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

Dietary Supplementation with n-3 Polyunsaturated Fatty Acids Delays the Phenotypic Manifestation of Krabbe Disease and Partially Restores Lipid Mediator Production in the Brain-Study in a Mouse Model of the Disease

Lipid mediators from fatty acid oxidation have been shown to be associated with the severity of Krabbe disease (KD), a disorder linked to mutations in the galactosylceramidase (GALC) gene. This study aims to investigate the effects of n-3 polyunsaturated fatty acid (PUFA) supplementation on KD traits and fatty acid metabolism using Twitcher (Tw) animals as a natural model for KD. Wild-type (Wt), heterozygous (Ht), and affected Tw animals were treated orally with 36 mg n-3 PUFAs/kg body weight/day from 10 to 35 days of life. The end product of PUFA peroxidation (8-isoprostane), the lipid mediator involved in the resolution of inflammatory exudates (resolvin D1), and the total amount of n-3 PUFAs were analyzed in the brains of mice. In Tw mice, supplementation with n-3 PUFAs delayed the manifestation of disease symptoms (p < 0.0001), and in the bran, decreased 8-isoprostane amounts (p < 0.0001), increased resolvin D1 levels (p < 0.005) and increased quantity of total n-3 PUFAs (p < 0.05). Furthermore, total brain n-3 PUFA levels were associated with disease severity (r = -0.562, p = 0.0001), resolvin D1 (r = 0.712, p < 0.0001), and 8-isoprostane brain levels (r = -0.690, p < 0.0001). For the first time in a natural model of KD, brain levels of n-3 PUFAs are shown to determine disease severity and to be involved in the peroxidation of brain PUFAs as well as in the production of pro-resolving lipid mediators. It is also shown that dietary supplementation with n-3 PUFAs leads to a slowing of the phenotypic presentation of the disease and restoration of lipid mediator production.

The Effect of Donepezil Hydrochloride in the Twitcher Mouse Model of Krabbe Disease

Krabbe disease (KD) is a rare demyelinating disorder characterized by demyelination caused by mutations in the GALC gene, resulting in toxic accumulation of psychosine. Psychosine has been identified as detrimental to oligodendrocytes, leading to demyelination through diverse hypothesized pathways. Reducing demyelination is essential to maintain neurological function in KD; however, therapeutic interventions are currently limited. Acetylcholinesterase inhibitors (AChEi) are commonly used for symptomatic management of Alzheimer's Disease and are suggested to have potential disease-modifying effects, including regulating myelin state. In particular, donepezil, an AChEi, has demonstrated promising effects in cellular and animal models, including promotion of the expression of myelin-related genes and reduction of glial cell reactivity. This drug also acts as an agonist for sigma-1 receptors (Sig-1R), which are implicated in demyelination diseases. In the context of drug repurposing, here, we demonstrate that administration of donepezil has protective effects in the twitcher mouse model of KD. We provide data showing that donepezil preserves myelin and reduces glial cell reactivity in the brains of twitcher mice. Moreover, donepezil also improves behavioral phenotypes and increases lifespan in twitcher animals. These findings suggest that donepezil, with its dual activity as an AChE inhibitor and Sig-1R agonist, may hold promise as a therapeutic candidate for demyelinating diseases, including KD.

Nanomedicines to treat rare neurological disorders: The case of Krabbe disease

The brain remains one of the most challenging therapeutic targets due to the low and selective permeability of the blood-brain barrier and complex architecture of the brain tissue. Nanomedicines, despite their relatively large size compared to small molecules and nucleic acids, are being heavily investigated as vehicles to delivery therapeutics into the brain. Here we elaborate on how nanomedicines may be used to treat rare neurodevelopmental disorders, using Krabbe disease (globoid cell leukodystrophy) to frame the discussion. As a monogenetic disorder and lysosomal storage disease affecting the nervous system, the lessons learned from examining nanoparticle delivery to the brain in the context of Krabbe disease can have a broader impact on the treatment of various other neurodevelopmental and neurodegenerative disorders. In this review, we introduce the epidemiology and genetic basis of Krabbe disease, discuss current in vitro and in vivo models of the disease, as well as current therapeutic approaches either approved or at different stage of clinical developments. We then elaborate on challenges in particle delivery to the brain, with a specific emphasis on methods to transport nanomedicines across the blood-brain barrier. We highlight nanoparticles for delivering therapeutics for the treatment of lysosomal storage diseases, classified by the therapeutic payload, including gene therapy, enzyme replacement therapy, and small molecule delivery. Finally, we provide some useful hints on the design of nanomedicines for the treatment of rare neurological disorders.

