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

An exploratory metabolomic comparison of participants with fast or absent functional progression from 2CARE, a randomized, double-blind clinical trial in Huntington's disease

Huntington's disease (HD) is increasingly recognized for diverse pathology outside of the nervous system. To describe the biology of HD in relation to functional progression, we previously analyzed the plasma and CSF metabolome in a cross-sectional study of participants who had various degrees of functional impairment. Here, we carried out an exploratory study in plasma from HD individuals over a 3-year time frame to assess whether differences exist between those with fast or absent clinical progression. There were more differences in circulating metabolite levels for fast progressors compared to absent progressors (111 vs 20, nominal p < 0.05). All metabolite changes in faster progressors were decreases, whereas some metabolite concentrations increased in absent progressors. Many of the metabolite levels that decreased in the fast progressors were higher at Screening compared to absent progressors but ended up lower by Year 3. Changes in faster progression suggest greater oxidative stress and inflammation (kynurenine, diacylglycerides, cysteine), disturbances in nitric oxide and urea metabolism (arginine, citrulline, ornithine, GABR), lower polyamines (putrescine and spermine), elevated glucose, and deficient AMPK signaling. Metabolomic differences between fast and absent progressors suggest the possibility of predicting functional decline in HD, and possibly delaying it with interventions to augment arginine, polyamines, and glucose regulation.

Sphingosine 1-Phosphate Lyase in the Developing and Injured Nervous System: a Dichotomy?

Sphingosine 1-phosphate lyase (SPL) is the terminal enzyme that controls the degradation of the bioactive lipid sphingosine 1-phosphate (S1P) within an interconnected sphingolipid metabolic network. The unique metabolic position of SPL in maintaining S1P levels implies SPL could be an emerging new therapeutic target. Over the past decade, an evolving effort has been made to unravel the role of SPL in the nervous system; however, to what extent SPL influences the developing and mature nervous system through altering S1P biosynthesis remains opaque. While congenital SPL deletion is associated with deficits in the developing nervous system, the loss of SPL activity in adults appears to be neuroprotective in acquired neurological disorders. The controversial findings concerning SPL's role in the nervous system are further constrained by the current genetic and pharmacological tools. This review attempts to focus on the multi-faceted nature of SPL function in the mammalian nervous systems, implying its dichotomy in the developing and adult central nervous system (CNS). This article also highlights SPL is emerging as a therapeutic molecule that can be selectively targeted to modulate S1P for the treatment of acquired neurodegenerative diseases, raising new questions for future investigation. The development of cell-specific inducible conditional SPL mutants and selective pharmacological tools will allow the precise understanding of SPL's function in the adult CNS, which will aid the development of a new strategy focusing on S1P-based therapies for neuroprotection.

Genome-wide screening in pluripotent cells identifies Mtf1 as a suppressor of mutant huntingtin toxicity

Huntington's disease (HD) is a neurodegenerative disorder caused by CAG-repeat expansions in the huntingtin (HTT) gene. The resulting mutant HTT (mHTT) protein induces toxicity and cell death via multiple mechanisms and no effective therapy is available. Here, we employ a genome-wide screening in pluripotent mouse embryonic stem cells (ESCs) to identify suppressors of mHTT toxicity. Among the identified suppressors, linked to HD-associated processes, we focus on Metal response element binding transcription factor 1 (Mtf1). Forced expression of Mtf1 counteracts cell death and oxidative stress caused by mHTT in mouse ESCs and in human neuronal precursor cells. In zebrafish, Mtf1 reduces malformations and apoptosis induced by mHTT. In R6/2 mice, Mtf1 ablates motor defects and reduces mHTT aggregates and oxidative stress. Our screening strategy enables a quick in vitro identification of promising suppressor genes and their validation in vivo, and it can be applied to other monogenic diseases.

Novel therapeutic approaches to target neurodegeneration

Ageing is the main risk factor common to most primary neurodegenerative disorders. Indeed, age-related brain alterations have been long considered to predispose to neurodegeneration. Although protein misfolding and the accumulation of toxic protein aggregates have been considered as causative events in neurodegeneration, several other biological pathways affected by brain ageing also contribute to pathogenesis. Here, we discuss the evidence showing the involvement of the mechanisms controlling neuronal structure, gene expression, autophagy, cell metabolism and neuroinflammation in the onset and progression of neurodegenerative disorders. Furthermore, we review the therapeutic strategies currently under development or as future approaches designed to normalize these pathways, which may then increase brain resilience to cope with toxic protein species. In addition to therapies targeting the insoluble protein aggregates specifically associated with each neurodegenerative disorder, these novel pharmacological approaches may be part of combined therapies designed to rescue brain function.

Repurposing drugs against Alzheimer's disease: can the anti-multiple sclerosis drug fingolimod (FTY720) effectively tackle inflammation processes in AD?

Therapeutic approaches providing effective medication for Alzheimer's disease (AD) patients after disease onset are urgently needed. Previous studies in AD mouse models and in humans suggested that physical exercise or changed lifestyle can delay AD-related synaptic and memory dysfunctions when treatment started in juvenile animals or in elderly humans before onset of disease symptoms. However, a pharmacological treatment that can reverse memory deficits in AD patients was thus far not identified. Importantly, AD disease-related dysfunctions have increasingly been associated with neuro-inflammatory mechanisms and searching for anti-inflammatory medication to treat AD seems promising. Like for other diseases, repurposing of FDA-approved drugs for treatment of AD is an ideally suited strategy to reduce the time to bring such medication into clinical practice. Of note, the sphingosine-1-phosphate analogue fingolimod (FTY720) was FDA-approved in 2010 for treatment of multiple sclerosis patients. It binds to the five different isoforms of Sphingosine-1-phosphate receptors (S1PRs) that are widely distributed across human organs. Interestingly, recent studies in five different mouse models of AD suggest that FTY720 treatment, even when starting after onset of AD symptoms, can reverse synaptic deficits and memory dysfunction in these AD mouse models. Furthermore, a very recent multi-omics study identified mutations in the sphingosine/ceramide pathway as a risk factor for sporadic AD, suggesting S1PRs as promising drug target in AD patients. Therefore, progressing with FDA-approved S1PR modulators into human clinical trials might pave the way for these potential disease modifying anti-AD drugs.

Treatment with the Glycosphingolipid Modulator THI Rescues Myelin Integrity in the Striatum of R6/2 HD Mice

Huntington's disease is one of the most common dominantly inherited neurodegenerative disorders caused by an expansion of a polyglutamine (polyQ) stretch in the N-terminal region of huntingtin (Htt). Among all the molecular mechanisms, affected by the mutation, emerging evidence proposes glycosphingolipid dysfunction as one of the major determinants. High levels of sphingolipids have been found to localize in the myelin sheaths of oligodendrocytes, where they play an important role in myelination stability and functions. In this study, we investigated any potential existing link between sphingolipid modulation and myelin structure by performing both ultrastructural and biochemical analyses. Our findings demonstrated that the treatment with the glycosphingolipid modulator THI preserved myelin thickness and the overall structure and reduced both area and diameter of pathologically giant axons in the striatum of HD mice. These ultrastructural findings were associated with restoration of different myelin marker protein, such as myelin-associated glycoprotein (MAG), myelin basic protein (MBP) and 2', 3' Cyclic Nucleotide 3'-Phosphodiesterase (CNP). Interestingly, the compound modulated the expression of glycosphingolipid biosynthetic enzymes and increased levels of GM1, whose elevation has been extensively reported to be associated with reduced toxicity of mutant Htt in different HD pre-clinical models. Our study further supports the evidence that the metabolism of glycosphingolipids may represent an effective therapeutic target for the disease.

The role of sphingosine 1-phosphate metabolism in brain health and disease

Lipids are essential structural and functional components of the central nervous system (CNS). Sphingolipids are ubiquitous membrane components which were discovered in the brain in the late 19^th century. In mammals, the brain contains the highest concentration of sphingolipids in the body. Sphingosine 1-phosphate (S1P) derived from membrane sphingolipids evokes multiple cellular responses which, depending on its concentration and localization, make S1P a double-edged sword in the brain. In the present review we highlight the role of S1P in brain development and focus on the often contrasting findings regarding its contributions to the initiation, progression and potential recovery of different brain pathologies, including neurodegeneration, multiple sclerosis (MS), brain cancers, and psychiatric illnesses. A detailed understanding of the critical implications of S1P in brain health and disease may open the door for new therapeutic options. Thus, targeting S1P-metabolizing enzymes and/or signaling pathways might help overcome, or at least ameliorate, several brain illnesses.

