Adaptive immune neuroprotection in G93A-SOD1 amyotrophic lateral sclerosis mice

Amyotrophic Lateral Sclerosis, a Multisystem Pathology: Insights into the Role of TNFα

Amyotrophic lateral sclerosis (ALS) is considered a multifactorial, multisystem disease in which inflammation and the immune system play important roles in development and progression. The pleiotropic cytokine TNFα is one of the major players governing the inflammation in the central nervous system and peripheral districts such as the neuromuscular and immune system. Changes in TNFα levels are reported in blood, cerebrospinal fluid, and nerve tissues of ALS patients and animal models. However, whether they play a detrimental or protective role on the disease progression is still not clear. Our group and others have recently reported opposite involvements of TNFR1 and TNFR2 in motor neuron death. TNFR2 mediates TNFα toxic effects on these neurons presumably through the activation of MAP kinase-related pathways. On the other hand, TNFR2 regulates the function and proliferation of regulatory T cells (Treg) whose expression is inversely correlated with the disease progression rate in ALS patients. In addition, TNFα is considered a procachectic factor with a direct catabolic effect on skeletal muscles, causing wasting. We review and discuss the role of TNFα in ALS in the light of its multisystem nature.

Inflammatory and non-inflammatory monocytes as novel prognostic biomarkers of survival in SOD1G93A mouse model of Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) has lately become a suitable scenario to study the interplay between the hematopoietic system and disease progression. Recent studies in C9orf72 null mice have demonstrated that C9orf72 is necessary for the normal function of myeloid cells. In this study, we aimed to analyze in depth the connection between the hematopoietic system and secondary lymphoid (spleen) and non-lymphoid (liver and skeletal muscle) organs and tissues along the disease progression in the transgenic SOD1G93A mice. Our findings suggested that the inflammatory response due to the neurodegeneration in this animal model affected all three organs and tissues, especially the liver and the skeletal muscle. However, the liver was able to compensate this inflammatory response by means of the action of non-inflammatory monocytes, while in the skeletal muscle inflammatory monocytes prompted a further inflammation process until the terminal state of the animals. Interestingly, in blood, a positive correlation was found between non-inflammatory monocytes and survival of the transgenic SOD1G93A mice, while the contrary (a negative correlation) was found in the case of inflammatory monocytes, supporting their potential role as biomarkers of disease progression and survival in this animal model. These findings could prompt future translational studies in ALS patients, promoting the identification of new reliable biomarkers of disease progression.

Immune dysregulation may contribute to disease pathogenesis in spinal muscular atrophy mice

Spinal muscular atrophy (SMA) has long been solely considered a neurodegenerative disorder. However, recent work has highlighted defects in many other cell types that could contribute to disease aetiology. Interestingly, the immune system has never been extensively studied in SMA. Defects in lymphoid organs could exacerbate disease progression by neuroinflammation or immunodeficiency. Smn depletion led to severe alterations in the thymus and spleen of two different mouse models of SMA. The spleen from Smn depleted mice was dramatically smaller at a very young age and its histological architecture was marked by mislocalization of immune cells in the Smn^2B/- model mice. In comparison, the thymus was relatively spared in gross morphology but showed many histological alterations including cortex thinning in both mouse models at symptomatic ages. Thymocyte development was also impaired as evidenced by abnormal population frequencies in the Smn^2B/- thymus. Cytokine profiling revealed major changes in different tissues of both mouse models. Consistent with our observations, we found that survival motor neuron (Smn) protein levels were relatively high in lymphoid organs compared to skeletal muscle and spinal cord during postnatal development in wild type mice. Genetic introduction of one copy of the human SMN2 transgene was enough to rescue splenic and thymic defects in Smn^2B/- mice. Thus, Smn is required for the normal development of lymphoid organs, and altered immune function may contribute to SMA disease pathogenesis.

New insights into SMA pathogenesis: immune dysfunction and neuroinflammation

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by motor neuron degeneration, although defects in multiple cell types and tissues have also been implicated. Three independent laboratories recently identified immune organ defects in SMA. We therefore propose a novel pathogenic mechanism contributory to SMA, resulting in higher susceptibility to infection and exacerbated disease progression caused by neuroinflammation. Overall, compromised immune function could significantly affect survival and quality of life of SMA patients. We highlight the recent findings in immune organ defects, their potential consequences on patients, our understanding of neuroinflammation in SMA, and new research hypotheses in SMA pathogenesis.

SMN deficiency negatively impacts red pulp macrophages and spleen development in mouse models of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a progressive neurodegenerative disease that is the leading genetic cause of infantile death. It is caused by a severe deficiency of the ubiquitously expressed Survival Motor Neuron (SMN) protein. SMA is characterized by α-lower motor neuron loss and muscle atrophy, however, there is a growing list of tissues impacted by a SMN deficiency beyond motor neurons. The non-neuronal defects are observed in the most severe Type I SMA patients and most of the widely used SMA mouse models, however, as effective therapeutics are developed, it is unclear whether additional symptoms will be uncovered in longer lived patients. Recently, the immune system and inflammation has been identified as a contributor to neurodegenerative diseases such as ALS. To determine whether the immune system is comprised in SMA, we analyzed the spleen and immunological components in SMA mice. In this report, we identify: a significant reduction in spleen size in multiple SMA mouse models and a pathological reduction in red pulp and extramedullary hematopoiesis. Additionally, red pulp macrophages, a discrete subset of yolk sac-derived macrophages, were found to be altered in SMA spleens even in pre-symptomatic post-natal day 2 animals. These cells, which are involved in iron metabolism and the phagocytosis of erythrocytes and blood-borne pathogens are significantly reduced prior to the development of the neurodegenerative hallmarks of SMA, implying a differential role of SMN in myeloid cell ontogeny. Collectively, these results demonstrate that SMN deficiency impacts spleen development and suggests a potential role for immunological development in SMA.

Optineurin in amyotrophic lateral sclerosis: Multifunctional adaptor protein at the crossroads of different neuroprotective mechanisms

When optineurin mutations showed up on the amyotrophic lateral sclerosis (ALS) landscape in 2010, they differed from most other ALS-causing genes. They seemed to act by loss- rather than gain-of-function, and it was unclear how a polyubiquitin-binding adaptor protein, which was proposed to regulate a variety of cellular functions including cell signaling and vesicle trafficking, could mediate neuroprotection. This review discusses the considerable progress that has been made since then. A large number of mutations in optineurin and optineurin-interacting proteins TANK-binding kinase (TBK1) and p62/SQSTM-1 have been found in the ALS patients, suggesting a common neuroprotective pathway. Moreover, functional studies of the ALS-causing optineurin mutations and the recently established optineurin ubiquitin-binding deficient and knockout mouse models helped identify three major mechanisms likely to mediate neuroprotection: regulation of autophagy, mitigation of (chronic) inflammatory signaling, and blockade of necroptosis. These three processes crosstalk, and require multiple levels of control, many of which can be mediated by optineurin. Based on the role of optineurin in multiple processes and the unexpected finding that targeted optineurin deletion in microglia and oligodendrocytes ultimately leads to the same phenotype of axonal degeneration despite different initial defects, we propose that the failure of the weakest link in the optineurin neuroprotective network is sufficient to disturb homeostasis and set-off the domino effect that could ultimately lead to neurodegeneration.