CD8+ T cell depletion prevents neuropathology in a mouse model of globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD) or Krabbe's disease is a fatal genetic demyelinating disease of the central nervous system caused by loss-of-function mutations in the galactosylceramidase (galc) gene. While the metabolic basis for disease is known, the understanding of how this results in neuropathology is not well understood. Herein, we report that the rapid and protracted elevation of CD8+ cytotoxic T lymphocytes occurs coincident with clinical disease in a mouse model of GLD. Administration of a function-blocking antibody against CD8α effectively prevented disease onset, reduced morbidity and mortality, and prevented CNS demyelination in mice. These data indicate that subsequent to the genetic cause of disease, neuropathology is driven by pathogenic CD8+ T cells, thus offering novel therapeutic potential for treatment of GLD.

The Effects of Antipsychotics in Experimental Models of Krabbe Disease

The role of altered myelin in the onset and development of schizophrenia and changes in myelin due to antipsychotics remains unclear. Antipsychotics are D₂ receptor antagonists, yet D₂ receptor agonists increase oligodendrocyte progenitor numbers and limit oligodendrocyte injury. Conflicting studies suggest these drugs promote the differentiation of neural progenitors to oligodendrocyte lineage, while others report antipsychotics inhibit the proliferation and differentiation of oligodendrocyte precursors. Here, we utilised in-vitro (human astrocytes), ex-vivo (organotypic slice cultures) and in-vivo (twitcher mouse model) experimental study designs of psychosine-induced demyelination, a toxin that accumulates in Krabbe disease (KD), to investigate direct effects of antipsychotics on glial cell dysfunction and demyelination. Typical and atypical antipsychotics, and selective D₂ and 5HT_2A receptor antagonists, attenuated psychosine-induced cell viability, toxicity, and morphological aberrations in human astrocyte cultures. Haloperidol and clozapine reduced psychosine-induced demyelination in mouse organotypic cerebellar slices. These drugs also attenuated the effects of psychosine on astrocytes and microglia and restored non-phosphorylated neurofilament levels, indicating neuroprotective effects. In the demyelinating twitcher mouse model of KD, haloperidol improved mobility and significantly increased the survival of these animals. Overall, this study suggests that antipsychotics directly regulate glial cell dysfunction and exert a protective effect on myelin loss. This work also points toward the potential use of these pharmacological agents in KD.

Fingolimod ameliorates schizophrenia-like cognitive impairments induced by phencyclidine in male rats

BACKGROUND AND PURPOSE

Improvement of cognitive deficits in schizophrenia remains an unmet need owing to the lack of new therapies and drugs. Recent studies have reported that fingolimod, an immunomodulatory drug for treating multiple sclerosis, demonstrates anti-inflammatory and neuroprotective effects in several neurological disease models. This suggests its usefulness for ameliorating cognitive dysfunction in schizophrenia. Herein, we assessed the efficacy profile and mechanism of fingolimod in a rat model of phencyclidine (PCP)-induced schizophrenia.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were treated with PCP for 14 days. The therapeutic effect of fingolimod on cognitive function was assessed using the Morris water maze and fear conditioning tests. Hippocampal neurogenesis and the expression of astrocytes and microglia were evaluated using immunostaining. Cytokine expression was quantified using multiplexed flow cytometry. Brain-derived neurotrophic factor expression and phosphorylation of extracellular signal-regulated kinase were determined using western blot analysis.

KEY RESULTS

Fingolimod attenuated cognitive deficits and restored hippocampal neurogenesis in a dose-dependent manner in PCP-treated rats. Fingolimod treatment exerted anti-inflammatory effects by inhibiting microglial activation and IL-6 and IL-1β pro-inflammatory cytokine expression. The underlying mechanism involves the upregulation of brain-derived neurotrophic factor protein expression and activation of the ERK signalling pathway.

CONCLUSION AND IMPLICATIONS

This is the first preclinical assessment of the effects of fingolimod on cognitive function in a model for schizophrenia. Our results suggest the immune system plays an crucial role in cognitive alterations in schizophrenia and highlight the potential of immunomodulatory strategies to improve cognitive deficits in schizophrenia.

