphingosine-1-phosphate (dhS1P) and dihydroceramide (dhCer). Recent advances in research related to sphingolipid biochemistry have shed light on the importance of sphingolipids in terms of cellular signalling in health and disease. However, dihydrosphingolipids have received less attention and research is lacking especially in terms of their molecular mechanisms of action. This is despite studies implicating them in the pathophysiology of disease, for example dhCer in predicting type 2 diabetes in obese individuals, dhS1P in cardiovascular diseases and dhSph in hepato-renal toxicity. This review gives a comprehensive summary of research in the last 10-15 years on the dihydrosphingolipids, 3-ketoSph, dhSph, dhS1P and dhCer, and their relevant roles in different diseases. It also highlights gaps in research that could be of future interest.

Dihydro-sphingosine 1-phosphate interacts with carrier proteins in a manner distinct from that of sphingosine 1-phosphate

Dihydro-sphingosine 1-phosphate (DH-S1P) is an analog of sphingosine 1-phosphate (S1P), which is a potent lysophospholipid mediator. DH-S1P has been proposed to exert physiological properties similar to S1P. Although S1P is known to be carried on HDL via apolipoprotein M (apoM), the association between DH-S1P and HDL/apoM has not been fully elucidated. Therefore, in the present study, we aimed to elucidate this association and to compare it with that of S1P and HDL/apoM. First, we investigated the distributions of S1P and DH-S1P among lipoproteins and lipoprotein-depleted fractions in human serum and plasma samples and observed that both S1P and DH-S1P were detected on HDL; furthermore, elevated amounts of DH-S1P in serum samples were distributed to the lipoprotein-depleted fraction to a greater degree than to the HDL fraction. Concordantly, a preference for HDL over albumin was only observed for S1P, and not for DH-S1P, when the molecules were secreted from platelets. Regarding the association with HDL, although both S1P and DH-S1P prefer to bind to HDL, HDL preferentially accepts S1P over DH-S1P. For the association with apoM, S1P was not detected on HDL obtained from apoM knockout mice, while DH-S1P was detected. Moreover, apoM retarded the degradation of S1P, but not of DH-S1P. These results suggest that S1P binds to HDL via apoM, while DH-S1P binds to HDL in a non-specific manner. Thus, DH-S1P is not a mere analog of S1P and might possess unique clinical significance.

The essential role of G protein-coupled receptor (GPCR) signaling in regulating T cell immunity

AIM

The aim of this paper is to clarify the critical role of GPCR signaling in T cell immunity.

METHODS

The G protein-coupled receptors (GPCRs) are the most common targets in current pharmaceutical industry, and represent the largest and most versatile family of cell surface communicating molecules. GPCRs can be activated by a diverse array of ligands including neurotransmitters, chemokines as well as sensory stimuli. Therefore, GPCRs are involved in many key cellular and physiological processes, such as sense of light, taste and smell, neurotransmission, metabolism, endocrine and exocrine secretion. In recent years, GPCRs have been found to play an important role in immune system. T cell is an important type of immune cell, which plays a central role in cell-mediated immunity. A variety of GPCRs and their signaling mediators (RGS proteins, GRKs and β-arrestin) have been found to express in T cells and involved T cell-mediated immunity. We will summarize the role of GPCR signaling and their regulatory molecules in T cell activation, homeostasis and function in this article.

RESULTS

GPCR signaling plays an important role in T cell activation, homeostasis and function.

CONCLUSION

GPCR signaling is critical in regulating T cell immunity.

T cell inhibitory mechanisms in a model of aggressive Non-Hodgkin's Lymphoma

A reduced immune surveillance due to immune deficiency or treatment with immunosuppressive drugs is associated with a higher risk to develop aggressive Non-Hodgkin's lymphoma (NHL). Nevertheless, NHL also develops in immunocompetent patients indicating an escape from the immune system. T cell function in advanced aggressive lymphoma is not well characterized and the molecular mechanisms how malignant B cells influence T cell function are ill-defined. We therefore studied T cell function in Eμ-myc transgenic mice that develop an aggressive B cell lymphoma with some similarities to human Burkitt-lymphoma (BL). In advanced lymphoma, the number of T cells was severely reduced and the remaining CD4⁺ and CD8⁺ T cells lost the capacity to produce effector cytokines and expand upon re-stimulation. T cells in lymphoma-bearing mice were characterized by the expression of the immune inhibitory molecules programmed death (PD)-1, 2B4 and lymphocyte activation protein (LAG)-3. The proto-oncogene c-Myc not only drives cell proliferation and disease progression but also induces apoptosis of the malignant cells. We found that apoptotic lymphoma cells release purine metabolites that inhibit T cell function. Taken together, our data document that the characteristic high cell turnover and apoptotic rate in aggressive NHL induce a severe T cell dysfunction mediated by several immune-inhibitory mechanisms including ligation of inhibitory ligands and purine metabolites. Blocking a single mechanism only partially restored T cell function and did not increase survival of lymphoma mice.

Ceramide inhibits PKCθ by regulating its phosphorylation and translocation to lipid rafts in Jurkat cells

Protein kinase C theta (PKCθ) is a novel, calcium-independent member of the PKC family of kinases that was identified as a central player in T cell signaling and proliferation. Upon T cell activation by antigen-presenting cells, PKCθ gets phosphorylated and activated prior to its translocation to the immunological synapse where it couples with downstream effectors. PKCθ may be regulated by ceramide, a crucial sphingolipid that is known to promote differentiation, growth arrest, and apoptosis. To further investigate the mechanism, we stimulated human Jurkat T cells with either PMA or anti-CD3/anti-CD28 antibodies following induction of ceramide accumulation by adding exogenous ceramide, bacterial sphingomyelinase, or Fas ligation. Our results suggest that ceramide regulates the PKCθ pathway through preventing its critical threonine 538 (Thr538) phosphorylation and subsequent activation, thereby inhibiting the kinase's translocation to lipid rafts. Moreover, this inhibition is not likely to be a generic effect of ceramide on membrane reorganization. Other lipids, namely dihydroceramide, palmitate, and sphingosine, did not produce similar effects on PKCθ. Addition of the phosphatase inhibitors okadaic acid and calyculin A reversed the inhibition exerted by ceramide, and this suggests involvement of a ceramide-activated protein phosphatase. Such previously undescribed mechanism of regulation of PKCθ raises the possibility that ceramide, or one of its derivatives, and may prove valuable in novel therapeutic approaches for disorders involving autoimmunity or excessive inflammation-where PKCθ plays a critical role.

