Role of p38MAPK in S1P receptor-mediated differentiation of human oligodendrocyte progenitors

p38γ MAPK delays myelination and remyelination and is abundant in multiple sclerosis lesions

Multiple sclerosis is a chronic inflammatory disease in which disability results from the disruption of myelin and axons. During the initial stages of the disease, injured myelin is replaced by mature myelinating oligodendrocytes that differentiate from oligodendrocyte precursor cells. However, myelin repair fails in secondary and chronic progressive stages of the disease and with ageing, as the environment becomes progressively more hostile. This may be attributable to inhibitory molecules in the multiple sclerosis environment including activation of the p38MAPK family of kinases. We explored oligodendrocyte precursor cell differentiation and myelin repair using animals with conditional ablation of p38MAPKγ from oligodendrocyte precursors. We found that p38γMAPK ablation accelerated oligodendrocyte precursor cell differentiation and myelination. This resulted in an increase in both the total number of oligodendrocytes and the migration of progenitors ex vivo and faster remyelination in the cuprizone model of demyelination/remyelination. Consistent with its role as an inhibitor of myelination, p38γMAPK was significantly downregulated as oligodendrocyte precursor cells matured into oligodendrocytes. Notably, p38γMAPK was enriched in multiple sclerosis lesions from patients. Oligodendrocyte progenitors expressed high levels of p38γMAPK in areas of failed remyelination but did not express detectable levels of p38γMAPK in areas where remyelination was apparent. Our data suggest that p38γ could be targeted to improve myelin repair in multiple sclerosis.

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.

Oscillatory calcium release and sustained store-operated oscillatory calcium signaling prevents differentiation of human oligodendrocyte progenitor cells

Endogenous remyelination in demyelinating diseases such as multiple sclerosis is contingent upon the successful differentiation of oligodendrocyte progenitor cells (OPCs). Signaling via the Gα_q-coupled muscarinic receptor (M_1/3R) inhibits human OPC differentiation and impairs endogenous remyelination in experimental models. We hypothesized that calcium release following Gα_q-coupled receptor (G_qR) activation directly regulates human OPC (hOPC) cell fate. In this study, we show that specific G_qR agonists activating muscarinic and metabotropic glutamate receptors induce characteristic oscillatory calcium release in hOPCs and that these agonists similarly block hOPC maturation in vitro. Both agonists induce calcium release from endoplasmic reticulum (ER) stores and store operated calcium entry (SOCE) likely via STIM/ORAI-based channels. siRNA mediated knockdown (KD) of obligate calcium sensors STIM1 and STIM2 decreased the magnitude of muscarinic agonist induced oscillatory calcium release and attenuated SOCE in hOPCs. In addition, STIM2 expression was necessary to maintain the frequency of calcium oscillations and STIM2 KD reduced spontaneous OPC differentiation. Furthermore, STIM2 siRNA prevented the effects of muscarinic agonist treatment on OPC differentiation suggesting that SOCE is necessary for the anti-differentiative action of muscarinic receptor-dependent signaling. Finally, using a gain-of-function approach with an optogenetic STIM lentivirus, we demonstrate that independent activation of SOCE was sufficient to significantly block hOPC differentiation and this occurred in a frequency dependent manner while increasing hOPC proliferation. These findings suggest that intracellular calcium oscillations directly regulate hOPC fate and that modulation of calcium oscillation frequency may overcome inhibitory Gα_q-coupled signaling that impairs myelin repair.

Fingolimod mitigates synaptic deficits and psychosis-like behavior in APP/PSEN1 mice

INTRODUCTION

Current treatments for psychosis in Alzheimer's disease (AD), a syndrome characterized by more rapid deterioration and reduced synaptic protein abundance relative to non-psychotic AD, are inadequate. Fingolimod, a currently US Food and Drug Administration (FDA)-approved pharmacotherapy for multiple sclerosis, alters synaptic protein expression and warrants preclinical appraisal as a candidate pharmacotherapy for psychosis in AD.

METHODS

Presenilin and amyloid precursor protein transgenic mice (APPswe/PSEN1dE9) and wild-type mice were randomized to fingolimod or saline for 7 days. Psychosis-associated behaviors were quantified by open field testing, pre-pulse inhibition of the acoustic startle response testing, and habituation of the acoustic startle response testing. Synaptic proteins were quantified by liquid chromatography/mass spectrometry in homogenate and postsynaptic density fractions.

RESULTS

Fingolimod treatment increased the synaptic protein abundance in cortical homogenates and normalized psychosis-associated behaviors in APPswe/PSEN1dE9 mice relative to saline. Mitochondrial-related proteins were preferentially altered by fingolimod treatment and correlated with improvements in psychosis-associated behaviors.

DISCUSSION

Preclinical studies employing complementary psychosis-associated behavioral assessments and proteomic evaluations across multiple AD-related models are warranted to replicate the current study and further investigate fingolimod as a candidate treatment for psychosis in AD.

Human oligodendrocyte myelination potential; relation to age and differentiation

OBJECTIVE

Myelin regeneration in the human central nervous system relies on progenitor cells within the tissue parenchyma, with possible contribution from previously myelinating oligodendrocytes. In multiple sclerosis, a demyelinating disorder, variables affecting remyelination efficiency include age, severity of initial injury, and progenitor cell properties. Our aim was to investigate the effects of age and differentiation on the myelination potential of human oligodendrocyte lineage cells.

METHODS

We derived viable primary oligodendrocyte lineage cells from surgical resections of pediatric and adult brain tissue. Ensheathment capacity using nanofiber assays and transcriptomic profiles from RNA sequencing were compared between A2B5+ antibody-selected progenitors and mature oligodendrocytes (non-selected cells).

RESULTS

We demonstrate that pediatric progenitor and mature cells ensheathed nanofibers more robustly than did adult progenitor and mature cells respectively. Within both age groups, the percentage of fibers ensheathed and ensheathment length per fiber were greater for A2B5+ progenitors. Gene expression of oligodendrocyte progenitor markers PDGFRA and PTPRZ1 were higher in A2B5+ vs A2B5- cells and in pediatric A2B5+ vs adult A2B5+ cells. p38 MAP kinases and actin cytoskeleton-associated pathways were upregulated in pediatric cells; both have been shown to regulate OL process outgrowth. Significant upregulation of "cell senescence" genes was detected in pediatric samples; this could reflect their role in development and the increased susceptibility of pediatric oligodendrocytes to activating cell death responses to stress.

