Multifaceted aspects of inflammation in multiple sclerosis: The role of microglia

Tryptophan metabolism as a 'reflex' feature of neuroimmune communication: Sensor and effector functions for the indoleamine-2, 3-dioxygenase kynurenine pathway

Although the central nervous system (CNS) and immune system were regarded as independent entities, it is now clear that immune system cells can influence the CNS, and neuroglial activity influences the immune system. Despite the many clinical implications for this 'neuroimmune interface', its detailed operation at the molecular level remains unclear. This narrative review focuses on the metabolism of tryptophan along the kynurenine pathway, since its products have critical actions in both the nervous and immune systems, placing it in a unique position to influence neuroimmune communication. In particular, since the kynurenine pathway is activated by pro-inflammatory mediators, it is proposed that physical and psychological stressors are the stimuli of an organismal protective reflex, with kynurenine metabolites as the effector arm co-ordinating protective neural and immune system responses. After a brief review of the neuroimmune interface, the general perception of tryptophan metabolism along the kynurenine pathway is expanded to emphasize this environmentally driven perspective. The initial enzymes in the kynurenine pathway include indoleamine-2,3-dioxygenase (IDO1), which is induced by tissue damage, inflammatory mediators or microbial products, and tryptophan-2,3-dioxygenase (TDO), which is induced by stress-induced glucocorticoids. In the immune system, kynurenic acid modulates leucocyte differentiation, inflammatory balance and immune tolerance by activating aryl hydrocarbon receptors and modulates pain via the GPR35 protein. In the CNS, quinolinic acid activates N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors, whereas kynurenic acid is an antagonist: the balance between glutamate, quinolinic acid and kynurenic acid is a significant regulator of CNS function and plasticity. The concept of kynurenine and its metabolites as mediators of a reflex coordinated protection against stress helps to understand the variety and breadth of their activity. It should also help to understand the pathological origin of some psychiatric and neurodegenerative diseases involving the immune system and CNS, facilitating the development of new pharmacological strategies for treatment.

Anatomical location of injected microglia in different activation states and time course of injury determines survival of retinal ganglion cells after optic nerve crush

Background: Activated microglia release harmful substances to retinal ganglion cells (RGCs), but may also benefit by removing cellular debris and secreting neurotrophic factors. These paradoxical roles remain controversial because the nature and time-course of the injury that defines their role is unknown. The aim of this study was to determine if pharmacological manipulation of microglia to acquire a pro-inflammatory or pro-survival phenotype will exacerbate or enhance neuronal survival after injury.Material and methods: Treated HAP I (highly aggressively proliferating immortalized) microglia were injected into the vitreous or tail vein (T V) of female Sprague-Dawley rats. Retinas were examined at 4-14 days following optic nerve crush (ONC) and the number of surviving RGCs was determined.Results: Injection of untreated HAP I cells resulted in the greater loss of RGCs early after ONC when injected into the vitreous and later after ONC when injected into the T V. LP S activated HAP I cells injected into the vitreous resulted in greater RGC loss with and without injury. When injected into the T V with ONC there was no loss of RGCs 4 days after ONC but greater loss afterwards. Minocycline treated HAP I cells injected into the vitreous resulted in greater RGC survival than untreated HAP I cells. However, when injected into the T V with ONC there was greater loss of RGCs. These results suggest that optic nerve signals attract extrinsic microglia to the retina, resulting in a proinflammatory response.Conclusion: Neuroprotection or cytotoxicity of microglia depends on the type of activation, time course of the injury, and if they act on the axon or cell body.

[Alexithymia in Multiple Sclerosis - Narrative Review]

Alexithymia is a multidimensional construct of personality implicating difficulties in identifying and describing another's feelings, and externally oriented thinking. It is broadly reported in psychiatric patients but has gained little attention regarding its occurrence and pathophysiology in multiple sclerosis (MS). This narrative review aims to address prevalence, etiology, neurobiological, and clinical findings of alexithymia. The prevalence of alexithymia in MS ranges from 10 to 53%. There seems to be an association with anxiety, depression, fatigue, and some aspects of social cognition, while the relationship with clinical and classical cognitive variables was rarely evaluated. Only a few studies referred to its pathophysiology assuming an aberrant interhemispheric transfer or regional cerebral abnormalities. The prevalence of alexithymia in MS and the potential negative impact on quality of life and interpersonal communication could severely impact clinical MS management and a screnning for these factors should be mandatory. Thus, further evaluation is needed concerning its relationship with clinical, emotional, and cognitive confounders. Large-scale studies employing neuroimaging techniques are needed for a better understanding of the neural underpinnings of this MS feature.

Microglial crosstalk with astrocytes and immune cells in amyotrophic lateral sclerosis

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

Comparing RNA-sequencing datasets from astrocytes, oligodendrocytes, and microglia in multiple sclerosis identifies novel dysregulated genes relevant to inflammation and myelination

Central nervous system (CNS) inflammation is a key factor in multiple sclerosis (MS). Invasion of peripheral immune cells into the CNS resulting from an unknown signal or combination of signals results in activation of resident immune cells and the hallmark feature of the disease: demyelinating lesions. These lesion sites are an amalgam of reactive peripheral and central immune cells, astrocytes, damaged and dying oligodendrocytes, and injured neurons and axons. Sustained inflammation affects cells directly located within the lesion site and further abnormalities are apparent diffusely throughout normal-appearing white matter and grey matter. It is only relatively recently, using animal models, new tissue sampling techniques, and next-generation sequencing, that molecular changes occurring in CNS resident cells have been broadly captured. Advances in cell isolation through Fluorescence Activated Cell Sorting (FACS) and laser-capture microdissection together with the emergence of single-cell sequencing have enabled researchers to investigate changes in gene expression in astrocytes, microglia, and oligodendrocytes derived from animal models of MS as well as from primary patient tissue. The contribution of some dysregulated pathways has been followed up in individual studies; however, corroborating results often go unreported between sequencing studies. To this end, we have consolidated results from numerous RNA-sequencing studies to identify and review novel patterns of differentially regulated genes and pathways occurring within CNS glial cells in MS. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

An integrated cytokine and kynurenine network as the basis of neuroimmune communication

Two of the molecular families closely associated with mediating communication between the brain and immune system are cytokines and the kynurenine metabolites of tryptophan. Both groups regulate neuron and glial activity in the central nervous system (CNS) and leukocyte function in the immune system, although neither group alone completely explains neuroimmune function, disease occurrence or severity. This essay suggests that the two families perform complementary functions generating an integrated network. The kynurenine pathway determines overall neuronal excitability and plasticity by modulating glutamate receptors and GPR35 activity across the CNS, and regulates general features of immune cell status, surveillance and tolerance which often involves the Aryl Hydrocarbon Receptor (AHR). Equally, cytokines and chemokines define and regulate specific populations of neurons, glia or immune system leukocytes, generating more specific responses within restricted CNS regions or leukocyte populations. In addition, as there is a much larger variety of these compounds, their homing properties enable the superimposition of dynamic variations of cell activity upon local, spatially limited, cell populations. This would in principle allow the targeting of potential treatments to restricted regions of the CNS. The proposed synergistic interface of 'tonic' kynurenine pathway affecting baseline activity and the superimposed 'phasic' cytokine system would constitute an integrated network explaining some features of neuroimmune communication. The concept would broaden the scope for the development of new treatments for disorders involving both the CNS and immune systems, with safer and more effective agents targeted to specific CNS regions.

