Tumor necrosis factor alpha mediates lipopolysaccharide-induced microglial toxicity to developing oligodendrocytes when astrocytes are present

Interaction of microglia with the microenvironment in spinal cord injury

This article discusses the peculiarities of microglia behaviour and their interaction with other cells of the central nervous system (CNS) during neural tissue injury with a focus on spinal cord injury (SCI). Taking into account the plasticity of microglia, the influence of the microenvironment should be taken into account to establish the mechanisms determining the polarization pathways of these cells. Determination of the system of microglia interactions with other CNS cells during injury will reveal the patterns of post-traumatic microglia responses, in particular, determining both pro-inflammatory and anti-inflammatory responses. This review compiles information on changes in microglia activation, migration and phagocytosis, as well as their reciprocal effects on other CNS cells, such as neurons, astrocytes and oligodendrocytes, in the background of SCI. The information contained in this article may be of interest not only to scientists studying traumatic injuries of the central nervous system, but also to specialists in the field of studying and treating neurodegenerative diseases, since the mechanisms occurring in the injured spinal cord may also be characteristic of pathological events in degenerative processes.

Botulinum neurotoxin serotype A inhibited ocular angiogenesis through modulating glial activation via SOCS3

BACKGROUND

Pathological angiogenesis causes significant vision loss in neovascular age-related macular degeneration and other retinopathies with neovascularization (NV). Neuronal/glial-vascular interactions influence the release of angiogenic and neurotrophic factors. We hypothesized that botulinum neurotoxin serotype A (BoNT/A) modulates pathological endothelial cell proliferation through glial cell activation and growth factor release.

METHODS

A laser-induced choroidal NV (CNV) was employed to investigate the anti-angiogenic effects of BoNT/A. Fundus fluorescence angiography, immunohistochemistry, and real-time PCR were used to assess BoNT/A efficacy in inhibiting CNV and the molecular mechanisms underlying this inhibition. Neuronal and glial suppressor of cytokine signaling 3 (SOCS3) deficient mice were used to investigate the molecular mechanisms of BoNT/A in inhibiting CNV via SOCS3.

FINDINGS

In laser-induced CNV mice with intravitreal BoNT/A treatment, CNV lesions decreased > 30%; vascular leakage and retinal glial activation were suppressed; and Socs3 mRNA expression was induced while vascular endothelial growth factor A (Vegfa) mRNA expression was suppressed. The protective effects of BoNT/A on CNV development were diminished in mice lacking neuronal/glial SOCS3.

CONCLUSION

BoNT/A suppressed laser-induced CNV and glial cell activation, in part through SOCS3 induction in neuronal/glial cells. BoNT/A treatment led to a decrease of pro-angiogenic factors, including VEGFA, highlighting the potential of BoNT/A as a therapeutic intervention for pathological angiogenesis in retinopathies.

Brain incoming call from glia during neuroinflammation: Roles of extracellular vesicles

The functionality of the central nervous system (CNS) relies on the connection, integration, and the exchange of information among neural cells. The crosstalk among glial cells and neurons is pivotal for a series of neural functions, such as development of the nervous system, electric conduction, synaptic transmission, neural circuit establishment, and brain homeostasis. Glial cells are crucial players in the maintenance of brain functionality in physiological and disease conditions. Neuroinflammation is a common pathological process in various brain disorders, such as neurodegenerative diseases, and infections. Glial cells, including astrocytes, microglia, and oligodendrocytes, are the main mediators of neuroinflammation, as they can sense and respond to brain insults by releasing pro-inflammatory or anti-inflammatory factors. Recent evidence indicates that extracellular vesicles (EVs) are pivotal players in the intercellular communication that underlies physiological and pathological processes. In particular, glia-derived EVs play relevant roles in modulating neuroinflammation, either by promoting or inhibiting the activation of glial cells and neurons, or by facilitating the clearance or propagation of pathogenic proteins. The involvement of EVs in neurodegenerative diseases such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Huntington's Disease (HD), and Multiple Sclerosis (MS)- which share hallmarks such as neuroinflammation and oxidative stress to DNA damage, alterations in neurotrophin levels, mitochondrial impairment, and altered protein dynamics- will be dissected, showing how EVs act as pivotal cell-cell mediators of toxic stimuli, thereby propagating degeneration and cell death signaling. Thus, this review focuses on the EVs secreted by microglia, astrocytes, oligodendrocytes and in neuroinflammatory conditions, emphasizing on their effects on neurons and on central nervous system functions, considering both their beneficial and detrimental effects.

Oligodendrocytes in central nervous system diseases: the effect of cytokine regulation

Cytokines including tumor necrosis factor, interleukins, interferons, and chemokines are abundantly produced in various diseases. As pleiotropic factors, cytokines are involved in nearly every aspect of cellular functions such as migration, survival, proliferation, and differentiation. Oligodendrocytes are the myelin-forming cells in the central nervous system and play critical roles in the conduction of action potentials, supply of metabolic components for axons, and other functions. Emerging evidence suggests that both oligodendrocytes and oligodendrocyte precursor cells are vulnerable to cytokines released under pathological conditions. This review mainly summarizes the effects of cytokines on oligodendrocyte lineage cells in central nervous system diseases. A comprehensive understanding of the effects of cytokines on oligodendrocyte lineage cells contributes to our understanding of central nervous system diseases and offers insights into treatment strategies.

Virtual screening, molecular docking, MD simulation studies, DFT calculations, ADMET, and drug likeness of Diaza-adamantane as potential MAPKERK inhibitors

Introduction: Multiple sclerosis (MS) is an autoimmune and inflammatory disease that destroys the protective coating of central nervous system (CNS) nerve fibers and affects over 2.8 million people worldwide. Despite several studies on new therapeutic targets and lead compounds, MS disease has limited treatment options. This condition may be caused by a complicated interaction of environmental and genetic variables. Studies showed that MS-associated microglial cells' increased MAPKERK activity may cause CNS inflammation and oligodendrocyte damage. Thus, screening for lead compounds that inhibit MAPKERK may protect brain cells and slow disease progression. Methods: The study aims to discover compounds that may inhibit MAPKERK as a novel approach for protecting the nervous system in managing MS. The study includes in silico methods, such as virtual screening, molecular docking, Density-functional theory (DFT) investigations (using the B3LYP/6-31++G(d,p) basis set in a gas phase environment), drug likeness scores, and molecular dynamic (MD) simulations. Results and Discussion:During the docking process with the MAPKERK protein, it was shown that the ligand L12 receptor had the best binding affinity, with a docking score of -6.18 kcal/mol. To investigate the stability of the binding, a 100 ns MD simulation was performed on the complex formed by the MAPKERK protein and L12. The receptor-ligand combination exhibited significant stability throughout the duration of the MD simulation. Additionally, the pharmacokinetic and drug-likeness properties of these ligands suggest that they have the potential to be considered viable candidates for future development in MS management.

Modeling demyelination and endogenous remyelination in spinal cord ex vivo rat organotypic slice cultures

Introduction

Demyelination of the spinal cord is a prominent feature of multiple sclerosis (MS) and spinal cord injuries (SCI), where impaired neuronal communication between the brain and periphery has devastating consequences on neurological function. Demyelination precedes remyelination, an endogenous process in which oligodendrocyte precursor cells (OPCs) differentiate into mature, myelinating oligodendrocytes with the ability to restore the myelin sheath and reinstate functional nerve signaling. However, in MS or SCI, demyelination is more severe, persistent, and inhibitory to OPC-mediated remyelination, leading to a permanent loss of neuronal function. Currently, there are no effective treatments for demyelination, and existing pre-clinical models typically focus on brain tissue with little characterization of demyelination within the spinal cord. Organotypic slice cultures are a useful tool to study neurological disease, providing a more complex 3-dimensional system than standard 2-dimensional in vitro cell cultures.

Methods

Building on our previously developed rat brain slice culture protocol, we have extended our findings to develop a rat longitudinal spinal cord ex vivo model of demyelination.

Results

We generated rat longitudinal spinal cord slice cultures that remain viable for up to 6 weeks in culture and retain key anatomical features of the spinal cord's cytoarchitecture. We show that treating longitudinal spinal cord slices with lysolecithin (LPC) induced robust demyelination with some endogenous remyelination, which was not seen following exposure to lipopolysaccharide (LPS).

Discussion

Our ex vivo organotypic spinal cord slice culture system provides a platform to model demyelination and endogenous remyelination long-term, mimicking that observed in LPC-induced rodent models of demyelination. This platform is suitable for the development and testing of novel therapeutic strategies with ease of manipulation prior to in vivo experimentation.