Fingolimod targets cerebral endothelial activation to block leukocyte recruitment in the central nervous system

Fingolimod (FTY720), an immunomodulator, is approved as an oral treatment for patients with relapsing forms of multiple sclerosis. Its effects are largely attributed to its mechanism of selectively retaining lymphocytes in the lymph nodes to reduce autoreactive T-cell recruitment in the CNS. In this study, we investigated the therapeutic effect of FTY720 on an animal model of CNS inflammation induced by intracerebral ventricle LPS injection. We found that FTY720 treatment significantly prevented LPS-induced neutrophil recruitment in the CNS by inhibiting leukocyte recruitment in cerebral microvessels. Furthermore, FTY720 also inhibited the expressions of adhesion molecules on the cerebral endothelium, but did not affect the expression levels of pro-inflammatory cytokines (TNF-α and IL-6) and chemokines (CXCL1 and CXCL2) in the CNS parenchyma. The inhibition of endothelial activation was accompanied by reduced phosphorylation of signaling molecules, including serine/threonine-specific protein kinase (Akt), STAT6, and nuclear factor-κB. This FTY720-attenuated inhibition of leukocyte recruitment and endothelial activation was reversed by blocking the functions of sphingosine kinase 2 or sphingosine-1-phosphate receptor 1. Our study demonstrated, for the first time, that FTY720 directly inhibits the phosphorylation of multiple signaling molecules in endothelial cells, thereby effectively blocking leukocyte recruitment in the CNS.

Sphingolipid pathway enzymes modulate cell fate and immune responses

Sphingolipids (SLs) are a class of essential, bioactive lipids. The SL family includes over 4000 distinct molecules, characterized by their sphingoid base (long-chain aliphatic amine) backbone. SLs are key components of cell membranes, yet their roles go well beyond structure. SLs are involved in many cellular processes including cell differentiation, apoptosis, growth arrest and senescence. As cancer cells routinely display increased growth properties and escape from cell death, it has been suggested that enzymes involved in SL synthesis or catabolism may be altered in cancer cells. In this review, we discuss the role of SL pathway enzymes in cancer, and in acquired resistance to therapy. The use of inhibitors and gene silencing approaches targeting these SL pathways is also explored. Finally, we elaborate on the role of SL pathway enzymes in the tumor microenvironment and their effect on immune cell function.

FTY720 ameliorates renal fibrosis by simultaneously affecting leucocyte recruitment and TGF-β signalling in fibroblasts

Renal fibrosis is the common final manifestation of chronic kidney diseases and usually results in end-stage renal failure. In this study, we evaluated the effect of fingolimod (FTY720), an analogue of sphingosine 1-phosphate (S1P), as a treatment for the unilateral ureteral obstruction (UUO)-induced renal fibrosis animal model. We treated mice with FTY720 at a dosage of 1 mg/kg/day by intragastric administration from day 1 until day 7. The control group received the same amount of saline. FTY720 reduced significantly the urine albumin/creatinine ratio (UACR) in treated UUO mice. FTY720 treatment also caused a significant decrease in interstitial expansion and collagen deposition in the kidney, accompanied by reduced mononuclear cell recruitment and inflammatory cytokine expression. In addition, the expression levels of the endothelial cell adhesion molecules P-selectin and vascular cell adhesion protein 1 (VCAM-1) were suppressed in the ligated kidney by FTY720 administration, suggesting reduced renal endothelial cell activation. Furthermore, in renal interstitial fibroblast normal rat kidney (NRK)-49F cells, FTY720 significantly affected transforming growth factor (TGF)-β-induced α-smooth muscle actin (SMA) expression and collagen synthesis by inhibiting both the Mothers against decapentaplegic homologue (Smad)2/3 and phosphatidylinositol 3-kinase/protein kinase B/glycogen synthase kinase 3 beta (PI3K/AKT/GSK3β) signalling pathways. S1P1 knock-down by siRNA reversed this effect significantly in our fibroblast cell culture model. Therefore, FTY720 attenuates renal fibrosis via two different mechanisms: first, FTY720 suppresses the synthesis of extracellular matrix in interstitial fibroblasts by interfering with TGF-β signalling; and secondly, FTY720 affects endothelial cell activation and chemokine expression, thereby reducing immune cell recruitment into the kidney.

Analysis of S1P Receptor Expression by Uterine Immune Cells Using Standardized Multi-parametric Flow Cytometry

Flow cytometry is a powerful tool for phenotypic and functional analyses of single immune cells. The increasing capability of flow cytometry technology has driven a more detailed understanding of immune cell subsets and functions in complex cellular systems such as the developing human decidua/placenta. We propose a standardized procedure for the isolation and analysis of human decidual natural killer (dNK) cells and this method can be extended to investigation of other uterine lymphocytes. Here this platform is used to examine the expression of sphingosine-1-phosphate (S1P) receptor and functional growth factors by dNK cells.

