Cytotoxic CD8+ T lymphocytes expressing ALS-causing SOD1 mutant selectively trigger death of spinal motoneurons

Neuroinflammation in amyotrophic lateral sclerosis: pathogenic insights and therapeutic implications

PURPOSE OF REVIEW

Neuroinflammation appears to be an important pathogenic process in amyotrophic lateral sclerosis (ALS). Dysfunction of central immune pathways, including activation of microglia and astrocytes, and peripherally derived immune cells, initiate noncell autonomous inflammatory mechanisms leading to degeneration. Cell autonomous pathways linked to ALS genetic mutations have been recently identified as contributing mechanism for neurodegeneration. The current review provides insights into the pathogenic importance of central and peripheral inflammatory processes in ALS pathogenesis and appraises their potential as therapeutic targets.

RECENT FINDINGS

ALS is a multistep process mediated by a complex interaction of genetic, epigenetic, and environmental factors. Noncell autonomous inflammatory pathways contribute to neurodegeneration in ALS. Activation of microglia and astrocytes, along with central nervous system infiltration of peripherally derived pro-inflammatory innate (NK-cells/monocytes) and adaptive (cell-mediated/humoral) immune cells, are characteristic of ALS. Dysfunction of regulatory T-cells, elevation of pro-inflammatory cytokines and dysbiosis of gut microbiome towards a pro-inflammatory phenotype, have been reported as pathogenic mechanisms in ALS.

SUMMARY

Dysregulation of adaptive and innate immunity is pathogenic in ALS, being associated with greater disease burden, more rapid disease course and reduced survival. Strategies aimed at modulating the pro-inflammatory immune components could be of therapeutic utility.

Effect of ultrasound-mediated blood-spinal cord barrier opening on survival and motor function in females in an amyotrophic lateral sclerosis mouse model

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by a progressive loss of motor neurons. The limited efficacy of recent therapies in clinical development may be linked to lack of drug penetration to the affected motor neurons due to the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB).

METHODS

In this work, the safety and efficacy of repeated short transient opening of the BSCB by low intensity pulsed ultrasound (US, sonication) was studied in females of an ALS mouse model (B6.Cg-Tg(SOD1∗G93A)1Gur/J). The BSCB was disrupted using a 1 MHz ultrasound transducer coupled to the spinal cord, with and without injection of insulin-like growth factor 1 (IGF1), a neurotrophic factor that has previously shown efficacy in ALS models.

FINDINGS

Results in wild-type (WT) animals demonstrated that the BSCB can be safely disrupted and IGF1 concentrations significantly enhanced after a single session of transient BSCB disruption (176 ± 32 μg/g vs. 0.16 ± 0.008 μg/g, p < 0.0001). Five repeated weekly US sessions performed in female ALS mice demonstrated a survival advantage in mice treated with IGF1 and US (US IGF1) compared to treatment with IGF1 alone (176 vs. 166 days, p = 0.0038). Surprisingly, this survival advantage was also present in mice treated with US alone vs. untreated mice (178.5 vs. 166.5 days, p = 0.0061). Muscle strength did not show difference among the groups. Analysis of glial cell immunoreactivity and microglial transcriptome showing reduced cell proliferation pathways, in addition to lymphocyte infiltration, suggested that the beneficial effect of US or US IGF1 could act through immune cell modulation.

INTERPRETATION

These results show the first step towards a possible beneficial impact of transient BSCB opening for ALS therapy and suggest implication of immune cells.

FUNDING

Fondation pour la Recherche Médicale (FRM). Investissements d'avenirANR-10-IAIHU-06, Société Française de Neurochirurgie (SFNC), Fond d'étude et de Recherche du Corps Medical (FERCM), Aide à la Recherche des Maladies du Cerveau (ARMC), SLA Fondation Recherche (SLAFR), French Ministry for High Education and Research (MENR), Carthera, Laboratoire de Recherche en Technologies Chirurgicales Avancées (LRTCA).

Peripheral immunity relate to disease progression and prognosis in amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. Abnormalities in the peripheral immune system in ALS have been paid attention; however, the results of changes in peripheral immune parameters were inconsistent.

METHODS

A total of 1109 ALS patients were enrolled in the study. All patients received clinical evaluation and peripheral immune parameters measurement. The outcomes were analyzed by correlation analysis, multiple linear regression and cox survival analysis.

RESULTS

We found that ALS patients had significantly higher percentage of CD4+ T cells (39.3 vs. 37.1%, p < 0.001) and CD4+/CD8+ ratio (1.88 vs. 1.72, p = 0.011), significantly lower IgG (11.73 vs.12.82, p < 0.001) and IgA (2130.70 vs. 2284.8, p = 0.013) compared with the health controls. In the multivariate linear model, we found that each increase of 1.262, 0.278, and 4.44E-4 in ALSFRS-R scores were significantly associated with each increment of lymphocyte count, IgG, and IgA, respectively. However, each decrease of 0.341, 0.068, and 0.682 in ALSFRS-R score was associated with each increment in neutrophils, CD4+ T cells, and CD4+/CD8+ ratio, respectively. Cox survival regression analysis showed that the death risk of ALS patients was related to the levels of C3 (HR 0.592, 95% CI 0.361-0.973).

CONCLUSION

We found that there were differences in peripheral immune parameters of ALS patients with the severity of the disease, especially neutrophil, lymphocyte, CD4+ T, and IgG; C3 is an independent predictor of survival in ALS patients. More studies are needed to elucidate the mechanisms associated with altered immune parameters in ALS.

Allogeneic B cell immunomodulatory therapy in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an orphan neurodegenerative disease. Immune system dysregulation plays an essential role in ALS onset and progression. Our preclinical studies have shown that the administration of exogenous allogeneic B cells improves outcomes in murine models of skin and brain injury through a process termed pligodraxis, in which B cells adopt an immunoregulatory and neuroprotective phenotype in an injured environment. Here, we investigated the effects of B-cell therapy in the SOD1G93A mouse preclinical model of ALS and in a person living with ALS. Purified splenic mature naïve B cells from haploidentical donor mice were administered intravenously in SOD1G93A mice for a total of 10 weekly doses. For the clinical study in a person with advanced ALS, IgA gammopathy of unclear significance, and B lymphopenia, CD19+ B cells were positively selected from a healthy haploidentical donor and infused intravenously twice, at a 60-day interval. Repeated intravenous B-cell administration was safe and significantly delayed disease onset, extended survival, reduced cellular apoptosis, and decreased astrogliosis in SOD1G93A mice. Repeated B-cell infusion in a person with ALS was safe and did not appear to generate a clinically evident inflammatory response. An improvement of 5 points on the ALSFRS-R scale was observed after the first infusion. Levels of inflammatory markers showed persistent reduction post-infusion. This represents a first demonstration of the efficacy of haploidentical B-cell infusion in the SOD1G93A mouse and the safety and feasibility of using purified haploidentical B lymphocytes as a cell-based therapeutic strategy for a person with ALS.

Cell-mediated cytotoxicity within CSF and brain parenchyma in spinal muscular atrophy unaltered by nusinersen treatment

5q-associated spinal muscular atrophy (SMA) is a motoneuron disease caused by mutations in the survival motor neuron 1 (SMN1) gene. Adaptive immunity may contribute to SMA as described in other motoneuron diseases, yet mechanisms remain elusive. Nusinersen, an antisense treatment, enhances SMN2 expression, benefiting SMA patients. Here we have longitudinally investigated SMA and nusinersen effects on local immune responses in the cerebrospinal fluid (CSF) - a surrogate of central nervous system parenchyma. Single-cell transcriptomics (SMA: N = 9 versus Control: N = 9) reveal NK cell and CD8+ T cell expansions in untreated SMA CSF, exhibiting activation and degranulation markers. Spatial transcriptomics coupled with multiplex immunohistochemistry elucidate cytotoxicity near chromatolytic motoneurons (N = 4). Post-nusinersen treatment, CSF shows unaltered protein/transcriptional profiles. These findings underscore cytotoxicity's role in SMA pathogenesis and propose it as a therapeutic target. Our study illuminates cell-mediated cytotoxicity as shared features across motoneuron diseases, suggesting broader implications.

