Influence of neurons on lipopolysaccharide-stimulated production of nitric oxide and tumor necrosis factor-alpha by cultured glia

Potassium and calcium channels in different nerve cells act as therapeutic targets in neurological disorders

The central nervous system, information integration center of the body, is mainly composed of neurons and glial cells. The neuron is one of the most basic and important structural and functional units of the central nervous system, with sensory stimulation and excitation conduction functions. Astrocytes and microglia belong to the glial cell family, which is the main source of cytokines and represents the main defense system of the central nervous system. Nerve cells undergo neurotransmission or gliotransmission, which regulates neuronal activity via the ion channels, receptors, or transporters expressed on nerve cell membranes. Ion channels, composed of large transmembrane proteins, play crucial roles in maintaining nerve cell homeostasis. These channels are also important for control of the membrane potential and in the secretion of neurotransmitters. A variety of cellular functions and life activities, including functional regulation of the central nervous system, the generation and conduction of nerve excitation, the occurrence of receptor potential, heart pulsation, smooth muscle peristalsis, skeletal muscle contraction, and hormone secretion, are closely related to ion channels associated with passive transmembrane transport. Two types of ion channels in the central nervous system, potassium channels and calcium channels, are closely related to various neurological disorders, including Alzheimer's disease, Parkinson's disease, and epilepsy. Accordingly, various drugs that can affect these ion channels have been explored deeply to provide new directions for the treatment of these neurological disorders. In this review, we focus on the functions of potassium and calcium ion channels in different nerve cells and their involvement in neurological disorders such as Parkinson's disease, Alzheimer's disease, depression, epilepsy, autism, and rare disorders. We also describe several clinical drugs that target potassium or calcium channels in nerve cells and could be used to treat these disorders. We concluded that there are few clinical drugs that can improve the pathology these diseases by acting on potassium or calcium ions. Although a few novel ion-channel-specific modulators have been discovered, meaningful therapies have largely not yet been realized. The lack of target-specific drugs, their requirement to cross the blood-brain barrier, and their exact underlying mechanisms all need further attention. This review aims to explain the urgent problems that need research progress and provide comprehensive information aiming to arouse the research community's interest in the development of ion channel-targeting drugs and the identification of new therapeutic targets for that can increase the cure rate of nervous system diseases and reduce the occurrence of adverse reactions in other systems.

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.

Lack of Direct Effects of Neurotrophic Factors in an In Vitro Model of Neuroinflammation

Neuroinflammation is associated with several neurological disorders including temporal lobe epilepsy. Seizures themselves can induce neuroinflammation. In an in vivo model of epilepsy, the supplementation of brain-derived neurotropic factor (BDNF) and fibroblast growth factor-2 (FGF-2) using a Herpes-based vector reduced epileptogenesis-associated neuroinflammation. The aim of this study was to test whether the attenuation of the neuroinflammation obtained in vivo with BDNF and FGF-2 was direct or secondary to other effects, for example, the reduction in the severity and frequency of spontaneous recurrent seizures. An in vitro model of neuroinflammation induced by lipopolysaccharide (LPS, 100 ng/mL) in a mouse primary mixed glial culture was used. The releases of cytokines and NO were analyzed via ELISA and Griess assay, respectively. The effects of LPS and neurotrophic factors on cell viability were determined by performing an MTT assay. BDNF and FGF-2 were tested alone and co-administered. LPS induced a significant increase in pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and NO. BDNF, FGF-2, and their co-administration did not counteract these LPS effects. Our study suggests that the anti-inflammatory effect of BDNF and FGF-2 in vivo in the epilepsy model was indirect and likely due to a reduction in seizure frequency and severity.