Microglial Potassium Channels: From Homeostasis to Neurodegeneration

The growing interest in the role of microglia in the progression of many neurodegenerative diseases is developing in an ever-expedited manner, in part thanks to emergent new tools for studying the morphological and functional features of the CNS. The discovery of specific biomarkers of the microglia phenotype could find application in a wide range of human diseases, and creates opportunities for the discovery and development of tailored therapeutic interventions. Among these, recent studies highlight the pivotal role of the potassium channels in regulating microglial functions in physiological and pathological conditions such as Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis. In this review, we summarize the current knowledge of the involvement of the microglial potassium channels in several neurodegenerative diseases and their role as modulators of microglial homeostasis and dysfunction in CNS disorders.

Conserved spinal cord bioenergetics in experimental autoimmune encephalomyelitis in C57BL6 mice, measured using phosphorescence oxygen analyzer

Background

We have previously reported that spinal cord respiration (cellular mitochondrial oxygen consumption) and ATP content are conserved in the studied model of experimental autoimmune encephalomyelitis (EAE), foreseeing a recovery of the diseased rats. This exemplary lesion of multiple sclerosis is used here to measure spinal cord bioenergetics in C57BL6 mice. Our hypothesis is that, despite the well-known focal axonal mitochondrial pathology, bioenergetics of the CNS is reasonably preserved in this disease.

Methods

EAE was induced with an immunodominant myelin oligodendrocyte glycoprotein epitope in complete Freund's adjuvant, appended by injections of pertussis toxin. A low- and high-dose of the encephalitogen, administered into base of tail or hind-flank, were investigated. Control mice received only the incomplete adjuvant into tail. Oxygen measurements were based on quenching the phosphorescence of Pd(II) meso-tetra (sulfophenyl) tetrabenzoporphyrin by molecular oxygen. Cellular ATP was measured using the luciferin/luciferase system.

Results

The kinetics of spinal cord oxygen consumption was zero-order (linear with time) and inhibited by cyanide, confirming oxygen was reduced by cytochrome oxidase. The rate of respiration (in μM O₂.min⁻¹.mg⁻¹; measured on Days 13–28) in control mice was (mean ± SD) 0.086 ± 0.024 (n = 8) and in immunized mice was 0.079 ± 0.020 (n = 15, P = 0.265, Mann-Whitney test). Consistently, cellular ATP (in μmol mg⁻¹ dry pellet weight; measured on Days 13–28) in control mice was 0.068 ± 0.079 (n = 11) and in immunized mice was 0.063 ± 0.061 (n = 24, P = 0.887, Mann-Whitney U test).

Conclusions

In vitro measurements of spinal cord bioenergetics show conservation of the mitochondrial function in mice with EAE. These results suggest the previously documented reduced mitochondrial electrochemical potential in this disease is alterable, and likely reflects the adverse events of neuroinflammation.

Microglia in Neuroinflammation and Neurodegeneration: From Understanding to Therapy

Microglia are the resident macrophages of the central nervous system (CNS) acting as the first line of defense in the brain by phagocytosing harmful pathogens and cellular debris. Microglia emerge from early erythromyeloid progenitors of the yolk sac and enter the developing brain before the establishment of a fully mature blood-brain barrier. In physiological conditions, during brain development, microglia contribute to CNS homeostasis by supporting cell proliferation of neural precursors. In post-natal life, such cells contribute to preserving the integrity of neuronal circuits by sculpting synapses. After a CNS injury, microglia change their morphology and down-regulate those genes supporting homeostatic functions. However, it is still unclear whether such changes are accompanied by molecular and functional modifications that might contribute to the pathological process. While comprehensive transcriptome analyses at the single-cell level have identified specific gene perturbations occurring in the "pathological" microglia, still the precise protective/detrimental role of microglia in neurological disorders is far from being fully elucidated. In this review, the results so far obtained regarding the role of microglia in neurodegenerative disorders will be discussed. There is solid and sound evidence suggesting that regulating microglia functions during disease pathology might represent a strategy to develop future therapies aimed at counteracting brain degeneration in multiple sclerosis, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis.

Qki is an essential regulator of microglial phagocytosis in demyelination

The mechanism underpinning the regulation of microglial phagocytosis in demyelinating diseases is unclear. Here, we showed that the Quaking protein (Qki) in microglia was greatly induced by demyelination in the brains of both mice and humans. Deletion of the Quaking gene (Qk) in microglia severely impaired the clearance of myelin debris. Transcriptomic profiling indicated that depletion of Qki impaired total RNA levels and splicing of the genes involved in phagosome formation and maturation. RNA immunoprecipitation (RIP) confirmed the physical interactions between the Qki protein and the mRNAs of Qki targets that are involved in phagocytosis, indicating that Qki regulates their RNA stability. Both Qki depletion and inhibition of Qki target Cd36 greatly reduced the phagocytic activity of microglia and macrophages. The defective uptake and degradation of myelin debris caused by Qki depletion in microglia resulted in unresolved myelin debris that impaired axon integrity, oligodendrocyte maturation, and subsequent remyelination. Thus, our results demonstrate that Qki is an essential regulator of microglia’s phagocytic activity under demyelinating conditions.

Anomalously warm weather and acute care visits in patients with multiple sclerosis: A retrospective study of privately insured individuals in the US

BACKGROUND

As the global climate changes in response to anthropogenic greenhouse gas emissions, weather and temperature are expected to become increasingly variable. Although heat sensitivity is a recognized clinical feature of multiple sclerosis (MS), a chronic demyelinating disorder of the central nervous system, few studies have examined the implications of climate change for patients with this disease.