Journey from lab to clinic: Design, preclinical, and clinical development of systemic, targeted dendrimer-N-acetylcysteine (D-NAC) nanomedicines

Drug discovery is challenging task with numerous obstacles in translating drug candidates into clinical products. Dendrimers are highly adaptable nanostructured polymers with significant potential to improve the chances of clinical success for drugs. Yet, dendrimer-based drug products are still in their infancy. However, Hydroxyl polyamidoamine (PAMAM) dendrimers showed significant promise in drug discovery efforts, owning their remarkable potential to selectively target and deliver drugs specifically to activated microglia and astrocytes at the site of brain injury in several preclinical models. After a decade's worth of academic research and pre-clinical efforts, the hydroxyl PAMAM dendrimer-N-acetyl cysteine conjugate (OP-101) nanomedicine has made a significant advancement in the field of nanomedicine and targeted delivery. The OP-101 conjugate, primarily developed and validated in academic labs, has now entered clinical trials as a potential treatment for hyperinflammation in hospitalized adults with severe COVID-19 through Ashvattha Therapeutics. This chapter, we delve into the journey of the hydroxyl PAMAM dendrimer-N-acetylcysteine (NAC) OP-101 formulation from the laboratory to the clinic. It will specifically focus on the design, synthesis, preclinical, and clinical development of OP-101, highlighting the potential it holds for the future of medicine and the positive Phase 2a results for treating severe COVID-19.

Dynamics of myelin deficits in the 5xFAD mouse model for Alzheimer's disease and the protective role of BDNF

Recent findings highlight myelin breakdown as a decisive early event in Alzheimer's Disease (AD) acting as aggravating factor of its progression. However, it is still unclear whether myelin loss is attributed to increased oligodendrocyte vulnerability, reduced repairing capacity or toxic stimuli. In the present study, we sought to clarify the starting point of myelin disruption accompanied with Oligodendrocyte Progenitor Cell (OPC) elimination in the brain of the 5xFAD mouse model of AD at 6 months of age in Dentate Gyrus of the hippocampus in relation to neurotrophin system. Prominent inflammation presence was detected since the age of 6 months playing a key role in myelin disturbance and AD progression. Expression analysis of neurotrophin receptors in OPCs was performed to identify new targets that could increase myelination in health and disease. OPCs in both control and 5xFAD mice express TrkB, TrkC and p75 receptors but not TrkA. Brain-derived neurotrophic factor (BDNF) that binds to TrkB receptor is well-known about its pro-myelination effect, promoting oligodendrocytes proliferation and differentiation, so we focused our investigation on its effects in OPCs under neurodegenerative conditions. Our in vitro results showed that BDNF rescues OPCs from death and promotes their proliferation and differentiation in presence of the toxic Amyloid-β 1-42. Collectively, our results indicate that BDNF possess an additional neuroprotective role through its actions on oligodendrocytic component and its use could be proposed as a drug-based myelin-enhancing strategy, complementary to amyloid and tau centered therapies in AD.

Exploring the heterogeneous transcriptional response of the CNS to systemic LPS and Poly(I:C)

Peripheral contact to pathogen-associated molecular patterns (PAMPs) evokes a systemic innate immune response which is rapidly relayed to the central nervous system (CNS). The remarkable cellular heterogeneity of the CNS poses a significant challenge to the study of cell type and stimulus dependent responses of neural cells during acute inflammation. Here we utilized single nuclei RNA sequencing (snRNAseq), serum proteome profiling and primary cell culture methods to systematically compare the acute response of the mammalian brain to the bacterial PAMP lipopolysaccharide (LPS) and the viral PAMP polyinosinic:polycytidylic acid (Poly(I:C)), at single cell resolution. Our study unveiled convergent transcriptional cytokine and cellular stress responses in brain vascular and ependymal cells and a downregulation of several key mediators of directed blood brain barrier (BBB) transport. In contrast the neuronal response to PAMPs was limited in acute neuroinflammation. Moreover, our study highlighted the dominant role of IFN signalling upon Poly(I:C) challenge, particularly in cells of the oligodendrocyte lineage. Collectively our study unveils heterogeneous, shared and distinct cell type and stimulus dependent acute responses of the CNS to bacterial and viral PAMP challenges. Our findings highlight inflammation induced dysregulations of BBB-transporter gene expression, suggesting potential translational implications on drug pharmacokinetics variability during acute neuroinflammation. The pronounced dependency of oligodendrocytes on IFN stimulation during viral PAMP challenges, emphasizes their limited molecular viral response repertoire.

An early glycolysis burst in microglia regulates mitochondrial dysfunction in oligodendrocytes under neuroinflammation

Metabolism and energy processes governing oligodendrocyte function during neuroinflammatory disease are of great interest. However, how varied cellular environments affect oligodendrocyte activity during neuroinflammation is unknown. We demonstrate that activated microglial energy metabolism controls oligodendrocyte mitochondrial respiration and activity. Lipopolysaccharide/interferon gamma promote glycolysis and decrease mitochondrial respiration and myelin protein synthesis in rat brain glial cells. Enriched microglia showed an early burst in glycolysis. In microglia-conditioned medium, oligodendrocytes did not respire and expressed less myelin. SCENITH revealed metabolic derangement in microglia and O4-positive oligodendrocytes in endotoxemia and experimental autoimmune encephalitogenic models. The early burst of glycolysis in microglia was mediated by PDPK1 and protein kinase B/AKT signaling. We found that microglia-produced NO and itaconate, a tricarboxylic acid bifurcated metabolite, reduced mitochondrial respiration in oligodendrocytes. During inflammation, we discovered a signaling pathway in microglia that could be used as a therapeutic target to restore mitochondrial function in oligodendrocytes and induce remyelination.

Chronic oligodendrocyte injury in central nervous system pathologies

Myelin, the membrane surrounding neuronal axons, is critical for central nervous system (CNS) function. Injury to myelin-forming oligodendrocytes (OL) in chronic neurological diseases (e.g. multiple sclerosis) ranges from sublethal to lethal, leading to OL dysfunction and myelin pathology, and consequent deleterious impacts on axonal health that drive clinical impairments. This is regulated by intrinsic factors such as heterogeneity and age, and extrinsic cellular and molecular interactions. Here, we discuss the responses of OLs to injury, and perspectives for therapeutic targeting. We put forward that targeting mature OL health in neurological disease is a promising therapeutic strategy to support CNS function.

Molecular Signature of Neuroinflammation Induced in Cytokine-Stimulated Human Cortical Spheroids

Crucial in the pathogenesis of neurodegenerative diseases is the process of neuroinflammation that is often linked to the pro-inflammatory cytokines Tumor necrosis factor alpha (TNFα) and Interleukin-1beta (IL-1β). Human cortical spheroids (hCSs) constitute a valuable tool to study the molecular mechanisms underlying neurological diseases in a complex three-dimensional context. We recently designed a protocol to generate hCSs comprising all major brain cell types. Here we stimulate these hCSs for three time periods with TNFα and with IL-1β. Transcriptomic analysis reveals that the main process induced in the TNFα- as well as in the IL-1β-stimulated hCSs is neuroinflammation. Central in the neuroinflammatory response are endothelial cells, microglia and astrocytes, and dysregulated genes encoding cytokines, chemokines and their receptors, and downstream NFκB- and STAT-pathway components. Furthermore, we observe sets of neuroinflammation-related genes that are specifically modulated in the TNFα-stimulated and in the IL-1β-stimulated hCSs. Together, our results help to molecularly understand human neuroinflammation and thus a key mechanism of neurodegeneration.

PSB0788 ameliorates maternal inflammation-induced periventricular leukomalacia-like injury

Studies have shown that periventricular leukomalacia (PVL) is a distinctive form of cerebral white matter injury that pertains to myelination disturbances. Maternal inflammation is a main cause of white matter injury. Intrauterine inflammation cellular will be propagated to the developing brain by the entire maternal-placental-fetal axis, and triggers neural immune injury. As a low-affinity receptor, adenosine A_2B receptor (A_2BAR) requires high concentrations of adenosine to be significantly activated in pathological conditions. We hypothesized that in the maternal inflammation-induced PVL model, a selective A_2BAR antagonist PSB0788 had the potential to prevent the injury. In this work, a total of 18 SD pregnant rats were divided into three groups, and treated with intraperitoneal injection of phosphate buffered saline (PBS), lipopolysaccharide (LPS), or LPS+PSB0788. Placental infection was determined by H&E staining and the inflammatory condition was determined by ELISA. Change of MBP, NG2 and CC-1 in the brain of the rats' offspring were detected by western blot and immunohistochemistry. Furthermore, LPS-induced maternal inflammation reduced the expression of MBP, which related to the decrease in the numbers of OPCs and mature oligodendrocytes in neonate rats. After treatment with PSB0788, the levels of MBP proteins increased in the rats' offspring, improved the remyelination. In conclusion, our study shows that the selective A_2BAR antagonist PSB0788 plays an important role in promoting the normal development of OPCs in vivo by the maternal inflammation-induced PVL model. Future studies will focus on the mechanism of PSB0788 in this model.