A neural cell adhesion molecule from oyster Crassostrea gigas: Molecular identification and immune functional characterization

Neural cell adhesion molecules (NCAMs) are large cell-surface glycoproteins playing important roles in cell-cell and cell-extracellular matrix interactions in nervous system. Recent study identified a homologue of NCAM (CgNCAM) from the Pacific oyster Crassostrea gigas. Its ORF was of 2634 bp which encodes a protein (877 amino acids) consisting of five immunoglobulin domains and two fibronectin type III domains. CgNCAM transcripts were broadly distributed in oyster tissues especially in mantle, labial palp and haemolymph. CgNCAM showed up-regulated expression in haemocytes of oysters after Vibrio splendidus and Staphylococcus aureus stimulation. The recombinant CgNCAM protein (rCgNCAM) was able to bind manose, lipopolysaccharide and glucan, as well as different microbes including Gram-negative bacteria and fungi. rCgNCAM displayed bacterial agglutination and hemagglutination activity. CgNCAM improved the phagocytosis of haemocytes towards V. splendidus by regulating the expression of CgIntegrin, CgRho J and CgMAPKK. Moreover, CgNCAM was involved in the extracellular trap establishment of haemocytes after V. splendidus stimulation. The results collectively indicated that CgNCAM acted as a recognition receptor executing multiple immune functions to recognize and eliminate invading microorganisms in innate immunity of oysters.

Neuro-immune deconvolution analysis of OAS3 as a transcriptomic central node in HIV-associated neurocognitive disorders

Neurological complications of AIDS (NeuroAIDS) include primary HIV-associated neurocognitive disorder (HAND). OAS3 is an enzyme belonging to the 2', 5' oligoadenylate synthase family induced by type I interferons and involved in the degradation of both viral and endogenous RNA. Here, we used microarray datasets from NCBI of brain samples of non-demented HIV-negative controls (NDC), HIV, deceased patients with HAND and encephalitis (HIVE) (treated and untreated with antiretroviral therapy, ART), and with HAND without HIVE. The HAND/HIVE patients were stratified according to the OAS3 gene expression. The genes positively and negatively correlated to the OAS3 gene expression were used to perform a genomic deconvolution analysis using neuroimmune signatures (NIS) belonging to sixteen signatures. Expression analysis revealed significantly higher OAS3 expression in HAND/HIVE and HAND/HIVE/ART compared with NDC. OAS3 expressed an excellent diagnostic ability to discriminate NDC from HAND/HIVE, HAND from HAND/HIVE, HAND from HAND/HIVE/ART, and HIV from HAND/HIVE. Noteworthy, OAS3 expression levels in the brains of HAND/HIVE patients were positively correlated with viral load in both peripheral blood and cerebrospinal fluid (CSF). Furthermore, deconvolution analysis revealed that the genes positively correlated to OAS3 expression were associated with inflammatory signatures. Neuronal activation profiles were significantly activated by the genes negatively correlated to OAS3 expression levels. Moreover, gene ontology analysis performed on genes characterizing the microglia signature highlighted an immune response as a main biological process. According to our results, genes positively correlated to OAS3 gene expression in the brains of HAND/HIVE patients are associated with inflammatory transcriptomic signatures and likely worse cognitive impairment.

The effects of nano-curcumin supplementation on Th2/tregulatory axis in migraine patients: a randomized, double-blind, placebo-controlled trial

AIM

In the present study we aimed to investigate the effects of nano-curcumin supplementation on gene expression and serum levels of IL-4 and TGF-β in migraine patients.

METHODS

Forty participants with episodic migraine were randomly allocated to receive 80 mg nano-curcumin (n = 20) or placebo (n = 20) in a randomized double-blind clinical trial for two months. At the beginning and the end of the study, the interictal serum levels and gene expression of IL-4 and TGF-β in peripheral blood mononuclear cells (PBMCs) isolated from migraine patients were measured, using ELISA and real-time PCR methods, respectively.

RESULTS

Intra-group assays showed a significant rise in the gene expression of both IL-4 and TGF-β (p < 0.05) in nano-curcumin group after two months of treatment, however the serum levels were only significantly changed for IL-4 (p < 0.05). On the contrast, inter-group assays revealed no statistical differences between nano-curcumin and placebo group in terms of IL-4 and TGF-β gene expression, while the serum levels of IL-4 was observed to be increased significantly (p = 0.03) following two month nano-curcumin supplementation.

CONCLUSION

The findings of the present trial suggest that the treatment with nano-curcumin could induce significant levels of IL-4, in favour of anti-inflammatory effects, while has a minimal effects on the both gene expression and serum levels of TGF-β. Further studies are required to determine the exact mechanism of action of curcumin in patients with migraine.