ALS patients' regulatory T lymphocytes are dysfunctional, and correlate with disease progression rate and severity

Neuroinflammation is a pathological hallmark of ALS in both transgenic rodent models and patients, and is characterized by proinflammatory T lymphocytes and activated macrophages/microglia. In ALS mouse models, decreased regulatory T lymphocytes (Tregs) exacerbate the neuroinflammatory process, leading to accelerated motoneuron death and shortened survival; passive transfer of Tregs suppresses the neuroinflammation and prolongs survival. Treg numbers and FOXP3 expression are also decreased in rapidly progressing ALS patients. A key question is whether the marked neuroinflammation in ALS can be attributed to the impaired suppressive function of ALS Tregs in addition to their decreased numbers. To address this question, T lymphocyte proliferation assays were performed. Compared with control Tregs, ALS Tregs were less effective in suppressing responder T lymphocyte proliferation. Although both slowly and rapidly progressing ALS patients had dysfunctional Tregs, the greater the clinically assessed disease burden or the more rapidly progressing the patient, the greater the Treg dysfunction. Epigenetically, the percentage methylation of the Treg-specific demethylated region was greater in ALS Tregs. After in vitro expansion, ALS Tregs regained suppressive abilities to the levels of control Tregs, suggesting that autologous passive transfer of expanded Tregs might offer a novel cellular therapy to slow disease progression.

Combined Metabolomics and Transcriptomics Approaches to Assess the IL-6 Blockade as a Therapeutic of ALS: Deleterious Alteration of Lipid Metabolism

In amyotrophic lateral sclerosis (ALS), motor neuron degeneration occurs simultaneously with systemic metabolic impairment and neuroinflammation. Playing an important role in the regulation of both phenomena, interleukin (IL)-6, a major cytokine of the inflammatory response has been proposed as a target for management of ALS. Although a pilot clinical trial provided promising results in humans, another recent preclinical study showed that knocking out the IL-6 gene in mice carrying ALS did not improve clinical outcome. In this study, we aimed to determine the relevance of the IL-6 pathway blockade in a mouse model of ALS by using a pharmacological antagonist of IL-6, a murine surrogate of tocilizumab, namely MR16-1. We analyzed the immunological and metabolic effects of IL-6 blockade by cytokine measurement, blood cell immunophenotyping, targeted metabolomics, and transcriptomics. A deleterious clinical effect of MR16-1 was revealed, with a speeding up of weight loss (p = 0.0041) and decreasing body weight (p < 0.05). A significant increase in regulatory T-cell count (p = 0.0268) and a decrease in C-X-C ligand-1 concentrations in plasma (p = 0.0479) were observed. Metabolomic and transcriptomic analyses revealed that MR16-1 mainly affected branched-chain amino acid, lipid, arginine, and proline metabolism. IL-6 blockade negatively affected body weight, despite a moderated anti-inflammatory effect. Metabolic effects of IL-6 were mild compared with metabolic disturbances observed in ALS, but a modification of lipid metabolism by therapy was identified. These results indicate that IL-6 blockade did not improve clinical outcome of a mutant superoxide dismutase 1 mouse model of ALS.

Increased ratio of circulating neutrophils to monocytes in amyotrophic lateral sclerosis

Objective:

To elucidate amyotrophic lateral sclerosis (ALS) biomarkers and potential mechanisms of disease, we measured immune cell populations in whole blood from a large cohort of patients with ALS.

Methods:

Leukocytes were isolated from the blood of 44 control patients and 90 patients with ALS. The percentages and total numbers of each cell population were analyzed using flow cytometry and matched with patient ALS Functional Rating Scale–Revised (ALSFRS-R) score to correlate leukocyte metrics with disease progression.

Results:

We show a significant increase in the percentage of neutrophils and a significant decrease in the percentage of CD4 T cells and CD16⁻ monocytes in the blood of patients with ALS compared to controls; however, only CD16⁻ monocyte levels correlated with disease progression. We also examined the monocyte surface expression of CCRL2 and CCR3; CD16⁻ monocytes displayed decreased percentages and total numbers expressing CCR3, but these numbers did not correlate with ALSFRS-R score. We found that combining multiple disease metrics yielded the most accurate predictor of disease progression: the ratio of neutrophils to CD16⁻ monocytes (N:M ratio) is significantly increased in patients with ALS and better correlates with disease progression than any other single metric.

Conclusions:

These observations implicate neutrophils and monocytes as important factors in late disease progression.

Th17 Cell Response in SOD1G93A Mice following Motor Nerve Injury

An increased risk of ALS has been reported for veterans, varsity athletes, and professional football players. The mechanism underlying the increased risk in these populations has not been identified; however, it has been proposed that motor nerve injury may trigger immune responses which, in turn, can accelerate the progression of ALS. Accumulating evidence indicates that abnormal immune reactions and inflammation are involved in the pathogenesis of ALS, but the specific immune cells involved have not been clearly defined. To understand how nerve injury and immune responses may contribute to ALS development, we investigated responses of CD4⁺ T cell after facial motor nerve axotomy (FNA) at a presymptomatic stage in a transgenic mouse model of ALS (B6SJL SOD1^G93A). SOD1^G93A mice, compared with WT mice, displayed an increase in the basal activation state of CD4⁺ T cells and higher frequency of Th17 cells, which were further enhanced by FNA. In conclusion, SOD1^G93A mice exhibit abnormal CD4⁺ T cell activation with increased levels of Th17 cells prior to the onset of neurological symptoms. Motor nerve injury exacerbates Th17 cell responses and may contribute to the development of ALS, especially in those who carry genetic susceptibility to this disease.

Is spinal muscular atrophy a disease of the motor neurons only: pathogenesis and therapeutic implications?

Spinal muscular atrophy (SMA) is a genetic neurological disease that causes infant mortality; no effective therapies are currently available. SMA is due to homozygous mutations and/or deletions in the survival motor neuron 1 gene and subsequent reduction of the SMN protein, leading to the death of motor neurons. However, there is increasing evidence that in addition to motor neurons, other cell types are contributing to SMA pathology. In this review, we will discuss the involvement of non-motor neuronal cells, located both inside and outside the central nervous system, in disease onset and progression. Even if SMN restoration in motor neurons is needed, it has been shown that optimal phenotypic amelioration in animal models of SMA requires a more widespread SMN correction. It has been demonstrated that non-motor neuronal cells are also involved in disease pathogenesis and could have important therapeutic implications. For these reasons it will be crucial to take this evidence into account for the clinical translation of the novel therapeutic approaches.

ACAID as a potential therapeutic approach to modulate inflammation in neurodegenerative diseases

The progressive loss of neurons and inflammation characterizes neurodegenerative diseases. Although the etiology, progression and outcome of different neurodegenerative diseases are varied, they share chronic inflammation maintained largely by central nervous system (CNS)-derived antigens recognized by T cells. Inflammation can be beneficial by recruiting immune cells to kill pathogens or to clear cell debris resulting from the primary insult. However, chronic inflammation exacerbates and perpetuates tissue damage. An increasing number of therapies that attempt to modulate neuroinflammation have been developed. However, so far none has succeeded in decreasing the secondary damage associated with chronic inflammation. A potential strategy to modulate the immune system is related to the induction of tolerance to CNS antigens. In this line, it is our hypothesis that this could be accomplished by using anterior chamber associated immune deviation (ACAID) as a strategy. Thus, we review current knowledge regarding some neurodegenerative diseases and the associated immune response that causes inflammation. In addition, we discuss further our hypothesis of the possible usefulness of ACAID as a therapeutic strategy to ameliorate damage to the CNS.