Time- and Sex-Dependent Effects of Fingolimod Treatment in a Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia. Fingolimod has previously shown beneficial effects in different animal models of AD. However, it has shown contradictory effects when it has been applied at early disease stages. Our objective was to evaluate fingolimod in two different treatment paradigms. To address this aim, we treated male and female APP-transgenic mice for 50 days, starting either before plaque deposition at 50 days of age (early) or at 125 days of age (late). To evaluate the effects, we investigated the neuroinflammatory and glial markers, the Aβ load, and the concentration of the brain-derived neurotrophic factor (BDNF). We found a reduced Aβ load only in male animals in the late treatment paradigm. These animals also showed reduced microglia activation and reduced IL-1β. No other treatment group showed any difference in comparison to the controls. On the other hand, we detected a linear correlation between BDNF and the brain Aβ concentrations. The fingolimod treatment has shown beneficial effects in AD models, but the outcome depends on the neuroinflammatory state at the start of the treatment. Thus, according to our data, a fingolimod treatment would be effective after the onset of the first AD symptoms, mainly affecting the neuroinflammatory reaction to the ongoing Aβ deposition.

Treatment with THI, an inhibitor of sphingosine-1-phosphate lyase, modulates glycosphingolipid metabolism and results therapeutically effective in experimental models of Huntington's disease

Huntington's disease (HD) is a fatal neurodegenerative disorder with no effective cure currently available. Over the past few years our research has shown that alterations in sphingolipid metabolism represent a critical determinant in HD pathogenesis. In particular, aberrant metabolism of sphingosine-1-phosphate (S1P) has been reported in multiple disease settings, including human postmortem brains from HD patients. In this study, we investigate the potential therapeutic effect of the inhibition of S1P degradative enzyme SGPL1, by the chronic administration of the 2-acetyl-5-tetrahydroxybutyl imidazole (THI) inhibitor. We show that THI mitigated motor dysfunctions in both mouse and fly models of HD. The compound evoked the activation of pro-survival pathways, normalized levels of brain-derived neurotrophic factor, preserved white matter integrity, and stimulated synaptic functions in HD mice. Metabolically, THI restored normal levels of hexosylceramides and stimulated the autophagic and lysosomal machinery, facilitating the reduction of nuclear inclusions of both wild-type and mutant huntingtin proteins.

Neuroinflammation in Parkinson"s Disease and its Treatment Opportunities

Parkinson’s disease (PD) is a complex, chronic, and progressive neurodegenerative disease that is characterized by irreversible dopaminergic neuronal loss in the substantia nigra. Alpha-synuclein is normally a synaptic protein that plays a key role in PD due to pathological accumulation as oligomers or fibrils. Clustered alpha-synuclein binds to the Toll-like receptors and activates the microglia, which initiates a process that continues with pro-inflammatory cytokine production and secretion. Pro-inflammatory cytokine overproduction and secretion induce cell death and accelerate PD progression. Microglia are found in a resting state in physiological conditions. Microglia became activated by stimulating Toll-like receptors on it under pathological conditions, such as alpha-synuclein aggregation, environmental toxins, or oxidative stress. The interaction between Toll-like receptors and its downstream pathway triggers an activation series, leads to nuclear factor-kappa B activation, initiates the inflammasome formation, and increases cytokine levels. This consecutive inflammatory process leads to dopaminergic cell damage and cell death. Microglia become overactive in response to chronic inflammation, which is observed in PD and causes excessive cytotoxic factor production, such as reactive oxidase, nitric oxide, and tumor necrosis factor-alpha. This inflammatory process contributes to the exacerbation of pathology by triggering neuronal damage or death. Current treatments, such as dopaminergic agonists, anticholinergics, or monoamine oxidase inhibitors alleviate PD symptoms, but they can not stop the disease progression. Finding a radical treatment option or stopping the progression is essential when considering that PD is the second most reported neurodegenerative disorder. Many cytokines are released during inflammation, and they can start the phagocytic process, which caused the degradation of infected cells along with healthy ones. Therefore, targeting the pathological mechanisms, such as microglial activation, mitochondrial dysfunction, and oxidative stress, that should be involved in the treatment program is important. Neuroinflammation is one of the key factors involved in PD pathogenesis as well as alpha-synuclein accumulation, synaptic dysfunction, or dopaminergic neuronal loss, especially in the substantia nigra. Therefore, evaluating the therapeutic efficiency of the mechanisms is important, such as microglial activation and nuclear factor-kappa B pathway or inflammasome formation inhibition, and cytokine release interruption against neuroinflammation may create new treatment possibilities for PD. This study examined the pathological relation between PD and neuroinflammation, and targeting neuroinflammation as an opportunity for PD treatments, such as Toll-like receptor antagonists, NOD-like receptor family pyrin domain containing-3 inflammasome inhibitors, cytokine inhibitors, peroxisome proliferator-activated receptor-γ agonists, reactive oxygen species inhibitors, and nonsteroidal anti-inflammatory drugs.

Positive effect of immunomodulatory therapies on disease progression in Huntington's disease? Data from a real-world cohort

Background:

The role of neuroinflammation and autoimmune processes in neurodegenerative diseases is not fully understood. Activation of microglia with expression of proinflammatory cytokines supports the hypothesis that immune processes may play an important role in the pathophysiology of Huntington’s disease (HD) and thus, immunomodulating therapies might have potential neuroprotective properties. Until now, no disease-modifying therapy (DMT) is available for HD.

Objective:

The aim of this research was to characterize a cohort of patients suffering from both HD and autoimmune demyelinating diseases of the central nervous system (classified as G35-37 in ICD-10; ADD-CNS) in comparison to HD cases without ADD-CNS. In particular, we were interested to investigate potential modulating effects on disease manifestation and progression of HD over time of prescribed immunomodulating medications (DMT).

Methods:

We analyzed the course of HD regarding motoric, functional, and cognitive aspects, using longitudinal data of up to 2 years from the worldwide registry study ENROLL-HD. Additional cross-sectional data in the largest cohort worldwide of HD patients was analyzed using demographic and molecular genetic parameters. Data were analyzed using analysis of variance (ANOVA) for cross-sectional and repeated-measures ANOVA for longitudinal parameters in IBM SPSS Statistics V.27.

Results:

Within the ENROLL-HD database, we investigated N = 21,116 participants and identified n = 60 participants suffering from ADD-CNS. Molecular, genetic, and demographic data did not differ between groups. The subgroup of n = 32 participants with motor-manifest HD revealed better cognitive performance in five out of eight cognitive tests at baseline with less progression over time in two tests (all p < 0.05). Differentiation between DMT-treated and untreated patients revealed better cognitive and motor performance in the DMT group; those patients, however, tended to be younger. Pre-manifest HD patients simultaneously diagnosed with ADD-CNS (n = 12) showed lower functional scores and more decline over time when compared with other pre-manifest HD (p < 0.05).

Conclusion:

Patients suffering from motor-manifest HD and simultaneously from ADD-CNS have better cognitive capacities compared with other motor-manifest HD patients. Moreover, DMTs might have beneficial effects on progression of neurodegeneration including the motor phenotype. However, this effect might have been biased by younger age in DMT-treated patients. Pre-manifest HD patients showed more functional impairment as expected due to their additional ADD-CNS disease.

Ceramide/Sphingosine 1-Phosphate Axis as a Key Target for Diagnosis and Treatment in Alzheimer’s Disease and Other Neurodegenerative Diseases

Alzheimer’s disease (AD) is considered the most prevalent neurodegenerative disease and the leading cause of dementia worldwide. Sphingolipids, such as ceramide or sphingosine 1-phosphate, are bioactive molecules implicated in structural and signaling functions. Metabolic dysfunction in the highly conserved pathways to produce sphingolipids may lead to or be a consequence of an underlying disease. Recent studies on transcriptomics and sphingolipidomics have observed alterations in sphingolipid metabolism of both enzymes and metabolites involved in their synthesis in several neurodegenerative diseases, including AD. In this review, we highlight the most relevant findings related to ceramide and neurodegeneration, with a special focus on AD.

A Brief Overview on BDNF-Trk Pathway in the Nervous System: A Potential Biomarker or Possible Target in Treatment of Multiple Sclerosis?