Sphingosine Kinase 2 Deficiency Attenuates Kidney Fibrosis via IFN-γ

Maladaptive repair after AKI may lead to progressive fibrosis and decline in kidney function. Sphingosine 1-phosphate has an important role in kidney injury and pleiotropic effects in fibrosis. We investigated the involvement of sphingosine kinase 1 and 2 (SphK1 and SphK2), which phosphorylate sphingosine to produce sphingosine 1-phosphate, in kidney fibrosis induced by folic acid (FA) or unilateral ischemia-reperfusion injury. Analysis of Masson trichrome staining and fibrotic marker protein and mRNA expression 14 days after AKI revealed that wild-type (WT) and Sphk1^-/- mice exhibited more kidney fibrosis than Sphk2^-/- mice. Furthermore, kidneys of FA-treated WT and Sphk1^-/- mice had greater immune cell infiltration and expression of fibrotic and inflammatory markers than kidneys of FA-treated Sphk2^-/- mice. In contrast, kidneys of Sphk2^-/- mice exhibited greater expression of Ifng and IFN-γ-responsive genes (Cxcl9 and Cxcl10) than kidneys of WT or Sphk1^-/- mice did at this time point. Splenic T cells from untreated Sphk2^-/- mice were hyperproliferative and produced more IFN-γ than did those of WT or Sphk1^-/- mice. IFN-γ blocking antibody administered to Sphk2^-/- mice or deletion of Ifng (Sphk2^-/-Ifng^-/- mice) blocked the protective effect of SphK2 deficiency in fibrosis. Moreover, adoptive transfer of Sphk2^-/- (but not Sphk2^-/-Ifng^-/- ) CD4 T cells into WT mice blocked FA-induced fibrosis. Finally, a selective SphK2 inhibitor blocked FA-induced kidney fibrosis in WT mice. These studies demonstrate that SphK2 inhibition may serve as a novel therapeutic approach for attenuating kidney fibrosis.

Sphingosine-1-phosphate, regulated by FSH and VEGF, stimulates granulosa cell proliferation

Sphingosine-1-phosphate (S1P) is a bioactive polar sphingolipid which stimulates proliferation, growth and survival in various cell types. In the ovary S1P has been shown protect the granulosa cells and oocytes from insults such as oxidative stress and radiotherapy, and S1P concentrations are greater in healthy than atretic large follicles. Hence, we postulate that S1P is fundamental in follicle development and that it is activated in ovarian granulosa cells in response to FSH and VEGF. To test this hypothesis we set out: i) to evaluate the effect of FSH and VEGF on S1P synthesis in cultured bovine granulosa cells and ii) to analyse the effect of S1P on proliferation and survival of bovine granulosa cells in vitro. Seventy five thousand bovine granulosa cells from healthy medium-sized (4-7mm) follicles were cultured in 96-well plates in McCoy's 5a medium containing 10ng/mL of insulin and 1ng/mL of LR-IGF-I at 37°C in a 5% CO2/air atmosphere at 37°C. Granulosa cell production of S1P was tested in response to treatment with FSH (0, 0.1, 1 and 10ng/mL) and VEGF (0, 0.01, 0.1, 1, 10 and 100ng/mL) and measured by HPLC. Granulosa cells produced S1P at 48 and 96h, with the maximum production observed with 1ng/mL of FSH. Likewise, 0.01ng/mL of VEGF stimulated S1P production at 48, but not 96h of culture. Further, the granulosa cell expression of sphingosine kinase-1 (SK1), responsible for S1P synthesis, was demonstrated by Western blot after 48h of culture. FSH increased the expression of phosphorylated SK1 (P<0.05) and the addition of a SK1 inhibitor reduced the constitutive and FSH-stimulated S1P synthesis (P<0.05). Sphingosine-1-phosphate had a biphasic effect on granulosa cell number after culture. At low concentration S1P (0.1μM) increased granulosa cell number after 48h of culture (P<0.05) and the proportion of cells in the G2 and M phase of the cell cycle (P<0.05), whereas higher concentrations decreased cell number (10μM; P<0.05) by an increase (P<0.05) in the proportion of cells in apoptosis (hypodiploid cells). In addition, treatment with SK-178 suppressed the FSH- and VEGF-stimulated rise of the granulosa cells number (P<0.05). Interestingly, the effect of 0.1μM S1P on granulosa cell number and their proportion in G2/M phases is similar to that observed with 1ng/mL FSH. The results of this study are the first to demonstrate sphingosine-1-phosphate (S1P) synthesis in granulosa cells under the control of FSH and VEGF. The later achieved through the regulation of sphingosine kinase 1 expression. This S1P augments the proportion of cells in the G2/M phase of the cell cycle that translates in increased granulosa cell proliferation.

Sphingosine 1-phosphate signaling impacts lymphocyte migration, inflammation and infection

Sphingosine 1-phosphate (S1P) is a sphingosine containing lipid intermediate obtained from ceramide. S1P is known to be an important signaling molecule and plays multiple roles in the context of immunity. This lysophospholipid binds and activates G-protein-coupled receptors (GPCRs) known as S1P receptors 1-5 (S1P1-5). Once activated, these GPCRs mediate signaling that can lead to alterations in cell proliferation, survival or migration, and can also have other effects such as promoting angiogenesis. In this review, we will present evidence demonstrating a role for S1P in lymphocyte migration, inflammation and infection, as well as in cancer. The therapeutic potential of targeting S1P receptors, kinases and lyase will also be discussed.

Oxidized lipids and lysophosphatidylcholine induce the chemotaxis, up-regulate the expression of CCR9 and CXCR4 and abrogate the release of IL-6 in human monocytes

Lipids through regulation of chronic inflammation play key roles in the development of various diseases. Here, we report that a mixed population of human primary monocytes migrated towards LPC, as well as oxidized linoleic acid isoforms 9-S-HODE, 9-R-HODE and 13-R-HODE. Incubation with 9-R-HODE, 13-R-HODE and LPC resulted in increased expression of CXCR4, the receptor for SDF-1α/CXCL12, correlated with increased monocyte migration towards SDF-1α/CXCL12. Further, we report increased expression of CCR9, the receptor for TECK/CCL25, after stimulation with these lipids. Upon examining the migratory response towards TECK/CCL25, it was observed that an increase in CCR9 expression upon pre-treatment with 9-S-HODE, 9-R-HODE, 13-R-HODE and LPC resulted in increased migration of monocytes expressing CCR9. Only LPC but not any other lipid examined increased the influx of intracellular Ca²⁺ in monocytes. Finally, 9-S-HODE, 9-R-HODE, 13-R-HODE, or LPC inhibited the release of IL-6 from monocytes suggesting that these lipids may play important role in controlling inflammatory responses.