Neuroinflammation in motor neuron disease

Increasing evidence suggests that the pathogenesis of neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) is not restricted to the neurons but attributed to the abnormal interactions of neurons and surrounding glial and lymphoid cells. These findings led to the concept of non-cell autonomous neurodegeneration. Neuroinflammation, which is mediated by activated glial cells and infiltrated lymphocytes and accompanied by the subsequent production of proinflammatory cytokines and neurotoxic or neuroprotective molecules, is characteristic to the pathology in ALS and is a key component for non-cell autonomous neurodegeneration. This review covers the involvement of microglia and astrocytes in the ALS mouse models and human ALS, and it also covers the deregulated pathways in motor neurons, which are involved in initiating the disease. Based on the cell-type specific pathomechanisms of motor neuron disease, targeting of neuroinflammation could lead to future therapeutic strategies for ALS and could be potentially applied to other neurodegenerative diseases.

Immunization with a Myelin-Derived Antigen Activates the Brain's Choroid Plexus for Recruitment of Immunoregulatory Cells to the CNS and Attenuates Disease Progression in a Mouse Model of ALS

Amyotrophic lateral sclerosis (ALS) is a devastating fatal motor neuron disease, for which there is currently no cure or effective treatment. In this disease, local neuroinflammation develops along the disease course and contributes to its rapid progression. In several models of CNS pathologies, circulating immune cells were shown to display an indispensable role in the resolution of the neuroinflammatory response. The recruitment of such cells to the CNS involves activation of the choroid plexus (CP) of the brain for leukocyte trafficking, through a mechanism that requires IFN-γ signaling. Here, we found that in the mutant SOD1(G93A) (mSOD1) mouse model of ALS, the CP does not support leukocyte trafficking during disease progression, due to a local reduction in IFN-γ levels. Therapeutic immunization of mSOD1 mice with a myelin-derived peptide led to CP activation, and was followed by the accumulation of immunoregulatory cells, including IL-10-producing monocyte-derived macrophages and Foxp3(+) regulatory T cells, and elevation of the neurotrophic factors IGF-1 and GDNF in the diseased spinal cord parenchyma. The immunization resulted in the attenuation of disease progression and an increased life expectancy of the mSOD1 mice. Collectively, our results demonstrate that recruitment of immunoregulatory cells to the diseased spinal cord in ALS, needed for fighting off the pathology, can be enhanced by transiently boosting peripheral immunity to myelin antigens.

Plasma Derived From Human Umbilical Cord Blood Modulates Mitogen-Induced Proliferation of Mononuclear Cells Isolated From the Peripheral Blood of ALS Patients

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by degeneration of motor neurons in the spinal cord and brain. This disease clinically manifests as gradual muscular weakness and atrophy leading to paralysis and death by respiratory failure. While multiple interdependent factors may contribute to the pathogenesis of ALS, increasing evidence shows the possible presence of autoimmune mechanisms that promote disease progression. The potential use of plasma derived from human umbilical cord blood (hUCB) as a therapeutic tool is currently in its infancy. The hUCB plasma is rich in cytokines and growth factors that are required for growth and survival of cells during hematopoiesis. In this study, we investigated the effects of hUCB plasma on the mitogen-induced proliferation of mononuclear cells (MNCs) isolated from the peripheral blood of ALS patients and apoptotic activity by detection of caspase 3/7 expression of the isolated MNCs in vitro. Three distinct responses to phytohemagglutinin (PHA)-induced proliferation of MNCs were observed, which were independent of age, disease duration, and the ALS rating scale: Group I responded normally to PHA, Group II showed no response to PHA, while Group III showed a hyperactive response to PHA. hUCB plasma attenuated the hyperactive response (Group III) and potentiated the normal response in Group I ALS patients, but did not alter that of the nonresponders to PHA (Group II). The elevated activity of caspase 3/7 observed in the MNCs from ALS patients was significantly reduced by hUCB plasma treatment. Thus, study results showing different cell responses to mitogen suggest alteration in lymphocyte functionality in ALS patients that may be a sign of immune deficiency in the nonresponders and autoimmunity alterations in the hyperactive responders. The ability of hUCB plasma to modulate the mitogen cell response and reduce caspase activity suggests that the use of hUCB plasma alone, or with stem cells, may prove useful as a therapeutic in ALS patients.

CD4 + T Cells and Neuroprotection: Relevance to Motoneuron Injury and Disease

We have established a physiologically relevant mechanism of CD4+ T cell-mediated neuroprotection involving axotomized wildtype (WT) mouse facial motoneurons (FMN) with significance in the treatment of amyotrophic lateral sclerosis (ALS), a fatal MN disease. Use of the transgenic mouse model of ALS involving expression of human mutant superoxide dismutase genes (SOD1(G93A); abbreviated here as mSOD1) has accelerated basic ALS research. Superimposition of facial nerve axotomy (FNA) on the mSOD1 mouse during pre-symptomatic stages indicates that they behave like immunodeficient mice in terms of increased FMN loss and decreased functional recovery, through a mechanism that, paradoxically, is not inherent within the MN itself, but, instead, involves a defect in peripheral immune: CNS glial cell interactions. Our goal is to utilize our WT mouse model of immune-mediated neuroprotection after FNA as a template to elucidate how a malfunctioning peripheral immune system contributes to motoneuron cell loss in the mSOD1 mouse. This review will discuss potential immune defects in ALS, as well as provide an up-to-date understanding of how the CD4+ effector T cells provide neuroprotection to motoneurons through regulation of the central microglial and astrocytic response to injury. We will discuss an IL-10 cascade within the facial nucleus that requires a functional CD4+ T cell trigger for activation. The review will discuss the role of T cells in ALS, and our recent reconstitution experiments utilizing our model of T cell-mediated neuroprotection in WT vs mSOD1 mice after FNA. Identification of defects in neural:immune interactions could provide targets for therapeutic intervention in ALS.

Humoral factors in ALS patients during disease progression

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting upper and lower motor neurons in the CNS and leading to paralysis and death. There are currently no effective treatments for ALS due to the complexity and heterogeneity of factors involved in motor neuron degeneration. A complex of interrelated effectors have been identified in ALS, yet systemic factors indicating and/or reflecting pathological disease developments are uncertain. The purpose of the study was to identify humoral effectors as potential biomarkers during disease progression.

METHODS

Thirteen clinically definite ALS patients and seven non-neurological controls enrolled in the study. Peripheral blood samples were obtained from each ALS patient and control at two visits separated by 6 months. The Revised ALS Functional Rating Scale (ALSFRS-R) was used to evaluate overall ALS-patient functional status at each visit. Eleven humoral factors were analyzed in sera. Cytokine levels (GM-CSF, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, and TNF-α) were determined using the Bio-Rad Bio-Plex® Luminex 200 multiplex assay system. Nitrite, a breakdown product of NO, was quantified using a Griess Reagent System. Glutathione (GSH) concentrations were measured using a Glutathione Fluorometric Assay Kit.

RESULTS

ALS patients had ALSFRS-R scores of 30.5 ± 1.9 on their first visit and 27.3 ± 2.7 on the second visit, indicating slight disease progression. Serum multiplex cytokine panels revealed statistically significant changes in IL-2, IL-5, IL-6, and IL-8 levels in ALS patients depending on disease status at each visit. Nitrite serum levels trended upwards in ALS patients while serum GSH concentrations were drastically decreased in sera from ALS patients versus controls at both visits.

