Microglia

Microglia signaling in health and disease - Implications in sex-specific brain development and plasticity

Microglia, the intrinsic neuroimmune cells residing in the central nervous system (CNS), exert a pivotal influence on brain development, homeostasis, and functionality, encompassing critical roles during both aging and pathological states. Recent advancements in comprehending brain plasticity and functions have spotlighted conspicuous variances between male and female brains, notably in neurogenesis, neuronal myelination, axon fasciculation, and synaptogenesis. Nevertheless, the precise impact of microglia on sex-specific brain cell plasticity, sculpting diverse neural network architectures and circuits, remains largely unexplored. This article seeks to unravel the present understanding of microglial involvement in brain development, plasticity, and function, with a specific emphasis on microglial signaling in brain sex polymorphism. Commencing with an overview of microglia in the CNS and their associated signaling cascades, we subsequently probe recent revelations regarding molecular signaling by microglia in sex-dependent brain developmental plasticity, functions, and diseases. Notably, C-X3-C motif chemokine receptor 1 (CX3CR1), triggering receptors expressed on myeloid cells 2 (TREM2), calcium (Ca2+), and apolipoprotein E (APOE) emerge as molecular candidates significantly contributing to sex-dependent brain development and plasticity. In conclusion, we address burgeoning inquiries surrounding microglia's pivotal role in the functional diversity of developing and aging brains, contemplating their potential implications for gender-tailored therapeutic strategies in neurodegenerative diseases.

Amlexanox attenuates LPS-induced neuroinflammatory responses in microglial cells via inhibition of NF-κB and STAT3 signaling pathways

Amlexanox is an anti-inflammatory and anti-allergic agent used clinically for the treatment of aphthous ulcers, allergic rhinitis, and asthma. Recent studies have demonstrated that amlexanox, a selective inhibitor of IkB kinase epsilon (IKKε) and TANK-binding kinase 1 (TBK1), suppresses a range of diseases or inflammatory conditions, such as obesity-related metabolic dysfunction and type 2 diabetes. However, the effects of amlexanox on neuroinflammatory responses to amlexanox have not yet been comprehensively studied. In this study, we investigated the novel therapeutic effect of amlexanox on LPS-induced neuroinflammation in vivo, and intraperitoneal injection of amlexanox markedly reduced LPS-induced IKKε levels, proinflammatory cytokines, and microglial activation, as evidenced by ionized calcium-binding adapter molecule 1 (Iba1) immunostaining. Furthermore, amlexanox significantly reduced proinflammatory cytokines and chemokines in LPS-induced bone marrow-derived macrophages (BMDM), murine BV2, and human HMC3 microglial cells. This data provided considerable evidence that amlexanox can be used as a preventive and curative therapy for neuroinflammatory and neurodegenerative diseases. In terms of mechanism aspects, our results demonstrated that the anti-inflammatory action of amlexanox in BV2 microglial cells was through the downregulation of NF-κB and STAT3 signaling pathways. In addition, the combination of amlexanox and SPI (a STAT3 selective inhibitor) showed high efficiency in inhibiting the production of neurotoxic and pro-inflammatory mediators. Overall, our data provide rational insights into the mechanisms of amlexanox as a potential therapeutic strategy for neuroinflammation-related diseases.

Investigation of Potential Drug Targets Involved in Inflammation Contributing to Alzheimer's Disease Progression

Alzheimer's disease has become a major public health issue. While extensive research has been conducted in the last few decades, few drugs have been approved by the FDA to treat Alzheimer's disease. There is still an urgent need for understanding the disease pathogenesis, as well as identifying new drug targets for further drug discovery. Alzheimer's disease is known to arise from a build-up of amyloid beta (Aβ) plaques as well as tangles of tau proteins. Along similar lines to Alzheimer's disease, inflammation in the brain is known to stem from the degeneration of tissue and build-up of insoluble materials. A minireview was conducted in this work assessing the genes, proteins, reactions, and pathways that link brain inflammation and Alzheimer's disease. Existing tools in Systems Biology were implemented to build protein interaction networks, mainly for the classical complement pathway and G protein-coupled receptors (GPCRs), to rank the protein targets according to their interactions. The top 10 protein targets were mainly from the classical complement pathway. With the consideration of existing clinical trials and crystal structures, proteins C5AR1 and GARBG1 were identified as the best targets for further drug discovery, through computational approaches like ligand-protein docking techniques.

Opioids, microglia, and temporal lobe epilepsy

A lack of treatment options for temporal lobe epilepsy (TLE) demands an urgent quest for new therapies to recover neuronal damage and reduce seizures, potentially interrupting the neurotoxic cascades that fuel hyper-excitability. Endogenous opioids, along with their respective receptors, particularly dynorphin and kappa-opioid-receptor, present as attractive candidates for controlling neuronal excitability and therapeutics in epilepsy. We perform a critical review of the literature to evaluate the role of opioids in modulating microglial function and morphology in epilepsy. We find that, in accordance with anticonvulsant effects, acute opioid receptor activation has unique abilities to modulate microglial activation through toll-like 4 receptors, regulating downstream secretion of cytokines. Abnormal activation of microglia is a dominant feature of neuroinflammation, and inflammatory cytokines are found to aggravate TLE, inspiring the challenge to alter microglial activation by opioids to suppress seizures. We further evaluate how opioids can modulate microglial activation in epilepsy to enhance neuroprotection and reduce seizures. With controlled application, opioids may interrupt inflammatory cycles in epilepsy, to protect neuronal function and reduce seizures. Research on opioid-microglia interactions has important implications for epilepsy and healthcare approaches. However, preclinical research on opioid modulation of microglia supports a new therapeutic pathway for TLE.

Low-intensity pulsed ultrasound stimulation (LIPUS) modulates microglial activation following intracortical microelectrode implantation

Microglia are important players in surveillance and repair of the brain. Their activation mediates neuroinflammation caused by intracortical microelectrode implantation, which impedes the application of intracortical brain-computer interfaces (BCIs). While low-intensity pulsed ultrasound stimulation (LIPUS) can attenuate microglial activation, its potential to modulate the microglia-mediated neuroinflammation and enhance the bio-integration of microelectrodes remains insufficiently explored. We found that LIPUS increased microglia migration speed from 0.59±0.04 to 1.35±0.07 µm/hr on day 1 and enhanced microglia expansion area from 44.50±6.86 to 93.15±8.77 µm 2 /min on day 7, indicating improved tissue healing and surveillance. Furthermore, LIPUS reduced microglial activation by 17% on day 6, vessel-associated microglia ratio from 70.67±6.15 to 40.43±3.87% on day 7, and vessel diameter by 20% on day 28. Additionally, microglial coverage of the microelectrode was reduced by 50% in week 1, indicating better tissue-microelectrode integration. These data reveal that LIPUS helps resolve neuroinflammation around chronic intracortical microelectrodes.

Far from home: the role of glial mRNA localization in synaptic plasticity

Neurons and glia are highly polarized cells, whose distal cytoplasmic functional subdomains require specific proteins. Neurons have axonal and dendritic cytoplasmic extensions containing synapses whose plasticity is regulated efficiently by mRNA transport and localized translation. The principles behind these mechanisms are equally attractive for explaining rapid local regulation of distal glial cytoplasmic projections, independent of their cell nucleus. However, in contrast to neurons, mRNA localization has received little experimental attention in glia. Nevertheless, there are many functionally diverse glial subtypes containing extensive networks of long cytoplasmic projections with likely localized regulation that influence neurons and their synapses. Moreover, glia have many other neuron-like properties, including electrical activity, secretion of gliotransmitters and calcium signaling, influencing, for example, synaptic transmission, plasticity and axon pruning. Here, we review previous studies concerning glial transcripts with important roles in influencing synaptic plasticity, focusing on a few cases involving localized translation. We discuss a variety of important questions about mRNA transport and localized translation in glia that remain to be addressed, using cutting-edge tools already available for neurons.

Obsessive-Compulsive Disorder, PANDAS, and Tourette Syndrome: Immuno-inflammatory Disorders

In the last years, much focus has been given to the possible role of inflammatory and immunologic alterations in the pathophysiology of obsessive-compulsive disorder (OCD) and some related conditions, such as pediatric autoimmune neuropsychiatric disorders associated with streptococcal infection (PANDAS) and Tourette syndrome (TS). Although the matter is intriguing, the available data are still controversial and/or limited. Therefore, the aim of this chapter was at reviewing and commenting on the literature on possible dysfunctions of inflammatory and immune system processes in OCD, PANDAS, and TS.This narrative review was carried out through searching PubMed and Google Scholar for English language papers from January 1985 to December 31, 2021.The data gathered up to now would suggest that the mechanisms involved might be heterogeneous according to the age of the patients and the disorder examined. Indeed, PANDAS seem more related to infections triggering autoimmunity not necessarily following group A beta-hemolytic streptococcal (GABHS) infection, as supposed in the past. Autoimmunity seems also important in TS, if coupled with an individual vulnerability that can be genetic and/or environmental. The data in adult OCD, albeit scattered and sometimes obtained in small samples of patients, would indicate that immune system and inflammatory processes are involved in the pathophysiology of the disorder. However, it is still unclear to conclude whether they are primary or secondary phenomena.In conclusion, taken together, the current findings pave that way towards novel and promising domains to explore the pathophysiology of OCD and related disorders, as well towards the development of innovative therapeutic strategy beyond current pharmacological paradigms.