METHODS AND FINDINGS

We conducted a retrospective cohort study of individuals with MS ages 18-64 years in a nationwide United States patient-level commercial and Medicare Advantage claims database from 2003 to 2017. We defined anomalously warm weather as any month in which local average temperatures exceeded the long-term average by ≥1.5°C. We estimated the association between anomalously warm weather and MS-related inpatient, outpatient, and emergency department visits using generalized log-linear models. From 75,395,334 individuals, we identified 106,225 with MS. The majority were women (76.6%) aged 36-55 years (59.0%). Anomalously warm weather was associated with increased risk for emergency department visits (risk ratio [RR] = 1.043, 95% CI: 1.025-1.063) and inpatient visits (RR = 1.032, 95% CI: 1.010-1.054). There was limited evidence of an association between anomalously warm weather and MS-related outpatient visits (RR = 1.010, 95% CI: 1.005-1.015). Estimates were similar for men and women, strongest among older individuals, and exhibited substantial variation by season, region, and climate zone. Limitations of the present study include the absence of key individual-level measures of socioeconomic position (i.e., race/ethnicity, occupational status, and housing quality) that may determine where individuals live-and therefore the extent of their exposure to anomalously warm weather-as well as their propensity to seek treatment for neurologic symptoms.

CONCLUSIONS

Our findings suggest that as global temperatures rise, individuals with MS may represent a particularly susceptible subpopulation, a finding with implications for both healthcare providers and systems.

The protective effect of the TSPO ligands 2,4-Di-Cl-MGV-1, CB86, and CB204 against LPS-induced M1 pro-inflammatory activation of microglia

We have shown previously, that the 18 ​kDa translocator protein (TSPO) synthetic ligands quinazoline derivatives (2-Cl-MGV-1 and MGV-1) can inhibit activation of in BV-2 microglial cells. In the present study we assessed the impact of novel TSPO ligands on lipopolysaccharide (LPS)-induced microglial activation as expressed by release of pro-inflammatory molecules, including cytokines [interleukin-6 (IL-6), IL-1β, interferon- γ (IFN-γ)] nitric oxide (NO), CD8, and cyclo-oxygenase-2 (COX-2). The TSPO ligands 2,4-Di-Cl-MGV-1, CB86, and CB204 counteracted with the LPS-induced microglial activation. Exposure to LPS along with the TSPO ligand 2,4-Di-Cl-MGV-1 (25 ​μM) reduced significantly the release of NO by 24-, IL-6 by 14-, IL-β by 14-, IFN- γ by 6-, and TNF-α by 29-folds, respectively. In contrast to the anti-neuroinflammatory effect of the TSPO ligands, the effect of diclofenac sodium (DS; 25 ​μM) did not reach statistical significance. No alterations in IL-10 and IL-13 were detected (M2 anti-inflammatory pathway) during the inhibition of M1 pro-inflammatory pathway.

Intracisternal delivery of PEG-coated gold nanoparticles results in high brain penetrance and long-lasting stability

Background

The increasing use of gold nanoparticles (AuNPs) in the field of neuroscience instilled hope for their rapid translation to the clinical practice. AuNPs can be engineered to carry therapeutics or diagnostics in the diseased brain, possibly providing greater cell specificity and low toxicity. Although there is a general enthusiasm for these tools, we are in early stages of their development. Overall, their brain penetrance, stability and cell specificity are critical issues that must be addressed to drive AuNPs to the clinic.

Results

We studied the kinetic, distribution and stability of PEG-coated AuNPs in mice receiving a single injection into the cisterna magna of the 4th ventricle. AuNPs were conjugated with the fluorescent tag Cy5.5 (Cy5.5-AuNPs) to track their in vivo distribution. Fluorescence levels from such particles were detected in mice for weeks. In situ analysis of brains by immunofluorescence and electron microscopy revealed that Cy5.5-AuNPs penetrated the brain parenchyma, spreading in the CNS parenchyma beneath the 4th ventricle. Cy5.5-AuNPs were preferentially found in neurons, although a subset of resting microglia also entrapped these particles.

Conclusions

Our results suggest that the ICM route for delivering gold particles allows the targeting of neurons. This approach might be pursued to carry therapeutics or diagnostics inside a diseased brain with a surgical procedure that is largely used in gene therapy approaches. Furthermore, this approach could be used for radiotherapy, enhancing the agent’s efficacy to kill brain cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12951-019-0481-3) contains supplementary material, which is available to authorized users.

Neuroinflammation, Microglia, and Cell-Association during Prion Disease

Prion disorders are transmissible diseases caused by a proteinaceous infectious agent that can infect the lymphatic and nervous systems. The clinical features of prion diseases can vary, but common hallmarks in the central nervous system (CNS) are deposition of abnormally folded protease-resistant prion protein (PrPres or PrPSc), astrogliosis, microgliosis, and neurodegeneration. Numerous proinflammatory effectors expressed by astrocytes and microglia are increased in the brain during prion infection, with many of them potentially damaging to neurons when chronically upregulated. Microglia are important first responders to foreign agents and damaged cells in the CNS, but these immune-like cells also serve many essential functions in the healthy CNS. Our current understanding is that microglia are beneficial during prion infection and critical to host defense against prion disease. Studies indicate that reduction of the microglial population accelerates disease and increases PrPSc burden in the CNS. Thus, microglia are unlikely to be a foci of prion propagation in the brain. In contrast, neurons and astrocytes are known to be involved in prion replication and spread. Moreover, certain astrocytes, such as A1 reactive astrocytes, have proven neurotoxic in other neurodegenerative diseases, and thus might also influence the progression of prion-associated neurodegeneration.

Temperature sensitivity in multiple sclerosis: An overview of its impact on sensory and cognitive symptoms

Multiple sclerosis (MS) is an autoimmune neurodegenerative disease characterized by demyelination of the central nervous system (CNS). The exact cause of MS is still unknown; yet its incidence and prevalence rates are growing worldwide, making MS a significant public health challenge. The heterogeneous distribution of demyelination within and between MS patients translates in a complex and varied array of autonomic, motor, sensory and cognitive symptoms. Yet a unique aspect of MS is the highly prevalent (60-80%) temperature sensitivity of its sufferers, where neurological symptoms are temporarily exacerbated by environmental- or exercise-induced increases (or decreases) in body temperature. MS temperature sensitivity is primarily driven by temperature-dependent slowing or blocking of neural conduction within the CNS due to changes in internal (core) temperature; yet changes in skin temperature could also contribute to symptom exacerbation (e.g. during sunlight and warm ambient exposure). The impact of temperature sensitivity, and particularly of increases in core temperature, on autonomic (e.g. thermoregulatory/cardiovascular function) and motor symptoms (e.g. fatigue) is well described. However, less attention has been given to how increases (and decreases) in core and skin temperature affect sensory and cognitive symptoms. Furthermore, it remains uncertain whether changes in skin temperature alone could also trigger worsening of symptoms. Here we review the impact of temperature sensitivity on MS sensory and cognitive function and discuss additional factors (e.g. changes in skin temperature) that potentially contribute to temperature-induced worsening of symptoms in the absence of alteration in core temperature.