CONCLUSIONS

Our results demonstrated a systemic pro-inflammatory state and impaired antioxidant system in ALS patients during disease progression. Increased levels of pro-inflammatory IL-6, IL-8, and nitrite and significantly decreased endogenous antioxidant GSH levels could identify these humoral constituents as systemic biomarkers for ALS. However, systemic changes in IL-2, IL-5, and IL-6 levels determined between visits in ALS patients might indicate adaptive immune system responses dependent on current disease stage. These novel findings, showing dynamic changes in humoral effectors during disease progression, could be important for development of an effective treatment for ALS.

Lack of TNF-alpha receptor type 2 protects motor neurons in a cellular model of amyotrophic lateral sclerosis and in mutant SOD1 mice but does not affect disease progression

Changes in the homeostasis of tumor necrosis factor α (TNFα) have been demonstrated in patients and experimental models of amyotrophic lateral sclerosis (ALS). However, the contribution of TNFα to the development of ALS is still debated. TNFα is expressed by glia and neurons and acts through the membrane receptors TNFR1 and TNFR2, which may have opposite effects in neurodegeneration. We investigated the role of TNFα and its receptors in the selective motor neuron death in ALS in vitro and in vivo. TNFR2 expressed by astrocytes and neurons, but not TNFR1, was implicated in motor neuron loss in primary SOD1-G93A co-cultures. Deleting TNFR2 from SOD1-G93A mice, there was partial but significant protection of spinal motor neurons, sciatic nerves, and tibialis muscles. However, no improvement of motor impairment or survival was observed. Since the sciatic nerves of SOD1-G93A/TNFR2-/- mice showed high phospho-TAR DNA-binding protein 43 (TDP-43) accumulation and low levels of acetyl-tubulin, two indices of axonal dysfunction, the lack of symptom improvement in these mice might be due to impaired function of rescued motor neurons. These results indicate the interaction between TNFR2 and membrane-bound TNFα as an innovative pathway involved in motor neuron death. Nevertheless, its inhibition is not sufficient to stop disease progression in ALS mice, underlining the complexity of this pathology. We show evidence of the involvement of neuronal and astroglial TNFR2 in the motor neuron degeneration in ALS. Both concur to cause motor neuron death in primary astrocyte/spinal neuron co-cultures. TNFR2 deletion partially protects motor neurons and sciatic nerves in SOD1-G93A mice but does not improve their symptoms and survival. However, TNFR2 could be a new target for multi-intervention therapies.

Protective and Toxic Neuroinflammation in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a clinically heterogeneous disorder characterized by loss of motor neurons, resulting in paralysis and death. Multiple mechanisms of motor neuron injury have been implicated based upon the more than 20 different genetic causes of familial ALS. These inherited mutations compromise diverse motor neuron pathways leading to cell-autonomous injury. In the ALS transgenic mouse models, however, motor neurons do not die alone. Cell death is noncell-autonomous dependent upon a well orchestrated dialogue between motor neurons and surrounding glia and adaptive immune cells. The pathogenesis of ALS consists of 2 stages: an early neuroprotective stage and a later neurotoxic stage. During early phases of disease progression, the immune system is protective with glia and T cells, especially M2 macrophages/microglia, and T helper 2 cells and regulatory T cells, providing anti-inflammatory factors that sustain motor neuron viability. As the disease progresses and motor neuron injury accelerates, a second rapidly progressing phase develops, characterized by M1 macrophages/microglia, and proinflammatory T cells. In rapidly progressing ALS patients, as in transgenic mice, neuroprotective regulatory T cells are significantly decreased and neurotoxicity predominates. Our own therapeutic efforts are focused on modulating these neuroinflammatory pathways. This review will focus on the cellular players involved in neuroinflammation in ALS and current therapeutic strategies to enhance neuroprotection and suppress neurotoxicity with the goal of arresting the progressive and devastating nature of ALS.

Effect of thymic stimulation of CD4+ T cell expansion on disease onset and progression in mutant SOD1 mice

BACKGROUND

The peripheral immune system is implicated in modulating microglial activation, neurodegeneration and disease progression in amyotrophic lateral sclerosis (ALS). Specifically, there is reduced thymic function and regulatory T cell (Treg) number in ALS patients and mutant superoxide dismutase 1 (SOD1) mice, while passive transfer of Tregs ameliorates disease in mutant SOD1 mice. Here, we assessed the effects of augmenting endogenous CD4+ T cell number by stimulating the thymus using surgical castration on the phenotype of transgenic SOD1(G93A) mice.

METHOD

Male SOD1(G93A) mice were castrated or sham operated, and weight loss, disease onset and progression were examined. Thymus atrophy and blood CD4+, CD8+ and CD4+ FoxP3+ T cell numbers were determined by fluorescence activated cell sorting (FACS). Motor neuron counts, glial cell activation and androgen receptor (AR) expression in the spinal cord were investigated using immunohistochemistry and Western blotting. Differences between castrated and sham mice were analysed using an unpaired t test or one-way ANOVA.

RESULTS

Castration significantly increased thymus weight and total CD4+ T cell numbers in SOD1(G93A) mice, although Tregs levels were not affected. Despite this, disease onset and progression were similar in castrated and sham SOD1(G93A) mice. Castration did not affect motor neuron loss or astrocytic activation in spinal cords of SOD1(G93A) mice; however, microglial activation was reduced, specifically M1 microglia. We also show that AR is principally expressed in spinal motor neurons and progressively downregulated in spinal cords of SOD1(G93A) mice from disease onset which is further enhanced by castration.

CONCLUSIONS

These results demonstrate that increasing thymic function and CD4+ T cell number by castration confers no clinical benefit in mutant SOD1 mice, which may reflect an inability to stimulate neuroprotective Tregs. Nonetheless, castration decreases M1 microglial activation in the spinal cord without any clinical improvement and motor neuron rescue, in contrast to other approaches to suppress microglia in mutant SOD1 mice. Lastly, diminished AR expression in spinal motor neurons, which links to another motor neuron disorder, spinal bulbar muscular atrophy (SBMA), may contribute to ALS pathogenesis and suggests a common disease pathway in ALS and SBMA mediated by disruption of AR signalling in motor neurons.

Early-stage treatment with Withaferin A reduces levels of misfolded superoxide dismutase 1 and extends lifespan in a mouse model of amyotrophic lateral sclerosis

Approximately 20% of cases of familial amyotrophic lateral sclerosis (ALS) are caused by mutations in the gene encoding Cu/Zn superoxide dismutase (SOD1). Recent studies have shown that Withaferin A (WA), an inhibitor of nuclear factor-kappa B activity, was efficient in reducing disease phenotype in a TAR DNA binding protein 43 transgenic mouse model of ALS. These findings led us to test WA in mice from 2 transgenic lines expressing different ALS-linked SOD1 mutations, SOD1(G93A) and SOD1(G37R). Intraperitoneal administration of WA at a dosage of 4 mg/kg of body weight was initiated from postnatal day 40 until end stage in SOD1(G93A) mice, and from 9 months until end stage in SOD1(G37R) mice. The beneficial effects of WA in the SOD1(G93A) mice model were accompanied by an alleviation of neuroinflammation, a decrease in levels of misfolded SOD1 species in the spinal cord, and a reduction in loss of motor neurons resulting in delayed disease progression and mortality. Interestingly, WA treatment triggered robust induction of heat shock protein 25 (a mouse ortholog of heat shock protein 27), which may explain the reduced level of misfolded SOD1 species in the spinal cord of SOD1(G93A) mice and the decrease of neuronal injury responses, as revealed by real-time imaging of biophotonic SOD1(G93A) mice expressing a luciferase transgene under the control of the growth-associated protein 43 promoter. These results suggest that WA may represent a potential lead compound for drug development aiming to treat ALS.

