The gut microbiota-oligodendrocyte axis: A promising pathway for modulating oligodendrocyte homeostasis and demyelination-associated disorders.

The bidirectional regulation between the gut microbiota and brain, known as gut-brain axis, has received significant attention. The myelin sheath, produced by oligodendrocytes or Schwann cells, is essential for efficient nervous signal transmission and the maintenance of brain function. Growing evidence shows that both oligodendrogenesis and myelination are modulated by gut microbiota and its metabolites, and when dysbiosis occurs, changes in the microbiota composition and/or associated metabolites may impact developmental myelination and the occurrence of neurodevelopmental disabilities. Although the link between the microbiota and demyelinating disease such as multiple sclerosis has been extensively studied, our knowledge about the role of the microbiota in other myelin-related disorders, such as neurodegenerative diseases, is limited. Mechanistically, the microbiota-oligodendrocyte axis is primarily mediated by factors such as inflammation, the vagus nerve, endocrine hormones, and microbiota metabolites as evidenced by metagenomics, metabolomics, vagotomy, and morphological and molecular approaches. Treatments targeting this axis include probiotics, prebiotics, microbial metabolites, herbal bioactive compounds, and specific dietary management. In addition to the commonly used approaches, viral vector-mediated tracing and gene manipulation, integrated multiomics and multicenter clinical trials will greatly promote the mechanistic and interventional studies and ultimately, the development of new preventive and therapeutic strategies against gut-oligodendrocyte axis-mediated brain impairments. Interestingly, recent findings showed that microbiota dysbiosis can be induced by hippocampal myelin damage and is reversible by myelin-targeted drugs, which provides new insights into understanding how hippocampus-based functional impairment (such as in neurodegenerative Alzheimer's disease) regulates the peripheral homeostasis of microbiota and associated systemic disorders.

Management of pediatric post-infectious neurological syndromes.

BACKGROUND: Post-Infectious Neurological Syndromes (PINS) are heterogeneous neurological disorders with post or para-infectious onset. PINS diagnosis is complex, mainly related to the absence of any recognized guidelines and a univocal definition. AIM OF THE STUDY: To elaborate a diagnostic guide for PINS. MATERIALS AND METHODS: We retrospectively analysed patients younger than 14 years old admitted to Bambino Gesù Children's Hospital in Rome for PINS from December 2005 to March 2018. Scientific literature using PubMed as research platform was analysed: the key words "Post-Infectious Neurological Syndromes" were used. RESULTS: A polysymptomatic presentation occurred in a percentage of 88% of the children. Motor signs and visual disturbances the most observed symptoms/signs were the most detached, followed by fever, speech disturbances, sleepiness, headache and bradipsychism. Blood investigations are compatible with inflammation, as a prodromal illnesses was documented in most cases. Normal cerebral spinal fluid (CSF) characteristics has been found in the majority of the study population. Magnetic resonance imaging (MRI) was positive for demyelinating lesions. Antibiotics, acyclovir and steroids have been given as treatment. DISCUSSION: We suggest diagnostic criteria for diagnosis of PINS, considering the following parameters: neurological symptoms, timing of disease onset, blood and CSF laboratory tests, MRI imaging. CONCLUSIONS: We propose criteria to guide clinician to diagnose PINS as definitive, probable or possible. Further studies are required to validate diagnostic criteria.

Deep DNA metagenomic sequencing reveals oral microbiome divergence between monozygotic twins discordant for multiple sclerosis severity.

In contrast to gut, the oral microbiome of MS patients has not been characterized. Deep sequencing of saliva DNA from a pair of monozygotic twins (MSF1 with relapsing remitting MS; MSF2 with clinically isolated syndrome) identified 2036 bacterial species. Relative abundances of 3 phyla were higher, and 3 lower in MSF1 versus MSF2. Species diversity was greater in MSF2, and 20 abundant species differed at least 2-fold. Pathway analysis identified 116 functional hierarchies differing 50% or more. Although limited to one pair of twins, our data suggests that oral microbiome analysis may be useful for diagnosis or monitoring therapeutic efficacy.

Demyelinating steroid-responsive neurobrucellosis.

Young man with acute onset nausea, vomiting, joint pain, abdominal pain, fever and weight loss was found to have gait ataxia and positive B rucella titres. He deteriorated despite appropriate antibiotics and developed confusion and disorientation. Lumbar puncture revealed lymphocytosis with high protein and low glucose. MRI showed diffuse demyelination. Pulse steroids resulted in rapid clinical, biochemical and radiological recovery.