A comprehensive review on the pharmacological role of gut microbiome in neurodegenerative disorders: potential therapeutic targets

Neurological disorders, including Alzheimer and Parkinson's, pose significant challenges to public health due to their complex etiologies and limited treatment options. Recent advances in research have highlighted the intricate bidirectional communication between the gut microbiome and the central nervous system (CNS), revealing a potential therapeutic avenue for neurological disorders. Thus, this review aims to summarize the current understanding of the pharmacological role of gut microbiome in neurological disorders. Mounting evidence suggests that the gut microbiome plays a crucial role in modulating CNS function through various mechanisms, including the production of neurotransmitters, neuroactive metabolites, and immune system modulation. Dysbiosis, characterized by alterations in gut microbial composition and function, has been observed in many neurological disorders, indicating a potential causative or contributory role. Pharmacological interventions targeting the gut microbiome have emerged as promising therapeutic strategies for neurological disorders. Probiotics, prebiotics, antibiotics, and microbial metabolite-based interventions have shown beneficial effects in animal models and some human studies. These interventions aim to restore microbial homeostasis, enhance microbial diversity, and promote the production of beneficial metabolites. However, several challenges remain, including the need for standardized protocols, identification of specific microbial signatures associated with different neurological disorders, and understanding the precise mechanisms underlying gut-brain communication. Further research is necessary to unravel the intricate interactions between the gut microbiome and the CNS and to develop targeted pharmacological interventions for neurological disorders.

Adaptive immune changes associate with clinical progression of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is the most frequent cause of dementia. Recent evidence suggests the involvement of peripheral immune cells in the disease, but the underlying mechanisms remain unclear.

METHODS

We comprehensively mapped peripheral immune changes in AD patients with mild cognitive impairment (MCI) or dementia compared to controls, using cytometry by time-of-flight (CyTOF).

RESULTS

We found an adaptive immune signature in AD, and specifically highlight the accumulation of PD1+ CD57+ CD8+ T effector memory cells re-expressing CD45RA in the MCI stage of AD. In addition, several innate and adaptive immune cell subsets correlated to cerebrospinal fluid (CSF) biomarkers of AD neuropathology and measures for cognitive decline. Intriguingly, subsets of memory T and B cells were negatively associated with CSF biomarkers for tau pathology, neurodegeneration and neuroinflammation in AD patients. Lastly, we established the influence of the APOE ε4 allele on peripheral immunity.

CONCLUSIONS

Our findings illustrate significant peripheral immune alterations associated with both early and late clinical stages of AD, emphasizing the necessity for further investigation into how these changes influence underlying brain pathology.

Human Motor Neurons Elicit Pathological Hallmarks of ALS and Reveal Potential Biomarkers of the Disease in Response to Prolonged IFNγ Exposure

Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disorder marked by progressive motor neuron degeneration and muscle denervation. A recent transcriptomic study integrating a wide range of human ALS samples revealed that the upregulation of p53, a downstream target of inflammatory stress, is commonly detected in familial and sporadic ALS cases by a mechanism linked to a transactive response DNA-binding protein 43 (TDP-43) dysfunction. In this study, we show that prolonged interferon-gamma (IFNγ) treatment of human induced pluripotent stem cell-derived spinal motor neurons results in a severe cytoplasmic aggregation of TDP-43. TDP-43 dysfunction resulting from either IFNγ exposure or an ALS-associated TDP-43 mutation was associated with the activation of the p53 pathway. This was accompanied by the hyperactivation of neuronal firing, followed by the complete loss of their electrophysiological function. Through a comparative single-cell transcriptome analysis, we have identified significant alterations in ALS-associated genes in motor neurons exposed to IFNγ, implicating their direct involvement in ALS pathology. Interestingly, IFNγ was found to induce significant levels of programmed death-ligand 1 (PD-L1) expression in motor neurons without affecting the levels of any other immune checkpoint proteins. This finding suggests a potential role of excessive PD-L1 expression in ALS development, given that PD-L1 was recently reported to impair neuronal firing ability in mice. Our findings suggest that exposing motor neurons to IFNγ could directly derive ALS pathogenesis, even without the presence of the inherent genetic mutation or functional glia component. Furthermore, this study provides a comprehensive list of potential candidate genes for future immunotherapeutic targets with which to treat sporadic forms of ALS, which account for 90% of all reported cases.

Neutrophil-to-Lymphocyte Ratio Dynamics From Pre-diagnosis to End-Stage Amyotrophic Lateral Sclerosis (ALS): A Case Study on Association With Progression and Clinical Events

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative condition characterized by the progressive degeneration of motor neurons, resulting in muscle weakness and paralysis. The neutrophil-to-lymphocyte ratio (NLR) has emerged as a potential marker for monitoring disease severity and progression in ALS, yet longitudinal analyses of NLR are limited. Our study conducts an in-depth examination of NLR dynamics from before diagnosis through the disease's progression to its end stage. We analyze the case of a 56-year-old Puerto Rican male with ALS, tracking his NLR over 13 years - six years before and seven years after his diagnosis - alongside assessments of clinical symptoms and lung function. Our findings indicate that NLR values were initially normal but significantly increased with the onset of symptoms. NLR remained elevated above the normal range, with a notable exception during a period of edaravone therapy when levels normalized. The study demonstrates a clear elevation in NLR associated with ALS progression and critical clinical events, such as symptom onset, diagnosis, and the initiation of respiratory support. This research is, to our knowledge, the first to provide a detailed characterization of NLR changes from the pre-diagnostic phase to end-stage ALS, showing its correlation with clinical deterioration, decreased pulmonary function, and key clinical events. Our results contribute to the body of evidence on NLR's role in ALS while enhancing our understanding of ALS's natural progression.

Dysregulated N6-methyladenosine modification in peripheral immune cells contributes to the pathogenesis of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurogenerative disorder with uncertain origins. Emerging evidence implicates N6-methyladenosine (m6A) modification in ALS pathogenesis. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and liquid chromatography-mass spectrometry were utilized for m6A profiling in peripheral immune cells and serum proteome analysis, respectively, in patients with ALS (n = 16) and controls (n = 6). The single-cell transcriptomic dataset (GSE174332) of primary motor cortex was further analyzed to illuminate the biological implications of differentially methylated genes and cell communication changes. Analysis of peripheral immune cells revealed extensive RNA hypermethylation, highlighting candidate genes with differential m6A modification and expression, including C-X3-C motif chemokine receptor 1 (CX3CR1). In RAW264.7 macrophages, disrupted CX3CR1 signaling affected chemotaxis, potentially influencing immune cell migration in ALS. Serum proteome analysis demonstrated the role of dysregulated immune cell migration in ALS. Cell type-specific expression variations of these genes in the central nervous system (CNS), particularly microglia, were observed. Intercellular communication between neurons and glial cells was selectively altered in ALS CNS. This integrated approach underscores m6A dysregulation in immune cells as a potential ALS contributor.

Exploring antioxidant strategies in the pathogenesis of ALS

The central nervous system is essential for maintaining homeostasis and controlling the body's physiological functions. However, its biochemical characteristics make it highly vulnerable to oxidative damage, which is a common factor in neurodegenerative diseases like amyotrophic lateral sclerosis (ALS). ALS is a leading cause of motor neuron disease, characterized by a rapidly progressing and incurable condition. ALS often results in death from respiratory failure within 3-5 years from the onset of the first symptoms, underscoring the urgent need to address this medical challenge. The aim of this study is to present available data supporting the role of oxidative stress in the mechanisms underlying ALS and to discuss potential antioxidant therapies currently in development. These therapies aim to improve the quality of life and life expectancy for patients affected by this devastating disease.