Targeting miR-155 restores abnormal microglia and attenuates disease in SOD1 mice

OBJECTIVE

To investigate miR-155 in the SOD1 mouse model and human sporadic and familial amyotrophic lateral sclerosis (ALS).

METHODS

NanoString microRNA, microglia and immune gene profiles, protein mass spectrometry, and RNA-seq analyses were measured in spinal cord microglia, splenic monocytes, and spinal cord tissue from SOD1 mice and in spinal cord tissue of familial and sporadic ALS. miR-155 was targeted by genetic ablation or by peripheral or centrally administered anti-miR-155 inhibitor in SOD1 mice.

RESULTS

In SOD1 mice, we found loss of the molecular signature that characterizes homeostatic microglia and increased expression of miR-155. There was loss of the microglial molecules P2ry12, Tmem119, Olfml3, transcription factors Egr1, Atf3, Jun, Fos, and Mafb, and the upstream regulators Csf1r, Tgfb1, and Tgfbr1, which are essential for microglial survival. Microglia biological functions were suppressed including phagocytosis. Genetic ablation of miR-155 increased survival in SOD1 mice by 51 days in females and 27 days in males and restored the abnormal microglia and monocyte molecular signatures. Disease severity in SOD1 males was associated with early upregulation of inflammatory genes, including Apoe in microglia. Treatment of adult microglia with apolipoprotein E suppressed the M0-homeostatic unique microglia signature and induced an M1-like phenotype. miR-155 expression was increased in the spinal cord of both familial and sporadic ALS. Dysregulated proteins that we identified in human ALS spinal cord were restored in SOD1(G93A) /miR-155(-/-) mice. Intraventricular anti-miR-155 treatment derepressed microglial miR-155 targeted genes, and peripheral anti-miR-155 treatment prolonged survival.

INTERPRETATION

We found overexpression of miR-155 in the SOD1 mouse and in both sporadic and familial human ALS. Targeting miR-155 in SOD1 mice restores dysfunctional microglia and ameliorates disease. These findings identify miR-155 as a therapeutic target for the treatment of ALS.

Dual destructive and protective roles of adaptive immunity in neurodegenerative disorders

Inappropriate T cell responses in the central nervous system (CNS) affect the pathogenesis of a broad range of neuroinflammatory and neurodegenerative disorders that include, but are not limited to, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. On the one hand immune responses can exacerbate neurotoxic responses; while on the other hand, they can lead to neuroprotective outcomes. The temporal and spatial mechanisms by which these immune responses occur and are regulated in the setting of active disease have gained significant recent attention. Spatially, immune responses that affect neurodegeneration may occur within or outside the CNS. Migration of antigen-specific CD4+ T cells from the periphery to the CNS and consequent immune cell interactions with resident glial cells affect neuroinflammation and neuronal survival. The destructive or protective mechanisms of these interactions are linked to the relative numerical and functional dominance of effector or regulatory T cells. Temporally, immune responses at disease onset or during progression may exhibit a differential balance of immune responses in the periphery and within the CNS. Immune responses with predominate T cell subtypes may differentially manifest migratory, regulatory and effector functions when triggered by endogenous misfolded and aggregated proteins and cell-specific stimuli. The final result is altered glial and neuronal behaviors that influence the disease course. Thus, discovery of neurodestructive and neuroprotective immune mechanisms will permit potential new therapeutic pathways that affect neuronal survival and slow disease progression.

Evidence for peripheral immune activation in amyotrophic lateral sclerosis

There is evidence of the activity of immune system in the spinal cords of patients with amyotrophic lateral sclerosis (ALS), however; few studies to date have explored the status of peripheral immune response in ALS patients. Blood samples from 284 ALS patients and 217 aged-match controls were evaluated, and parameters of T cell subset, humoral immunity, and complement system activation were observed. CD4+ T lymphocytes and circulating immune complexes (CICs) were significantly decreased, and component C3 was significantly increased in ALS patients compared with normal controls. Patients with severe or moderate impairment had a higher CD4+ T cell percentage and a lower IgG levels when compared to those with mild impairment. There was an inverse correlation between CD4 T cell percentage and both revised ALS Functional Rating Scale (ALSFRS-R) score and disease duration, but the correlation was positive between IgG level and both ALSFRS-R score and disease duration among ALS patients. These correlations were gender-specific. This investigation demonstrated the existence of peripheral immune abnormalities in ALS patients.

NP001 regulation of macrophage activation markers in ALS: a phase I clinical and biomarker study

This is a phase I, placebo-controlled, single ascending dose safety and tolerability study of NP001 in patients with ALS. NP001 is a novel regulator of inflammatory macrophages and monocytes. As ALS progression is thought to be related to neuroinflammation, an additional objective of the study was to assess the effects of NP001 administration on monocyte activation markers. Thirty-two ALS patients were enrolled and received either placebo (eight) or one of four (six at each dose) ascending single i.v. doses (0.2, 0.8, 1.6 and 3.2 mg/kg NP001). Patients were monitored for safety, and blood monocyte immune activation markers CD16 and HLA-DR were assessed pre- and 24 h post-dosing. Changes from baseline were calculated. Results showed that NP001 was generally safe and well tolerated. Importantly, a single dose of NP001 caused a dose-dependent reduction in expression of monocyte CD16, a marker of monocyte activation/inflammation. Additionally, monocyte HLA-DR expression was also decreased in those patients with elevated values at baseline. In conclusion, these data indicate that NP001 has an acute effect on inflammatory monocytes in ALS patient blood. The potential for modulation of inflammation in the context of ALS disease progression will require further study with long-term follow-up.

SOD1(G93A) transgenic mouse CD4(+) T cells mediate neuroprotection after facial nerve axotomy when removed from a suppressive peripheral microenvironment

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving motoneuron (MN) axonal withdrawal and cell death. Previously, we established that facial MN (FMN) survival levels in the SOD1(G93A) transgenic mouse model of ALS are reduced and nerve regeneration is delayed, similar to immunodeficient RAG2(-/-) mice, after facial nerve axotomy. The objective of this study was to examine the functionality of SOD1(G93A) splenic microenvironment, focusing on CD4(+) T cells, with regard to defects in immune-mediated neuroprotection of injured MN. We utilized the RAG2(-/-) and SOD1(G93A) mouse models, along with the facial nerve axotomy paradigm and a variety of cellular adoptive transfers, to assess immune-mediated neuroprotection of FMN survival levels. We determined that adoptively transferred SOD1(G93A) unfractionated splenocytes into RAG2(-/-) mice were unable to support FMN survival after axotomy, but that adoptive transfer of isolated SOD1(G93A) CD4(+) T cells could. Although WT unfractionated splenocytes adoptively transferred into SOD1(G93A) mice were able to maintain FMN survival levels, WT CD4(+) T cells alone could not. Importantly, these results suggest that SOD1(G93A) CD4(+) T cells retain neuroprotective functionality when removed from a dysfunctional SOD1(G93A) peripheral splenic microenvironment. These results also indicate that the SOD1(G93A) central nervous system microenvironment is able to re-activate CD4(+) T cells for immune-mediated neuroprotection when a permissive peripheral microenvironment exists. We hypothesize that a suppressive SOD1(G93A) peripheral splenic microenvironment may compromise neuroprotective CD4(+) T cell activation and/or differentiation, which, in turn, results in impaired immune-mediated neuroprotection for MN survival after peripheral axotomy in SOD1(G93A) mice.