Daphne genkwa flower extract promotes the neuroprotective effects of microglia

BACKGROUND

Microglia are innate immune cells in the central nervous system that play a crucial role in neuroprotection by releasing neurotrophic factors, removing pathogens through phagocytosis, and regulating brain homeostasis. The constituents extracted from the roots and stems of the Daphne genkwa plant have shown neuroprotective effects in an animal model of Parkinson's disease. However, the effect of Daphne genkwa plant extract on microglia has yet to be demonstrated.

PURPOSE

To study the anti-inflammatory and neuroprotective effects of Daphne genkwa flower extract (GFE) in microglia and explore the underlying mechanisms.

METHODS

In-vitro mRNA expression levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), inducible nitric oxide synthase, Arginase1, and brain derived neurotropic factor (BDNF) were analyzed by reverse transcription polymerase chain reaction in microglia cells. Nitric oxide (NO) and TNF-α protein were respectively analyzed by Griess reagent and Enzyme Linked Immunosorbent Assay. Immunoreactivity of Iba-1, Neu-N, and BDNF in mouse brain were analyzed by immunofluorescence staining. Phagocytosis capacity of microglia was examined using fluorescent zymosan-red particles.

RESULTS

GFE significantly inhibited lipopolysaccharide (LPS)-induced neuroinflammation and promoted neuroprotection both in vitro and in vivo. First, GFE inhibited the LPS-induced inflammatory factors NO, iNOS, and TNF-α in microglial cell lines and primary glial cells, thus demonstrating anti-inflammatory effects. Arginase1 and BDNF mRNA levels were increased in primary glial cells treated with GFE. Phagocytosis was also increased in microglia treated with GFE, suggesting a neuroprotective effect of GFE. In vivo, neuroprotective and anti-neuroinflammatory effects of GFE were also found in the mouse brain, as oral administration of GFE significantly inhibited LPS-induced neuronal loss and inflammatory activation of microglia.

CONCLUSION

GFE has anti-inflammatory effects and promotes microglial neuroprotective effects. GFE inhibited the pro-inflammatory mediators and enhanced neuroprotective microglia activity by increasing BDNF expression and phagocytosis. These novel findings of the GFE effect on microglia show an innovative approach that can potentially promote neuroprotection for the prevention of neurodegenerative diseases.

Immunoregulation via Cell Density and Quorum Sensing-like Mechanisms: An Underexplored Emerging Field with Potential Translational Implications

Quorum sensing (QS) was historically described as a mechanism by which bacteria detect and optimize their population density via gene regulation based on dynamic environmental cues. Recently, it was proposed that QS or similar mechanisms may have broader applications across different species and cell types. Indeed, emerging evidence shows that the mammalian immune system can also elicit coordinated responses on a population level to regulate cell density and function, thus suggesting that QS-like mechanisms may also be a beneficial trait of the immune system. In this review, we explore and discuss potential QS-like mechanisms deployed by the immune system to coordinate cellular-level responses, such as T cell responses mediated via the common gamma chain (γc) receptor cytokines and the aryl hydrocarbon receptors (AhRs). We present evidence regarding a novel role of QS as a multifunctional mechanism coordinating CD4⁺ and CD8⁺ T cell behavior during steady state and in response to infection, inflammatory diseases, and cancer. Successful clinical therapies such as adoptive cell transfer for cancer treatment may be re-evaluated to harness the effects of the QS mechanism(s) and enhance treatment responsiveness. Moreover, we discuss how signaling threshold perturbations through QS-like mediators may result in disturbances of the complex crosstalk between immune cell populations, undesired T cell responses, and induction of autoimmune pathology. Finally, we discuss the potential therapeutic role of modulating immune-system-related QS as a promising avenue to treat human diseases.

Cell types of origin of the cell-free transcriptome

Cell-free RNA from liquid biopsies can be analyzed to determine disease tissue of origin. We extend this concept to identify cell types of origin using the Tabula Sapiens transcriptomic cell atlas as well as individual tissue transcriptomic cell atlases in combination with the Human Protein Atlas RNA consensus dataset. We define cell type signature scores, which allow the inference of cell types that contribute to cell-free RNA for a variety of diseases.

Minocycline Attenuates Microglia/Macrophage Phagocytic Activity and Inhibits SAH-Induced Neuronal Cell Death and Inflammation

Background

Neuroprotective treatment strategies aiming at interfering with either inflammation or cell death indicate the importance of these mechanisms in the development of brain injury after subarachnoid hemorrhage (SAH). This study was undertaken to evaluate the influence of minocycline on microglia/macrophage cell activity and its neuroprotective and anti-inflammatory impact 14 days after aneurismal SAH in mice.

Methods

Endovascular filament perforation was used to induce SAH in mice. SAH + vehicle-operated mice were used as controls for SAH vehicle-treated mice and SAH + minocycline-treated mice. The drug administration started 4 h after SAH induction and was daily repeated until day 7 post SAH and continued until day 14 every second day. Brain cryosections were immunolabeled for Iba1 to detect microglia/macrophages and NeuN to visualize neurons. Phagocytosis assay was performed to determine the microglia/macrophage activity status. Apoptotic cells were stained using terminal deoxyuridine triphosphate nick end labeling. Real-time quantitative polymerase chain reaction was used to estimate cytokine gene expression.

Results

We observed a significantly reduced phagocytic activity of microglia/macrophages accompanied by a lowered spatial interaction with neurons and reduced neuronal apoptosis achieved by minocycline administration after SAH. Moreover, the SAH-induced overexpression of pro-inflammatory cytokines and neuronal cell death was markedly attenuated by the compound.

Conclusions

Minocycline treatment may be implicated as a therapeutic approach with long-term benefits in the management of secondary brain injury after SAH in a clinically relevant time window.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12028-022-01511-5.

Microbiota-microglia connections in age-related cognition decline

Aging is an inevitable process that all individuals experience, of which the extent differs among individuals. It has been recognized as the risk factor of neurodegenerative diseases by affecting gut microbiota compositions, microglia, and cognition abilities. Aging‐induced changes in gut microbiota compositions have a critical role in orchestrating the morphology and functions of microglia through the gut‐brain axis. Gut microbiota communicates with microglia by its secreted metabolites and neurotransmitters. This is highly associated with age‐related cognitive declines. Here, we review the main composition of microbiota in the aged individuals, outline the changes of the brain in age‐related cognitive decline from a neuroinflammation perspective, especially the changes of morphology and functions of microglia, discuss the crosstalk between microbiota and microglia in the aged brain and further highlight the role of microbiota‐microglia connections in neurodegenerative diseases (Alzheimer's disease and Parkinson's disease).

Long-term in vivo imaging of mouse spinal cord through an optically cleared intervertebral window

The spinal cord accounts for the main communication pathway between the brain and the peripheral nervous system. Spinal cord injury is a devastating and largely irreversible neurological trauma, and can result in lifelong disability and paralysis with no available cure. In vivo spinal cord imaging in mouse models without introducing immunological artifacts is critical to understand spinal cord pathology and discover effective treatments. We developed a minimally invasive intervertebral window by retaining the ligamentum flavum to protect the underlying spinal cord. By introducing an optical clearing method, we achieve repeated two-photon fluorescence and stimulated Raman scattering imaging at subcellular resolution with up to 15 imaging sessions over 6-167 days and observe no inflammatory response. Using this optically cleared intervertebral window, we study neuron-glia dynamics following laser axotomy and observe strengthened contact of microglia with the nodes of Ranvier during axonal degeneration. By enabling long-term, repetitive, stable, high-resolution and inflammation-free imaging of mouse spinal cord, our method provides a reliable platform in the research aiming at interpretation of spinal cord physiology and pathology.