Bioactive lipids and the control of Bax pro-apoptotic activity

Lipids are key regulators of cell physiology through the control of many aspects of cellular life and survival. In particular, lipids have been implicated at different levels and through many different mechanisms in the cell death program called apoptosis. Here, we discuss the action of lipids in the regulation of the activation and the integration of Bax into the mitochondrial outer membrane, a key pro-apoptotic member of the BCL-2 family. We describe how, during apoptosis, lipids can act simultaneously or in parallel as receptors or ligands for Bax to stimulate or inhibit its pro-death activity.

Non-genomic rapid responses via progesterone in human peripheral T cells are not indirectly mimicked by sphingosine 1-phosphate

Progesterone is an endogenous immunomodulator that suppresses T cell activation during pregnancy. Progesterone has been shown to induce rapid responses that cause intracellular calcium ([Ca(2+)]i) elevation and acidification followed by inhibition of phytohemagglutinin (PHA)-stimulated proliferation. These rapid responses involve T cell plasma membrane sites, but the mechanisms remain unclear. Three new membrane progesterone receptors (mPRα/mPRβ/mPRγ) have been identified as expressed in T cells. These proteins have been identified as G-protein-coupled receptors. Recently, mPRs have been classified as progestin and adipoQ receptors (PAQRs). Furthermore, they have been suggested to be alkaline ceramidases, possibly involved in mediating sphingolipid signaling. Alkaline ceramidases are capable of converting ceramide to sphingosine, which might then be further phosphorylated sphingosine via sphingosine kinase to sphingosine 1-phosphate (S1P). This pathway could result in progesterone acting indirectly via S1P on membrane sphingosine 1-phosphate receptors (S1PRs) in T cells to induce rapid responses. Therefore, our aim was to investigate whether progesterone rapid responses occur indirectly in T cells via S1P. We found that S1P induces [Ca(2+)]i elevation however there was no change in intracellular pH. This is different from the situation with progesterone: S1P alone does not suppress PHA-stimulated cell proliferation and does not act synergistically with progesterone on the inhibition of PHA-induced cell proliferation. In contrast, S1P at 1μM is able to antagonize the proliferation inhibitory effect of progesterone. Thus the rapid responses that are induced by progesterone in human peripheral T cells probably do not involve indirect signaling via S1P and S1PRs.

Effects of vitamin D3, calcipotriol and FTY720 on the expression of surface molecules and cytolytic activities of human natural killer cells and dendritic cells

We describe here the effects of three drugs that are either approved or have the potential for treating multiple sclerosis (MS) patients through the in vitro activities of human natural killer (NK) cells and dendritic cells (DCs). Our results indicate that 1,25(OH)₂D₃, the biologically active metabolite vitamin D₃, calcipotriol and FTY720 augment IL-2-activated NK cell lysis of K562 and RAJI tumor cell lines as well as immature (i) and mature (m) DCs, with variable efficacies. These results are corroborated with the ability of the drugs to up-regulate the expression of NK cytotoxicity receptors NKp30 and NKp44, as well as NKG2D on the surfaces of NK cells. Also, they down-regulate the expression of the killer inhibitory receptor CD158. The three drugs down-regulate the expression of CCR6 on the surface of iDCs, whereas vitamin D₃ and calcipotriol tend to up-regulate the expression of CCR7 on mDCs, suggesting that they may influence the migration of DCs into the lymph nodes. Finally, vitamin D₃, calcipotriol and FTY720 enhance NK17/NK1 cell lysis of K562 cells, suggesting that a possible mechanism of action for these drugs is via activating these newly described cells. In conclusion, our results show novel mechanisms of action for vitamin D₃, calcipotriol and FTY720 on cells of the innate immune system.

Sphingosine-1-phosphate suppresses TLR-induced CXCL8 secretion from human T cells

T cells produce a number of cytokines and chemokines upon stimulation with TLR agonists in the presence or absence of TCR signals. Here, we show that secretion of neutrophil chemoattractant CXCL8 from human T cell line Jurkat in response to stimulation with TLR agonists is reduced when cell stimulation is carried out in presence of serum. Serum does not, however, inhibit TCR-activated secretion of CXCL8 nor does it down-regulate TLR-costimulated IL-2 secretion from activated T cells. The molecule that can mimic the ability to bring about suppression in CXCL8 from TLR-activated T cells is serum-borne bioactive lipid, S1P. Serum and S1P-mediated inhibition require intracellular calcium. S1P also suppresses CXCL8 secretion from peripheral blood-derived human T cells activated ex vivo with various TLR ligands. Our findings reveal a previously unrecognized role for S1P in regulating TLR-induced CXCL8 secretion from human T cells.

S1P2 receptor promotes mouse skeletal muscle regeneration

Sphingosine 1-phosphate is a bioactive lipid that modulates skeletal muscle growth through its interaction with specific receptors localized in the cell membrane of muscle fibers and satellite cells. This study analyzes the role of S1P2 receptor during in vivo regeneration of soleus muscle in two models of S1P2 deficiency: the S1P2-null mouse and wild-type mice systemically treated with the S1P2 receptor antagonist JTE-013. To stimulate regeneration, muscle degeneration was induced by injecting into soleus muscle the myotoxic drug notexin. Both ablation of S1P2 receptor and its functional inactivation delayed regeneration of soleus muscle. The exogenous supplementation of S1P or its removal, by a specific antibody, two conditions known to stimulate or inhibit, respectively, soleus muscle regeneration, were without effects when the S1P2 receptor was absent or inactive. The delayed regeneration was associated with a lower level of myogenin, a muscle differentiation marker, and reduced phosphorylation of Akt, a key marker of muscle growth. Consistently, silencing of S1P2 receptor abrogated the pro-myogenic action of S1P in satellite cells, paralleled by low levels of the myogenic transcription factor myogenin. The study indicates that S1P2 receptor plays a key role in the early phases of muscle regeneration by sustaining differentiation and growth of new-forming myofibers.