Neuroimmune interactions and their roles in neurodegenerative diseases

The nervous system possesses bidirectional, sophisticated and delicate communications with the immune system. These neuroimmune interactions play a vitally important role in the initiation and development of many disorders, especially neurodegenerative diseases. Although scientific advancements have made tremendous progress in this field during the last few years, neuroimmune communications are still far from being elucidated. By organizing recent research, in this review, we discuss the local and intersystem neuroimmune interactions and their roles in Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Unveiling these will help us gain a better understanding of the process of interplay inside the body and how the organism maintains homeostasis. It will also facilitate a view of the diseases from a holistic, pluralistic and interconnected perspective, thus providing a basis of developing novel and effective methods to diagnose, intervene and treat diseases.

The prognostic value of systematic genetic screening in amyotrophic lateral sclerosis patients

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with complex genetic architecture. Emerging evidence has indicated comorbidity between ALS and autoimmune conditions, suggesting a potential shared genetic basis. The objective of this study is to assess the prognostic value of systematic screening for rare deleterious mutations in genes associated with ALS and aberrant inflammatory responses.

METHODS

A discovery cohort of 494 patients and a validation cohort of 69 patients were analyzed in this study, with population-matched healthy subjects (n = 4961) served as controls. Whole exome sequencing (WES) was performed to identify rare deleterious variants in 50 ALS genes and 1177 genes associated with abnormal inflammatory responses. Genotype-phenotype correlation was assessed, and an integrative prognostic model incorporating genetic and clinical factors was constructed.

RESULTS

In the discovery cohort, 8.1% of patients carried confirmed ALS variants, and an additional 15.2% of patients carried novel ALS variants. Gene burden analysis revealed 303 immune-implicated genes with enriched rare variants, and 13.4% of patients harbored rare deleterious variants in these genes. Patients with ALS variants exhibited a more rapid disease progression (HR 2.87 [95% CI 2.03-4.07], p < 0.0001), while no significant effect was observed for immune-implicated variants. The nomogram model incorporating genetic and clinical information demonstrated improved accuracy in predicting disease outcomes (C-index, 0.749).

CONCLUSION

Our findings enhance the comprehension of the genetic basis of ALS within the Chinese population. It also appears that rare deleterious mutations occurring in immune-implicated genes exert minimal influence on the clinical trajectories of ALS patients.

The Inflammatory Puzzle: Piecing together the Links between Neuroinflammation and Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease that has a complex genetic basis. Through advancements in genetic screening, researchers have identified more than 40 mutant genes associated with ALS, some of which impact immune function. Neuroinflammation, with abnormal activation of immune cells and excessive production of inflammatory cytokines in the central nervous system, significantly contributes to the pathophysiology of ALS. In this review, we examine recent evidence on the involvement of ALS-associated mutant genes in immune dysregulation, with a specific focus on the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway and N6-methyladenosine (m6A)-mediated immune regulation in the context of neurodegeneration. We also discuss the perturbation of immune cell homeostasis in both the central nervous system and peripheral tissues in ALS. Furthermore, we explore the advancements made in the emerging genetic and cell-based therapies for ALS. This review underscores the complex relationship between ALS and neuroinflammation, highlighting the potential to identify modifiable factors for therapeutic intervention. A deeper understanding of the connection between neuroinflammation and the risk of ALS is crucial for advancing effective treatments for this debilitating disorder.

Immunology of amyotrophic lateral sclerosis - role of the innate and adaptive immunity

This review aims to summarize the latest evidence about the role of innate and adaptive immunity in Amyotrophic Lateral Sclerosis (ALS). ALS is a devastating neurodegenerative disease affecting upper and lower motor neurons, which involves essential cells of the immune system that play a basic role in innate or adaptive immunity, that can be neurotoxic or neuroprotective for neurons. However, distinguishing between the sole neurotoxic or neuroprotective function of certain cells such as astrocytes can be challenging due to intricate nature of these cells, the complexity of the microenvironment and the contextual factors. In this review, in regard to innate immunity we focus on the involvement of monocytes/macrophages, microglia, the complement, NK cells, neutrophils, mast cells, and astrocytes, while regarding adaptive immunity, in addition to humoral immunity the most important features and roles of T and B cells are highlighted, specifically different subsets of CD4+ as well as CD8+ T cells. The role of autoantibodies and cytokines is also discussed in distinct sections of this review.

CD8+ T cells in brain injury and neurodegeneration

The interaction between the peripheral immune system and the brain is increasingly being recognized as an important layer of neuroimmune regulation and plays vital roles in brain homeostasis as well as neurological disorders. As an important population of T-cell lymphocytes, the roles of CD8+ T cells in infectious diseases and tumor immunity have been well established. Recently, increasing number of complex functions of CD8+ T cells in brain disorders have been revealed. However, an advanced summary and discussion of the functions and mechanisms of CD8+ T cells in brain injury and neurodegeneration are still lacking. Here, we described the differentiation and function of CD8+ T cells, reviewed the involvement of CD8+ T cells in the regulation of brain injury including stroke and traumatic brain injury and neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), and discussed therapeutic prospects and future study goals. Understanding these processes will promote the investigation of T-cell immunity in brain disorders and provide new intervention strategies for the treatment of brain injury and neurodegeneration.

The Molecular Link Between TDP-43, Endogenous Retroviruses and Inflammatory Neurodegeneration in Amyotrophic Lateral Sclerosis: a Potential Target for Triumeq, an Antiretroviral Therapy

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is a progressive neurological disorder, characterised by the death of upper and lower motor neurons. The aetiology of ALS remains unknown, and treatment options are limited. Endogenous retroviruses (ERVs), specifically human endogenous retrovirus type K (HERV-K), have been proposed to be involved in the propagation of neurodegeneration in ALS. ERVs are genomic remnants of ancient viral infection events, with most being inactive and not retaining the capacity to encode a fully infectious virus. However, some ERVs retain the ability to be activated and transcribed, and ERV transcripts have been found to be elevated within the brain tissue of MND patients. A hallmark of ALS pathology is altered localisation of the transactive response (TAR) DNA binding protein 43 kDa (TDP-43), which is normally found within the nucleus of neuronal and glial cells and is involved in RNA regulation. In ALS, TDP-43 aggregates within the cytoplasm and facilitates neurodegeneration. The involvement of ERVs in ALS pathology is thought to occur through TDP-43 and neuroinflammatory mediators. In this review, the proposed involvement of TDP-43, HERV-K and immune regulators on the onset and progression of ALS will be discussed. Furthermore, the evidence supporting a therapy based on targeting ERVs in ALS will be reviewed.

IL-33/ST2 Axis: A Potential Therapeutic Target in Neurodegenerative Diseases

Interleukin 33 (IL-33) belongs to the IL-1 family and is localized in the nucleus. IL-33 is primarily composed of three distinct domains, namely the N-terminal domain responsible for nuclear localization, the intermediate sense protease domain, and the C-terminal cytokine domain. Its specific receptor is the suppression of tumorigenicity 2 (ST2), which is detected in serum-stimulated fibroblasts and oncogenes. While most other cytokines are actively produced in cells, IL-33 is passively produced in response to tissue damage or cell necrosis, thereby suggesting its role as an alarm following cell infection, stress, or trauma. IL-33 plays a crucial role in congenital and acquired immunity, which assists in the response to environmental stress and maintains tissue homeostasis. IL-33/ST2 interaction further produces many pro-inflammatory cytokines. Moreover, IL-33 is crucial for central nervous system (CNS) homeostasis and the pathogenic mechanisms underlying CNS degenerative disorders. The present work summarizes the structure of IL-33, its fundamental activities, and its role in immunoregulation and neurodegenerative diseases. Therefore, this work proposes that IL-33 may play a role in the pathogenic mechanism of diseases and can be used in the development of treatment strategies.