Microglia: Key Players in Retinal Ageing and Neurodegeneration

Microglia are the resident immune cells of the central nervous system (CNS) and play a key role in maintaining the normal function of the retina and brain. During early development, microglia migrate into the retina, transform into a highly ramified phenotype, and scan their environment constantly. Microglia can be activated by any homeostatic disturbance that may endanger neurons and threaten tissue integrity. Once activated, the young microglia exhibit a high diversity in their phenotypes as well as their functions, which relate to either beneficial or harmful consequences. Microglial activation is associated with the release of cytokines, chemokines, and growth factors that can determine pathological outcomes. As the professional phagocytes in the retina, microglia are responsible for the clearance of pathogens, dead cells, and protein aggregates. However, their phenotypic diversity and phagocytic capacity is compromised with ageing. This may result in the accumulation of protein aggregates and myelin debris leading to retinal neuroinflammation and neurodegeneration. In this review, we describe microglial phenotypes and functions in the context of the young and ageing retina, and the mechanisms underlying changes in ageing. Additionally, we review microglia-mediated retinal neuroinflammation and discuss the mechanisms of microglial involvement in retinal neurodegenerative diseases.

A selective inhibitor of the NLRP3 inflammasome as a potential therapeutic approach for neuroprotection in a transgenic mouse model of Huntington’s disease

Background

Huntington’s disease (HD) is a neurodegenerative disorder caused by the expansion of the CAG repeat in the huntingtin (HTT) gene. When the number of CAG repeats exceeds 36, the translated expanded polyglutamine-containing HTT protein (mutant HTT [mHTT]) interferes with the normal functions of many cellular proteins and subsequently jeopardizes important cellular machineries in major types of brain cells, including neurons, astrocytes, and microglia. The NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome, which comprises NLRP3, ASC, and caspase-1, is involved in the activation of IL-1β and IL-18 and has been implicated in various biological functions. Although the existence of the NLRP3 inflammasome in the brain has been documented, the roles of the NLRP3 inflammasome in HD remain largely uncharacterized. MCC950 is a highly selective and potent small-molecule inhibitor of NLRP3 that has been used for the treatment of several diseases such as Alzheimer’s disease. However, whether MCC950 is also beneficial in HD remains unknown. Therefore, we hypothesized that MCC950 exerts beneficial effects in a transgenic mouse model of HD.

Methods

To evaluate the effects of MCC950 in HD, we used the R6/2 (B6CBA-Tg[HDexon1]62Gpb/1J) transgenic mouse model of HD, which expresses exon 1 of the human HTT gene carrying 120 ± 5 CAG repeats. Male transgenic R6/2 mice were treated daily with MCC950 (10 mg/kg of body weight; oral administration) or water for 5 weeks from the age of 7 weeks. We examined neuronal density, neuroinflammation, and mHTT aggregation in the striatum of R6/2 mice vs. their wild-type littermates. We also evaluated the motor function, body weight, and lifespan of R6/2 mice.

Results

Systematic administration of MCC950 to R6/2 mice suppressed the NLRP3 inflammasome, decreased IL-1β and reactive oxygen species production, and reduced neuronal toxicity, as assessed based on increased neuronal density and upregulation of the NeuN and PSD-95 proteins. Most importantly, oral administration of MCC950 increased neuronal survival, reduced neuroinflammation, extended lifespan, and improved motor dysfunction in R6/2 mice.

Conclusions

Collectively, our findings indicate that MCC950 exerts beneficial effects in a transgenic mouse model of HD and has therapeutic potential for treatment of this devastating neurodegenerative disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02419-9.

Decrypting the potential role of α-lipoic acid in Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases with motor disturbances, cognitive decline, and behavioral impairment. It is characterized by the extracellular aggregation of amyloid-β plaques and the intracellular accumulation of tau protein. AD patients show a cognitive decline, which has been associated with oxidative stress, as well as mitochondrial dysfunction. Alpha-lipoic acid (α-LA), a natural antioxidant present in food and used as a dietary supplement, has been considered a promising agent for the prevention or treatment of neurodegenerative disorders. Despite multiple preclinical studies indicating beneficial effects of α-LA in memory functioning, and pointing to its neuroprotective effects, to date only a few studies have examined its effects in humans. Studies performed in animal models of memory loss associated with aging and AD have shown that α-LA improves memory in a variety of behavioral paradigms. Furthermore, molecular mechanisms underlying α-LA effects have also been investigated. Accordingly, α-LA shows antioxidant, antiapoptotic, anti-inflammatory, glioprotective, metal chelating properties in both in vivo and in vitro studies. In addition, it has been shown that α-LA reverses age-associated loss of neurotransmitters and their receptors. The review article aimed at summarizing and discussing the main studies investigating the neuroprotective effects of α-LA on cognition as well as its molecular effects, to improve the understanding of the therapeutic potential of α-LA in patients suffering from neurodegenerative disorders, supporting the development of clinical trials with α-LA.

Targeting innate immunity to protect and cure Alzheimer's disease: opportunities and pitfalls

Innate immunity has been the focus of many new directions to understand the mechanisms involved in the aetiology of brain diseases, especially Alzheimer's disease (AD). AD is a multifactorial disorder, with the innate immune response and neuroinflammation at the forefront of the pathology. Thus, microglial cells along with peripheral circulating monocytes and more generally the innate immune response have been the target of several pre-clinical and clinical studies. More than a decade ago, inhibiting innate immune cells was considered to be the critical angle for preventing and treating brain diseases. After the failing of numerous clinical trials and the discovery that it may actually be the opposite in various pre-clinical models, the field has changed considerably. Here, we present both sides of the story with a particular emphasis on the beneficial properties of innate immune cells and how they can be targeted to have neuroprotective properties.

Mechanistic insights into the anti-depressant effect of emodin: an integrated systems pharmacology study and experimental validation

Depression is a complex neuropsychiatric disease involved multiple targets and signaling pathways. Systems pharmacology studies could potentially present a comprehensive molecular mechanism to delineate the anti-depressant effect of emodin (EMO). In this study, we investigated the anti-depressant effects of EMO in the chronic unpredictable mild stress (CUMS) rat model of depression and gained insights into the underlying mechanisms using systems pharmacology and molecular simulation analysis. Forty-three potential targets of EMO for treatment of depression were obtained. GO biological process analysis suggested that the biological functions of these targets mainly involve the regulation of reactive oxygen species metabolic process, response to lipopolysaccharide, regulation of inflammatory response, etc. KEGG pathway enrichment analysis showed that the PI3K-Akt signaling pathway, insulin resistance, IL-17 signaling pathway were the most significantly enriched signaling pathways. The molecular docking analysis revealed that EMO might have a strong combination with ESR1, AKT1 and GSK3B. Immunohistochemical staining and Western blotting showed that 2 weeks' EMO treatment (80 mg/kg/day) reduced depression related microglial activation, neuroinflammation and altered PI3K-Akt signaling pathway. Our findings provide a systemic pharmacology basis for the anti-depressant effects of EMO.

Neurons and Glia Interplay in α-Synucleinopathies

Accumulation of the neuronal presynaptic protein alpha-synuclein within proteinaceous inclusions represents the key histophathological hallmark of a spectrum of neurodegenerative disorders, referred to by the umbrella term a-synucleinopathies. Even though alpha-synuclein is expressed predominantly in neurons, pathological aggregates of the protein are also found in the glial cells of the brain. In Parkinson's disease and dementia with Lewy bodies, alpha-synuclein accumulates mainly in neurons forming the Lewy bodies and Lewy neurites, whereas in multiple system atrophy, the protein aggregates mostly in the glial cytoplasmic inclusions within oligodendrocytes. In addition, astrogliosis and microgliosis are found in the synucleinopathy brains, whereas both astrocytes and microglia internalize alpha-synuclein and contribute to the spread of pathology. The mechanisms underlying the pathological accumulation of alpha-synuclein in glial cells that under physiological conditions express low to non-detectable levels of the protein are an area of intense research. Undoubtedly, the presence of aggregated alpha-synuclein can disrupt glial function in general and can contribute to neurodegeneration through numerous pathways. Herein, we summarize the current knowledge on the role of alpha-synuclein in both neurons and glia, highlighting the contribution of the neuron-glia connectome in the disease initiation and progression, which may represent potential therapeutic target for a-synucleinopathies.

Transcriptional Assessment of Striatal mRNAs as Valid Biomarkers of Disease Progression in Three Mouse Models of Huntington's Disease

BACKGROUND

Huntington's disease (HD) is a progressive neurodegenerative disorder that prominently affects the basal ganglia, leading to affective, cognitive, behavioral, and motor decline. The primary site of neuron loss in HD is the striatal part of the basal ganglia, with GABAergic medium size spiny neurons (MSNs) being nearly completely lost in advanced HD.

OBJECTIVE

Based on the hypothesis that mutant huntingtin (mHTT) protein injures neurons via transcriptional dysregulation, we set out to establish a transcriptional profile of HD disease progression in the well characterized transgenic mouse model, R6/2, and two Knock-in models (KI); zQ175KI (expressing mutant mouse/human chimeric Htt protein) and HdhQ200 HET KI (carrying one allele of expanded mouse CAG repeats).