INTERPRETATION

Our findings identify specific biological pathways relevant to myelination that are differentially enriched in human pediatric and adult oligodendrocyte lineage cells and suggest potential targets for remyelination enhancing therapies. This article is protected by copyright. All rights reserved.

Understanding Abnormal c-JNK/p38MAPK Signaling Overactivation Involved in the Progression of Multiple Sclerosis: Possible Therapeutic Targets and Impact on Neurodegenerative Diseases

Demyelination, immune dysregulation, and neuroinflammation are the most common triggers of motor neuron disorders such as multiple sclerosis (MS). MS is a chronic demyelinating neurodegenerative disease of the central nervous system caused by abnormal immune activation, which causes myelin sheath damage. Cell signal transduction pathways are required for a variety of physiological and pathological processes in the brain. When these signaling systems become overactive, they can lead to disease progression. In various physiological conditions, abnormal mitogen-activated protein kinase (MAPK) activation is associated with several physiological dysfunctions that cause neurodegeneration. Previous research indicates that c-JNK and p38MAPK signaling play critical roles in neuronal growth and differentiation. c-JNK/p38MAPK is a member of the MAPK family, which regulates metabolic pathways, cell proliferation, differentiation, and apoptosis that control certain neurological activities. During brain injuries, c-JNK/p38MAPK also affects neuronal elastic properties, nerve growth, and cognitive processing. This review systematically linked abnormal c-JNK/p38MAPK signaling activation to multiple neuropathological pathways in MS and related neurological dysfunctions. MS progression is linked to genetic defects, oligodendrocyte destruction, glial overactivation, and immune dysregulation. We concluded that inhibiting both the c-JNK/p38MAPK signaling pathways can promote neuroprotection and neurotrophic effects against the clinical-pathological presentation of MS and influence other neurological disorders. As a result, the potential benefits of c-JNK/p38MAPK downregulation for the development of disease-modifying treatment interventions in the future could include MS prevention and related neurocomplications.

A2 B Adenosine Receptors and Sphingosine 1-Phosphate Signaling Cross-Talk in Oligodendrogliogenesis

Oligodendrocyte-formed myelin sheaths allow fast synaptic transmission in the brain. Impairments in the process of myelination, or demyelinating insults, might cause chronic diseases such as multiple sclerosis (MS). Under physiological conditions, remyelination is an ongoing process throughout adult life consisting in the differentiation of oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes (OLs). During pathological events, this process fails due to unfavorable environment. Adenosine and sphingosine kinase/sphingosine 1-phosphate signaling axes (SphK/S1P) play important roles in remyelination processes. Remarkably, fingolimod (FTY720), a sphingosine analog recently approved for MS treatment, plays important roles in OPC maturation. We recently demonstrated that the selective stimulation of A_{2 B} adenosine receptors (A_{2 B} Rs) inhibit OPC differentiation in vitro and reduce voltage-dependent outward K⁺ currents (I _K ) necessary to OPC maturation, whereas specific SphK1 or SphK2 inhibition exerts the opposite effect. During OPC differentiation A_{2 B} R expression increases, this effect being prevented by SphK1/2 blockade. Furthermore, selective silencing of A_{2 B} R in OPC cultures prompts maturation and, intriguingly, enhances the expression of S1P lyase, the enzyme responsible for irreversible S1P catabolism. Finally, the existence of an interplay between SphK1/S1P pathway and A_{2 B} Rs in OPCs was confirmed since acute stimulation of A_{2 B} Rs activates SphK1 by increasing its phosphorylation. Here the role of A_{2 B} R and SphK/S1P signaling during oligodendrogenesis is reviewed in detail, with the purpose to shed new light on the interaction between A_{2 B} Rs and S1P signaling, as eventual innovative targets for the treatment of demyelinating disorders.

Sphingosine-1-Phosphate Receptor Modulators and Oligodendroglial Cells: Beyond Immunomodulation

Multiple sclerosis (MS) is an autoimmune inflammatory disease characterized by demyelination, axonal loss, and synaptic impairment in the central nervous system (CNS). The available therapies aim to reduce the severity of the pathology during the early inflammatory stages, but they are not effective in the chronic stage of the disease. In this phase, failure in endogenous remyelination is associated with the impairment of oligodendrocytes progenitor cells (OPCs) to migrate and differentiate into mature myelinating oligodendrocytes. Therefore, stimulating differentiation of OPCs into myelinating oligodendrocytes has become one of the main goals of new therapeutic approaches for MS. Different disease-modifying therapies targeting sphingosine-1-phosphate receptors (S1PRs) have been approved or are being developed to treat MS. Besides their immunomodulatory effects, growing evidence suggests that targeting S1PRs modulates mechanisms beyond immunomodulation, such as remyelination. In this context, this review focuses on the current understanding of S1PR modulators and their direct effect on OPCs and oligodendrocytes.

Fingolimod increases oligodendrocytes markers expression in epidermal neural crest stem cells

Epidermal neural crest stem cells (EPI-NCSCs) are propitious candidates for cell replacement therapy and supplying neurotrophic factors in the neurological disorders. Considering the potential remyelinating and regenerative effects of fingolimod, in this study, we evaluated its effects on EPI-NCSCs viability and the expression of neurotrophic and oligodendrocyte differentiation factors. EPI-NCSCs, extracted from the bulge of rat hair follicles, were characterized and treated with fingolimod (0, 50, 100, 200, 400, 600, 1000, and 5000 nM). The cell viability was evaluated by MTT assay at 6, 24 and 72 h. The expression of neurotrophic and differentiation factors in the cells treated with 100 and 400 nM fingolimod were measured at 24 and 120 h. Fingolimod at 50-600 nM increased the cells viability after 6 h, with no change at the higher concentrations. The highest concentration (5000nM) induced toxicity at 24 and 72 h. NGF and GDNF genes expression were decreased at 120 h, but on the contrary, brain derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3) were increased by both concentrations at both time points. Oligodendrocyte markers including platelet-derived growth factor receptor A (PDGFRα), neuron-glial antigen 2 (NG2) and growth associated protein 43 (GAP43) were elevated at 120 h, which was accompanied with reduce in stemness markers (Nestin and early growth response 1 (EGR1)). Fingolimod increased the expression of neurotrophic factors in EPI-NCSCs, and guided them to oligodendrocyte fate. Therefore, fingolimod in combination with EPI-NCSCs, can be considered as a promising approach for demyelinating neurological disorders.

