Implications of Microglia in Amyotrophic Lateral Sclerosis and Frontotemporal Dementia

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are neurodegenerative disorders with clear similarities regarding their clinical, genetic and pathological features. Both are progressive, lethal disorders, with no current curative treatment available. Several genes that correlated with ALS and FTD are implicated in the same molecular pathways. Strikingly, many of these genes are not exclusively expressed in neurons, but also in glial cells, suggesting a multicellular pathogenesis. Moreover, chronic inflammation is a common feature observed in ALS and FTD, indicating an essential role of microglia, the resident immune cells of the central nervous system, in disease development and progression. In this review, we will provide a comprehensive overview of the implications of microglia in ALS and FTD. Specifically, we will focus on the role of impaired phagocytosis and increased inflammatory responses and their impact on microglial function. Several genes associated with the disorders can directly be linked to microglial activation, phagocytosis and neuroinflammation. Other genes associated with the disorders are implicated in biological pathways involved in protein degradation and autophagy. In general such mutations have been shown to cause abnormal protein accumulation and impaired autophagy. These impairments have previously been linked to affect the innate immune system in the central nervous system through inappropriate activation of microglia and neuroinflammation, highlighted in this review. Although it has been well established that microglia play essential roles in neurodegenerative disorders, the precise underlying mechanisms remain to be elucidated.     

运动调控肠道菌群在阿尔茨海默病防治中的应用

阿尔茨海默病（Alzheimer's disease,AD）是一种起病隐匿且呈进行性发展的中枢神经系统退行性疾病,以记忆障碍、语言功能和其他认知能力衰退为主要症状,可导致患者日常生活能力下降,出现精神行为异常,给家庭和社会带来极大的负担。肠道菌群已被发现不仅是免疫和代谢健康的重要组成部分,而且对胃肠道和中枢神经系统的发育具有重要作用。运动医学作为一种新兴的治疗手段,能显著改善肠道菌群紊乱,调节脾胃功能,改善代谢和睡眠,延缓AD的进程。本文通过总结运动及其相关因素对肠道菌群的影响,探讨AD的预防和控制。

     

Glycosphingolipids as Potential Diagnostic Markers and/or Antigens in Neurological Disorders

Glycosphingolipids are most abundant in the nervous system within which there are developmental, regional, structural and cellular differences regarding their composition. They are shedded to the cerebrospinal fluid and thus potential markers for pathogenic alterations in the brain, such as developmental abnormalities, demyelination, gliosis, neuronal cell destruction. The glycosphingolipids have also been found to be antigens in autoimmune processes involving the nervous system, in particular in peripheral neuropathies like Guillain Barré syndrome, multifocal motor neuropathy etc. The immune response might have been triggered by infectious agents with an antigen epitope which mimic the glycosphingolipid or by a primary nerve tissue damage leading to release of glycosphingolipids. There is a series of support for a clinical significance of cerebrospinal fluid glycosphingolipid determinations and the presence of anti-glycosphingolipid antibodies but this has to be further explored. This paper is a mini review of the state of the art and discuss methodological aspects and improvements that might help to explore the relevance of glycosphingolipids in neurological disorders.     

Regulatory T cells for amyotrophic lateral sclerosis/motor neuron disease: A clinical and preclinical systematic review

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by neuronal degeneration and inflammation in the nerves. The role of the immune system has been concentrated by researchers in the etiopathogenesis of the disease. Given the inhibitory roles of regulatory T cells (Tregs), it is expected that increasing or activating their populations in patients with ALS can have significant therapeutic effects. Here we searched databases, including CENTRAL, MEDLINE, CINAHL Plus, clinicaltrials.gov , and ICTRP for randomized clinical trials (RCTs) and non-RCTs until March 2019. For preclinical studies, we searched PubMed, Scopus, and Google Scholar up to June 2019. We also included preclinical studies, due to the lack of clinical information available, which used Tregs (or directly targeting them) for treating mice models of ALS. We identified 29 records (CENTRAL 7, MEDLINE 4, CINAHL Plus 8, and clinicaltrials.gov 10) and removed 10 duplicated publications. After screening, we identified one RCT which had been published as an abstract, three non-RCTs, and four ongoing studies. We also identified 551 records (PubMed 446, Google Scholar 68, and Scopus 37) for preclinical studies and performed a meta-analysis. Finally, we found three papers that matched our inclusion criteria for preclinical studies. Results indicated the effectiveness of the application of Tregs in the treatment of ALS. Our meta-analysis on preclinical studies revealed that Tregs significantly prolonged survival in mice models of ALS. Overall, our analysis testified that exertion of Tregs in the treatment of ALS is a promising approach, that notwithstanding, requires further evaluations.     