METHODS

In this study, we used quantitative PCR (qPCR) to evaluate striatal mRNA levels of markers of neurotransmission, neuroinflammation, and energy metabolism.

RESULTS

After analyzing and comparing transcripts from pre-symptomatic and symptomatic stages, markers expressed in the basal ganglia MSNs, which are typically involved in maintaining normal neurotransmission, showed a genotype-specific decrease in mRNA expression in a pattern consistent with human studies. In contrast, transcripts associated with neuroinflammation and energy metabolism were mostly unaffected in these animal models of HD.

CONCLUSION

Our results show that transcripts linked to neurotransmission are significantly reduced and are consistent with disease progression in both zQ175KI and R6/2 transgenic mouse models.

Snapshot of microglial physiological functions

Microglia as a defensive arm of the nervous system emerged early in evolution. The surveilling microglia with motile and ramified processes are the main phenotype in the healthy CNS; the surveilling microglial patrol neuronal somata, dendrites, dendritic spines and axons. Increasing evidence suggests that microglia play fundamental roles in development, maturation and ageing of the brain, as well as contribute to a variety of physiological brain processes including sleep and circadian rhythm. Physiological state of microglia is tightly regulated by brain microenvironment and controlled by a sophisticated system of receptors and signalling cascades including ionotropic and metabotropic purinoceptors, pattern-recognition receptors, and receptors for chemokines and cytokines. Microglia also utilise ion channels and transporters in regulating ionic homeostasis and various aspects of microglial function. The major ion transporters expressed by microglia include Na⁺/H⁺ exchanger 1 and Na⁺/Ca²⁺ exchangers, which are involved in regulation of pH_i and Ca²⁺ homeostasis during microglial physiological responses. Microglial cells control development, maturation and plasticity of neuronal ensembles through controlled physiological phagocytosis of synapses or synaptic fragments - processes known as synaptic pruning and trogocytosis. This special issue on "Physiological roles of microglia" is an assembly of papers written by the leading experts in this research field. We start this special issue with this snapshot of microglial physiological functions as a prelude to the indepth discussion of microglia in physiological processes in the nervous system.

Disruptions of Circadian Rhythms and Thrombolytic Therapy During Ischemic Stroke Intervention

Several endogenous and exogenous factors interact to influence stroke occurrence, in turn contributing to discernable daily distribution patterns in the frequency and severity of cerebrovascular events. Specifically, strokes that occur during the morning tend to be more severe and are associated with elevated diastolic blood pressure, increased hospital stay, and worse outcomes, including mortality, compared to strokes that occur later in the day. Furthermore, disrupted circadian rhythms are linked to higher risk for stroke and play a role in stroke outcome. In this review, we discuss the interrelation among core clock genes and several factors contributing to ischemic outcomes, sources of disrupted circadian rhythms, the implications of disrupted circadian rhythms in foundational stroke scientific literature, followed by a review of clinical implications. In addition to highlighting the distinct daily pattern of onset, several aspects of physiology including immune response, endothelial/vascular and blood brain barrier function, and fibrinolysis are under circadian clock regulation; disrupted core clock gene expression patterns can adversely affect these physiological processes, leading to a prothrombotic state. Lastly, we discuss how the timing of ischemic onset increases morning resistance to thrombolytic therapy and the risk of hemorrhagic transformation.

NOD1/RIP2 signalling enhances the microglia-driven inflammatory response and undergoes crosstalk with inflammatory cytokines to exacerbate brain damage following intracerebral haemorrhage in mice

BACKGROUND

Secondary brain damage caused by the innate immune response and subsequent proinflammatory factor production is a major factor contributing to the high mortality of intracerebral haemorrhage (ICH). Nucleotide-binding oligomerization domain 1 (NOD1)/receptor-interacting protein 2 (RIP2) signalling has been reported to participate in the innate immune response and inflammatory response. Therefore, we investigated the role of NOD1/RIP2 signalling in mice with collagenase-induced ICH and in cultured primary microglia challenged with hemin.

METHODS

Adult male C57BL/6 mice were subjected to collagenase for induction of ICH model in vivo. Cultured primary microglia and BV2 microglial cells (microglial cell line) challenged with hemin aimed to simulate the ICH model in vitro. We first defined the expression of NOD1 and RIP2 in vivo and in vitro using an ICH model by western blotting. The effect of NOD1/RIP2 signalling on ICH-induced brain injury volume, neurological deficits, brain oedema, and microglial activation were assessed following intraventricular injection of either ML130 (a NOD1 inhibitor) or GSK583 (a RIP2 inhibitor). In addition, levels of JNK/P38 MAPK, IκBα, and inflammatory factors, including tumour necrosis factor-α (TNF-α), interleukin (IL)-1β, and inducible nitric oxide synthase (iNOS) expression, were analysed in ICH-challenged brain and hemin-exposed cultured primary microglia by western blotting. Finally, we investigated whether the inflammatory factors could undergo crosstalk with NOD1 and RIP2.

RESULTS

The levels of NOD1 and its adaptor RIP2 were significantly elevated in the brains of mice in response to ICH and in cultured primary microglia, BV2 cells challenged with hemin. Administration of either a NOD1 or RIP2 inhibitor in mice with ICH prevented microglial activation and neuroinflammation, followed by alleviation of ICH-induced brain damage. Interestingly, the inflammatory factors interleukin (IL)-1β and tumour necrosis factor-α (TNF-α), which were enhanced by NOD1/RIP2 signalling, were found to contribute to the NOD1 and RIP2 upregulation in our study.

CONCLUSION

NOD1/RIP2 signalling played an important role in the regulation of the inflammatory response during ICH. In addition, a vicious feedback cycle was observed between NOD1/RIP2 and IL-1β/TNF-α, which could to some extent result in sustained brain damage during ICH. Hence, our study highlights NOD1/RIP2 signalling as a potential therapeutic target to protect the brain against secondary brain damage during ICH.

Microglia mediated neuroinflammation in autism spectrum disorder

BACKGROUND

Although the precise pathophysiologies underlying autism spectrum disorder (ASD) has not yet been fully clarified, growing evidence supports the involvement of neuroinflammation in the pathogenesis of this disorder, with microglia being particular relevance in the pathophysiologic processes.

OBJECTIVE

The present review aimed to systematically characterize existing literature regarding the role of microglia mediated neuroinflammation in the etiology of ASD.

METHODS

A systematic search was conducted for records indexed within Pubmed, EMBASE, or Web of Science to identify potentially eligible publications. Study selection and data extraction were performed by two authors, and the discrepancies in each step were settled through discussions.

RESULTS

A total of 14 studies comprising 1007 subjects met the eligibility criteria for this review, including 8 immunohistochemistry (IHC) studies, 5 genetic analysis studies, and 1 positron emission tomography (PET) studies. Although small in quantity, the included studies collectively pointed to a role of microglia mediated neuroinflammation in the pathogenesis of ASD.

CONCLUSION

Findings generated from this review consistently supported the involvement of neuroinflammation in the development of ASD, confirmed by the activation of microglia in different brain regions, involving increased cell number or cell density, morphological alterations, and phenotypic shifts.

Cholinergic Modulation of Glial Function During Aging and Chronic Neuroinflammation

Aging is a complex biological process that increases the risk of age-related cognitive degenerative diseases such as dementia, including Alzheimer’s disease (AD), Lewy Body Dementia (LBD), and mild cognitive impairment (MCI). Even non-pathological aging of the brain can involve chronic oxidative and inflammatory stress, which disrupts the communication and balance between the brain and the immune system. There has been an increasingly strong connection found between chronic neuroinflammation and impaired memory, especially in AD. While microglia and astrocytes, the resident immune cells of the central nervous system (CNS), exerting beneficial effects during the acute inflammatory phase, during chronic neuroinflammation they can become more detrimental. Central cholinergic circuits are involved in maintaining normal cognitive function and regulating signaling within the entire cerebral cortex. While neuronal-glial cholinergic signaling is anti-inflammatory and anti-oxidative, central cholinergic neuronal degeneration is implicated in impaired learning, memory sleep regulation, and attention. Although there is evidence of cholinergic involvement in memory, fewer studies have linked the cholinergic anti-inflammatory and anti-oxidant pathways to memory processes during development, normal aging, and disease states. This review will summarize the current knowledge of cholinergic effects on microglia and astroglia, and their role in both anti-inflammatory and anti-oxidant mechanisms, concerning normal aging and chronic neuroinflammation. We provided details on how stimulation of α7 nicotinic acetylcholine (α7nACh) receptors can be neuroprotective by increasing amyloid-β phagocytosis, decreasing inflammation and reducing oxidative stress by promoting the nuclear factor erythroid 2-related factor 2 (Nrf2) pathways and decreasing the release of pro-inflammatory cytokines. There is also evidence for astroglial α7nACh receptor stimulation mediating anti-inflammatory and antioxidant effects by inhibiting the nuclear factor-κB (NF-κB) pathway and activating the Nrf2 pathway respectively. We conclude that targeting cholinergic glial interactions between neurons and glial cells via α7nACh receptors could regulate neuroinflammation and oxidative stress, relevant to the treatment of several neurodegenerative diseases.