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.

Lysophospholipids and Their G-Coupled Protein Signaling in Alzheimer's Disease: From Physiological Performance to Pathological Impairment

Lysophospholipids (LPLs) are bioactive signaling lipids that are generated from phospholipase-mediated hydrolyzation of membrane phospholipids (PLs) and sphingolipids (SLs). Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two of the best-characterized LPLs which mediate a variety of cellular physiological responses via specific G-protein coupled receptor (GPCR) mediated signaling pathways. Considerable evidence now demonstrates the crucial role of LPA and S1P in neurodegenerative diseases, especially in Alzheimer’s disease (AD). Dysfunction of LPA and S1P metabolism can lead to aberrant accumulation of amyloid-β (Aβ) peptides, the formation of neurofibrillary tangles (NFTs), neuroinflammation and ultimately neuronal death. Summarizing LPA and S1P signaling profile may aid in profound health and pathological processes. In the current review, we will introduce the metabolism as well as the physiological roles of LPA and S1P in maintaining the normal functions of the nervous system. Given these pivotal functions, we will further discuss the role of dysregulation of LPA and S1P in promoting AD pathogenesis.

Fingolimod after a first unilateral episode of acute optic neuritis (MOVING) - preliminary results from a randomized, rater-blind, active-controlled, phase 2 trial

Background

Neuroprotection and promotion of remyelination represent important therapeutic gaps in multiple sclerosis (MS). Acute optic neuritis (ON) is a frequent MS manifestation. Based on the presence and properties of sphingosine-1-phosphate receptors (S1PR) on astrocytes and oligodendrocytes, we hypothesized that remyelination can be enhanced by treatment with fingolimod, a S1PR modulator currently licensed for relapsing-remitting MS.

Methods

MOVING was an investigator-driven, rater-blind, randomized clinical trial. Patients with acute unilateral ON, occurring as a clinically isolated syndrome or MS relapse, were randomized to 6 months of treatment with 0.5 mg oral fingolimod or subcutaneous IFN-β 1b 250 μg every other day. The change in multifocal visual evoked potential (mfVEP) latency of the qualifying eye was examined as the primary (month 6 vs. baseline) and secondary (months 3, 6 and 12 vs. baseline) outcome. In addition, full field visual evoked potentials, visual acuity, optical coherence tomography as well as clinical relapses and measures of disability, cerebral MRI, and self-reported visual quality of life were obtained for follow-up. The study was halted due to insufficient recruitment (n = 15), and available results are reported.

Results

Per protocol analysis of the primary endpoint revealed a significantly larger reduction of mfVEP latency at 6 months compared to baseline with fingolimod treatment (n = 5; median decrease, 15.7 ms) than with IFN-β 1b treatment (n = 4; median increase, 8.15 ms) (p <  0.001 for interaction). Statistical significance was maintained in the secondary endpoint analysis. Descriptive results are reported for other endpoints.

Conclusion

Preliminary results of the MOVING trial argue in support of a beneficial effect of fingolimod on optic nerve remyelination when compared to IFN-β treatment. Interpretation is limited by the small number of complete observations, an unexpected deterioration of the control group and a difference in baseline mfVEP latencies. The findings need to be confirmed in larger studies.

Trial registration

The trial was registered as EUDRA-CT 2011–004787-30 on October 26, 2012 and as NCT01647880 on July 24, 2012.

Sphingosine 1-phosphate promotes the proliferation of olfactory ensheathing cells through YAP signaling and participates in the formation of olfactory nerve layer

Olfactory ensheathing cells (OECs) are unique glial cells with axonal growth-promoting properties in the olfactory epithelium and olfactory bulb, covering the entire length of the olfactory nerve. The proliferation of OECs is necessary for the formation of the presumptive olfactory nerve layer (ONL) during development and OECs transplantation. However, the molecular mechanism underlying the regulation of OEC proliferation in the ONL still remains unknown. In the present study, we examined the role of sphingosine 1-phosphate (S1P) and S1P receptors (S1PRs) on OEC proliferation. Initially, reverse transcription-PCR (RT-PCR), western blot and immunostaining revealed that S1PRs were highly expressed in the OECs in vitro and in vivo. Furthermore, we found that S1P treatment promoted the proliferation of primary cultured OECs mediated by S1PR1. Mechanistically, yes-associated protein (YAP) was required for S1P-induced OEC proliferation through RhoA signaling. Finally, conditional knockout of YAP in OECs reduced OEC proliferation in ONL, which impaired the axonal projection and growth of olfactory sensory neurons, and olfactory functions. Taken together, these results reveal a previously unrecognized function of S1P/RhoA/YAP pathway in the proliferation of OECs, contributing to the formation of ONL and the projection, growth, and function of olfactory sensory neurons during development.