Melittin ameliorates the inflammation of organs in an amyotrophic lateral sclerosis animal model

Amyotrophic lateral sclerosis (ALS) is a devastating progressive neurodegenerative disorder characterized by a selective loss of motor neurons in the spinal cord, brainstem, and motor cortex, leading to weakness of the limb and bulbar muscles. Although the immediate cause of death in ALS is the destruction of motor neurons, ALS is a multi-organ disease that also affects the lungs, spleen, and liver. Melittin is one of components of bee venom and has anti-neuroinflammatory effects in the spinal cord, as shown in an ALS animal model. To investigate the effects of melittin on inflammation in the lungs and spleen, we used hSOD1(G93A) transgenic mice that are mimic for ALS. Melittin treatment reduced the expression of inflammatory proteins, including Iba-1 and CD14 by 1.9- and 1.3-fold (p<0.05), respectively, in the lungs of symptomatic hSOD1(G93A) transgenic mice. In the spleen, the expression of CD14 and COX2 that are related to inflammation were decreased by 1.4 fold (p<0.05) and cell survival proteins such as pERK and Bcl2 were increased by 1.3- and 1.5-fold (p<0.05) in the melittin-treated hSOD1G93A transgenic mice. These findings suggest that melittin could be a candidate to regulate the immune system in organs affected by ALS.

Bridge between neuroimmunity and traumatic brain injury

The pathophysiology of degenerative, infectious, inflammatory and traumatic diseases of the central nervous system includes a significant immune component. As to the latter, damage to the cerebral vasculature and neural cell bodies, caused by traumatic brain injury (TBI) activates innate immunity with concomitant infiltration of immunocytes into the damaged nervous system. This leads to proinflammatory cytokine and prostaglandin production and lost synaptic integrity and more generalized neurotoxicity. Engagement of adaptive immune responses follows including the production of antibodies and lymphocyte proliferation. These affect the tempo of disease along with tissue repair and as such provide a number of potential targets for pharmacological treatments for TBI. However, despite a large body of research, no such treatment intervention is currently available. In this review we will discuss the immune response initiated following brain injuries, drawing on knowledge gained from a broad array of experimental and clinical studies. Our discussion seeks to address potential therapeutic targets and propose ways in which the immune system can be controlled to promote neuroprotection.

IFN-γ-dependent activation of the brain's choroid plexus for CNS immune surveillance and repair

Infiltrating T cells and monocyte-derived macrophages support central nervous system repair. Although infiltration of leucocytes to the injured central nervous system has recently been shown to be orchestrated by the brain's choroid plexus, the immunological mechanism that maintains this barrier and regulates its activity as a selective gate is poorly understood. Here, we hypothesized that CD4(+) effector memory T cells, recently shown to reside at the choroid plexus stroma, regulate leucocyte trafficking through this portal through their interactions with the choroid plexus epithelium. We found that the naïve choroid plexus is populated by T helper 1, T helper 2 and regulatory T cells, but not by encephalitogenic T cells. In vitro findings revealed that the expression of immune cell trafficking determinants by the choroid plexus epithelium is specifically induced by interferon-γ. Tumour necrosis factor-α and interferon-γ reciprocally controlled the expression of their receptors by the choroid plexus epithelium, and had a synergistic effect in inducing the epithelial expression of trafficking molecules. In vivo, interferon-γ-dependent signalling controlled trafficking through the choroid plexus; interferon-γ receptor knockout mice exhibited reduced levels of T cells and monocyte entry to the cerebrospinal fluid and impaired recovery following spinal cord injury. Moreover, reduced expression of trafficking molecules by the choroid plexus was correlated with reduced CD4(+) T cells in the choroid plexus and cerebrospinal fluid of interferon-γ receptor knockout mice. Similar effect on the expression of trafficking molecules by the choroid plexus was found in bone-marrow chimeric mice lacking interferon-γ receptor in the central nervous system, or reciprocally, lacking interferon-γ in the circulation. Collectively, our findings attribute a novel immunological plasticity to the choroid plexus epithelium, allowing it to serve, through interferon-γ signalling, as a tightly regulated entry gate into the central nervous system for circulating leucocytes immune surveillance under physiological conditions, and for repair following acute injury.

The innate and adaptive immunological aspects in neurodegenerative diseases

Neurodegenerative diseases affect a considerable percentage of the elderly population. New therapeutic approaches are warranted, aiming to at least delay and possibly reverse disease progression. Strategies to elaborate such approaches require knowledge of specific immune system involvement in disease pathogenesis. In this review, innate and adaptive immunological aspects of neurodegenerative disorders, in particular Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis (ALS), are discussed. Initiating disease factors, as well as common mechanistic pathways, are detailed and potential immunological therapeutic targets are identified.

Analysis of microRNA expression profile by small RNA sequencing in Down syndrome fetuses

Down syndrome (DS) is caused by trisomy of human chromosome 21 (Hsa21) and is associated with numerous deleterious phenotypes, including cognitive impairment, childhood leukemia and immune defects. Five Hsa21‑derived microRNAs (i.e., hsa-miR-99a, let-7c, miR-125b-2, miR-155 and miR-802) are involved in variable phenotypes of DS. However, the changes involved in the genome-wide microRNA expression of DS fetuses under the influence of trisomy 21 have yet to be determined. To investigate the expression characteristic of microRNAs during the development of DS fetuses and identify whether another microRNA gene resides in the Hsa21, Illumina high-throughput sequencing technology was employed to comprehensively characterize the microRNA expression profiles of the DS and normal fetal cord blood mononuclear cells (CBMCs). In total, 149 of 395 identified microRNAs were significantly differentially expressed (fold change >2.0 and P<0.001) and 2 of 181 candidate novel microRNAs were identified as residing within the ̔DS critical region̓ of human chromosome 21 (chr21q22.2‑22.3). Additionally, 7 of 14 Hsa21-derived microRNAs were detected, although not all seven were overexpressed in DS CBMCs compared with the control. Gene ontology enrichment analyses revealed that a set of abnormally expressed microRNAs were involved in the regulation of transcription, gene expression, cellular biosynthetic process and nucleic acid metabolic process. Significantly, most of the mRNA targets in these categories were associated with immune modulation (i.e., SOD1, MXD4, PBX1, BCLAF1 and FOXO1). Findings of the present study provided a considerable insight into understanding the expression characteristic of microRNAs in the DS fetal CBMCs. To the best of our knowledge, this is the first study to examine genome-wide microRNA expression profiles in the DS fetus. Differentially expressed microRNAs may be involved in hemopoietic abnormalities and the immune defects of DS fetuses and newborns.

Immune-mediated mechanisms in the pathoprogression of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease with selective loss of upper and lower motor neurons. At sites of motor neuron injury, neuroinflammation is a prominent pathological finding and is characterized by microglial activation, astrogliosis, and infiltration of monocytes and T-cells. Both innate and adaptive immune responses actively influence disease progression in animal models and in ALS patients, and promote neuroprotection or neurotoxicity at different stages of disease. The early immune reaction to signals from injured motor neurons is to rescue and repair damaged tissue. As disease accelerates, a shift occurs from beneficial immune responses (involving M2 microglia and regulatory T-cells) to deleterious immune responses (involving M1 microglia and Th1 cells). In this review, we underscore the importance of immune-mediated mechanisms in the pathogenesis of ALS and discuss the alterations and distinct phenotypes of immune cells at the different stages of disease. The better we understand the dynamic changes that occur within the immune system over the course of disease, the better we will be able to develop effective therapeutic regimens in ALS.

