Phosphorylated FTY720 stimulates ERK phosphorylation in astrocytes via S1P receptors

Interplay between the SAFE and the sphingolipid pathway for cardioprotection

AIM

Activation of both the Survivor Activating Factor Enhancement (SAFE) pathway (including Tumor Necrosis Factor-alpha (TNF-α) and Signal Transducer and Activator of Transcription-3 (STAT-3)) and the sphingolipid signalling pathway (including sphingosine kinase-1 (SK1) and sphingosine-1 phosphate (S1P)) play a key role in promoting cardioprotection against ischemia-reperfusion injury (IRI). We investigated whether the activation of the SAFE pathway by exogenous S1P is dependent on the activation of SK1 for cardioprotection.

MATERIALS AND METHODS

Isolated cardiomyocytes from TNF-α knockout (KO) mice, cardiomyocyte-specific STAT-3 KO mice and their wild-type (WT) littermates were exposed to simulated ischemia in the presence of a trigger of the SAFE pathway (S1P) and SK1 inhibitor (SK1-I). Similarly, isolated perfused hearts from adult TNF-α KO, STAT-3 KO and WT mice were subjected to IRI with S1P and/or SK1-I. Cell viability, infarct size (IS) and SK1 activity were assessed.

KEY FINDINGS

In isolated cardiomyocytes and in isolated hearts subjected to simulated ischemia/IRI, S1P pretreatment decreased cell death in WT mice, an effect that was abrogated in the presence of SK1-I. S1P failed to reduce cell death after simulated ischemia/IRI in both cardiomyocytes or hearts isolated from TNF-α KO and STAT-3 KO mice. Interestingly, S1P pretreatment increased SK1 activity in WT and STAT-3 KO mice, with no changes in TNF-α KO mice.

SIGNIFICANCE

Our data strongly suggest SK1 as a key component to activate STAT-3 downstream of TNF-α in the SAFE pathway, paving the way for the development of novel cardioprotective strategies that may target SK1 to modulate the SAFE pathway and increase cell survival following IRI.

Glial Cells as Key Regulators in Neuroinflammatory Mechanisms Associated with Multiple Sclerosis

Even though several highly effective treatments have been developed for multiple sclerosis (MS), the underlying pathological mechanisms and drivers of the disease have not been fully elucidated. In recent years, there has been a growing interest in studying neuroinflammation in the context of glial cell involvement as there is increasing evidence of their central role in disease progression. Although glial cell communication and proper function underlies brain homeostasis and maintenance, their multiple effects in an MS brain remain complex and controversial. In this review, we aim to provide an overview of the contribution of glial cells, oligodendrocytes, astrocytes, and microglia in the pathology of MS during both the activation and orchestration of inflammatory mechanisms, as well as of their synergistic effects during the repair and restoration of function. Additionally, we discuss how the understanding of glial cell involvement in MS may provide new therapeutic targets either to limit disease progression or to facilitate repair.

The sphingosine 1-phosphate analogue, FTY720, modulates the lipidomic signature of the mouse hippocampus

The small-molecule drug, FTY720 (fingolimod), is a synthetic sphingosine 1-phosphate (S1P) analogue currently used to treat relapsing-remitting multiple sclerosis in both adults and children. FTY720 can cross the blood-brain barrier (BBB) and, over time, accumulate in lipid-rich areas of the central nervous system (CNS) by incorporating into phospholipid membranes. FTY720 has been shown to enhance cell membrane fluidity, which can modulate the functions of glial cells and neuronal populations involved in regulating behaviour. Moreover, direct modulation of S1P receptor-mediated lipid signalling by FTY720 can impact homeostatic CNS physiology, including neurotransmitter release probability, the biophysical properties of synaptic membranes, ion channel and transmembrane receptor kinetics, and synaptic plasticity mechanisms. The aim of this study was to investigate how chronic FTY720 treatment alters the lipid composition of CNS tissue in adolescent mice at a key stage of brain maturation. We focused on the hippocampus, a brain region known to be important for learning, memory, and the processing of sensory and emotional stimuli. Using mass spectrometry-based lipidomics, we discovered that FTY720 increases the fatty acid chain length of hydroxy-phosphatidylcholine (PCOH) lipids in the mouse hippocampus. It also decreases PCOH monounsaturated fatty acids (MUFAs) and increases PCOH polyunsaturated fatty acids (PUFAs). A total of 99 lipid species were up-regulated in the mouse hippocampus following 3 weeks of oral FTY720 exposure, whereas only 3 lipid species were down-regulated. FTY720 also modulated anxiety-like behaviours in young mice but did not affect spatial learning or memory formation. Our study presents a comprehensive overview of the lipid classes and lipid species that are altered in the hippocampus following chronic FTY720 exposure and provides novel insight into cellular and molecular mechanisms that may underlie the therapeutic or adverse effects of FTY720 in the central nervous system.

Molecular and neuroimmune pharmacology of S1P receptor modulators and other disease-modifying therapies for multiple sclerosis

Multiple sclerosis (MS) is a neurological, immune-mediated demyelinating disease that affects people in the prime of life. Environmental, infectious, and genetic factors have been implicated in its etiology, although a definitive cause has yet to be determined. Nevertheless, multiple disease-modifying therapies (DMTs: including interferons, glatiramer acetate, fumarates, cladribine, teriflunomide, fingolimod, siponimod, ozanimod, ponesimod, and monoclonal antibodies targeting ITGA4, CD20, and CD52) have been developed and approved for the treatment of MS. All the DMTs approved to date target immunomodulation as their mechanism of action (MOA); however, the direct effects of some DMTs on the central nervous system (CNS), particularly sphingosine 1-phosphate (S1P) receptor (S1PR) modulators, implicate a parallel MOA that may also reduce neurodegenerative sequelae. This review summarizes the currently approved DMTs for the treatment of MS and provides details and recent advances in the molecular pharmacology, immunopharmacology, and neuropharmacology of S1PR modulators, with a special focus on the CNS-oriented, astrocyte-centric MOA of fingolimod.

Morus alba L. root decreases melanin synthesis via sphingosine-1-phosphate signaling in B16F10 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Morus alba L. has long been used for beauty in many Asian countries and regions, including anti-aging and hyperpigmentation.

AIM OF THE STUDY

This study aimed at the inhibitory effect of Morus alba L. root on melanogenesis in B16F10 melanoma cells and the mechanism involved.

MATERIALS AND METHODS

This study evaluated the anti-melanogenic effect of Morus alba L. root extract (MAR) on B16F10 melanoma cells by assessing cell viability, melanin accumulation, cellular tyrosinase activity, intra/inter-cellular S1P levels, cellular S1P-related metabolic enzyme activity, and western blot analysis. In addition, the potential S1P lyase (S1PL) inhibitory constituents in MAR were identified by LC-MS/MS.

RESULTS

Without affecting the viability of B16F10 melanoma cells, MAR inhibited intracellular tyrosinase activity in a dose-dependent manner, thereby reducing the accumulation of melanin. MAR also downregulated the expression level of MITF via activating the ERK signaling pathway. Furthermore, MAR increased the intra/inter-cellular S1P by inhibiting S1PL. Several compounds with inhibitory S1PL activity have been identified in MAR, such as mulberroside A and oxyresveratrol.

CONCLUSIONS

The anti-melanogenic effects of MAR mainly involve promoting MITF degradation mediated via S1P-S1PR3-ERK signaling through increasing cellular S1P levels by inhibiting S1PL activity.

Multiple Sclerosis: Therapeutic Strategies on the Horizon

Multiple sclerosis (MS) is a chronic disease affecting the brain and the spinal cord. It is a chronic inflammatory demyelinating disease of the central nervous system. It is the leading cause of non-traumatic disability in young adults. The clinical course of the disease is quite variable, ranging from stable chronic disease to rapidly evolving debilitating disease. The pathogenesis of MS is not fully understood. Still, there has been a rapid shift in understanding the immune pathology of MS away from pure T cell-mediated disease to B cells and microglia/astrocytes having a vital role in the pathogenesis of MS. This has helped in the emergence of new therapies for management. Effective treatment of MS requires a multidisciplinary approach to manage acute attacks, prevent relapses and disease progression and treat the disabling symptoms associated with the disease. In this review, we discuss the pathogenesis of MS, management of acute relapses, disease-modifying therapies in MS, new drugs and drugs currently in trial for MS and the symptomatic treatment of MS.  All language search was conducted on Google Scholar, PubMed, MEDLINE, and Embase till February 2022. The following search strings and medical subheadings (MeSH) were used: "Multiple Sclerosis", "Pathogenesis of MS", and "Disease-modifying therapies in MS". We explored literature on the pathogenic mechanisms behind MS, management of acute relapses, disease-modifying therapies in MS and symptomatic management.