Quelling the storm: utilization of sphingosine-1-phosphate receptor signaling to ameliorate influenza virus-induced cytokine storm

Initial and early tissue injury associated with severe influenza virus infection is the result of both virus-mediated lysis of infected pulmonary cells coupled with an exuberant immune response generated against the virus. The excessive host immune response associated with influenza virus infection has been termed "cytokine storm." Therapies that target virus replication are available; however, the selective pressure by such antiviral drugs on the virus often results in mutation and the escape of virus progeny now resistant to the antiviral regimen, thereby rendering such treatments ineffective. This event highlights the necessity for developing novel methods to combat morbidity and mortality caused by influenza virus infection. One potential method is restricting the host's immune response. However, prior treatment regimens employing drugs like corticosteroids that globally suppress the host's immune response were found unsatisfactory in large part because they disrupted the host's ability to control virus replication. Here, we discuss a novel therapy that utilizes sphingosine-1-phosphate (S1P) receptor signaling that has the ability to significantly limit immunopathologic injury caused by the host's innate and adaptive immune response, thereby significantly aborting morbidity and mortality associated with influenza virus infection. Moreover, S1P analog therapy allows for sufficient anti-influenza T cell and antibody formation to control infection. We review the anti-inflammatory effects of S1P signaling pathways and how modulation of these pathways during influenza virus infection restricts immunopathology. Finally, we discuss that combinatorial administration of S1P simultaneously with a current antiviral enhances the treatment efficacy for virulent influenza virus infections above that of either drug treatment alone. Interestingly, the scope of S1P receptor therapy reported here is likely to extend beyond influenza virus infection and could prove useful for the treatment of multiple maladies like other viral infections and autoimmune diseases where the host's inflammatory response is a major component in the disease process.

Sphingosine kinase inhibition exerts both pro- and anti-atherogenic effects in low-density lipoprotein receptor-deficient (LDL-R(-/-)) mice

Sphingosine 1-phosphate (S1P), a lysosphingolipid associated with high-density lipoprotein (HDL), contributes to the anti-atherogenic potential attributed to this lipoprotein. This study examined whether a reduction of S1P plasma levels affects atherosclerosis in a murine model of disease. LDL-R(-/-)mice on Western diet were given ABC294640, an inhibitor of sphingosine kinase (SphK) for 16 weeks. ABC294640 decreased plasma S1P by approximately 30%. However, ABC294640 failed to affect atherosclerotic lesion formation. Plasma triglycerides were reduced whereas total and HDL-cholesterol remained unchanged in course of ABC294640 treatment. ABC294640 increased plasma interleukin (IL)-12p70 and RANTES concentration as well as IL-12p70, RANTES and interferon (IFN)-γ production by peritoneal cells and this was paralleled by enhanced activity of peritoneal and spleen dendritic cells as evidenced by up-regulation of CD86 and MHC-II on CD11c(+) cells. As a consequence, increased T-cell activation was noted in ABC294640-treated mice as indicated by enhanced CD4(+) splenocyte proliferation, IFN-γ and IL-2 production, and CD69 expression. Concomitantly, however, ABC294640 treatment redistributed CD4(+) and CD8(+) cells from blood to lymphatic organs and reduced T-cell number within atherosclerotic lesions. In addition, plasma sVCAM-1, sICAM-1, and MCP-1 levels as well as in vivo leukocyte adhesion and CCL19-induced T-cell penetration into peritoneum were lower in ABC294640-treated animals. In vitro experiments demonstrated reduced VCAM-1 and ICAM-1 expression and lymphocyte adhesion to endothelial cells exposed to ABC294640. In conclusion, treatment with SphK inhibitor leads to both pro- and anti-atherogenic effects in LDL-R(-/-) mice. As a consequence, SphK inhibition fails to affect atherosclerosis despite significant S1P reduction in plasma.

Effects of lysophospholipids on tumor microenvironment

The effects of lysophospholipids (LPLs) on cancer microenvironment is a vast and growing field. These lipids are secreted physiologically by various cell types. They play highly important roles in the development, activation and regulation of the immune system. They are also secreted by cancerous cells and there is a strong association between LPLs and cancer. It is clear that these lipids and in particular sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) play major roles in regulating the growth of tumor cells, and in manipulating the immune system. These activities can be divided into two parts; the first involves the ability of S1P and LPA to either directly or through some of the enzymes that generate them such as sphingosine kinases or phospholipases, induce the motility and invasiveness of tumor cells. The second mechanism involves the recently discovered effects of these lipids on the anti-tumor effector natural killer (NK) cells. Whereas S1P and LPA induce the recruitment of these effector cells, they also inhibit their cytolysis of tumor cells. This may support the environment of cancer and the ability of cancer cells to grow, spread and metastasize. Consequently, LPLs or their receptors may be attractive targets for developing drugs in the treatment of cancer where LPLs or their receptors are up-regulated.

Sphingosine-1-phosphate receptor type 1 regulates glioma cell proliferation and correlates with patient survival

Sphingosine-1-phosphate (S1P) is a bioactive lipid that signals through a family of G protein-coupled receptors consisting of 5 members termed S1P(1-5), and it regulates cellular proliferation, migration and survival. We investigated the expression and role of S1P receptors in glioma. Human glioma expressed S1P(1), S1P(2), S1P(3), and S1P(5) by quantitative real-time PCR analysis. Expression of the S1P(1) was significantly lower in glioblastoma than in the normal brain (p < 0.01) and diffuse astrocytoma (p < 0.05). Immunoblotting showed that normal brain expressed more S1P(1) protein than did glioblastoma. Immunohistochemistry showed that S1P(1) was localized predominantly in the astrocytes in the normal brain, but no staining was observed in glioblastoma. Downregulation of S1P(1) expression correlated with poor survival of patients with glioblastoma (p < 0.05). S1P(1) small interfering RNA promoted cell proliferation in high-expressor glioma cell lines (T98G, G112). Cell proliferation was promoted by the pertussis toxin, which deactivates G(i/o) type of G proteins; the S1P(1) is exclusively coupled to these proteins. Forced expression of the S1P(1) in low-expressor cell lines (U87, U251) resulted in decreased cell growth and led to suppressed tumor growth in transplanted gliomas in vivo. Furthermore, we found a significant association between the S1P(1) expression and early growth response-1, a transcriptional factor that exhibits tumor suppression in glioblastoma cells (p < 0.05). These data indicate that the downregulation of S1P(1) expression enhances the malignancy of glioblastoma by increasing cell proliferation and correlates with the shorter survival of patients with glioblastoma.