Spinal microglia-neuron interactions in chronic pain

Current deficiency in our understanding of acute-to-chronic pain transition remains a hurdle for developing effective treatments against chronic pain. Whereas neurocentric mechanisms alone are insufficient to provide satisfactory explanation for such transition, neuro-immune crosstalk has attracted attention in recent pain research. In contrast to brain microglia, spinal microglia are activated immediately in various pain states. The fast-responsive enrichment and activation of spinal microglia among different pain conditions have highlighted the crucial role of neuroinflammation caused by microglia-neuron crosstalk in pain initiation. Recent studies have revealed spinal microglia-neuron interactions are also involved in chronic pain maintenance, albeit, with different anatomic distribution, cellular and molecular mechanisms, and biologic functions. Delineating the exact temporal discrepancies of spinal microglia distribution and functions along acute-to-chronic pain transition may provide additional mechanistic insights for drug development to prevent deterioration of acute pain into the chronic state. This narrative review summerizes the longitudinal alterations of spinal microglia-neuron interactions in the initiation of pain hypersensitivity, acute-to-chronic pain progression, and chronic pain maintenance, followed by an overview of current clinical translation of preclinical studies on spinal microglia. This review highlights the crucial role of the interaction between spinal microglia and neighboring neurons in the initiation and maintenance of pain hypersensitivity, in relation to the release of cytokines, chemokines, and neuroactive substances, as well as the modulation of synaptic plasticity. Further exploration of the uncharted functions of spinal microglia-neuron crosstalk may lead to the design of novel drugs for preventing acute-to-chronic pain transition.

L-3-n-butylphthalide attenuates inflammation response and brain edema in rat intracerebral hemorrhage model

L-3-n-butylphthalide(NBP), a compound found in Apium graveolens Linn seed extracts, has a therapeutic effect on acute ischemic stroke. The pathological inflammatory pathways and consequent brain edema in intracerebral hemorrhage (ICH) share some similar characteristics with ischemic stroke. We hypothesized that NBP has anti-inflammatory and therapeutic effects on rats with ICH. ICH was induced by an infusion of bacterial collagenase type IV into the unilateral striatum of anesthetized rats. The therapeutic effect of NBP was measured by assessing neurological function, brain water content, blood-brain barrier permeability, and expression of tumor necrosis factor-alpha (TNF-α) and matrix metalloproteinase-9 (MMP-9) around the hematoma 48 hours after surgery. Magnetic resonance imaging was performed 4 and 48 hours after ICH induction, and ICH-induced injured area volumes were measured using T2-weighted images. The NBP treatment group performed better in the neurological function test than the vehicle group. Moreover, in comparison with the vehicle group, NBP group showed a lower expanded hematoma volume, brain water content, blood-brain barrier permeability, and TNF-α/ MMP-9 expression level. Our results indicate that NBP attenuates inflammation and brain edema in rat ICH model. Therefore, our findings also provide a potential therapeutic strategy for the treatment of ICH with NBP.

Targeting Inflammation, PHA-767491 Shows a Broad Spectrum in Protein Aggregation Diseases

Many protein aggregation diseases (PAD) affect the nervous system. Deposits of aggregated disease-specific proteins are found within or around the neuronal cells of neurodegenerative diseases. Although the main protein component is disease-specific, oligomeric aggregates are presumed to be the key agents causing the neurotoxicity. Evidence has shown that protein aggregates cause a chronic inflammatory reaction in the brain, resulting in neurodegeneration. Therefore, strategies targeting anti-inflammation could be beneficial to the therapeutics of PAD. PHA-767491 was originally identified as an inhibitor of CDC7/CDK9 and was found to reduce TDP-43 phosphorylation and prevent neurodegeneration in TDP-43 transgenic animals. We recently identified PHA-767491 as a GSK-3β inhibitor. In this study, we established mouse hippocampal primary culture with tau-hyperphosphorylation through the activation of GSK-3β using Wortmannin and GF109203X. We found that PHA-767491 significantly improved the neurite outgrowth of hippocampal primary neurons against the neurotoxicity induced by GSK-3β. We further showed that PHA-767491 had neuroprotective ability in hippocampal primary culture under oligomeric Aβ treatment. In addition, PHA-767491 attenuated the neuroinflammation in mouse cerebellar slice culture with human TBP-109Q agitation. Further study of SCA17 transgenic mice carrying human TBP-109Q showed that PHA-767491 ameliorated the gait ataxia and the inflammatory response both centrally and peripherally. Our findings suggest that PHA-767491 has a broad spectrum of activity in the treatment of different PAD and that this activity could be based on the anti-inflammation mechanism.

The Clinical Effect of Electroconvulsive Therapy and Its Relationship with Serum Levels of MMP-9 and CXCL12 in Patients with Mania

INTRODUCTION

Electroconvulsive therapy (ECT) is a non-pharmacological method for the treatment of psychiatric disorders. The precise biochemical mechanism of the effects of ECT is not clear, and since the two factors including matrix metalloproteinase-9 (MMP-9) and stromal cell-derived factor-1 alpha (CXCL12) play an important role in improving nerve damage, the effects of ECT and its relation with serum levels of MMP-9 and CXCL12 in patients with mania were investigated in this study.

METHODS

In this before and after intervention study, the patients with mania, referring to the Qods Hospital in Sanandaj, were selected by the census method during the years 2015-2018. Young's test was performed 24 hrs before and after the first, third, and sixth sessions of ECT. For biochemical analysis, 3 mL of peripheral blood were taken prior to any anesthesia and 6 hrs after the first, third, and sixth sessions. Data were analyzed by two-way ANOVA and Pearson correlation coefficient by using the SPSS16 software.

RESULTS

The results showed a significant decrease in Young's test scores during the first to the sixth session of ECT (P≤0.05). Although the levels of CXCL12 were slightly increased after the sixth course of ECT, they were not significant. Moreover, there were no significant relationship between the Young's test score and the serum levels of both MMP-9 and CXCL12 (P≥0.05).

CONCLUSION

ECT improved patients clinically, but this effect was independent of serum levels of MMP-9 and CXCL12, and possibly other biochemical factors are involved in this pathway.

Cross-talk between microglia and neurons regulates HIV latency

Despite effective antiretroviral therapy (ART), HIV-associated neurocognitive disorders (HAND) are found in nearly one-third of patients. Using a cellular co-culture system including neurons and human microglia infected with HIV (hμglia/HIV), we investigated the hypothesis that HIV-dependent neurological degeneration results from the periodic emergence of HIV from latency within microglial cells in response to neuronal damage or inflammatory signals. When a clonal hμglia/HIV population (HC69) expressing HIV, or HIV infected human primary and iPSC-derived microglial cells, were cultured for a short-term (24 h) with healthy neurons, HIV was silenced. The neuron-dependent induction of latency in HC69 cells was recapitulated using induced pluripotent stem cell (iPSC)-derived GABAergic cortical (iCort) and dopaminergic (iDopaNer), but not motor (iMotorNer), neurons. By contrast, damaged neurons induce HIV expression in latently infected microglial cells. After 48-72 h co-culture, low levels of HIV expression appear to damage neurons, which further enhances HIV expression. There was a marked reduction in intact dendrites staining for microtubule associated protein 2 (MAP2) in the neurons exposed to HIV-expressing microglial cells, indicating extensive dendritic pruning. To model neurotoxicity induced by methamphetamine (METH), we treated cells with nM levels of METH and suboptimal levels of poly (I:C), a TLR3 agonist that mimics the effects of the circulating bacterial rRNA found in HIV infected patients. This combination of agents potently induced HIV expression, with the METH effect mediated by the σ1 receptor (σ1R). In co-cultures of HC69 cells with iCort neurons, the combination of METH and poly(I:C) induced HIV expression and dendritic damage beyond levels seen using either agent alone, Thus, our results demonstrate that the cross-talk between healthy neurons and microglia modulates HIV expression, while HIV expression impairs this intrinsic molecular mechanism resulting in the excessive and uncontrolled stimulation of microglia-mediated neurotoxicity.