Anti-Inflammatory Action of Dexmedetomidine on Human Microglial Cells

Neuroinflammation, where inflammatory cytokines are produced in excess, contributes to the pathogenesis of delirium. Microglial cells play a central role in neuroinflammation by producing and releasing inflammatory cytokines in response to infection, tissue damage and neurodegeneration. Dexmedetomidine (DEX) is a sedative, which reduces the incidence of delirium. Thus, we hypothesized that DEX may alleviate delirium by exhibiting anti-inflammatory action on microglia. In the present study, we investigated the anti-inflammatory action of DEX on human microglial HMC3 cells. The results indicated that DEX partially suppressed the IL-6 and IL-8 production by lipopolysaccharide (LPS)-stimulated HMC3 cells as well as the phosphorylation of p38 MAPK and IκB and the translocation of NF-κB. Furthermore, DEX substantially suppressed IL-6 and IL-8 production by unstimulated HMC3 cells as wells as the phosphorylation of p38 MAPK and IκB and the translocation of NF-κB. These observations suggest that DEX exhibits anti-inflammatory action on not only LPS-stimulated but also unstimulated microglial cells via the suppression of inflammatory signaling and cytokine production.

Polysialic Acid in the Immune System

Polysialic acid (polySia) is a highly regulated polymer of sialic acid (Sia) with such potent biophysical characteristics that when expressed drastically influences the interaction properties of cells. Although much of what is known of polySia in mammals has been elucidated from the study of its role in the central nervous system (CNS), polySia is also expressed in other tissues, including the immune system where it presents dynamic changes during differentiation, maturation, and activation of different types of immune cells of the innate and adaptive response, being involved in key regulatory mechanisms. At least six polySia protein carriers (CCR7, ESL-1, NCAM, NRP2, ST8Sia 2, and ST8Sia 4) are expressed in different types of immune cells, but there is still much to be explored in regard not only to the regulatory mechanisms that determine their expression and the structure of polySia chains but also to the identification of the cis- and trans- ligands of polySia that establish signaling networks. This review summarizes the current knowledge on polySia in the immune system, addressing its biosynthesis, its tools for identification and structural characterization, and its functional roles and therapeutic implications.

Important role of microglia in HIV-1 associated neurocognitive disorders and the molecular pathways implicated in its pathogenesis

The development of effective combined anti-retroviral therapy (cART) led to a significant reduction in the death rate associated with human immunodeficiency virus type 1 (HIV-1) infection. However, recent studies indicate that considerably more than 50% of all HIV-1 infected patients develop HIV-1-associated neurocognitive disorder (HAND). Microglia are the foremost cells infected by HIV-1 in the central nervous system (CNS), and so, are also likely to contribute to the neurotoxicity observed in HAND. The activation of microglia induces the release of pro-inflammatory markers and altered secretion of cytokines, chemokines, secondary messengers, and reactive oxygen species (ROS) which activate signalling pathways that initiate neuroinflammation. In turn, ROS and inflammation also play critical roles in HAND. However, more efforts are required to understand the physiology of microglia and the processes involved in their activation in order to better understand the how HIV-1-infected microglia are involved in the development of HAND. In this review, we summarize the current state of knowledge about the involvement of oxidative stress mechanisms and role of HIV-induced ROS in the development of HAND. We also examine the academic literature regarding crucial HIV-1 pathogenicity factors implicated in neurotoxicity and inflammation in order to identify molecular pathways that could serve as potential therapeutic targets for treatment of this disease. KEY MESSAGES Neuroinflammation and excitotoxicity mechanisms are crucial in the pathogenesis of HAND. CNS infiltration by HIV-1 and immune cells through the blood brain barrier is a key process involved in the pathogenicity of HAND. Factors including calcium dysregulation and autophagy are the main challenges involved in HAND.