FTY720 and SEW2871 reverse the inhibitory effect of S1P on natural killer cell mediated lysis of K562 tumor cells and dendritic cells but not on cytokine release

The aims of this study are to examine the effect of sphingosine 1-phosphate (S1P) on IL-2-activated natural killer (NK) cell lysis of K562 tumor cells and immature dendritic cells (iDCs), and to investigate the mechanisms involved in S1P activity. Our results show that S1P protected K562 cells or iDCs from NK cell lysis, which was reversed by FTY720 and SEW2871, the antagonists of S1P(1). S1P did not modulate the expression of NKG2D, NKp30, NKp44 or CD158 on the surface of NK cells, and neither affected the expression of CD80, CD83, or CD86 on the surface of DCs. In contrast, it increased the expression of HLA-I and HLA-E on DCs, an activity that was inhibited by FTY720 or SEW2871. Similarly, the inhibitory effect of S1P for NK cell lysis of K562 cells was directed toward S1P(1) expressed on the tumor cells but not on NK cells. Further analysis indicates that NK cells secreted various cytokines and chemokines with various intensities: (1) low (IL-4, IL-6, IL-12, TNF-alpha and MCP-1); (2) intermediate (IL-1beta, IL-10, TGF-beta1, and IL-17A); (3) high (IFN-gamma, and MIP-1alpha); and (4) very high (MIP-1beta). S1P significantly reduced the release of IL-17A and IFN-gamma from NK cells, but this inhibition was S1P(1)-independent. These results indicate that S1P is an anti-inflammatory molecule, and that S1P(1) is important for the interaction among NK cells and tumor cells or DCs leading to up-regulation of HLA-I and HLA-E on the surface of DCs, but not in S1P inhibition of the release of inflammatory cytokines from NK cells. Further, the results suggest that FTY720 and SEW2871 may potentially be used as prophylactic and/or therapeutic drugs to treat cancer patients.

Regulatory activity of azabisphosphonate-capped dendrimers on human CD4+ T cell proliferation enhances ex-vivo expansion of NK cells from PBMCs for immunotherapy

Background

Adoptive cell therapy with allogenic NK cells constitutes a promising approach for the treatment of certain malignancies. Such strategies are currently limited by the requirement of an efficient protocol for NK cell expansion. We have developed a method using synthetic nanosized phosphonate-capped dendrimers allowing such expansion. We are showing here that this is due to a specific inhibitory activity towards CD4⁺ T cell which could lead to further medical applications of this dendrimer.

Methods

Mononuclear cells from human peripheral blood were used to investigate the immunomodulatory effects of nanosized phosphonate-capped dendrimers on interleukin-2 driven CD4⁺T cell expansion. Proliferation status was investigated using flow cytometry analysis of CFSE dilution and PI incorporation experiments. Magnetic bead cell sorting was used to address activity towards individual or mixed cell sub-populations. We performed equilibrium binding assay to assess the interaction of fluorescent dendrimers with pure CD4⁺ T cells.

Results

Phosphonate-capped dendrimers are inhibiting the activation, and therefore the proliferation; of CD4⁺ T cells in IL-2 stimulated PBMCs, without affecting their viability. This allows a rapid enrichment of NK cells and further expansion. We found that dendrimer acts directly on T cells, as their regulatory property is maintained when stimulating purified CD4⁺ T cells with anti-CD3/CD28 microbeads. Performing equilibrium binding assays using a fluorescent analogue, we show that the phosphonate capped-dendrimers are specifically interacting with purified CD4⁺ T cells. Ultimately, we found that our protocol prevents the IL-2 related expansion of regulatory T cells that would be deleterious for the activity of infused NK cells.

Conclusion

High yield expansion of NK cells from human PBMCs by phosphonate-capped dendrimers and IL-2 occurs through the specific inhibition of the CD4⁺ lymphocyte compartment. Given the specificity of the interaction of dendrimers with CD4⁺ T cell, we hypothesize that regulatory activity may signal through a specific receptor that remains to be indentified. Therefore phosphonate-capped dendrimers constitute not only tools for the ex-vivo expansion of NK cells in immunotherapy of cancers but their mode of action could also lead to further medical applications where T cell activation and proliferation need to be dampened.

The sphingosine 1-phosphate receptor agonist FTY720 potently inhibits regulatory T cell proliferation in vitro and in vivo

CD4(+)CD25(+) regulatory T cell (Treg) entry into secondary lymphoid organs and local expansion is critical for their immunosuppressive function. Long-term application of the sphingosine-1 phosphate receptor agonist FTY720 exerts pleiotropic anti-inflammatory effects, whereas short-term FTY720 boosts antiviral immunity. In this study, we provide evidence that FTY720 potently inhibits Treg proliferation in vitro and in vivo without affecting their viability, phenotype, or in vitro immunosuppression. In contrast, adoptively transferred Treg exposed ex vivo to FTY720 lost their protective effects in murine models of acute glomerulonephritis and acute graft-vs-host disease. On a cellular level, FTY720 inhibits IL-2-induced STAT-5 phosphorylation, paralleled by a loss of FoxP3 expression during Treg expansion in vitro. Notably, loss of in vivo immunosuppression is not due to impaired migration to or localization within secondary lymphoid organs. We could even show a selective trapping of adoptively transferred Treg in inflammatory lymph nodes by FTY720. Finally, Treg isolated from animals systemically exposed to FTY720 also exhibit a significantly impaired proliferative response upon restimulation when compared with Treg isolated from solvent-treated animals. In summary, our data suggest that sphingosine-1 phosphate receptor-mediated signals induced by FTY720 abrogate their in vivo immunosuppressive potential by blocking IL-2 induced expansion, which is indispensable for their in vivo immunosuppressive activity.

