Molecular triggers of neuroinflammation in mouse models of demyelinating diseases

Microbiota gut-brain axis: implications for pediatric-onset leukodystrophies

Neurodegenerative disorders are a group of diseases characterized by progressive degeneration of the nervous system, leading to a gradual loss of previously acquired motor, sensory and/or cognitive functions. Leukodystrophies are amongst the most frequent childhood-onset neurodegenerative diseases and primarily affect the white matter of the brain, often resulting in neuro-motor disability. Notably, gastrointestinal (GI) symptoms and complications, such as gastroesophageal reflux disease (GERD) and dysphagia, significantly impact patients' quality of life, highlighting the need for comprehensive management strategies. Gut dysbiosis, characterized by microbial imbalance, has been implicated in various GI disorders and neurodegenerative diseases. This narrative review explores the intricate relationship between GI symptoms, Gut Microbiota (GM), and neurodegeneration. Emerging evidence underscores the profound influence of GM on neurological functions via the microbiota gut-brain axis. Animal models have demonstrated alterations in GM composition associated with neuroinflammation and neurodegeneration. Our single-centre experience reveals a high prevalence of GI symptoms in leukodystrophy population, emphasizing the importance of gastroenterological assessment and nutritional intervention in affected children. The bidirectional relationship between GI disorders and neurodegeneration suggests a potential role of gut dysbiosis in disease progression. Prospective studies investigating the GM in leukodystrophies are essential to understand the role of gut-brain axis dysfunction in disease progression and identify novel therapeutic targets. In conclusion, elucidating the interplay between GI disorders, GM, and neurodegeneration holds promise for precision treatments aimed at improving patient outcomes and quality of life.

Metachromatic leukodystrophy: To screen or not to screen?

Metachromatic leukodystrophy (MLD) is a neurodegenerative lysosomal storage disorder caused by biallelic pathogenic variants in the gene encoding arylsulfatase A. Disease onset is variable (with late infantile, early and late juvenile, and adult forms) and treatment options depend on age and disease symptoms at onset. In the past, allo-hematopoietic stem cell transplantation (allo-HSCT) has been the best treatment option, following strict selection criteria. The outcome however is variable and morbidity remains high. This paved the way to the development of new treatment options, some of them aiming to be curative. In the light of this changing therapeutic field, newborn screening is becoming a valuable option. This narrative review aims to describe the outcome of allo-HSCT in the different MLD disease forms, and, in addition, reviews new treatment options. Finally, the shift of the field towards newborn screening for MLD is discussed.

Comprehensive clinical, biochemical, radiological and genetic analysis of 28 Turkish cases with suspected metachromatic leukodystrophy and their relatives

Metachromatic leukodystrophy (MLD) is a glycosphingolipid storage disease caused by deficiency of the lysosomal enzyme arylsulfatase A (ASA) or its activator protein saposin B. MLD can affect all age groups in severity varying from a severe fatal form to milder adult onset forms. Diagnosis is usually made by measuring leukocyte ASA activity. However, this test can give false negative or false positive laboratory results due to pseudodeficiency of ASA and saposin B deficiency, respectively. Therefore, we aimed to evaluate patients with suspected MLD in a Turkish population by comprehensive clinical, biochemical, radiological, and genetic analyses for molecular and phenotypic characterization. We analyzed 28 suspected MLD patients and 41 relatives from 24 families. ASA activity was found to be decreased in 21 of 28 patients. Sixteen patients were diagnosed as MLD (11 late infantile, 2 juvenile and 3 adult types), 2 MSD, 2 pseudodeficiency (PD) and the remaining 8 patients were diagnosed as having other leukodystrophies. Enzyme analysis showed that the age of onset of MLD did not correlate with residual ASA activity. Sequence analysis showed 11 mutations in ARSA, of which 4 were novel (p.Trp195GlyfsTer5, p.Gly298Asp, p.Arg301Leu, and p.Gly311Asp), and 2 mutations in SUMF1 causing multiple sulfatase deficiency, and confirmed the diagnosis of MLD in 2 presymptomatic relatives. All individuals with confirmed mutations had low ASA activity and urinary sulfatide excretion. Intra- and inter-familial variability was high for the same ARSA missense genotypes, indicating the contribution of other factors to disease expression. Imaging findings were evaluated through a modified brain MRI scoring system which indicated patients with protein-truncating mutations had more severe MRI findings and late-infantile disease onset. MRI findings were not specific for the diagnosis. Anti-sulfatide IgM was similar to control subjects, and IgG, elevated in multiple sulfatase deficiency. In conclusion, the knowledge on the biochemical, clinical and genetic basis of MLD was expanded, a modified diagnostic laboratory algorithm for MLD based on integrated evaluation of ASA activity, urinary sulfatide excretion and genetic tests was devised.