Detrimental and protective action of microglial extracellular vesicles on myelin lesions: astrocyte involvement in remyelination failure

Microglia are highly plastic immune cells which exist in a continuum of activation states. By shaping the function of oligodendrocyte precursor cells (OPCs), the brain cells which differentiate to myelin-forming cells, microglia participate in both myelin injury and remyelination during multiple sclerosis. However, the mode(s) of action of microglia in supporting or inhibiting myelin repair is still largely unclear. Here, we analysed the effects of extracellular vesicles (EVs) produced in vitro by either pro-inflammatory or pro-regenerative microglia on OPCs at demyelinated lesions caused by lysolecithin injection in the mouse corpus callosum. Immunolabelling for myelin proteins and electron microscopy showed that EVs released by pro-inflammatory microglia blocked remyelination, whereas EVs produced by microglia co-cultured with immunosuppressive mesenchymal stem cells promoted OPC recruitment and myelin repair. The molecular mechanisms responsible for the harmful and beneficial EV actions were dissected in primary OPC cultures. By exposing OPCs, cultured either alone or with astrocytes, to inflammatory EVs, we observed a blockade of OPC maturation only in the presence of astrocytes, implicating these cells in remyelination failure. Biochemical fractionation revealed that astrocytes may be converted into harmful cells by the inflammatory EV cargo, as indicated by immunohistochemical and qPCR analyses, whereas surface lipid components of EVs promote OPC migration and/or differentiation, linking EV lipids to myelin repair. Although the mechanisms through which the lipid species enhance OPC maturation still remain to be fully defined, we provide the first demonstration that vesicular sphingosine 1 phosphate stimulates OPC migration, the first fundamental step in myelin repair. From this study, microglial EVs emerge as multimodal and multitarget signalling mediators able to influence both OPCs and astrocytes around myelin lesions, which may be exploited to develop novel approaches for myelin repair not only in multiple sclerosis, but also in neurological and neuropsychiatric diseases characterized by demyelination.

Pleotropic Roles of Autotaxin in the Nervous System Present Opportunities for the Development of Novel Therapeutics for Neurological Diseases

Autotaxin (ATX) is a soluble extracellular enzyme that is abundant in mammalian plasma and cerebrospinal fluid (CSF). It has two known enzymatic activities, acting as both a phosphodiesterase and a phospholipase. The majority of its biological effects have been associated with its ability to liberate lysophosphatidic acid (LPA) from its substrate, lysophosphatidylcholine (LPC). LPA has diverse pleiotropic effects in the central nervous system (CNS) and other tissues via the activation of a family of six cognate G protein-coupled receptors. These LPA receptors (LPARs) are expressed in some combination in all known cell types in the CNS where they mediate such fundamental cellular processes as proliferation, differentiation, migration, chronic inflammation, and cytoskeletal organization. As a result, dysregulation of LPA content may contribute to many CNS and PNS disorders such as chronic inflammatory or neuropathic pain, glioblastoma multiforme (GBM), hemorrhagic hydrocephalus, schizophrenia, multiple sclerosis, Alzheimer's disease, metabolic syndrome-induced brain damage, traumatic brain injury, hepatic encephalopathy-induced cerebral edema, macular edema, major depressive disorder, stress-induced psychiatric disorder, alcohol-induced brain damage, HIV-induced brain injury, pruritus, and peripheral nerve injury. ATX activity is now known to be the primary biological source of this bioactive signaling lipid, and as such, represents a potentially high-value drug target. There is currently one ATX inhibitor entering phase III clinical trials, with several additional preclinical compounds under investigation. This review discusses the physiological and pathological significance of the ATX-LPA-LPA receptor signaling axis and summarizes the evidence for targeting this pathway for the treatment of CNS diseases.

Inhibition of astrocyte FAK-JNK signaling promotes subventricular zone neurogenesis through CNTF

Astrocyte-derived ciliary neurotrophic factor (CNTF) promotes adult subventricular zone (SVZ) neurogenesis. We found that focal adhesion kinase (FAK) and JNK, but not ERK or P38, repress CNTF in vitro. Here, we defined the FAK-JNK pathway and its regulation of CNTF in mice, and the related leukemia inhibitory factor (LIF) and interleukin-6 (IL-6), which promote stem cell renewal at the expense of neurogenesis. Intrastriatal injection of FAK inhibitor, FAK14, in adult male C57BL/6 mice reduced pJNK and increased CNTF expression in the SVZ-containing periventricular region. Injection of a JNK inhibitor increased CNTF without affecting LIF and IL-6, and increased SVZ proliferation and neuroblast formation. The JNK inhibitor had no effect in CNTF-/- mice, suggesting that JNK inhibits SVZ neurogenesis by repressing CNTF. Inducible deletion of FAK in astrocytes increased SVZ CNTF and neurogenesis, but not LIF and IL-6. Intrastriatal injection of inhibitors suggested that P38 reduces LIF and IL-6 expression, whereas ERK induces CNTF and LIF. Intrastriatal FAK inhibition increased LIF, possibly through ERK, and IL-6 through another pathway that does not involve P38. Systemic injection of FAK14 also inhibited JNK while increasing CNTF, but did not affect P38 and ERK activation, or LIF and IL-6 expression. Importantly, systemic FAK14 increased SVZ neurogenesis in wild-type C57BL/6 and CNTF+/+ mice, but not in CNTF-/- littermates, indicating that it acts by upregulating CNTF. These data show a surprising differential regulation of related cytokines and identify the FAK-JNK-CNTF pathway as a specific target in astrocytes to promote neurogenesis and possibly neuroprotection in neurological disorders.

Combination Therapy With Fingolimod and Neural Stem Cells Promotes Functional Myelination in vivo Through a Non-immunomodulatory Mechanism

Myelination, which occurs predominantly postnatally and continues throughout life, is important for proper neurologic function of the mammalian central nervous system (CNS). We have previously demonstrated that the combination therapy of fingolimod (FTY720) and transplanted neural stem cells (NSCs) had a significantly enhanced therapeutic effect on the chronic stage of experimental autoimmune encephalomyelitis, an animal model of CNS autoimmunity, compared to using either one of them alone. However, reduced disease severity may be secondary to the immunomodulatory effects of FTY720 and NSCs, while whether this therapy directly affects myelinogenesis remains unknown. To investigate this important question, we used three myelination models under minimal or non-inflammatory microenvironments. Our results showed that FTY720 drives NSCs to differentiate into oligodendrocytes and promotes myelination in an ex vivo brain slice culture model, and in the developing CNS of healthy postnatal mice in vivo. Elevated levels of neurotrophic factors, e.g., brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor, were observed in the CNS of the treated infant mice. Further, FTY720 and NSCs efficiently prolonged the survival and improved sensorimotor function of shiverer mice. Together, these data demonstrate a direct effect of FTY720, beyond its known immunomodulatory capacity, in NSC differentiation and myelin development as a novel mechanism underlying its therapeutic effect in demyelinating diseases.