Effects Mediated by Dimethyl Fumarate on In Vitro Oligodendrocytes: Implications in Multiple Sclerosis

Background: Dimethyl fumarate (DMF) is a drug currently in use in oral therapy for the treatment of relapsing-remitting multiple sclerosis (RRMS) due to its immunomodulatory and neuroprotective effects. The mechanisms by which DMF exerts its therapeutic effects in MS and in particular its influence on the oligodendrocytes (OLs) survival or differentiation have not yet been fully understood. Methods: Characterization of Oli neu cells was performed by immunocytochemistry and RT-PCR. The effect of DMF on cell proliferation and morphology was assessed by MTT assay, trypan blue staining, RT-PCR and Western blot analysis. The antioxidant and anti-inflammatory properties of DMF were analysed by ROS detection through DCFDA staining and lipid content analysis by Oil Red O staining and TLC. Results: DMF has been observed to induce a slowdown of cell proliferation, favoring the oligodendrocyte lineage cells (OLCs) differentiation. DMF has an antioxidant effect and is able to modify the lipid content even after the LPS-mediated inflammatory stimulus in Oli neu cells. Conclusions: The results obtained confirm that DMF has anti-inflammatory and antioxidant effects also on Oli neu cells. Interestingly, it appears to promote the OLCs differentiation towards mature and potentially myelinating cells.

Platelets, Thromboinflammation and Neurovascular Disease

The brain and spinal cord are immune-privileged organs, but in the disease state protection mechanisms such as the blood brain barrier (BBB) are ineffective or overcome by pathological processes. In neuroinflammatory diseases, microglia cells and other resident immune cells contribute to local vascular inflammation and potentially a systemic inflammatory response taking place in parallel. Microglia cells interact with other cells impacting on the integrity of the BBB and propagate the inflammatory response through the release of inflammatory signals. Here, we discuss the activation and response mechanisms of innate and adaptive immune processes in response to neuroinflammation. Furthermore, the clinical importance of neuroinflammatory mediators and a potential translational relevance of involved mechanisms are addressed also with focus on non-classical immune cells including microglia cells or platelets. As illustrative examples, novel agents such as Anfibatide or Revacept, which result in reduced recruitment and activation of platelets, a subsequently blunted activation of the coagulation cascade and further inflammatory process, demonstrating that mechanisms of neuroinflammation and thrombosis are interconnected and should be further subject to in depth clinical and basic research.

Neuroinflammatory Modulation of Extracellular Vesicle Biogenesis and Cargo Loading

Increasing evidence suggests neuroinflammation is a highly coordinated response involving multiple cell types and utilising several different forms of cellular communication. In addition to the well documented cytokine and chemokine messengers, extracellular vesicles (EVs) have emerged as key regulators of the inflammatory response. EVs act as vectors of intercellular communication, capable of travelling between different cells and tissues to deliver selectively packaged protein, miRNA, and lipids from the parent cell. During neuroinflammation, EVs transmit specific inflammatory mediators, particularly from microglia, to promote inflammatory resolution. This mini-review will highlight the novel neuroinflammatory mechanisms contributing to the biogenesis and selective packaging of EVs.

Central nervous system macrophages in progressive multiple sclerosis: relationship to neurodegeneration and therapeutics

There are over 15 disease-modifying drugs that have been approved over the last 20 years for the treatment of relapsing–remitting multiple sclerosis (MS), but there are limited treatment options available for progressive MS. The development of new drugs for the treatment of progressive MS remains challenging as the pathophysiology of progressive MS is poorly understood.

The progressive phase of MS is dominated by neurodegeneration and a heightened innate immune response with trapped immune cells behind a closed blood–brain barrier in the central nervous system. Here we review microglia and border-associated macrophages, which include perivascular, meningeal, and choroid plexus macrophages, during the progressive phase of MS. These cells are vital and are largely the basis to define lesion types in MS. We will review the evidence that reactive microglia and macrophages upregulate pro-inflammatory genes and downregulate homeostatic genes, that may promote neurodegeneration in progressive MS. We will also review the factors that regulate microglia and macrophage function during progressive MS, as well as potential toxic functions of these cells. Disease-modifying drugs that solely target microglia and macrophage in progressive MS are lacking. The recent treatment successes for progressive MS include include B-cell depletion therapies and sphingosine-1-phosphate receptor modulators. We will describe several therapies being evaluated as a potential treatment option for progressive MS, such as immunomodulatory therapies that can target myeloid cells or as a potential neuroprotective agent.

The roles of microglia and astrocytes in phagocytosis and myelination: Insights from the cuprizone model of multiple sclerosis

In human demyelinating diseases such as multiple sclerosis (MS), an imbalance between demyelination and remyelination can trigger progressive degenerative processes. The clearance of myelin debris (phagocytosis) from the site of demyelination by microglia is critically important to achieve adequate remyelination and to slow the progression of the disease. However, how microglia phagocytose the myelin debris, and why clearance is impaired in MS, is not fully known; likewise, the role of the microglia in remyelination remains unclear. Recent studies using cuprizone (CPZ) as an animal model of central nervous system demyelination revealed that the up‐regulation of signaling proteins in microglia facilitates effective phagocytosis of myelin debris. Moreover, during demyelination, protective mediators are released from activated microglia, resulting in the acceleration of remyelination in the CPZ model. In contrast, inadequate microglial activation or recruitment to the site of demyelination, and the production of toxic mediators, impairs remyelination resulting in progressive demyelination. In addition to the microglia‐mediated phagocytosis, astrocytes play an important role in the phagocytic process by recruiting microglia to the site of demyelination and producing regenerative mediators. The current review is an update of these emerging findings from the CPZ animal model, discussing the roles of microglia and astrocytes in phagocytosis and myelination.

A peripheral lipid sensor GPR120 remotely contributes to suppression of PGD2-microglia-provoked neuroinflammation and neurodegeneration in the mouse hippocampus

BACKGROUND

Neuroinflammation is a key pathological component of neurodegenerative disease and is characterized by microglial activation and the secretion of proinflammatory mediators. We previously reported that a surge in prostaglandin D₂ (PGD₂) production and PGD₂-induced microglial activation could provoke neuroinflammation. We also reported that a lipid sensor GPR120 (free fatty acid receptor 4), which is expressed in intestine, could be activated by polyunsaturated fatty acids (PUFA), thereby mediating secretion of glucagon-like peptide-1 (GLP-1). Dysfunction of GPR120 results in obesity in both mice and humans.

METHODS

To reveal the relationship between PGD₂-microglia-provoked neuroinflammation and intestinal PUFA/GPR120 signaling, we investigated neuroinflammation and neuronal function with gene and protein expression, histological, and behavioral analysis in GPR120 knockout (KO) mice.

RESULTS

In the current study, we discovered notable neuroinflammation (increased PGD₂ production and microglial activation) and neurodegeneration (declines in neurogenesis, hippocampal volume, and cognitive function) in GPR120 KO mice. We also found that Hematopoietic-prostaglandin D synthase (H-PGDS) was expressed in microglia, microglia were activated by PGD₂, H-PGDS expression was upregulated in GPR120 KO hippocampus, and inhibition of PGD₂ production attenuated this neuroinflammation. GPR120 KO mice exhibited reduced intestinal, plasma, and intracerebral GLP-1 contents. Peripheral administration of a GLP-1 analogue, liraglutide, reduced PGD₂-microglia-provoked neuroinflammation and further neurodegeneration in GPR120 KO mice.

CONCLUSIONS

Our results suggest that neurological phenotypes in GPR120 KO mice are probably caused by dysfunction of intestinal GPR120. These observations raise the possibility that intestinal GLP-1 secretion, stimulated by intestinal GPR120, may remotely contributed to suppress PGD₂-microglia-provoked neuroinflammation in the hippocampus.

Oligodendrocytes and Microglia: Key Players in Myelin Development, Damage and Repair

Oligodendrocytes, the myelin-making cells of the CNS, regulate the complex process of myelination under physiological and pathological conditions, significantly aided by other glial cell types such as microglia, the brain-resident, macrophage-like innate immune cells. In this review, we summarize how oligodendrocytes orchestrate myelination, and especially myelin repair after damage, and present novel aspects of oligodendroglial functions. We emphasize the contribution of microglia in the generation and regeneration of myelin by discussing their beneficial and detrimental roles, especially in remyelination, underlining the cellular and molecular components involved. Finally, we present recent findings towards human stem cell-derived preclinical models for the study of microglia in human pathologies and on the role of microbiome on glial cell functions.