Fingolimod Rescues Memory and Improves Pathological Hallmarks in the 3xTg-AD Model of Alzheimer's Disease

Therapeutic strategies for Alzheimer's disease (AD) have largely focused on the regulation of amyloid pathology while those targeting tau pathology, and inflammatory mechanisms are less explored. In this regard, drugs with multimodal and concurrent targeting of Aβ, tau, and inflammatory processes may offer advantages. Here, we investigate one such candidate drug in the triple transgenic 3xTg-AD mouse model of AD, namely the disease-modifying oral neuroimmunomodulatory therapeutic used in patients with multiple sclerosis, called fingolimod. In this study, administration of fingolimod was initiated after behavioral symptoms are known to emerge, at 6 months of age. Treatment continued to 12 months when behavioral tests were performed and thereafter histological and biochemical analysis was conducted on postmortem tissue. The results demonstrate that fingolimod reverses deficits in spatial working memory at 8 and 12 months of age as measured by novel object location and Morris water maze tests. Inflammation in the brain is alleviated as demonstrated by reduced Iba1-positive and CD3-positive cell number, less ramified microglial morphology, and improved cytokine profile. Finally, treatment with fingolimod was shown to reduce phosphorylated tau and APP levels in the hippocampus and cortex. These results highlight the potential of fingolimod as a multimodal therapeutic for the treatment of AD.

Signaling through the S1P-S1PR Axis in the Gut, the Immune and the Central Nervous System in Multiple Sclerosis: Implication for Pathogenesis and Treatment

Sphingosine 1-phosphate (S1P) is a signaling molecule with complex biological functions that are exerted through the activation of sphingosine 1-phosphate receptors 1–5 (S1PR1–5). S1PR expression is necessary for cell proliferation, angiogenesis, neurogenesis and, importantly, for the egress of lymphocytes from secondary lymphoid organs. Since the inflammatory process is a key element of immune-mediated diseases, including multiple sclerosis (MS), S1PR modulators are currently used to ameliorate systemic immune responses. The ubiquitous expression of S1PRs by immune, intestinal and neural cells has significant implications for the regulation of the gut–brain axis. The dysfunction of this bidirectional communication system may be a significant factor contributing to MS pathogenesis, since an impaired intestinal barrier could lead to interaction between immune cells and microbiota with a potential to initiate abnormal local and systemic immune responses towards the central nervous system (CNS). It appears that the secondary mechanisms of S1PR modulators affecting the gut immune system, the intestinal barrier and directly the CNS, are coordinated to promote therapeutic effects. The scope of this review is to focus on S1P−S1PR functions in the cells of the CNS, the gut and the immune system with particular emphasis on the immunologic effects of S1PR modulation and its implication in MS.

Lessons from S1P receptor targeting in multiple sclerosis

Sphingosine 1-phosphate (S1P) is a potent bioactive sphingolipid binding to specific G protein-coupled receptors expressed in several organs. The relevance of S1P-S1P receptor axis in the pathophysiology of immune and nervous systems has encouraged the development of S1P receptor modulators for the treatment of neurological, autoimmune and/or inflammatory disorders. Currently, four S1P receptor modulators are approved drugs for multiple sclerosis (MS), an inflammatory disorder of the central nervous system. As main pharmacologic effect, these treatments induce lymphopenia due to the loss of responsiveness to S1P gradients guiding lymphocyte egress from lymphoid organs into the bloodstream. Recent data point to immunological effects of the S1P modulators beyond the inhibition of lymphocyte trafficking. Further, these drugs may cross the blood-brain barrier and directly target CNS resident cells expressing S1P receptors. Here we review the role of S1P signalling in neuroimmunology at the light of the evidences generated from the study of the mechanism of action of S1P receptor modulators in MS and integrate this information with findings derived from neuroinflammatory animal models and in vitro observations. These insights can direct the application of therapeutic approaches targeting S1P receptors in other disease areas.

Critical Roles of Lysophospholipid Receptors in Activation of Neuroglia and Their Neuroinflammatory Responses

Activation of microglia and/or astrocytes often releases proinflammatory molecules as critical pathogenic mediators that can promote neuroinflammation and secondary brain damages in diverse diseases of the central nervous system (CNS). Therefore, controlling the activation of glial cells and their neuroinflammatory responses has been considered as a potential therapeutic strategy for treating neuroinflammatory diseases. Recently, receptor-mediated lysophospholipid signaling, sphingosine 1-phosphate (S1P) receptor- and lysophosphatidic acid (LPA) receptor-mediated signaling in particular, has drawn scientific interest because of its critical roles in pathogenies of diverse neurological diseases such as neuropathic pain, systemic sclerosis, spinal cord injury, multiple sclerosis, cerebral ischemia, traumatic brain injury, hypoxia, hydrocephalus, and neuropsychiatric disorders. Activation of microglia and/or astrocytes is a common pathogenic event shared by most of these CNS disorders, indicating that lysophospholipid receptors could influence glial activation. In fact, many studies have reported that several S1P and LPA receptors can influence glial activation during the pathogenesis of cerebral ischemia and multiple sclerosis. This review aims to provide a comprehensive framework about the roles of S1P and LPA receptors in the activation of microglia and/or astrocytes and their neuroinflammatory responses in CNS diseases.

Sphingosine 1-Phosphate Receptors in Cerebral Ischemia

Sphingosine 1-phosphate (S1P) is an important lipid biomolecule that exerts pleiotropic cellular actions as it binds to and activates its five G-protein-coupled receptors, S1P_1-5. Through these receptors, S1P can mediate diverse biological activities in both healthy and diseased conditions. S1P is produced by S1P-producing enzymes, sphingosine kinases (SphK1 and SphK2), and is abundantly present in different organs, including the brain. The medically important roles of receptor-mediated S1P signaling are well characterized in multiple sclerosis because FTY720 (Gilenya™, Novartis), a non-selective S1P receptor modulator, is currently used as a treatment for this disease. In cerebral ischemia, its role is also notable because of FTY720's efficacy in both rodent models and human patients with cerebral ischemia. In particular, some of the S1P receptors, including S1P₁, S1P₂, and S1P₃, have been identified as pathogenic players in cerebral ischemia. Other than these receptors, S1P itself and S1P-producing enzymes have been shown to play certain roles in cerebral ischemia. This review aims to compile the current updates and overviews about the roles of S1P signaling, along with a focus on S1P receptors in cerebral ischemia, based on recent studies that used in vivo rodent models of cerebral ischemia.

Molecular Effects of FDA-Approved Multiple Sclerosis Drugs on Glial Cells and Neurons of the Central Nervous System

Multiple sclerosis (MS) is characterized by peripheral and central inflammatory features, as well as demyelination and neurodegeneration. The available Food and Drug Administration (FDA)-approved drugs for MS have been designed to suppress the peripheral immune system. In addition, however, the effects of these drugs may be partially attributed to their influence on glial cells and neurons of the central nervous system (CNS). We here describe the molecular effects of the traditional and more recent FDA-approved MS drugs Fingolimod, Dimethyl Fumarate, Glatiramer Acetate, Interferon-β, Teriflunomide, Laquinimod, Natalizumab, Alemtuzumab and Ocrelizumab on microglia, astrocytes, neurons and oligodendrocytes. Furthermore, we point to a possible common molecular effect of these drugs, namely a key role for NFκB signaling, causing a switch from pro-inflammatory microglia and astrocytes to anti-inflammatory phenotypes of these CNS cell types that recently emerged as central players in MS pathogenesis. This notion argues for the need to further explore the molecular mechanisms underlying MS drug action.

Fingolimod Rescues Demyelination in a Mouse Model of Krabbe's Disease

Krabbe's disease is an infantile neurodegenerative disease, which is affected by mutations in the lysosomal enzyme galactocerebrosidase, leading to the accumulation of its metabolite psychosine. We have shown previously that the S1P receptor agonist fingolimod (FTY720) attenuates psychosine-induced glial cell death and demyelination both in vitro and ex vivo models.

Krabbe's disease is an infantile neurodegenerative disease, which is affected by mutations in the lysosomal enzyme galactocerebrosidase, leading to the accumulation of its metabolite psychosine. We have shown previously that the S1P receptor agonist fingolimod (FTY720) attenuates psychosine-induced glial cell death and demyelination both in vitro and ex vivo models. These data, together with a lack of therapies for Krabbe's disease, prompted the current preclinical study examining the effects of fingolimod in twitcher mice, a murine model of Krabbe's disease. Twitcher mice, both male and female, carrying a natural mutation in the galc gene were given fingolimod via drinking water (1 mg/kg/d). The direct impact of fingolimod administration was assessed via histochemical and biochemical analysis using markers of myelin, astrocytes, microglia, neurons, globoid cells, and immune cells. The effects of fingolimod on twitching behavior and life span were also demonstrated. Our results show that treatment of twitcher mice with fingolimod significantly rescued myelin levels compared with vehicle-treated animals and also regulated astrocyte and microglial reactivity. Furthermore, nonphosphorylated neurofilament levels were decreased, indicating neuroprotective and neurorestorative processes. These protective effects of fingolimod on twitcher mice brain pathology was reflected by an increased life span of fingolimod-treated twitcher mice. These in vivo findings corroborate initial in vitro studies and highlight the potential use of S1P receptors as drug targets for treatment of Krabbe's disease.