Myelin breakdown favours Mycobacterium leprae survival in Scwann cells

Leprosy neuropathy is a chronic degenerative infectious disorder of the peripheral nerve caused by the intracellular obligate pathogen Mycobacterium leprae (M. leprae). Among all nonneuronal cells that constitute the nerve, Schwann cells are remarkable in supporting M. leprae persistence intracellularly. Notably, the success of leprosy infection has been attributed to its ability in inducing the demyelination phenotype after contacting myelinated fibres. However, the exact role M. leprae plays during the ongoing process of myelin breakdown is entirely unknown. Here, we provided evidence showing an unexpected predilection of leprosy pathogen for degenerating myelin ovoids inside Schwann cells. In addition, M. leprae infection accelerated the rate of myelin breakdown and clearance leading to increased formation of lipid droplets, by modulating a set of regulatory genes involved in myelin maintenance, autophagy, and lipid storage. Remarkably, the blockage of myelin breakdown significantly reduced M. leprae content, demonstrating a new unpredictable role of myelin dismantling favouring M. leprae physiology. Collectively, our study provides novel evidence that may explain the demyelination phenotype as an evolutionarily conserved mechanism used by leprosy pathogen to persist longer in the peripheral nerve.

Spectrum of Microbial Sequences and a Bacterial Cell Wall Antigen in Primary Demyelination Brain Specimens Obtained from Living Patients.

Multiple sclerosis (MS) is an autoimmune disease characterized by multiple lesions in the brain and spinal cord. We used RNA sequencing to identify microbial sequences and characterize human gene expression patterns in 30 human brain biopsy specimens. RNAs which aligned to known microbial taxa, were significantly enriched in 10 of 12 primary demyelination (MS) brain specimens compared to a group of 15 epilepsy controls, leading to a list of 29 MS microbial candidate genera from 11 different phyla. Most of the candidate MS microbes are anaerobic bacteria. While there were some shared candidates, each of the 10 MS samples with significant microbial RNA enrichment had a distinct set microbial candidates. The fraction of microbial sequencing reads was greater for the MS group (128.8 PPM) compared to the controls (77.4 PPM, p = 0.016). Bacterial peptidoglycan was demonstrated in brain tissue sections from several MS subjects. Human gene expression analysis showed increased expression of inflammation-related pathways in the MS group. This data shows that demyelinating brain lesions are associated with the presence of microbial RNA sequences and bacterial antigen. This suggests that MS is triggered by the presence of a diverse set of microbes within a lesion.

TLR signals license CD8 T cells to destroy oligodendrocytes expressing an antigen shared with a Listeria pathogen.

Increasing evidence suggests a role of CD8 T cells in autoimmune demyelinating CNS disease, which, however, is still controversially discussed. Mice, which express ovalbumin (OVA) as cytosolic self-antigen in oligodendrocytes (ODC-OVA mice), respond to CNS infection induced by OVA-expressing attenuated Listeria with CD8 T cell-mediated inflammatory demyelination. This model is suitable to decipher the contribution of CD8 T cells and the pathogen in autoimmune CNS disease. Here, we show that both antigen and pathogen are required in the CNS for disease induction, though not in a physically linked fashion. Intracerebral challenge with combined toll like receptor (TLR) TLR2 and TLR9 as well as TLR7 and TLR9 agonists substituted for the bacterial stimulus, but not with individual TLR agonists (TLR2, TLR3,TLR5,TLR7, TLR9). Furthermore, MyD88 inactivation rendered ODC-OVA mice resistant to disease induction. Collectively, CD8 T cell-mediated destruction of oligodendrocytes is activated if (i) an antigen shared with an infectious agent is provided in the CNS microenvironment and (ii) innate immune signals inform the CNS microenvironment that pathogen removal warrants an immune attack by CD8 T cells, even at the expense of locally restricted demyelination.

Brain microbiota disruption within inflammatory demyelinating lesions in multiple sclerosis.