The growing incidence of neurodegenerative disorders in our populations is leading the research to identify potential biomarkers and targets for facilitating their early management and treatments. Biomarkers represent the crucial indicators of both physiological and pathological processes. Specific changes in molecular and cellular mechanisms of physiological processes result in biochemical alterations at systemic level, which can give us comprehensive information regarding the nature of any disease. In addition, any disease biomarker should be specific and reliable, able to consent of distinguishing the physiological condition of a tissue, organ, or system from disease, and be diverse among the various diseases, or subgroups or phenotypes of them. Accordingly, biomarkers can predict chances for diseases, facilitate their early diagnosis, and set guidelines for the development of new therapies for treating diseases and disease-making process. Here, we focus our attention on brain neurotrophic factor (BDNF)–tropomyosin receptor kinase (Trk) pathway, describing its multiple roles in the maintenance of central nervous system (CNS) health, as well as its implication in the pathogenesis of multiple sclerosis (MS). In addition, we also evidence the features of such pathway, which make of it a potential MS biomarker and therapeutic target.

Molecular Pharmacology and Novel Potential Therapeutic Applications of Fingolimod

Fingolimod is a well-tolerated, highly effective disease-modifying therapy successfully utilized in the management of multiple sclerosis. The active metabolite, fingolimod-phosphate, acts on sphingosine-1-phosphate receptors (S1PRs) to bring about an array of pharmacological effects. While being initially recognized as a novel agent that can profoundly reduce T-cell numbers in circulation and the CNS, thereby suppressing inflammation and MS, there is now rapidly increasing knowledge on its previously unrecognized molecular and potential therapeutic effects in diverse pathological conditions. In addition to exerting inhibitory effects on sphingolipid pathway enzymes, fingolimod also inhibits histone deacetylases, transient receptor potential cation channel subfamily M member 7 (TRMP7), cytosolic phospholipase A2α (cPLA2α), reduces lysophosphatidic acid (LPA) plasma levels, and activates protein phosphatase 2A (PP2A). Furthermore, fingolimod induces apoptosis, autophagy, cell cycle arrest, epigenetic regulations, macrophages M1/M2 shift and enhances BDNF expression. According to recent evidence, fingolimod modulates a range of other molecular pathways deeply rooted in disease initiation or progression. Experimental reports have firmly associated the drug with potentially beneficial therapeutic effects in immunomodulatory diseases, CNS injuries, and diseases including Alzheimer's disease (AD), Parkinson's disease (PD), epilepsy, and even cancer. Attractive pharmacological effects, relative safety, favorable pharmacokinetics, and positive experimental data have collectively led to its testing in clinical trials. Based on the recent reports, fingolimod may soon find its way as an adjunct therapy in various disparate pathological conditions. This review summarizes the up-to-date knowledge about molecular pharmacology and potential therapeutic uses of fingolimod.

Implications of Sphingolipids on Aging and Age-Related Diseases

Aging is a process leading to a progressive loss of physiological integrity and homeostasis, and a primary risk factor for many late-onset chronic diseases. The mechanisms underlying aging have long piqued the curiosity of scientists. However, the idea that aging is a biological process susceptible to genetic manipulation was not well established until the discovery that the inhibition of insulin/IGF-1 signaling extended the lifespan of C. elegans. Although aging is a complex multisystem process, López-Otín et al. described aging in reference to nine hallmarks of aging. These nine hallmarks include: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. Due to recent advances in lipidomic, investigation into the role of lipids in biological aging has intensified, particularly the role of sphingolipids (SL). SLs are a diverse group of lipids originating from the Endoplasmic Reticulum (ER) and can be modified to create a vastly diverse group of bioactive metabolites that regulate almost every major cellular process, including cell cycle regulation, senescence, proliferation, and apoptosis. Although SL biology reaches all nine hallmarks of aging, its contribution to each hallmark is disproportionate. In this review, we will discuss in detail the major contributions of SLs to the hallmarks of aging and age-related diseases while also summarizing the importance of their other minor but integral contributions.

Sphingosine 1-phosphate receptor modulators in multiple sclerosis and other conditions

The sphingosine 1-phosphate (S1P) signalling pathways have important and diverse functions. S1P receptors (S1PRs) have been proposed as a therapeutic target for various diseases due to their involvement in regulation of lymphocyte trafficking, brain and cardiac function, vascular permeability, and vascular and bronchial tone. S1PR modulators were first developed to prevent rejection by the immune system following renal transplantation, but the only currently approved indication is multiple sclerosis. The primary mechanism of action of S1PR modulators in multiple sclerosis is through binding S1PR subtype 1 on lymphocytes resulting in internalisation of the receptor and loss of responsiveness to the S1P gradient that drives lymphocyte egress from lymph nodes. The reduction in circulating lymphocytes presumably limits inflammatory cell migration into the CNS. Four S1PR modulators (fingolimod, siponimod, ozanimod, and ponesimod) have regulatory approval for multiple sclerosis. Preclinical evidence and ongoing and completed clinical trials support development of S1PR modulators for other therapeutic indications.

Novelty of Sphingolipids in the Central Nervous System Physiology and Disease: Focusing on the Sphingolipid Hypothesis of Neuroinflammation and Neurodegeneration

For decades, lipids were confined to the field of structural biology and energetics as they were considered only structural constituents of cellular membranes and efficient sources of energy production. However, with advances in our understanding in lipidomics and improvements in the technological approaches, astounding discoveries have been made in exploring the role of lipids as signaling molecules, termed bioactive lipids. Among these bioactive lipids, sphingolipids have emerged as distinctive mediators of various cellular processes, ranging from cell growth and proliferation to cellular apoptosis, executing immune responses to regulating inflammation. Recent studies have made it clear that sphingolipids, their metabolic intermediates (ceramide, sphingosine-1-phosphate, and N-acetyl sphingosine), and enzyme systems (cyclooxygenases, sphingosine kinases, and sphingomyelinase) harbor diverse yet interconnected signaling pathways in the central nervous system (CNS), orchestrate CNS physiological processes, and participate in a plethora of neuroinflammatory and neurodegenerative disorders. Considering the unequivocal importance of sphingolipids in CNS, we review the recent discoveries detailing the major enzymes involved in sphingolipid metabolism (particularly sphingosine kinase 1), novel metabolic intermediates (N-acetyl sphingosine), and their complex interactions in CNS physiology, disruption of their functionality in neurodegenerative disorders, and therapeutic strategies targeting sphingolipids for improved drug approaches.

Differential Diagnosis of Chorea-HIV Infection Delays Diagnosis of Huntington's Disease by Years

Background: There is a broad range of potential differential diagnoses for chorea. Besides rare, inherited neurodegenerative diseases such as Huntington’s disease (HD) chorea can accompany basal ganglia disorders due to vasculitis or infections, e.g., with the human immunodeficiency virus (HIV). The clinical picture is complicated by the rare occurrence of HIV infection and HD. Methods: First, we present a case suffering simultaneously from HIV and HD (HIV/HD) focusing on clinical manifestation and disease onset. We investigated cross-sectional data regarding molecular genetic, motoric, cognitive, functional, and psychiatric disease manifestation of HIV/HD in comparison to motor-manifest HD patients without HIV infection (nonHIV/HD) in the largest cohort of HD patients worldwide using the registry study ENROLL-HD. Data were analyzed using ANCOVA analyses controlling for covariates of age and CAG repeat length between groups in IBM SPSS Statistics V.25. Results: The HD diagnosis in our case report was delayed by approximately nine years due to the false assumption that the HIV infection might have been the cause of chorea. Out of n = 21,116 participants in ENROLL-HD, we identified n = 10,125 motor-manifest HD patients. n = 23 male participants were classified as suffering from HIV infection as a comorbidity, compared to n = 4898 male non-HIV/HD patients. Except for age, with HIV/HD being significantly younger (p < 0.050), we observed no group differences regarding sociodemographic, genetic, educational, motoric, functional, and cognitive parameters. Male HIV/HD patients reported about a 5.3-year-earlier onset of HD symptoms noticed by themselves compared to non-HIV/HD (p < 0.050). Moreover, patients in the HIV/HD group had a longer diagnostic delay of 1.8 years between onset of symptoms and HD diagnosis and a longer time regarding assessment of first symptoms by the rater and judgement of the patient (all p < 0.050). Unexpectedly, HIV/HD patients showed less irritability in the Hospital Anxiety and Depression Scale (all p < 0.05). Conclusions: The HD diagnosis in HIV-infected male patients is secured with a diagnostic delay between first symptoms noticed by the patient and final diagnosis. Treating physicians therefore should be sensitized to think of potential alternative diagnoses in HIV-infected patients also afflicted by movement disorders, especially if there is evidence of subcortical atrophy and a history of hyperkinesia, even without a clear HD-family history. Those patients should be transferred for early genetic testing to avoid further unnecessary diagnostics and improve sociomedical care.