Behaviorally conditioned suppression of the immune response by antilymphocyte serum

Previous studies have shown that cyclophosphamide, a drug with a broad spectrum of cytotoxic activity and one that produces noxious gastrointestinal side effects, can elicit taste aversion conditioning when paired with a non-immunosuppressive oral stimulus (saccharin) resulting in immunosuppression after subsequent exposure to the paired stimulus (1). The study reported here indicates that rabbit anti-rat lymphocyte serum (ALS) which is selectively cytotoxic for lymphocytes and does not produce sensory side effects can similarly induce taste aversion conditioning of the immune response. Rats were exposed to oral saccharin paired with ALS injection. Upon subsequent reexposure to saccharin alone the immunosuppressive effects of ALS were reenlisted and the primary mixed lymphocyte culture response of conditioned rats to allogeneic lymphocytes was suppressed by 35% compared to controls. The demonstrated influence of psychologic factors on the immune response has far reaching implications, especially to human medicine, and their role in the course of disease and recovery in man demands further investigation.     

Relative importance of factors affecting nestling immune response differs between junior and senior nestlings within broods of hoopoes Upupa epops

Animals should invest in the immune system to protect themselves from parasites, but the cost of immune responses may limit investment depending on resource availability. In birds' broods, senior and junior chicks in size hierarchies face different rearing conditions, and thus we predicted that factors affecting immune response should differ between them. In asynchronously hatched hoopoe Upupa epops broods, we found that the immune response of senior nestlings was not related to their body condition, but positively related to risk of parasitism (which was indirectly estimated by laying date). This suggests that their immunocompetence is not limited by access to resources, and they can differentially invest in immune response with increasing risk of parasitism. On the other hand, immune response of junior nestlings was related to their body condition, but secondarily also to risk of parasitism. Our results agree with previous studies that have found significant influence of nutritional status and risk of parasitism on nestlings immune defence, but show that the effects of these environmental factors on nestling immunocompetence differ between nestlings occupying high and low rank positions in size hierarchies. The possible influence of maternal effects on the results found is also discussed.     

Disease Mechanisms in ALS: Misfolded SOD1 Transferred Through Exosome-Dependent and Exosome-Independent Pathways

Amyotrophic lateral sclerosis (ALS) is a fatal adult-onset neuromuscular degenerative disorder with a poorly defined etiology. ALS patients experience motor weakness, which starts focally and spreads throughout the nervous system, culminating in paralysis and death within a few years of diagnosis. While the vast majority of clinical ALS is sporadic with no known cause, mutations in human copper-zinc superoxide dismutase 1 (SOD1) cause about 20 % of inherited cases of ALS. ALS with SOD1 mutations is caused by a toxic gain of function associated with the propensity of mutant SOD1 to misfold, presenting a non-native structure. The mechanisms responsible for the progressive spreading of ALS pathology have been the focus of intense study. We have shown that misfolded SOD1 protein can seed misfolding and aggregation of endogenous wild-type SOD1 similar to amyloid-β and prion protein seeding. Our recent observations demonstrate a transfer of the misfolded SOD1 species from cell to cell, modeling the intercellular transmission of disease through the neuroaxis. We have shown that both mutant and misfolded wild-type SOD1 can traverse cell-to-cell, either as protein aggregates that are released from dying cells and taken up by neighboring cells via macropinocytosis, or in association with vesicles which are released into the extracellular environment. Furthermore, once misfolding of wild-type SOD1 has been initiated in a human cell culture, it can induce misfolding in naïve cell cultures over multiple passages of media transfer long after the initial misfolding template is degraded. Herein we review the data on mechanisms of intercellular transmission of misfolded SOD1.     

Cellular ageing of Alzheimer's disease and Down syndrome cells in culture.