SIGNIFICANCE STATEMENT This study demonstrates that the administration of the therapy known as fingolimod in a mouse model of Krabbe's disease (namely, the twitcher mouse model) significantly rescues myelin levels. Further, the drug fingolimod also regulates the reactivity of glial cells, astrocytes and microglia, in this mouse model. These protective effects of fingolimod result in an increased life span of twitcher mice.

FTY720 (Fingolimod) Ameliorates Brain Injury through Multiple Mechanisms and is a Strong Candidate for Stroke Treatment

FTY720 (Fingolimod) is a known sphingosine-1-phosphate (S1P) receptor agonist that exerts strong anti-inflammatory effects and was approved as the first oral drug for the treatment of multiple sclerosis by the US Food and Drug Administration (FDA) in 2010. FTY720 is mainly associated with unique functional "antagonist" and "agonist" mechanisms. The functional antagonistic mechanism is mediated by the transient down-regulation and degradation of S1P receptors on lymphocytes, which prevents lymphocytes from entering the blood stream from the lymph node. This subsequently results in the development of lymphopenia and reduces lymphocytic inflammation. Functional agonistic mechanisms are executed through S1P receptors expressed on the surface of various cells including neurons, astrocytes, microglia, and blood vessel endothelial cells. These functions might play important roles in regulating anti-apoptotic systems, modulating brain immune and phagocytic activities, preserving the Blood-Brain-Barrier (BBB), and the proliferation of neural precursor cells. Recently, FTY720 have shown receptor-independent effects, including intracellular target bindings and epigenetic modulations. Many researchers have recognized the positive effects of FTY720 and launched basic and clinical experiments to test the use of this agent against stroke. Although the mechanism of FTY720 has not been fully elucidated, its efficacy against cerebral stroke is becoming clear, not only in animal models, but also in ischemic stroke patients through clinical trials. In this article, we review the data obtained from laboratory findings and preliminary clinical trials using FTY720 for stroke treatment.

Sphingosine 1-phosphate but not Fingolimod protects neurons against excitotoxic cell death by inducing neurotrophic gene expression in astrocytes

Sphingosine 1-phosphate (S1P) is an essential lipid metabolite that signals through a family of five G protein-coupled receptors, S1PR1-S1PR5, to regulate cell physiology. The multiple sclerosis drug Fingolimod (FTY720) is a potent S1P receptor agonist that causes peripheral lymphopenia. Recent research has demonstrated direct neuroprotective properties of FTY720 in several neurodegenerative paradigms; however, neuroprotective properties of the native ligand S1P have not been established. We aimed to establish the significance of neurotrophic factor up-regulation by S1P for neuroprotection, comparing S1P with FTY720. S1P induced brain-derived neurotrophic factor (BDNF), leukemia inhibitory factor (LIF), platelet-derived growth factor B (PDGFB), and heparin-binding EGF-like growth factor (HBEGF) gene expression in primary human and murine astrocytes, but not in neurons, and to a much greater extent than FTY720. Accordingly, S1P but not FTY720 protected cultured neurons against excitotoxic cell death in a primary murine neuron-glia coculture model, and a neutralizing antibody to LIF blocked this S1P-mediated neuroprotection. Antagonists of S1PR1 and S1PR2 both inhibited S1P-mediated neurotrophic gene induction in human astrocytes, indicating that simultaneous activation of both receptors is required. S1PR2 signaling was transduced through Gα₁₃ and the small GTPase Rho, and was necessary for the up-regulation and activation of the transcription factors FOS and JUN, which regulate LIF, BDNF, and HBEGF transcription. In summary, we show that S1P protects hippocampal neurons against excitotoxic cell death through up-regulation of neurotrophic gene expression, particularly LIF, in astrocytes. This up-regulation requires both S1PR1 and S1PR2 signaling. FTY720 does not activate S1PR2, explaining its relative inefficacy compared to S1P.

Metformin protects against sevoflurane-induced neuronal apoptosis through the S1P1 and ERK signaling pathways

The aim of the current study was to investigate whether metformin could counteract sevoflurane-induced neurotoxicity. In vitro experiments on the sevoflurane-induced nerve injury were performed using hippocampal neurons. Neuronal apoptosis was detected by an MTT assay. Protein expression levels of apoptosis-associated genes, including cleaved-caspase-3, apoptosis regulator BAX and apoptosis regulator Bcl-2 were detected by western blot analysis. The mechanism of the effect of metformin on sevoflurane-induced neuronal apoptosis was investigated using a sphingosine 1-phosphate receptor 1 (S1P1) antagonist (VPC23019) and mitogen-activated protein kinase kinase inhibitor (U0126). The current study revealed that metformin may reduce sevoflurane-induced neuronal apoptosis via activating mitogen-activated protein kinase (ERK)1/2 phosphorylation. VPC23019 and U0126 eliminated the neuroprotective effects of metformin on neuronal apoptosis, which suggests that metformin is able to protect against sevoflurane-induced neurotoxicity via activation of the S1P1-dependent ERK1/2 signaling pathway.

Mechanism of Siponimod: Anti-Inflammatory and Neuroprotective Mode of Action

Multiple sclerosis (MS) is a neuroinflammatory disorder of the central nervous system (CNS), and represents one of the main causes of disability in young adults. On the histopathological level, the disease is characterized by inflammatory demyelination and diffuse neurodegeneration. Although on the surface the development of new inflammatory CNS lesions in MS may appear consistent with a primary recruitment of peripheral immune cells, questions have been raised as to whether lymphocyte and/or monocyte invasion into the brain are really at the root of inflammatory lesion development. In this review article, we discuss a less appreciated inflammation-neurodegeneration interplay, that is: Neurodegeneration can trigger the formation of new, focal inflammatory lesions. We summarize old and recent findings suggesting that new inflammatory lesions develop at sites of focal or diffuse degenerative processes within the CNS. Such a concept is discussed in the context of the EXPAND trial, showing that siponimod exerts anti-inflammatory and neuroprotective activities in secondary progressive MS patients. The verification or rejection of such a concept is vital for the development of new therapeutic strategies for progressive MS.

Functional antagonism of sphingosine-1-phosphate receptor 1 prevents cuprizone-induced demyelination

Recent evidence suggests that the oral drug Fingolimod (FTY720) for relapsing-remitting multiple sclerosis (MS) may act directly on the central nervous system (CNS) and modulate disease pathogenesis and progression in experimental models of MS. However, the specific subtype of sphingosine-1-phosphate (S1P) receptors that mediates the effect of FTY720 on the CNS cells has not been fully elucidated. Here, we report that S1P receptor 1 (S1PR1) is elevated in reactive astrocytes in an autoimmunity independent mouse model of MS and that selective S1PR1 modulation is sufficient to ameliorate the loss of oligodendrocytes and demyelination. The non-selective S1PR modulator, FTY720, or a short-lived S1PR1-specific modulator, CYM5442, was administered daily to mice while on cuprizone diet. Both FTY720- and CYM5422-treated mice displayed a significant reduction in oligodendrocyte apoptosis and astrocyte and microglial activation in comparison to vehicle-treated groups, which was associated with decreased production of proinflammatory mediators and down-regulation of astrocytic S1PR1 protein. Interestingly, S1PR1 modulation during the early phase of cuprizone intoxication was required to suppress oligodendrocyte death and consequent demyelination as drug treatment from 10 days after the initiation of cuprizone feeding was no longer effective. CYM5442 treatment during the brief cuprizone exposure significantly prevented Il-1β, Il-6, Cxcl10, and Cxcl3 induction, resulting in suppression of subsequent reactive gliosis and demyelination. Our study identifies functional antagonism of S1PR1 as a major mechanism for the protective effect of FTY720 in the cuprizone model and suggests pathogenic contributions of astrocyte S1PR1 signaling in primary demyelination and its potential as a therapeutic target for CNS inflammation.

Sphingosine 1-phosphate receptors regulate TLR4-induced CXCL5 release from astrocytes and microglia

Sphingosine 1-phosphate receptors (S1PR) are G protein-coupled and compose a family with five subtypes, S1P1R-S1P5R. The drug Gilenya^® (Novartis, Basel, Switzerland) (Fingolimod; FTY720) targets S1PRs and was the first oral therapy for patients with relapsing-remitting multiple sclerosis (MS). The phosphorylated form of FTY720 (pFTY720) binds S1PRs causing initial agonism, then subsequent receptor internalization and functional antagonism. Internalization of S1P1R attenuates sphingosine 1-phosphate (S1P)-mediated egress of lymphocytes from lymph nodes, limiting aberrant immune function in MS. pFTY720 also exerts direct actions on neurons and glial cells which express S1PRs. In this study, we investigated the regulation of pro-inflammatory chemokine release by S1PRs in enriched astrocytes and microglial cultures. Astrocytes and microglia were stimulated with lipopolysaccharide (LPS) and increases in C-X-C motif chemokine 5 (CXCL5), also known as LIX (lipopolysaccharide-induced CXC chemokine) expression were quantified. Results showed that pFTY720 attenuated LPS-induced CXCL5 (LIX) protein release from astrocytes, as did the S1P1R selective agonist, SEW2871. In addition, pFTY720 blocked messenger ribonucleic acid (mRNA) transcription of the chemokines, (i) CXCL5/LIX, (ii) C-X-C motif chemokine 10 (CXCL10) also known as interferon gamma-induced protein 10 (IP10) and (iii) chemokine (C-C motif) ligand 2 (CCL2) also known as monocyte chemoattractant protein 1 (MCP1). Interestingly, inhibition of sphingosine kinase attenuated LPS-induced increases in mRNA levels of all three chemokines, suggesting that LPS-TLR4 (Toll-like receptor 4) signalling may enhance chemokine expression via S1P-S1PR transactivation. Lastly, these observations were not limited to astrocytes since we also found that pFTY720 attenuated LPS-induced release of CXCL5 from microglia. These data highlight a role for S1PR signalling in regulating the levels of chemokines in glial cells and support the notion that pFTY720 efficacy in multiple sclerosis may involve the direct modulation of astrocytes and microglia.