An Overview of the Efficacy and Safety of Ozanimod for the Treatment of Relapsing Multiple Sclerosis

Multiple sclerosis (MS) is a complex disease of the central nervous system that can cause permanent disability in young adults. A large armamentarium is available for its management and is increasing over time. Ozanimod is an oral drug belonging to the sphingosine-1-phosphate receptor (S1PR) modulator family recently approved in different countries for MS with active disease. It selectively modulates S1PR1 and S1PR5 to prevent autoreactive lymphocytes from entering the central nervous system (CNS), where they can determine inflammation and neurodegeneration. Ozanimod was tested in one Phase II and two Phase III pivotal trials and was shown to be effective and well tolerated. Moreover, further investigations, including comparative trials with other S1P modulators and MS disease-modifying drugs, are needed to better define placement in MS treatment. Furthermore, ozanimod is currently under evaluation for inflammatory bowel diseases, such as ulcerative colitis and Crohn’s disease, in international phase III studies. This article retraces the itinerary leading to the approval of ozanimod for MS treatment and its peculiarities and potentiality inside the S1PR modulator family.

Anti-Inflammatory Treatment with FTY720 Starting after Onset of Symptoms Reverses Synaptic Deficits in an AD Mouse Model

Therapeutic approaches providing effective medication for Alzheimer's disease (AD) patients after disease onset are urgently needed. Previous studies in AD mouse models suggested that physical exercise or changed lifestyle can delay AD-related synaptic and memory dysfunctions when treatment started in juvenile animals long before onset of disease symptoms, while a pharmacological treatment that can reverse synaptic and memory deficits in AD mice was thus far not identified. Repurposing food and drug administration (FDA)-approved drugs for treatment of AD is a promising way to reduce the time to bring such medication into clinical practice. The sphingosine-1 phosphate analog fingolimod (FTY720) was approved recently for treatment of multiple sclerosis patients. Here, we addressed whether fingolimod rescues AD-related synaptic deficits and memory dysfunction in an amyloid precursor protein/presenilin-1 (APP/PS1) AD mouse model when medication starts after onset of symptoms (at five months). Male mice received intraperitoneal injections of fingolimod for one to two months starting at five to six months. This treatment rescued spine density as well as long-term potentiation in hippocampal cornu ammonis-1 (CA1) pyramidal neurons, that were both impaired in untreated APP/PS1 animals at six to seven months of age. Immunohistochemical analysis with markers of microgliosis (ionized calcium-binding adapter molecule 1; Iba1) and astrogliosis (glial fibrillary acid protein; GFAP) revealed that our fingolimod treatment regime strongly down regulated neuroinflammation in the hippocampus and neocortex of this AD model. These effects were accompanied by a moderate reduction of Aβ accumulation in hippocampus and neocortex. Our results suggest that fingolimod, when applied after onset of disease symptoms in an APP/PS1 mouse model, rescues synaptic pathology that is believed to underlie memory deficits in AD mice, and that this beneficial effect is mediated via anti-neuroinflammatory actions of the drug on microglia and astrocytes.

Curcumin-Loaded Nanoparticles Based on Amphiphilic Hyaluronan-Conjugate Explored as Targeting Delivery System for Neurodegenerative Disorders

Identification of molecules able to promote neuroprotective mechanisms can represent a promising therapeutic approach to neurodegenerative disorders including Huntington's disease. Curcumin is an antioxidant and neuroprotective agent, even though its efficacy is limited by its poor absorption, rapid metabolism, systemic elimination, and limited blood-brain barrier (BBB) permeability. Herein, we report on novel biodegradable curcumin-containing nanoparticles to favor the compound delivery and potentially enhance its brain bioavailability. The prepared hyaluronan-based materials able to self-assemble in stable spherical nanoparticles, consist of natural fatty acids chemically conjugated to the natural polysaccharide. The aim of this study is to provide a possible effective delivery system for curcumin with the expectation that, after having released the drug at the specific site, the biopolymer can degrade to nontoxic fragments before renal excretion, since all the starting materials are provided by natural resource. Our findings demonstrate that curcumin-encapsulated nanoparticles enter the cells and reduce their susceptibility to apoptosis in an in vitro model of Huntington's disease.

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).

The longevity-associated variant of BPIFB4 improves a CXCR4-mediated striatum-microglia crosstalk preventing disease progression in a mouse model of Huntington's disease

The longevity-associated variant (LAV) of the bactericidal/permeability-increasing fold-containing family B member 4 (BPIFB4) has been found significantly enriched in long-living individuals. Neuroinflammation is a key player in Huntington's disease (HD), a neurodegenerative disorder caused by neural death due to expanded CAG repeats encoding a long polyglutamine tract in the huntingtin protein (Htt). Herein, we showed that striatal-derived cell lines with expanded Htt (STHdh Q^111/111) expressed and secreted lower levels of BPIFB4, when compared with Htt expressing cells (STHdh Q^7/7), which correlated with a defective stress response to proteasome inhibition. Overexpression of LAV-BPIFB4 in STHdh Q^111/111 cells was able to rescue both the BPIFB4 secretory profile and the proliferative/survival response. According to a well-established immunomodulatory role of LAV-BPIFB4, conditioned media from LAV-BPIFB4-overexpressing STHdh Q111^/111 cells were able to educate Immortalized Human Microglia-SV40 microglial cells. While STHdh Q^111/111 dying cells were ineffective to induce a CD163 + IL-10^high pro-resolving microglia compared to normal STHdh Q^7/7, LAV-BPIFB4 transduction promptly restored the central immune control through a mechanism involving the stromal cell-derived factor-1. In line with the in vitro results, adeno-associated viral-mediated administration of LAV-BPIFB4 exerted a CXCR4-dependent neuroprotective action in vivo in the R6/2 HD mouse model by preventing important hallmarks of the disease including motor dysfunction, body weight loss, and mutant huntingtin protein aggregation. In this view, LAV-BPIFB4, due to its pleiotropic ability in both immune compartment and cellular homeostasis, may represent a candidate for developing new treatment for HD.

Treatment with K6PC-5, a selective stimulator of SPHK1, ameliorates intestinal homeostasis in an animal model of Huntington's disease

Emerging evidence indicates that Huntington's disease (HD) may be described as multi-organ pathology. In this context, we and others have contributed to demonstrate that the disease is characterized by an impairment of the homeostasis of gastro-intestinal (GI) tract. Sphingolipids represent a class of molecules involved in the regulation and maintenance of different tissues and organs including GI system. In this study, we investigated whether the alteration of Sphingosine-1-phosphate (S1P) metabolism, previously described in human HD brains and animal models, is also detectable peripherally in R6/2 HD mice. Our findings indicate, for the first time, that sphingolipid metabolism is perturbed early in the disease in the intestinal tract of HD mice and, its modulation by K6PC-5, a selective activator of S1P synthesis, preserved intestinal integrity and homeostasis. These results further support the evidence that modulation of sphingolipid pathways may represent a potential therapeutic option in HD and suggest that it has also the potential to counteract the peripheral disturbances which may usually complicate the management of the disease and affect patient's quality of life.

Role of sphingolipid metabolism in neurodegeneration

Sphingolipids are a class of lipids highly enriched in the central nervous system (CNS), which shows great diversity and complexity, and has been implicated in CNS development and function. Alterations in sphingolipid metabolism have been described in multiple diseases, including those affecting the central nervous system (CNS). In this review, we discuss the role of sphingolipid metabolism in neurodegeneration, evaluating its direct roles in neuron development and health, and also in the induction of neurotoxic activities in CNS-resident astrocytes and microglia in the context of neurologic diseases such as multiple sclerosis and Alzheimer's disease. Finally, we focus on the metabolism of gangliosides and sphingosine-1-phosphate, its contribution to the pathogenesis of neurologic diseases, and its potential as a candidate target for the therapeutic modulation of neurodegeneration.

Increased translation as a novel pathogenic mechanism in Huntington's disease

Huntington's disease is a neurodegenerative disorder caused by a CAG repeat expansion in exon 1 of the huntingtin gene. Striatal projection neurons are mainly affected, leading to motor symptoms, but molecular mechanisms involved in their vulnerability are not fully characterized. Here, we show that eIF4E binding protein (4E-BP), a protein that inhibits translation, is inactivated in Huntington's disease striatum by increased phosphorylation. Accordingly, we detected aberrant de novo protein synthesis. Proteomic characterization indicates that translation specifically affects sets of proteins as we observed upregulation of ribosomal and oxidative phosphorylation proteins and downregulation of proteins related to neuronal structure and function. Interestingly, treatment with the translation inhibitor 4EGI-1 prevented R6/1 mice motor deficits, although corticostriatal long-term depression was not markedly changed in behaving animals. At the molecular level, injection of 4EGI-1 normalized protein synthesis and ribosomal content in R6/1 mouse striatum. In conclusion, our results indicate that dysregulation of protein synthesis is involved in mutant huntingtin-induced striatal neuron dysfunction.

