MCP-1 chemokine receptor CCR2 is decreased on circulating monocytes in sporadic amyotrophic lateral sclerosis (sALS)

Biomarkers and molecular mechanisms of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease in adults involving non-demyelinating motor disorders. About 90% of ALS cases are sporadic, while 10-12% of cases are due to some genetic reasons. Mutations in superoxide dismutase 1 (SOD1), TAR, c9orf72 (chromosome 9 open reading frame 72) and VAPB genes are commonly found in ALS patients. Therefore, the mechanism of ALS development involves oxidative stress, endoplasmic reticulum stress, glutamate excitotoxicity and aggregation of proteins, neuro-inflammation and defective RNA function. Cholesterol and LDL/HDL levels are also associated with ALS development. As a result, sterols could be a suitable biomarker for this ailment. The main mechanisms of ALS development are reticulum stress, neuroinflammation and RNA metabolism. The multi-nature development of ALS makes it more challenging to pinpoint a treatment.

ALS monocyte-derived microglia-like cells reveal cytoplasmic TDP-43 accumulation, DNA damage, and cell-specific impairment of phagocytosis associated with disease progression

Background

Amyotrophic lateral sclerosis (ALS) is a multifactorial neurodegenerative disease characterised by the loss of upper and lower motor neurons. Increasing evidence indicates that neuroinflammation mediated by microglia contributes to ALS pathogenesis. This microglial activation is evident in post-mortem brain tissues and neuroimaging data from patients with ALS. However, the role of microglia in the pathogenesis and progression of amyotrophic lateral sclerosis remains unclear, partly due to the lack of a model system that is able to faithfully recapitulate the clinical pathology of ALS. To address this shortcoming, we describe an approach that generates monocyte-derived microglia-like cells that are capable of expressing molecular markers, and functional characteristics similar to in vivo human brain microglia.

Methods

In this study, we have established monocyte-derived microglia-like cells from 30 sporadic patients with ALS, including 15 patients with slow disease progression, 6 with intermediate progression, and 9 with rapid progression, together with 20 non-affected healthy controls.

Results

We demonstrate that patient monocyte-derived microglia-like cells recapitulate canonical pathological features of ALS including non-phosphorylated and phosphorylated-TDP-43-positive inclusions. Moreover, ALS microglia-like cells showed significantly impaired phagocytosis, altered cytokine profiles, and abnormal morphologies consistent with a neuroinflammatory phenotype. Interestingly, all ALS microglia-like cells showed abnormal phagocytosis consistent with the progression of the disease. In-depth analysis of ALS microglia-like cells from the rapid disease progression cohort revealed significantly altered cell-specific variation in phagocytic function. In addition, DNA damage and NOD-leucine rich repeat and pyrin containing protein 3 (NLRP3) inflammasome activity were also elevated in ALS patient monocyte-derived microglia-like cells, indicating a potential new pathway involved in driving disease progression.

Conclusions

Taken together, our work demonstrates that the monocyte-derived microglia-like cell model recapitulates disease-specific hallmarks and characteristics that substantiate patient heterogeneity associated with disease subgroups. Thus, monocyte-derived microglia-like cells are highly applicable to monitor disease progression and can be applied as a functional readout in clinical trials for anti-neuroinflammatory agents, providing a basis for personalised treatment for patients with ALS.

Neuroinflammation in Amyotrophic Lateral Sclerosis and Frontotemporal Dementia and the Interest of Induced Pluripotent Stem Cells to Study Immune Cells Interactions With Neurons

Inflammation is a shared hallmark between amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). For long, studies were conducted on tissues of post-mortem patients and neuroinflammation was thought to be only bystander result of the disease with the immune system reacting to dying neurons. In the last two decades, thanks to improving technologies, the identification of causal genes and the development of new tools and models, the involvement of inflammation has emerged as a potential driver of the diseases and evolved as a new area of intense research. In this review, we present the current knowledge about neuroinflammation in ALS, ALS-FTD, and FTD patients and animal models and we discuss reasons of failures linked to therapeutic trials with immunomodulator drugs. Then we present the induced pluripotent stem cell (iPSC) technology and its interest as a new tool to have a better immunopathological comprehension of both diseases in a human context. The iPSC technology giving the unique opportunity to study cells across differentiation and maturation times, brings the hope to shed light on the different mechanisms linking neurodegeneration and activation of the immune system. Protocols available to differentiate iPSC into different immune cell types are presented. Finally, we discuss the interest in studying monocultures of iPS-derived immune cells, co-cultures with neurons and 3D cultures with different cell types, as more integrated cellular approaches. The hope is that the future work with human iPS-derived cells helps not only to identify disease-specific defects in the different cell types but also to decipher the synergistic effects between neurons and immune cells. These new cellular tools could help to find new therapeutic approaches for all patients with ALS, ALS-FTD, and FTD.

Clearance of peripheral nerve misfolded mutant protein by infiltrated macrophages correlates with motor neuron disease progression

Macrophages expressing C-C chemokine receptor type 2 (CCR2) infiltrate the central and peripheral neural tissues of amyotrophic lateral sclerosis (ALS) patients. To identify the functional role of CCR2⁺ macrophages in the pathomechanisms of ALS, we used an ALS animal model, mutant Cu/Zn superoxide dismutase 1^G93A (mSOD1)-transgenic (Tg) mice. To clarify the CCR2 function in the model, we generated SOD1^G93A/CCR2^{Red fluorescence protein (RFP)/Wild type (WT)}/CX3CR1^{Green fluorescence protein (GFP)/WT}-Tg mice, which heterozygously express CCR2-RFP and CX3CR1-GFP, and SOD1^G93A/CCR2^RFP/RFP-Tg mice, which lack CCR2 protein expression and present with a CCR2-deficient phenotype. In mSOD1-Tg mice, mSOD1 accumulated in the sciatic nerve earlier than in the spinal cord. Furthermore, spinal cords of SOD1^G93A/CCR2^RFP/WT/CX3CR1^GFP/WT mice showed peripheral macrophage infiltration that emerged at the end-stage, whereas in peripheral nerves, macrophage infiltration started from the pre-symptomatic stage. Before disease onset, CCR2⁺ macrophages harboring mSOD1 infiltrated sciatic nerves earlier than the lumbar cord. CCR2-deficient mSOD1-Tg mice showed an earlier onset and axonal derangement in the sciatic nerve than CCR2-positive mSOD1-Tg mice. CCR2-deficient mSOD1-Tg mice showed an increase in deposited mSOD1 in the sciatic nerve compared with CCR2-positive mice. These findings suggest that CCR2⁺ and CX3CR1⁺ macrophages exert neuroprotective functions in mSOD1 ALS via mSOD1 clearance from the peripheral nerves.