EBI2 regulates pro-inflammatory signalling and cytokine release in astrocytes

The endogenous oxysterol 7α, 25-dihydroxycholesterol (7α25HC) ligand activates the G protein-coupled receptor EBI2 to regulate T cell-dependant antibody response and B cell migration. We have demonstrated that EBI2 is expressed in human and mouse astrocytes, that 7α25HC induces intracellular signalling and astrocyte migration, and that EBI2 plays a role in the crosstalk between astrocytes and macrophages. Recently, we demonstrate that EBI2 regulates myelin development and inhibits LPC-induced demyelination. Here, we show that 7α25HC inhibits LPS- and IL17/TNF-induced pro-inflammatory cytokine release in astrocytes. We observe the following: 1. Human astrocytes treated with IL17/TNF increases the nuclear translocation of NFκB, which is attenuated by pre-treatment with 7α25HC; 2. IL17/TNF increases cell impedance in human astrocytes, which is also attenuated by pre-treatment with 7α25HC; 3. The EBI2 antagonist NIBR189 inhibits these effects of 7α25HC, supporting the role of EBI2; 4. in vivo data corroborate these in vitro findings, showing that EBI2 knock-out (KO) animals display enhanced pro-inflammatory cytokine in response to LPS challenge, in the brain. These results demonstrate a role for oxysterol/EBI2 signalling in attenuating the response of astrocytes to pro-inflammatory signals as well as limiting the levels of pro-inflammatory cytokines in the brain.

Clinical studies and anti-inflammatory mechanisms of treatments

In this exciting era, we are coming closer and closer to bringing an anti-inflammatory therapy to the clinic for the purpose of seizure prevention, modification, and/or suppression. At present, it is unclear what this approach might entail, and what form it will take. Irrespective of the therapy that ultimately reaches the clinic, there will be some commonalities with regard to clinical trials. A number of animal models have now been used to identify inflammation as a major underlying mechanism of both chronic seizures and the epileptogenic process. These models have demonstrated that specific anti-inflammatory treatments can be effective at both suppressing chronic seizures and interfering with the process of epileptogenesis. Some of these have already been evaluated in early phase clinical trials. It can be expected that there will soon be more clinical trials of both "conventional, broad spectrum" anti-inflammatory agents and novel new approaches to utilizing specific anti-inflammatory therapies with drugs or other therapeutic interventions. A summary of some of those approaches appears below, as well as a discussion of the issues facing clinical trials in this new domain.

FTY720 Attenuates Infection-Induced Enhancement of Aβ Accumulation in APP/PS1 Mice by Modulating Astrocytic Activation

It is well established that infection has a significant detrimental effect on patients with Alzheimer's disease (AD), accelerating cognitive decline and, even in healthy ageing individuals, increasing amyloid-β (Aβ) accumulation in the brain. In animal models of AD infection can also cause damage, with evidence of increased neuroinflammation, amyloid pathology and deterioration of cognitive function. These changes are against a backdrop of an age- and AD-related increase in susceptibility to infection. Here we set out to determine whether FTY720, a molecule that binds sphingosine-1-phosphate (S1P) receptors and with known immunosuppressant effects mediating its therapeutic action in multiple sclerosis (MS), might modulate the impact of infection in a mouse model of AD. Transgenic mice that overexpress amyloid precursor protein (APP) and presenilin 1 (PS1; APP/PS1 mice) and their littermates were/were not infected with Bordetella pertussis and were treated orally with FTY720 or vehicle beginning 3 days before infection. Infection increased astrocytic activation and enhanced blood brain barrier (BBB) permeability and these changes were attenuated in FTY720-treated B. pertussis-infected mice. Significantly, infection increased Aβ containing plaques and soluble Aβ and these infection-related changes were also attenuated in FTY720-treated B. pertussis-infected mice. The data suggest that this effect results from an FTY720-induced increase in Aβ phagocytosis by astrocytes. FTY720 did not impact on genotype-related changes in the absence of an infection indicating that its potential usefulness is restricted to reducing the impact of acute inflammatory stimuli in AD.

Sphingosine-1-phosphate induces Ca2+ signaling and CXCL1 release via TRPC6 channel in astrocytes

A biologically active lipid, sphingosine-1-phosphate (S1P) is highly abundant in blood, and plays an important role in regulating the growth, survival, and migration of many cells. Binding of the endogenous ligand S1P results in activation of various signaling pathways via G protein-coupled receptors, some of which generates Ca²⁺ mobilization. In astrocytes, S1P is reported to evoke Ca²⁺ signaling, proliferation, and migration; however, the precise mechanisms underlying such responses in astrocytes remain to be elucidated. Transient receptor potential canonical (TRPC) channels are Ca²⁺ -permeable cation channels expressed in astrocytes and involved in Ca²⁺ influx after receptor stimulation. In this study, we investigated the involvement of TRPC channels in S1P-induced cellular responses. In Ca²⁺ imaging experiments, S1P at 1 μM elicited a transient increase in intracellular Ca²⁺ in astrocytes, followed by sustained elevation. The sustained Ca²⁺ response was markedly suppressed by S1P₂ receptor antagonist JTE013, S1P₃ receptor antagonist CAY10444, or non-selective TRPC channel inhibitor Pyr2. Additionally, S1P increased chemokine CXCL1 mRNA expression and release, which were suppressed by TRPC inhibitor, inhibition of Ca²⁺ mobilization, MAPK pathway inhibitors, or knockdown of the TRPC channel isoform TRPC6. Taken together, these results demonstrate that S1P induces Ca²⁺ signaling in astrocytes via G_q -coupled receptors S1P₂ and S1P₃ , followed by Ca²⁺ influx through TRPC6 that could activate MAPK signaling, which leads to increased secretion of the proinflammatory or neuroprotective chemokine CXCL1.

The effect of low levels of lead (Pb) in the blood on levels of sphingosine-1-phosphate (S1P) and expression of S1P receptor 1 in the brain of the rat in the perinatal period

Sphingolipids are the main components of the lipid membrane. They also perform structural functions and participate in many signal transmission processes. One of the bioactive sphingolipids is sphingosine-1-phosphate (S1P), a ligand for five G protein-coupled receptors (S1PRs1-5), which can also act as an intracellular second messenger. S1P is responsible for the stimulation of progenitor cells in the brain, but it can also induce apoptosis of mature neurons. This study is aimed at assessing the effect of pre- and neonatal exposure to permissible Pb concentrations on S1P levels and S1PR1 (EDG1) expression in the prefrontal cortex, cerebellum, and hippocampus of rats. The concentrations of S1P were determined by RP-HPLC, S1PR1 expression was determined by RT PCR and Western Blot, and receptor immunolocalization was determined by immunohistochemistry method. Our results showed that even low blood Pb concentrations, i.e. within the acceptable limit of 10 μg/dL caused changes in the concentration of S1P in the cerebellum, prefrontal cortex, and hippocampus. Our data also showed a significant decrease in the level of S1PR1 in all studied part of brain, without significant changes in S1PR1 gene expression. Pre- and neonatal exposure to Pb also resulted in a decrease in the expression of S1PR1 in glial cells in all regions of the Cornu Ammonis (CA1-CA4) and Dentate Gyrus in the hippocampus, as well as in all layers of the cerebellum and prefrontal cortex, compared to the unexposed control group.

The sphingosine-1-phosphate analogue, FTY-720, promotes the proliferation of embryonic neural stem cells, enhances hippocampal neurogenesis and learning and memory abilities in adult mice

BACKGROUND AND PURPOSE

Fingolimod (FTY-720) is the first oral therapeutic drug approved for the relapsing-remitting forms of multiple sclerosis. Neural stem cells (NSCs) are capable of continuous self-renewal and differentiation. The dentate gyrus of the hippocampus in the adult mammalian brain contains a population of NSCs and is one of the regions where neurogenesis takes place. FTY-720 has been shown to have neuroprotective effects in several model systems, so we investigated the direct effects of FTY-720 on NSCs and adult neurogenesis.

EXPERIMENTAL APPROACHES

We assessed the effects of FTY-720 on the proliferation and differentiation of cultured embryonic hippocampal NSCs using the 5-bromo-2-deoxyuridine incorporation assay, the neurosphere formation assay and western blot analysis. Receptor selective agonists and antagonists were used to identify the mechanisms involved. Neurogenesis in the hippocampus of C57BL/6 mice was also assessed by immunohistochemistry. The Morris water maze and fear conditioning tests were used to detect the learning and memory abilities of mice.