Aiding and Abetting Anhedonia: Impact of Inflammation on the Brain and Pharmacological Implications

Exogenous administration of inflammatory stimuli to humans and laboratory animals and chronic endogenous inflammatory states lead to motivational deficits and ultimately anhedonia, a core and disabling symptom of depression present in multiple other psychiatric disorders. Inflammation impacts neurotransmitter systems and neurocircuits in subcortical brain regions including the ventral striatum, which serves as an integration point for reward processing and motivational decision-making. Many mechanisms contribute to these effects of inflammation, including decreased synthesis, release and reuptake of dopamine, increased synaptic and extrasynaptic glutamate, and activation of kynurenine pathway metabolites including quinolinic acid. Neuroimaging data indicate that these inflammation-induced neurotransmitter effects manifest as decreased activation of ventral striatum and decreased functional connectivity in reward circuitry involving ventral striatum and ventromedial prefrontal cortex. Neurocircuitry changes in turn mediate nuanced effects on motivation that include decreased willingness to expend effort for reward while maintaining the ability to experience reward. Taken together, the data reveal an inflammation-induced pathophysiologic phenotype that is agnostic to diagnosis. Given the many mechanisms involved, this phenotype represents an opportunity for development of novel and/or repurposed pharmacological strategies that target inflammation and associated cellular and systemic immunometabolic changes and their downstream effects on the brain. To date, clinical trials have failed to capitalize on the unique nature of this transdiagnostic phenotype, leaving the field bereft of interpretable data for meaningful clinical application. However, novel trial designs incorporating established targets in the brain and/or periphery using relevant outcome variables (e.g., anhedonia) are the future of targeted therapy in psychiatry. SIGNIFICANCE STATEMENT: Emerging understanding of mechanisms by which peripheral inflammation can affect the brain and behavior has created unprecedented opportunities for development of pharmacological strategies to treat deficits in motivation including anhedonia, a core and disabling symptom of depression well represented in multiple psychiatric disorders. Mechanisms include inflammation and cellular and systemic immunometabolism and alterations in dopamine, glutamate, and kynurenine metabolites, revealing a target-rich environment that nevertheless has yet to be fully exploited by current clinical trial designs and drugs employed.

Multiple sclerosis is linked to MAPKERK overactivity in microglia

Reassessment of published observations in patients with multiple sclerosis (MS) suggests a microglial malfunction due to inappropriate (over)activity of the mitogen-activated protein kinase pathway ERK (MAPK^ERK). These observations regard biochemistry as well as epigenetics, and all indicate involvement of this pathway. Recent preclinical research on neurodegeneration already pointed towards a role of MAPK pathways, in particular MAPK^ERK. This is important as microglia with overactive MAPK have been identified to disturb local oligodendrocytes which can lead to locoregional demyelination, hallmark of MS. This constitutes a new concept on pathophysiology of MS, besides the prevailing view, i.e., autoimmunity. Acknowledged risk factors for MS, such as EBV infection, hypovitaminosis D, and smoking, all downregulate MAPK^ERK negative feedback phosphatases that normally regulate MAPK^ERK activity. Consequently, these factors may contribute to inappropriate MAPK^ERK overactivity, and thereby to neurodegeneration. Also, MAPK^ERK overactivity in microglia, as a factor in the pathophysiology of MS, could explain ongoing neurodegeneration in MS patients despite optimized immunosuppressive or immunomodulatory treatment. Currently, for these patients with progressive disease, no effective treatment exists. In such refractory MS, targeting the cause of overactive MAPK^ERK in microglia merits further investigation as this phenomenon may imply a novel treatment approach.

Harnessing the Benefits of Neuroinflammation: Generation of Macrophages/Microglia with Prominent Remyelinating Properties

Excessive inflammation within the CNS is injurious, but an immune response is also required for regeneration. Macrophages and microglia adopt different properties depending on their microenvironment, and exposure to IL4 and IL13 has been used to elicit repair. Unexpectedly, while LPS-exposed macrophages and microglia killed neural cells in culture, the addition of LPS to IL4/IL13-treated macrophages and microglia profoundly elevated IL10, repair metabolites, heparin binding epidermal growth factor trophic factor, antioxidants, and matrix-remodeling proteases. In C57BL/6 female mice, the generation of M(LPS/IL4/IL13) macrophages required TLR4 and MyD88 signaling, downstream activation of phosphatidylinositol-3 kinase/mTOR and MAP kinases, and convergence on phospho-CREB, STAT6, and NFE2. Following mouse spinal cord demyelination, local LPS/IL4/IL13 deposition markedly increased lesional phagocytic macrophages/microglia, lactate and heparin binding epidermal growth factor, matrix remodeling, oligodendrogenesis, and remyelination. Our data show that a prominent reparative state of macrophages/microglia is generated by the unexpected integration of pro- and anti-inflammatory activation cues. The results have translational potential, as the LPS/IL4/IL13 mixture could be locally applied to a focal CNS injury to enhance neural regeneration and recovery.SIGNIFICANCE STATEMENT The combination of LPS and regulatory IL4 and IL13 signaling in macrophages and microglia produces a previously unknown and particularly reparative phenotype devoid of pro-inflammatory neurotoxic features. The local administration of LPS/IL4/IL13 into spinal cord lesion elicits profound oligodendrogenesis and remyelination. The careful use of LPS and IL4/IL13 mixture could harness the known benefits of neuroinflammation to enable repair in neurologic insults.

TGFα preserves oligodendrocyte lineage cells and improves white matter integrity after cerebral ischemia

Transforming growth factor α (TGF-α) has been reported to play important roles in neurogenesis and angiogenesis in the injured brain. The present study characterizes a novel role for TGFα in oligodendrocyte lineage cell survival and white matter integrity after ischemic stroke. Three days after transient (60 min) middle cerebral artery occlusion (tMCAO), TGFα expression was significantly increased in microglia/macrophages and neurons. Expression of the receptor of TGFα-epidermal growth factor receptor (EGFR)-was increased in glial cells after ischemia, including in oligodendrocyte lineage cells. TGFα knockout enlarged brain infarct volumes and exacerbated cell death in oligodendrocyte precursor cells (OPCs) and oligodendrocytes three days after tMCAO. TGFα-deficient mice displayed long-term exacerbation of sensorimotor deficits after tMCAO, and these functional impairments were accompanied by loss of white matter integrity and impaired oligodendrocyte replacement. In vitro studies confirmed that 5 or 10 ng/mL TGFα directly protected OPCs and oligodendrocytes against oxygen and glucose deprivation (OGD)-induced cell death, but exerted no effects on OPC differentiation. Further studies identified STAT3 as a key transcription factor mediating the effects of TGFα on OPCs and oligodendrocytes. In conclusion, TGFα provides potent oligodendrocyte protection against cerebral ischemia, thereby maintaining white matter integrity and improving neurological recovery after stroke.

Deep rTMS Mitigates Behavioral and Neuropathologic Anomalies in Cuprizone-Exposed Mice Through Reducing Microglial Proinflammatory Cytokines

In comparison to conventional repetitive transcranial magnetic stimulation (rTMS), theta burst stimulation is stronger and more effective as a brain stimulation approach within short periods. Although this deep rTMS technique is being applied in treating neuropsychiatric disorders, few animal studies have attempted to clarify the neurobiological mechanisms underlying its beneficial effects. This animal study examined the effects of deep rTMS on the cuprizone-induced neuropathologic and behavioral anomalies and explored the underlying mechanism. Adolescent male C57BL/6 mice were fed a rodent chow without or with cuprizone (CPZ; 0.2% w/w) for 5 weeks. Another two groups of mice were subjected to deep rTMS or sham rTMS once a day during weeks 2-5 of the CPZ-feeding period. The behaviors of all mice were assessed after the withdrawal of CPZ before neuropathological and immunological analyses. Compared to the CNT group, mice in CPZ and CPZ + Sham groups showed deficits in social recognition and spatial working memory as well as anxiety-like behavior, in addition to myelin breakdown and OL loss in the corpus callosum (CC), caudate putamen, cerebral cortex, and hippocampus of the brain. Deep rTMS effectively reduced behavioral anomalies and blocked myelin breakdown and OL loss in CPZ-fed mice. Besides, it also dampened microglia activation at lesion sites and rectified cytokines levels (IL-1β, IL-6, and IL-10) in CPZ-affected regions. The most significant effect was seen in the cerebral cortex where alleviated neuropathology co-existed with less microglia activation and higher IL-10 level. These data provided experimental evidence for the beneficial effects of deep rTMS in CPZ-fed mice and revealed a neurobiological mechanism of the modality.