Microbial communities reside in healthy tissues but are often disrupted during disease. Bacterial genomes and proteins are detected in brains from humans, nonhuman primates, rodents and other species in the absence of neurological disease. We investigated the composition and abundance of microbiota in frozen and fixed autopsied brain samples from patients with multiple sclerosis (MS) and age- and sex-matched nonMS patients as controls, using neuropathological, molecular and bioinformatics tools. 16s rRNA sequencing revealed Proteobacteria to be the dominant phylum with restricted diversity in cerebral white matter (WM) from MS compared to nonMS patients. Both clinical groups displayed 1,200-1,400 bacterial genomes/cm3 and low bacterial rRNA:rDNA ratios in WM. RNAseq analyses showed a predominance of Proteobacteria in progressive MS patients' WM, associated with increased inflammatory gene expression, relative to a broader range of bacterial phyla in relapsing-remitting MS patients' WM. Although bacterial peptidoglycan (PGN) and RNA polymerase beta subunit immunoreactivities were observed in all patients, PGN immunodetection was correlated with demyelination and neuroinflammation in MS brains. Principal component analysis revealed that demyelination, PGN and inflammatory gene expression accounted for 86% of the observed variance. Thus, inflammatory demyelination is linked to an organ-specific dysbiosis in MS that could contribute to underlying disease mechanisms.

Molecular mimicry between Mycobacterium leprae proteins (50S ribosomal protein L2 and Lysyl-tRNA synthetase) and myelin basic protein: a possible mechanism of nerve damage in leprosy.

Autoantibodies against various components of host are known to occur in leprosy. Nerve damage is the primary cause of disability associated with leprosy. The aim of this study was to detect the level of autoantibodies and lympho-proliferative response against myelin basic protein (MBP) in leprosy patients (LPs) and their correlation with clinical phenotypes of LPs. Further, probable role of molecular mimicry in nerve damage of LPs was investigated. We observed significantly high level of anti-MBP antibodies in LPs across the spectrum and a positive significant correlation between the level of anti-MBP antibodies and the number of nerves involved in LPs. We report here that 4 B cell epitopes of myelin A1 and Mycobacterium leprae proteins, 50S ribosomal L2 and lysyl tRNA synthetase are cross-reactive. Further, M. leprae sonicated antigen hyperimmunization was responsible for induction of autoantibody response in mice which could be adoptively transferred to naive mice. For the first time our findings suggest the role of molecular mimicry in nerve damage in leprosy.

Gut commensalism, cytokines, and central nervous system demyelination.

There is increasing support for the importance of risk factors such as genetic makeup, obesity, smoking, vitamin D insufficiency, and antibiotic exposure contributing to the development of autoimmune diseases, including human multiple sclerosis (MS). Perhaps the greatest environmental risk factor associated with the development of immune-mediated conditions is the gut microbiome. Microbial and helminthic agents are active participants in shaping the immune systems of their hosts. This concept is continually reinforced by studies in the burgeoning area of commensal-mediated immunomodulation. The clinical importance of these findings for MS is suggested by both their participation in disease and, perhaps of greater clinical importance, attenuation of disease severity. Observations made in murine models of central nervous system demyelinating disease and a limited number of small studies in human MS suggest that immune homeostasis within the gut microbiome may be of paramount importance in maintaining a disease-free state. This review describes three immunological factors associated with the gut microbiome that are central to cytokine network activities in MS pathogenesis: T helper cell polarization, T regulatory cell function, and B cell activity. Comparisons are drawn between the regulatory mechanisms attributed to first-line therapies and those described in commensal-mediated amelioration of central nervous system demyelination.

Digesting the emerging role for the gut microbiome in central nervous system demyelination.

The fields of microbiology, immunology, neurology and nutrition are rapidly converging, as advanced sequencing and genomics-based methodologies have enabled the mapping out of the microbial diversity of humans for the first time. Bugs, guts, brains and behavior were once believed to be separate domains of clinical practice and research; however, recent observations in our understanding of the microbiome indicate that the boundaries between domains are becoming permeable. This permeability is multidirectional: Biological systems are operating simultaneously in a vastly complex and interconnected web. Understanding the microbiome-gut-brain axis will entail fleshing out the mechanisms by which transduction across each domain occurs, allowing us ultimately to appreciate the role of commensal organisms in shaping and modulating host immunity. This article will highlight animal and human research to date, as well as highlight directions for future research. We speculate that the gut microbiome is potentially the premier environmental risk factor mediating inflammatory central nervous system demyelination, in particular multiple sclerosis.

An unusual case of neurobrucellosis presenting as demyelination disorder.