Disability progression in relapse-free multiple sclerosis patients on fingolimod versus interferon-beta/glatiramer acetate

BACKGROUND

Disability progression independent of relapses (PIRA) has been described as a frequent phenomenon in relapsing-remitting multiple sclerosis (RRMS).

OBJECTIVE

To compare the occurrence of disability progression in relapse-free RRMS patients on interferon-beta/glatiramer acetate (IFN/GA) versus fingolimod.

METHODS

This study is based on data from the Swiss association for joint tasks of health insurers. Time to relapse and 12-month confirmed disability progression were compared between treatment groups using multivariable Cox regression analysis with confounder adjustment. Inverse-probability weighting was applied to correct for the bias that patients on fingolimod have a higher chance to remain relapse-free than patients on IFN/GA.

RESULTS

We included 1640 patients (64% IFN/GA, 36% fingolimod, median total follow-up time = 4-5 years). Disease-modifying treatment (DMT) groups were well balanced with regard to potential confounders. Disability progression was observed in 155 patients (8.8%) on IFN/GA and 51 (7.6%) on fingolimod, of which 44 and 23 were relapse-free during the initial DMT, respectively. Adjusted standard regression analysis on all patients indicated that those on fingolimod experience less frequently disability progression compared with IFN/GA (hazard ratio = 0.53 (95% confidence interval = 0.37-0.76)). After bias correction, this was also true for patients without relapses (hazard ratio=0.56 (95% confidence interval = 0.32-0.98).

CONCLUSION

Our analysis indicates that fingolimod is superior to IFN/GA in preventing disability progression in both relapsing and relapse-free, young, newly diagnosed RRMS patients.

Beneficial Effects of Fingolimod on Social Interaction, CNS and Peripheral Immune Response in the BTBR Mouse Model of Autism

Autism Spectrum Disorders (ASD) are neurodevelopmental disorders characterized by social communication deficits and repetitive/stereotyped behaviours. We evaluated the effects of a chronic treatment with the immunomodulator drug Fingolimod (FTY720 - a non-selective Sphingosine 1-Phosphate Receptor ligand) in an ASD model, the BTBR T⁺tf/J (BTBR) mouse strain. In adult BTBR males, chronic FTY720 treatment (4 weeks) increased social and vocal response during a male-female interaction and hippocampal expression of BDNF and Neuregulin 1, two trophic factors reduced in BTBR when compared to control C57 mice. FTY720 also re-established the expression of IL-1β and MnSOD in the hippocampus, whereas it did not modify IL-6 mRNA content. In addition to its central effect, FTY720 modulated the activation state of peripheral macrophages in the BTBR model, both in basal conditions and after stimulation with an immune challenge. Furthermore, IL-6 mRNA colonic content of BTBR mice, reduced when compared with C57 mice, was normalized by chronic treatment with FTY720. Our study, while indicating FTY720 as a tool to attenuate relevant alterations of the BTBR neurobehavioural phenotype, emphasizes the importance of gut mucosal immune evaluation as an additional target that deserve to be investigated in preclinical studies of anti-inflammatory therapeutic approaches in ASD.

Lipid rafts and neurodegeneration: structural and functional roles in physiologic aging and neurodegenerative diseases

Lipid rafts are small, dynamic membrane areas characterized by the clustering of selected membrane lipids as the result of the spontaneous separation of glycolipids, sphingolipids, and cholesterol in a liquid-ordered phase. The exact dynamics underlying phase separation of membrane lipids in the complex biological membranes are still not fully understood. Nevertheless, alterations in the membrane lipid composition affect the lateral organization of molecules belonging to lipid rafts. Neural lipid rafts are found in brain cells, including neurons, astrocytes, and microglia, and are characterized by a high enrichment of specific lipids depending on the cell type. These lipid rafts seem to organize and determine the function of multiprotein complexes involved in several aspects of signal transduction, thus regulating the homeostasis of the brain. The progressive decline of brain performance along with physiological aging is at least in part associated with alterations in the composition and structure of neural lipid rafts. In addition, neurodegenerative conditions, such as lysosomal storage disorders, multiple sclerosis, and Parkinson's, Huntington's, and Alzheimer's diseases, are frequently characterized by dysregulated lipid metabolism, which in turn affects the structure of lipid rafts. Several events underlying the pathogenesis of these diseases appear to depend on the altered composition of lipid rafts. Thus, the structure and function of lipid rafts play a central role in the pathogenesis of many common neurodegenerative diseases.jlr;61/5/636/F1F1f1.

Pharmacological Tools to Modulate Autophagy in Neurodegenerative Diseases

Considerable evidences suggest a link between autophagy dysfunction, protein aggregation, and neurodegenerative diseases. Given that autophagy is a conserved intracellular housekeeping process, modulation of autophagy flux in various model organisms have highlighted its importance for maintaining proteostasis. In postmitotic cells such as neurons, compromised autophagy is sufficient to cause accumulation of ubiquitinated aggregates, neuronal dysfunction, degeneration, and loss of motor coordination-all hallmarks of neurodegenerative diseases. Reciprocally, enhanced autophagy flux augments cellular and organismal health, in addition to extending life span. These genetic studies not-withstanding a plethora of small molecule modulators of autophagy flux have been reported that alleviate disease symptoms in models of neurodegenerative diseases. This review summarizes the potential of such molecules to be, perhaps, one of the first autophagy drugs for treating these currently incurable diseases.

Sphingosine-1-Phosphate Receptors Modulators Decrease Signs of Neuroinflammation and Prevent Parkinson's Disease Symptoms in the 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Mouse Model

Sphingosine-1-phosphate (S1P) is a potent bioactive lipid mediator that acts as a natural ligand upon binding to five different receptors that are located in astrocytes, oligodendrocytes, microglial and neuronal cells. Recently, global activation of these receptors by FTY720 (fingolimod) has been suggested to provide neuroprotection in animal model of Parkinson’s disease (PD). Among S1P receptors, the subtype 1 (S1P1R) has been linked to features of neuroprotection and, using the selective agonist SEW2871, the present investigation assessed potential benefits (and mechanisms) of this receptor subtype in an established animal model of PD. We demonstrated that oral treatments with SEW2871 are able to provide protection to the same levels as FTY720 against loss of dopaminergic neurons and motor deficits in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg, i.p., 5 days) mouse model of PD. At the molecular level, we observed that the beneficial effects of both S1PR agonists were not associated with alterations in ERK and Akt levels, two markers of molecular adaptations in the striatum neurons. However, these compounds have the capacity to prevent signs of neuroinflammation such as the activation of astrocytes and glial cells, as well as MPTP-induced reduction of BDNF levels in key regions of the brain implicated in motor functions. These findings suggest that selective S1P1R modulation has the ability to provide neuroprotection in response to MPTP neurotoxicity. Targeting S1P1R in PD therapy may represent a prominent candidate for treatment of this neurodegenerative conditions.

Sphingolipids as prognostic biomarkers of neurodegeneration, neuroinflammation, and psychiatric diseases and their emerging role in lipidomic investigation methods

Lipids play an important role in neurodegeneration, neuroinflammation, and psychiatric disorders and an imbalance in sphingolipid levels is associated with disease. Although early diagnosis and intervention of these disorders would clearly have favorable long-term outcomes, no diagnostic tests currently exist that can accurately identify people at risk. Reliable prognostic biomarkers that are easily accessible would be beneficial to determine therapy and treatment response in clinical trials. Recent advances in lipidomic investigation methods have greatly progressed the knowledge of sphingolipids in neurodegenerative and psychiatric disorders over the past decades although more longitudinal studies are needed to understand its exact role in these disorders to be used as potential tools in the clinic. In this review, we give an overview of the current knowledge of sphingolipids in neurodegenerative and psychiatric disorders and explore recent advances in investigation methods. Finally, the potential of sphingolipid metabolism products and signaling molecules as potential biomarkers for diagnosis, prognostic, or surrogate markers of treatment response is discussed.

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.