Cyclophosphamide-induced cystitis results in NLRP3-mediated inflammation in the hippocampus and symptoms of depression in rats

Recent breakthroughs demonstrate that peripheral diseases can trigger inflammation in the brain, causing psychosocial maladies, including depression. While few direct studies have been made, anecdotal reports associate urological disorders with mental dysfunction. Thus, we investigated if insults targeted at the bladder might elicit behavioral alterations. Moreover, the mechanism of neuroinflammation elicited by other peripheral diseases involves the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, which is present in microglia in the brain and cleaves and activates proinflammatory cytokines such as IL-1β. Thus, we further explored the importance of NLRP3 in behavioral and neuroinflammatory changes. Here, we used the well-studied cyclophosphamide (CP)-treated rat model. Importantly, CP and its metabolites do not cross the blood-brain barrier or trigger inflammation in the gut, so that any neuroinflammation is likely secondary to bladder injury. We found that CP triggered an increase in inflammasome activity (caspase-1 activity) in the hippocampus but not in the pons. Evans blue extravasation demonstrated breakdown of the blood-brain barrier in the hippocampal region and activated microglia were present in the fascia dentata. Both changes were dependent on NLRP3 activation and prevented with 2-mercaptoethane sulfonate sodium (Mesna), which masks the effects of the CP metabolite acrolein in the urine. Finally, CP-treated rats displayed depressive symptoms that were prevented by NLRP3 inhibition or treatment with Mesna or an antidepressant. Thus, we conclude that CP-induced cystitis causes NLRP3-dependent hippocampal inflammation leading to depression symptoms in rats. This study proposes the first-ever causative explanation of the previously anecdotal link between benign bladder disorders and mood disorders.

TNF-α antagonist attenuates systemic lipopolysaccharide-induced brain white matter injury in neonatal rats

Background

Systemic inflammation is an important risk factor for neurodevelopmental impairments in preterm infants. Premyelinating oligodendrocytes are main building blocks of white matter in preterm infants and vulnerable to oxidative stress and excitotoxic stress. Tumour necrosis factor-α (TNF-α) plays important roles in systemic inflammation and local inflammation leading to apoptosis of premyelinating oligodendrocytes and white matter injury (WMI) in brain tissue. This study was conducted to investigate whether etanercept, a TNF-α antagonist, could attenuate systemic lipopolysaccharide (LPS)-induced WMI in the immature brain.

Results

We found that intraperitoneal LPS administration caused systemic and local inflammation in brain tissue. Subsequent etanercept treatment significantly attenuated LPS-induced inflammation in brain tissue as well as in systemic circulation. Intraperitoneal LPS also induced microgliosis and astrocytosis in the cingulum and etanercept treatment reduced LPS-induced microgliosis and astrocytosis. Additionally, systemic LPS-induced apoptosis of oligodendrocyte precursor cells was observed, which was lessened by etanercept treatment. The concentration of etanercept in the CSF was higher when it was administrated with LPS than when administrated with a vehicle.

Conclusions

It appears that etanercept reduce WMI in the neonatal rat brain via attenuation of systemic and local inflammation. This study provides preclinical data suggesting etanercept-mediated modulation of inflammation as a promising approach to reduce WMI caused by sepsis or necrotizing enterocolitis in preterm infants.

Astrocytes in multiple sclerosis and experimental autoimmune encephalomyelitis: Star-shaped cells illuminating the darkness of CNS autoimmunity

Neuropathology in the human autoimmune disease multiple sclerosis (MS) is considered to be mediated by autoreactive leukocytes, such as T cells, B cells, and macrophages. However, the inflammation and tissue damage in MS and its animal model experimental autoimmune encephalomyelitis (EAE) is also critically regulated by astrocytes, the most abundant cell population in the central nervous system (CNS). Under physiological conditions, astrocytes are integral to the development and function of the CNS, whereas in CNS autoimmunity, astrocytes influence the pathogenesis, progression, and recovery of the diseases. In this review, we summarize recent advances in astrocytic functions in the context of MS and EAE, which are categorized into two opposite aspects, one being detrimental and the other beneficial. Inhibition of the detrimental functions and/or enhancement of the beneficial functions of astrocytes might be favorable for the treatment of MS.

Microglia-derived TNF-α mediates endothelial necroptosis aggravating blood brain-barrier disruption after ischemic stroke

Endothelium (EC) is a key component of blood–brain barrier (BBB), and has an important position in the neurovascular unit. Its dysfunction and death after cerebral ischemic/reperfusion (I/R) injury not only promote evolution of neuroinflammation and brain edema, but also increase the risk of intracerebral hemorrhage of thrombolytic therapies. However, the mechanism and specific interventions of EC death after I/R injury are poorly understood. Here we showed that necroptosis was a mechanism underlying EC death, which promoted BBB breakdown after I/R injury. Treatment of rats with receptor interacting protein kinase 1 (RIPK1)-inhibitor, necrostatin-1 reduced endothelial necroptosis and BBB leakage. We furthermore showed that perivascular M1-like microglia-induced endothelial necroptosis leading to BBB disruption requires tumor necrosis factor-α (TNF-α) secreted by M1 type microglia and its receptor, TNF receptor 1 (TNFR1), on endothelium as the primary mediators of these effects. More importantly, anti-TNFα (infliximab, a potent clinically used drug) treatment significantly ameliorate endothelial necroptosis, BBB destruction and improve stroke outcomes. Our data identify a previously unexplored role for endothelial necroptosis in BBB disruption and suggest infliximab might serve as a potential drug for stroke therapy.

Toll-like receptors in the pathogenesis of neuroinflammation

Toll-like receptors (TLRs) are discovered as crucial pattern recognition receptors (PRRs) involved in the recognition of pathogen-associated molecular patterns (PAMPs). Later studies showed their involvement in the recognition of various damage/danger-associated molecular patterns (DAMPs) generated by host itself. Thus, TLRs are capable of recognizing wide-array of patterns/molecules derived from pathogens and host as well and initiating a proinflammatory immune response through the activation of NF-κB and other transcription factors causing synthesis of proinflammatory molecules. The process of neuroinflammation is seen under both sterile and infectious inflammatory diseases of the central nervous system (CNS) and may lead to the development of neurodegeneration. The present article is designed to highlight the importance of TLRs in the pathogenesis of neuroinflammation under diverse conditions. TLRs are expressed by various immune cells present in CNS along with neurons. However out of thirteen TLRs described in mammals, some are present and active in these cells, while some are absent and are described in detail in main text. The role of various immune cells present in the brain and their role in the pathogenesis of neuroinflammation depending on the type of TLR expressed is described. Thereafter the role of TLRs in bacterial meningitis, viral encephalitis, stroke, Alzheimer's disease (AD), Parkinson's disease (PD), and autoimmune disease including multiple sclerosis (MS) is described. The article is designed for both neuroscientists needing information regarding TLRs in neuroinflammation and TLR biologists or immunologists interested in neuroinflammation.

In utero transplantation of neural stem cells ameliorates maternal inflammation-induced prenatal white matter injury

Prenatal white matter injury is a serious problem due to maternal inflammation leading to postnatal disabilities. In this study, we used the periventricular leukomalacia (PVL) model as a common prenatal white matter injury by maternal administration of lipopolysaccharide (LPS). Neural stem cells (NSCs) have shown therapeutic ability in neurological disorders through a different mechanism such as immunomodulation. Here, we studied the preventive potential of NSCs following in utero transplantation into the embryonic lateral ventricle in an LPS-induced white matter injury model. Pregnant animals were divided into three groups and received phosphate buffered saline, LPS, or LPS + NSCs. The brains of offspring were obtained and evaluated by real-time polymerase chain reaction (PCR), immunohistochemy, enzyme-linked immunosorbent assay (ELISA), terminal deoxynucleotidyl transferase-mediated biotinylated-dUTP nick-end labeling (TUNEL), and caspase-3 activity assay. The LPS-induced maternal inflammation degenerated the myelin sheath in the offspring periventricular region which was associated with an increased microglial number, oligodendrocytes degeneration, proinflammatory cytokine secretion, and cell apoptosis. The transplanted NSCs homed into the brain and ameliorated the evaluated parameters. The expression of proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), cell apoptosis and caspase-3 activity were inhibited by NSCs. In addition, Olig2 and myelin basic protein immunohistochemy staining showed that prenatal NSCs transplantation augmented the myelination in the periventricular white matter of offspring. In conclusion, we think that prenatal therapeutic strategies, such as in utero NSCs transplantation, may prevent prenatal white matter injury after birth.