Insights on the Multifaceted Roles of Wild-Type and Mutated Superoxide Dismutase 1 in Amyotrophic Lateral Sclerosis Pathogenesis

Amyotrophic Lateral Sclerosis (ALS) is a progressive motor neurodegenerative disease. Cell damage in ALS is the result of many different, largely unknown, pathogenetic mechanisms. Astrocytes and microglial cells play a critical role also for their ability to enhance a deranged inflammatory response. Excitotoxicity, due to excessive glutamate levels and increased intracellular Ca2+ concentration, has also been proposed to play a key role in ALS pathogenesis/progression. Reactive Oxygen Species (ROS) behave as key second messengers for multiple receptor/ligand interactions. ROS-dependent regulatory networks are usually mediated by peroxides. Superoxide Dismutase 1 (SOD1) physiologically mediates intracellular peroxide generation. About 10% of ALS subjects show a familial disease associated with different gain-of-function SOD1 mutations. The occurrence of sporadic ALS, not clearly associated with SOD1 defects, has been also described. SOD1-dependent pathways have been involved in neuron functional network as well as in immune-response regulation. Both, neuron depolarization and antigen-dependent T-cell activation mediate SOD1 exocytosis, inducing increased interaction of the enzyme with a complex molecular network involved in the regulation of neuron functional activity and immune response. Here, alteration of SOD1-dependent pathways mediating increased intracellular Ca2+ levels, altered mitochondria functions and defective inflammatory process regulation have been proposed to be relevant for ALS pathogenesis/progression.

The role of the CD8+ T cell compartment in ageing and neurodegenerative disorders

CD8+ lymphocytes are adaptive immunity cells with the particular function to directly kill the target cell following antigen recognition in the context of MHC class I. In addition, CD8+ T cells may release pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), and a plethora of other cytokines and chemoattractants modulating immune and inflammatory responses. A role for CD8+ T cells has been suggested in aging and several diseases of the central nervous system (CNS), including Alzheimer's disease, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, limbic encephalitis-induced temporal lobe epilepsy and Susac syndrome. Here we discuss the phenotypic and functional alterations of CD8+ T cell compartment during these conditions, highlighting similarities and differences between CNS disorders. Particularly, we describe the pathological changes in CD8+ T cell memory phenotypes emphasizing the role of senescence and exhaustion in promoting neuroinflammation and neurodegeneration. We also discuss the relevance of trafficking molecules such as selectins, mucins and integrins controlling the extravasation of CD8+ T cells into the CNS and promoting disease development. Finally, we discuss how CD8+ T cells may induce CNS tissue damage leading to neurodegeneration and suggest that targeting detrimental CD8+ T cells functions may have therapeutic effect in CNS disorders.

Microglial crosstalk with astrocytes and immune cells in amyotrophic lateral sclerosis

In recent years, biomedical research efforts aimed to unravel the mechanisms involved in motor neuron death that occurs in amyotrophic lateral sclerosis (ALS). While the main causes of disease progression were first sought in the motor neurons, more recent studies highlight the gliocentric theory demonstrating the pivotal role of microglia and astrocyte, but also of infiltrating immune cells, in the pathological processes that take place in the central nervous system microenvironment. From this point of view, microglia-astrocytes-lymphocytes crosstalk is fundamental to shape the microenvironment toward a pro-inflammatory one, enhancing neuronal damage. In this review, we dissect the current state-of-the-art knowledge of the microglial dialogue with other cell populations as one of the principal hallmarks of ALS progression. Particularly, we deeply investigate the microglia crosstalk with astrocytes and immune cells reporting in vitro and in vivo studies related to ALS mouse models and human patients. At last, we highlight the current experimental therapeutic approaches that aim to modulate microglial phenotype to revert the microenvironment, thus counteracting ALS progression.

Low T-cell reactivity to TDP-43 peptides in ALS

Background

Dysregulation of the immune system in amyotrophic lateral sclerosis (ALS) includes changes in T-cells composition and infiltration of T cells in the brain and spinal cord. Recent studies have shown that cytotoxic T cells can directly induce motor neuron death in a mouse model of ALS and that T cells from ALS patients are cytotoxic to iPSC-derived motor neurons from ALS patients. Furthermore, a clonal expansion to unknown epitope(s) was recently found in familial ALS and increased peripheral and intrathecal activation of cytotoxic CD8+ T cells in sporadic ALS.

Results

Here, we show an increased activation of peripheral T cells from patients with sporadic ALS by IL-2 treatment, suggesting an increase of antigen-experienced T cells in ALS blood. However, a putative antigen for T-cell activation in ALS has not yet been identified. Therefore, we investigated if peptides derived from TDP-43, a key protein in ALS pathogenesis, can act as epitopes for antigen-mediated activation of human T cells by ELISPOT and flow cytometry. We found that TDP-43 peptides induced only a weak MHCI or MHCII-restricted activation of both naïve and antigen-experienced T cells from healthy controls and ALS patients. Interestingly, we found less activation in T cells from ALS patients to TDP-43 and control stimuli. Furthermore, we found no change in the levels of naturally occurring auto-antibodies against full-length TDP-43 in ALS.

Conclusion

Our data suggests a general increase in antigen-experienced T cells in ALS blood, measured by in-vitro culture with IL-2 for 14 days. Furthermore, it suggests that TDP-43 is a weak autoantigen.

Structure of a superoxide dismutase from a tardigrade: Ramazzottius varieornatus strain YOKOZUNA-1

Superoxide dismutase (SOD) is an essential and ubiquitous antioxidant protein that is widely present in biological systems. The anhydrobiotic tardigrades are some of the toughest micro-animals. They have an expanded set of genes for antioxidant proteins such as SODs. These proteins are thought to play an essential role in oxidative stress resistance in critical situations such as desiccation, although their functions at the molecular level have yet to be explored. Here, crystal structures of a copper/zinc-containing SOD (RvSOD15) from an anhydrobiotic tardigrade, Ramazzottius varieornatus strain YOKOZUNA-1, are reported. In RvSOD15, one of the histidine ligands of the catalytic copper center is replaced by a valine (Val87). The crystal structures of the wild type and the V87H mutant show that even though a histidine is placed at position 87, a nearby flexible loop can destabilize the coordination of His87 to the Cu atom. Model structures of other RvSODs were investigated and it was found that some of them are also unusual SODs, with features such as deletion of the electrostatic loop or β3 sheet and unusual metal-binding residues. These studies show that RvSOD15 and some other RvSODs may have evolved to lose the SOD function, suggesting that gene duplications of antioxidant proteins do not solely explain the high stress tolerance of anhydrobiotic tardigrades.

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.

Age-associated systemic factors change central and peripheral immunity in adult male mice

Aging coincides with major changes in brain immunity that aid in a decline in neuronal function. Here, we postulate that systemic, pro-aging factors contribute to immunological changes that occur within the brain during aging. To investigate this hypothesis, we comprehensively characterized the central and peripheral immune landscape of 20-month-old male mice using cytometry by time-of-flight (CyTOF) and investigated the role of age-associated circulating factors. We found that CD8+ T cells expressing programmed cell death protein 1 (PD1) and tissue-resident memory CD8+ T cells accumulated in the aged brain while levels of memory T cells rose in the periphery. Injections of plasma derived from 20-month-old mice into 5-month-old receiving mice decreased the frequency of splenic and circulating naïve T cells, increased memory CD8+ T cells, and non-classical, patrolling monocytes in the spleen, and elevated levels of regulatory T cells and non-classical monocytes in the blood. Notably, CD8+ T cells accumulated within white matter areas of plasma-treated mice, which coincided with the expression of vascular cell adhesion molecule 1 (VCAM-1), a mediator of immune cell trafficking, on the brain vasculature. Taken together, we here describe age-related immune cell changes in the mouse brain and circulation and show that age-associated systemic factors induce the expansion of CD8+ T cells in the aged brain.