KEY RESULTS

FTY-720 promoted the proliferation of embryonic hippocampal NSCs probably via the activation of ERK signalling, Gi/o proteins and S1P1 receptors. However, FTY-720 did not affect the differentiation of cultured hippocampal NSCs. In vivo, chronic treatment with FTY-720 promoted hippocampal neurogenesis in adult C57BL/6 mice and enhanced their learning and memory abilities.

CONCLUSIONS AND IMPLICATIONS

Our results suggest a new target for the activation of NSCs and provide an insight into the therapeutic effects of FTY-720 in neuropsychiatric disorders, neurodegenerative diseases and age-related cognitive decline where hippocampal neurogenesis is compromised.

The EBI2 signalling pathway plays a role in cellular crosstalk between astrocytes and macrophages

EBI2 is a G protein-coupled receptor activated by oxysterol 7α, 25-dihydroxycholesterol (7α25HC) and regulates T cell-dependant antibody response and B cell migration. We recently found EBI2 is expressed in human astrocytes, regulates intracellular signalling and modulates astrocyte migration. Here, we report that LPS treatment of mouse astrocytes alters mRNA levels of EBI2 and oxysterols suggesting that the EBI2 signalling pathway is sensitive to LPS-mediated immune challenge. We also find that conditioned media obtained from LPS-stimulated mouse astrocytes induces macrophage migration, which is inhibited by the EBI2 antagonist NIBR189. These results demonstrate a role for the EBI2 signalling pathway in astrocytes as a sensor for immune challenge and for communication with innate immune cells such as macrophages.

Sphingosine-1-phosphate receptor antagonism enhances proliferation and migration of engrafted neural progenitor cells in a model of viral-induced demyelination

The oral drug FTY720 affects sphingosine-1-phosphate (S1P) signaling on targeted cells that bear the S1P receptors S1P1, S1P3, S1P4, and S1P5. We examined the effect of FTY720 treatment on the biology of mouse neural progenitor cells (NPCs) after transplantation in a viral model of demyelination. Intracerebral infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) resulted in an acute encephalomyelitis, followed by demyelination similar in pathology to the human demyelinating disease, multiple sclerosis. We have previously reported that intraspinal transplantation of mouse NPCs into JHMV-infected animals resulted in selective colonization of demyelinated lesions, preferential differentiation into oligodendroglia accompanied by axonal preservation, and increased remyelination. Cultured NPCs expressed transcripts for S1P receptors S1P1, S1P2, S1P3, S1P4, and S1P5. FTY720 treatment of cultured NPCs resulted in increased mitogen-activated protein kinase phosphorylation and migration after exposure to the chemokine CXCL12. Administration of FTY720 to JHMV-infected mice resulted in enhanced migration and increased proliferation of transplanted NPCs after spinal cord engraftment. FTY720 treatment did not improve clinical disease, diminish neuroinflammation or the severity of demyelination, nor increase remyelination. These findings argue that FTY720 treatment selectively increases NPC proliferation and migration but does not either improve clinical outcome or enhance remyelination after transplantation into animals in which immune-mediated demyelination is initiated by the viral infection of the central nervous system.

Blockade of Sphingosine 1-Phosphate Receptor 2 Signaling Attenuates High-Fat Diet-Induced Adipocyte Hypertrophy and Systemic Glucose Intolerance in Mice

Sphingosine 1-phosphate (S1P) is known to regulate insulin resistance in hepatocytes, skeletal muscle cells, and pancreatic β-cells. Among its 5 cognate receptors (S1pr1-S1pr5), S1P seems to counteract insulin signaling and confer insulin resistance via S1pr2 in these cells. S1P may also regulate insulin resistance in adipocytes, but the S1pr subtype(s) involved remains unknown. Here, we investigated systemic glucose/insulin tolerance and phenotypes of epididymal adipocytes in high-fat diet (HFD)-fed wild-type and S1pr2-deficient (S1pr2(-/-)) mice. Adult S1pr2(-/-) mice displayed smaller body/epididymal fat tissue weights, but the differences became negligible after 4 weeks with HFD. However, HFD-fed S1pr2(-/-) mice displayed better scores in glucose/insulin tolerance tests and had smaller epididymal adipocytes that expressed higher levels of proliferating cell nuclear antigen than wild-type mice. Next, proliferation/differentiation of 3T3-L1 and 3T3-F442A preadipocytes were examined in the presence of various S1pr antagonists: JTE-013 (S1pr2 antagonist), VPC-23019 (S1pr1/S1pr3 antagonist), and CYM-50358 (S1pr4 antagonist). S1P or JTE-013 treatment of 3T3-L1 preadipocytes potently activated their proliferation and Erk phosphorylation, whereas VPC-23019 inhibited both of these processes, and CYM-50358 had no effects. In contrast, S1P or JTE-013 treatment inhibited adipogenic differentiation of 3T3-F442A preadipocytes, whereas VPC-23019 activated it. The small interfering RNA knockdown of S1pr2 promoted proliferation and inhibited differentiation of 3T3-F442A preadipocytes, whereas that of S1pr1 acted oppositely. Moreover, oral JTE-013 administration improved glucose tolerance/insulin sensitivity in ob/ob mice. Taken together, S1pr2 blockade induced proliferation but suppressed differentiation of (pre)adipocytes both in vivo and in vitro, highlighting a novel therapeutic approach for obesity/type 2 diabetes.

Ozanimod (RPC1063) is a potent sphingosine-1-phosphate receptor-1 (S1P1 ) and receptor-5 (S1P5 ) agonist with autoimmune disease-modifying activity

BACKGROUND AND PURPOSE

Sphingosine1-phosphate (S1P) receptors mediate multiple events including lymphocyte trafficking, cardiac function, and endothelial barrier integrity. Stimulation of S1P1 receptors sequesters lymphocyte subsets in peripheral lymphoid organs, preventing their trafficking to inflamed tissue sites, modulating immunity. Targeting S1P receptors for treating autoimmune disease has been established in clinical studies with the non-selective S1P modulator, FTY720 (fingolimod, Gilenya™). The purpose of this study was to assess RPC1063 for its therapeutic utility in autoimmune diseases.

EXPERIMENTAL APPROACH

The specificity and potency of RPC1063 (ozanimod) was evaluated for all five S1P receptors, and its effect on cell surface S1P1 receptor expression, was characterized in vitro. The oral pharmacokinetic (PK) parameters and pharmacodynamic effects were established in rodents, and its activity in three models of autoimmune disease (experimental autoimmune encephalitis, 2,4,6-trinitrobenzenesulfonic acid colitis and CD4(+) CD45RB(hi) T cell adoptive transfer colitis) was assessed.

KEY RESULTS

RPC1063 was specific for S1P1 and S1P5 receptors, induced S1P1 receptor internalization and induced a reversible reduction in circulating B and CCR7(+) T lymphocytes in vivo. RPC1063 showed high oral bioavailability and volume of distribution, and a circulatory half-life that supports once daily dosing. Oral RPC1063 reduced inflammation and disease parameters in all three autoimmune disease models.

CONCLUSIONS AND IMPLICATIONS

S1P receptor selectivity, favourable PK properties and efficacy in three distinct disease models supports the clinical development of RPC1063 for the treatment of relapsing multiple sclerosis and inflammatory bowel disease, differentiates RPC1063 from other S1P receptor agonists, and could result in improved safety outcomes in the clinic.

The multiple sclerosis drug fingolimod (FTY720) stimulates neuronal gene expression, axonal growth and regeneration

Fingolimod (FTY720) is a new generation oral treatment for multiple sclerosis (MS). So far, FTY720 was mainly considered to target trafficking of immune cells but not brain cells such as neurons. Herein, we analyzed FTY720's potential to directly alter neuronal function. In CNS neurons, we identified a FTY720 governed gene expression response. FTY720 upregulated immediate early genes (IEGs) encoding for neuronal activity associated transcription factors such as c-Fos, FosB, Egr1 and Egr2 and induced actin cytoskeleton associated genes (actin isoforms, tropomyosin, calponin). Stimulation of primary neurons with FTY720 enhanced neurite growth and altered growth cone morphology. In accordance, FTY720 enhanced axon regeneration in mice upon facial nerve axotomy. We identified components of a FTY720 engaged signaling cascade including S1P receptors, G12/13G-proteins, RhoA-GTPases and the transcription factors SRF/MRTF. In summary, we uncovered a broader cellular and therapeutic operation mode of FTY720, suggesting beneficial FTY720 effects also on CNS neurons during MS therapy and for treatment of other neurodegenerative diseases requiring neuroprotective and neurorestorative processes.

The dual S1PR1/S1PR5 drug BAF312 (Siponimod) attenuates demyelination in organotypic slice cultures

Background

BAF312 (Siponimod) is a dual agonist at the sphingosine-1 phosphate receptors, S1PR1 and S1PR5. This drug is currently undergoing clinical trials for the treatment of secondary progressive multiple sclerosis (MS). Here, we investigated the effects of BAF312 on isolated astrocyte and microglia cultures as well as in slice culture models of demyelination.