The role of oligodendrocytes and their progenitors on neural interface technology: A novel perspective on tissue regeneration and repair

Oligodendrocytes and their precursors are critical glial facilitators of neurophysiology, which is responsible for cognition and behavior. Devices that are used to interface with the brain allow for a more in-depth analysis of how neurons and these glia synergistically modulate brain activity. As projected by the BRAIN Initiative, technologies that acquire a high resolution and robust sampling of neural signals can provide a greater insight in both the healthy and diseased brain and support novel discoveries previously unobtainable with the current state of the art. However, a complex series of inflammatory events triggered during device insertion impede the potential applications of implanted biosensors. Characterizing the biological mechanisms responsible for the degradation of intracortical device performance will guide novel biomaterial and tissue regenerative approaches to rehabilitate the brain following injury. Glial subtypes which assist with neuronal survival and exchange of electrical signals, mainly oligodendrocytes, their precursors, and the insulating myelin membranes they produce, are sensitive to inflammation commonly induced from insults to the brain. This review explores essential physiological roles facilitated by oligodendroglia and their precursors and provides insight into their pathology following neurodegenerative injury and disease. From this knowledge, inferences can be made about the impact of device implantation on these supportive glia in order to engineer effective strategies that can attenuate their responses, enhance the efficacy of neural interfacing technology, and provide a greater understanding of the challenges that impede wound healing and tissue regeneration during pathology.

Minocycline plus N-acteylcysteine induces remyelination, synergistically protects oligodendrocytes and modifies neuroinflammation in a rat model of mild traumatic brain injury

Mild traumatic brain injury afflicts over 2 million people annually and little can be done for the underlying injury. The Food and Drug Administration-approved drugs Minocycline plus N-acetylcysteine (MINO plus NAC) synergistically improved cognition and memory in a rat mild controlled cortical impact (mCCI) model of traumatic brain injury.³ The underlying cellular and molecular mechanisms of the drug combination are unknown. This study addressed the effect of the drug combination on white matter damage and neuroinflammation after mCCI. Brain tissue from mCCI rats given either sham-injury, saline, MINO alone, NAC alone, or MINO plus NAC was investigated via histology and qPCR at four time points (2, 4, 7, and 14 days post-injury) for markers of white matter damage and neuroinflammation. MINO plus NAC synergistically protected resident oligodendrocytes and decreased the number of oligodendrocyte precursor cells. Activation of microglia/macrophages (MP/MG) was synergistically increased in white matter two days post-injury after MINO plus NAC treatment. Patterns of M1 and M2 MP/MG were also altered after treatment. The modulation of neuroinflammation is a potential mechanism to promote remyelination and improve cognition and memory. These data also provide new and important insights into how drug treatments can induce repair after traumatic brain injury.

Molecular Mechanisms of Oligodendrocyte Regeneration in White Matter-Related Diseases

Even in adult brains, restorative mechanisms are still retained to maintain the microenvironment. Under the pathological conditions of central nervous system (CNS) diseases, several immature cells in the brain would be activated as a compensative response. As the concept of the neurovascular unit emphasizes, cell-cell interactions play important roles in this restorative process. White matter damage and oligodendrocyte loss are representative characteristics for many neurodegenerative diseases. In response to oligodendrocyte damage, residual oligodendrocyte precursor cells (OPCs) initiate their proliferation and differentiation for the purpose of remyelination. Although mechanisms of oligodendrogenesis and remyelination in CNS diseases are still mostly unknown and understudied, accumulated evidence now suggests that support from neighboring cells is necessary for OPC proliferation and differentiation. In this review, we first overview basic mechanisms of interaction between oligodendrocyte lineage cells and neighboring cells, and then introduce how oligodendrogenesis occurs under the conditions of neurodegenerative diseases, focusing on vascular cognitive impairment syndrome, Alzheimer’s disease, and multiple sclerosis.

Functional antagonism of sphingosine-1-phosphate receptor 1 prevents cuprizone-induced demyelination

Recent evidence suggests that the oral drug Fingolimod (FTY720) for relapsing-remitting multiple sclerosis (MS) may act directly on the central nervous system (CNS) and modulate disease pathogenesis and progression in experimental models of MS. However, the specific subtype of sphingosine-1-phosphate (S1P) receptors that mediates the effect of FTY720 on the CNS cells has not been fully elucidated. Here, we report that S1P receptor 1 (S1PR1) is elevated in reactive astrocytes in an autoimmunity independent mouse model of MS and that selective S1PR1 modulation is sufficient to ameliorate the loss of oligodendrocytes and demyelination. The non-selective S1PR modulator, FTY720, or a short-lived S1PR1-specific modulator, CYM5442, was administered daily to mice while on cuprizone diet. Both FTY720- and CYM5422-treated mice displayed a significant reduction in oligodendrocyte apoptosis and astrocyte and microglial activation in comparison to vehicle-treated groups, which was associated with decreased production of proinflammatory mediators and down-regulation of astrocytic S1PR1 protein. Interestingly, S1PR1 modulation during the early phase of cuprizone intoxication was required to suppress oligodendrocyte death and consequent demyelination as drug treatment from 10 days after the initiation of cuprizone feeding was no longer effective. CYM5442 treatment during the brief cuprizone exposure significantly prevented Il-1β, Il-6, Cxcl10, and Cxcl3 induction, resulting in suppression of subsequent reactive gliosis and demyelination. Our study identifies functional antagonism of S1PR1 as a major mechanism for the protective effect of FTY720 in the cuprizone model and suggests pathogenic contributions of astrocyte S1PR1 signaling in primary demyelination and its potential as a therapeutic target for CNS inflammation.

Lipopolysaccharide Associates with Amyloid Plaques, Neurons and Oligodendrocytes in Alzheimer's Disease Brain: A Review

This review proposes that lipopolysaccharide (LPS, found in the wall of all Gram-negative bacteria) could play a role in causing sporadic Alzheimer’s disease (AD). This is based in part upon recent studies showing that: Gram-negative E. coli bacteria can form extracellular amyloid; bacterial-encoded 16S rRNA is present in all human brains with over 70% being Gram-negative bacteria; ultrastructural analyses have shown microbes in erythrocytes of AD patients; blood LPS levels in AD patients are 3-fold the levels in control; LPS combined with focal cerebral ischemia and hypoxia produced amyloid-like plaques and myelin injury in adult rat cortex. Moreover, Gram-negative bacterial LPS was found in aging control and AD brains, though LPS levels were much higher in AD brains. In addition, LPS co-localized with amyloid plaques, peri-vascular amyloid, neurons, and oligodendrocytes in AD brains. Based upon the postulate LPS caused oligodendrocyte injury, degraded Myelin Basic Protein (dMBP) levels were found to be much higher in AD compared to control brains. Immunofluorescence showed that the dMBP co-localized with β amyloid (Aβ) and LPS in amyloid plaques in AD brain, and dMBP and other myelin molecules were found in the walls of vesicles in periventricular White Matter (WM). These data led to the hypothesis that LPS acts on leukocyte and microglial TLR4-CD14/TLR2 receptors to produce NFkB mediated increases of cytokines which increase Aβ levels, damage oligodendrocytes and produce myelin injury found in AD brain. Since Aβ_1–42 is also an agonist for TLR4 receptors, this could produce a vicious cycle that accounts for the relentless progression of AD. Thus, LPS, the TLR4 receptor complex, and Gram-negative bacteria might be treatment or prevention targets for sporadic AD.

Brain-immune interactions in perinatal hypoxic-ischemic brain injury

Perinatal hypoxia-ischemia remains the primary cause of acute neonatal brain injury, leading to a high mortality rate and long-term neurological deficits, such as behavioral, social, attentional, cognitive and functional motor deficits. An ever-increasing body of evidence shows that the immune response to acute cerebral hypoxia-ischemia is a major contributor to the pathophysiology of neonatal brain injury. Hypoxia-ischemia provokes an intravascular inflammatory cascade that is further augmented by the activation of resident immune cells and the cerebral infiltration of peripheral immune cells response to cellular damages in the brain parenchyma. This prolonged and/or inappropriate neuroinflammation leads to secondary brain tissue injury. Yet, the long-term effects of immune activation, especially the adaptive immune response, on the hypoxic-ischemic brain still remain unclear. The focus of this review is to summarize recent advances in the understanding of post-hypoxic-ischemic neuroinflammation triggered by the innate and adaptive immune responses and to discuss how these mechanisms modulate the brain vulnerability to injury. A greater understanding of the reciprocal interactions between the hypoxic-ischemic brain and the immune system will open new avenues for potential immunomodulatory therapy in the treatment of neonatal brain injury.