Role of the immune system in amyotrophic lateral sclerosis. Analysis of the natural killer cells and other circulating lymphocytes in a cohort of ALS patients

AIMS

Neuroinflammation might be involved in the degeneration and progression of Amyotrophic Lateral Sclerosis (ALS). Here, we studied the role of the circulating lymphocytes in ALS, in particular the NK cells. We focused on the relationship between blood lymphocytes, ALS clinical subtype and disease severity.

SUBJECTS AND METHODS

Blood samples were collected from 92 patients with sporadic ALS, 21 patients with Primary Lateral Sclerosis (PLS) and 37 patients affected by primary progressive multiple sclerosis (PPMS) with inactive plaques. Blood was taken from ALS and controls at the time of diagnosis/referral. Circulating lymphocytes were analyzed by flow cytometry with specific antibodies. Values were expressed as absolute number (n°/µl) of viable lymphocytes subpopulations in ALS were compared with controls. Multivariable analysis was made using site of onset, gender changes in ALSFRS-R and disease progression rate (calculated as ΔFS score).

RESULTS

Age at onset was 65y (58-71) in ALS (spinal 67.4%; bulbar, 32.6%), 57y (48-78) in PLS and 56y (44-68) PPMS. Absolute blood levels of the lymphocytes in the different cohorts were within normal range. Furthermore, while levels of lymphocytes T and B were not different between disease groups, NK cells were increased in the ALS cohort (ALS = 236 [158-360] vs. Controls = 174[113-240], p < 0.001). In ALS, blood levels of NK cells were not related with the main clinical-demographic variables, including the rate of disease progression. Multivariable analysis suggested that male gender and bulbar onset were independently associated with a risk of high blood NK cells levels.

CONCLUSIONS

We show that blood NK cells are selectively increased in ALS, though their level appear unaffected in patients with an estimated rapidly progressing disease. Being of a male gender and with a bulbar onset seems to confer higher susceptibility to have increased NK lymphocytes levels at diagnosis/referral. Our experiments provides a further clear-cut evidence of the role of the NK lymphocytes as a significant player in ALS pathogenesis.

The contribution of the peripheral immune system to neurodegeneration

Microglial cells are the major immune cells of the central nervous system (CNS), and directly react to neurodegeneration, but other immune cell types are also able to react to pathology and can modify the course of neurodegenerative processes. These mainly include monocytes/macrophages and lymphocytes. While these peripheral immune cells were initially considered to act only after infiltrating the CNS, recent evidence suggests that some of them can also act directly from the periphery. We will review the existing and emerging evidence for a role of peripheral immune cells in neurodegenerative diseases, both with and without CNS infiltration. Our focus will be on amyotrophic lateral sclerosis, but we will also compare to Alzheimer's disease and Parkinson's disease to highlight similarities or differences. Peripheral immune cells are easily accessible, and therefore may be an attractive therapeutic target for neurodegenerative diseases. Thus, understanding how these peripheral immune cells communicate with the CNS deserves deeper investigation.

Successes and Challenges in Taming the Beast: Cytotoxic Immune Effectors in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurological disease characterized by the progressive loss of motor neurons in the brain and spinal cord. No effective therapeutic strategies have been established thus far, and therefore there is a significant unmet need for effective therapeutics to arrest the disease and reverse the pathologies induced by it. Although the cause of ALS is not well-defined, it appears to be heterogenous. Currently over 20 genes have been found to be associated with ALS. Family history can only be found in 10% of ALS patients, but in the remaining 90% no association with family history is found. The most common genetic causes are expansion in the C9orf72 gene and mutations in superoxide dismutase 1, TDP-43, and FUS. In our recent study, we also found mutations in TDP43 and FUS in ALS patients. To understand the pathogenesis of the disease, we set ourselves the task of analyzing the phenotype and function of all key immune effectors in ALS patients, comparing them with either a genetically healthy twin or healthy individuals. Our study demonstrated a significant increase in functional activation of NK and CD8+ T cytotoxic immune effectors and release of significant IFN-γ not only by the effector cells but also in the serum of ALS patients. Longitudinal analysis of CD8+ T cell-mediated IFN-γ secretion from ALS patients demonstrated continued and sustained increase in IFN-γ secretion with periods of decrease which coincided with certain treatments; however, the effects were largely short-lived. N-acetyl cysteine (NAC), one of the treatments used, is known to block cell death; however, even though such treatment was able to block most of the proinflammatory cytokines, chemokines, and growth factor release, it was not able to block IFN-γ and TNF-α, the two cytokines we had demonstrated previously to induce differentiation of the cells. In this review, we discuss the contribution of cytotoxic effector cells, especially primary NK cells, supercharged NK cells (sNK), and the contribution of sNK cells in expansion and functional activation of CD8+ T cells to memory/effector T cells in the pathogenesis of ALS. Potential new targeted therapeutic strategies are also discussed.

Immunology and microbiome: Implications for motor systems

Immune-inflammatory mechanisms seem to play a relevant role in neurodegenerative disorders affecting motor systems, particularly Parkinson's disease, where activity changes in inflammatory cells and evidence of neuroinflammation in experimental models and patients is available. Amyotrophic lateral sclerosis is also characterized by neuroinflammatory changes that involve primarily glial cells, both microglia and astrocytes, as well as systemic immune dysregulation associated with more rapid progression. Similarly, the exploration of gut dysbiosis in these two prototypical neurodegenerative motor disorders is advancing rapidly. Altered composition of gut microbial constituents and related metabolic and putative functional pathways is supporting a pathophysiological link that is currently explored in preclinical, germ-free animal models. Less compelling, but still intriguing, evidence suggests that motor neurodevelopmental disorders, e.g., Tourette syndrome, are associated with abnormal trajectories of maturation that include also immune system development. Microglia has a key role also in these disorders, and new therapeutic avenues aiming at its modulation are exciting prospects. Preclinical and clinical research on the role of gut dysbiosis in Tourette syndrome and related behavioral disorders is still in its infancy, but early findings support the rationale to delve deeper into its contribution to neural and immune maturation abnormalities in its spectrum.

Analysis of shared underlying mechanism in neurodegenerative disease

In this review, the relationship between bioenergetics, mitochondrial dysfunction, and inflammation will be and how they contribute to neurodegeneration, specifically in Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS) will be reviewed. Long-term changes in mitochondrial function, autophagy dysfunction, and immune activation are commonalities shared across these age-related disorders. Genetic risk factors for these diseases support an autophagy-immune connection in the underlying pathophysiology. Critical areas of deeper evaluation in these bioenergetic processes may lead to potential therapeutics with efficacy across multiple neurodegenerative diseases.

Hemizygous Granzyme A Mice Expressing the hSOD1G93A Transgene Show Slightly Extended Lifespan

Granzyme A (gzmA), a serine protease involved in the modulation of the inflammatory immune response, is found at an elevated level in the serum from ALS patients. However, the influence of gzmA on the progression of ALS remains unclear. The aim of our work was to assess whether the absence of gzmA in an ALS murine model could help slow down the progression of the disease. Homozygous and hemizygous gzmA-deficient mice expressing the hSOD1G93A transgene were generated, and survival of these mice was monitored. Subsequently, gene and protein expression of inflammatory and oxidative stress markers was measured in the spinal cord and quadriceps of these mice. We observed the longest lifespan in gzmA+/- mice. GzmA gene and protein expression was downregulated in the spinal cord and serum from gmzA+/- mice, confirming that the increased survival of hemizygous mice is correlated with lower levels of gzmA. In addition, mRNA and protein levels of glutathione reductase (GSR), involved in oxidative stress, were found downregulated in the spinal cord and quadriceps of gmzA+/- mice, together with lower IL-1β and IL-6 mRNA levels in hemyzigous mice. In summary, our findings indicate for the first time that reduced levels, but not the absence, of gzmA could slightly ameliorate the disease progression in this animal model.