Galactosylceramidase deficiency and pathological abnormalities in cerebral white matter of Krabbe disease

Krabbe Disease (KD) is an autosomal recessive disorder that results from loss-of-function mutations in the GALC gene, which encodes lysosomal enzyme galactosylceramidase (GALC). Functional deficiency of GALC is toxic to myelin-producing cells, which leads to progressive demyelination in both the central and peripheral nervous systems. It is hypothesized that accumulation of psychosine, which can only be degraded by GALC, is a primary initiator of pathologic cascades. Despite the central role of GALC in KD pathomechanism, investigations of GALC deficiency at a protein level are largely absent, due in part, to the lack of sensitive antibodies in the field. Leveraging two custom antibodies that can detect GALC at endogenous levels, we demonstrated that GALC protein is predominantly localized to oligodendrocytes in cerebral white matter of an infant brain, consistent with its functional role in myelination. Mature GALC could also be quantitatively detected as a 26 kDa band by western blotting and correlated to enzyme activity in brain tissues. The p.Ile562Thr polymorphic variant, which is over-represented in the KD population, was associated with reduced mature GALC protein and activity. In three infantile KD cases, homozygous null mutations in GALC lead to deficiency in total GALC protein and activity. Interestingly, although GALC activity was absent, normal levels of total GALC protein were detected by a sandwich ELISA using our custom antibodies in a later-onset KD brain, which suggests that the assay has the potential to differentiate infantile- and later-onset KD cases. Among the infantile KD cases, we quantified a 5-fold increase in psychosine levels, and observed increased levels of acid ceramidase, a key enzyme for psychosine production, and hyperglycosylated lysosomal-associated membrane protein 1, a marker for lysosomal activation, in periventricular white matter, a major pathological brain region, when compared with age-matched normal controls. While near complete demyelination was observed in these cases, we quantified that an early-infantile case (age of death at 10 months) had about 3-fold increases in both globoid cells, a pathological hallmark for KD, and CD8-positive T lymphocytes, a pathological marker for multiple sclerosis, in the white matter when compared with a slower progressing infantile case (age of death at 21 months), which suggests a positive correlation between clinical severity and neuropathology. Taken together, our findings have advanced the understanding of GALC protein biology in the context of normal and KD brain white matter. We also revealed new neuropathological changes that may provide insights to understand KD pathogenesis.

Fingolimod effects on the brain are mediated through biochemical modulation of bioenergetics, autophagy, and neuroinflammatory networks

Fingolimod (FTY720) is an oral drug approved by the Food and Drug Administration (FDA) for management of multiple sclerosis (MS) symptoms, which has also shown beneficial effects against Alzheimer's (AD) and Parkinson's (PD) diseases pathologies. Although an extensive effort has been made to identify mechanisms underpinning its therapeutic effects, much remains unknown. Here, we investigated Fingolimod induced proteome changes in the cerebellum (CB) and frontal cortex (FC) regions of the brain which are known to be severely affected in MS, using a tandem mass tag (TMT) isobaric labeling-based quantitative mass-spectrometric approach to investigate the mechanism of action of Fingolimod. This study identified 6749 and 6319 proteins in CB and FC, respectively, and returned 2609 and 3086 differentially expressed proteins in mouse CB and FC, respectively, between Fingolimod treated and control groups. Subsequent bioinformatics analyses indicated a metabolic reprogramming in both brain regions of the Fingolimod treated group, where oxidative phosphorylation was upregulated while glycolysis and pentose phosphate pathway were downregulated. In addition, modulation of neuroinflammation in the Fingolimod treated group was indicated by upregulation of retrograde endocannabinoid signaling and autophagy pathways, and downregulation of neuroinflammation related pathways including neutrophil degranulation and the IL-12 mediated signaling pathway. Our findings suggest that Fingolimod may exert its protective effects on the brain by inducing metabolic reprogramming and neuroinflammation pathway modulation.