Novel therapies hijack the blood-brain barrier to eradicate glioblastoma cancer stem cells

Glioblastoma (GBM) is amongst the most aggressive brain tumors with a dismal prognosis. Despite significant advances in the current multimodality therapy including surgery, postoperative radiotherapy (RT) and temozolomide (TMZ)-based concomitant and adjuvant chemotherapy (CT), tumor recurrence is nearly universal with poor patient outcomes. These limitations are in part due to poor drug penetration through the blood-brain barrier (BBB) and resistance to CT and RT by a small population of cancer cells recognized as tumor-initiating cells or cancer stem cells (CSCs). Though CT and RT kill the bulk of the tumor cells, they fail to affect CSCs, resulting in their enrichment and their development into more refractory tumors. Therefore, identifying the mechanisms of resistance and developing therapies that specifically target CSCs can improve response, prevent the development of refractory tumors and increase overall survival of GBM patients. Small molecule inhibitors that can breach the BBB and selectively target CSCs are emerging. In this review, we have summarized the recent advancements in understanding the GBM CSC-specific signaling pathways, the CSC-tumor microenvironment niche that contributes to CT and RT resistance and the use of novel combination therapies of small molecule inhibitors that may be used in conjunction with TMZ-based chemoradiation for effective management of GBM.

Astroglia in Leukodystrophies

Leukodystrophies are genetically determined disorders affecting the white matter of the central nervous system. The combination of MRI pattern recognition and next-generation sequencing for the definition of novel disease entities has recently demonstrated that many leukodystrophies are due to the primary involvement and/or mutations in genes selectively expressed by cell types other than the oligodendrocytes, the myelin-forming cells in the brain. This has led to a new definition of leukodystrophies as genetic white matter disorders resulting from the involvement of any white matter structural component. As a result, the research has shifted its main focus from oligodendrocytes to other types of neuroglia. Astrocytes are the housekeeping cells of the nervous system, responsible for maintaining homeostasis and normal brain physiology and to orchestrate repair upon injury. Several lines of evidence show that astrocytic interactions with the other white matter cellular constituents play a primary pathophysiologic role in many leukodystrophies. These are thus now classified as astrocytopathies. This chapter addresses how the crosstalk between astrocytes, other glial cells, axons and non-neural cells are essential for the integrity and maintenance of the white matter in health. It also addresses the current knowledge of the cellular pathomechanisms of astrocytic leukodystrophies, and specifically Alexander disease, vanishing white matter, megalencephalic leukoencephalopathy with subcortical cysts and Aicardi-Goutière Syndrome.

Rapid neuroinflammatory changes in human acute intracerebral hemorrhage

OBJECTIVE

Spontaneous intracerebral hemorrhage (ICH) is the commonest form of hemorrhagic stroke and is associated with a poor prognosis. Neurosurgical removal of intracerebral hematoma has limited benefit and no pharmacotherapies are available. In acute ICH, primary tissue damage is followed by secondary pathology, where the cellular and neuroinflammatory changes are poorly understood.

METHODS

We studied histological changes in postmortem tissue from a cohort of spontaneous supra-tentorial primary ICH cases (n = 27) with survival of 1-12 days, compared to a matched control group (n = 16) examined in corresponding regions. Hematoxylin-eosin and microglial (Iba1) immunolabelled sections were assessed at 0-2, 3-5, and 7-12 days post-ICH.

RESULTS

Peri-hematoma, the observed ICH-related changes include edema, tissue neutrophils and macrophages from day 1. Ischemic neurons and swollen endothelial cells were common at day 1 and universal after day 5, as were intramural erythrocytes within small vessel walls. Activated microglia were evident at day 1 post-ICH. There was a significant increase in Iba1 positive area fraction at 0-2 (threefold), 3-5 (fourfold), and 7-12 days post ICH (ninefold) relative to controls. Giant microglia were detected peri-hematoma from day 5 and consistently 7-12 days post-ICH.

INTERPRETATION

Our data indicate that neuroinflammatory processes commence from day 1 post-ICH with changing microglial size and morphology following ICH and up to day 12. From day 5 some microglia exhibit a novel multiply nucleated morphology, which may be related to changing phagocytic function. Understanding the time course of neuroinflammatory changes, post-ICH may reveal novel targets for therapy and brain restoration.

Glatiramer Acetate Reverses Motor Dysfunction and the Decrease in Tyrosine Hydroxylase Levels in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease and there are no effective treatments that either slow or reverse the degeneration of the dopamine (DA) pathway. Using a 4-week progressive MPTP (1-methyl-1,2,3,6-tetrahydropyridine) neurotoxin model of PD, which is characterized by neuroinflammation, loss of nigrostriatal DA, and motor dysfunction, as seen in patients with PD, we tested whether post-MPTP treatment with glatiramer acetate (GA), an immunomodulatory drug, could reverse these changes. GA restored the grip dysfunction and gait abnormalities that were evident in the MPTP treated group. The reversal of the motor dysfunction was attributable to the substantial recovery in tyrosine hydroxylase (TH) protein expression in the striatum. Within the substantia nigra pars compacta, surface cell count analysis showed a slight increase in TH+ cells following GA treatment in the MPTP group, which was not statistically different from the vehicle (VEH) group. This was associated with the recovery of BDNF (brain derived neurotrophic factor) protein levels and a reduction in the microglial marker, IBA1, protein expression within the midbrain. Alpha synuclein (syn-1) levels within the midbrain and striatum were decreased following MPTP, while GA facilitated recovery to VEH levels in the striatum in the MPTP group. Although DA tissue analysis revealed no significant increase in striatal DA or 3,4-Dihydroxyphenylacetic acid levels (DOPAC) in the MPTP group treated with GA, DA turnover (DOPAC/DA) recovered back to VEH levels following GA treatment. GA treatment effectively reversed clinical (motor dysfunction) and pathology (TH, IBA1, BDNF expression) of PD in a murine model.

The Glucocorticoid Receptor Is a Critical Regulator of HIV Latency in Human Microglial Cells

We have developed models of HIV latency using microglia derived from adult human patient brain cortex and transformed with the SV40 T large and hTERT antigens. Latent clones infected by HIV reporter viruses display high levels of spontaneous HIV reactivation in culture. BrainPhys, a medium highly representative of the CNS extracellular environment, containing low glucose and 1% FBS, reduced, but did not prevent, HIV reactivation. We hypothesized that spontaneous HIV reactivation in culture was due to the expression of pro-inflammatory genes, such as TNF-α, taking place in the absence of the natural inhibitory signals from astrocytes and neurons. Indeed, expression and secretion of TNF-α is strongly reduced in HIV-latently infected microglia compared to the subset of cells that have undergone spontaneous HIV reactivation. Whereas inhibitors of NF-κB or of macrophage activation only had a short-term silencing effect, addition of dexamethasone (DEXA), a glucocorticoid receptor (GR) agonist and mediator of anti-inflammation, silenced the HIV provirus in a long-term, and shRNA-mediated knock-down of GR activated HIV. DEXA also decreased secretion of a number of cytokines, including TNF-α. Chromatin immunoprecipitation analysis revealed that DEXA strongly increased GR occupancy at the HIV promoter, and reduced histone 3 acetylated levels. Moreover, TNF-α expression inhibitors in combination with DEXA induced further HIV silencing and increased the histone 3 lysine 27 tri-methylated epigenetic mark of repression at the HIV promoter region. We conclude that GR is a critical repressor of HIV transcription in microglia, and a novel potential pharmacological target to restrict HIV expression in the CNS.

Inhibition of spinal 15-LOX-1 attenuates TLR4-dependent, nonsteroidal anti-inflammatory drug-unresponsive hyperalgesia in male rats

Although nonsteroidal anti-inflammatory drugs are the first line of therapeutics for the treatment of mild to moderate somatic pain, they are not generally considered to be effective for neuropathic pain. In the current study, direct activation of spinal Toll-like 4 receptors (TLR4) by the intrathecal (IT) administration of KDO2 lipid A (KLA), the active component of lipopolysaccharide, elicits a robust tactile allodynia that is unresponsive to cyclooxygenase inhibition, despite elevated expression of cyclooxygenase metabolites in the spinal cord. Intrathecal KLA increases 12-lipoxygenase-mediated hepoxilin production in the lumbar spinal cord, concurrent with expression of the tactile allodynia. The TLR4-induced hepoxilin production was also observed in primary spinal microglia, but not in astrocytes, and was accompanied by increased microglial expression of the 12/15-lipoxygenase enzyme 15-LOX-1. Intrathecal KLA-induced tactile allodynia was completely prevented by spinal pretreatment with the 12/15-lipoxygenase inhibitor CDC or a selective antibody targeting rat 15-LOX-1. Similarly, pretreatment with the selective inhibitors ML127 or ML351 both reduced activity of the rat homolog of 15-LOX-1 heterologously expressed in HEK-293T cells and completely abrogated nonsteroidal anti-inflammatory drug-unresponsive allodynia in vivo after IT KLA. Finally, spinal 12/15-lipoxygenase inhibition by nordihydroguaiaretic acid (NDGA) both prevents phase II formalin flinching and reverses formalin-induced persistent tactile allodynia. Taken together, these findings suggest that spinal TLR4-mediated hyperpathic states are mediated at least in part through activation of microglial 15-LOX-1.