Intraspinal TLR4 activation promotes iron storage but does not protect neurons or oligodendrocytes from progressive iron-mediated damage

Iron is essential for basic cellular functions but in excess is highly toxic. For this reason, free iron and iron storage are controlled in the periphery by elaborate regulatory mechanisms. In contrast, iron regulation in the central nervous system (CNS) is not well defined. Given that excess iron is present after trauma, hemorrhagic stroke and neurodegeneration, understanding normal iron regulation and promoting iron uptake in CNS pathology is crucial. Peripherally, toll-like receptor 4 (TLR4) activation promotes iron sequestration by macrophages. Notably, iron-rich sites of CNS pathology typically contain TLR4 agonists, which may promote iron uptake. Indeed, our recent work showed impaired iron storage after acute spinal cord injury in mice with TLR4 deficiency. Here we used a reductionist model to ask if TLR4 activation in the CNS stimulates iron uptake and promotes neuroprotection from iron-induced toxicity. For this, we measured the ability of microglia/macrophages to sequester exogenous iron and prevent pathology with and without concomitant intraspinal TLR4 activation. Results show that, similar to the periphery, activating intraspinal TLR4 via focal LPS injection increased mRNA encoding iron uptake and storage proteins and promoted iron sequestration into ferritin-expressing macrophages. However, this did not prevent oligodendrocyte and neuron loss. Moreover, replacement of oligodendrocytes by progenitor cells - a normally robust response to in vivo macrophage TLR4 activation - was significantly reduced if iron was present concomitant with TLR4 activation. Thus, while TLR4 signaling promotes CNS iron uptake, future work needs to determine ways to enhance iron removal without blocking the reparative effects of innate immune receptor signaling.

Creatine Enhances Mitochondrial-Mediated Oligodendrocyte Survival After Demyelinating Injury

Chronic oligodendrocyte loss, which occurs in the demyelinating disorder multiple sclerosis (MS), contributes to axonal dysfunction and neurodegeneration. Current therapies are able to reduce MS severity, but do not prevent transition into the progressive phase of the disease, which is characterized by chronic neurodegeneration. Therefore, pharmacological compounds that promote oligodendrocyte survival could be beneficial for neuroprotection in MS. Here, we investigated the role of creatine, an organic acid involved in adenosine triphosphate (ATP) buffering, in oligodendrocyte function. We found that creatine increased mitochondrial ATP production directly in oligodendrocyte lineage cell cultures and exerted robust protection on oligodendrocytes by preventing cell death in both naive and lipopolysaccharide-treated mixed glia. Moreover, lysolecithin-mediated demyelination in mice deficient in the creatine-synthesizing enzyme guanidinoacetate-methyltransferase (Gamt) did not affect oligodendrocyte precursor cell recruitment, but resulted in exacerbated apoptosis of regenerated oligodendrocytes in central nervous system (CNS) lesions. Remarkably, creatine administration into Gamt-deficient and wild-type mice with demyelinating injury reduced oligodendrocyte apoptosis, thereby increasing oligodendrocyte density and myelin basic protein staining in CNS lesions. We found that creatine did not affect the recruitment of macrophages/microglia into lesions, suggesting that creatine affects oligodendrocyte survival independently of inflammation. Together, our results demonstrate a novel function for creatine in promoting oligodendrocyte viability during CNS remyelination.SIGNIFICANCE STATEMENT We report that creatine enhances oligodendrocyte mitochondrial function and protects against caspase-dependent oligodendrocyte apoptosis during CNS remyelination. This work has important implications for the development of therapeutic targets for diseases characterized by oligodendrocyte death, including multiple sclerosis.

Mesenchymal stem cell-derived extracellular vesicles ameliorate inflammation-induced preterm brain injury

OBJECTIVE

Preterm brain injury is a major cause of disability in later life, and may result in motor, cognitive and behavioural impairment for which no treatment is currently available. The aetiology is considered as multifactorial, and one underlying key player is inflammation leading to white and grey matter injury. Extracellular vesicles secreted by mesenchymal stem/stromal cells (MSC-EVs) have shown therapeutic potential in regenerative medicine. Here, we investigated the effects of MSC-EV treatment on brain microstructure and maturation, inflammatory processes and long-time outcome in a rodent model of inflammation-induced brain injury.

METHODS

3-Day-old Wistar rats (P3) were intraperitoneally injected with 0.25mg/kg lipopolysaccharide or saline and treated with two repetitive doses of 1×10⁸ cell equivalents of MSC-EVs per kg bodyweight. Cellular degeneration and reactive gliosis at P5 and myelination at P11 were evaluated by immunohistochemistry and western blot. Long-term cognitive and motor function was assessed by behavioural testing. Diffusion tensor imaging at P125 evaluated long-term microstructural white matter alterations.

RESULTS

MSC-EV treatment significantly ameliorated inflammation-induced neuronal cellular degeneration reduced microgliosis and prevented reactive astrogliosis. Short-term myelination deficits and long-term microstructural abnormalities of the white matter were restored by MSC-EV administration. Morphological effects of MSC-EV treatment resulted in improved long-lasting cognitive functions INTERPRETATION: MSC-EVs ameliorate inflammation-induced cellular damage in a rat model of preterm brain injury. MSC-EVs may serve as a novel therapeutic option by prevention of neuronal cell death, restoration of white matter microstructure, reduction of gliosis and long-term functional improvement.

Preterm birth: Inflammation, fetal injury and treatment strategies

Preterm birth (PTB) is the leading cause of childhood mortality in children under 5 and accounts for approximately 11% of births worldwide. Premature babies are at risk of a number of health complications, notably cerebral palsy, but also respiratory and gastrointestinal disorders. Preterm deliveries can be medically indicated/elective procedures or they can occur spontaneously. Spontaneous PTB is commonly associated with intrauterine infection/inflammation. The presence of inflammatory mediators in utero has been associated with fetal injury, particularly affecting the fetal lungs and brain. This review will outline (i) the role of inflammation in term and PTB, (ii) the effect infection/inflammation has on fetal development and (iii) recent strategies to target PTB. Further research is urgently required to develop effective methods for the prevention and treatment of PTB and above all, to reduce fetal injury.

Evaluation of neuron-glia integrity by in vivo proton magnetic resonance spectroscopy: Implications for psychiatric disorders

Proton magnetic resonance spectroscopy (¹H-MRS) has been widely applied in human studies. There is now a large literature describing findings of brain MRS studies with mental disorder patients including schizophrenia, bipolar disorder, major depressive disorder, and anxiety disorders. However, the findings are mixed and cannot be reconciled by any of the existing interpretations. Here we proposed the new theory of neuron-glia integrity to explain the findings of brain ¹H-MRS stuies. It proposed the neurochemical correlates of neuron-astrocyte integrity and axon-myelin integrity on the basis of update of neurobiological knowledge about neuron-glia communication and of experimental MRS evidence for impairments in neuron-glia integrity from the authors and the other investigators. Following the neuron-glia integrity theories, this review collected evidence showing that glutamate/glutamine change is a good marker for impaired neuron-astrocyte integrity and that changes in N-acetylaspartate and lipid precursors reflect impaired myelination. Moreover, this new theory enables us to explain the differences between MRS findings in neuropsychiatric and neurodegenerative disorders.

N-Docosahexaenoylethanolamine ameliorates LPS-induced neuroinflammation via cAMP/PKA-dependent signaling

Background

Brain inflammation has been implicated as a critical mechanism responsible for the progression of neurodegeneration and characterized by glial cell activation accompanied by production of inflammation-related cytokines and chemokines. Growing evidence also suggests that metabolites derived from docosahexaenoic acid (DHA) have anti-inflammatory and pro-resolving effects; however, the possible role of N-docosahexaenoylethanolamine (synaptamide), an endogenous neurogenic and synaptogenic metabolite of DHA, in inflammation, is largely unknown. (The term “synaptamide” instead of “DHEA” was used for N-docosahexaenoylethanolamine since DHEA is a widely used and accepted term for the steroid, dehydroepiandrosterone.) In the present study, we tested this possibility using a lipopolysaccharide (LPS)-induced neuroinflammation model both in vitro and in vivo.

Methods

For in vitro studies, we used P3 primary rat microglia and immortalized murine microglia cells (BV2) to assess synaptamide effects on LPS-induced cytokine/chemokine/iNOS (inducible nitric oxide synthase) expression by quantitative PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). To evaluate in vivo effects, mice were intraperitoneally (i.p.) injected with LPS followed by synaptamide, and expression of proinflammatory mediators was measured by qPCR and western blot analysis. Activation of microglia and astrocyte in the brain was examined by Iba-1 and GFAP immunostaining.