The role of glutamate and the immune system in organophosphate-induced CNS damage

Organophosphate (OP) poisoning is associated with long-lasting neurological damage, which is attributed mainly to the excessive levels of glutamate caused by the intoxication. Glutamate toxicity, however, is not specific to OP poisoning, and is linked to propagation of damage in both acute and chronic neurodegenerative conditions in the central nervous system (CNS). In addition to acute excitotoxic effects of glutamate, there is now a growing amount of evidence of its intricate immunomodulatory effects in the brain, involving both the innate and the adaptive immune systems. Moreover, it was demonstrated that immunomodulatory treatments, aimed at regulating the interaction between the resident immune cells of the brain (microglia) and the peripheral immune system, can support buffering of excessive levels of glutamate and restoration of the homeostasis. In this review, we will discuss the role of glutamate as an excitotoxic agent in the acute phase of OP poisoning, and the possible functions it may have as both a neuroprotectant and an immunomodulator in the sub-acute and chronic phases of OP poisoning. In addition, we will describe the novel immune-based neuroprotective strategies aimed at counteracting the long-term neurodegenerative effects of glutamate in the CNS.

A system mathematical model of a cell-cell communication network in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating and chronic neurodegenerative disease without any known cure. In the brain and spinal cord of both patients and animal models with ALS, neuroinflammation is a prominent pathological hallmark which is characterized by infiltrating T cells at sites of motor neuron injury. Their presence in mutant Cu(2+)/Zn(2+) superoxide dismutase (mSOD1) induced ALS plays an important role in shifting the response of microglia from neuroprotective to neurotoxic. In order to better understand how these cells and their communication network collectively modulate the disease progression, we have established a mathematical model integrating diverse cells and cytokines. According to the experimental data sets, we first refined this model by identifying a link between TGFβ and M1 microglia which can produce an optimized model to fit data sets better. Then based on this model, parameters were estimated using genetic algorithm. Sensitivity analysis of these parameters identified several factors such as the release rate of IFNγ by T helper 1 (Th1) cells, which may be related to the heterogeneity between the patients with different survival times. Furthermore, the tests on T cell based therapeutic strategies indicated that elimination of Th1 cells is the most effective approach extending survival time. This confirmed the dominant role of Th1 cells in leading the rapid disorder in the later stage of ALS. For the therapies targeting cytokines, injection of IL6 can essentially augment the neuroprotective response and extend the life effectively by elevating the level of IL4, a neuroprotective cytokine, while directly injected IL4 will decay rapidly in the ALS microenvironment and cannot provide a persistent protective effect. On the other hand, in spite of the attractive effect of direct elimination of mSOD1 or self-antigen, it is difficult to implement in CNS. As an alternative, elimination of IFNγ can be chosen as another effective therapy. In the future, if we combine the side effects of different therapies, this model can be used to optimize the therapeutic strategies so that they can effectively improve survival rates and quality of life for patients with ALS.

Inflammation and neurovascular changes in amyotrophic lateral sclerosis

Neuroinflammation in now established as an important factor in the pathogenesis of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). At various time points, astrocytes and microglia are markedly activated, either producing neuroprotective or pro-inflammatory molecules, which can decrease or increase the rate of primary motor neuron degeneration respectively. Recent research has shown that this neuroinflammatory component is affected by the peripheral immune system; T lymphocytes in particular are able to cross into the brain and spinal cord parenchyma, where they interact with resident microglia, either inducing them to adopt an M1 (cytotoxic) or M2 (protective) phenotype, depending on the stage of disease. Clearly understanding the changes that occur to allow the interaction between peripheral and central immune responses will be essential in any attempt to manipulate the disease process via neuroinflammatory mechanisms. However, our understanding of the endothelial changes, which facilitate the infiltration of peripheral immune cells into the brain and spinal cord, is still in its infancy. There are suggestions, though, of up-regulation of cellular adhesion molecules, which are able to arrest circulating leukocytes and facilitate diapedesis into the brain parenchyma. In addition, tight junction proteins appear to be down-regulated, leading to an increase in vascular permeability, an effect that is amplified by vascular damage late in the disease process. This review summarises our current knowledge regarding neuroinflammation, peripheral immune involvement, and endothelial changes in ALS. This article is part of a Special Issue entitled 'Neuroinflammation in neurodegeneration and neurodysfunction'.

Delayed functional recovery in presymptomatic mSOD1G93A mice following facial nerve crush axotomy

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving progressive loss of motoneurons (MN). Axonal pathology and presynaptic deaf-ferentation precede MN degeneration during disease progression in patients and the ALS mouse model (mSOD1). Previously, we determined that a functional adaptive immune response is required for complete functional recovery following a facial nerve crush axotomy in wild-type (WT) mice. In this study, we investigated the effects of facial nerve crush axotomy on functional recovery and facial MN survival in presymptomatic mSOD1 mice, relative to WT mice. The results indicate that functional recovery and facial MN survival levels are significantly reduced in presymptomatic mSOD1, relative to WT, and similar to what has previously been observed in immunodeficient mice. It is concluded that a potential immune system defect exists in the mSOD1 mouse that negatively impacts neuronal survival and regeneration following target disconnection associated with peripheral nerve axotomy.

Regulatory T-lymphocytes mediate amyotrophic lateral sclerosis progression and survival

In amyotrophic lateral sclerosis (ALS) mice, regulatory T-lymphocytes (Tregs) are neuroprotective, slowing disease progression. To address whether Tregs and FoxP3, a transcription factor required for Treg function, similarly influence progression rates of ALS patients, T-lymphocytes from patients were assessed by flow cytometry. Both numbers of Tregs and their FoxP3 protein expressions were reduced in rapidly progressing ALS patients and inversely correlated with progression rates. The mRNA levels of FoxP3, TGF-β, IL4 and Gata3, a Th2 transcription factor, were reduced in rapidly progressing patients and inversely correlated with progression rates. Both FoxP3 and Gata3 were accurate indicators of progression rates. No differences in IL10, Tbx21, a Th1 transcription factor or IFN-γ expression were found between slow and rapidly progressing patients. A 3.5-year prospective study with a second larger cohort revealed that early reduced FoxP3 levels were indicative of progression rates at collection and predictive of future rapid progression and attenuated survival. Collectively, these data suggest that Tregs and Th2 lymphocytes influence disease progression rates. Importantly, early reduced FoxP3 levels could be used to identify rapidly progressing patients.