Co-Administration of Gagam-Sipjeondaebo-Tang and Ibuprofen Alleviates the Inflammatory Response in MPTP-Induced Parkinson's Disease Mouse Model and RAW264.7 Macrophages

Parkinson’s disease (PD), a common neurodegenerative disease, is characterized by degeneration of dopaminergic neurons with neuroinflammation. Gagam-Sipjeondaebo-Tang (GST), a traditional herbal formula made of twelve medicinal herbs, is known to be effective in PD, and the use of ibuprofen has been associated with a lower risk of PD. The aim of this study was to evaluate whether the combined administration of GST and ibuprofen affects the inflammatory response of Parkinson’s disease. MPTP-induced parkinsonian mouse models were treated with GST or ibuprofen using oral gavage once a day for 5 days. The effects of GST were examined by measuring the TH level and expression of CD68 in the mice brain in addition to behavioral tests. The anti-inflammatory effect of GST on the LPS-treated RAW264.7 murine macrophages was examined using the NO assay. Inflammatory cytokines were analyzed using quantitative-PCR and flow cytometry. In the results, GST significantly improved the loss of dopaminergic neurons and alleviated PD-induced behavioral deficits. GST also decreased macrophage activation in the MPTP-induced PD mouse model. Interestingly, co-administration of GST and ibuprofen showed a synergistic effect in improving the loss of dopaminergic neurons and decreasing the activation of macrophages. Moreover, the NO level decreased in LPS-stimulated macrophages with this combined treatment. GST reduced iNOS, COX-2, IL-1β, and IL-6 levels, and co-administration with ibuprofen showed a synergistic effect. Furthermore, pretreatment of GST reduced the expression levels of MCP-1 and IL-12 p70 in LPS-stimulated RAW264.7 cells. These results can possibly suggest a future therapeutic approach for PD patients.

Bushen-Yizhi Formula Alleviates Neuroinflammation via Inhibiting NLRP3 Inflammasome Activation in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD), the second most common neurodegenerative disease, is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Although the molecular mechanisms underlying dopaminergic neuronal degeneration in PD remain unclear, neuroinflammation is considered as the vital mediator in the pathogenesis and progression of PD. Bushen-Yizhi Formula (BSYZ), a traditional Chinese medicine, has been demonstrated to exert antineuroinflammation in our previous studies. However, it remains unclear whether BSYZ is effective for PD. Here, we sought to assess the neuroprotective effects and explore the underlying mechanisms of BSYZ in a 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine- (MPTP-) induced mouse model of PD. Our results indicate that BSYZ significantly alleviates the motor impairments and dopaminergic neuron degeneration of MPTP-treated mice. Furthermore, BSYZ remarkably attenuates microglia activation, inhibits NLPR3 activation, and decreases the levels of inflammatory cytokines in MPTP-induced mouse brain. Also, BSYZ inhibits NLRP3 activation and interleukin-1β production of the 1-methyl-4-phenyl-pyridinium (MPP⁺) stimulated BV-2 microglia cells. Taken together, our results indicate that BSYZ alleviates MPTP-induced neuroinflammation probably via inhibiting NLRP3 inflammasome activation in microglia. Collectively, BSYZ may be a potential therapeutic agent for PD and the related neurodegeneration diseases.

Cellular phenotypes as inflammatory mediators in Parkinson's disease: Interventional targets and role of natural products

Pathogenesis of Parkinson's disease (PD) is undoubtedly a multifactorial phenomenon, with diverse etiological agents. Pro-inflammatory mediators act as a skew that directs disease progression during neurodegenerative diseases. Understanding the dynamics of inflammation and inflammatory mediators in preventing or reducing disease progression has recently gained much attention. Inflammatory neuro-degeneration is regulated via cytokines, chemokines, lipid mediators and immune cell subsets; however, individual cellular phenotypes in the Central Nervous System (CNS) acts in diverse ways whose persistent activation leads to unresolving inflammation often causing unfavorable outcomes in neurodegenerative disease like PD. Specifically, activation of cellular phenotypes like astrocytes, microglia, activation of peripheral immune cells requires different activation signals and agents like (cytokines, misfolded protein aggregates, infectious agents, pesticides like organophosphates, etc.,). However, what is unknown is how the different cellular phenotypes respond uniquely and the role of the factors they secrete alters the signal cascades in the complex neuron-microglial connections in the CNS. Hence, understanding the role of cellular phenotypes and the inflammatory mediators, the cross talk among the signals and their receptors can help us to identify the potential therapeutic target using natural products. In this review we have tried to put together the role of cellular phenotypes as a skew that favors PD progression and we have also discussed how the lack of experimental approaches and challenges that affects understanding the cellular targets that can be used against natural derivatives in alleviating PD pathophysiology. Together, this review will provide the better insights into the role of cellular phenotypes of neuroinflammation, inflammatory mediators and the orchestrating factors of inflammation and how they can be targeted in a more specific way that can be used in the clinical management of PD.