Peripheral neuropathy in metachromatic leukodystrophy: current status and future perspective

Metachromatic leukodystrophy (MLD) is an autosomal recessively inherited metabolic disease characterized by deficient activity of the lysosomal enzyme arylsulfatase A. Its deficiency results in accumulation of sulfatides in neural and visceral tissues, and causes demyelination of the central and peripheral nervous system. This leads to a broad range of neurological symptoms and eventually premature death. In asymptomatic patients with juvenile and adult MLD, treatment with allogeneic hematopoietic stem cell transplantation (HCT) provides a symptomatic and survival benefit. However, this treatment mainly impacts brain white matter, whereas the peripheral neuropathy shows no or only limited response. Data about the impact of peripheral neuropathy in MLD patients are currently lacking, although in our experience peripheral neuropathy causes significant morbidity due to neuropathic pain, foot deformities and neurogenic bladder disturbances. Besides, the reasons for residual and often progressive peripheral neuropathy after HCT are not fully understood. Preliminary studies suggest that peripheral neuropathy might respond better to gene therapy due to higher enzyme levels achieved than with HCT. However, histopathological and clinical findings also suggest a role of neuroinflammation in the pathology of peripheral neuropathy in MLD. In this literature review, we discuss clinical aspects, pathological findings, distribution of mutations, and treatment approaches in MLD with particular emphasis on peripheral neuropathy. We believe that future therapies need more emphasis on the management of peripheral neuropathy, and additional research is needed to optimize care strategies.

Tanshinone IIA attenuates demyelination and promotes remyelination in A. cantonensis-infected BALB/c mice

BACKGROUND

Angiostrongylus cantonensis infection can cause demyelination in the central nervous system, and there is no effective treatment.

METHODS

We used dexamethasone, Tanshinone IIA (TSIIA) and Cryptotanshinone(Two traditional Chinese medicine monomers) in combination with albendazole (AB, a standard anti-helminthic compound) to observe their therapeutic effect on demyelination in A. cantonensis-infected mice. Luxol fast blue staining and electron microscope of myelin sheath, Oligodendrocyte (OL) number and myelin basic protein (MBP) expression in brain was detected in above groups.

RESULTS

TSIIA+AB facilitated OL proliferation and significantly increased both myelin sheath thickness and the population of small-diameter axons. In addition, TSIIA treatment inhibited the expression of inflammation-related factors (interleukin [IL]-6, IL-1β, tumor necrosis factor [TNF]-α, inducible nitric oxide synthase [iNOS]) rather than inhibiting eosinophil infiltration in brain. TSIIA also decreased microglial activation and shifted their phenotype from M1 to M2.

CONCLUSIONS

Taken together, these results provide evidence that TSIIA combined with AB may be an effective treatment for demyelination caused by A. cantonensis infection and other demyelinating diseases.

Teriflunomide attenuates neuroinflammation-related neural damage in mice carrying human PLP1 mutations

BACKGROUND

Genetically caused neurological disorders of the central nervous system (CNS) are mostly characterized by poor or even fatal clinical outcome and few or no causative treatments are available. Often, these disorders are associated with low-grade, disease-promoting inflammation, another feature shared by progressive forms of multiple sclerosis (PMS). We previously generated two mouse lines carrying distinct mutations in the oligodendrocytic PLP1 gene that have initially been identified in patients diagnosed with MS. These mutations cause a loss of PLP function leading to a histopathological and clinical phenotype common to both PMS and genetic CNS disorders, like hereditary spastic paraplegias. Importantly, neuroinflammation promotes disease progression in these models, suggesting that pharmacological modulation of inflammation might ameliorate disease outcome.

METHODS

We applied teriflunomide, an approved medication for relapsing-remitting MS targeting activated T-lymphocytes, in the drinking water (10 mg/kg body weight/day). Experimental long-term treatment of PLP mutant mice was non-invasively monitored by longitudinal optical coherence tomography and by rotarod analysis. Immunomodulatory effects were subsequently analyzed by flow cytometry and immunohistochemistry and treatment effects regarding neural damage, and neurodegeneration were assessed by histology and immunohistochemistry.