The Peripheral Immune System and Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a severe neurodegenerative disease that is defined by loss of upper and lower motor neurons, associated with accumulation of protein aggregates in cells. There is also pathology in extra-motor areas of the brain, Possible causes of cell death include failure to deal with the aggregated proteins, glutamate toxicity and mitochondrial failure. ALS also involves abnormalities of metabolism and the immune system, including neuroinflammation in the brain and spinal cord. Strikingly, there are also abnormalities of the peripheral immune system, with alterations of T lymphocytes, monocytes, complement and cytokines in the peripheral blood of patients with ALS. The precise contribution of the peripheral immune system in ALS pathogenesis is an active area of research. Although some trials of immunomodulatory agents have been negative, there is strong preclinical evidence of benefit from immune modulation and further trials are currently underway. Here, we review the emerging evidence implicating peripheral immune alterations contributing to ALS, and their potential as future therapeutic targets for clinical intervention.

MCP1-CCR2 and neuroinflammation in the ALS motor cortex with TDP-43 pathology

BACKGROUND

The involvement of non-neuronal cells and the cells of innate immunity has been attributed to the initiation and progression of ALS. TDP-43 pathology is observed in a broad spectrum of ALS cases and is one of the most commonly shared pathologies. The potential involvement of the neuroimmune axis in the motor cortex of ALS patients with TDP-43 pathology needs to be revealed. This information is vital for building effective treatment strategies.

METHODS

We investigated the presence of astrogliosis and microgliosis in the motor cortex of ALS patients with TDP-43 pathology. prpTDP-43^A315T-UeGFP mice, corticospinal motor neuron (CSMN) reporter line with TDP-43 pathology, are utilized to reveal the timing and extent of neuroimmune interactions and the involvement of non-neuronal cells to neurodegeneration. Electron microscopy and immunolabeling techniques are used to mark and monitor cells of interest.

RESULTS

We detected both activated astrocytes and microglia, especially rod-like microglia, in the motor cortex of patients and TDP-43 mouse model. Besides, CCR2+ TMEM119- infiltrating monocytes were detected as they penetrate the brain parenchyma. Interestingly, Betz cells, which normally do not express MCP1, were marked with high levels of MCP1 expression when diseased.

CONCLUSIONS

There is an early contribution of a neuroinflammatory response for upper motor neuron (UMN) degeneration with respect to TDP-43 pathology, and MCP1-CCR2 signaling is important for the recognition of diseased upper motor neurons by infiltrating monocytes. The findings are conserved among species and are observed in both ALS and ALS-FTLD patients.

Targeting Macrophage for the Treatment of Amyotrophic Lateral Sclerosis

Background & Objective:

Amyotrophic lateral sclerosis is a progressive neurodegenerative disease that specifically affects motor neurons in the brain and in the spinal cord. Patients with amyotrophic lateral sclerosis usually die from respiratory failure within 3 to 5 years from when the symptoms first appear. Currently, there is no cure for amyotrophic lateral sclerosis. Accumulating evidence suggests that dismantling of neuromuscular junction is an early event in the pathogenesis of amyotrophic lateral sclerosis.

Conclusion:

It is starting to realized that macrophage malfunction contributes to the disruption of neuromuscular junction. Modulation of macrophage activation states may stabilize neuromuscular junction and provide protection against motor neuron degeneration in amyotrophic lateral sclerosis.

Inflammation, immunity, and amyotrophic lateral sclerosis: II. immune-modulating therapies

With the emerging popularity of immune-modulatory therapies to treat human diseases there is a need to step back from hypotheses aimed at assessing a condition in a single-system context and instead take into account the disease pathology as a whole. In complex diseases, such as amyotrophic lateral sclerosis (ALS), the use of these therapies to treat patients has been largely unsuccessful and likely premature given our lack of understanding of how the immune system influences disease progression and initiation. In addition, we still have an incomplete understanding of the role of these responses in our model systems and how this may translate clinically to human patients. In this review we discuss preclinical evidence and clinical trial results for a selection of recently conducted studies in ALS. We provide evidence-based reasoning for the failure of these trials and offer suggestions to improve the design of future investigations. Muscle Nerve 59:23-33, 2019.

Dysregulation of chemokine receptor expression and function in leukocytes from ALS patients

Amyotrophic lateral sclerosis (ALS) is rapidly progressive adult-onset motor neuron disease characterized by the neurodegeneration of both upper and lower motor neurons in the cortex and the spinal cord; the majority of patients succumb to respiratory failure. Although the etiology is not yet fully understood, there is compelling evidence that ALS is a multi-systemic disorder, with peripheral inflammation critically contributing to the disease process. However, the full extent and nature of this immunological dysregulation remains to be established, particularly within circulating blood cells. Therefore, the aim of the present study was to identify dysregulated inflammatory molecules in peripheral blood cells of ALS patients and analyze for functional consequences of the observed findings. To this end, we employed flow cytometry-based screening to quantify the surface expression of major chemokine receptors and integrins. A significantly increased expression of CXCR3, CXCR4, CCL2, and CCL5 was observed on T cells in ALS patients compared to healthy controls. Intriguingly, the expression was even more pronounced in patients with a slow progressive phenotype. To further investigate the functional consequences of this altered surface expression, we used a modified Boyden chamber assay to measure chemotaxis in ALS patient-derived lymphocytes. Interestingly, chemoattraction with the CXCR3-Ligand IP10 led to upregulated migratory behavior of ALS lymphocytes compared to healthy controls. Taken together, our data provides evidence for a functional dysregulation of IP10-directed chemotaxis in peripheral blood cells in ALS patients. However, whether the chemokine itself or its receptor CXCR3, or both, could serve as potential therapeutic targets in ALS requires further investigations.

Correlation of Peripheral Immunity With Rapid Amyotrophic Lateral Sclerosis Progression

Importance

Amyotrophic lateral sclerosis (ALS) has an immune component, but previous human studies have not examined immune changes over time.

Objectives

To assess peripheral inflammatory markers in participants with ALS and healthy control individuals and to track immune changes in ALS and determine whether these changes correlate with disease progression.

Design, Setting, and Participants

In this longitudinal cohort study, leukocytes were isolated from peripheral blood samples from 35 controls and 119 participants with ALS at the ALS Clinic of the University of Michigan, Ann Arbor, from June 18, 2014, through May 26, 2016. Follow-up visits occurred every 6 to 12 months. Fifty-one participants with ALS provided samples at multiple points. Immune cell populations were measured and compared between control and ALS groups. Surface marker expression of CD11b+ myeloid cells was also assessed. Changes over time were correlated with disease progression using multivariate regression.

Main Outcomes and Measures

The number of immune cells per milliliter of blood and the fold expression of cell surface markers. Multivariate regression models were used to correlate changes in immune metrics with changes on the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R).