In Alzheimer's disease, the typical clinical symptoms and the pathological findings are restricted to the nervous system. Nevertheless, like in some other neurologic-metabolic disorders, several alterations are found in peripheral tissues. The aim of this study was to examine whether cellular properties which can be studied in vitro on skin fibroblast cultures obtained from Alzheimer's disease patients differ from those of age-matched controls. Down syndrome patients were also included, since the same neuropathological findings are present in nearly 100% of Down syndrome patients. Since Alzheimer's disease is an age-related disorder, we examined the growth characteristics of skin fibroblast cultures. The in vitro senescence of cultured fibroblasts is widely accepted as a model for in vivo ageing. Normal growth properties were found. We can conclude that there is no premature ageing in Alzheimer's disease nor in Down syndrome and that the abnormalities found in peripheral tissues are related to the disease itself. The beta amyloid precursor protein (beta APP) has been shown to have adhesive interactions. We therefore investigated several parameters of adhesion in the skin fibroblast cultures: adhesion to a fibronectin coat, adhesion to extracellular matrix of Alzheimer's disease cultures and semi-quantification of adhesion-related molecules (beta 1-integrin, cell surface proteoglycans, extracellular matrix proteoglycans, extracellular matrix fibronectin). No significant difference was found in the parameters examined.     

Label-free quantitative proteomic analysis reveals dysfunction of complement pathway in peripheral blood of schizophrenia patients: evidence for the immune hypothesis of schizophrenia

Schizophrenia is a complex mental disease caused by a combination of serial alterations in genetic and environmental factors. Although the brain is usually considered as the most relevant organ in schizophrenia, accumulated evidence suggests that peripheral tissues also contribute to this disease. In particular, abnormalities of the immune system have been identified in the peripheral blood of schizophrenia patients. To screen the serum proteomic signature of schizophrenia patients, we conducted shotgun proteomic analysis on serum samples of schizophrenia patients and healthy controls. High-abundance proteins were eliminated by immunoaffinity before LC-MS/MS analysis. The multivariate statistical test partial least squares-discriminant analysis (PLS-DA) was applied to build models for screening out variable importance in the projection (VIP) and 27 proteins were identified as being responsible for discriminating between the proteomic profiles of schizophrenia patients and healthy controls. Pathway analysis based on these 27 proteins revealed that complement and coagulation cascades was the most significant pathway. ELISA-based activity analyses indicated that the alternative complement pathway was suppressed in schizophrenia patients. Ingenuity pathways analysis was used to conduct the interaction network of 27 proteins. The network exhibited common features such as, nervous system development and function, humoral immune response and inflammatory response, and highlighted some proteins with important roles in the immune system, such as hub nodes. Our findings indicate dysregulation of the alternative complement pathway in schizophrenia patients. The protein interaction network enhances the interpretation of proteomic data and provides evidence that the immune system may contribute to schizophrenia.     

Experimental allergic encephalomyelitis: role of fibrin deposition in immunopathogenesis of inflammation in rats.

The immunopathogenesis of experimental allergic encephalomyelitis (EAE) is reviewed with special focus on the role of central nervous system fibrin deposition in the inflammatory cascade characterizing this autoimmune disease. Among rats sensitized to whole spinal cord or myelin basic protein of either guinea pig or bovine origin, there is a striking degree of concordance of perivascular fibrin deposits and occurrence of clinical paralytic signs. Neither paralytic signs nor fibrin deposition are temporally related to development of perivascular cellular infiltrates. Rats sensitized to neuroantigen and treated with ancrod, a polypeptide derived from the venom of Agkistrodon rhodostoma, develop profound hypofibrinogenemia, have a marked inhibition of fibrin deposition, and often exhibit no paralytic signs whatsoever. In contrast, cellular infiltrates are not demonstrably influenced by ancrod treatment. Activation of the clotting cascade at loci of developing immune injury of nervous tissue appears to result from and lead to increasing neurovascular permeability and accumulation of edema fluid. Distention of the extracellular space in central and peripheral nervous system tissues by edema fluid appears to be directly responsible for clinical abnormalities characterizing EAE in rats. Cellular infiltrates, on the other hand, appear to be an independent immune response to neuroantigenic sensitization.     