The role of regulatory T cells in neurodegenerative diseases

A sustained neuroinflammatory response is the hallmark of many neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, multiple sclerosis, and HIV-associated neurodegeneration. A specific subset of T cells, currently recognized as FOXP3(+) CD25(+) CD4(+) regulatory T cells (Tregs), are pivotal in suppressing autoimmunity and maintaining immune homeostasis by mediating self-tolerance at the periphery as shown in autoimmune diseases and cancers. A growing body of evidence shows that Tregs are not only important for maintaining immune balance at the periphery but also contribute to self-tolerance and immune privilege in the central nervous system. In this article, we first review the current status of knowledge concerning the development and the suppressive function of Tregs. We then discuss the evidence supporting a dysfunction of Tregs in several neurodegenerative diseases. Interestingly, a dysfunction of Tregs is mainly observed in the early stages of several neurodegenerative diseases, but not in their chronic stages, pointing to a causative role of inflammation in the pathogenesis of neurodegenerative diseases. Furthermore, we provide an overview of a number of molecules, such as hormones, neuropeptides, neurotransmitters, or ion channels, that affect the dysfunction of Tregs in neurodegenerative diseases. We also emphasize the effects of the intestinal microbiome on the induction and function of Tregs and the need to study the crosstalk between the enteric nervous system and Tregs in neurodegenerative diseases. Finally, we point out the need for a systems biology approach in the analysis of the enormous complexity regulating the function of Tregs and their potential role in neurodegenerative diseases.

Modulating inflammatory monocytes with a unique microRNA gene signature ameliorates murine ALS

Amyotrophic lateral sclerosis (ALS) is a progressive disease associated with neuronal cell death that is thought to involve aberrant immune responses. Here we investigated the role of innate immunity in a mouse model of ALS. We found that inflammatory monocytes were activated and that their progressive recruitment to the spinal cord, but not brain, correlated with neuronal loss. We also found a decrease in resident microglia in the spinal cord with disease progression. Prior to disease onset, splenic Ly6Chi monocytes expressed a polarized macrophage phenotype (M1 signature), which included increased levels of chemokine receptor CCR2. As disease onset neared, microglia expressed increased CCL2 and other chemotaxis-associated molecules, which led to the recruitment of monocytes to the CNS by spinal cord-derived microglia. Treatment with anti-Ly6C mAb modulated the Ly6Chi monocyte cytokine profile, reduced monocyte recruitment to the spinal cord, diminished neuronal loss, and extended survival. In humans with ALS, the analogous monocytes (CD14+CD16-) exhibited an ALS-specific microRNA inflammatory signature similar to that observed in the ALS mouse model, linking the animal model and the human disease. Thus, the profile of monocytes in ALS patients may serve as a biomarker for disease stage or progression. Our results suggest that recruitment of inflammatory monocytes plays an important role in disease progression and that modulation of these cells is a potential therapeutic approach.

Glycans in sera of amyotrophic lateral sclerosis patients and their role in killing neuronal cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease caused by degeneration of upper and lower motor neurons. To date, glycosylation patterns of glycoproteins in fluids of ALS patients have not been described. Moreover, the aberrant glycosylation related to the pathogenesis of other neurodegenerative diseases encouraged us to explore the glycome of ALS patient sera. We found high levels of sialylated glycans and low levels of core fucosylated glycans in serum-derived N-glycans of patients with ALS, compared to healthy volunteer sera. Based on these results, we analyzed the IgG Fc N²⁹⁷-glycans, as IgG are major serum glycoproteins affected by sialylation or core fucosylation and are found in the motor cortex of ALS patients. The analyses revealed a distinct glycan, A2BG2, in IgG derived from ALS patient sera (ALS-IgG). This glycan increases the affinity of IgG to CD16 on effector cells, consequently enhancing Antibody-Dependent Cellular Cytotoxicity (ADCC). Therefore, we explore whether the Fc-N²⁹⁷-glycans of IgG may be involved in ALS disease. Immunostaining of brain and spinal cord tissues revealed over-expression of CD16 and co-localization of intact ALS-IgG with CD16 and in brain with activated microglia of G93A-SOD1 mice. Intact ALS-IgG enhanced effector cell activation and ADCC reaction in comparison to sugar-depleted or control IgG. ALS-IgG were localized in the synapse between brain microglia and neurons of G93A-SOD1 mice, manifesting a promising in vivo ADCC reaction. Therefore, glycans of ALS-IgG may serve as a biomarker for the disease and may be involved in neuronal damage.

The Neuroinflammatory Response in ALS: The Roles of Microglia and T Cells

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by upper and lower motoneuron death. Mutations in the gene for superoxide dismutase 1 (SOD1) cause a familial form of ALS and have been used to develop transgenic mice which overexpress human mutant SOD1 (mSOD) and these mice exhibit a motoneuron disease which is pathologically and phenotypically similar to ALS. Neuroinflammation is a pathological hallmark of many neurodegenerative diseases including ALS and is typified by the activation and proliferation of microglia and the infiltration of T cells into the brain and spinal cord. Although the neuroinflammatory response has been considered a consequence of neuronal dysfunction and death, evidence indicates that manipulation of this response can alter disease progression. Previously viewed as deleterious to neuronal survival, recent reports suggest a trophic role for activated microglia in the mSOD mouse during the early stages of disease that is dependent on instructive signals from infiltrating T cells. However, at advanced stages of disease, activated microglia acquire increased neurotoxic potential, warranting further investigation into factors capable of skewing microglial activation towards a neurotrophic phenotype as a means of therapeutic intervention in ALS.

Early functional deficit and microglial disturbances in a mouse model of amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by selective motoneurons degeneration. There is today no clear-cut pathogenesis sequence nor any treatment. However growing evidences are in favor of the involvement, besides neurons, of several partners such as glia and muscles. To better characterize the time course of pathological events in an animal model that recapitulates human ALS symptoms, we investigated functional and cellular characteristics of hSOD1(G93A) mice.

METHODS AND FINDINGS

We have evaluated locomotor function of hSOD1(G93A) mice through dynamic walking patterns and spontaneous motor activity analysis. We detected early functional deficits that redefine symptoms onset at 60 days of age, i.e. 20 days earlier than previously described. Moreover, sequential combination of these approaches allows monitoring of motor activity up to disease end stage. To tentatively correlate early functional deficit with cellular alterations we have used flow cytometry and immunohistochemistry approaches to characterize neuromuscular junctions, astrocytes and microglia. We show that (1) decrease in neuromuscular junction's number correlates with motor impairment, (2) astrocytes number is not altered at pre- and early-symptomatic ages but intraspinal repartition is modified at symptoms onset, and (3) microglia modifications precede disease onset. At pre-symptomatic age, we show a decrease in microglia number whereas at onset of the disease two distinct microglia sub-populations emerge.

CONCLUSIONS

In conclusion, precise motor analysis updates the onset of the disease in hSOD1(G93A) mice and allows locomotor monitoring until the end stage of the disease. Early functional deficits coincide with alterations of neuromuscular junctions. Importantly, we identify different sets of changes in microglia before disease onset as well as at early-symptomatic stage. This finding not only brings a new sequence of cellular events in the natural history of the disease, but it may also provide clues in the search for biomarkers of the disease, and potential therapeutic targets.

Ablation of proliferating cells in the CNS exacerbates motor neuron disease caused by mutant superoxide dismutase

Proliferation of glia and immune cells is a common pathological feature of many neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). Here, to investigate the role of proliferating cells in motor neuron disease, SOD1(G93A) transgenic mice were treated intracerebroventicularly (i.c.v.) with the anti-mitotic drug cytosine arabinoside (Ara-C). I.c.v. delivery of Ara-C accelerated disease progression in SOD1(G93A) mouse model of ALS. Ara-C treatment caused substantial decreases in the number of microglia, NG2+ progenitors, Olig2+ cells and CD3+ T cells in the lumbar spinal cord of symptomatic SOD1(G93A) transgenic mice. Exacerbation of disease was also associated with significant alterations in the expression inflammatory molecules IL-1β, IL-6, TGF-β and the growth factor IGF-1.