Human iPSC-derived astrocytes generated from donors with globoid cell leukodystrophy display phenotypes associated with disease

Globoid cell leukodystrophy (Krabbe disease) is a fatal neurodegenerative, demyelinating disease caused by dysfunctional activity of galactosylceramidase (GALC), leading to the accumulation of glycosphingolipids including psychosine. While oligodendrocytes have been extensively studied due to their high levels of GALC, the contribution of astrocytes to disease pathogenesis remains to be fully elucidated. In the current study, we generated induced pluripotent stem cells (iPSCs) from two donors with infantile onset Krabbe disease and differentiated them into cultures of astrocytes. Krabbe astrocytes recapitulated many key findings observed in humans and rodent models of the disease, including the accumulation of psychosine and elevated expression of the pro-inflammatory cytokine IL-6. Unexpectedly, Krabbe astrocytes had higher levels of glucosylceramide and ceramide, and displayed compensatory changes in genes encoding glycosphingolipid biosynthetic enzymes, suggesting a shunting away from the galactosylceramide and psychosine pathway. In co-culture, Krabbe astrocytes negatively impacted the survival of iPSC-derived human neurons while enhancing survival of iPSC-derived human microglia. Substrate reduction approaches targeting either glucosylceramide synthase or serine palmitoyltransferase to reduce the sphingolipids elevated in Krabbe astrocytes failed to rescue their detrimental impact on neuron survival. Our results suggest that astrocytes may contribute to the progression of Krabbe disease and warrant further exploration into their role as therapeutic targets.

Inflammasome Inhibition Prevents Motor Deficit and Cerebellar Degeneration Induced by Chronic Methamphetamine Administration

Methamphetamine (METH), a psychostimulant, has the potential to cause neurodegeneration by targeting the cerebrum and cerebellum. It has been suggested that the NLRP3 inflammasome may be responsible for the neurotoxicity caused by METH. However, the role of NLRP3 in METH-induced cerebellar Purkinje cell (PC) degeneration and the underlying mechanism remain elusive. This study aims to determine the consequences of NLRP3 modulation and the underlying mechanism of chronic METH-induced cerebellar PC degeneration. In METH mice models, increased NLRP3 expression, PC degeneration, myelin sheath destruction, axon degeneration, glial cell activation, and motor coordination impairment were observed. Using the NLRP3 inhibitor MCC950, we found that inhibiting NLRP3 alleviated the above-mentioned motor deficits and cerebellar pathologies. Furthermore, decreased mature IL-1β expression mediated by Caspase 1 in the cerebellum may be associated with the neuroprotective effects of NLRP3 inflammasome inhibition. Collectively, these findings suggest that mature IL-1β secretion mediated by NLRP3-ASC-Caspase 1 may be a critical step in METH-induced cerebellar degeneration and highlight the neuroprotective properties of inflammasome inhibition in cerebellar degeneration.

Astrocytic phagocytosis contributes to demyelination after focal cortical ischemia in mice

Ischemic stroke can cause secondary myelin damage in the white matter distal to the primary injury site. The contribution of astrocytes during secondary demyelination and the underlying mechanisms are unclear. Here, using a mouse of distal middle cerebral artery occlusion, we show that lipocalin-2 (LCN2), enriched in reactive astrocytes, expression increases in nonischemic areas of the corpus callosum upon injury. LCN2-expressing astrocytes acquire a phagocytic phenotype and are able to uptake myelin. Myelin removal is impaired in Lcn2^−/− astrocytes. Inducing re-expression of truncated LCN2(Δ2–20) in astrocytes restores phagocytosis and leads to progressive demyelination in Lcn2^−/− mice. Co-immunoprecipitation experiments show that LCN2 binds to low-density lipoprotein receptor-related protein 1 (LRP1) in astrocytes. Knockdown of Lrp1 reduces LCN2-induced myelin engulfment by astrocytes and reduces demyelination. Altogether, our findings suggest that LCN2/LRP1 regulates astrocyte-mediated myelin phagocytosis in a mouse model of ischemic stroke.

Ischemic stroke can cause secondary demyelination. Whether phagocytic astrocytes can contribute to such demyelination is unclear. Here, the authors show that lipocalin-2 (LCN-2) expression increased in astrocytes upon injury. LCN-2 expressing astrocytes acquire a phagocytic phenotype and contribute to secondary demyelination in a mouse model of ischemic stroke.