Lyase to live by: sphingosine phosphate lyase as a therapeutic target

BACKGROUND

Sphingosine 1-phosphate (S1P) is a bioactive lipid that regulates cell proliferation, survival and migration and plays an essential role in angiogenesis and lymphocyte trafficking. S1P levels in the circulation and tissues are tightly regulated for proper cell functioning, and dysregulation of this system may contribute to the pathophysiology of certain human diseases. Sphingosine phosphate lyase (SPL) irreversibly degrades S1P and thereby acts as a gatekeeper that regulates S1P signaling by modulating intracellular S1P levels and the chemical S1P gradient that exists between lymphoid organs and circulating blood and lymph. However, SPL also generates biochemical products that may be relevant in human disease. SPL has been directly implicated in various physiological and pathological processes, including cell stress responses, cancer, immunity, hematopoietic function, muscle homeostasis, inflammation and development.

OBJECTIVE/METHODS

This review summarizes the current know-ledge of SPL structure, function and regulation, its involvement in various disease states and currently available small molecules known to modulate SPL activity.

RESULTS/CONCLUSION

This review provides evidence that SPL is a potential target for pharmacological manipulation for the treatment of malignant, autoimmune, inflammatory and other diseases.

Splenic natural killer cell activity in two models of experimental neurodegenerative diseases

Natural killer (NK) cells are antitumour/anti-viral effectors and play important roles in shaping the immune system, but their role in neurodegenerative diseases is not clear. Here, we investigated the fate of these cells in two neurodegenerative diseases. In the first model, the activity of NK cells was examined in mice with experimental autoimmune encephalomyelitis (EAE) treated with glatiramer acetate (GA or Copaxone), a drug used to treat EAE in animals and multiple sclerosis in human. The second disease model is twitcher (Galc(twi)/Galc(twi)) mice, which represents an authentic model of human Krabbe's disease. Administration of GA ameliorated EAE in SJL mice corroborated with isolating NK cells that expressed higher killing than cells isolated from vehicle-dosed animals against immature or mature dendritic cells (DCs). However, this drug showed no effect on the numbers of NK cells or the expression of CD69 molecule. On the other hand, NK cells either disappeared from the spleens or were present in low numbers in the white pulp areas of Galc(twi)/Galc(twi) mice, which have increased D-galactosyl-beta1-1'-sphingosine (GalSph) levels. Analysis by confocal microscopy shows that NK cells found in the spleens of Galc(twi)/Galc(twi) mice were apoptotic. Incubating NK cells in vitro with GalSph induced the apoptosis in these cells, confirming the results of twitcher mice. Our results provide the first evidence showing that amelioration of EAE in mice is corroborated with NK cell lysis of antigen-presenting DCs, whereas NK cell distribution into the spleen is altered in a devastating lipid disorder corroborated with induction of their apoptosis.

Splenic natural killer cell activity in two models of experimental neurodegenerative diseases

Natural killer (NK) cells are antitumour/anti-viral effectors and play important roles in shaping the immune system, but their role in neurodegenerative diseases is not clear. Here, we investigated the fate of these cells in two neurodegenerative diseases. In the first model, the activity of NK cells was examined in mice with experimental autoimmune encephalomyelitis (EAE) treated with glatiramer acetate (GA or Copaxone), a drug used to treat EAE in animals and multiple sclerosis in human. The second disease model is twitcher (Galc(twi)/Galc(twi)) mice, which represents an authentic model of human Krabbe's disease. Administration of GA ameliorated EAE in SJL mice corroborated with isolating NK cells that expressed higher killing than cells isolated from vehicle-dosed animals against immature or mature dendritic cells (DCs). However, this drug showed no effect on the numbers of NK cells or the expression of CD69 molecule. On the other hand, NK cells either disappeared from the spleens or were present in low numbers in the white pulp areas of Galc(twi)/Galc(twi) mice, which have increased D-galactosyl-beta1-1'-sphingosine (GalSph) levels. Analysis by confocal microscopy shows that NK cells found in the spleens of Galc(twi)/Galc(twi) mice were apoptotic. Incubating NK cells in vitro with GalSph induced the apoptosis in these cells, confirming the results of twitcher mice. Our results provide the first evidence showing that amelioration of EAE in mice is corroborated with NK cell lysis of antigen-presenting DCs, whereas NK cell distribution into the spleen is altered in a devastating lipid disorder corroborated with induction of their apoptosis.

The alliance of sphingosine-1-phosphate and its receptors in immunity

Sphingosine-1-phosphate (S1P) is a biologically active metabolite of plasma-membrane sphingolipids that is essential for immune-cell trafficking. Its concentration is increased in many inflammatory conditions, such as asthma and autoimmunity. Much of the immune function of S1P results from the engagement of a family of G-protein-coupled receptors (S1PR1-S1PR5). Recent findings on the role of S1P in immunosurveillance, the discovery of regulatory mechanisms in S1P-mediated immune-cell trafficking and new advances in understanding the mechanism by which S1P affects immune-cell function indicate that the alliance between S1P and its receptors has a fundamental role in immunity.