The Potential Role of Cytotoxic Immune Effectors in Induction, Progression and Pathogenesis of Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is an auto-immune neurodegenerative disorder affecting the motor-neuron system. The causes of ALS are heterogeneous, and are only partially understood. We studied different aspects of immune pathogenesis in ALS and found several basic mechanisms which are potentially involved in the disease. Our findings demonstrated that ALS patients' peripheral blood contains higher proportions of NK and B cells in comparison to healthy individuals. Significantly increased IFN-γ secretion by anti-CD3/28 mAbs-treated peripheral blood mononuclear cells (PBMCs) were observed in ALS patients, suggesting that hyper-responsiveness of T cell compartment could be a potential mechanism for ALS progression. In addition, elevated granzyme B and perforin secretion at a single cell level, and increased cytotoxicity and secretion of IFN-γ by patients' NK cells under specific treatment conditions were also observed. Increased IFN-γ secretion by ALS patients' CD8+ T cells in the absence of IFN-γ receptor expression, and increased CD8+ T cell effector/memory phenotype as well as increased granzyme B at the single cell level points to the CD8+ T cells as potential cells in targeting motor neurons. Along with the hyper-responsiveness of cytotoxic immune cells, significantly higher levels of inflammatory cytokines including IFN-γ was observed in peripheral blood-derived serum of ALS patients. Supernatants obtained from ALS patients' CD8+ T cells induced augmented cell death and differentiation of the epithelial cells. Weekly N-acetyl cysteine (NAC) infusion in patients decreased the levels of many inflammatory cytokines in peripheral blood of ALS patient except IFN-γ, TNF-α, IL-17a and GMCSF which remained elevated. Findings of this study indicated that CD8+ T cells and NK cells are likely culprits in targeting motor neurons and therefore, strategies should be designed to decrease their function, and eliminate the aggressive nature of these cells. Analysis of genetic mutations in ALS patient in comparison to identical twin revealed a number of differences and similarities which may be important in the pathogenesis of the disease.

Amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal CNS neurodegenerative disease. Despite intensive research, current management of amyotrophic lateral sclerosis remains suboptimal from diagnosis to prognosis. Recognition of the phenotypic heterogeneity of amyotrophic lateral sclerosis, global CNS dysfunction, genetic architecture, and development of novel diagnostic criteria is clarifying the spectrum of clinical presentation and facilitating diagnosis. Insights into the pathophysiology of amyotrophic lateral sclerosis, identification of disease biomarkers and modifiable risks, along with new predictive models, scales, and scoring systems, and a clinical trial pipeline of mechanism-based therapies, are changing the prognostic landscape. Although most recent advances have yet to translate into patient benefit, the idea of amyotrophic lateral sclerosis as a complex syndrome is already having tangible effects in the clinic. This Seminar will outline these insights and discuss the status of the management of amyotrophic lateral sclerosis for the general neurologist, along with future prospects that could improve care and outcomes for patients with amyotrophic lateral sclerosis.

How the immune system shapes neurodegenerative diseases

Neurodegenerative diseases are a major cause of death and disability worldwide and are influenced by many factors including age, genetics, and injuries. While these diseases are often thought to result from the accumulation and spread of aberrant proteins, recent studies have demonstrated that they can be shaped by the innate and adaptive immune system. Resident myeloid cells typically mount a sustained response to the degenerating CNS, but peripheral leukocytes such as T and B cells can also alter disease trajectories. Here, we review the sometimes-dichotomous roles played by immune cells during neurodegenerative diseases and explore how brain trauma can serve as a disease initiator or accelerant. We also offer insights into how failure to properly resolve a CNS injury might promote the development of a neurodegenerative disease.

Catching a killer: Mechanisms of programmed cell death and immune activation in Amyotrophic Lateral Sclerosis

In the central nervous system (CNS), execution of programmed cell death (PCD) is crucial for proper neurodevelopment. However, aberrant activation of these pathways in adult CNS leads to neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). How a cell dies is critical, as it can drive local immune activation and tissue damage. Classical apoptosis engages several mechanisms to evoke "immunologically silent" responses, whereas other forms of programmed death such as pyroptosis, necroptosis, and ferroptosis release molecules that can potentiate immune responses and inflammation. In ALS, a fatal neuromuscular disorder marked by progressive death of lower and upper motor neurons, several cell types in the CNS express machinery for multiple PCD pathways. The specific cell types engaging PCD, and ultimate mechanisms by which neuronal death occurs in ALS are not well defined. Here, we provide an overview of different PCD pathways implicated in ALS. We also examine immune activation in ALS and differentiate apoptosis from necrotic mechanisms based on downstream immunological consequences. Lastly, we highlight therapeutic strategies that target cell death pathways in the treatment of neurodegeneration and inflammation in ALS.

Blocking immune cell infiltration of the central nervous system to tame Neuroinflammation in Amyotrophic lateral sclerosis

Neuroinflammation is one of the main hallmarks of amyotrophic lateral sclerosis (ALS). Recently, peripheral immune cells were discovered as pivotal players that promptly participate in this process, speeding up neurodegeneration during progression of the disease. In particular, infiltrating T cells and natural killer cells release inflammatory cytokines that switch glial cells toward a pro-inflammatory/detrimental phenotype, and directly attack motor neurons with specific ligand-receptor signals. Here, we assessed the presence of lymphocytes in the spinal cord of sporadic ALS patients. Furthermore, we demonstrate that blocking the extravasation of immune cells in the central nervous system using Natalizumab (NAT), an antibody for the α4 integrin, reduces the level of interferon-γ in the spinal cord of ALS mouse models, such as the hSOD1^G93A and TDP43^A315T mice, modifying microglia and astrocytes phenotype, increasing motor neuron number and prolonging the survival time. Taken together, our results establish a central role for the immune cells as drivers of inflammation in ALS.

Crossing borders in Alzheimer's disease: A T cell's perspective

Alzheimer's disease (AD) is the most common form of dementia affecting millions of people worldwide. While different immunotherapies are imminent, currently only disease-modifying medications are available and a cure is lacking. Over the past decade, immunological interfaces of the central nervous system (CNS) and their role in neurodegenerative diseases received increasing attention. Specifically, emerging evidence shows that subsets of circulating CD8⁺ T cells cross the brain barriers and associate with AD pathology. To gain more insight into how the adaptive immune system is involved in disease pathogenesis, we here provide a comprehensive overview of the contribution of T cells to AD pathology, incorporating changes at the brain barriers. In addition, we review studies that provide translation of these findings by targeting T cells to combat AD pathology and cognitive decline. Importantly, these data show that immunological changes in AD are not confined to the CNS and that AD-associated systemic immune changes appear to affect brain homeostasis.

Influenza vaccination induces autoimmunity against orexinergic neurons in a mouse model for narcolepsy

Narcolepsy with cataplexy or narcolepsy type 1 is a disabling chronic sleep disorder resulting from the destruction of orexinergic neurons in the hypothalamus. The tight association of narcolepsy with HLA-DQB1*06:02 strongly suggest an autoimmune origin to this disease. Furthermore, converging epidemiological studies have identified an increased incidence for narcolepsy in Europe following Pandemrix® vaccination against the 2009-2010 pandemic 'influenza' virus strain. The potential immunological link between the Pandemrix® vaccination and narcolepsy remains, however, unknown. Deciphering these mechanisms may reveal pathways potentially at play in most cases of narcolepsy. Here, we developed a mouse model allowing to track and study the T-cell response against 'influenza' virus haemagglutinin, which was selectively expressed in the orexinergic neurons as a new self-antigen. Pandemrix® vaccination in this mouse model resulted in hypothalamic inflammation and selective destruction of orexin-producing neurons. Further investigations on the relative contribution of T-cell subsets in this process revealed that haemagglutinin-specific CD4 T cells were necessary for the development of hypothalamic inflammation, but insufficient for killing orexinergic neurons. Conversely, haemagglutinin-specific CD8 T cells could not initiate inflammation but were the effectors of the destruction of orexinergic neurons. Additional studies revealed pathways potentially involved in the disease process. Notably, the interferon-γ pathway was proven essential, as interferon-γ-deficient CD8 T cells were unable to elicit the loss of orexinergic neurons. Our work demonstrates that an immunopathological process mimicking narcolepsy can be elicited by immune cross-reactivity between a vaccine antigen and a neuronal self-antigen. This process relies on a synergy between autoreactive CD4 and CD8 T cells for disease development. This work furthers our understanding of the mechanisms and pathways potentially involved in the development of a neurological side effect due to a vaccine and, likely, to narcolepsy in general.