Brucellosis is a public health problem in most countries in the Mediterranean. Involvement of the central nervous system is seen in 4-13% of patients with brucellosis. A 13-year-old girl was admitted because of gait disturbance, diplopia, and dizziness. Her complaints began about 1.5 years ago. The second symptomatic episode repeated about three months ago and the third two months ago. In total, attacks repeated 3 times over 1.5 years. The magnetic resonance imaging (MRI) and the clinical features mimicked multiple sclerosis. The patient was given pulse steroid treatments. After steroid treatment, her gait disturbance and diplopia improved over the short term. Following positive developments, her symptoms recurred. The tests were repeated; the MRI showed increasingly high signal abnormalities, and Brucella melitensis was grown in cerebrospinal fluid. The patient was started on an oral combination of rifampin, doxycycline, and ciprofloxacin. MRI findings improved markedly after nine months of treatment. Although neurobrucellosis is associated rarely with demyelination in adults, this finding has not been reported previously in children or adolescents. Additionally, this case is the first in terms of involvement of the corpus callosum in neurobrucellosis. In this article, we present an unusual case of neurobrucellosis.

Early-life hygiene-related factors affect risk of central nervous system demyelination and asthma differentially.

The increasing prevalence of immune-related diseases, including multiple sclerosis, may be partly explained by reduced microbial burden during childhood. Within a multi-centre case-control study population, we examined: (i) the co-morbid immune diseases profile of adults with a first clinical diagnosis of central nervous system demyelination (FCD) and (ii) sibship structure in relation to an autoimmune (FCD) and an allergic (asthma) disease. FCD cases (n = 282) were aged 18-59 years; controls (n = 558) were matched on age, sex and region. Measures include: history of doctor-diagnosed asthma; sibling profile (number; dates of birth); and regular childcare attendance. FCD cases did not differ from controls with regard to personal or family history of allergy, but had a greater likelihood of chronic fatigue syndrome [odds ratio (OR) = 3·11; 95% confidence interval (CI) 1·11, 8·71]. Having any younger siblings showed reduced odds of FCD (OR = 0·68; 95% CI: 0·49, 0·95) but not asthma (OR = 1·47; 95% CI: 0·91, 2·38). In contrast, an increasing number of older siblings was associated with reduced risk of asthma (P trend = 0·04) but not FCD (P trend = 0·66). Allergies were not over-represented among people presenting with FCD. Sibship characteristics influence both FCD and asthma risk but the underlying mechanisms differ, possibly due to the timing of the putative 'sibling effect'.

Infection with B. burgdorferi s.l., and the CNS demyelinating disease. A case report.

The work describes three cases of patients at various ages, diagnosed for CNS demyelinating disease. The presence of specific antibodies to B. burgdorferi sensu lato, and findings of B. burgdorferi s.l. DNA, identified in one case as the genospecies B. garinii in the liquor, indicated previous experience with the infection. Presumably, persistence of borrelia in the organism could act as one of the autoimmune process triggers, resulting in the demyelinating disease.

Acute disseminating encephalomyelitis following legionnaires disease.

OBJECTIVE: To describe 2 patients presenting with severe neurological deficits and extensive lesions on brain magnetic resonance imaging after having experienced Legionella pneumonia. DESIGN: Case reports. SETTING: University hospital. PATIENTS: Two patients who developed severe neurological symptoms, including encephalopathic signs, following Legionella infection, with widespread lesions on magnetic resonance imaging compatible with demyelination. RESULTS: After extensive ancillary investigations, a diagnosis of acute disseminating encephalomyelitis was considered most likely. Steroid therapy was initiated in 1 of the patients, followed by plasmapheresis. In both patients, clinical and radiological signs gradually recovered, with only slight residual deficits. CONCLUSION: In patients presenting with neurological symptoms after an episode of pneumonia, Legionella infection and a subsequent immune-mediated process such as acute disseminating encephalomyelitis should be considered.

Neurogenic exacerbation of microglial and astrocyte responses to Neisseria meningitidis and Borrelia burgdorferi.

Although glial cells are recognized for their roles in maintaining neuronal function, there is growing appreciation of the ability of resident CNS cells to initiate and/or augment inflammation following trauma or infection. The tachykinin, substance P (SP), is well known to augment inflammatory responses at peripheral sites and its presence throughout the CNS raises the possibility that this neuropeptide might serve a similar function within the brain. In support of this hypothesis, we have recently demonstrated the expression of high affinity receptors for SP (Neurokinin-1 (NK-1) receptors) on microglia and shown that this tachykinin can significantly elevate bacterially induced inflammatory prostanoid production by isolated cultures of these cells. In the present study, we demonstrate that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation in vivo following exposure to two clinically relevant bacterial CNS pathogens, Neisseria meningitidis and Borrelia burgdorferi. We show that in vivo elevations in inflammatory cytokine production and decreases in the production of an immunosuppressive cytokine are markedly attenuated in mice genetically deficient in the expression of the NK-1R or in mice treated with a specific NK-1R antagonist. Furthermore, we have used isolated cultures of microglia and astrocytes to demonstrate that SP can augment inflammatory cytokine production by these resident CNS cell types following exposure to either of these bacterial pathogens. Taken together, these studies indicate a potentially important role for neurogenic exacerbation of resident glial immune responses in CNS inflammatory diseases, such as bacterial meningitis.