Cyclical and dose-dependent responses of adult human mature oligodendrocytes to fingolimod

Fingolimod is a sphingosine-1-phosphate (S1P) analogue that has been used in clinical trials as a systemic immunomodulatory therapy for multiple sclerosis. Fingolimod readily accesses the central nervous system, raising the issue of its direct effects on neural cells. We assessed the effects of active fingolimod on dissociated cultures of mature, myelin-producing oligodendrocytes (OLGs) derived from adult human brain. Human OLGs express S1P receptor transcripts in relative abundance of S1P5>S1P3>S1P1, with undetectable levels of S1P4. Low doses of fingolimod (100 pmol/L to 1 nmol/L) induced initial membrane elaboration (2 days), subsequent retraction (4 days), and recurrence of extension with prolonged treatment (8 days). Higher doses (10 nmol/L to 1 mumol/L) caused the opposite modulation of membrane dynamics. Retraction was rescued by co-treatment with the S1P3/S1P5 pathway antagonist, suramin, and was associated with RhoA-mediated cytoskeletal signaling. Membrane elaboration was mimicked using the S1P1 agonist SEW2871. Fingolimod rescued human OLGs from serum and glucose deprivation-induced apoptosis, which was reversed with suramin co-treatment and mimicked using an S1P5 agonist. High doses of fingolimod induced an initial down-regulation of S1P5 mRNA levels relative to control (4 hours), subsequent up-regulation (2 days), and recurrent down-regulation (8 days). S1P1 mRNA levels were inversely regulated compared with S1P5. These results indicate that fingolimod modulates maturity- and species-specific OLG membrane dynamics and survival responses that are directly relevant for myelin integrity.

FTY720 modulates human oligodendrocyte progenitor process extension and survival

OBJECTIVE

FTY720, a sphingosine-1-phosphate (S1P) receptor agonist that crosses the blood-brain barrier, is a potential immuno-therapy for multiple sclerosis. Our objective was to assess the effect of FTY720 on process extension, differentiation, and survival of human oligodendrocyte progenitor cells (OPCs), and link the functional effects with S1P receptor expression and signaling.

METHODS

Functional assays and receptor expression studies were conducted on A2B5+ OPCs derived from the human fetal central nervous system. Cells were treated with physiologically relevant concentrations of the active phosphorylated form of FTY720. S1P receptor/signaling modulators were used to elucidate the basis of the FTY720-induced functional responses.

RESULTS

Short-term (1 day) FTY720 treatment caused initial process retraction that was reversed by uncoupling S1P3 and 5 from their G protein using suramin, and with a Rho-kinase inhibitor H1152. Retraction was associated with RhoA-mediated cytoskeletal signaling and with inhibition of OPC differentiation into more mature phenotypes. Continued FTY720 treatment (2 days) induced process extension and enhanced cell survival associated with increased extracellular signal-regulated kinases 1 and 2 phosphorylation, mimicked with the S1P1-specific agonist SEW2871, but not reversed with suramin. Quantitative real-time polymerase chain reaction showed that FTY720 induced reciprocal and cyclic modulation of S1P1 and S1P5 messenger RNA levels. The observed initial downregulation of S1P5 and subsequently of S1P1 messenger RNA supports functional responses being mediated sequentially by S1P5- and later S1P1-associated signaling.

INTERPRETATION

FTY720 induces time-dependent modulation of S1P receptors on human OPCs with consequent functional responses that are directly relevant for the remyelination process.

Silencing S1P1 receptors regulates collagen-V reactive lymphocyte-mediated immunobiology in the transplanted lung

Type V collagen (col[V])-reactive lymphocytes contribute to lung transplant rejection, but the mechanisms for emigration into the graft are unknown. Sphingosine-1-phosphate-1 receptors (S1P(1R)) are believed to be required for lymphocyte emigration in other studies, but their role in col(V)-reactive lymphocyte rejection responses is not known. Utilizing small interfering RNA (siRNA) to reduce S1P(1R) expression on col(V)-reactive lymphocytes, we examined the role of S1P(1R) in the rejection response. Quantitative polymerase chain reaction (PCR) revealed strong expression of S1P(1R) messenger RNA (mRNA)on col(V)-reactive lymphocytes isolated from immunized rats. S1P(1R)-specific siRNA (S1P(1R) siRNA) reduced expression of S1P(1R) mRNA and protein, whereas scramble siRNA (SC siRNA) had no effect. Adoptive transfer of lymphocytes treated with S1P(1R) siRNA to rat Wistar Kyoto (WKY) lung isograft recipients resulted in retention of cells within the liver with fewer cells in mediastinal lymph nodes when compared to cells exposed to SC siRNA. S1P(1R)-deficient cells proliferated in response to alloantigens, but not in response to col(V), and produced less interferon (IFN)-gamma in response to col(V) compared to controls. Downregulating S1P(1R) did not affect production of interleukin (IL)-10and tumor necrosis factor (TNF)-alpha, or expression of adhesion molecules critical for migration, but prevented rejection pathology and lowered local levels of IFN-gamma post adoptive transfer. These data demonstrate novel roles of S1P(1R,) which include regulating emigration and modulating lymphocyte activation.

Sphingosine 1-Phosphate Mediates Proliferation and Survival of Mesoangioblasts

Mesoangioblasts are stem cells capable of differentiating in various mesodermal tissues and are presently regarded as suitable candidates for cell therapy of muscle degenerative diseases, as well as myocardial infarction. The enhancement of their proliferation and survival after injection in vivo could greatly improve their ability to repopulate damaged tissues. In this study, we show that the bioactive sphingolipid sphingosine 1-phosphate (S1P) regulates critical functions of mesoangioblast cell biology. S1P evoked a full mitogenic response in mesoangioblasts, measured by labeled thymidine incorporation and cell counting. Moreover, S1P strongly counteracted the apoptotic process triggered by stimuli as diverse as serum deprivation, C2-ceramide treatment, or staurosporine treatment, as assessed by cell counting, as well as histone-associated fragments and caspase-3 activity determinations. S1P acts both as an intracellular messenger and through specific membrane receptors. Real-time polymerase chain reaction analysis revealed that mesoangioblasts express the S1P-specific receptor S1P3 and, to a minor extent, S1P1 and S1P2. By using S1P receptor subtype-specific agonists and antagonists, we found that the proliferative response to S1P was mediated mainly by S1P2. By contrast, the antiapoptotic effect did not implicate S1P receptors. These findings demonstrate an important role of S1P in mesoangioblast proliferation and survival and indicate that targeting modulation of S1P-dependent signaling pathways may be used to improve the efficiency of muscle repair by these cells. Disclosure of potential conflicts of interest is found at the end of this article.