Network Analyses Reveal Novel Aspects of ALS Pathogenesis

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease characterized by selective loss of motor neurons, muscle atrophy and paralysis. Mutations in the human VAMP-associated protein B (hVAPB) cause a heterogeneous group of motor neuron diseases including ALS8. Despite extensive research, the molecular mechanisms underlying ALS pathogenesis remain largely unknown. Genetic screens for key interactors of hVAPB activity in the intact nervous system, however, represent a fundamental approach towards understanding the in vivo function of hVAPB and its role in ALS pathogenesis. Targeted expression of the disease-causing allele leads to neurodegeneration and progressive decline in motor performance when expressed in the adult Drosophila, eye or in its entire nervous system, respectively. By using these two phenotypic readouts, we carried out a systematic survey of the Drosophila genome to identify modifiers of hVAPB-induced neurotoxicity. Modifiers cluster in a diverse array of biological functions including processes and genes that have been previously linked to hVAPB function, such as proteolysis and vesicular trafficking. In addition to established mechanisms, the screen identified endocytic trafficking and genes controlling proliferation and apoptosis as potent modifiers of ALS8-mediated defects. Surprisingly, the list of modifiers was mostly enriched for proteins linked to lipid droplet biogenesis and dynamics. Computational analysis reveals that most modifiers can be linked into a complex network of interacting genes, and that the human genes homologous to the Drosophila modifiers can be assembled into an interacting network largely overlapping with that in flies. Identity markers of the endocytic process were also found to abnormally accumulate in ALS patients, further supporting the relevance of the fly data for human biology. Collectively, these results not only lead to a better understanding of hVAPB function but also point to potentially relevant targets for therapeutic intervention.     

Regulation of pituitary peptides by the immune system

It has long been thought that the central nervous system is able to influence the progression of disease. Furthermore, there is now overwhelming evidence that the communication pathways are bidirectional. A variety of immune system peptides are now known to be capable of transmitting information from the immune system to the central nervous system. These immunotransmitters include interleukins, interferons and thymosine peptides which have the capability of modulating slow-wave sleep as well as the release of neuro- and pituitary peptides. In some instances, release of these peptides during early development may have long lasting, if not permanent effects upon the normal development of neuroendocrine circuits. Collectively these various brain mediated events appear to contribute in various and diverse ways to defense against pathogens. It is becoming more and more apparent that certain abnormalities within the immune system may be the consequence of a neurological abnormality. The converse is also true.     

Mitochondrial involvement in amyotrophic lateral sclerosis

Despite numerous reports demonstrating mitochondrial abnormalities associated with amyotrophic lateral sclerosis (ALS), the role of mitochondrial dysfunction in the disease onset and progression remains unknown. The intrinsic mitochondrial apoptotic program is activated in the central nervous system of mouse models of ALS harboring mutant superoxide dismutase 1 protein. This is associated with the release of cytochrome-c from the mitochondrial intermembrane space and mitochondrial swelling. However, it is unclear if the observed mitochondrial changes are caused by the decreasing cellular viability or if these changes precede and actually trigger apoptosis. This article discusses the current evidence for mitochondrial involvement in familial and sporadic ALS and concludes that mitochondria is likely to be both a trigger and a target in ALS and that their demise is a critical step in the motor neuron death.     

Sera from amyotrophic lateral sclerosis patients induce the non-canonical activation of NMDA receptors "in vitro"

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease characterized by the selective loss of both upper and lower motoneurons (MNs). The familial form of the illness is associated with mutations in the gene encoding Cu/Zn superoxide dismutase 1 (SOD-1) enzyme, but it accounts for fewer than 10% of cases; the rest, more than 90%, correspond to the sporadic form of ALS. Although many proposals have been suggested over the years, the mechanisms underlying the characteristic selective killing of MN in ALS remain unknown. In this study we tested the effect of sera from sporadic ALS patients on NMDA receptors (NMDAR). We hypothesize that an endogenous seric factor is implicated in neuronal death in ALS, mediated by the modulation of NMDAR.Sera from ALS patients and from healthy subjects were pretreated to inactivate complement pathways and dialyzed to remove glutamate and glycine. IgGs from ALS patients and healthy subjects were obtained by affinity chromatography and dialyzed against phosphate-buffered saline. Human NMDAR were expressed in Xenopus laevis oocytes, and ionic currents were recorded using the two-electrode voltage clamp technique.Sera from sporadic ALS patients induced transient oscillatory currents in oocytes expressing NMDAR with a significantly higher total electrical charge than that induced by sera from healthy subjects. Sera from patients with other neuromuscular diseases did not exert this effect. The currents were inhibited by MK-801, a noncompetitive blocker of NMDAR. The PLC inhibitor, U-73122, and the IP₃ receptor antagonist, 2-APB, also inhibited the sera-induced currents. The oscillatory signal recorded was due to internal calcium mobilization. Isolated IgGs from ALS patients significantly affected the activity of oocytes injected with NMDAR, causing a 2-fold increase over the response recorded for IgGs from healthy subjects.Our data support the notion that ALS sera contain soluble factors that mobilize intracellular calcium, not opening directly the ionic conductance, but through the non-canonical activation of NMDAR.     