Calcitonin gene-related peptide decreases IL-1beta, IL-6 as well as Ym1, Arg1, CD163 expression in a brain tissue context-dependent manner while ameliorating experimental autoimmune encephalomyelitis

Activation states of immune cells (among them, the so-called pro- or anti-inflammatory states) influence the pathogenesis of multiple sclerosis (MS). The neuropeptide calcitonin gene-related peptide (CGRP) can exert a pro- or anti-inflammatory role in a context-dependent manner. In mice CGRP was found to attenuate the development of experimental autoimmune encephalomyelitis (EAE, a common MS animal model). We analyzed CGRP effects on the expression of cytokines and markers of activation states, as well as its intracellular cascade, following intrathecal administration during EAE immunization. Real Time quantitative-PCR (RT-PCR) showed that IL-1beta and IL-6 (associated to a pro-inflammatory state in EAE), but also Ym1 (also known as Chil3), Arg1 and CD163 (associated to an anti-inflammatory state in EAE) were decreased in the encephalon (devoid of cerebellum). In the cerebellum itself, IL-1beta and Ym1 were decreased. TNF-alpha (associated to a pro-inflammatory state in EAE), but also IL-10 (associated to another type of anti-inflammatory state) and BDNF were unchanged in these two regions. No changes were detected in the spinal cord. Additional tendencies toward a change (as revealed by RT-PCR) were again decreases: IL-10 in the encephalon and Arg1 in the spinal cord. CGRP decreased percentage of Ym1⁺/CD68⁺ immunoreactive cells and cell density of infiltrates in the cervical spinal cord pia mater. Instead, Ym1 in the underlying parenchyma and at thoracic and lumbar levels, as well as Arg1, were unchanged. In cultured microglia the neuropeptide decreased Ym1, but not Arg1, immunoreactivity. Inducible NOS (iNOS) was unchanged in spinal cord microglia and astrocytes. The neuropeptide increased the activation of ERK1/2 in the astrocytes of the spinal cord and in culture, but did not influence the activation of ERK1/2 or p38 in the spinal cord microglia. Finally, in areas adjacent to infiltration sites CGRP-treated microglia showed a larger ramification radius. In conclusion, CGRP-induced EAE amelioration was associated to a concomitant, context-dependent decrease in the expression of markers belonging to both pro- or anti-inflammatory activation states of immune cells. It can be hypothesized that CGRP-induced EAE attenuation is obtained through a novel mechanism that promotes down-regulation of immune cell activation that facilitates the establishment of a beneficial environment in EAE provided possibly also by other factors.

Microglia Are Critical in Host Defense against Prion Disease

Microglial cells in the central nervous system play important roles in neurodevelopment and resistance to infection, yet microglia can become neurotoxic under some conditions. An early event during prion infection is the activation of microglia and astrocytes in the brain prior to damage or death of neurons. Previous prion disease studies using two different strategies to manipulate signaling through the microglial receptor CSF-1R reported contrary effects on survival from prion disease. However, in these studies, reductions of microglial numbers and function were variable, thus confounding interpretation of the results. In the present work, we used oral treatment with a potent inhibitor of CSF-1R, PLX5622, to eliminate 78 to 90% of microglia from cortex early during the course of prion infection. Oral drug treatment early after infection with the RML scrapie strain significantly accelerated vacuolation, astrogliosis, and deposition of disease-associated prion protein. Furthermore, drug-treated mice had advanced clinical disease requiring euthanasia 31 days earlier than untreated control mice. Similarly, PLX5622 treatment during the preclinical phase at 80 days postinfection with RML scrapie also accelerated disease and resulted in euthanasia of mice 33 days earlier than infected controls. PLX5622 also accelerated clinical disease after infection with scrapie strains ME7 and 22L. Thus, microglia are critical in host defense during prion disease. The early accumulation of PrPSc in the absence of microglia suggested that microglia may function by clearing PrPSc, resulting in longer survival.IMPORTANCE Microglia contribute to many aspects of health and disease. When activated, microglia can be beneficial by repairing damage in the central nervous system (CNS) or they can turn harmful by becoming neurotoxic. In prion and prionlike diseases, the involvement of microglia in disease is unclear. Previous studies suggest that microglia can either speed up or slow down disease. In this study, we infected mice with prions and depleted microglia from the brains of mice using PLX5622, an effective CSF-1R tyrosine kinase inhibitor. Microglia were markedly reduced in brains, and prion disease was accelerated, so that mice needed to be euthanized 20 to 33 days earlier than infected control mice due to advanced clinical disease. Similar results occurred when mice were treated with PLX5622 at 80 days after infection, which was just prior to the start of clinical signs. Thus, microglia are important for removing prions, and the disease is faster when microglia are depleted.

What role does multiple sclerosis play in the development of untreatable painful conditions?

Clinical data outline the high incidence of pain syndromes in patients with multiple sclerosis, with a significant prevalence of craniofacial manifestations, including trigeminal neuralgia and migraine, which are very difficult to be managed pharmacologically. The common explanation of a localization of demyelinating plaques in areas devoted to pain modulation and integration as a trigger for pain development seems now partially unsatisfactory, since pain is often manifested well before the clinical signs of the pathology and its severity does not correlate with disease progression. This review focuses on additional mechanisms which could be at the basis of pain development in multiple sclerosis, whose identification will help identifying new targets to design more effective analgesic strategies.

HMGB1 Activates Proinflammatory Signaling via TLR5 Leading to Allodynia

Infectious and sterile inflammatory diseases are correlated with increased levels of high mobility group box 1 (HMGB1) in tissues and serum. Extracellular HMGB1 is known to activate Toll-like receptors (TLRs) 2 and 4 and RAGE (receptor for advanced glycation endproducts) in inflammatory conditions. Here, we find that TLR5 is also an HMGB1 receptor that was previously overlooked due to lack of functional expression in the cell lines usually used for studying TLR signaling. HMGB1 binding to TLR5 initiates the activation of NF-κB signaling pathway in a MyD88-dependent manner, resulting in proinflammatory cytokine production and pain enhancement in vivo. Biophysical and in vitro results highlight an essential role for the C-terminal tail region of HMGB1 in facilitating interactions with TLR5. These results suggest that HMGB1-modulated TLR5 signaling is responsible for pain hypersensitivity.

A novel pleiotropic effect of aspirin: Beneficial regulation of pro- and anti-inflammatory mechanisms in microglial cells

Aspirin, one of the most widely used non-steroidal anti-inflammatory drugs, has extensively studied effects on the cardiovascular system. To reveal further pleiotropic, beneficial effects of aspirin on a number of pro- and anti-inflammatory microglial mechanisms, we performed morphometric and functional studies relating to phagocytosis, pro- and anti-inflammatory cytokine production (IL-1β, tumor necrosis factor-α (TNF-α) and IL-10, respectively) and analyzed the expression of a number of inflammation-related genes, including those related to the above functions, in pure microglial cells. We examined the effects of aspirin (0.1mM and 1mM) in unchallenged (control) and bacterial lipopolysaccharide (LPS)-challenged secondary microglial cultures. Aspirin affected microglial morphology and functions in a dose-dependent manner as it inhibited LPS-elicited microglial activation by promoting ramification and the inhibition of phagocytosis in both concentrations. Remarkably, aspirin strongly reduced the pro-inflammatory IL-1β and TNF-α production, while it increased the anti-inflammatory IL-10 level in LPS-challenged cells. Moreover, aspirin differentially regulated the expression of a number of inflammation-related genes as it downregulated such pro-inflammatory genes as Nos2, Kng1, IL1β, Ptgs2 or Ccr1, while it upregulated some anti-inflammatory genes such as IL10, Csf2, Cxcl1, Ccl5 or Tgfb1. Thus, the use of aspirin could be beneficial for the prophylaxis of certain neurodegenerative disorders as it effectively ameliorates inflammation in the brain.