Results

Thirty-five controls (17 women [48.6%] and 18 men [51.4%]; mean [SD] age, 63.5 [9.9] years) and 119 participants with ALS (50 women [42.0%] and 69 men [68.0%]; mean [SD] age, 61.4 [11.5] years) were enrolled. Compared with controls, participants with ALS had increased mean (SEM) counts ( × 106/mL) of total leukocytes (4.57 [0.29; 95% CI, 3.94-5.11] vs 5.53 [0.16; 95% CI, 5.21-5.84]), neutrophils (2.87 [0.23; 95% CI, 2.40-3.35] vs 3.80 [0.12; 95% CI, 3.56-4.04]), CD16+ monocytes (0.03 [0.003; 95% CI, 0.02-0.04] vs 0.04 [0.002; 95% CI, 0.03-0.04]), CD16- monocytes (0.25 [0.02; 95% CI, 0.21-0.30] vs 0.29 [0.01; 95% CI, 0.27-0.31]), and natural killer cells (0.13 [0.02; 95% CI, 0.10-0.17] vs 0.18 [0.01; 95% CI, 0.16-0.21]). We also observed an acute, transient increase in a population of CD11b+ myeloid cells expressing HLA-DR, CD11c, and CX3CR1. Finally, early changes in immune cell numbers had a significant correlation with disease progression measured by change in ALSFRS-R score, particularly neutrophils (-4.37 [95% CI, -6.60 to -2.14] per 11.47 × 104/mL [SD, 58.04 × 104/mL] per year) and CD4 T cells (-30.47 [95% CI, -46.02 to -14.94] per -3.72 × 104/mL [SD, 26.21 × 104/mL] per year).

Conclusions and Relevance

Changes in the immune system occur during ALS and may contribute to the pathologic features of ALS.

Differential contribution of microglia and monocytes in neurodegenerative diseases

Neuroinflammation is a hallmark of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). Microglia, the innate immune cells of the CNS, are the first to react to pathological insults. However, multiple studies have also demonstrated an involvement of peripheral monocytes in several neurodegenerative diseases. Due to the different origins of these two cell types, it is important to distinguish their role and function in the development and progression of these diseases. In this review, we will summarize and discuss the current knowledge of the differential contributions of microglia and monocytes in the common neurodegenerative diseases AD, PD, and ALS, as well as multiple sclerosis, which is now regarded as a combination of inflammatory processes and neurodegeneration. Until recently, it has been challenging to differentiate microglia from monocytes, as there were no specific markers. Therefore, the recent identification of specific molecular signatures of both cell types will help to advance our understanding of their differential contribution in neurodegenerative diseases.

Inflammatory Gene Expression in Whole Peripheral Blood at Early Stages of Sporadic Amyotrophic Lateral Sclerosis

OBJECTIVE

Characterization of altered expression of selected transcripts linked to inflammation in the peripheral blood of sporadic amyotrophic lateral sclerosis (sALS) patients at early stage of disease to increase knowledge about peripheral inflammatory response in sALS.

METHODS

RNA expression levels of 45 genes were assessed by RT-qPCR in 22 sALS cases in parallel with 13 age-matched controls. Clinical and serum parameters were assessed at the same time.

RESULTS

Upregulation of genes coding for factors involved in leukocyte extravasation (ITGB2, INPP5D, SELL, and ICAM1) and extracellular matrix remodeling (MMP9 and TIMP2), as well as downregulation of certain chemokines (CCL5 and CXC5R), anti-inflammatory cytokines (IL10, TGFB2, and IL10RA), pro-inflammatory cytokines (IL-6), and T-cell regulators (CD2 and TRBC1) was found in sALS cases independently of gender, clinical symptoms at onset (spinal, respiratory, or bulbar), progression, peripheral leukocyte number, and integrity of RNA. MMP9 levels positively correlated with age, whereas CCR5, CCL5, and TRBC1 negatively correlated with age in sALS but not in controls. Relatively higher TNFA expression levels correlate with higher creatinine kinase protein levels in plasma.

CONCLUSION

Present findings show early inflammatory responses characterized by upregulation of factors enabling extravasation of leukocytes and extracellular matrix remodeling in blood in sALS cases, in addition to increased TNFA levels paralleling skeletal muscle damage.

Immunoregulatory effect of mast cells influenced by microbes in neurodegenerative diseases

When related to central nervous system (CNS) health and disease, brain mast cells (MCs) can be a source of either beneficial or deleterious signals acting on neural cells. We review the current state of knowledge about molecular interactions between MCs and glia in neurodegenerative diseases such as Multiple Sclerosis, Alzheimer's disease, Amyotrophic Lateral Sclerosis, Parkinson's disease, Epilepsy. We also discuss the influence on MC actions evoked by the host microbiota, which has a profound effect on the host immune system, inducing important consequences in neurodegenerative disorders. Gut dysbiosis, reduced intestinal motility and increased intestinal permeability, that allow bacterial products to circulate and pass through the blood-brain barrier, are associated with neurodegenerative disease. There are differences between the microbiota of neurologic patients and healthy controls. Distinguishing between cause and effect is a challenging task, and the molecular mechanisms whereby remote gut microbiota can alter the brain have not been fully elucidated. Nevertheless, modulation of the microbiota and MC activation have been shown to promote neuroprotection. We review this new information contributing to a greater understanding of MC-microbiota-neural cells interactions modulating the brain, behavior and neurodegenerative processes.

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.

Increased peripheral blood inflammatory cytokine levels in amyotrophic lateral sclerosis: a meta-analysis study

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with poorly understood etiology. Increasing evidence suggest that inflammation may play a critical role in the pathogenesis of ALS. Several studies have demonstrated altered levels of blood cytokines in ALS, but results were inconsistent. Therefore, we did a systematic review of studies comparing blood inflammatory cytokines between ALS patients and control subjects, and quantitatively combined the clinical data with a meta-analysis. The systematic review of Pubmed and Web of Science identified 25 studies encompassing 812 ALS patients and 639 control subjects. Random-effects meta-analysis demonstrated that blood tumor necrosis factor-α (TNF; Hedges' g = 0.655; p = 0.001), TNF receptor 1 (Hedges' g = 0.741; p < 0.001), interleukin 6 (IL-6; Hedges' g = 0.25; p = 0.005), IL-1β (Hedges' g = 0.296; p = 0.038), IL-8 (Hedges' g = 0.449; p < 0.001) and vascular endothelial growth factor (Hedges' g = 0.891; p = 0.003) levels were significantly elevated in patients with ALS compared with control subjects. These results substantially enhance our knowledge of the inflammatory response in ALS, and peripheral blood inflammatory cytokines may be used as diagnostic biomarkers for ALS in the future.

Inflammatory role of dendritic cells in Amyotrophic Lateral Sclerosis revealed by an analysis of patients' peripheral blood

Chronic inflammation is one of the causes of neurodegeneration in Amyotrophic lateral sclerosis (ALS). Here we examined whether circulating dendritic cells (DCs) can contribute to disease progression. We found ALS patients show a significant reduction in the number of circulating DCs. Also, patients' DCs present an increased expression of CD62L and a tendency to overexpress CCR2 compared with healthy donors. Moreover, DCs derived from a subpopulation of ALS patients produced higher levels of IL-8 and CCL-2 upon lipopolysaccharide (LPS)-stimulation. Finally, we found a significant inverse correlation between the time from onset of the pathology to its diagnosis and the levels of IL-6 secretion induced by LPS. Our data support the hypothesis, in a subpopulation of patients, DCs recruited at the diseased tissue produce high levels of CCL-2 and IL-8 and contribute to the inflammatory process promoting the recruitment of other inflammatory cells. An increased efficiency of IL-6 production may accelerate only the initial phases of disease progression. Blood DC analysis can be used to identify ALS patients with an altered course of inflammatory cell recruitment at the diseased central nervous system (CNS). The high levels of CD62L expression suggests this molecule could be a target for treatment of CNS inflammation.