Methods

Mouse and human astrocytes were treated with S1PR modulators and changes in the levels of pERK, pAkt, and calcium signalling as well as S1PR1 internalization and cytokine levels was investigated using Western blotting, immunochemistry, ELISA and confocal microscopy. Organotypic slice cultures were prepared from the cerebellum of 10-day-old mice and treated with lysophosphatidylcholine (LPC), psychosine and/or S1PR modulators, and changes in myelination states were measured by fluorescence of myelin basic protein and neurofilament H.

Results

BAF312 treatment of human and mouse astrocytes activated pERK, pAKT and Ca²⁺ signalling as well as inducing S1PR1 internalization. Notably, activation of S1PR1 increased pERK and pAKT in mouse astrocytes while both S1PR1 and S1PR3 equally increased pERK and pAKT in human astrocytes, suggesting that the coupling of S1PR1 and S1PR3 to pERK and pAKT differ in mouse and human astrocytes. We also observed that BAF312 moderately attenuated lipopolysaccharide (LPS)- or TNFα/IL17-induced levels of IL6 in both astrocyte and microglia cell cultures. In organotypic slice cultures, BAF312 reduced LPC-induced levels of IL6 and attenuated LPC-mediated demyelination. We have shown previously that the toxic lipid metabolite psychosine induces demyelination in organotypic slice cultures, without altering the levels of cytokines, such as IL6. Importantly, psychosine-induced demyelination was also attenuated by BAF312.

Conclusions

Overall, this study suggests that BAF312 can modulate glial cell function and attenuate demyelination, highlighting this drug as a further potential therapy in demyelinating disorders, beyond MS.

Fingolimod induces neurogenesis in adult mouse hippocampus and improves contextual fear memory

Fingolimod (FTY720) was the first per os administered disease-modifying agent approved for the treatment of relapsing-remitting multiple sclerosis. It is thought that fingolimod modulates the immune response by activating sphingosine-1 phosphate receptor type 1 (S1P1) on lymphocytes following its in vivo phosphorylation. In addition to its immune-related effects, there is evidence that fingolimod exerts several other effects in the central nervous system, including regulation of the proliferation, survival and differentiation of various cell types and their precursors. In the present study, we have investigated the effect of fingolimod on the production of new neurons in the adult mouse hippocampus and the association of this effect with the ability for pattern separation, an established adult neurogenesis-dependent memory function. Immunofluorescence analysis after chronic administration of a physiologic dose of fingolimod (0.3 mg kg(-1)) revealed a significant increase in both the proliferation and the survival of neural progenitors in the area of dentate gyrus of hippocampus, compared with control animals. These effects were replicated in vitro, in cultures of murine hippocampal neural stem/precursor cells that express S1P1 receptor, suggesting cell-autonomous actions. The effects of fingolimod on neurogenesis were correlated to enhanced ability for context discrimination after fear conditioning. Since impairment of adult hippocampal neurogenesis and memory is a common feature of many neuropsychiatric conditions, fingolimod treatment may be beneficial in therapeutic armamentarium of these disorders.

AKP-11 - A Novel S1P1 Agonist with Favorable Safety Profile Attenuates Experimental Autoimmune Encephalomyelitis in Rat Model of Multiple Sclerosis

Sphingosine-1-phosphate receptor 1 (S1P1) mediated regulation of lymphocyte egress from lymphoid organs is recognized as the mechanism of FTY720 (Fingolimod, Gilenya) efficacy in relapsing-remitting forms of multiple sclerosis (RRMS). In this study we describe a novel S1P1 agonist AKP-11, next generation of S1P1 agonist, with immunomodulatory activities in cell culture model and for therapeutic efficacy against an animal model of MS, i.e. experimental autoimmune encephalomyelitis (EAE) but without the adverse effects observed with FTY720. Like FTY720, AKP-11 bound to S1P1 is internalized and activates intracellular AKT and ERKs cellular signaling pathways. In contrast to FTY720, AKP-11 mediated S1P1 downregulation is independent of sphingosine kinase activity indicating it to be a direct agonist of S1P1. The S1P1 loss and inhibition of lymphocyte egress by FTY720 leads to lymphopenia. In comparison with FTY720, oral administration of AKP-11 caused milder and reversible lymphopenia while providing a similar degree of therapeutic efficacy in the EAE animal model. Consistent with the observed reversible lymphopenia with AKP-11, the S1P1 recycled back to cell membrane in AKP-11 treated cells following its withdrawal, but not with withdrawal of FTY720. Accordingly, a smaller degree of ubiquitination and proteolysis of S1P1 was observed in AKP-11 treated cells as compared to FTY720. Consistent with previous observations, FTY720 treatment is associated with adverse effects of bradycardia and lung vascular leaks in rodents, whereas AKP-11 treatment had undetectable effects on bradycardia and reduced lung vascular leaks as compared to FTY720. Taken together, the data documents that AKP-11 treatment cause milder and reversible lymphopenia with milder adverse effects while maintaining therapeutic efficacy similar to that observed with FTY720, thus indicating therapeutic potential of AKP-11 for treatment of MS and related autoimmune disorders.

Connective-Tissue Growth Factor (CTGF/CCN2) Induces Astrogenesis and Fibronectin Expression of Embryonic Neural Cells In Vitro

Connective-tissue growth factor (CTGF) is a modular secreted protein implicated in multiple cellular events such as chondrogenesis, skeletogenesis, angiogenesis and wound healing. CTGF contains four different structural modules. This modular organization is characteristic of members of the CCN family. The acronym was derived from the first three members discovered, cysteine-rich 61 (CYR61), CTGF and nephroblastoma overexpressed (NOV). CTGF is implicated as a mediator of important cell processes such as adhesion, migration, proliferation and differentiation. Extensive data have shown that CTGF interacts particularly with the TGFβ, WNT and MAPK signaling pathways. The capacity of CTGF to interact with different growth factors lends it an important role during early and late development, especially in the anterior region of the embryo. ctgf knockout mice have several cranio-facial defects, and the skeletal system is also greatly affected due to an impairment of the vascular-system development during chondrogenesis. This study, for the first time, indicated that CTGF is a potent inductor of gliogenesis during development. Our results showed that in vitro addition of recombinant CTGF protein to an embryonic mouse neural precursor cell culture increased the number of GFAP- and GFAP/Nestin-positive cells. Surprisingly, CTGF also increased the number of Sox2-positive cells. Moreover, this induction seemed not to involve cell proliferation. In addition, exogenous CTGF activated p44/42 but not p38 or JNK MAPK signaling, and increased the expression and deposition of the fibronectin extracellular matrix protein. Finally, CTGF was also able to induce GFAP as well as Nestin expression in a human malignant glioma stem cell line, suggesting a possible role in the differentiation process of gliomas. These results implicate ctgf as a key gene for astrogenesis during development, and suggest that its mechanism may involve activation of p44/42 MAPK signaling. Additionally, CTGF-induced differentiation of glioblastoma stem cells into a less-tumorigenic state could increase the chances of successful intervention, since differentiated cells are more vulnerable to cancer treatments.

Effect of FTY720-phosphate on the expression of inflammation-associated molecules in astrocytes in vitro

FTY720 is a new oral immunomodulatory therapy for the treatment of multiple sclerosis (MS). There is strong evidence that FTY720 has direct effects on brain resident cells such as astrocytes acting via sphingosine‑1‑phosphate (S1P) receptors. In the present study, the mRNA expression of S1P receptors as well as selected cytokines, chemokines and growth factors were investigated in primary murine astrocytes under inflammatory conditions in the presence or absence of the phosphorylated form of FTY720 (FTY720‑P). Following stimulation with either the pro‑inflammatory cytokine tumor necrosis factor‑α (TNF‑α) or with bacterial lipopolysaccharide, there was an increased expression of the receptors S1P1 and S1P3, the cytokines and chemokines interleukin (IL)‑1β, chemokine (C‑C‑motif) ligand 2 (CCL‑2), CCL‑20 and chemokine (C‑X‑C‑motif) ligand 12 as well as the growth factors insulin‑like growth factor‑1, ciliary neurotrophic factor and glial cell line‑derived neurotrophic factor (GDNF). FTY720‑P led to an increased expression of IL‑1β and GDNF at distinct time points following co‑stimulation with TNF‑α compared with TNF‑α treatment alone. However, the presence of FTY720‑P did not have any further significant effects on the expression of S1P receptors, cytokines or growth factors, suggesting that the regulation of these target genes in astrocytes is not likely to be a major mechanism underlying the effect of FTY720‑P in diseases such as MS.