Proteomic Analysis of the Human Olfactory Bulb

The importance of olfaction to human health and disease is often underappreciated. Olfactory dysfunction has been reported in association with a host of common complex diseases, including neurological diseases such as Alzheimer's disease and Parkinson's disease. For health, olfaction or the sense of smell is also important for most mammals, for optimal engagement with their environment. Indeed, animals have developed sophisticated olfactory systems to detect and interpret the rich information presented to them to assist in day-to-day activities such as locating food sources, differentiating food from poisons, identifying mates, promoting reproduction, avoiding predators, and averting death. In this context, the olfactory bulb is a vital component of the olfactory system receiving sensory information from the axons of the olfactory receptor neurons located in the nasal cavity and the first place that processes the olfactory information. We report in this study original observations on the human olfactory bulb proteome in healthy subjects, using a high-resolution mass spectrometry-based proteomic approach. We identified 7750 nonredundant proteins from human olfactory bulbs. Bioinformatics analysis of these proteins showed their involvement in biological processes associated with signal transduction, metabolism, transport, and olfaction. These new observations provide a crucial baseline molecular profile of the human olfactory bulb proteome, and should assist the future discovery of biomarker proteins and novel diagnostics associated with diseases characterized by olfactory dysfunction.

Anti‑inflammatory effect of Migri‑Heal® in an in vitro inflammatory model of primary mixed glial cells

Migri‑Heal®, is a novel herbal remedy that was introduced for the treatment of migraine headaches. Previous studies revealed that this drug may reduce nitric oxide (NO) in an in vitro inflammatory model. The aim of the present study was to investigate the anti‑inflammatory effect of Migri‑Heal® on primary mix glial cells stimulated with LPS. In the current study, neonatal rat primary mix glial cells were isolated from the mixed glial cultures via shaking, and cultured in Dulbecco's' modified Eagle's medium supplemented with 10% fetal bovine serum. Following pretreatment with Migri‑Heal® (25, 75, 100, 150, 200 and 300 µg/ml) and cells were treated with LPS (10 µg/ml) for 1 h, and incubated for 48 h. The present study determined that 150 µg/ml Migri‑Heal® significantly reduced the production of NO in rat mix glial cells stimulated with 10 µg/ml LPS. Migri‑Heal® also suppressed mRNA expression level of LPS‑induced inducible nitric oxide synthase and tumor necrosis factor α, which was accompanied by inhibition of the transcription factor nuclear factor‑κB. Additionally, MTT assay determined that Migri‑Heal® was not cytotoxic, suggesting that the anti‑inflammatory effects of Migri‑Heal® observed were not due to cell death. In conclusion, the findings of the present study demonstrated that Migri‑Heal® may be useful as a potential anti‑inflammatory agent in inflammatory diseases. However, additional studies are required to confirm these findings.

The Role of Microglia in Retinal Neurodegeneration: Alzheimer's Disease, Parkinson, and Glaucoma

Microglia, the immunocompetent cells of the central nervous system (CNS), act as neuropathology sensors and are neuroprotective under physiological conditions. Microglia react to injury and degeneration with immune-phenotypic and morphological changes, proliferation, migration, and inflammatory cytokine production. An uncontrolled microglial response secondary to sustained CNS damage can put neuronal survival at risk due to excessive inflammation. A neuroinflammatory response is considered among the etiological factors of the major aged-related neurodegenerative diseases of the CNS, and microglial cells are key players in these neurodegenerative lesions. The retina is an extension of the brain and therefore the inflammatory response in the brain can occur in the retina. The brain and retina are affected in several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and glaucoma. AD is an age-related neurodegeneration of the CNS characterized by neuronal and synaptic loss in the cerebral cortex, resulting in cognitive deficit and dementia. The extracellular deposits of beta-amyloid (Aβ) and intraneuronal accumulations of hyperphosphorylated tau protein (pTau) are the hallmarks of this disease. These deposits are also found in the retina and optic nerve. PD is a neurodegenerative locomotor disorder with the progressive loss of dopaminergic neurons in the substantia nigra. This is accompanied by Lewy body inclusion composed of α-synuclein (α-syn) aggregates. PD also involves retinal dopaminergic cell degeneration. Glaucoma is a multifactorial neurodegenerative disease of the optic nerve, characterized by retinal ganglion cell loss. In this pathology, deposition of Aβ, synuclein, and pTau has also been detected in retina. These neurodegenerative diseases share a common pathogenic mechanism, the neuroinflammation, in which microglia play an important role. Microglial activation has been reported in AD, PD, and glaucoma in relation to protein aggregates and degenerated neurons. The activated microglia can release pro-inflammatory cytokines which can aggravate and propagate neuroinflammation, thereby degenerating neurons and impairing brain as well as retinal function. The aim of the present review is to describe the contribution in retina to microglial-mediated neuroinflammation in AD, PD, and glaucomatous neurodegeneration.