FTY720-Mitoxy reduces synucleinopathy and neuroinflammation, restores behavior and mitochondria function, and increases GDNF expression in Multiple System Atrophy mouse models

Multiple system atrophy (MSA) is a fatal disorder with no effective treatment. MSA pathology is characterized by α-synuclein (aSyn) accumulation in oligodendrocytes, the myelinating glial cells of the central nervous system (CNS). aSyn accumulation in oligodendrocytes forms the pathognomonic glial cytoplasmic inclusions (GCIs) of MSA. MSA aSyn pathology is also associated with motor and autonomic dysfunction, including an impaired ability to sweat. MSA patients have abnormal CNS expression of glial-cell-line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF). Our prior studies using the parent compound FTY720, a food and drug administration (FDA) approved immunosuppressive for multiple sclerosis, reveal that FTY720 protects parkinsonian mice by increasing BDNF. Our FTY720-derivative, FTY720-Mitoxy, is known to increase expression of oligodendrocyte BDNF, GDNF, and nerve growth factor (NGF) but does not reduce levels of circulating lymphocytes as it is not phosphorylated so cannot modulate sphingosine 1 phosphate receptors (S1PRs). To preclinically assess FTY720-Mitoxy for MSA, we used mice expressing human aSyn in oligodendrocytes under a 2,' 3'-cyclic nucleotide 3'-phosphodiesterase (CNP) promoter. CNP-aSyn transgenic (Tg) mice develop motor dysfunction between 7 and 9 mo, and progressive GCI pathology. Using liquid chromatography-mass spectrometry (LC-MS/MS) and enzymatic assays, we confirmed that FTY720-Mitoxy was stable and active. Vehicle or FTY720-Mitoxy (1.1 mg/kg/day) was delivered to wild type (WT) or Tg littermates from 8.5-11.5 mo by osmotic pump. We behaviorally assessed their movement by rotarod and sweat production by starch‑iodine test. Postmortem tissues were evaluated by qPCR for BDNF, GDNF, NGF and GDNF-receptor RET mRNA and for aSyn, BDNF, GDNF, and Iba1 protein by immunoblot. MicroRNAs (miRNAs) were also assessed by qPCR. FTY720-Mitoxy normalized movement, sweat function and soleus muscle mass in 11.5 mo Tg MSA mice. FTY720-Mitoxy also increased levels of brain GDNF and reduced brain miR-96-5p, a miRNA that acts to decrease GDNF expression. Moreover, FTY720-Mitoxy blocked aSyn pathology measured by sequential protein extraction and immunoblot, and microglial activation assessed by immunohistochemistry and immunoblot. In the 3-nitropropionic acid (3NP) toxin model of MSA, FTY720-Mitoxy protected movement and mitochondria in WT and CNP-aSyn Tg littermates. Our data confirm potent in vivo protection by FTY720-Mitoxy, supporting its further evaluation as a potential therapy for MSA and related synucleinopathies.

Dual dose-dependent effects of fingolimod in a mouse model of Alzheimer's disease

Lipid metabolism is abnormal in Alzheimer’s disease (AD) brain leading to ceramide and sphingosine accumulation and reduced levels of brain sphingosine-1-phosphate (S1P). We hypothesize that changes in S1P signaling are central to the inflammatory and immune-pathogenesis of AD and the therapeutic benefits of fingolimod, a structural analog of sphingosine that is FDA approved for the treatment of multiple sclerosis. We recently reported that the neuroprotective effects of fingolimod in 5xFAD transgenic AD mice treated from 1–3 months of age were greater at 1 mg/kg/day than at 5 mg/kg/day. Here we performed a dose-response study using fingolimod from 0.03 to 1 mg/kg/day in 5xFAD mice treated from 1–8 months of age. At 1 mg/kg/day, fingolimod decreased both peripheral blood lymphocyte counts and brain Aβ levels, but at the lowest dose tested (0.03 mg/kg/day), we detected improved memory, decreased activation of brain microglia and astrocytes, and restored hippocampal levels of GABA and glycerophosphocholine with no effect on circulating lymphocyte counts. These findings suggests that, unlike the case in multiple sclerosis, fingolimod may potentially have therapeutic benefits in AD at low doses that do not affect peripheral lymphocyte function.

Sphingosine 1-Phosphate Receptors and Metabolic Enzymes as Druggable Targets for Brain Diseases

The central nervous system is characterized by a high content of sphingolipids and by a high diversity in terms of different structures. Stage- and cell-specific sphingolipid metabolism and expression are crucial for brain development and maintenance toward adult age. On the other hand, deep dysregulation of sphingolipid metabolism, leading to altered sphingolipid pattern, is associated with the majority of neurological and neurodegenerative diseases, even those totally lacking a common etiological background. Thus, sphingolipid metabolism has always been regarded as a promising pharmacological target for the treatment of brain disorders. However, any therapeutic hypothesis applied to complex amphipathic sphingolipids, components of cellular membranes, has so far failed probably because of the high regional complexity and specificity of the different biological roles of these structures. Simpler sphingosine-based lipids, including ceramide and sphingosine 1-phosphate, are important regulators of brain homeostasis, and, thanks to the relative simplicity of their metabolic network, they seem a feasible druggable target for the treatment of brain diseases. The enzymes involved in the control of the levels of bioactive sphingoids, as well as the receptors engaged by these molecules, have increasingly allured pharmacologists and clinicians, and eventually fingolimod, a functional antagonist of sphingosine 1-phosphate receptors with immunomodulatory properties, was approved for the therapy of relapsing-remitting multiple sclerosis. Considering the importance of neuroinflammation in many other brain diseases, we would expect an extension of the use of such analogs for the treatment of other ailments in the future. Nevertheless, many aspects other than neuroinflammation are regulated by bioactive sphingoids in healthy brain and dysregulated in brain disease. In this review, we are addressing the multifaceted possibility to address the metabolism and biology of bioactive sphingosine 1-phosphate as novel targets for the development of therapeutic paradigms and the discovery of new drugs.

FTY720-Mitoxy reduces toxicity associated with MSA-like α-synuclein and oxidative stress by increasing trophic factor expression and myelin protein in OLN-93 oligodendroglia cell cultures

Multiple system atrophy (MSA) is a fatal demyelinating disorder lacking any disease-modifying therapies. MSA pathology stems from aggregated α-synuclein (aSyn) accumulation in glial cytosolic inclusions of oligodendroglial cell (OLGs), the myelinating cells of brain. In MSA brains and in MSA animal models with aSyn accumulation in OLGs, aberrant expression of brain-derived neurotrophic factor (BDNF) and glial-cell-line-derived neurotrophic factor (GDNF) occur. Nerve growth factor (NGF) expression can also be altered in neurodegenerative diseases. It is unclear if oxidative stress impacts the viability of aSyn-accumulating OLG cells. Here, we show that OLN-93 cells stably expressing human wild type aSyn or the MSA-associated-aSyn-mutants G51D or A53E, are more vulnerable to oxidative stress. In dose response studies we found that OLN-93 cells treated 48 h with 160 nM FTY720 or our new non-immunosuppressive FTY720-C2 or FTY720-Mitoxy derivatives sustained normal viability. Also, FTY720, FTY720-C2, and FTY720-Mitoxy all stimulated NGF expression at 24 h. However only FTY720-Mitoxy also increased BDNF and GDNF mRNA at 24 h, an effect paralleled by increases in histone 3 acetylation and ERK1/2 phosphorylation. Myelin associated glycoprotein (MAG) levels were also increased in OLN-93 cells after 48 h treatment with FTY720-Mitoxy. FTY720, FTY720-C2, and FTY720-Mitoxy all prevented oxidative-stress-associated-cell-death of OLN-93 cells that lack any aSyn expression. However, only FTY720-Mitoxy protected MSA-like aSyn-expressing-OLN-93-cells against oxidative-cell-death. These data identify potent protective effects for FTY720-Mitoxy with regard to trophic factors as well as MAG expression by OLG cells. Testing of FTY720-Mitoxy in mice is thus a judicious next step for neuropharmacological preclinical development.