Neuroimmune Crosstalk Between the Peripheral and the Central Immune System in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disease characterized by the degeneration and death of motor neurons. Systemic neuroinflammation contributes to the pathogenesis of ALS. The proinflammatory milieu depends on the continuous crosstalk between the peripheral immune system (PIS) and central immune system (CIS). Central nervous system (CNS) resident immune cells interact with the peripheral immune cells via immune substances. Dysfunctional CNS barriers, including the blood–brain barrier, and blood–spinal cord barrier, accelerate the inflammatory process, leading to a systemic self-destructive cycle. This review focuses on the crosstalk between PIS and CIS in ALS. Firstly, we briefly introduce the cellular compartments of CIS and PIS, respectively, and update some new understanding of changes specifically occurring in ALS. Then, we will review previous studies on the alterations of the CNS barriers, and discuss their crucial role in the crosstalk in ALS. Finally, we will review the moveable compartments of the crosstalk, including cytokines, chemokines, and peripheral immune cells which were found to infiltrate the CNS, highlighting the interaction between PIS and CIS. This review aims to provide new insights into pathogenic mechanisms and innovative therapeutic approaches for ALS.

Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease. The discovery of genes associated with amyotrophic lateral sclerosis, commencing with SOD1 in 1993, started fairly gradually. Recent advances in genetic technology have led to the rapid identification of multiple new genes associated with the disease, and to a new understanding of oligogenic and polygenic disease risk. The overlap of genes associated with amyotrophic lateral sclerosis with those of other neurodegenerative diseases is shedding light on the phenotypic spectrum of neurodegeneration, leading to a better understanding of genotype-phenotype correlations. A deepening knowledge of the genetic architecture is allowing the characterisation of the molecular steps caused by various mutations that converge on recurrent dysregulated pathways. Of crucial relevance, mutations associated with amyotrophic lateral sclerosis are amenable to novel gene-based therapeutic options, an approach in use for other neurological illnesses. Lastly, the exposome-the summation of lifetime environmental exposures-has emerged as an influential component for amyotrophic lateral sclerosis through the gene-time-environment hypothesis. Our improved understanding of all these aspects will lead to long-awaited therapies and the identification of modifiable risks factors.

The Emerging Role of Central and Peripheral Immune Systems in Neurodegenerative Diseases

For decades, it has been widely believed that the blood-brain barrier (BBB) provides an immune privileged environment in the central nervous system (CNS) by blocking peripheral immune cells and humoral immune factors. This view has been revised in recent years, with increasing evidence revealing that the peripheral immune system plays a critical role in regulating CNS homeostasis and disease. Neurodegenerative diseases are characterized by progressive dysfunction and the loss of neurons in the CNS. An increasing number of studies have focused on the role of the connection between the peripheral immune system and the CNS in neurodegenerative diseases. On the one hand, peripherally released cytokines can cross the BBB, cause direct neurotoxicity and contribute to the activation of microglia and astrocytes. On the other hand, peripheral immune cells can also infiltrate the brain and participate in the progression of neuroinflammatory and neurodegenerative diseases. Neurodegenerative diseases have a high morbidity and disability rate, yet there are no effective therapies to stop or reverse their progression. In recent years, neuroinflammation has received much attention as a therapeutic target for many neurodegenerative diseases. In this review, we highlight the emerging role of the peripheral and central immune systems in neurodegenerative diseases, as well as their interactions. A better understanding of the emerging role of the immune systems may improve therapeutic strategies for neurodegenerative diseases.

Correlation between leukocyte phenotypes and prognosis of amyotrophic lateral sclerosis

The prognostic role of immune cells in amyotrophic lateral sclerosis (ALS) remains undetermined. Therefore, we conducted a longitudinal cohort study including 288 ALS patients with up to 5-year follow-up during 2015–2020 recruited at the only tertiary referral center for ALS in Stockholm, Sweden, and measured the levels of differential leukocytes and lymphocyte subpopulations. The primary outcome was risk of death after diagnosis of ALS and the secondary outcomes included functional status and disease progression rate. Cox model was used to evaluate the associations between leukocytes and risk of death. Generalized estimating equation model was used to assess the correlation between leukocytes and functional status and disease progression rate. We found that leukocytes, neutrophils, and monocytes increased gradually over time since diagnosis and were negatively correlated with functional status, but not associated with risk of death or disease progression rate. For lymphocyte subpopulations, NK cells (HR= 0.61, 95% CI = [0.42–0.88] per SD increase) and Th2-diffrentiated CD4⁺ central memory T cells (HR= 0.64, 95% CI = [0.48–0.85] per SD increase) were negatively associated with risk of death, while CD4⁺ effector memory cells re-expressing CD45RA (EMRA) T cells (HR= 1.39, 95% CI = [1.01–1.92] per SD increase) and CD8⁺ T cells (HR= 1.38, 95% CI = [1.03–1.86] per SD increase) were positively associated with risk of death. None of the lymphocyte subpopulations was correlated with functional status or disease progression rate. Our findings suggest a dual role of immune cells in ALS prognosis, where neutrophils and monocytes primarily reflect functional status whereas NK cells and different T lymphocyte populations act as prognostic markers for survival.

Biomarkers in Human Peripheral Blood Mononuclear Cells: The State of the Art in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease, characterized by the progressive loss of lower motor neurons, weakness and muscle atrophy. ALS lacks an effective cure and diagnosis is often made by exclusion. Thus, it is imperative to search for biomarkers. Biomarkers can help in understanding ALS pathomechanisms, identification of targets for treatment and development of effective therapies. Peripheral blood mononuclear cells (PBMCs) represent a valid source for biomarkers compared to cerebrospinal fluid, as they are simple to collect, and to plasma, because of the possibility of detecting lower expressed proteins. They are a reliable model for patients’ stratification. This review provides an overview on PBMCs as a potential source of biomarkers in ALS. We focused on altered RNA metabolism (coding/non-coding RNA), including RNA processing, mRNA stabilization, transport and translation regulation. We addressed protein abnormalities (aggregation, misfolding and modifications); specifically, we highlighted that SOD1 appears to be the most characterizing protein in ALS. Finally, we emphasized the correlation between biological parameters and disease phenotypes, as regards prognosis, severity and clinical features. In conclusion, even though further studies are needed to standardize the use of PBMCs as a tool for biomarker investigation, they represent a promising approach in ALS research.

Motoneuron Diseases

Motoneuron diseases (MNDs) represent a heterogeneous group of progressive paralytic disorders, mainly characterized by the loss of upper (corticospinal) motoneurons, lower (spinal) motoneurons or, often both. MNDs can occur from birth to adulthood and have a highly variable clinical presentation, even within gene-positive forms, suggesting the existence of environmental and genetic modifiers. A combination of cell autonomous and non-cell autonomous mechanisms contributes to motoneuron degeneration in MNDs, suggesting multifactorial pathogenic processes.

Dysfunction of RNA/RNA-Binding Proteins in ALS Astrocytes and Microglia

Amyotrophic Lateral Sclerosis is a neurological disease that primarily affects motor neurons in the cortex, brainstem, and spinal cord. The process that leads to motor neuron degeneration is strongly influenced by non-motor neuronal events that occur in a variety of cell types. Among these, neuroinflammatory processes mediated by activated astrocytes and microglia play a relevant role. In recent years, it has become clear that dysregulation of essential steps of RNA metabolism, as a consequence of alterations in RNA-binding proteins (RBPs), is a central event in the degeneration of motor neurons. Yet, a causal link between dysfunctional RNA metabolism and the neuroinflammatory processes mediated by astrocytes and microglia in ALS has been poorly defined. In this review, we will discuss the available evidence showing that RBPs and associated RNA processing are affected in ALS astrocytes and microglia, and the possible mechanisms involved in these events.