Microglia contact induces synapse formation in developing somatosensory cortex

Microglia are the immune cells of the central nervous system that play important roles in brain pathologies. Microglia also help shape neuronal circuits during development, via phagocytosing weak synapses and regulating neurogenesis. Using in vivo multiphoton imaging of layer 2/3 pyramidal neurons in the developing somatosensory cortex, we demonstrate here that microglial contact with dendrites directly induces filopodia formation. This filopodia formation occurs only around postnatal day 8-10, a period of intense synaptogenesis and when microglia have an activated phenotype. Filopodia formation is preceded by contact-induced Ca(2+) transients and actin accumulation. Inhibition of microglia by genetic ablation decreases subsequent spine density, functional excitatory synapses and reduces the relative connectivity from layer 4 neurons. Our data provide the direct demonstration of microglial-induced spine formation and provide further insights into immune system regulation of neuronal circuit development, with potential implications for developmental disorders of immune and brain dysfunction.

Gene dysregulation is restored in the Parkinson's disease MPTP neurotoxic mice model upon treatment of the therapeutic drug Cu(II)(atsm)

The administration of MPTP selectively targets the dopaminergic system resulting in Parkinsonism-like symptoms and is commonly used as a mice model of Parkinson’s disease. We previously demonstrated that the neuroprotective compound Cu^II(atsm) rescues nigral cell loss and improves dopamine metabolism in the MPTP model. The mechanism of action of Cu^II(atsm) needs to be further defined to understand how the compound promotes neuronal survival. Whole genome transcriptomic profiling has become a popular method to examine the relationship between gene expression and function. Substantia nigra samples from MPTP-lesioned mice were evaluated using whole transcriptome sequencing to investigate the genes altered upon Cu^II(atsm) treatment. We identified 143 genes affected by MPTP lesioning that are associated with biological processes related to brain and cognitive development, dopamine synthesis and perturbed synaptic neurotransmission. Upon Cu^II(atsm) treatment, the expression of 40 genes involved in promoting dopamine synthesis, calcium signaling and synaptic plasticity were restored which were validated by qRT-PCR. The study provides the first detailed whole transcriptomic analysis of pathways involved in MPTP-induced Parkinsonism. In addition, we identify key therapeutic pathways targeted by a potentially new class of neuroprotective agents which may provide therapeutic benefits for other neurodegenerative disorders.

Contributions of nonhematopoietic cells and mediators to immune responses: implications for immunotoxicology

Immunotoxicology assessments have historically focused on the effects that xenobiotics exhibit directly on immune cells. These studies are invaluable as they identify immune cell targets and help characterize mechanisms and/or adverse outcome pathways of xenobiotics within the immune system. However, leukocytes can receive environmental cues by cell-cell contact or via released mediators from cells of organs outside of the immune system. These organs include, but are not limited to, the mucosal areas such as the lung and the gut, the liver, and the central nervous system. Homeostatic perturbation in these organs induced directly by toxicants can initiate and alter the outcome of local and systemic immunity. This review will highlight some of the identified nonimmune influences on immune homeostasis and provide summaries of how immunotoxic mechanisms of selected xenobiotics involve nonimmune cells or mediators. Thus, this review will identify data gaps and provide possible alternative mechanisms by which xenobiotics alter immune function that could be considered during immunotoxicology safety assessment.