Innate immune regulation of autoimmunity in multiple sclerosis: Focus on the role of Toll-like receptor 2

Innate immunity relies on a set of germline-encoded receptors including Toll-like receptors (TLRs) that enable the host to discriminate between self and non-self. Multiple sclerosis (MS) is an autoimmune inflammatory demyelinating disease of the central nervous system (CNS). Infections are thought to play an important role in disease susceptibility. The role of innate immunity in MS has been recently appreciated. TLR2, a member of the TLR family, forms heterodimers with either TLR1 or TLR6 and detects a wide range of microbial as well as self-derived molecular structures. It may thus be important both in fighting infection and in activating autoimmunity. In this review, we discuss innate regulation of autoimmunity in MS with a focus on the role of TLR2 signaling.

Inflammatory cytokines influence measures of white matter integrity in Bipolar Disorder

BACKGROUND

Bipolar Disorder (BD) is associated with elevated biomarkers of cell-mediated immune activation and inflammation and with signs of widespread disruption of white matter (WM) integrity in adult life. Consistent findings in animal models link WM damage in inflammatory diseases of the brain and serum levels of cytokines.

METHODS

With an exploratory approach, we tested the effects of 22 serum analytes, including pro- and anti-inflammatory cytokines and neurotrophic/hematopoietic factors, on DTI measures of WM microstructure in a sample of 31 patients with a major depressive episode in course of BD. We used whole brain tract-based spatial statistics in the WM skeleton with threshold-free cluster enhancement of DTI measures of WM microstructure: axial (AD), radial (RD), and mean diffusivity (MD), and fractional anisotropy (FA).

RESULTS

The inflammation-related cytokines TNF-α, IL-8, IFN-γ and IL-10, and the growth factors IGFBP2 and PDGF-BB, shared the same significant associations with lower FA, and higher MD and RD, in large overlapping networks of WM fibers mostly located in the anterior part of the brain and including corpus callosum, cingulum, superior and inferior longitudinal fasciculi, inferior fronto-occipital fasciculi, uncinate, forceps, corona radiata, thalamic radiation, internal capsule.

CONCLUSIONS

Higher RD is thought to signify increased space between fibers, suggesting demyelination or dysmyelination. The pattern of higher RD and MD with lower FA suggests that inflammation-related cytokine and growth factor levels inversely associate with integrity of myelin sheaths. The activated inflammatory response system might contribute to BD pathophysiology by hampering structural connectivity in critical cortico-limbic networks.

Siponimod (BAF312) prevents synaptic neurodegeneration in experimental multiple sclerosis

Background

Data from multiple sclerosis (MS) and the MS rodent model, experimental autoimmune encephalomyelitis (EAE), highlighted an inflammation-dependent synaptopathy at the basis of the neurodegenerative damage causing irreversible disability in these disorders. This synaptopathy is characterized by an imbalance between glutamatergic and GABAergic transmission and has been proposed to be a potential therapeutic target.

Siponimod (BAF312), a selective sphingosine 1-phosphate1,5 receptor modulator, is currently under investigation in a clinical trial in secondary progressive MS patients. We investigated whether siponimod, in addition to its peripheral immune modulation, may exert direct neuroprotective effects in the central nervous system (CNS) of mice with chronic progressive EAE.

Methods

Minipumps allowing continuous intracerebroventricular (icv) infusion of siponimod for 4 weeks were implanted into C57BL/6 mice subjected to MOG_35-55-induced EAE. Electrophysiology, immunohistochemistry, western blot, qPCR experiments, and peripheral lymphocyte counts were performed. In addition, the effect of siponimod on activated microglia was assessed in vitro to confirm the direct effect of the drug on CNS-resident immune cells.

Results

Siponimod administration (0.45 μg/day) induced a significant beneficial effect on EAE clinical scores with minimal effect on peripheral lymphocyte counts. Siponimod rescued defective GABAergic transmission in the striatum of EAE, without correcting the EAE-induced alterations of glutamatergic transmission. We observed a significant attenuation of astrogliosis and microgliosis together with reduced lymphocyte infiltration in the striatum of EAE mice treated with siponimod. Interestingly, siponimod reduced the release of IL-6 and RANTES from activated microglial cells in vitro, which might explain the reduced lymphocyte infiltration. Furthermore, the loss of parvalbumin-positive (PV+) GABAergic interneurons typical of EAE brains was rescued by siponimod treatment, providing a plausible explanation of the selective effects of this drug on inhibitory synaptic transmission.

Conclusions

Altogether, our results show that siponimod has neuroprotective effects in the CNS of EAE mice, which are likely independent of its peripheral immune effect, suggesting that this drug could be effective in limiting neurodegenerative pathological processes in MS.

Efficacy and Safety of Human Retinal Progenitor Cells

PURPOSE

We assessed the long-term efficacy and safety of human retinal progenitor cells (hRPC) using established rodent models.

METHODS

Efficacy of hRPC was tested initially in Royal College of Surgeons (RCS) dystrophic rats immunosuppressed with cyclosporine/dexamethasone. Due to adverse effects of dexamethasone, this drug was omitted from a subsequent dose-ranging study, where different hRPC doses were tested for their ability to preserve visual function (measured by optokinetic head tracking) and retinal structure in RCS rats at 3 to 6 months after grafting. Safety of hRPC was assessed by subretinal transplantation into wild type (WT) rats and NIH-III nude mice, with analysis at 3 to 6 and 9 months after grafting, respectively.

RESULTS

The optimal dose of hRPC for preserving visual function/retinal structure in dystrophic rats was 50,000 to 100,000 cells. Human retinal progenitor cells integrated/survived in dystrophic and WT rat retina up to 6 months after grafting and expressed nestin, vimentin, GFAP, and βIII tubulin. Vision and retinal structure remained normal in WT rats injected with hRPC and there was no evidence of tumors. A comparison between dexamethasone-treated and untreated dystrophic rats at 3 months after grafting revealed an unexpected reduction in the baseline visual acuity of dexamethasone-treated animals.

CONCLUSIONS

Human retinal progenitor cells appear safe and efficacious in the preclinical models used here.