Local delivery of FTY720 in PCL membrane improves SCI functional recovery by reducing reactive astrogliosis

FTY720 has recently been approved as an oral drug for treating relapsing forms of multiple sclerosis, and exerts its therapeutic effect by acting as an immunological inhibitor targeting the sphingosine-1-phosphate (S1P) receptor subtype (S1P1) of T cells. Recently studies demonstrated positive efficacy of this drug on spinal cord injury (SCI) in animal models after systemic administration, albeit with significant adverse side effects. We hereby hypothesize that localized delivery of FTY720 can promote SCI recovery by reducing pathological astrogliosis. The mechanistic functions of FTY720 were investigated in vitro and in vivo utilizing immunofluorescence, histology, MRI and behavioral analysis. The in vitro study showed that FTY720 can reduce astrocyte migration and proliferation activated by S1P. FTY720 can prolong internalization of S1P1 and exert antagonistic effects on S1P1. In vivo study of SCI animal models demonstrated that local delivery of FTY720 with polycaprolactone (PCL) membrane significantly decreased S1P1 expression and glial scarring compared with the control group. Furthermore, FTY720-treated groups exhibited less cavitation volume and neuron loss, which significantly improved recovery of motor function. These findings demonstrated that localized delivery of FTY720 can promote SCI recovery by targeting the S1P1 receptor of astrocytes, provide a new therapeutic strategy for SCI treatment.

Pathway specific modulation of S1P1 receptor signalling in rat and human astrocytes

BACKGROUND AND PURPOSE

The sphingosine 1-phosphate receptor subtype 1 (S1P1R) is modulated by phosphorylated FTY720 (pFTY720), which causes S1P1R internalization preventing lymphocyte migration thus limiting autoimmune response. Studies indicate that internalized S1P1Rs continue to signal, maintaining an inhibition of cAMP, thus raising question whether the effects of pFTY720 are due to transient initial agonism, functional antagonism and/or continued signalling. To further investigate this, the current study first determined if continued S1P1R activation is pathway specific.

EXPERIMENTAL APPROACH

Using human and rat astrocyte cultures, the effects of S1P1R activation on cAMP, pERK and Ca(2+) signalling was investigated. In addition, to examine the role of S1P1R redistribution on these events, a novel biologic (MNP301) that prevented pFTY720-mediated S1P1R redistribution was engineered.

KEY RESULTS

The data showed that pFTY720 induced long-lasting S1P1R redistribution and continued cAMP signalling in rat astrocytes. In contrast, pFTY720 induced a transient increase of Ca(2+) in astrocytes and subsequent antagonism of Ca(2+) signalling. Notably, while leaving pFTY720-induced cAMP signalling intact, the novel MNP301 peptide attenuated S1P1R-mediated Ca(2+) and pERK signalling in cultured rat astrocytes.

CONCLUSIONS AND IMPLICATIONS

These findings suggested that pFTY720 causes continued cAMP signalling that is not dependent on S1P1R redistribution and induces functional antagonism of Ca(2+) signalling after transient stimulation. To our knowledge, this is the first report demonstrating that pFTY720 causes continued signalling in one pathway (cAMP) versus functional antagonism of another pathway (Ca(2+)) and which also suggests that redistributed S1P1Rs may have differing signalling properties from those expressed at the surface.

Immunohistochemical detection of sphingosine-1-phosphate receptor 1 and 5 in human multiple sclerosis lesions

AIMS

Sphingosine-1-phosphate receptor (S1PR) modulating therapies are currently in the clinic or undergoing investigation for multiple sclerosis (MS) treatment. However, the expression of S1PRs is still unclear in the central nervous system under normal conditions and during neuroinflammation.

METHODS

Using immunohistochemistry we examined tissues from both grey and white matter MS lesions for sphingosine-1-phosphate receptor 1 (S1P1 ) and 5 (S1P5 ) expression. Tissues from Alzheimer's disease (AD) cases were also examined.

RESULTS

S1P1 expression was restricted to astrocytes and endothelial cells in control tissues and a decrease in endothelial cell expression was found in white matter MS lesions. In grey matter MS lesions, astrocyte expression was lost in active lesions, while in quiescent lesions it was restored to normal expression levels. CNPase colocalization studies demonstrated S1P5 expression on myelin and both were reduced in demyelinated lesions. In AD tissues we found no difference in S1P1 expression.

CONCLUSION

These data demonstrate a differential modulation of S1PRs in MS lesions, which may have an impact on S1PR-directed therapies.

Galactosylsphingosine (psychosine) induced demyelination is attenuated by sphingosine 1-phosphate signalling

Globoid cell leukodystrophy (Krabbe disease, KD) is a rare infantile neurodegenerative disorder. KD is caused by deficiency in the lysosomal enzyme galactocerebrosidase (GALC) resulting in brain accumulation, in the micromolar range, of the toxic metabolite galactosylsphingosine (psychosine). Here we find psychosine induces human astrocyte cell death likely via an apoptotic process in a concentration- and time-dependent manner (EC50 ∼15 µM at 4h). We show these effects of psychosine are attenuated by pre-treatment with the sphingosine 1-phosphate receptor agonist pFTY720 (Fingolimod) (IC50 ∼100nM). Psychosine (1 µM, 10 µM) also potentiates LPS-induced (EC50 ∼100ng/ml) production of pro-inflammatory cytokines in mouse astrocytes, which is also attenuated by pFTY720 (1 µM). Most notably, for the first time, we show that psychosine, at a concentration found in the brains of patients with KD (EC50 ∼100nM) directly induces demyelination in mouse organotypic cerebellar slices in a manner that is independent of proinflammatory cytokine response and that pFTY720 (0.1nM) significantly inhibits. These results support the idea that psychosine is a pathogenic agent in KD and suggest that sphingosine 1-phosphate signalling could be a potential drug target for this illness.

Increased levels of sphingosine-1-phosphate in cerebrospinal fluid of patients diagnosed with tick-borne encephalitis

Background

Tick-borne encephalitis (TBE) is a serious acute central nervous system infection that can result in death or long-term neurological dysfunctions. We hypothesize that changes in sphingosine-1-phosphate (S1P) concentration occur during TBE development.

Methods

S1P and interleukin-6 (IL-6) concentrations in blood plasma and cerebrospinal fluid (CSF) were measured using HPLC and ELISA, respectively. The effects of S1P on cytoskeletal structure and IL-6 production were assessed using rat astrocyte primary cultures with and without addition of plasma gelsolin and the S1P receptor antagonist fingolimod phosphate (FTY720P).

Results

We report that acute inflammation due to TBE virus infection is associated with elevated levels of S1P and IL-6 in the CSF of infected patients. This elevated concentration is observed even at the earliest neurologic stage of disease, and may be controlled by glucocorticosteroid anti-inflammatory treatment, administered to patients unresponsive to antipyretic drugs and who suffer from a fever above 39°C. In vitro, treatment of confluent rat astrocyte monolayers with a high concentration of S1P (5 μM) results in cytoskeletal actin remodeling that can be prevented by the addition of recombinant plasma gelsolin, FTY720P, or their combination. Additionally, gelsolin and FTY720P significantly decreased S1P-induced release of IL-6.

Conclusions

TBE is associated with increased concentration of S1P and IL-6 in CSF, and this increase might promote development of inflammation. The consequences of increased extracellular S1P can be modulated by gelsolin and FTY720P. Therefore, blocking the inflammatory response at sites of infection by agents modulating S1P pathways might aid in developing new strategies for TBE treatment.

Cardiac and vascular effects of fingolimod: mechanistic basis and clinical implications

Fingolimod, a sphingosine-1-phosphate receptor (S1PR) modulator, was the first oral disease-modifying therapy approved for relapsing forms of multiple sclerosis; it reduces autoreactive lymphocytes' egress from lymphoid tissues by down-regulating S1PRs. Sphingosine-1-phosphate signaling is implicated in a range of physiologic functions, and S1PRs are expressed differentially in various tissues, including the cardiovascular system. Modulation of S1PRs on cardiac cells provides an explanation for the transient effects of fingolimod on heart rate and atrioventricular conduction at initiation of fingolimod therapy, and for the mild but more persistent effects on blood pressure observed in some patients on long-term treatment. This review describes the nontherapeutic actions of fingolimod in the context of sphingosine-1-phosphate signaling in the cardiovascular system, as well as providing a summary of the associated clinical implications useful to physicians considering initiation of fingolimod therapy in patients. A transient reduction in heart rate (mean decrease of 8 beats per minute) and, less commonly, a temporary delay in atrioventricular conduction observed in some patients when initiating fingolimod therapy are both due to activation of S1PR subtype 1 on cardiac myocytes. These effects are a reflection of fingolimod first acting as a full S1PR agonist and thereafter functioning as an S1PR antagonist after down-regulation of S1PR subtype 1 at the cell surface. For most individuals, first-dose effects of fingolimod are asymptomatic, but all patients need to be monitored for at least 6 hours after the first dose, in accordance with the label recommendations.

FTY720 (fingolimod) is a neuroprotective and disease-modifying agent in cellular and mouse models of Huntington disease

Huntington disease (HD) is a genetic neurodegenerative disorder for which there is currently no cure and no way to stop or even slow the brain changes it causes. In the present study, we aimed to investigate whether FTY720, the first approved oral therapy for multiple sclerosis, may be effective in HD models and eventually constitute an alternative therapeutic approach for the treatment of the disease. Here, we utilized preclinical target validation paradigms and examined the in vivo efficacy of chronic administration of FTY720 in R6/2 HD mouse model. Our findings indicate that FTY720 improved motor function, prolonged survival and reduced brain atrophy in R6/2 mice. The beneficial effect of FTY720 administration was associated with a significant strengthening of neuronal activity and connectivity and, with reduction of mutant huntingtin aggregates, and it was also paralleled by increased phosphorylation of mutant huntingtin at serine 13/16 residues that are predicted to attenuate protein toxicity.