Existing Evidence for the Repurposing of PARP-1 Inhibitors in Rare Demyelinating Diseases

Simple Summary

Poly (ADP-ribose) polymerase-1 (PARP-1) inhibitors are successful cancer therapeutics that impair DNA repair machinery, leading to an accumulation of DNA damage and consequently cell death. The shared underlying mechanisms driving malignancy and demyelinating disease, together with the success of anticancer drugs as repurposed therapeutics, makes the repurposing of PARP-1 inhibitors for demyelinating diseases a worthy concept to consider. In addition, PARP-1 inhibitors demonstrate notable neuroprotective effects in demyelinating disorders, including multiple sclerosis which is considered the archetypical demyelinating disease.

Abstract

Over the past decade, Poly (ADP-ribose) polymerase-1 (PARP-1) inhibitors have arisen as a novel and promising targeted therapy for breast cancer gene (BRCA)-mutated ovarian and breast cancer patients. Therapies targeting the enzyme, PARP-1, have since established their place as maintenance drugs for cancer. Here, we present existing evidence that implicates PARP-1 as a player in the development and progression of both malignancy and demyelinating disease. These findings, together with the proven clinical efficacy and marketed success of PARP-1 inhibitors in cancer, present the repurposing of these drugs for demyelinating diseases as a desirable therapeutic concept. Indeed, PARP-1 inhibitors are noted to demonstrate neuroprotective effects in demyelinating disorders such as multiple sclerosis and Parkinson’s disease, further supporting the use of these drugs in demyelinating, neuroinflammatory, and neurodegenerative diseases. In this review, we discuss the potential for repurposing PARP-1 inhibitors, with a focus on rare demyelinating diseases. In particular, we address the possible use of PARP-1 inhibitors in examples of rare leukodystrophies, for which there are a paucity of treatment options and an urgent need for novel therapeutic approaches.

Hospitalization Burden and Incidence of Krabbe Disease

OBJECTIVE

The purpose of our study was to understand the healthcare burden and incidence of Krabbe disease (Krabbe).

METHODS

Retrospective analysis of Krabbe patients identified October 1, 2015 through December 31, 2020, ages birth through age 3, evaluated in two national databases. We estimated point prevalence and incidence from year 2016 data.

RESULTS

We identified 98 unique Krabbe patients with 736 visits including 260 were inpatient admissions. Total healthcare charges were $51.5 million dollars. We determined a point prevalence of 34 68 Krabbe patients in 2016 ages 0 3 years. This estimates a birth incidence of ~1 in 310,000 live births. Significance: Krabbe disease patients had over $51 million in health care charges and hundreds of hospitalizations. Estimated prevalence and birth incidence is similar to rates observed from newborn screening. Our findings show the tremendous health impacts of Krabbe disease, and provide guidance for efforts in screening and treatment planning.

Krabbe Disease: Prospects of Finding a Cure Using AAV Gene Therapy

Krabbe Disease (KD) is an autosomal metabolic disorder that affects both the central and peripheral nervous systems. It is caused by a functional deficiency of the lysosomal enzyme, galactocerebrosidase (GALC), resulting in an accumulation of the toxic metabolite, psychosine. Psychosine accumulation affects many different cellular pathways, leading to severe demyelination. Although there is currently no effective therapy for Krabbe disease, recent gene therapy-based approaches in animal models have indicated a promising outlook for clinical treatment. This review highlights recent findings in the pathogenesis of Krabbe disease, and evaluates AAV-based gene therapy as a promising strategy for treating this devastating pediatric disease.

National U.S. Patient and Transplant Data for Krabbe Disease

Krabbe disease (KD) is a leukodystrophy caused by mutations in the galactosylceramidase gene. Presymptomatic hematopoietic stem cell transplantation (HSCT) is associated with improved outcomes, but most data are from single-center studies. Our objective was to characterize national patterns of HSCT for KD including whether there were disparities in HSCT utilization and outcomes. We conducted a retrospective study of KD patients ≤ age 18 years from November 1, 2015, through December 31, 2019, using the U.S. Children's Hospital Association's Pediatric Health Information System database. We evaluated outcomes for HSCT, intensive care unit days, and mortality, comparing age, sex, race/ethnicity, rural/urban location, and median household income. We identified 91 KD patients. HSCT, performed in 32% of patients, was associated with reduced mortality, 31 vs. 68% without HSCT (p < 0.003). Trends included the fact that more males than females had HSCT (39 vs. 23%); more Asian and White patients had HSCT compared to Black or Hispanic patients (75, 33, 25, and 17%, respectively); and patients from households with the lowest-income quartile (< $25,000) had more HSCT compared to higher-income quartiles (44 vs. 33, 30, and 0%). Overall, receiving HSCT was associated with reduced mortality. We noted trends in patient groups who received HSCT. Our findings suggest that disparities in receiving HSCT could affect outcomes for KD patients.