TRANSLATIONAL RELEVANCE

Human retinal progenitor cells could be deployed during early stages of retinal degeneration or in regions of intact retina, without adverse effects on visual function. The ability of dexamethasone to reduce baseline visual acuity in RCS dystrophic rats has important implications for the interpretation of preclinical and clinical cell transplant studies.

Fatigue in Multiple Sclerosis: Neural Correlates and the Role of Non-Invasive Brain Stimulation

Multiple sclerosis (MS) is a chronic progressive inflammatory disease of the central nervous system (CNS) and the major cause of non-traumatic disability in young adults. Fatigue is a frequent symptom reported by the majority of MS patients during their disease course and drastically affects their quality of life. Despite its significant prevalence and impact, the underlying pathophysiological mechanisms are not well elucidated. MS fatigue is still considered the result of multifactorial and complex constellations, and is commonly classified into “primary” fatigue related to the pathological changes of the disease itself, and “secondary” fatigue attributed to mimicking symptoms, comorbid sleep and mood disorders, and medications side effects. Radiological, physiological, and endocrine data have raised hypotheses regarding the origin of this symptom, some of which have succeeded in identifying an association between MS fatigue and structural or functional abnormalities within various brain networks. Hence, the aim of this work is to reappraise the neural correlates of MS fatigue and to discuss the rationale for the emergent use of noninvasive brain stimulation (NIBS) techniques as potential treatments. This will include a presentation of the various NIBS modalities and a suggestion of their potential mechanisms of action in this context. Specific issues related to the value of transcranial direct current stimulation (tDCS) will be addressed.

Brain innate immunity in the regulation of neuroinflammation: therapeutic strategies by modulating CD200-CD200R interaction involve the cannabinoid system

The central nervous system (CNS) innate immune response includes an arsenal of molecules and receptors expressed by professional phagocytes, glial cells and neurons that is involved in host defence and clearance of toxic and dangerous cell debris. However, any uncontrolled innate immune responses within the CNS are widely recognized as playing a major role in the development of autoimmune disorders and neurodegeneration, with multiple sclerosis (MS) Alzheimer's disease (AD) being primary examples. Hence, it is important to identify the key regulatory mechanisms involved in the control of CNS innate immunity and which could be harnessed to explore novel therapeutic avenues. Neuroimmune regulatory proteins (NIReg) such as CD95L, CD200, CD47, sialic acid, complement regulatory proteins (CD55, CD46, fH, C3a), HMGB1, may control the adverse immune responses in health and diseases. In the absence of these regulators, when neurons die by apoptosis, become infected or damaged, microglia and infiltrating immune cells are free to cause injury as well as an adverse inflammatory response in acute and chronic settings. We will herein provide new emphasis on the role of the pair CD200-CD200R in MS and its experimental models: experimental autoimmune encephalomyelitis (EAE) and Theiler’s virus induced demyelinating disease (TMEV-IDD). The interest of the cannabinoid system as inhibitor of inflammation prompt us to introduce our findings about the role of endocannabinoids (eCBs) in promoting CD200-CD200 receptor (CD200R) interaction and the benefits caused in TMEV-IDD. Finally, we also review the current data on CD200-CD200R interaction in AD, as well as, in the aging brain.

Microglia activation in a model of retinal degeneration and TUDCA neuroprotective effects

Background

Retinitis pigmentosa is a heterogeneous group of inherited neurodegenerative retinal disorders characterized by a progressive peripheral vision loss and night vision difficulties, subsequently leading to central vision impairment. Chronic microglia activation is associated with various neurodegenerative diseases including retinitis pigmentosa. The objective of this study was to quantify microglia activation in the retina of P23H rats, an animal model of retinitis pigmentosa, and to evaluate the therapeutic effects of TUDCA (tauroursodeoxycholic acid), which has been described as a neuroprotective compound.

Methods

For this study, homozygous P23H line 3 and Sprague-Dawley (SD) rats were injected weekly with TUDCA (500 mg/kg, ip) or vehicle (saline) from 20 days to 4 months old. Vertical retinal sections and whole-mount retinas were immunostained for specific markers of microglial cells (anti-CD11b, anti-Iba1 and anti-MHC-II). Microglial cell morphology was analyzed and the number of retinal microglial was quantified.

Results

Microglial cells in the SD rat retinas were arranged in regular mosaics homogenously distributed within the plexiform and ganglion cell layers. In the P23H rat retina, microglial cells increased in number in all layers compared with control SD rat retinas, preserving the regular mosaic distribution. In addition, a large number of amoeboid CD11b-positive cells were observed in the P23H rat retina, even in the subretinal space. Retinas of TUDCA-treated P23H animals exhibited lower microglial cell number in all layers and absence of microglial cells in the subretinal space.

Conclusions

These results report novel TUDCA anti-inflammatory actions, with potential therapeutic implications for neurodegenerative diseases, including retinitis pigmentosa.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Microfluidic chemotaxis platform for differentiating the roles of soluble and bound amyloid-β on microglial accumulation

Progressive microglial accumulation at amyloid-β (Aβ) plaques is a well-established signature of the pathology of Alzheimer's disease, but how and why microglia accumulate in the vicinity of Aβ plaques is unknown. To understand the distinct roles of Aβ on microglial accumulation, we quantified microglial responses to week-long lasting gradients of soluble Aβ and patterns of surface-bound Aβ in microfluidic chemotaxis platforms. We found that human microglia chemotaxis in gradients of soluble Aβ₄₂ was most effective at two distinct concentrations of 23 pg.mL⁻¹ and 23 ng.mL⁻¹Aβ₄₂ in monomers and oligomers. We uncovered that while the chemotaxis at higher Aβ concentrations was exclusively due to Aβ gradients, chemotaxis at lower concentrations was enhanced by Aβ-induced microglial production of MCP-1. Microglial migration was inhibited by surface-bound Aβ₄₂ in oligomers and fibrils above 45 pg.mm⁻². Better understanding of microglial migration can provide insights into the pathophysiology of senile plaques in AD.

The microglial sensome revealed by direct RNA sequencing

Microglia, the principal neuroimmune sentinels of the brain, continuously sense changes in their environment and respond to invading pathogens, toxins and cellular debris. Microglia exhibit plasticity and can assume neurotoxic or neuroprotective priming states that determine their responses to danger. We used direct RNA sequencing, without amplification or cDNA synthesis, to determine the quantitative transcriptomes of microglia of healthy adult and aged mice. We validated our findings using fluorescence dual in situ hybridization, unbiased proteomic analysis and quantitative PCR. We found that microglia have a distinct transcriptomic signature and express a unique cluster of transcripts encoding proteins for sensing endogenous ligands and microbes that we refer to as the sensome. With aging, sensome transcripts for endogenous ligand recognition were downregulated, whereas those involved in microbe recognition and host defense were upregulated. In addition, aging was associated with an overall increase in the expression of microglial genes involved in neuroprotection.