Evidence for an early innate immune response in the motor cortex of ALS

Background

Recent evidence indicates the importance of innate immunity and neuroinflammation with microgliosis in amyotrophic lateral sclerosis (ALS) pathology. The MCP1 (monocyte chemoattractant protein-1) and CCR2 (CC chemokine receptor 2) signaling system has been strongly associated with the innate immune responses observed in ALS patients, but the motor cortex has not been studied in detail.

Methods

After revealing the presence of MCP1 and CCR2 in the motor cortex of ALS patients, to elucidate, visualize, and define the timing, location and the extent of immune response in relation to upper motor neuron vulnerability and progressive degeneration in ALS, we developed MCP1-CCR2-hSOD1^G93A mice, an ALS reporter line, in which cells expressing MCP1 and CCR2 are genetically labeled by monomeric red fluorescent protein-1 and enhanced green fluorescent protein, respectively.

Results

In the motor cortex of MCP1-CCR2-hSOD1^G93A mice, unlike in the spinal cord, there was an early increase in the numbers of MCP1+ cells, which displayed microglial morphology and selectively expressed microglia markers. Even though fewer CCR2+ cells were present throughout the motor cortex, they were mainly infiltrating monocytes. Interestingly, MCP1+ cells were found in close proximity to the apical dendrites and cell bodies of corticospinal motor neurons (CSMN), further implicating the importance of their cellular interaction to neuronal pathology. Similar findings were observed in the motor cortex of ALS patients, where MCP1+ microglia were especially in close proximity to the degenerating apical dendrites of Betz cells.

Conclusions

Our findings reveal that the intricate cellular interplay between immune cells and upper motor neurons observed in the motor cortex of ALS mice is indeed recapitulated in ALS patients. We generated and characterized a novel model system, to study the cellular and molecular basis of this close cellular interaction and how that relates to motor neuron vulnerability and progressive degeneration in ALS.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0896-4) contains supplementary material, which is available to authorized users.

Systemic and ocular fluid compounds as potential biomarkers in age-related macular degeneration

Biomarkers can help unravel mechanisms of disease and identify new targets for therapy. They can also be useful in clinical practice for monitoring disease progression, evaluation of treatment efficacy, and risk assessment in multifactorial diseases, such as age-related macular degeneration (AMD). AMD is a highly prevalent progressive retinal disorder for which multiple genetic and environmental risk factors have been described, but the exact etiology is not yet fully understood. Many compounds have been evaluated for their association with AMD. We performed an extensive literature review of all compounds measured in serum, plasma, vitreous, aqueous humor, and urine of AMD patients. Over 3600 articles were screened, resulting in more than 100 different compounds analyzed in AMD studies, involved in neovascularization, immunity, lipid metabolism, extracellular matrix, oxidative stress, diet, hormones, and comorbidities (such as kidney disease). For each compound, we provide a short description of its function and discuss the results of the studies in relation to its usefulness as AMD biomarker. In addition, biomarkers identified by hypothesis-free techniques, including metabolomics, proteomics, and epigenomics, are covered. In summary, compounds belonging to the oxidative stress pathway, the complement system, and lipid metabolism are the most promising biomarker candidates for AMD. We hope that this comprehensive survey of the literature on systemic and ocular fluid compounds as potential biomarkers in AMD will provide a stepping stone for future research and possible implementation in clinical practice.

Down-regulation of purinergic P2X7 receptor expression and intracellular calcium dysregulation in peripheral blood mononuclear cells of patients with amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder associated with intracellular Ca(2+) dysregulation. The P2X receptor family is comprised of ligand-gated ion channels that respond to extracellular adenosine triphosphate (ATP) and increases permeability of calcium into the cell. The underlying mechanisms of purinergic signalling on peripheral blood mononuclear cells (PBMCs) in ALS remain unclear. Herein, we studied the expression of P2X4/P2X7 receptors and calcium homeostasis in blood cells of ALS patients.

METHODS

We used PBMCs from 42 ALS patients and 19 controls. Purinergic receptors P2X4 (P2X4R) and P2X7 (P2X7R) were examined using western blot analysis. The effect of exogenous ATP on intracellular Ca(2+) homeostasis in monocytes was measured using fluorimetry by Fura-2 on a single-cell level.

RESULTS

Western blot analysis revealed stable P2X4R expression in patients and controls. P2X7R expression was significantly reduced (p=0.012) in ALS patients. Repetitive long-term ATP stimulation caused a sustained decrease in Ca(2+) levels in the ALS group as measured by the area under the curve, peak amplitude and peak height.

CONCLUSION

These results confirm our hypothesis that Ca(2+) abnormalities in ALS are measurable in immune cells. These findings suggest that the reduction of P2X7 receptor expression on PBMCs leads to intracellular calcium dysregulation. Our study improves the understanding of ALS pathophysiology and proposes PBMCs as a non-invasive source to study ALS.

Further development of biomarkers in amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is an idiopathic neurodegenerative disease usually fatal in less than three years. Even if standard guidelines are available to diagnose ALS, the mean diagnosis delay is more than one year. In this context, biomarker discovery is a priority. Research has to focus on new diagnostic tools, based on combined explorations.

AREAS COVERED

In this review, we specifically focus on biology and imaging markers. We detail the innovative field of 'omics' approach and imaging and explain their limits to be useful in routine practice. We describe the most relevant biomarkers and suggest some perspectives for biomarker research. Expert commentary: The successive failures of clinical trials in ALS underline the need for new strategy based on innovative tools to stratify patients and to evaluate their responses to treatment. Biomarker data may be useful to improve the designs of clinical trials. Biomarkers are also needed to better investigate disease pathophysiology, to identify new therapeutic targets, and to improve the performance of clinical assessments for diagnosis and prognosis in the clinical setting. A consensus on the best management of neuroimaging and 'omics' methods is necessary and a systematic independent validation of findings may add robustness to future studies.

Advances in the Development of Disease-Modifying Treatments for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive adult-onset, neurodegenerative disease characterized by the degeneration of upper and lower motor neurons. Over recent years, numerous genes ha ve been identified that promote disease pathology, including SOD1, TARDBP, and the expanded hexanucleotide repeat (GGGGCC) within C9ORF72. However, despite these major advances in identifying genes contributing to ALS pathogenesis, there remains only one currently approved therapeutic: the glutamate antagonist, riluzole. Seminal breakthroughs in the pathomechanisms and genetic factors associated with ALS have heavily relied on the use of rodent models that recapitulate the ALS phenotype; however, while many therapeutics have proved to be significant in animal models by prolonging life and rescuing motor deficits, they have failed in human clinical trials. This may be due to fundamental differences between rodent models and human disease, the fact that animal models are based on overexpression of mutated genes, and confounding issues such as difficulties mimicking the dosing schedules and regimens implemented in mouse models to humans. Here, we review the major pathways associated with the pathology of ALS, the rodent models engineered to test efficacy of candidate drugs, the advancements being made in stem cell therapy for ALS, and what strategies may be important to circumvent the lack of successful translational studies in the clinic.