RESULTS

Preventive treatment with teriflunomide attenuated the increase in number of CD8+ cytotoxic effector T cells and fostered the proliferation of CD8+ CD122+ PD-1+ regulatory T cells in the CNS. This led to an amelioration of axonopathic features and neuron loss in the retinotectal system, also reflected by reduced thinning of the innermost retinal composite layer in longitudinal studies and ameliorated clinical outcome upon preventive long-term treatment. Treatment of immune-incompetent PLP mutants did not provide evidence for a direct, neuroprotective effect of the medication. When treatment was terminated, no rebound of neuroinflammation occurred and histopathological improvement was preserved for at least 75 days without treatment. After disease onset, teriflunomide halted ongoing axonal perturbation and enabled a recovery of dendritic arborization by surviving ganglion cells. However, neither neuron loss nor clinical features were ameliorated, likely due to already advanced neurodegeneration before treatment onset.

CONCLUSIONS

We identify teriflunomide as a possible medication not only for PMS but also for inflammation-related genetic diseases of the nervous system for which causal treatment options are presently lacking.

Epigenomic signature of adrenoleukodystrophy predicts compromised oligodendrocyte differentiation

Epigenomic changes may either cause disease or modulate its expressivity, adding a layer of complexity to mendelian diseases. X‐linked adrenoleukodystrophy (X‐ALD) is a rare neurometabolic condition exhibiting discordant phenotypes, ranging from a childhood cerebral inflammatory demyelination (cALD) to an adult‐onset mild axonopathy in spinal cords (AMN). The AMN form may occur with superimposed inflammatory brain demyelination (cAMN). All patients harbor loss of function mutations in the ABCD1 peroxisomal transporter of very‐long chain fatty acids. The factors that account for the lack of genotype‐phenotype correlation, even within the same family, remain largely unknown. To gain insight into this matter, here we compared the genome‐wide DNA methylation profiles of morphologically intact frontal white matter areas of children affected by cALD with adult cAMN patients, including male controls in the same age group. We identified a common methylomic signature between the two phenotypes, comprising (i) hypermethylation of genes harboring the H3K27me3 mark at promoter regions, (ii) hypermethylation of genes with major roles in oligodendrocyte differentiation such as MBP, CNP, MOG and PLP1 and (iii) hypomethylation of immune‐associated genes such as IFITM1 and CD59. Moreover, we found increased hypermethylation in CpGs of genes involved in oligodendrocyte differentiation, and also in genes with H3K27me3 marks in their promoter regions in cALD compared with cAMN, correlating with transcriptional and translational changes. Further, using a penalized logistic regression model, we identified the combined methylation levels of SPG20, UNC45A and COL9A3 and also, the combined expression levels of ID4 and MYRF to be good markers capable of discriminating childhood from adult inflammatory phenotypes. We thus propose the hypothesis that an epigenetically controlled, altered transcriptional program may drive an impaired oligodendrocyte differentiation and aberrant immune activation in X‐ALD patients. These results shed light into disease pathomechanisms and uncover putative biomarkers of interest for prognosis and phenotypic stratification.

Role of the innate immune system in the neuropathological consequences induced by adolescent binge drinking

Adolescence is a critical stage of brain maturation in which important plastic and dynamic processes take place in different brain regions, leading to development of the adult brain. Ethanol drinking in adolescence disrupts brain plasticity and causes structural and functional changes in immature brain areas (prefrontal cortex, limbic system) that result in cognitive and behavioral deficits. These changes, along with secretion of sexual and stress-related hormones in adolescence, may impact self-control, decision making, and risk-taking behaviors that contribute to anxiety and initiation of alcohol consumption. New data support the participation of the neuroimmune system in the effects of ethanol on the developing and adult brain. This article reviews the potential pathological bases that underlie the effects of alcohol on the adolescent brain, such as the contribution of genetic background, the perturbation of epigenetic programming, and the influence of the neuroimmune response. Special emphasis is given to the actions of ethanol in the innate immune receptor toll-like receptor 4 (TLR4), since recent studies have demonstrated that by activating the inflammatory TLR4/NFκB signaling response in glial cells, binge drinking of ethanol triggers the release of cytokines/chemokines and free radicals, which exacerbate the immune response that causes neuroinflammation/neural damage as well as short- and long-term neurophysiological, cognitive, and behavioral dysfunction. Finally, potential treatments that target the neuroimmune response to treat the neuropathological and behavioral consequences of adolescent alcohol abuse are discussed.