Endogenously regulated Dab2 worsens inflammatory injury in experimental autoimmune encephalomyelitis

Background

Neuroinflammation regulates both disease pathogenesis and repair in multiple sclerosis. In early multiple sclerosis lesion development, neuroinflammation causes demyelination and axonal injury, the likely final common determinant of disability. Here we report the identification of a novel neuroinflammatory mediator, Disabled-2 (Dab2). Dab2 is an intracellular adaptor protein with previously unknown function in the central nervous system.

Results

We report that Dab2 is up-regulated in lesional macrophages/microglia in the spinal cord in murine experimental autoimmune encephalomyelitis, a model of multiple sclerosis. We demonstrate that dab2 expression is positively correlated with experimental autoimmune encephalomyelitis disease severity during the acute disease phase. Furthermore, dab2-deficient mice have a less severe experimental autoimmune encephalomyelitis disease course and suffer less neuroinflammation and less axonal injury than their wild-type littermates. We demonstrate that dab2 expression is strongly associated with the expression of inducible nitric oxide synthase. We further demonstrate that Dab2 is expressed at the protein level by macrophages in early acute human multiple sclerosis lesions and that this correlates with axonal injury.

Conclusions

Together, these results suggest that endogenous Dab2 exacerbates central nervous system inflammation, potentially acting to up-regulate reactive oxygen species expression in macrophages and microglia, and that it is of potential pathogenic relevance in Multiple Sclerosis.

Inflammation in Alzheimer disease-a brief review of the basic science and clinical literature

Biochemical and neuropathological studies of brains from individuals with Alzheimer disease (AD) provide clear evidence for an activation of inflammatory pathways, and long-term use of anti-inflammatory drugs is linked with reduced risk to develop the disease. As cause and effect relationships between inflammation and AD are being worked out, there is a realization that some components of this complex molecular and cellular machinery are most likely promoting pathological processes leading to AD, whereas other components serve to do the opposite. The challenge will be to find ways of fine tuning inflammation to delay, prevent, or treat AD.

Microglia and monocyte-derived macrophages: functionally distinct populations that act in concert in CNS plasticity and repair

Functional macrophage heterogeneity is recognized outside the central nervous system (CNS), where alternatively activated macrophages can perform immune-resolving functions. Such functional heterogeneity was largely ignored in the CNS, with respect to the resident microglia and the myeloid-derived cells recruited from the blood following injury or disease, previously defined as blood-derived microglia; both were indistinguishably perceived detrimental. Our studies have led us to view the myeloid-derived infiltrating cells as functionally distinct from the resident microglia, and accordingly, to name them monocyte-derived macrophages (mo-MΦ). Although microglia perform various maintenance and protective roles, under certain conditions when they can no longer provide protection, mo-MΦ are recruited to the damaged CNS; there, they act not as microglial replacements but rather assistant cells, providing activities that cannot be timely performed by the resident cells. Here, we focus on the functional heterogeneity of microglia/mo-MΦ, emphasizing that, as opposed to the mo-MΦ, microglia often fail to timely acquire the phenotype essential for CNS repair.

Targeting metabotropic glutamate receptors in neuroimmune communication

L-Glutamate (L-Glu) is the principal excitatory neurotransmitter in the Central Nervous System (CNS), where it regulates cellular and synaptic activity, neuronal plasticity, cell survival and other relevant functions. Glutamatergic neurotransmission is complex and involves both ionotropic (ligand-gated ion channels; iGluRs) and metabotropic receptors (G-protein coupled receptors). Recent evidence suggests that glutamatergic receptors are also expressed by immune cells, regulating the degree of cell activation. In this review we primarily focus on mGluRs and their role in the crosstalk between the central nervous and immune systems during neuroinflammation.

Immune system in the brain: a modulatory role on dendritic spine morphophysiology?

The central nervous system is closely linked to the immune system at several levels. The brain parenchyma is separated from the periphery by the blood brain barrier, which under normal conditions prevents the entry of mediators such as activated leukocytes, antibodies, complement factors, and cytokines. The myeloid cell lineage plays a crucial role in the development of immune responses at the central level, and it comprises two main subtypes: (1) resident microglia, distributed throughout the brain parenchyma; (2) perivascular macrophages located in the brain capillaries of the basal lamina and the choroid plexus. In addition, astrocytes, oligodendrocytes, endothelial cells, and, to a lesser extent, neurons are implicated in the immune response in the central nervous system. By modulating synaptogenesis, microglia are most specifically involved in restoring neuronal connectivity following injury. These cells release immune mediators, such as cytokines, that modulate synaptic transmission and that alter the morphology of dendritic spines during the inflammatory process following injury. Thus, the expression and release of immune mediators in the brain parenchyma are closely linked to plastic morphophysiological changes in neuronal dendritic spines. Based on these observations, it has been proposed that these immune mediators are also implicated in learning and memory processes.

Intravenous administration of human embryonic stem cell-derived neural precursor cells attenuates cuprizone-induced central nervous system (CNS) demyelination

AIMS

Previous studies have demonstrated the therapeutic potential for human embryonic stem cell-derived neural precursor cells (hES-NPCs) in autoimmune and genetic animal models of demyelinating diseases. Herein, we tested whether intravenous (i.v.) administration of hES-NPCs would impact central nervous system (CNS) demyelination in a cuprizone model of demyelination.

METHODS

C57Bl/6 mice were fed cuprizone (0.2%) for 2 weeks and then separated into two groups that either received an i.v. injection of hES-NPCs or i.v. administration of media without these cells. After an additional 2 weeks of dietary cuprizone treatment, CNS tissues were analysed for detection of transplanted cells and differences in myelination in the region of the corpus callosum (CC).

RESULTS

Cuprizone-induced demyelination in the CC was significantly reduced in mice treated with hES-NPCs compared with cuprizone-treated controls that did not receive stem cells. hES-NPCs were identified within the brain tissues of treated mice and revealed migration of transplanted cells into the CNS. A limited number of human cells were found to express the mature oligodendrocyte marker, O1, or the astrocyte marker, glial fibrillary acidic protein. Reduced apoptosis and attenuated microglial and astrocytic responses were also observed in the CC of hES-NPC-treated mice.

CONCLUSIONS

These findings indicated that systemically administered hES-NPCs migrated from circulation into a demyelinated lesion within the CNS and effectively reduced demyelination. Observed reductions in astrocyte and microglial responses, and the benefit of hES-NPC treatment in this model of myelin injury was not obviously accountable to tissue replacement by exogenously administered cells.