The role of sphingosine 1-phosphate receptors in the treatment of demyelinating diseases

Sphingosine 1-phosphate receptors (S1PRs) are a family of G-protein coupled receptors composed of subtypes S1PR1–5 and activated by the endogenous ligand sphingosine 1-phosphate. S1PRs are modulated by the recently approved oral therapy for relapsing–remitting multiple sclerosis, called fingolimod (FTY720). The phosphorylated version of FTY720 (pFTY720) is a pan-S1PR agonist, with the exception of S1PR2. This drug promotes the internalization of S1PR1s in T cells and is said to act as a ‘functional antagonist’ making lymphocytes ‘blind’ to sphingosine 1-phosphate gradients and limiting cell egress from lymph nodes. This immunomodulatory effect of pFTY720 is proposed to be the prime mechanism by which this compound is efficacious in the treatment of multiple sclerosis. Importantly, however, S1PRs are also expressed in many other cell types, for example, cells of the cardiovascular system and the CNS. Studies have shown that pFTY720 enters the CNS and that modulation of S1PRs can alter the cellular physiology of neurons, astrocytes, microglia and oligodendrocytes. These works are suggestive of a potential role for S1PRs expressed in brain cells as targets for pFTY720. This article reviews the role of S1PRs in oligodendrocytes. The authors start by first debating whether pFTY720-mediated internalization of S1PRs causes ‘functional antagonism’ and/or ‘pathway-specific continued signaling’. The authors then describe the signaling pathways that are modulated by S1PRs expressed in oligodendrocytes and also outline the role of S1PRs in oligodendrocyte differentiation, process extension, survival and migration. Finally, the authors discuss the in vitro studies that suggest pFTY720 promotes myelination state versus the in vivo studies that suggest pFTY720 may not alter myelination. The authors conclude by suggesting that S1PRs in the CNS may be of potential use as drug targets not only for multiple sclerosis, but possibly for a number of other demyelinating disorders.

Therapeutic potential of targeting SK1 in human cancers

Sphingosine kinase 1 (SK1) is a lipid enzyme with oncogenic properties that converts the proapoptotic lipids ceramide and sphingosine into the antiapoptotic lipid sphingosine-1-phosphate and activates the signal transduction pathways that lead to cell proliferation, migration, the activation of the inflammatory response, and the impairment of apoptosis. There is compelling evidence that SK1 activation contributes to cancer progression leading to increased oncogenic transformation, tumor growth, resistance to therapies, tumor neovascularization, and metastatic spread. High levels of SK1 expression or activity have been associated with a poor prognosis in several human cancers. Recent studies using cancer cell and mouse models demonstrate a significant potential for SK1-targeting therapies to synergize with the effects of chemotherapy and radiotherapy; however, until recently the absence of clinically applicable SK1 inhibitors has limited the translation of these findings into patients. With the recent discovery of SK1 inhibiting properties of a clinically approved drug FTY720 (Fingolimod), SK1 has gained significant attention from both clinicians and the pharmaceutical industry and it is hoped that trials of newly developed SK1 inhibitors may follow soon. This review provides an overview of the SK1 signaling, its relevance to cancer progression, and the potential clinical significance of targeting SK1 for improved local or systemic control of human cancers.

Fingolimod phosphate attenuates oligomeric amyloid β-induced neurotoxicity via increased brain-derived neurotrophic factor expression in neurons

The neurodegenerative processes that underlie Alzheimer's disease are mediated, in part, by soluble oligomeric amyloid β, a neurotoxic protein that inhibits hippocampal long-term potentiation, disrupts synaptic plasticity, and induces the production of reactive oxygen species. Here we show that the sphingosine-1-phosphate (S1P) receptor (S1PR) agonist fingolimod phosphate (FTY720-P)-a new oral drug for multiple sclerosis-protects neurons against oligomeric amyloid β-induced neurotoxicity. We confirmed that primary mouse cortical neurons express all of the S1P receptor subtypes and FTY720-P directly affects the neurons. Treatment with FTY720-P enhanced the expression of brain-derived neurotrophic factor (BDNF) in neurons. Moreover, blocking BDNF-TrkB signaling with a BDNF scavenger, TrkB inhibitor, or ERK1/2 inhibitor almost completely ablated these neuroprotective effects. These results suggested that the neuroprotective effects of FTY720-P are mediated by upregulated neuronal BDNF levels. Therefore, FTY720-P may be a promising therapeutic agent for neurodegenerative diseases, such as Alzheimer's disease.

Fingolimod: direct CNS effects of sphingosine 1-phosphate (S1P) receptor modulation and implications in multiple sclerosis therapy

Fingolimod is the first oral disease-modifying therapy approved for relapsing forms of multiple sclerosis (MS). Following phosphorylation in vivo, the active agent, fingolimod phosphate (fingolimod-P), acts as a sphingosine 1-phosphate (S1P) receptor modulator, binding with high affinity to four of the five known S1P receptors (S1P1, S1P3, S1P4 and S1P5). The mechanism of action of fingolimod in MS has primarily been considered as immunomodulatory, whereby fingolimod-P modulates S1P1 on lymphocytes, selectively retaining autoreactive lymphocytes in lymph nodes to reduce damaging infiltration into the central nervous system (CNS). However, emerging evidence indicates that fingolimod has direct effects in the CNS in MS. For example, in the MS animal model of experimental autoimmune encephalomyelitis (EAE), fingolimod is highly efficacious in both a prophylactic and therapeutic setting, yet becomes ineffective in animals selectively deficient for S1P1 on astrocytes, despite maintained normal immunologic receptor expression and functions, and S1P-mediated immune activities. Here we review S1P signaling effects relevant to MS in neural cell types expressing S1P receptors, including astrocytes, oligodendrocytes, neurons, microglia and dendritic cells. The direct effects of fingolimod on these CNS cells observed in preclinical studies are discussed in view of the functional consequences of reducing neurodegenerative processes and promoting myelin preservation and repair. The therapeutic implications of S1P modulation in the CNS are considered in terms of the clinical outcomes of MS, such as reducing MS-related brain atrophy, and other CNS disorders. Additionally, we briefly outline other existing and investigational MS therapies that may also have effects in the CNS.

Dual effects of daily FTY720 on human astrocytes in vitro: relevance for neuroinflammation

Background

FTY720 (fingolimod, Gilenya™) is a daily oral therapy for multiple sclerosis that readily accesses the central nervous system (CNS). FTY720 is a structural analog to the sphingolipid sphingosine-1-phosphate (S1P) and is a cognate ligand for the S1P G-protein coupled receptors (S1PR). Studies in experimental autoimmune encephalomyelitis using mice with conditionally deleted S1P₁R from astrocytes indicate that one beneficial effect of FTY720 in this model is via downregulating external receptors, which inhibits responses induced by the natural ligand. Another proposed effect of FTY720 on neuroinflammation is its ability to maintain persistent signaling in cells via internalized S1P₁R resulting in functional responses that include suppressing intracellular calcium release. We used human fetal astrocytes to investigate potential dual inhibitory- and function-inducing effects of daily FTY720 on responses relevant to neuroinflammation. For the inhibitory effects, we used signaling and proliferation induced by the natural ligand S1P. For the function-inducing responses, we measured inhibition of intracellular calcium release stimulated by the proinflammatory cytokine, interleukin (IL)-1β.

Methods

Astrocytes derived from human fetal CNS specimens and maintained in dissociated cultures were exposed to 100 nM of the biologically active form of FTY720 over a dosing regimen that ranged from a single exposure (with or without washout after 1 h) to daily exposures up to 5 days. Responses measured include: phosphorylation of extracellular-signal-regulated kinases (pERK1/2) by Western blotting, Ki-67 immunolabeling for cell proliferation, IL-1β-induced calcium release by ratiometric fluorescence, and cytokine/chemokine (IL-6, CXCL10) secretions by ELISA.

Results

We observed that a single addition of FTY720 inhibited subsequent S1PR ligand-induced pERK1/2 signaling for >24 h. Daily FTY720 treatments (3-5 days) maintained this effect together with a loss of proliferative responses to the natural ligand S1P. Repeated FTY720 dosing concurrently maintained a functional cell response as measured by the inhibition of intracellular calcium release when stimulated by the cytokine IL-1β. Recurrent FTY720 treatments did not inhibit serum- or IL-1β-induced pERK1/2. The secretions of IL-6 and CXCL10 in response to IL-1β were unaffected by FTY720 treatment(s).

Conclusion

Our results indicate that daily FTY720 exposures may regulate specific neuroinflammatory responses by desensitizing astrocytes to external S1PR stimuli while sustaining cellular influences that are independent of new surface S1PR activation.