Immunological considerations for treating globoid cell leukodystrophy

Globoid cell leukodystrophy (GLD, or Krabbe's disease) is a severe inherited neurodegenerative disease caused by the lack of a lysosomal enzyme, GALC. The disease has been characterized in humans as well as three naturally occurring animal models, murine, canine, and nonhuman primate. Multiple treatment strategies have been explored for GLD, including enzyme replacement therapy, small-molecule pharmacological approaches, gene therapy, and bone marrow transplant. No single therapeutic approach has proved to be entirely effective, and the reason for this is not well understood. It is unclear whether initiation of a neuroinflammatory cascade in GLD precedes demyelination, a hallmark of the disease, but it does precede overt symptoms. This Review explores what is known about the role of inflammation and the immune response in the progression of GLD as well as how various treatment strategies might interplay with innate and adaptive immune responses involved in GLD. The focus of this Review is on GLD, but these concepts may have relevance for other, related diseases. © 2016 Wiley Periodicals, Inc.

Neuroinflammation as modifier of genetically caused neurological disorders of the central nervous system: Understanding pathogenesis and chances for treatment

Genetically caused neurological disorders of the central nervous system (CNS) are usually orphan diseases with poor or even fatal clinical outcome and few or no treatments that will improve longevity or at least quality of life. Neuroinflammation is common to many of these disorders, despite the fact that a plethora of distinct mutations and molecular changes underlie the disorders. In this article, data from corresponding animal models are analyzed to define the roles of innate and adaptive inflammation as modifiers and amplifiers of disease. We describe both common and distinct patterns of neuroinflammation in genetically mediated CNS disorders and discuss the contrasting mechanisms that lead to adverse versus neuroprotective effects. Moreover, we identify the juxtaparanode as a neuroanatomical compartment commonly associated with inflammatory cells and ongoing axonopathic changes, in models of diverse diseases. The identification of key immunological effector pathways that amplify neuropathic features should lead to realistic possibilities for translatable therapeutic interventions using existing immunomodulators. Moreover, evidence emerges that neuroinflammation is not only able to modify primary neural damage-related symptoms but also may lead to unexpected clinical outcomes such as neuropsychiatric syndromes.

Fingolimod and Teriflunomide Attenuate Neurodegeneration in Mouse Models of Neuronal Ceroid Lipofuscinosis

CLN diseases are rare lysosomal storage diseases characterized by progressive axonal degeneration and neuron loss in the CNS, manifesting in disability, blindness, and premature death. We have previously demonstrated that, in animal models of infantile and juvenile forms of CLN disease (CLN1 and CLN3, respectively), secondary neuroinflammation in the CNS substantially amplifies neural damage, opening the possibility that immunomodulatory treatment might improve disease outcome. First, we recapitulated the inflammatory phenotype, originally seen in mice in autopsies of CLN patients. We then treated mouse models of CLN1 and CLN3 disease with the clinically approved immunomodulatory compounds fingolimod (0.5 mg/kg/day) and teriflunomide (10 mg/kg/day) by consistent supply in the drinking water for 5 months. The treatment was well tolerated and reduced T cell numbers and microgliosis in the CNS of both models. Moreover, axonal damage, neuron loss, retinal thinning, and brain atrophy were substantially attenuated in both models, along with reduced frequency of myoclonic jerks in Ppt1^−/− mice. Based on these findings, and because side effects were not detected, we suggest that clinically approved immune modulators such as fingolimod and teriflunomide may be suitable to attenuate progression of CLN1 and CLN3 disease and, possibly, other orphan diseases with pathogenically relevant neuroinflammation.