Mind over immunity.

The central nervous system regulates the innate immune system by elaborating anti-inflammatory hormone cascades in response to bacterial products and immune mediators. We recently discovered that the central nervous system also responds via acetylcholine-mediated efferent signals carried through the vagus nerve. Nicotinic cholinergic receptors expressed on macrophages detect these signals and respond with a dampened cytokine response. Vagus nerve stimulators can mimic this response and can prevent lethal endotoxemia. This newly appreciated cholinergic anti-inflammatory pathway provides a neural substrate to study brain-immune interactions and might be harnessed for therapy of cytokine-mediated disease.     

Mitochondrial dysfunction and its role in motor neuron degeneration in ALS

Mitochondria play a pivotal role in many metabolic and apoptotic pathways that regulate the life and death of cells. Accumulating evidence suggests that mitochondrial dysfunction is involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). Mitochondrial dysfunction may cause motor neuron death by predisposing them to calcium-mediated excitotoxicity, by increasing generation of reactive oxygen species, and by initiating the intrinsic apoptotic pathway. Morphological and biochemical mitochondrial abnormalities have been described in sporadic human ALS cases, but the implications of these findings in terminally ill individuals or in post-mortem tissues are difficult to decipher. However, remarkable mitochondrial abnormalities have also been identified in transgenic mouse models of familial ALS expressing mutant Cu, Zn superoxide dismutase (SOD1). Detailed studies in these mouse models indicate that mitochondrial abnormalities begin prior to the clinical and pathological onset of the disease, suggesting that mitochondrial dysfunction may be causally involved in the pathogenesis of ALS. Although the mechanisms whereby mutant SOD1 damages mitochondria remain to be fully understood, the finding that a portion of mutant SOD1 is localized in mitochondria, where it forms aberrant aggregates and protein interactions, has opened a number of avenues of investigation. The future challenges are to devise models to better understand the effects of mutant SOD1 in mitochondria and the relative contribution of mitochondrial dysfunction to the pathogenesis of ALS, as well as to identify therapeutic approaches that target mitochondrial dysfunction and its consequences.     

Harnessing the immune system for neuroprotection: therapeutic vaccines for acute and chronic neurodegenerative disorders

Nerve injury causes degeneration of directly injured neurons and the damage spreads to neighboring neurons. Research on containing the damage has been mainly pharmacological, and has not recruited the immune system. We recently discovered that after traumatic injury to the central nervous system (spinal cord or optic nerve), the immune system apparently recognizes certain injury-associated self-compounds as potentially destructive and comes to the rescue with a protective antiself response mediated by a T-cell subpopulation that can recognize self-antigens. We further showed that individuals differ in their ability to manifest this protective autoimmunity, which is correlated with their ability to resist the development of autoimmune diseases. This finding led us to suggest that the antiself response must be tightly regulated to be expressed in a beneficial rather than a destructive way. In seeking to develop a neuroprotective therapy by boosting the beneficial autoimmune response to injury-associated self-antigens, we looked for an antigen that would not induce an autoimmune disease. Candidate vaccines were the safe synthetic copolymer Cop-1, known to cross-react with self-antigens, or altered myelin-derived peptides. Using these compounds as vaccines, we could safely boost the protective autoimmune response in animal models of acute and chronic insults of mechanical or biochemical origin. Since this vaccination is effective even when given after the insult, and because it protects against the toxicity of glutamate (the most common mediator of secondary degeneration), it can be used to treat chronic neurodegenerative disorders such as glaucoma, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.