Imaging immunological processes from blood to brain in amyotrophic lateral sclerosis

Neuropathology studies of amyotrophic lateral sclerosis (ALS) and animal models of ALS reveal a strong association between aberrant protein accumulation and motor neurone damage, as well as activated microglia and astrocytes. While the role of neuroinflammation in the pathology of ALS is unclear, imaging studies of the central nervous system (CNS) support the idea that innate immune activation occurs early in disease in both humans and rodent models of ALS. In addition, emerging studies also reveal changes in monocytes, macrophages and lymphocytes in peripheral blood as well as at the neuromuscular junction. To more clearly understand the association of neuroinflammation (innate and adaptive) with disease progression, the use of biomarkers and imaging modalities allow monitoring of immune parameters in the disease process. Such approaches are important for patient stratification, selection and inclusion in clinical trials, as well as to provide readouts of response to therapy. Here, we discuss the different imaging modalities, e.g. magnetic resonance imaging, magnetic resonance spectroscopy and positron emission tomography as well as other approaches, including biomarkers of inflammation in ALS, that aid the understanding of the underlying immune mechanisms associated with motor neurone degeneration in ALS.

Amyotrophic lateral sclerosis transcriptomics reveals immunological effects of low-dose interleukin-2

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease causing upper and lower motor neuron loss and currently no effective disease-modifying treatment is available. A pathological feature of this disease is neuroinflammation, a mechanism which involves both CNS-resident and peripheral immune system cells. Regulatory T-cells are immune-suppressive agents known to be dramatically and progressively decreased in patients with amyotrophic lateral sclerosis. Low-dose interleukin-2 promotes regulatory T-cell expansion and was proposed as an immune-modulatory strategy for this disease. A randomized placebo-controlled pilot phase-II clinical trial called Immuno-Modulation in Amyotrophic Lateral Sclerosis was carried out to test safety and activity of low-dose interleukin-2 in 36 amyotrophic lateral sclerosis patients (NCT02059759). Participants were randomized to 1MIU, 2MIU-low-dose interleukin-2 or placebo and underwent one injection daily for 5 days every 28 days for three cycles. In this report, we describe the results of microarray gene expression profiling of trial participants' leukocyte population. We identified a dose-dependent increase in regulatory T-cell markers at the end of the treatment period. Longitudinal analysis revealed an alteration and inhibition of inflammatory pathways occurring promptly at the end of the first treatment cycle. These responses are less pronounced following the end of the third treatment cycle, although an activation of immune-regulatory pathways, involving regulatory T-cells and T helper 2 cells, was evident only after the last cycle. This indicates a cumulative effect of repeated low-dose interleukin-2 administration on regulatory T-cells. Our analysis suggested the existence of inter-individual variation amongst trial participants and we therefore classified patients into low, moderate and high-regulatory T-cell-responders. NanoString profiling revealed substantial baseline differences between participant immunological transcript expression profiles with the least responsive patients showing a more inflammatory-prone phenotype at the beginning of the trial. Finally, we identified two genes in which pre-treatment expression levels correlated with the magnitude of drug responsiveness. Therefore, we proposed a two-biomarker based regression model able to predict patient regulatory T-cell-response to low-dose interleukin-2. These findings and the application of this methodology could be particularly relevant for future precision medicine approaches to treat amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis patients show increased peripheral and intrathecal T-cell activation

Several studies suggest a role for the peripheral immune system in the pathophysiology of amyotrophic lateral sclerosis. However, comprehensive studies investigating the intrathecal immune system in amyotrophic lateral sclerosis are rare. To elucidate whether compartment-specific inflammation contributes to amyotrophic lateral sclerosis pathophysiology, we here investigated intrathecal and peripheral immune profiles in amyotrophic lateral sclerosis patients and compared them with controls free of neurological disorders (controls) and patients with dementia or primary progressive multiple sclerosis. Routine CSF parameters were examined in 308 patients, including 132 amyotrophic lateral sclerosis patients. In a subgroup of 41 amyotrophic lateral sclerosis patients, extensive flow-cytometric immune cell profiling in peripheral blood and CSF was performed and compared with data from 26 controls, 25 dementia and 21 multiple sclerosis patients. Amyotrophic lateral sclerosis patients presented with significantly altered proportions of monocyte subsets in peripheral blood and increased frequencies of CD4⁺ and CD8⁺ T cells expressing the activation marker HLA-DR in peripheral blood (CD8⁺) and CSF (CD4⁺ and CD8⁺) compared with controls. While dementia and multiple sclerosis patients exhibited a comparable increase in intrathecal CD8⁺ T-cell activation, CD8⁺ T-cell activation in the peripheral blood in amyotrophic lateral sclerosis was higher than in multiple sclerosis patients. Furthermore, intrathecal CD4⁺ T-cell activation in amyotrophic lateral sclerosis surpassed levels in dementia patients. Intrathecal T-cell activation resulted from in situ activation rather than transmigration of activated T cells from the blood. While T-cell activation did not correlate with amyotrophic lateral sclerosis progression, patients with rapid disease progression showed reduced intrathecal levels of immune-regulatory CD56^bright natural killer cells. The integration of these parameters into a composite score facilitated the differentiation of amyotrophic lateral sclerosis patients from patients of all other cohorts. To conclude, alterations in peripheral monocyte subsets, as well as increased peripheral and intrathecal activation of CD4⁺ and CD8⁺ T cells concomitant with diminished immune regulation by CD56^bright natural killer cells, suggest an involvement of these immune cells in amyotrophic lateral sclerosis pathophysiology.

The pathogenic role of c-Kit+ mast cells in the spinal motor neuron-vascular niche in ALS

Degeneration of motor neurons, glial cell reactivity, and vascular alterations in the CNS are important neuropathological features of amyotrophic lateral sclerosis (ALS). Immune cells trafficking from the blood also infiltrate the affected CNS parenchyma and contribute to neuroinflammation. Mast cells (MCs) are hematopoietic-derived immune cells whose precursors differentiate upon migration into tissues. Upon activation, MCs undergo degranulation with the ability to increase vascular permeability, orchestrate neuroinflammation and modulate the neuroimmune response. However, the prevalence, pathological significance, and pharmacology of MCs in the CNS of ALS patients remain largely unknown. In autopsy ALS spinal cords, we identified for the first time that MCs express c-Kit together with chymase, tryptase, and Cox-2 and display granular or degranulating morphology, as compared with scarce MCs in control cords. In ALS, MCs were mainly found in the niche between spinal motor neuron somas and nearby microvascular elements, and they displayed remarkable pathological abnormalities. Similarly, MCs accumulated in the motor neuron-vascular niche of ALS murine models, in the vicinity of astrocytes and motor neurons expressing the c-Kit ligand stem cell factor (SCF), suggesting an SCF/c-Kit-dependent mechanism of MC differentiation from precursors. Mechanistically, we provide evidence that fully differentiated MCs in cell cultures can be generated from the murine ALS spinal cord tissue, further supporting the presence of c-Kit+ MC precursors. Moreover, intravenous administration of bone marrow-derived c-Kit+ MC precursors infiltrated the spinal cord in ALS mice but not in controls, consistent with aberrant trafficking through a defective microvasculature. Pharmacological inhibition of c-Kit with masitinib in ALS mice reduced the MC number and the influx of MC precursors from the periphery. Our results suggest a previously unknown pathogenic mechanism triggered by MCs in the ALS motor neuron-vascular niche that might be targeted pharmacologically.