Complex Inflammation mRNA-Related Response in ALS Is Region Dependent

Inflammatory changes are analyzed in the anterior spinal cord and frontal cortex area 8 in typical spinal-predominant ALS cases. Increased numbers of astrocytes and activated microglia are found in the anterior horn of the spinal cord and pyramidal tracts. Significant increased expression of TLR7, CTSS, and CTSC mRNA and a trend to increased expression of IL10RA, TGFB1, and TGFB2 are found in the anterior lumbar spinal cord in ALS cases compared to control cases, whereas C1QTNF7 and TNFRSF1A mRNA expression levels are significantly decreased. IL6 is significantly upregulated and IL1B shows a nonsignificant increased expression in frontal cortex area 8 in ALS cases. IL-6 immunoreactivity is found in scattered monocyte-derived macrophages/microglia and TNF-α in a few cells of unknown origin in ALS cases. Increased expression and abnormal distribution of IL-1β occurred in motor neurons of the lumbar spinal cord in ALS. Strong IL-10 immunoreactivity colocalizes with TDP-43-positive inclusions in motor neurons in ALS cases. The present observations show a complex participation of cytokines and mediators of the inflammatory response in ALS consistent with increased proinflammatory cytokines and sequestration of anti-inflammatory IL-10 in affected neurons.

Randomized phase 2 trial of NP001-a novel immune regulator: Safety and early efficacy in ALS

Objective:

To assess the safety, tolerability, and preliminary efficacy of NP001, a novel immune regulator of inflammatory monocytes/macrophages, for slowing progression of amyotrophic lateral sclerosis (ALS).

Methods:

This was a phase 2 randomized, double-blind, placebo-controlled trial of NP001 in 136 patients with ALS of <3 years' duration and forced vital capacity ≥70%. Participants received NP001 2 mg/kg, NP001 1 mg/kg, or placebo for 6 months. Safety, tolerability, and inflammatory biomarkers were assessed throughout the study. Preliminary efficacy was evaluated using the ALS Functional Rating Scale-Revised (ALSFRS-R) slope and change from baseline, with and without matched historical placebo controls, after 6 months of treatment. A post hoc analysis of the percentage of patients (“responders”) whose ALSFRS-R did not change from baseline was also conducted.

Results:

NP001 was generally safe and well-tolerated, except for infusion site pain and dizziness. No significant slowing of decline in the primary or secondary measures was observed. However, slowing of progression was observed in the high-dose group in patients with greater inflammation (wide range C-reactive protein). Moreover, NP001 may have dose dependently halted symptom progression in a subset of patients. More than 2 times as many patients on high-dose NP001 (25%) did not progress during 6 months of treatment compared with those on placebo (11%). Most “responders” had an elevated biomarker of inflammation, interleukin-18, and were positive for lipopolysaccharide at baseline, which decreased after treatment with NP001.

Conclusion:

The arresting of progression of ALS symptoms by NP001 in a subset of patients with marked neuroinflammation, as observed here, will represent a novel therapeutic approach for patients with ALS, if confirmed.

Classification of evidence:

This study provides Class I evidence that for patients with ALS, NP001 is safe and did not significantly slow progression of the disease (difference in slope of the ALSFRS-R/month 0.12 favoring NP001, p = 0.55). The study lacks the precision to exclude an important effect of NP001.

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.

Blood biomarkers for amyotrophic lateral sclerosis: myth or reality?

Amyotrophic lateral sclerosis (ALS) is a fatal condition primarily characterized by the selective loss of upper and lower motor neurons. At present, the diagnosis and monitoring of ALS is based on clinical examination, electrophysiological findings, medical history, and exclusion of confounding disorders. There is therefore an undeniable need for molecular biomarkers that could give reliable information on the onset and progression of ALS in clinical practice and therapeutic trials. From a practical point of view, blood offers a series of advantages, including easy handling and multiple testing at a low cost, that make it an ideal source of biomarkers. In this review, we revisited the findings of many studies that investigated the presence of systemic changes at the molecular and cellular level in patients with ALS. The results of these studies reflect the diversity in the pathological mechanisms contributing to disease (e.g., excitotoxicity, oxidative stress, neuroinflammation, metabolic dysfunction, and neurodegeneration, among others) and provide relatively successful evidence of the usefulness of a wide-ranging panel of molecules as potential biomarkers. More studies, hopefully internationally coordinated, would be needed, however, to translate the application of these biomarkers into benefit for patients.

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.

Clinical perspective on oxidative stress in sporadic amyotrophic lateral sclerosis

Sporadic amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological diseases; most patients die within 3 to 4 years after symptom onset. Oxidative stress is a disturbance in the pro-oxidative/antioxidative balance favoring the pro-oxidative state. Autopsy and laboratory studies in ALS indicate that oxidative stress plays a major role in motor neuron degeneration and astrocyte dysfunction. Oxidative stress biomarkers in cerebrospinal fluid, plasma, and urine are elevated, suggesting that abnormal oxidative stress is generated outside of the central nervous system. Our review indicates that agricultural chemicals, heavy metals, military service, professional sports, excessive physical exertion, chronic head trauma, and certain foods might be modestly associated with ALS risk, with a stronger association between risk and smoking. At the cellular level, these factors are all involved in generating oxidative stress. Experimental studies indicate that a combination of insults that induce modest oxidative stress can exert additive deleterious effects on motor neurons, suggesting that multiple exposures in real-world environments are important. As the disease progresses, nutritional deficiency, cachexia, psychological stress, and impending respiratory failure may further increase oxidative stress. Moreover, accumulating evidence suggests that ALS is possibly a systemic disease. Laboratory, pathologic, and epidemiologic evidence clearly supports the hypothesis that oxidative stress is central in the pathogenic process, particularly in genetically susceptive individuals. If we are to improve ALS treatment, well-designed biochemical and genetic epidemiological studies, combined with a multidisciplinary research approach, are needed and will provide knowledge crucial to our understanding of ALS etiology, pathophysiology, and prognosis.