FTY720 Inhibits MPP+-Induced Microglial Activation by Affecting NLRP3 Inflammasome Activation

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons and excessive microglial activation in the substantia nigra pars compacta (SNpc). In the present study, we aimed to demonstrate the therapeutic effectiveness of the potent sphingosine-1-phosphate receptor antagonist fingolimod (FTY720) in an animal model of PD induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and to identify the potential mechanisms underlying these therapeutic effects. C57BL/6J mice were orally administered FTY720 before subcutaneous injection of MPTP. Open-field and rotarod tests were performed to determine the therapeutic effect of FTY720. The damage to dopaminergic neurons and the production of monoamine neurotransmitters were assessed using immunohistochemistry, high-performance liquid chromatography, and flow cytometry. Immunofluorescence (CD68- positive) and enzyme-linked immunosorbent assay were used to analyze the activation of microglia, and the levels of activated signaling molecules were measured using Western blotting. Our findings indicated that FTY720 significantly attenuated MPTP-induced behavioral deficits, reduced the loss of dopaminergic neurons, and increased dopamine release. FTY720 directly inhibited MPTP-induced microglial activation in the SNpc, suppressed the production of interleukin (IL)-6, IL-1β, and tumor necrosis factor-α in BV-2 microglial cells treated with 1-methyl-4-phenylpyridinium (MPP⁺), and subsequently decreased apoptosis in SH-SY5Y neuroblastoma cells. Moreover, in MPP⁺-treated BV-2 cells and primary microglia, FTY720 treatment significantly attenuated the increases in the phosphorylation of PI3K/AKT/GSK-3β, reduced ROS generation and p65 activation, and also inhibited the activation of NLRP3 inflammasome and caspase-1. In conclusion, FTY720 may reduce PD progression by inhibiting NLRP3 inflammasome activation via its effects on ROS generation and p65 activation in microglia. These findings provide novel insights into the mechanisms underlying the therapeutic effects of FTY720, suggesting its potential as a novel therapeutic strategy against PD. Graphical Abstract FTY720 may reduce ROS production by inhibiting the PI3K/AKT/GSK-3β signaling pathway, while at the same time reducing p65 phosphorylation, thus decreasing NLRP3 inflammasome activation through these two pathways, ultimately reducing microglia activation-induced neuronal damage.

Stimulation of Sphingosine Kinase 1 (SPHK1) Is Beneficial in a Huntington's Disease Pre-clinical Model

Although several agents have been identified to provide therapeutic benefits in Huntington disease (HD), the number of conventionally used treatments remains limited and only symptomatic. Thus, it is plausible that the need to identify new therapeutic targets for the development of alternative and more effective treatments is becoming increasingly urgent. Recently, the sphingosine-1-phosphate (S1P) axis has been reported to be a valid potential novel molecular target for therapy development in HD. Modulation of aberrant metabolism of S1P in HD has been proved to exert neuroprotective action in vitro settings including human HD iPSC-derived neurons. In this study, we investigated whether promoting S1P production by stimulating Sphingosine Kinase 1 (SPHK1) by the selective activator, K6PC-5, may have therapeutic benefit in vivo in R6/2 HD mouse model. Our findings indicate that chronic administration of 0.05 mg/kg K6PC-5 exerted an overall beneficial effect in R6/2 mice. It significantly slowed down the progressive motor deficit associated with disease progression, modulated S1P metabolism, evoked the activation of pro-survival pathways and markedly reduced the toxic mutant huntingtin (mHtt) aggregation. These results suggest that K6PC-5 may represent a future therapeutic option in HD and may potentially counteract the perturbed brain function induced by deregulated S1P pathways.

Stimulation of S1PR5 with A-971432, a selective agonist, preserves blood-brain barrier integrity and exerts therapeutic effect in an animal model of Huntington's disease

Huntington's disease (HD) is the most common neurodegenerative disorder for which no effective cure is yet available. Although several agents have been identified to provide benefits so far, the number of therapeutic options remains limited with only symptomatic treatment available. Over the past few years, we have demonstrated that sphingolipid-based approaches may open the door to new and more targeted treatments for the disease. In this study, we investigated the therapeutic potential of stimulating sphingosine-1-phosphate (S1P) receptor 5 by the new selective agonist A-971432 (provided by AbbVie) in R6/2 mice, a widely used HD animal model. Chronic administration of low-dose (0.1 mg/kg) A-971432 slowed down the progression of the disease and significantly prolonged lifespan in symptomatic R6/2 mice. Such beneficial effects were associated with activation of pro-survival pathways (BDNF, AKT and ERK) and with reduction of mutant huntingtin aggregation. A-971432 also protected blood-brain barrier (BBB) homeostasis in the same mice. Interestingly, when administered early in the disease, before any overt symptoms, A-971432 completely protected HD mice from the classic progressive motor deficit and preserved BBB integrity. Beside representing a promising strategy to take into consideration for the development of alternative therapeutic options for HD, selective stimulation of S1P receptor 5 may be also seen as an effective approach to target brain vasculature defects in the disease.

Early Downregulation of p75NTR by Genetic and Pharmacological Approaches Delays the Onset of Motor Deficits and Striatal Dysfunction in Huntington's Disease Mice

Deficits in striatal brain-derived neurotrophic factor (BDNF) delivery and/or BDNF/tropomyosin receptor kinase B (TrkB) signaling may contribute to neurotrophic support reduction and selective early degeneration of striatal medium spiny neurons in Huntington's disease (HD). Furthermore, we and others have demonstrated that TrkB/p75NTR imbalance in vitro increases the vulnerability of striatal neurons to excitotoxic insults and induces corticostriatal synaptic alterations. We have now expanded these studies by analyzing the consequences of BDNF/TrkB/p75NTR imbalance in the onset of motor behavior and striatal neuropathology in HD mice. Our findings demonstrate for the first time that the onset of motor coordination abnormalities, in a full-length knock-in HD mouse model (KI), correlates with the reduction of BDNF and TrkB levels, along with an increase in p75NTR expression. Genetic normalization of p75NTR expression in KI mutant mice delayed the onset of motor deficits and striatal neuropathology, as shown by restored levels of striatal-enriched proteins and dendritic spine density and reduced huntingtin aggregation. We found that the BDNF/TrkB/p75NTR imbalance led to abnormal BDNF signaling, manifested as a diminished activation of TrkB-phospholipase C-gamma pathway but upregulation of c-Jun kinase pathway. Moreover, we confirmed the contribution of the proper balance of BDNF/TrkB/p75NTR on HD pathology by a pharmacological approach using fingolimod. We observed that chronic infusion of fingolimod normalizes p75NTR levels, which is likely to improve motor coordination and striatal neuropathology in HD transgenic mice. We conclude that downregulation of p75NTR expression can delay disease progression suggesting that therapeutic approaches aimed to restore the balance between BDNF, TrkB, and p75NTR could be promising to prevent motor deficits in HD.

The Role of Ceramide and Sphingosine-1-Phosphate in Alzheimer's Disease and Other Neurodegenerative Disorders

Bioactive sphingolipids-ceramide, sphingosine, and their respective 1-phosphates (C1P and S1P)-are signaling molecules serving as intracellular second messengers. Moreover, S1P acts through G protein-coupled receptors in the plasma membrane. Accumulating evidence points to sphingolipids' engagement in brain aging and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. Metabolic alterations observed in the course of neurodegeneration favor ceramide-dependent pro-apoptotic signaling, while the levels of the neuroprotective S1P are reduced. These trends are observed early in the diseases' development, suggesting causal relationship. Mechanistic evidence has shown links between altered ceramide/S1P rheostat and the production, secretion, and aggregation of amyloid β/α-synuclein as well as signaling pathways of critical importance for the pathomechanism of protein conformation diseases. Sphingolipids influence multiple aspects of Akt/protein kinase B signaling, a pathway that regulates metabolism, stress response, and Bcl-2 family proteins. The cross-talk between sphingolipids and transcription factors including NF-κB, FOXOs, and AP-1 may be also important for immune regulation and cell survival/death. Sphingolipids regulate exosomes and other secretion mechanisms that can contribute to either the spread of neurotoxic proteins between brain cells, or their clearance. Recent discoveries also suggest the importance of intracellular and exosomal pools of small regulatory RNAs in the creation of disturbed signaling environment in the diseased brain. The identified interactions of bioactive sphingolipids urge for their evaluation as potential therapeutic targets. Moreover, the early disturbances in sphingolipid metabolism may deliver easily accessible biomarkers of neurodegenerative disorders.