Functional mechanism of Ginsenosides on tumor growth and metastasis

Ginsengs, has long been used as one medicinal herb in China for more than two thousand years. Many studies have shown that ginsengs have preventive and therapeutic roles for cancer, and play a good complementary role in cancer treatment. Ginsenosides, as most important constituents of ginseng, have been extensively investigated and emphasized in cancer chemoprevention and therapeutics. However, the functional mechanism of Ginsenosides on cancer is not well known. This review will focus on introducing the functional mechanisms of ginsenosides and their metabolites, which regulate signaling pathways related with tumor growth and metastasis. Ginsenosides inhibit tumor growth via upregulating tumor apoptosis, inducing tumor cell differentiation and targeting cancer stem cells. In addition, Ginsenosides regulate tumor microenvironment via suppressing tumor angiogenesis-related proteins and pathways. Structural modification of ginsenosides and their administration alone or combinations with other Chinese medicines or chemical medicines have recently been developed to be a new therapeutic strategy for cancer.

The effect of fingolimod on focal and diffuse grey matter damage in active MS patients

INTRODUCTION

The mechanism of action of fingolimod within the central nervous system and its efficacy in reducing/preventing both focal and diffuse grey matter (GM) damage in active multiple sclerosis (MS) are not completely understood.

METHODS

In this longitudinal, 2-year prospective, phase IV, single-blind study, 40 MS patients treated with fingolimod and 39 untreated age, gender, and disability-matched MS patients were enrolled. Each patient underwent a neurological examination every 6 months and a 3T MRI at the beginning of the treatment and after 24 months. The accumulation of new cortical lesions (CLs) and the progression of regional GM atrophy were compared between the two groups.

RESULTS

At the end of the study (T24), the percentage of patients with new CLs (13.5 vs. 89%, p < 0.001) and the percentage of GM volume change was lower in the treated group (p < 0.001). The regional analysis revealed that the treated group had also less volume loss in thalamus, caudatus, globus pallidus, cingulate cortex, and hippocampus (p < 0.001), as well as in, cerebellum, superior frontal gyrus, and insular-long gyrus (p < 0.05). Patients with no evidence of disease activity were 60% in the treated group and 10% in the untreated group (p < 0.001).

CONCLUSIONS

These results suggest a possible protective effect of fingolimod on focal and diffuse GM damage.

Immunology of oligodendrocyte precursor cells in vivo and in vitro

Remyelination following myelin/oligodendrocyte injury in the central nervous system (CNS) is dependent on oligodendrocyte progenitor cells (OPCs) migrating into lesion sites, differentiating into myelinating oligodendrocytes (OLs), and ensheathing axons. Experimental models indicate that robust OPC-dependent remyelination can occur in the CNS; in contrast, histologic and imaging studies of lesions in the human disease multiple sclerosis (MS) indicate the variable extent of this response, which is particularly limited in more chronic MS lesions. Immune-mediated mechanisms can contribute either positively or negatively to the presence and functional responses of OPCs. This review addresses i) the molecular signature and functional properties of OPCs in the adult human brain; ii) the status (presence and function) of OPCs in MS lesions; iii) experimental models and in vitro data highlighting the contribution of adaptive and innate immune constituents to OPC injury and remyelination; and iv) effects of MS-directed immunotherapies on OPCs, either directly or indirectly via effects on specific immune constituents.

Potential neuroprotective effect of Fingolimod in multiple sclerosis and its association with clinical variables

INTRODUCTION

Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system affecting both white matter and grey matter in the earliest phases of its course. The crucial role of neurodegeneration in disability progression in MS, regardless of white matter damage, has been confirmed by several imaging and neuropathological studies. Fingolimod is an effective immunomodulator of the sphingosine 1-phosphate receptor, approved in relapsing remitting MS and able to cross the blood-brain barrier and to slow disability progression and brain volume loss. However, it remains unclear whether this neuroprotective action is due to a peripheral anti-inflammatory effect and/or to a direct effect on neuronal cells.

AREAS COVERED

In this review, the authors summarize the published preclinical and clinical studies on the effect of Fingolimod in limiting the focal and diffuse grey matter damage in MS.

EXPERT OPINION

Fingolimod might have a significant neuroprotective effect on relapsing remitting MS based on its modulatory effect on oligodendroglial cells and astrocytes, and on its direct effect on cortical neurons. Future clinical studies including measures of grey matter damage are required to confirm in vivo such neuroprotective effect.

Mapping Protein Targets of Bioactive Small Molecules Using Lipid-Based Chemical Proteomics

Lipids play critical roles in cell biology, often through direct interactions with proteins. We recently described the use of photoreactive lipid probes combined with quantitative mass spectrometry to globally map lipid-protein interactions, and the effects of drugs on these interactions, in cells. Here, we investigate the broader potential of lipid-based chemical proteomic probes for determining the cellular targets of biologically active small molecules, including natural product derivatives and repurposed drugs of ill-defined mechanisms. We identify the prostaglandin-regulatory enzyme PTGR2 as a target of the antidiabetic hops derivative KDT501 and show that miconazole-an antifungal drug that attenuates disease severity in preclinical models of multiple sclerosis-inhibits SGPL1, an enzyme that degrades the signaling lipid sphingosine-1-phosphate, drug analogues of which are used to treat multiple sclerosis in humans. Our findings highlight the versatility of lipid-based chemical proteomics probes for mapping small molecule-protein interactions in human cells to gain mechanistic understanding of bioactive compounds.

Effects of FTY720 on brain neurogenic niches in vitro and after kainic acid-induced injury

Background

FTY720 (fingolimod, Gilenya™) is an oral, blood-brain barrier (BBB)-passing drug approved as immunomodulatory treatment for relapsing-remitting form of the multiple sclerosis (MS). In addition, FTY720 exerts several effects in the central nervous system (CNS), ranging from neuroprotection to reduction of neuroinflammation. However, the neurogenic and oligodendrogenic potential of FTY720 has been poorly investigated. In this study, we assessed the effect of FTY720 on the production of new neurons and oligodendrocytes from neural stem/precursor cells both in vitro and in vivo.