Potential therapeutic role of melatonin on STZ-induced diabetic central neuropathy: A biochemical, histopathological, immunohistochemical and ultrastructural study

The aim of the present study was to assess the therapeutic potential of melatonin (Mel) in diabetic central neuropathy in a rat model of streptozotocin (STZ)-induced diabetes. The rats were injected with 60 mg/kg STZ and diabetes was confirmed by blood glucose levels (BGL) ≥ 250 mg/dL. Mel treatment (50 mg/kg) was started 72 h before the STZ injection and continued for 45 days. In addition, normal control, vehicle (5% ethanol) control, and Mel-treated non-diabetic control were also included. STZ induced a diabetic phenotype with persistent hyperglycemia and elevated oxidative stress in the brain, liver, and kidneys compared to the control groups. In addition, the diabetic rats showed severe β-cell necrosis with reduced insulin levels, cerebral neuronopathy, myelinopathy, axonopathy, microglial and astroglial activation, and vascular damage. While Mel treatment did not prevent the development of STZ-induced diabetes mellitus and had no significant effect on the BGLs of the diabetic rats, it significantly ameliorated the diabetes-induced oxidative stress and neurodegeneration. Taken together, Mel showed potent therapeutic effects against the neurological complications of hyperglycemia and therefore can be used to treat diabetic neuropathy.

Opioids, gliosis and central immunomodulation

Neuropathic pain is a common health problem that affects millions of people worldwide. Despite being studied extensively, the cellular and molecular events underlying the central immunomodulation and the pathophysiology of neuropathic pain is still controversial. The idea that 'glial cells are merely housekeepers' is incorrect and with respect to initiation and maintenance of neuropathic pain, microglia and astrocytes have important roles to play. Glial cells differentially express opioid receptors and are thought to be functionally modulated by the activation of these receptors. In this review, we discuss evidence for glia-opioid modulation of pain by focusing on the pattern of astrocyte and microglial activation throughout the progress of nerve injury/neuropathic pain. Activation of astrocytes and microglia is a key step in central immunomodulation in terms of releasing pro-inflammatory markers and propagation of a 'central immune response'. Inhibition of astrocytes before and after induction of neuropathic pain has been found to prevent and reverse neuropathic pain, respectively. Moreover, microglial inhibitors have been found to prevent (but not to reverse) neuropathic pain. As they are expressed by glia, opioid receptors are expected to have a role to play in neuropathic pain.

Activin A increases phagocytosis of Escherichia coli K1 by primary murine microglial cells activated by toll-like receptor agonists

Background

Bacterial meningitis is associated with high mortality and long-term neurological sequelae. Increasing the phagocytic activity of microglia could improve the resistance of the CNS against infections. We studied the influence of activin A, a member of the TGF-β family with known immunoregulatory and neuroprotective effects, on the functions of microglial cells in vitro.

Methods

Primary murine microglial cells were treated with activin A (0.13 ng/ml–13 μg/ml) alone or in combination with agonists of TLR2, 4, and 9. Phagocytosis of Escherichia coli K1 as well as release of TNF-α, IL-6, CXCL1, and NO was assessed.

Results

Activin A dose-dependently enhanced the phagocytosis of Escherichia coli K1 by microglial cells activated by agonists of TLR2, 4, and 9 without further increasing NO and proinflammatory cytokine release. Cell viability of microglial cells was not affected by activin A.

Conclusions

Priming of microglial cells with activin A could increase the elimination of bacteria in bacterial CNS infections. This preventive strategy could improve the resistance of the brain to infections, particularly in elderly and immunocompromised patients.

Piperlongumine inhibits neuroinflammation via regulating NF-κB signaling pathways in lipopolysaccharide-stimulated BV2 microglia cells

Inflammatory processes in the central nervous system are feature among biological reactions to harmful stimuli such as pathogens and damaged cells. In resting conditions, microglia are involved in immune surveillance and brain homeostasis. However, the activation of abnormal microglia can be detrimental to neurons, even resulting in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Therefore, normalization of microglial activation is considered a promising strategy for developing drugs that can treat or prevent inflammation-related brain diseases. In the present study, we investigated the effects of piperlongumine, an active component of Piper longum, on lipopolysaccharide (LPS)-induced neuroinflammation using BV2 microglial cells. We found that piperlongumine significantly inhibited the production of nitric oxide and prostaglandin E2 induced by LPS. Piperlongumine also reduced the expression of inducible nitric oxide synthase and cyclooxygenase-2 as well as proinflammatory cytokines such as tumor necrosis factor-α and interleukin-6. Piperlongumine exerted its anti-neuroinflammatory effects by suppressing the nuclear factor kappa B signaling pathway. These findings suggest that piperlongumine could be a candidate agent for the treatment of inflammation-related neurodegenerative diseases.

Correction to: Neuroimmune Response in Ischemic Preconditioning

Ischemic preconditioning (IPC) is a robust neuroprotective phenomenon in which a brief period of cerebral ischemia confers transient tolerance to subsequent ischemic challenge. Research on IPC has implicated cellular, molecular, and systemic elements of the immune response in this phenomenon. Potent molecular mediators of IPC include innate immune signaling pathways such as Toll-like receptors and type 1 interferons. Brain ischemia results in release of pro- and anti-inflammatory cytokines and chemokines that orchestrate the neuroinflammatory response, resolution of inflammation, and transition to neurological recovery and regeneration. Cellular mediators of IPC include microglia, the resident central nervous system immune cells, astrocytes, and neurons. All of these cell types engage in cross-talk with each other using a multitude of signaling pathways that modulate activation/suppression of each of the other cell types in response to ischemia. As the postischemic neuroimmune response evolves over time there is a shift in function toward provision of trophic support and neuroprotection. Peripheral immune cells infiltrate the central nervous system en masse after stroke and are largely detrimental, with a few subtypes having beneficial, protective effects, though the role of these immune cells in IPC is largely unknown. The role of neural progenitor cells in IPC-mediated neuroprotection is another active area of investigation as is the role of microglial proliferation in this setting. A mechanistic understanding of these molecular and cellular mediators of IPC may not only facilitate more effective direct application of IPC to specific clinical scenarios, but also, more broadly, reveal novel targets for therapeutic intervention in stroke.

Coordinate effects of P2X7 and extracellular acidification in microglial cells

Extracellular adenosine 5′-triphosphate (ATP) is a damage-associated molecular pattern and contributes to inflammation associated diseases including cancer. Extracellular acidosis is a novel danger signal in the inflammatory sites, where it can modulate inflammation, immunity and tumor growth. Extracellular acidification was shown to inhibit P2X7-mediated channel currents, while it remains unknown how acidification and P2X7 together affect cellular responses. Here, we treated BV-2 microglial cells with ATP in a short period (<15 min) or a sustained acidified condition. For short acidification we compared the actions of neutralized ATP and acidic ATP in a condition with pH buffering. For sustained acidification, we treated cells with neutralized ATP in acidic medium or acidic ATP in medium without pH buffering. In the short acidified condition, neutralized ATP induced higher responses than acidic ATP to increase intracellular calcium and reactive oxygen species, decrease intracellular potassium and induce cell death. In contrast, these cellular responses and mitochondrial fission caused by neutralized ATP were enhanced by pH 6.0 and pH 4.5 media. P2X7 activation can also rapidly block mitochondrial ATP turnover and respiration capacity, both of which were mimicked by nigericin and enhanced by acidity. Taken together P2X7-mediated ionic fluxes and reactive oxygen species production are attenuated under short acidification, while sustained acidification itself can induce mitochondrial toxicity which deteriorates the mitochondrial function under P2X7 activation.

The Relevance of Iron in the Pathogenesis of Multiple System Atrophy: A Viewpoint

Iron is essential for cellular development and maintenance of multiple physiological processes in the central nervous system. The disturbance of its homeostasis leads to abnormal iron deposition in the brain and causes neurotoxicity via generation of free radicals and oxidative stress. Iron toxicity has been established in the pathogenesis of Parkinson's disease; however, its contribution to multiple system atrophy (MSA) remains elusive. MSA is characterized by cytoplasmic inclusions of misfolded α-synuclein (α-SYN) in oligodendrocytes referred to as glial cytoplasmic inclusions (GCIs). Remarkably, the oligodendrocytes possess high amounts of iron, which together with GCI pathology make a contribution toward MSA pathogenesis likely. Consistent with this observation, the GCI density is associated with neurodegeneration in central autonomic networks as well as olivopontocerebellar and striatonigral pathways. Iron converts native α-SYN into a β-sheet conformation and promotes its aggregation either directly or via increasing levels of oxidative stress. Interestingly, α-SYN possesses ferrireductase activity and α-SYN expression underlies iron mediated translational control via RNA stem loop structures. Despite a correlation between progressive putaminal atrophy and iron accumulation as well as clinical decline, it remains unclear whether pathologic iron accumulation in MSA is a secondary event in the cascade of neuronal degeneration rather than a primary cause. This review summarizes the current knowledge of iron in MSA and gives evidence for perturbed iron homeostasis as a potential pathogenic factor in MSA-associated neurodegeneration.