Inhibition of TLR ligand- and interferon gamma-induced murine microglial activation by Panax notoginseng

Among the many products which influence microglial activation and resulting neuroinflammation, herbal medicine has recently drawn much attention due to its immunomodulatory and neuroprotective activities. The purpose of the current study was to investigate the effects of an extract of Panax notoginseng (NotoG™) on TLR ligand- and IFNγ-induced activation in N9 and EOC20 microglial cells lines. NotoG suppressed microglial activation as measured by reduced expression of accessory molecules (CD40 and CD86), decreased production of inflammatory mediators (IL-6 and TNFα), and diminished release of antibacterial products (nitric oxide). Furthermore, this immunosuppressive activity was neither dependent on the glucocorticoid receptor, nor the result of a single ginsenosides (Rb1, Rg1, or Re), which are the major active constituents of the whole extract. NotoG and select ginsenosides may therefore be of therapeutic benefit in treating or preventing neurodegenerative diseases such as multiple sclerosis and parkinson's disease.

Cannabinoid CB1 receptors regulate neuronal TNF-α effects in experimental autoimmune encephalomyelitis

Cannabinoid CB1 receptors (CB1Rs) regulate the neurodegenerative damage of experimental autoimmune encephalomyelitis (EAE) and of multiple sclerosis (MS). The mechanism by which CB1R stimulation exerts protective effects is still unclear. Here we show that pharmacological activation of CB1Rs dampens the tumor necrosis factor α (TNFα)-mediated potentiation of striatal spontaneous glutamate-mediated excitatory postsynaptic currents (EPSCs), which is believed to cogently contribute to the inflammation-induced neurodegenerative damage observed in EAE mice. Furthermore, mice lacking CB1Rs showed a more severe clinical course and, in parallel, exacerbated alterations of sEPSC duration after induction of EAE, indicating that endogenous cannabinoids activate CB1Rs and mitigate the synaptotoxic action of TNFα in EAE. Consistently, we found that mice lacking the fatty acid amide hydrolase (FAAH), and thus expressing abnormally high brain levels of the endocannabinoid anandamide, developed a less severe EAE associated with preserved TNFα-induced sEPSC alterations. CB1Rs are important modulators of EAE pathophysiology, and might play a mechanistic role in the neurodegenerative damage of MS patients.

Inhibition of lipopolysaccharide-induced microglia activation by calcitonin gene related peptide and adrenomedullin

Calcitonin gene related peptide (CGRP) and adrenomedullin are potent biologically active peptides that have been proposed to play an important role in vascular and inflammatory diseases. Their function in the central nervous system is still unclear since they have been proposed as either pro-inflammatory or neuroprotective factors. We investigated the effects of the two peptides on astrocytes and microglia, cells of the central nervous system that exert a strong modulatory activity in the neuroinflammatory processes. In particular, we studied the ability of CGRP and adrenomedullin to modulate microglia activation, i.e. its competence of producing and releasing pro-inflammatory cytokines/chemokines that are known to play a crucial role in neuroinflammation. In this work we show that the two neuropeptides exert a potent inhibitory effect on lipopolysaccharide-induced microglia activation in vitro, with strong inhibition of the release of pro-inflammatory mediators (such as NO, cytokines and chemokines). Both CGRP and adrenomedullin are known to promote cAMP elevation, this second messenger cannot fully account for the observed inhibitory effects, thereby suggesting that other signaling pathways are involved. Interestingly, the inhibitory effect of CGRP and adrenomedullin appears to be stimulus specific, since direct activation with pro-inflammatory cytokines was not affected. Our findings clarify aspects of microglia activation, and contribute to the comprehension of the switch from reparative to detrimental function that occurs when glia is exposed to different conditions. Moreover, they draw the attention to potential targets for novel pharmacological intervention in pathologies characterized by glia activation and neuroinflammation.

Bilirubin injury to neurons and glial cells: new players, novel targets, and newer insights

Encephalopathy by hyperbilirubinemia in infants has been described for decades, but neither the underlying cellular and molecular mechanisms nor the selective pattern of bilirubin deposition in the brain is well understood. The brain is composed of highly specialized and diverse populations of cells, represented by neurons and glia that comprise astrocytes, oligodendrocytes, and microglia. Although microscopic evaluation of icteric brain sections revealed bilirubin within neurons, neuronal processes, and microglia, cell dependent-sensitivity to bilirubin toxicity and the role of each nerve cell type are poorly understood. Even less considered are glial and neuronal pathologic alterations as integrated phenomena. The available knowledge on reactivity of glial cells to bilirubin and on the impairment to neuronal network dynamics that it causes, here summarized, suggests that a better comprehension of the interplay between neurons and glia is essential to understand bilirubin neurotoxicity and highlight potential molecular targets that may lead to disease-modifying therapeutic approaches.

The mechanism of action of interferon-β in relapsing multiple sclerosis

Multiple sclerosis (MS) is characterized by autoimmune inflammation and subsequent neurodegeneration. It is believed that early in the disease course, proinflammatory T cells that are activated in the periphery by antigen presentation cross the blood-brain barrier (BBB) into the CNS directed by various chemotaxic agents. However, to date, there has been no formal demonstration of a specific precipitating antigen. Once inside the CNS, activated T cells including T helper-1 (T(h)1), T(h)17, γδ and CD8+ types are believed to secrete proinflammatory cytokines. Decreased levels of T(h)2 cells also correlate with relapses and disease progression in MS, since T(h)2-derived cytokines are predominantly anti-inflammatory. In healthy tissue, inflammatory effects are opposed by specific subsets of regulatory T cells (T(regs)) including CD4+, CD25+ and FoxP3+ cells that have the ability to downregulate the activity of proinflammatory T cells, allowing repair and recovery to generally follow inflammatory insult. Given their function, the pathogenesis of MS most likely involves deficits of T(reg) function, which allow autoimmune inflammation and resultant neurodegeneration to proceed relatively unchecked. Interferons (IFNs) are naturally occurring cytokines possessing a wide range of anti-inflammatory properties. Recombinant forms of IFNβ are widely used as first-line treatment in relapsing forms of MS. The mechanism of action of IFNβ is complex, involving effects at multiple levels of cellular function. IFNβ appears to directly increase expression and concentration of anti-inflammatory agents while downregulating the expression of proinflammatory cytokines. IFNβ treatment may reduce the trafficking of inflammatory cells across the BBB and increase nerve growth factor production, leading to a potential increase in neuronal survival and repair. IFNβ can also increase the number of CD56bright natural killer cells in the peripheral blood. These cells are efficient producers of anti-inflammatory mediators, and may have the ability to curb neuron inflammation. The mechanistic effects of IFNβ manifest clinically as reduced MRI lesion activity, reduced brain atrophy, increased time to reach clinically definite MS after the onset of neurological symptoms, decreased relapse rate and reduced risk of sustained disability progression. The mechanism of action of IFNβ in MS is multifactorial and incompletely understood. Ongoing and future studies will increase our understanding of the actions of IFNβ on the immune system and the CNS, which will in turn aid advances in the management of MS.