Methods

Neural stem cells (NSCs) derived from the young rat subventricular zone (SVZ) were exposed to FTY720 (10, 100 nM), and their differentiation into neurons and oligodendrocytes was measured using immunofluorescence for anti-β-III tubulin or CNPase (2′,3′-cyclic nucleotide 3′-phosphodiesterase) as markers of mature neurons or oligodendrocytes, respectively. In addition, intracerebroventricular (icv) administration of kainic acid (KA; 0.5 μg/2 μl) in Sprague-Dawley rats was used as an in vivo model of neuronal death and inflammation. FTY720 was applied icv (1 μg/2 μl), together with KA, plus intraperitoneally (ip; 1 mg/kg) 24 h before, and daily, until sacrifice 8 days after KA injection. To visualize cell proliferation in the hippocampus and in white matter regions, rats were administered 5-bromo-2-deoxyuridine (BrdU) 100 mg/kg, ip injected every 2 days. Immunohistochemical analyses were performed on rat brain slices to measure the production of new neuronal precursors (doublecortin/DCX⁺ cells) and new oligodendrocytes precursors (proteoglycan/NG2⁺ cells).

Results

In this study, we observed that FTY720 increased postnatal NSCs differentiation into both neurons and oligodendrocytes in vitro. In turn, in adult animals, FTY720 enhanced the percentage of BrdU⁺ cells coexpressing DCX marker, both in basal (FTY720 alone) and in neurodegenerative (FTY720 + KA) conditions. However, FTY720 had only a partial effect on proliferation and differentiation of oligodendrocyte progenitor cell (OPC) population in vivo.

Conclusions

FTY720 promotes neurogenesis and oligodendrogenesis in vitro under basal conditions. In addition, it increases the generation of neuroblasts and oligodendrocytes after excitotoxic brain injury. This suggests that FTY720 has the potential to activate the neurogenic niche and thus favour tissue repair after lesion.

Electronic supplementary material

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Differentiation of human olfactory bulb-derived neural stem cells toward oligodendrocyte

In the central nervous system (CNS), oligodendrocytes are the glial element in charge of myelin formation. Obtaining an overall presence of oligodendrocyte precursor cells/oligodendrocytes (OPCs/OLs) in culture from different sources of NSCs is an important research area, because OPCs/OLs may provide a promising therapeutic strategy for diseases affecting myelination of axons. The present study was designed to differentiate human olfactory bulb NSCs (OBNSCs) into OPCs/OLs and using expression profiling (RT-qPCR) gene, immunocytochemistry, and specific protein expression to highlight molecular mechanism(s) underlying differentiation of human OBNSCs into OPCs/OLs. The differentiation of OBNSCs was characterized by a simultaneous appearance of neurons and glial cells. The differentiation medium, containing cAMP, PDGFA, T3, and all-trans-retinoic acid (ATRA), promotes OBNSCs to generate mostly oligodendrocytes (OLs) displaying morphological changes, and appearance of long cytoplasmic processes. OBNSCs showed, after 5 days in OLs differentiation medium, a considerable decrease in the number of nestin positive cells, which was associated with a concomitant increase of NG2 immunoreactive cells and few O4(+)-OPCs. In addition, a significant up regulation in gene and protein expression profile of stage specific cell markers for OPCs/OLs (CNPase, Galc, NG2, MOG, OLIG1, OLIG2, MBP), neurons, and astrocytes (MAP2, β-TubulinIII, GFAP) and concomitant decrease of OBNSCs pluripotency markers (Oct4, Sox2, Nestin), was demonstrated following induction of OBNSCs differentiation. Taken together, the present study demonstrate the marked ability of a cocktail of factors containing PDGFA, T3, cAMP, and ATRA, to induce OBNSCs differentiation into OPCs/OLs and shed light on the key genes and pathological pathways involved in this process.

FTY720 (Fingolimod) reverses α-synuclein-induced downregulation of brain-derived neurotrophic factor mRNA in OLN-93 oligodendroglial cells

Multiple system atrophy (MSA) is a demyelinating neurodegenerative disorder characterized by accumulation of aggregated α-synuclein (aSyn) inside oligodendrocyte precursors, mature oligodendroglia, and neurons. MSA dysfunction is associated with loss of trophic factor production by glial and neuronal cells. Here, we report that recombinant wild type human aSyn uptake by OLN-93, an oligodendroglia cell-line, reduced brain-derived neurotrophic factor (BDNF) expression. Furthermore, OLN-93 cells stably transfected with human wild type or an MSA-associated mutant aSyn, A53E that produces neuronal and glial inclusions, reduced BDNF mRNA to nearly unmeasurable qPCR levels. Curiously, another MSA-associated aSyn mutant, G51D that also produces neuronal and glial inclusions, caused only a trend toward BDNF mRNA reduction in transfected OLN-93 cells. This suggests that oligodendrocyte-associated BDNF loss occurs in response to specific aSyn types. Treating OLN-93 cells with 160 nM FTY720 (Fingolimod, Gilenya^®), a Food and Drug Administration (FDA) approved therapeutic for multiple sclerosis, counteracted BDNF downregulation in all aSyn OLN-93 cells. FTY720 also restored BDNF mRNA in OLN-93 cells treated with recombinant aSyn, as measured by qPCR or semiquantitatively on agarose gels. Immunoblots confirmed that FTY720 increased histone 3 acetylation in OLN-93, and chromatin immunoprecipitation assays showed increased acetylated histone 3 at BDNF promoter 1 after FTY720. Moreover, OLN-93 cells treated with valproic acid, a classic histone deacetylase inhibitor, confirmed that increasing acetylated histone 3 levels increases BDNF expression. Cumulatively, the data suggest that FTY720-associated histone deacetylase inhibition stimulates BDNF expression in oligodendroglial cells, raising the possibility that MSA patients may also benefit by treatment with FTY720.