Altered Translational Control of Fragile X Mental Retardation Protein on Myelin Proteins in Neuropsychiatric Disorders

Myelin is a specialized structure of the nervous system that both enhances electrical conductance and insulates neurons from external risk factors. In the central nervous system, polarized oligodendrocytes form myelin by wrapping processes in a spiral pattern around neuronal axons through myelin-related gene regulation. Since these events occur at a distance from the cell body, post-transcriptional control of gene expression has strategic advantage to fine-tune the overall regulation of protein contents in situ. Therefore, many research interests have been focused to identify RNA binding proteins and their regulatory mechanism in myelinating compartments. Fragile X mental retardation protein (FMRP) is one such RNA binding protein, regulating its target expression by translational control. Although the majority of works on FMRP have been performed in neurons, it is also found in the developing or mature glial cells including oligodendrocytes, where its function is not well understood. Here, we will review evidences suggesting abnormal translational regulation of myelin proteins with accompanying white matter problem and neurological deficits in fragile X syndrome, which can have wider mechanistic and pathological implication in many other neurological and psychiatric disorders.

Interleukin-1β impedes oligodendrocyte progenitor cell recruitment and white matter repair following chronic cerebral hypoperfusion

Subcortical ischemic vascular dementia (SIVD) caused by chronic cerebral hypoperfusion exhibits progressive white matter and cognitive impairments. However, its pathogenetic mechanisms are poorly understood. We investigated the role of interleukin-1β (IL-1β) and its receptor IL-1 receptor type 1 (IL-1R1) in an experimental SIVD model generated via right unilateral common carotid arteries occlusion (rUCCAO) in mice. We found that IL-1β expression was elevated in the corpus callosum at the early stages after rUCCAO. IL-1 receptor antagonist (IL-1Ra), when delivered at an early stage, as well as IL-1R1 knockout, rescued the downregulation of myelin basic protein (MBP) and improved remyelination at the later stage after rUCCAO. Our data suggest that the recruitment of OPCs, but not the proliferation or differentiation of OPCs, is the only compromised step of remyelination following chronic cerebral ischemia. IL-1Ra treatment and IL-1R1 knockout had no effect on the oligodendrocyte progenitor cell (OPC) proliferation, but did promote the recruitment of newly generated OPCs to the corpus callosum, which can be reversed by compensatory expression of IL-1R1 in the SVZ of IL-1R1 knockout mice. Further, we found that recruited OPCs contribute to oligodendrocyte regeneration and functional recovery. In transwell assays, IL-1β inhibited OPC migration through IL-1R1. Moreover, KdPT which can enter the brain to block IL-1R1 also showed comparable protection when intraperitoneally delivered. Our results suggest that IL-1β during the early stages following chronic cerebral hypoperfusion impedes OPC recruitment via IL-1R1, which inhibits white matter repair and functional recovery. IL-1R1 inhibitors may have potential uses in the treatment of SIVD.

Is involvement of inflammation underestimated in Pelizaeus-Merzbacher disease?

Pelizaeus-Merzbacher disease (PMD) is a severe hypomyelinating leukodystrophy resulting from proteolipid protein 1 gene (PLP1) mutations leading to oligodendrocyte loss. While neuroinflammation has recently become a common feature and actor in neurodegenerative diseases, the involvement of inflammation in PMD physiopathology is still highly debated despite evidence for strong astrogliosis and microglial cell activation. Activation of the innate immune system, and more particularly, of microglia and astrocytes, is mostly associated with the deleterious role of neuroinflammation. However, in diseases such as multiple sclerosis, microglia appear beneficial for repair based on their role in myelin debris removal or recruitment and differentiation of oligodendrocyte progenitor cells. In this review, we will discuss recent published data in terms of their relevance to the role of microglia in PMD evolution, and of their impact on the improvement of therapeutic approaches combining immunomodulation and cell therapy to promote optimal recovery. © 2016 Wiley Periodicals, Inc.

Myelination of the nervous system: mechanisms and functions

Myelination of axons in the nervous system of vertebrates enables fast, saltatory impulse propagation, one of the best-understood concepts in neurophysiology. However, it took a long while to recognize the mechanistic complexity both of myelination by oligodendrocytes and Schwann cells and of their cellular interactions. In this review, we highlight recent advances in our understanding of myelin biogenesis, its lifelong plasticity, and the reciprocal interactions of myelinating glia with the axons they ensheath. In the central nervous system, myelination is also stimulated by axonal activity and astrocytes, whereas myelin clearance involves microglia/macrophages. Once myelinated, the long-term integrity of axons depends on glial supply of metabolites and neurotrophic factors. The relevance of this axoglial symbiosis is illustrated in normal brain aging and human myelin diseases, which can be studied in corresponding mouse models. Thus, myelinating cells serve a key role in preserving the connectivity and functions of a healthy nervous system.