Assessment of Translocator Protein Density, as Marker of Neuroinflammation, in Major Depressive Disorder: A Pilot, Multicenter, Comparative, Controlled, Brain PET Study (INFLADEP Study)

Background: Major depressive disorder (MDD) is a serious public health problem with high lifetime prevalence (4.4-20%) in the general population. The monoamine hypothesis is the most widespread etiological theory of MDD. Also, recent scientific data has emphasized the importance of immuno-inflammatory pathways in the pathophysiology of MDD. The lack of data on the magnitude of brain neuroinflammation in MDD is the main limitation of this inflammatory hypothesis. Our team has previously demonstrated the relevance of [18F] DPA-714 as a neuroinflammation biomarker in humans. We formulated the following hypotheses for the current study: (i) Neuroinflammation in MDD can be measured by [18F] DPA-714; (ii) its levels are associated with clinical severity; (iii) it is accompanied by anatomical and functional alterations within the frontal-subcortical circuits; (iv) it is a marker of treatment resistance. Methods: Depressed patients will be recruited throughout 4 centers (Bordeaux, Montpellier, Tours, and Toulouse) of the French network from 13 expert centers for resistant depression. The patient population will be divided into 3 groups: (i) experimental group-patients with current MDD (n = 20), (ii) remitted depressed group-patients in remission but still being treated (n = 20); and, (iii) control group without any history of MDD (n = 20). The primary objective will be to compare PET data (i.e., distribution pattern of neuroinflammation) between the currently depressed group and the control group. Secondary objectives will be to: (i) compare neuroinflammation across groups (currently depressed group vs. remitted depressed group vs. control group); (ii) correlate neuroinflammation with clinical severity across groups; (iii) correlate neuroinflammation with MRI parameters for structural and functional integrity across groups; (iv) correlate neuroinflammation and peripheral markers of inflammation across groups. Discussion: This study will assess the effects of antidepressants on neuroinflammation as well as its role in the treatment response. It will contribute to clarify the putative relationships between neuroinflammation quantified by brain neuroimaging techniques and peripheral markers of inflammation. Lastly, it is expected to open innovative and promising therapeutic perspectives based on anti-inflammatory strategies for the management of treatment-resistant forms of MDD commonly seen in clinical practice. Clinical trial registration (reference: NCT03314155): https://www.clinicaltrials.gov/ct2/show/NCT03314155?term=neuroinflammation&cond=depression&cntry=FR&rank=1.

Electroconvulsive therapy, depression, the immune system and inflammation: A systematic review

BACKGROUND

The management and treatment of major depressive disorder are major public health challenges, the lifetime prevalence of this illness being 4.4%-20% in the general population. Major depressive disorder and treatment resistant depression appear to be, in part, related to a dysfunction of the immune response. Among the treatments for depression ECT occupies an important place. The underlying cerebral mechanisms of ECT remain unclear.

OBJECTIVES/HYPOTHESIS

The aim of this review is to survey the potential actions of ECT on the immuno-inflammatory cascade activated during depression.

METHODS

A systematic search of the literature was carried out, using the bibliographic search engines PubMed and Embase. The search covered articles published up until october 2017. The following MESH terms were used: Electroconvulsive therapy AND (inflammation OR immune OR immunology).

RESULTS

Our review shows that there is an acute immuno-inflammatory response immediately following an ECT session. There is an acute stress reaction. Studies show an increase in the plasma levels of cortisol and of interleukins 1 and 6. However, at the end of the course of treatment, ECT produces, in the long term, a fall in the plasma level of cortisol, a reduction in the levels of TNF alpha and interleukin 6.

LIMITATIONS

One of the limitations of this review is that a large number of studies are relatively old, with small sample sizes and methodological bias.

CONCLUSION

Advances in knowledge of the immuno-inflammatory component of depression seem to be paving the way towards models to explain the mechanism of action of ECT.

Ulinastatin inhibited sepsis-induced spinal inflammation to alleviate peripheral neuromuscular dysfunction in an experimental rat model of neuromyopathy

Sepsis initiates a neuroinflammatory cascade that contributes to spinal cord inflammation and behavioral impairment, and Toll-like receptor 4 (TLR4) is an important mediator of this cascade. In this study, we tested the hypothesis that ulinastatin (ULI) inhibits sepsis-induced spinal inflammation to alleviate peripheral neuromuscular dysfunction through the TLR4/myeloid differentiation factor 88 (MyD88)/NF-κB signaling pathway. Muscular function, spinal cord water content, and cytokine levels of spinal cord were tested in TLR4-inhibited rats subjected to cecal ligation and puncture (CLP). The normal rats were intrathecally injected with different concentrations of ULI or normal saline 60 min before CLP. At 24 h after CLP, the activation of microglia/macrophage was detected by immunofluorescence staining; and the cytokines were assayed by ELISA. The protein expression level of the TLR4 and its downstream effectors (MyD88 and NF-κB), the neuregulin-1, and the γ- and α7-nicotinic acetylcholine receptor was measured using western blotting. The protein expression of TLR4 in the spinal cord reached a maximum at 24 h post-CLP. Compared to the sham rats, the TLR4-inhibited rats showed attenuated functional impairment and cytokine release. ULI (5000 U/kg ) treatment pre-CLP significantly reduced the number of TLR4-positive microglia/macrophages as well as inflammatory mediator release in septic rats. Furthermore, the levels of TLR4, MyD88, and NF-κB and the expression level of γ-/α7-nicotinic acetylcholine receptors also decreased after ULI treatment. ULI administration may improve patient outcome by reducing the spinal inflammation through a mechanism involving the TLR4/MyD88/NF-κB signaling in sepsis.

Long-Term Kinetics of Immunologic Components and Neurological Deficits in Rats Following Repetitive Mild Traumatic Brain Injury

Background

Despite growing awareness of repetitive mild traumatic brain injury (rmTBI), understanding of the involvement of long-term kinetics of immunologic components in the central and peripheral immune system took part remains incomplete. The present study aimed to provide a quantitative assay for certain immune system parameters in rmTBI rats.

Material/Methods

Neurological functions were assessed by modified Neurological Severity Score (mNSS) and Morris Water Maze (MWM), immunologic components from brain and peripheral blood were analyzed by flow cytometry (FCM), and concentrations of inflammatory cytokines, including tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-10 were measure by enzyme-linked immunosorbent assay (ELISA).

Results

Neurological functions of rmTBI rats were seriously impaired. In the brain, T cells were up-regulated and peaked at week 1. The percentage of CD4⁺ T cells decreased from week 1 to week 4, while CD8⁺ T cells notably decreased at week 1, then increased until week 4. The infiltration proportion of Treg cells was reduced at week 1 and peaked at week 2. CD86⁺/CD11b⁺ M1 peaked at week 4 and CD206⁺/CD11b⁺ M2 rose at week 1. IL-6/IL-10 showed a similar pattern, whose rise corresponded to the decrease in TNF-α at week 2 after rmTBI. FCM demonstrated peripheral immune dysfunction after rmTBI.

Conclusions

mNSS and MWM demonstrated neuronal deficits in rmTBI rats, and central and peripheral immune systems were implicated in the pathophysiological processes of rmTBI. Long-term immune response may play dual roles in injury and repair of rmTBI.

Senicapoc: Repurposing a Drug to Target Microglia KCa3.1 in Stroke

Stroke is the leading cause of serious long-term disability and the fifth leading cause of death in the United States. Treatment options for stroke are few in number and limited in efficacy. Neuroinflammation mediated by microglia and infiltrating peripheral immune cells is a major component of stroke pathophysiology. Interfering with the inflammation cascade after stroke holds the promise to modulate stroke outcome. The calcium activated potassium channel K_Ca3.1 is expressed selectively in the injured CNS by microglia. K_Ca3.1 function has been implicated in pro-inflammatory activation of microglia and there is recent literature suggesting that this channel is important in the pathophysiology of ischemia/reperfusion (stroke) related brain injury. Here we describe the potential of repurposing Senicapoc, a K_Ca3.1 inhibitor, to intervene in the inflammation cascade that follows ischemia/reperfusion.