Inflammation and primary demyelination induced by the intraspinal injection of lipopolysaccharide.

Inflammation is a prominent feature of several disorders characterized by primary demyelination, but it is not clear whether a relationship exists between inflammation and myelin damage. We have found that substantial demyelination results from the focal inflammatory lesion caused by the injection of lipopolysaccharide (LPS; 200 ng) directly into the rat dorsal funiculus. Within 24 h, such injections caused a focal inflammatory response consisting of a substantial number of polymorphonuclear cells and ED1-positive and inducible nitric oxide synthase (iNOS)-positive macrophages/microglia. The number of inflammatory cells was substantially reduced by day 7. OX-52-positive T-cells were less frequently observed but were present in the meninges at 8 h, reached a maximum in the dorsal funiculus at 7 days, and were rare at 14 days. The inflammation was followed by the appearance of a large lesion of primary demyelination that encompassed up to approximately 75% of the cross-sectional area of the dorsal funiculus. Treatment with dexamethasone significantly reduced the number of cells expressing iNOS, but did not prevent the demyelination. By 28 days the lesions were largely remyelinated, usually by Schwann cells. These changes were not observed in control, saline-injected animals. We conclude that the intraspinal injection of LPS results in inflammation and subsequently in prominent demyelination. The mechanisms underlying the demyelination are not clear, but it is notable that it typically begins with disruption of the adaxonal myelin. Indeed, there is an early loss of myelin-associated glycoprotein within the lesion, despite the persistence of proteolipid protein. This combination is a feature of the pattern III lesion recently described in multiple sclerosis (Lucchinetti et al., 2000), and we therefore suggest that LPS-induced demyelination may serve as the first experimental model available for the study of this type of multiple sclerosis lesion.

Acute central and peripheral demyelination associated with Mycoplasma pneumoniae.

A 7-year-old female presented with Mycoplasma pneumoniae pneumonitis and a progressive ascending limb paralysis. She developed severe respiratory distress, requiring ventilation, and became apparently unresponsive with fixed dilated pupils. Peripheral nerves were inexcitable in nerve-conduction studies. Magnetic resonance imaging of the brain revealed evidence of extensive demyelination. Anti-GM1 immunoglobulin M antibody titers were raised. She improved after a second course of intravenous immunoglobulin and eventually made a full recovery.

Differential distribution of HLA-DQ beta/DR beta epitopes in the two forms of Guillain-Barré syndrome, acute motor axonal neuropathy and acute inflammatory demyelinating polyneuropathy (AIDP): identification of DQ beta epitopes associated with susceptibility to and protection from AIDP.

Guillain-Barré syndrome (GBS), an acute, immune-mediated paralytic disorder affecting the peripheral nervous system, is the most common cause of acute flaccid paralysis in the post-polio era. GBS is classified into several subtypes based on clinical and pathologic criteria, with acute inflammatory demyelinating polyneuropathy (AIDP) and acute motor axonal neuropathy (AMAN) being the most common forms observed. To better understand the pathogenesis of GBS and host susceptibility to developing the disease, the distribution of HLA class II Ags along with the seroreactivity to Campylobacter jejuni were investigated in a population of GBS patients from northern China. Using DNA-based typing methods, 47 patients with AMAN, 25 patients with AIDP, and 97 healthy controls were studied for the distribution of class II alleles. We found that the DQ beta RLD(55-57)/ED(70-71) and DR beta E(9)V(11)H(13) epitopes were associated with susceptibility to AIDP (p = 0.009 and p = 0.004, respectively), and the DQ beta RPD(55-57) epitope was associated with protection (p = 0.05) from AIDP. These DQ beta/DR beta positional residues are a part of pockets 4 (DQ beta 70, 71, DR beta 13), 6 (DR beta 11), and 9 (DQ beta 56, 57, DR beta 9); have been demonstrated to be important in peptide binding and T cell recognition; and are associated with other diseases that have a pathoimmunological basis. Class II HLA associations were not identified with AMAN, suggesting a different immunological mechanism of disease induction in the two forms of GBS. These findings provide immunogenetic evidence for differentiating the two disease entities (AMAN and AIDP) and focuses our attention on particular DR beta/DQ beta residues that may be instrumental in understanding the pathophysiology of AIDP.