Early gene expression changes in spinal cord from SOD1(G93A) Amyotrophic Lateral Sclerosis animal model

Amyotrophic Lateral Sclerosis (ALS) is an adult-onset and fast progression neurodegenerative disease that leads to the loss of motor neurons. Mechanisms of selective motor neuron loss in ALS are unknown. The early events occurring in the spinal cord that may contribute to motor neuron death are not described, neither astrocytes participation in the pre-symptomatic phases of the disease. In order to identify ALS early events, we performed a microarray analysis employing a whole mouse genome platform to evaluate the gene expression pattern of lumbar spinal cords of transgenic SOD1^G93A mice and their littermate controls at pre-symptomatic ages of 40 and 80 days. Differentially expressed genes were identified by means of the Bioconductor packages Agi4×44Preprocess and limma. FunNet web based tool was used for analysis of over-represented pathways. Furthermore, immunolabeled astrocytes from 40 and 80 days old mice were submitted to laser microdissection and RNA was extracted for evaluation of a selected gene by qPCR. Statistical analysis has pointed to 492 differentially expressed genes (155 up and 337 down regulated) in 40 days and 1105 (433 up and 672 down) in 80 days old ALS mice. KEGG analysis demonstrated the over-represented pathways tight junction, antigen processing and presentation, oxidative phosphorylation, endocytosis, chemokine signaling pathway, ubiquitin mediated proteolysis and glutamatergic synapse at both pre-symptomatic ages. Ube2i gene expression was evaluated in astrocytes from both transgenic ages, being up regulated in 40 and 80 days astrocytes enriched samples. Our data points to important early molecular events occurring in pre-symptomatic phases of ALS in mouse model. Early SUMOylation process linked to astrocytes might account to non-autonomous cell toxicity in ALS. Further studies on the signaling pathways presented here may provide new insights to better understand the events triggering motor neuron death in this devastating disorder.

Biological and neuroimaging biomarkers for amyotrophic lateral sclerosis: 2013 and beyond

SUMMARY Amyotrophic lateral sclerosis is an idiopathic, incurable neurodegenerative disease that is fatal for most patients in less than 3 years from the time weakness first appears. Alongside identification of etiologies and stronger neuroprotective agents, the development of biomarkers is a main research priority. Since the original description, diagnosis and progression measurement in amyotrophic lateral sclerosis has been clinical. The time from symptom onset to diagnosis is usually more than a year, and clinical research studies utilize clinical end points that have low sensitivity. Few eligible patients and inefficient trials mean that just one or a few new therapies can be tested each year. Biological markers are needed not only to improve the sensitivity of clinical assessments, but also to better examine disease pathophysiology in vivo.

Immunology primer for neurosurgeons and neurologists part 2: Innate brain immunity

Over the past several decades we have learned a great deal about microglia and innate brain immunity. While microglia are the principle innate immune cells, other cell types also play a role, including invading macrophages, astrocytes, neurons, and endothelial cells. The fastest reacting cell is the microglia and despite its name, resting microglia (also called ramified microglia) are in fact quite active. Motion photomicrographs demonstrate a constant movement of ramified microglial foot processes, which appear to be testing the microenvironment for dangerous alteration in extracellular fluid content. These foot processes, in particular, interact with synapses and play a role in synaptic function. In event of excitatory overactivity, these foot processes can strip selected synapses, thus reducing activation states as a neuroprotective mechanism. They can also clear extracellular glutamate so as to reduce the risk of excitotoxicity. Microglia also appear to have a number of activation phenotypes, such as: (1) phagocytic, (2) neuroprotective and growth promoting, or (3) primarily neurodestructive. These innate immune cells can migrate a great distance under pathological conditions and appear to have anatomic specificity, meaning they can accumulate in specifically selected areas of the brain. There is some evidence that there are several types of microglia. Macrophage infiltration into the embryonic brain is the source of resident microglia and in adulthood macrophages can infiltrate the brain and are for the most part pathologically indistinguishable from resident microglia, but may react differently. Activation itself does not imply a destructive phenotype and can be mostly neuroprotective via phagocytosis of debris, neuron parts and dying cells and by the release of neurotrophins such as nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF). Evidence is accumulating that microglia undergo dynamic fluctuations in phenotype as the neuropathology evolves. For example, in the early stages of neurotrauma and stroke, microglia play a mostly neuroprotective role and only later switch to a neurodestructive mode. A great number of biological systems alter microglia function, including neurohormones, cannabinoids, other neurotransmitters, adenosine triphosphate (ATP), adenosine, and corticosteroids. One can appreciate that with aging many of these systems are altered by the aging process itself or by disease thus changing the sensitivity of the innate immune system.

MCP-1/CCR2 signaling-mediated astrocytosis is accelerated in a transgenic mouse model of SOD1-mutated familial ALS

Background

Emerging evidence suggests that innate immunity and increased oxidative stress contribute to pathomechanisms in amyotrophic lateral sclerosis (ALS). The aim of the present study was to verify the involvement of monocyte chemoattractant protein-1 (MCP-1) and its specific CC chemokine receptor 2 (CCR2) in the disease progression of ALS. We here demonstrate the expression state of MCP-1 and CCR2 in lumbar spinal cords of mice overexpressing a transgene for G93A mutant human superoxide dismutase 1 (SOD1) (ALS mice) as a mouse model of ALS as well as the involvement of MCP-1/CCR2-mediated signaling in behavior of cultured astrocytes derived from those mice.

Results

Quantitative polymerase chain reaction analysis revealed that MCP-1 and CCR2 mRNA levels were significantly higher in ALS mice than those in nontransgenic littermates (control mice) at the presymptomatic stage. Immunoblot analysis disclosed a significantly higher CCR2/β-actin optical density ratio in the postsymptomatic ALS mouse group than those in the age-matched control mouse group. Immunohistochemically, MCP-1 determinants were mainly localized in motor neurons, while CCR2 determinants were exclusively localized in reactive astrocytes. Primary cultures of astrocytes derived from ALS mice showed a significant increase in proliferation activity under recombinant murine MCP-1 stimuli as compared to those from control mice.

Conclusions

Our results provide in vivo and in vitro evidence that MCP-1 stimulates astrocytes via CCR2 to induce astrocytosis in ALS with SOD1 gene mutation. Thus, it is likely that MCP-1/CCR2-mediated sigaling is involved in the disease progression of ALS.

Systemic immune system alterations in early stages of Alzheimer's disease

Immune activation and inflammation play significant roles in the pathogenesis of Alzheimer's disease (AD). To test whether AD patients showed systemic manifestations of inflammation, blood from 41 patients with early stages of AD and 31 aged-match elderly controls were evaluated. Cellular markers for monocyte/macrophage (MO) activation and CD8 T lymphocyte were increased in early AD patients. Expression of monocyte CCR2, the receptor for monocyte chemoattractant protein-1 (MCP-1), was decreased; however, plasma MCP-1 levels were significantly increased and were related to the degree of MO activation in AD. These findings suggest that AD pathogenesis may be influenced by systemic immunologic dysfunction and provides potential immunologic targets for therapeutic intervention.