Sphingolipids in neurodegeneration (with focus on ceramide and S1P)

For many decades, research on sphingolipids associated with neurodegenerative disease focused on alterations in glycosphingolipids, particularly glycosylceramides (cerebrosides), sulfatides, and gangliosides. This seemed quite natural since many of these glycolipids are constituents of myelin and accumulated in lipid storage diseases (sphingolipidoses) resulting from enzyme deficiencies in glycolipid metabolism. With the advent of recognizing ceramide and its derivative, sphingosine-1-phosphate (S1P), as key players in lipid cell signaling and regulation of cell death and survival, research focus shifted toward these two sphingolipids. Ceramide and S1P are invoked in a plethora of cell biological processes participating in neurodegeneration such as ER stress, autophagy, dysregulation of protein and lipid transport, exosome secretion and neurotoxic protein spreading, neuroinflammation, and mitochondrial dysfunction. Hence, it is timely to discuss various functions of ceramide and S1P in neurodegenerative disease and to define sphingolipid metabolism and cell signaling pathways as potential targets for therapy.

Fingolimod (FTY720) is not protective in the subacute MPTP mouse model of Parkinson's disease and does not lead to a sustainable increase of brain-derived neurotrophic factor

Parkinson's disease (PD) is characterized by the loss of midbrain dopaminergic neurons and aggregates of α-synuclein termed Lewy bodies. Fingolimod (FTY720) is an agonist of sphingosine-1 phosphate receptors and an approved oral treatment for multiple sclerosis. Fingolimod elevates brain-derived neurotrophic factor (BDNF), an important neurotrophic factor for dopaminergic neurons. BDNF and fingolimod are beneficial in several animal models of PD. In order to validate the therapeutic potential of fingolimod for the treatment of PD, we tested its effect in the subacute MPTP mouse model of PD. MPTP or vehicle was applied i.p. in doses of 30 mg/kg MPTP on five consecutive days. In order to recapitulate the combination of dopamine loss and α-synuclein aggregates found in PD, MPTP was first administered in Thy1-A30P-α-synuclein transgenic mice. Fingolimod was administered i.p. at a dose of 0.1 mg/kg every second day. Nigrostriatal degeneration was assayed by stereologically counting the number of dopaminergic neurons in the substantia nigra pars compacta, by analysing the concentration of catecholamines and the density of dopaminergic fibres in the striatum. MPTP administration produced a robust nigrostriatal degeneration, comparable to previous studies. Unexpectedly, we found no difference between mice with and without fingolimod treatment, neither at baseline, nor at 14 or 90 days after MPTP. Also, we found no effect of fingolimod in the subacute MPTP mouse model when we used wildtype mice instead of α-synuclein transgenic mice, and no effect with an increased dose of 1 mg/kg fingolimod administered every day. In order to explain these findings, we analysed BDNF regulation by fingolimod. We did find an increase of BDNF protein after a single injection of fingolimod 0.1 or 1.0 mg/kg, but not after multiple injections, indicating that the BDNF response to fingolimod is unsustainable over time. Taken together we did not observe a neuroprotective effect of fingolimod in the subacute MPTP mouse model of PD. We discuss possible explanations for this discrepancy with previous findings and conclude fingolimod might be beneficial for the nonmotor symptoms of PD. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* and *Open Data* because it provided all relevant information to reproduce the study in the manuscript and because it made the data publicly available. The data can be accessed at https://osf.io/6xgfn/. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Huntington's disease: novel therapeutic perspectives hanging in the balance

INTRODUCTION

Huntington's disease (HD), an autosomal dominant neurodegenerative disorder caused by an expansion of CAG repeats in the huntingtin gene, has long been characterized by the presence of motor symptoms due to the loss of striatal projection neurons. Cognitive dysfunction and neuropsychiatric symptoms are also present and they occur in the absence of cell death in most mouse models, pointing to neuronal dysfunction and abnormal synaptic plasticity as causative mechanisms. Areas covered: Here, we focus on those common mechanisms altered by the presence of mutant huntingtin affecting corticostriatal and hippocampal function as therapeutic targets that could prove beneficial to ameliorate both cognitive and motor function in HD. Specifically, we discuss the importance of reestablishing the balance in (1) synaptic/extrasynaptic N-methyl-D-aspartate receptor signaling, (2) mitochondrial dynamics/trafficking, (3) TrkB/p75^NTR signaling, and (4) transcriptional activity. Expert opinion: Mutant huntingtin has a broad impact on multiple cellular processes, which makes it very challenging to design a curative therapeutic strategy. As we point out here, novel therapeutic interventions should look for multi-purpose drugs targeting common and early affected processes leading to corticostriatal and hippocampal dysfunction that additionally operate in a feedforward vicious cycle downstream the activation of extrasynaptic N-methyl-D-aspartate receptor.

Sphingolipid Metabolism: A New Therapeutic Opportunity for Brain Degenerative Disorders

Neurodegenerative diseases represent a class of fatal brain disorders for which the number of effective therapeutic options remains limited with only symptomatic treatment accessible. Multiple studies show that defects in sphingolipid pathways are shared among different brain disorders including neurodegenerative diseases and may contribute to their complex pathogenesis. In this mini review, we discuss the hypothesis that modulation of sphingolipid metabolism and their related signaling pathways may represent a potential therapeutic approach for those devastating conditions. The plausible “druggability” of sphingolipid pathways is greatly promising and represent a relevant feature that brings real advantage to the development of new therapeutic options for these conditions. Indeed, several molecules that selectively target sphingolipds are already available and many of them currently in clinical trial for human diseases. A deeper understanding of the “sphingolipid scenario” in neurodegenerative disorders would certainly enhance therapeutic perspectives for these conditions, by taking advantage from the already available molecules and by promoting the development of new ones.

The S1P Axis: New Exciting Route for Treating Huntington's Disease

Huntington's disease (HD) is a single-gene inheritable neurodegenerative disorder with an associated complex molecular pathogenic profile that renders it the most 'curable incurable' brain disorder. Continuous effort in the field has contributed to the recent discovery of novel potential pathogenic mechanisms. Findings in preclinical models of the disease as well as in human post-mortem brains from affected patients demonstrate that alteration of the sphingosine-1-phosphate (S1P) axis may represent a possible key player in the pathogenesis of the disease and may act as a potential actionable drug target for the development of more targeted and effective therapeutic approaches. The relevance of the path of this new 'therapeutic route' is underscored by the fact that some drugs targeting the S1P axis are currently in clinical trials for the treatment of other brain disorders.

Fingolimod inhibits brain atrophy and promotes brain-derived neurotrophic factor in an animal model of multiple sclerosis

Longitudinal brain atrophy quantification is a critical efficacy measurement in multiple sclerosis (MS) clinical trials and the determination of No Evidence of Disease Activity (NEDA). Utilising fingolimod as a clinically validated therapy we evaluated the use of repeated brain tissue volume measures during chronic experimental autoimmune encephalomyelitis (EAE) as a new preclinical efficacy measure. Brain volume changes were quantified using magnetic resonance imaging (MRI) at 7 Tesla and correlated to treatment-induced brain derived neurotrophic factor (BDNF) measured in blood, cerebrospinal fluid, spinal cord and brain. Serial brain MRI measurements revealed slow progressive brain volume loss in vehicle treated EAE mice despite a stable clinical score. Fingolimod (1 mg/kg) significantly ameliorated brain tissue atrophy in the cerebellum and striatum when administered from established EAE disease onwards. Fingolimod-dependent tissue preservation was associated with induction of BDNF specifically within the brain and co-localized with neuronal soma. In contrast, therapeutic teriflunomide (3 mg/kg) treatment failed to inhibit CNS autoimmune mediated brain degeneration. Finally, weekly anti-IL-17A antibody (15 mg/kg) treatment was highly efficacious and preserved whole brain, cerebellum and striatum volume. Fingolimod-mediated BDNF increases within the CNS may contribute to limiting progressive tissue loss during chronic neuroinflammation.

Cognitive dysfunction in Huntington's disease: mechanisms and therapeutic strategies beyond BDNF

One of the main focuses in Huntington's disease (HD) research, as well as in most neurodegenerative diseases, is the development of new therapeutic strategies, as currently there is no treatment to delay or prevent the progression of the disease. Neuronal dysfunction and neuronal death in HD are caused by a combination of interrelated pathogenic processes that lead to motor, cognitive and psychiatric symptoms. Understanding how mutant huntingtin impacts on a plethora of cellular functions could help to identify new molecular targets. Although HD has been classically classified as a neurodegenerative disease affecting voluntary movement, lately cognitive dysfunction is receiving increased attention as it is very invalidating for patients. Thus, an ambitious goal in HD research is to find altered molecular mechanisms that contribute to cognitive decline. In this review, we have focused on those findings related to corticostriatal and hippocampal cognitive dysfunction in HD, as well as on the underlying molecular mechanisms, which constitute potential therapeutic targets. These include alterations in synaptic plasticity, transcriptional machinery and neurotrophic and neurotransmitter signaling.