Computer design, synthesis, and bioactivity analyses of drugs like fingolimod used in the treatment of multiple sclerosis

Multiple sclerosis (MS) is a very common disease of vital importance. In the MS treatment, some drugs such as fingolimod which help to protect nerves from damage are used. The main goal of the drug therapy in MS is to take control of the inflammation which leads to the destruction of myelin and axons in nerve cell and thus prevent and stop the progression of the disease. Fingolimod (FTY720) is an orally active immunomodulatory drug that has been used for the treatment of relapsing-remitting multiple sclerosis. It is a sphingosine-1-phosphate receptor modulator which prevents lymphocytes from contributing to an autoimmune reaction by inhibiting egress of lymphocytes them from lymph nodes. In this study, we have computer designed, synthesized and characterized two novel derivatives of FTY720, F1-12h and F2-9, and have determined their underlying mechanism of their beneficial effect in SH-SY5Y, SK-N-SH, and U-118 MG cell lines. For this purpose, we first determined the regulation of the cAMP response element (CRE) activity and cAMP concentration by F1-12h and F2-9 together with FTY720 using pGL4.29 luciferase reporter assay and cAMP immunoassay, respectively. Then, we have determined their effect on MS- and GPCR-related gene expression profiles using custom arrays along with FTY720 treatment at non-toxic doses (EC10). It was found that both derivatives significantly activate CRE and increase cAMP concentration in all three cell lines, indicating that they activate cAMP pathway through cell surface receptors as FTY720 does. Furthermore, F1-12h and F2-9 modulate the expression of the pathway related genes that are important in inflammatory signaling, cAMP signaling pathway, cell migration as well as diverse receptor and transcription factors. Expression of the genes involved in myelination was also increased by the treatment with F1-12h and F2-9. In summary, our data demonstrate that the two novel FTY720 derivatives act as anti-inflammatory ultimately by influencing the gene expression via the cAMP and downstream transcription factor CRE pathway. In conclusion, F1-12h and F2-9 might contribute future therapies for autoimmune diseases such as multiple sclerosis.

Effects of FTY720 (Fingolimod) on Proliferation, Differentiation, and Migration of Brain-Derived Neural Stem Cells

Insufficient proliferation, differentiation, and migration are the main pitfalls of neural stem cells (NSCs) in reparative therapeutics for the central nervous system (CNS) diseases. The potent lipid mediator sphingosine-1-phosphate (S1P) regulates cells' biological behavior broadly in the CNS. However, the effects of activating S1P on NSCs are not quite clear. In the current study, FTY720 (Fingolimod), an analog of S1P, was employed to induce the proliferation, differentiation, and migration of cultured brain-derived NSCs. The results indicated that proliferation and migration ability of NSCs were promoted by FTY720. Though we observed no obvious neuron prefers differentiation of NSCs, there were more protoplasmic astrocytes developed in the presence of certain concentration of FTY720. This work gives more comprehensive understanding of how FTY720 affects NSCs.

Extracellular cues influencing oligodendrocyte differentiation and (re)myelination

There is an increasing number of neurologic disorders found to be associated with loss and/or dysfunction of the CNS myelin sheath, ranging from the classic demyelinating disease, multiple sclerosis, through CNS injury, to neuropsychiatric diseases. The disabling burden of these diseases has sparked a growing interest in gaining a better understanding of the molecular mechanisms regulating the differentiation of the myelinating cells of the CNS, oligodendrocytes (OLGs), and the process of (re)myelination. In this context, the importance of the extracellular milieu is becoming increasingly recognized. Under pathological conditions, changes in inhibitory as well as permissive/promotional cues are thought to lead to an overall extracellular environment that is obstructive for the regeneration of the myelin sheath. Given the general view that remyelination is, even though limited in human, a natural response to demyelination, targeting pathologically 'dysregulated' extracellular cues and their downstream pathways is regarded as a promising approach toward the enhancement of remyelination by endogenous (or if necessary transplanted) OLG progenitor cells. In this review, we will introduce the extracellular cues that have been implicated in the modulation of (re)myelination. These cues can be soluble, part of the extracellular matrix (ECM) or mediators of cell-cell interactions. Their inhibitory and permissive/promotional roles with regard to remyelination as well as their potential for therapeutic intervention will be discussed.

Effects of sphingosine-1-phosphate receptor 1 phosphorylation in response to FTY720 during neuroinflammation

Fingolimod (FTY720, Gilenya), a sphingosine-1-phosphate receptor (S1PR) modulator, is one of the first-line immunomodulatory therapies for treatment of relapsing-remitting multiple sclerosis (MS). Human S1PR1 variants have been reported to have functional heterogeneity in vitro, suggesting that S1PR1 function may influence FTY720 efficacy. In this study, we examined the influence of S1PR1 phosphorylation on response to FTY720 in neuroinflammation. We found that mice carrying a phosphorylation-defective S1pr1 gene [S1PR1(S5A) mice] were refractory to FTY720 treatment in MOG_35-55-immunized and Th17-mediated experimental autoimmune encephalomyelitis (EAE) models. Long-term treatment with FTY720 induced significant lymphopenia and suppressed Th17 response in the peripheral immune system via downregulating STAT3 phosphorylation in both WT and S1PR1(S5A) mice. However, FTY720 did not effectively prevent neuroinflammation in the S1PR1(S5A) EAE mice as a result of encephalitogenic cells expressing C-C chemokine receptor 6 (CCR6). Combined treatment with FTY720 and anti-CCR6 delayed disease progression in S1PR1(S5A) EAE mice, suggesting that CCR6-mediated cell trafficking can overcome the effects of FTY720. This work may have translational relevance regarding FTY720 efficacy in MS patients and suggests that cell type-specific therapies may enhance therapeutic efficacy in MS.

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.

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.