CD200 fusion protein decreases microglial activation in the hippocampus of aged rats

The glycoprotein, CD200, is primarily expressed on neurons and its cognate receptor CD200R is expressed principally on cells of the myeloid lineage, including microglia. The interaction of CD200 with its receptor plays a significant role in maintaining microglia in a quiescent state and therefore a decrease in CD200 expression in brain is associated with evidence of microglial activation. Conversely, activation of CD200R, for example using a CD200 fusion protein (CD200Fc), should result in a decrease in microglial activation. Here we assessed the effect of delivery of CD200Fc intrahippocampally on microglial activation and on long-term potentiation (LTP) in perforant path-granule cell synapses in young and aged rats. We hypothesized that the age-related changes in microglial activation would be attenuated by CD200Fc resulting in an improved ability of aged rats to sustain LTP. The data indicate that expression of markers of microglial activation including major histocompatibility complex Class II (MHCII) and CD40 mRNA, as well as MHCII immunoreactivity, were increased in hippocampus of aged, compared with young, rats and that these changes were associated with a deficit in LTP; these changes were attenuated in hippocampal tissue prepared from aged rats which received CD200Fc. Microglial activation and a deficit in LTP have also been reported in lipopolysaccharide (LPS)-treated rats and, here, we report that these changes were also attenuated in CD200Fc-treated animals. Thus the negative impact of microglial activation on the ability of aged and LPS-treated rats to sustain LTP is ameliorated when CD200R is activated by CD200Fc.

Possible association between expression of chemokine receptor-2 (CCR2) and amyotrophic lateral sclerosis (ALS) patients of North India

Background and Objectives

We earlier reported elevated chemokine ligand-2 (CCL2) in Indian amyotrophic lateral sclerosis (ALS) patients. We now analysed chemokine receptor-2 (CCR2), the receptor of CCL2, in these ALS patients.

Methods

Indian sporadic ALS patients (n = 50) were included on the basis of El Escorial criteria. Percentage (%) of CCR2 expressing peripheral blood mononuclear cells (PBMCs) was evaluated using Flow Cytometry. Real Time Polymerase Chain Reaction (PCR) was used to quantitate CCR2 mRNA expression in PBMCs. Normal controls (n = 40) were also included for comparison.

Results

Flow Cytometry revealed significantly reduced CCR2 expressing PBMCs in the ALS patients. We also found a significant decline in number of CCR2 expressing PBMCs in limb onset ALS when compared to bulbar onset ALS. PBMCs from ALS patients showed substantial down-regulation of CCR2 mRNA. CCR2 mRNA expression was found to be decreased among limb ALS patients as compared to bulbar onset ALS. Further, the count of CCR2+ PBMCs and CCR2 mRNA transcript in PBMCs was significantly lower in severe and moderate ALS as compared to ALS patients with mild impairments.

Conclusions

Downregulation of PBMCs CCR2 may indicate its etio-pathological relevance in ALS pathogenesis. Reduced PBMCs CCR2 may result in decreased infiltration of leukocytes at the site of degeneration as a compensatory response to ALS. CCR2 levels measurements in hematopoietic stem cells and estimation of comparative PBMCs count among ALS, disease controls and normal controls can unveil its direct neuroprotective role. However, the conclusions are restricted by the absence of neurological/non-neurological disease controls in the study.

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.

Excess circulating alternatively activated myeloid (M2) cells accelerate ALS progression while inhibiting experimental autoimmune encephalomyelitis

BACKGROUND

Circulating immune cells including autoreactive T cells and monocytes have been documented as key players in maintaining, protecting and repairing the central nervous system (CNS) in health and disease. Here, we hypothesized that neurodegenerative diseases might be associated, similarly to tumors, with increased levels of circulating peripheral myeloid derived suppressor cells (MDSCs), representing a subset of suppressor cells that often expand under pathological conditions and inhibit possible recruitment of helper T cells needed for fighting off the disease.

METHODS AND FINDINGS

We tested this working hypothesis in amyotrophic lateral sclerosis (ALS) and its mouse model, which are characterized by a rapid progression once clinical symptoms are evident. Adaptive transfer of alternatively activated myeloid (M2) cells, which homed to the spleen and exhibited immune suppressive activity in G93A mutant superoxide dismutase-1 (mSOD1) mice at a stage before emergence of disease symptoms, resulted in earlier appearance of disease symptoms and shorter life expectancy. The same protocol mitigated the inflammation-induced disease model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), which requires circulating T cells for disease induction. Analysis of whole peripheral blood samples obtained from 28 patients suffering from sporadic ALS (sALS), revealed a two-fold increase in the percentage of circulating MDSCs (LIN(-/Low)HLA-DR(-)CD33(+)) compared to controls.

CONCLUSIONS

Taken together, these results emphasize the distinct requirements for fighting the inflammatory neurodegenerative disease, multiple sclerosis, and the neurodegenerative disease, ALS, though both share a local inflammatory component. Moreover, the increased levels of circulating MDSCs in ALS patients indicates the operation of systemic mechanisms that might lead to an impairment of T cell reactivity needed to overcome the disease conditions within the CNS. This high level of suppressive immune cells might represent a risk factor and a novel target for therapeutic intervention in ALS at least at the early stage.

Dysfunction of constitutive and inducible ubiquitin-proteasome system in amyotrophic lateral sclerosis: implication for protein aggregation and immune response

The ubiquitin-proteasome system (UPS) is the major intracellular proteolytic mechanism controlling the degradation of misfolded/abnormal proteins. A common hallmark in amyotrophic lateral sclerosis (ALS) and in other neurodegenerative disorders is the accumulation of misfolded/abnormal proteins into the damaged neurons, leading to the formation of cellular inclusions that are mostly ubiquitin-positive. Although proteolysis is a complex mechanism requiring the participation of different pathways, the abundant accumulation of ubiquitinated proteins strongly suggests an important contribution of UPS to these neuropathological features. The use of cellular and animal models of ALS, particularly those expressing mutant SOD1, the gene mutation most represented in familiar ALS, has provided significant evidence for a role of UPS in protein inclusions formation and motor neuron death. This review will specifically discuss this piece of evidence and provide suggestions of potential strategies for therapeutic intervention. We will also discuss the finding that, unlike the constitutive proteasome subunits, the inducible subunits are overexpressed early during disease progression in SOD1 mice models of ALS. These subunits form the immunoproteasome and generate peptides for the major histocompatibility complex class I molecules, suggesting a role of this system in the immune responses associated with the pathological features of ALS. Since recent discoveries indicate that innate and adaptive immunity may influence the disease process, in this review we will also provide evidence of a possible connection between immune-inflammatory reactions and UPS function, in the attempt to better understand the etiopathology of ALS and to identify appropriate targets for novel treatment strategies of this devastating disease.

The Role of immune and inflammatory mechanisms in ALS

Amyotrophic lateral sclerosis (ALS) is a severe progressive neurodegenerative disease. The cause is unknown, but genetic abnormalities have been identified in subjects with familial ALS and also in subjects with sporadic ALS. Environmental factors such as occupational exposure have been shown to be risk factors for the development of ALS. Patients differ in their clinical features and differ in the clinical course of disease. Immune abnormalities have been found in the central nervous system by pathological studies and also in the blood and CSF of subjects with ALS. Inflammation and immune abnormalities are also found in animals with a model of ALS due to mutations in the SOD1 gene. Previously it has been considered that immune abnormalities might contribute to the pathogenesis of disease. However more recently it has become apparent that an immune response can occur as a response to damage to the nervous system and this can be protective.