Results

Synaptamide significantly reduced LPS-induced production of TNF-α and NO in cultured microglia cells. Synaptamide increased intracellular cAMP levels, phosphorylation of PKA, and phosphorylation of CREB but suppressed LPS-induced nuclear translocation of NF-κB p65. Conversely, adenylyl cyclase or PKA inhibitors abolished the synaptamide effect on p65 translocation as well as TNF-α and iNOS expression. Administration of synaptamide following LPS injection (i.p.) significantly reduced neuroinflammatory responses, such as microglia activation and mRNA expression of inflammatory cytokines, chemokine, and iNOS in the brain.

Conclusions

DHA-derived synaptamide is a potent suppressor of neuroinflammation in an LPS-induced model, by enhancing cAMP/PKA signaling and inhibiting NF-κB activation. The anti-inflammatory capability of synaptamide may provide a new therapeutic avenue to ameliorate the inflammation-associated neurodegenerative conditions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0751-z) contains supplementary material, which is available to authorized users.

The role of tumour necrosis factor alpha and soluble tumour necrosis factor alpha receptors in the symptomatology of schizophrenia

Background Immunological mechanisms may be responsible for the development and maintenance of schizophrenia symptoms. Aim The aim of this study is to measure tumour necrosis factor-alpha (TNF-α), soluble tumour necrosis factor-alpha receptor I (sTNF-αRI), and soluble tumour necrosis factor-alpha receptor II (sTNF-αRII) levels in patients with schizophrenia and healthy individuals, and to determine their relationship with the symptoms of schizophrenia. Methods Serum TNF-α, sTNF-αRI and sTNF-αRII levels were measured. The Positive and Negative Syndrome Scale (PANSS) was administered for patients with schizophrenia (n = 35), and the results were compared with healthy controls (n = 30). Hierarchical regression analyses were undertaken to predict the levels of TNF-α, sTNF-αRI and sTNF-αRII. Results No significant difference was observed in TNF-α levels, but sTNF-αRI and sTNF-αRII levels were lower in patients with schizophrenia. Serum sTNF-αRI and sTNF-αRII levels were found to be negatively correlated with the negative subscale score of the PANSS, and sTNF-αRI levels were also negatively correlated with the total score of the PANSS. Smoking, gender, body mass index were not correlated with TNF-α and sTNF-α receptor levels. Conclusions These results suggest that there may be a change in anti-inflammatory response in patients with schizophrenia due to sTNF-αRI and sTNF-αRII levels. The study also supports low levels of TNF activity in schizophrenia patients with negative symptoms.

Oligodendrocyte, Astrocyte, and Microglia Crosstalk in Myelin Development, Damage, and Repair

Oligodendrocytes are the myelinating glia of the central nervous system. Myelination of axons allows rapid saltatory conduction of nerve impulses and contributes to axonal integrity. Devastating neurological deficits caused by demyelinating diseases, such as multiple sclerosis, illustrate well the importance of the process. In this review, we focus on the positive and negative interactions between oligodendrocytes, astrocytes, and microglia during developmental myelination and remyelination. Even though many lines of evidence support a crucial role for glia crosstalk during these processes, the nature of such interactions is often neglected when designing therapeutics for repair of demyelinated lesions. Understanding the cellular and molecular mechanisms underlying glial cell communication and how they influence oligodendrocyte differentiation and myelination is fundamental to uncover novel therapeutic strategies for myelin repair.

A silver lining of neuroinflammation: Beneficial effects on myelination

Myelin accelerates action potential conduction velocity and provides essential energy support for axons. Unfortunately, myelin and myelinating cells are often vulnerable to injury or disease, resulting in myelin damage, which in turn can lead to axon dysfunction, overt pathology and neurological impairment. Inflammation is a common component of trauma and disease in both the CNS and PNS and therefore an active inflammatory response is often considered deleterious to myelin health. While inflammation can certainly damage myelin, inflammatory processes also can positively affect oligodendrocyte lineage progression, myelin debris clearance, oligodendrocyte metabolism and myelin repair. In the periphery, inflammatory cascades can also augment myelin repair, including processes initiated by infiltrating immune cells as well as by local Schwann cells. In this review, various aspects of inflammation beneficial to myelin repair are discussed and should be considered when designing or implementing anti-inflammatory therapies for CNS and PNS injury involving myelinating cells.

Lipopolysaccharide-Induced Apoptosis of Astrocytes: Therapeutic Intervention by Minocycline

Astrocytes are most abundant glial cell type in the brain and play a main defensive role in central nervous system against glutamate-induced toxicity by virtue of numerous transporters residing in their membranes and an astrocyte-specific enzyme glutamine synthetase (GS). In view of that, a dysregulation in the astrocytic activity following an insult may result in glutamate-mediated toxicity accompanied with astrocyte and microglial activation. The present study suggests that the lipopolysaccharide (LPS)-induced inflammation results in significant astrocytic apoptosis compared to other cell types in hippocampus and minocycline could not efficiently restrict the glutamate-mediated toxicity and apoptosis of astrocytes. Upon LPS exposure 76 % astrocytes undergo degeneration followed by 44 % oligodendrocytes, 26 % neurons and 10 % microglia. The pronounced astrocytic apoptosis resulted from the LPS-induced glutamate excitotoxicity leading to their hyperactivation as evident from their hypertrophied morphology, glutamate transporter 1 upregulation and downregulation of GS. Therapeutic minocycline treatment to LPS-infused rats efficiently restricted the inflammatory response and degeneration of other cell types but could not significantly combat with the apoptosis of astrocytes. Our study demonstrates a novel finding on cellular degeneration in the hippocampus revealing more of astrocytic death and suggests a more careful consideration on the protective efficacy of minocycline.

Activation of oligodendroglial Stat3 is required for efficient remyelination

Multiple sclerosis is the most prevalent demyelinating disease of the central nervous system (CNS) and is histologically characterized by perivascular demyelination as well as neurodegeneration. While the degree of axonal damage is correlated with clinical disability, it is believed that remyelination can protect axons from degeneration and slow disease progression. Therefore, understanding the intricacies associated with myelination and remyelination may lead to therapeutics that can enhance the remyelination process and slow axon degeneration and loss of function. Ciliary neurotrophic factor (CNTF) family cytokines such as leukemia inhibitory factor (LIF) and interleukin 11 (IL-11) are known to promote oligodendrocyte maturation and remyelination in experimental models of demyelination. Because CNTF family member binding to the gp130 receptor results in activation of the JAK2/Stat3 pathway we investigated the necessity of oligodendroglial Stat3 in transducing the signal required for myelination and remyelination. We found that Stat3 activation in the CNS coincides with myelination during development. Stimulation of oligodendrocyte precursor cells (OPCs) with CNTF or LIF promoted OPC survival and final differentiation, which was completely abolished by pharmacologic blockade of Stat3 activation with JAK2 inhibitor. Similarly, genetic ablation of Stat3 in oligodendrocyte lineage cells prevented CNTF-induced OPC differentiation in culture. In vivo, while oligodendroglial Stat3 signaling appears to be dispensable for developmental CNS myelination, it is required for oligodendrocyte regeneration and efficient remyelination after toxin-induced focal demyelination in the adult brain. Our data suggest a critical function for oligodendroglial Stat3 signaling in myelin repair.

Lipopolysaccharide Upregulates the Expression of CINC-3 and LIX in Primary NG2 Cells

Numerous NG2 cells, also called oligodendrocyte progenitor cells (OPCs), exist ubiquitously in the gray and white matter in the adult central nervous system (CNS). Although NG2 cells could become active by upregulation of NG2 expression and hypertrophy or extension of their processes under various neuropathological conditions, their actual role in the brain remains to be illustrated. In view of the fact that the synergy of cytokine and chemokine networks plays an important role in CNS inflammation and immunity, we have assumed that the NG2 cells might take part in brain inflammation and immunity by making a contribution to the pool of cytokines or chemokines. In the current study, NG2-expressing OPCs were prepared from cerebral hemispheres of postnatal day 0 or 1 Sprague-Dawley rats. Our results showed that NG2-expressing OPCs, verified by immunohistological staining of anti-NG2 antibody and anti-platelet-derived growth factor receptor alpha (PDGFRα) antibody, presented binding affinity to lipopolysaccharide (LPS), a commonly used stimulator in a neuroinflammatory model. Using cytokine antibody array, QPCR and ELISA, we have further shown that LPS could upregulate the expression of cytokine induced neutrophil chemoattractant-3 (CINC-3) and LPS induced CXC chemokine (LIX) in primary NG2-expressing OPCs, without the alteration in cell number of NG2-expressing OPCs. In addition, the cells bearing the receptor for these two cytokines included microglia and OPCs. Taken together, our results suggest that NG2-expressing OPCs could response to LPS and may take part in neuroinflammatory process, through secreting cytokines and chemokines to exert an effect on target cells (OPCs and microglia).