Sphingosine kinase inhibition ameliorates chronic hypoperfusion-induced white matter lesions

White matter lesions (WML) are thought to contribute to vascular cognitive impairment in elderly patients. Growing evidence show that failure of myelin formation arising from the disruption of oligodendrocyte progenitor cell (OPC) differentiation is a cause of chronic vascular white matter damage. The sphingosine kinase (SphK)/sphingosine-1-phosphate (S1P) signaling pathway regulates oligodendroglia differentiation and function, and is known to be altered in hypoxia. In this study, we measured SphK, S1P as well as markers of WML, hypoxia and OPC (NG2) in a mouse bilateral carotid artery stenosis (BCAS) model of chronic cerebral hypoperfusion. Our results indicated that BCAS induced hypoxia inducible factor (HIF)-1α, Sphk2, S1P, and NG2 up-regulation together with accumulation of WML. In contrast, BCAS mice treated with the SphK inhibitor, SKI-II, showed partial reversal of SphK2, S1P and NG2 elevation and amelioration of WML. In an in vitro model of hypoxia, SKI-II reversed the suppression of OPC differentiation. Our study suggests a mechanism for hypoperfusion-associated WML involving HIF-1α-SphK2-S1P-mediated disruption of OPC differentiation, and proposes the SphK signaling pathway as a potential therapeutic target for white matter disease.

Fingolimod protects against neonatal white matter damage and long-term cognitive deficits caused by hyperoxia

Cerebral white matter injury is a leading cause of adverse neurodevelopmental outcome in prematurely born infants involving cognitive deficits in later life. Despite increasing knowledge about the pathophysiology of perinatal brain injury, therapeutic options are limited. In the adult demyelinating disease multiple sclerosis the sphingosine-1-phosphate (S1P) receptor modulating substance fingolimod (FTY720) has beneficial effects. Herein, we evaluated the neuroprotective potential of FTY720 in a neonatal model of oxygen-toxicity, which is associated with hypomyelination and impaired neuro-cognitive outcome. A single dose of FTY720 (1mg/kg) at the onset of neonatal hyperoxia (24h 80% oxygen on postnatal day 6) resulted in improvement of neuro-cognitive development persisting into adulthood. This was associated with reduced microstructural white matter abnormalities 4 months after the insult. In search of the underlying mechanisms potential non-classical (i.e. lymphocyte-independent) pathways were analysed shortly after the insult, comprising modulation of oxidative stress and local inflammatory responses as well as myelination, oligodendrocyte degeneration and maturation. Treatment with FTY720 reduced hyperoxia-induced oxidative stress, microglia activation and associated pro-inflammatory cytokine expression. In vivo and in vitro analyses further revealed that oxygen-induced hypomyelination is restored to control levels, which was accompanied by reduced oligodendrocyte degeneration and enhanced maturation. Furthermore, hyperoxia-induced elevation of S1P receptor 1 (S1P1) protein expression on in vitro cultured oligodendrocyte precursor cells was reduced by activated FTY720 and protection from degeneration is abrogated after selective S1P1 blockade. Finally, FTY720s' classical mode of action (i.e. retention of immune cells within peripheral lymphoid organs) was analysed demonstrating that FTY720 diminished circulating lymphocyte counts independent from hyperoxia. Cerebral immune cell counts remained unchanged by hyperoxia and by FTY720 treatment. Taken together, these results suggest that beneficial effects of FTY720 in neonatal oxygen-induced brain injury may be rather attributed to its anti-oxidative and anti-inflammatory capacity acting in concert with a direct protection of developing oligodendrocytes than to a modulation of peripheral lymphocyte trafficking. Thus, FTY720 might be a potential new therapeutic option for the treatment of neonatal brain injury through reduction of white matter damage.

The p38α mitogen-activated protein kinase is a key regulator of myelination and remyelination in the CNS

The p38α mitogen-activated protein kinase (MAPK) is one of the serine/threonine kinases regulating a variety of biological processes, including cell-type specification, differentiation and migration. Previous in vitro studies using pharmacological inhibitors suggested that p38 MAPK is essential for oligodendrocyte (OL) differentiation and myelination. To investigate the specific roles of p38α MAPK in OL development and myelination in vivo, we generated p38α conditional knockout (CKO) mice under the PLP and nerve/glial antigen 2 (NG2) gene promoters, as these genes are specifically expressed in OL progenitor cells (OPCs). Our data revealed that myelin synthesis was completely inhibited in OLs differentiated from primary OPC cultures derived from the NG2 Cre-p38α CKO mouse brains. Although an in vivo myelination defect was not obvious after gross examination of these mice, electron microscopic analysis showed that the ultrastructure of myelin bundles was severely impaired. Moreover, the onset of myelination in the corpus callosum was delayed in the knockout mice compared with p38α fl/fl control mice. A delay in OL differentiation in the central nervous system was observed with concomitant downregulation in the expression of OPC- and OL-specific genes such as Olig1 and Zfp488 during early postnatal development. OPC proliferation was not affected during this time. These data indicate that p38α is a positive regulator of OL differentiation and myelination. Unexpectedly, we observed an opposite effect of p38α on remyelination in the cuprizone-induced demyelination model. The p38α CKO mice exhibited better remyelination capability compared with p38α fl/fl mice following demyelination. The opposing roles of p38α in myelination and remyelination could be due to a strong anti-inflammatory effect of p38α or a dual reciprocal regulatory action of p38α on myelin formation during development and on remyelination after demyelination.

Fingolimod induces the transition to a nerve regeneration promoting Schwann cell phenotype

Successful regeneration of injured peripheral nerves is mainly attributed to the plastic behavior of Schwann cells. Upon loss of axons, these cells trans-differentiate into regeneration promoting repair cells which provide trophic support to regrowing axons. Among others, activation of cJun was revealed to be involved in this process, initiating the stereotypic pattern of Schwann cell phenotype alterations during Wallerian degeneration. Nevertheless, the ability of Schwann cells to adapt and therefore the nerve's potential to regenerate can be limited in particular after long term denervation or in neuropathies leading to incomplete regeneration only and thus emphasizing the need for novel therapeutic approaches. Here we stimulated primary neonatal and adult rat Schwann cells with Fingolimod/FTY720P and investigated its impact on the regeneration promoting phenotype. FTY720P activated a number of de-differentiation markers including cJun and interfered with maturation marker and myelin expression. Functionally, FTY720P treated Schwann cells upregulated growth factor expression and these cells enhanced dorsal root ganglion neurite outgrowth on inhibitory substrates. Our results therefore provide strong evidence that FTY720P application supports the generation of a repair promoting cellular phenotype and suggest that Fingolimod could be used as treatment for peripheral nerve injuries and diseases.