Mechanisms of demyelination and neurodegeneration in globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD), also known as Krabbe disease, is a lysosomal storage disorder causing extensive demyelination in the central and peripheral nervous systems. GLD is caused by loss-of-function mutations in the lysosomal hydrolase, galactosylceramidase (GALC), which catabolizes the myelin sphingolipid galactosylceramide. The pathophysiology of GLD is complex and reflects the expression of GALC in a number of glial and neural cell types in both the central and peripheral nervous systems (CNS and PNS), as well as leukocytes and kidney in the periphery. Over the years, GLD has garnered a wide range of scientific and medical interests, especially as a model system to study gene therapy and novel preclinical therapeutic approaches to treat the spontaneous murine model for GLD. Here, we review recent findings in the field of Krabbe disease, with particular emphasis on novel aspects of GALC physiology, GLD pathophysiology, and therapeutic strategies.

Sphingosine kinase 2 is essential for remyelination following cuprizone intoxication

Therapeutics that promote oligodendrocyte survival and remyelination are needed to restore neurological function in demyelinating diseases. Sphingosine 1-phosphate (S1P) is an essential lipid metabolite that signals through five G-protein coupled receptors. S1P receptor agonists such as Fingolimod are valuable immunosuppressants used to treat multiple sclerosis, and promote oligodendrocyte survival. However, the role for endogenous S1P, synthesized by the enzyme sphingosine kinase 2 (SphK2), in oligodendrocyte survival and myelination has not been established. This study investigated the requirement for SphK2 in oligodendrocyte survival and remyelination using the cuprizone mouse model of acute demyelination, followed by spontaneous remyelination. Oligodendrocyte density did not differ between untreated wild-type (WT) and SphK2 knockout (SphK2^-/- ) mice. However, cuprizone treatment caused significantly greater loss of mature oligodendrocytes in SphK2^-/- compared to WT mice. Following cuprizone withdrawal, spontaneous remyelination occurred in WT but not SphK2^-/- mice, even though progenitor and mature oligodendrocyte density increased in both genotypes. Levels of cytotoxic sphingosine and ceramide were higher in the corpus callosum of SphK2^-/- mice, and in contrast to WT mice, did not decline following cuprizone withdrawal in SphK2^-/- mice. We also observed a significant reduction in myelin thickness with aging in SphK2^-/- compared to WT mice. These results provide the first evidence that SphK2, the dominant enzyme catalyzing S1P synthesis in the adult brain, is essential for remyelination following a demyelinating insult and myelin maintenance with aging. We propose that persistently high levels of sphingosine and ceramide, a direct consequence of SphK2 deficiency, may block remyelination.

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.

Fingolimod as a Treatment in Neurologic Disorders Beyond Multiple Sclerosis

Fingolimod is an approved treatment for relapsing-remitting multiple sclerosis (MS), and its properties in different pathways have raised interest in therapy research for other neurodegenerative diseases. Fingolimod is an agonist of sphingosine-1-phosphate (S1P) receptors. Its main pharmacologic effect is immunomodulation by lymphocyte homing, thereby reducing the numbers of T and B cells in circulation. Because of the ubiquitous expression of S1P receptors, other effects have also been described. Here, we review preclinical experiments evaluating the effects of treatment with fingolimod in neurodegenerative diseases other than MS, such as Alzheimer's disease or epilepsy. Fingolimod has shown neuroprotective effects in different animal models of neurodegenerative diseases, summarized here, correlating with increased brain-derived neurotrophic factor and improved disease phenotype (cognition and/or motor abilities). As expected, treatment also induced reductions in different neuroinflammatory markers because of not only inhibition of lymphocytes but also direct effects on astrocytes and microglia. Furthermore, fingolimod treatment exhibited additional effects for specific neurodegenerative disorders, such as reduction of amyloid-β production, and antiepileptogenic properties. The neuroprotective effects exerted by fingolimod in these preclinical studies are reviewed and support the translation of fingolimod into clinical trials as treatment in neurodegenerative diseases beyond neuroinflammatory conditions (MS).

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.