Endogenous regulatory T lymphocytes ameliorate amyotrophic lateral sclerosis in mice and correlate with disease progression in patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a relentless and devastating adult-onset neurodegenerative disease with no known cure. In mice with amyotrophic lateral sclerosis, CD4⁺ T lymphocytes and wild-type microglia potentiate protective inflammatory responses and play a principal role in disease pathoprogression. Using this model, we demonstrate that endogenous T lymphocytes, and more specifically regulatory T lymphocytes, are increased at early slowly progressing stages, augmenting interleukin-4 expression and protective M2 microglia, and are decreased when the disease rapidly accelerates, possibly through the loss of FoxP3 expression in the regulatory T lymphocytes. Without ex vivo activation, the passive transfer of wild-type CD4⁺ T lymphocytes into amyotrophic lateral sclerosis mice lacking functional T lymphocytes lengthened disease duration and prolonged survival. The passive transfer of endogenous regulatory T lymphocytes from early disease stage mutant Cu²⁺/Zn²⁺ superoxide dismutase mice into these amyotrophic lateral sclerosis mice, again without ex vivo activation, were substantially more immunotherapeutic sustaining interleukin-4 levels and M2 microglia, and resulting in lengthened disease duration and prolonged survival; the stable disease phase was extended by 88% using mutant Cu²⁺/Zn²⁺ superoxide dismutase regulatory T lymphocytes. A potential mechanism for this enhanced life expectancy may be mediated by the augmented secretion of interleukin-4 from mutant Cu²⁺/Zn²⁺ superoxide dismutase regulatory T lymphocytes that directly suppressed the toxic properties of microglia; flow cytometric analyses determined that CD4⁺/CD25⁺/FoxP3⁺ T lymphocytes co-expressed interleukin-4 in the same cell. These observations were extended into the amyotrophic lateral sclerosis patient population where patients with more rapidly progressing disease had decreased numbers of regulatory T lymphocytes; the numbers of regulatory T lymphocytes were inversely correlated with disease progression rates. These data suggest a cellular mechanism whereby endogenous regulatory T lymphocytes are immunocompetent and actively contribute to neuroprotection through their interactions with microglia. Furthermore, these data suggest that immunotherapeutic interventions must begin early in the pathogenic process since immune dysfunction occurs at later stages. Thus, the cumulative mouse and human amyotrophic lateral sclerosis data suggest that increasing the levels of regulatory T lymphocytes in patients with amyotrophic lateral sclerosis at early stages in the disease process may be of therapeutic value, and slow the rate of disease progression and stabilize patients for longer periods of time.

Gene expression profiling in peripheral blood mononuclear cells from patients with sporadic amyotrophic lateral sclerosis (sALS)

The aim of this study was to identify gene expression profiles in peripheral blood mononuclear cells (PBMCs) from sporadic amyotrophic lateral sclerosis (sALS) patients to gain insights into the pathogenesis of ALS. We found that upregulation of LPS/TLR4-signaling associated genes was observed in the PMBCs from sALS patients after short-term cultivation, and that elevated levels of gene expression correlated with degree of peripheral blood monocyte activation and plasma LPS levels in sALS. Similar patterns of gene expression were reproduced in LPS stimulated PBMCs from healthy controls. These data suggest that chronic monocyte/macrophage activation may be through LPS/TLR4-signaling pathways in ALS.

The multifaceted profile of activated microglia

Although relatively neglected previously, research efforts in the past decade or so have identified a pivotal role for glial cells in regulating neuronal function. Particular emphasis has been placed on increasing our understanding of the function of microglia because a change from the ramified "resting" state of these cells has been associated with the pathogenesis of several neurodegenerative diseases, notably Alzheimer's disease. However, it is not clear whether activation of microglia and the associated inflammatory changes play a part in triggering disease processes or whether cell activation is a response to the early changes associated with the disease. In either case, the possibility exists that modulation of microglial activation may be beneficial in some circumstances, underlying the need to pursue research in this area. The original morphological categorization of microglia by Del Rio Hortega into ameboid, ramified, and intermediate forms, must now be elaborated to encompass a functional description. The evidence which has been generated recently suggests that microglia are probably never in a "resting" state and that several intermediate transitional states, based on function and morphology, probably exist. A more complete understanding of these states and the triggers which lead to a change from one to another state, and the factors which modulate the molecular switch that determines the persistence of the "activated" state remain to be identified.

Immune system alterations in sporadic amyotrophic lateral sclerosis patients suggest an ongoing neuroinflammatory process

In this work we show that patients with sporadic amyotrophic lateral sclerosis exhibit immunological alterations in their blood, with respect to healthy controls, such as: i) increased levels of CD4+ cells and decreased levels of CD8+ T lymphocytes, the latter due to the reduced expression of the anti-apoptotic molecule Bcl-2; ii) significantly reduced CD4+CD25+ regulatory T (Treg) cells and monocytes (CD14+) levels in patients at a less severe stage of disease, suggesting their early recruitment towards the CNS area of primary neurodegeneration; iii) reduced expression of HLA-DR and CCR2 expression, as markers of activation, in monocytes. Since resident microglia partially derives from circulating activated monocytes and Treg cells are known to interact with the local microglia, this study strengthens the hypothesis of an involvement of the adaptive immune system associated with a neuroinflammatory process in the pathobiology of ALS.

Nitroproteomics of peripheral blood mononuclear cells from patients and a rat model of ALS

Increased levels of 3-nitrotyrosine in the central nervous system have been found in patients and mouse models of familial ALS (fALS), suggesting a possible use of nitrated proteins as biomarkers. We analyzed peripheral blood mononuclear cells (PBMCs), easily accessible samples, from sporadic ALS (sALS) patients and a rat model of fALS (a) to establish whether an increased level of nitrated proteins was present in PBMCs, too, and (b) to identify possible candidate biomarkers. With a proteomic approach, we identified for the first time the major overnitrated proteins in PBMCs from patients and rats at different disease stages. In the rats, their increased levels already were measured at a presymptomatic stage. Among them, actin, ATP synthase, and vinculin overlap between sALS patients and the rat model. Interestingly, in a previous study, actin and ATPase have been found overnitrated in the spinal cord of a mouse model of fALS before disease onset, suggesting their possible involvement in motor neuron degeneration. In conclusion, we observed that an increased level of nitrated proteins was not restricted to the spinal cord but also was present in peripheral cells of patients and an animal model, and that nitrated proteins are promising candidate biomarkers for early diagnosis of ALS.

Circulating endotoxin and systemic immune activation in sporadic amyotrophic lateral sclerosis (sALS)

The present study reports elevated levels of endotoxin/lipopolysaccharide (LPS) concentrations in plasma from patients with sporadic amyotrophic lateral sclerosis (sALS) and Alzheimer's (AD) as compared to healthy controls. Levels of plasma LPS showed a significant positive correlation with degree of blood monocyte/macrophage activation in disease groups and was most elevated in patients with advanced sALS disease. There was a significant negative relationship between plasma LPS and levels of monocyte/macrophage IL-10 expression in sALS blood. These data suggest that systemic LPS levels and activated monocyte/macrophages may play significant roles in the pathogenesis of sALS.