Neuroinflammation in Parkinson's disease and its potential as therapeutic target

Parkinson’s disease (PD), the second most common age-associated neurodegenerative disorder, is characterized by the loss of dopaminergic (DA) neurons and the presence of α-synuclein-containing aggregates in the substantia nigra pars compacta (SNpc). Chronic neuroinflammation is one of the hallmarks of PD pathophysiology. Post-mortem analyses of human PD patients and experimental animal studies indicate that activation of glial cells and increases in pro-inflammatory factor levels are common features of the PD brain. Chronic release of pro-inflammatory cytokines by activated astrocytes and microglia leads to the exacerbation of DA neuron degeneration in the SNpc. Besides, peripheral immune system is also implicated in the pathogenesis of PD. Infiltration and accumulation of immune cells from the periphery are detected in and around the affected brain regions of PD patients. Moreover, inflammatory processes have been suggested as promising interventional targets for PD and even other neurodegenerative diseases. A better understanding of the role of inflammation in PD will provide new insights into the pathological processes and help to establish effective therapeutic strategies. In this review, we will summarize recent progresses in the neuroimmune aspects of PD and highlight the potential therapeutic interventions targeting neuroinflammation.

Transcription factor myocyte enhancer factor 2D regulates interleukin-10 production in microglia to protect neuronal cells from inflammation-induced death

BACKGROUND

Neuroinflammatory responses have been recognized as an important aspect in the pathogenesis of Parkinson's disease (PD). Transcriptional regulation plays a critical role in the process of inflammation. Transcription factor myocyte enhancer factor 2D (MEF2D) is identified as a central factor in transmission of extracellular signals and activation of the genetic programs in response to a wide range of stimuli in several cell types, including neurons. But its presence and function in microglia have not been reported. We therefore investigated the effect of MEF2D in activated microglia on the progress of neuroinflammation and the survival of neurons.

METHODS

BV2 cells and primary cultured glial cells were stimulated with lipopolysaccharide (LPS). Samples from cells were examined for MEF2D expression, interleukin-10 (IL-10), and tumor necrosis factor alpha (TNF-α) by immunoblotting, quantitative real-time PCR (qPCR) or enzyme-linked immunosorbent assay (ELISA). The activity of MEF2D was examined by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation assay (ChIP). Recombinant lentivirus expressing shRNA specific to MEF2D was used to silence MEF2D expression in BV2 cells. The role of IL-10 transcriptionally induced by MEF2D on neuronal survival was assessed by anti-IL-10 neutralizing antibody. The survival of neurons was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. Male C57bl/6 mice were used to establish an acute PD model. Brain sections and cell slides were tested by immunofluorescence.

RESULTS

We demonstrated that MEF2D was present in microglia. Activation of microglia was associated with an increase in MEF2D level and activity in response to different stimuli in vivo and in vitro. MEF2D bound to a MEF2 consensus site in the promoter region of IL-10 gene and stimulated IL-10 transcription. Silencing MEF2D decreased the level of IL-10, increased the TNF-α mRNA, and promoted inflammation-induced cytotoxicity, consistent with the result of inhibiting IL-10 activity with an anti-IL-10 neutralizing antibody.

CONCLUSIONS

Our study identifies MEF2D as a critical regulator of IL-10 gene expression that negatively controls microglia inflammation response and prevents inflammation-mediated cytotoxicity.

Juliprosopine and juliprosine from prosopis juliflora leaves induce mitochondrial damage and cytoplasmic vacuolation on cocultured glial cells and neurons

Prosopis juliflora is a shrub largely used for animal and human consumption. However, ingestion has been shown to induce intoxication in animals, which is characterized by neuromuscular alterations induced by mechanisms that are not yet well understood. In this study, we investigated the cytotoxicity of a total alkaloid extract (TAE) and one alkaloid fraction (F32) obtained from P. juliflora leaves to rat cortical neurons and glial cells. Nuclear magnetic resonance characterization of F32 showed that this fraction is composed of a mixture of two piperidine alkaloids, juliprosopine (majority constituent) and juliprosine. TAE and F32 at concentrations between 0.3 and 45 μg/mL were tested for 24 h on neuron/glial cell primary cocultures. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test revealed that TAE and F32 were cytotoxic to cocultures, and their IC50 values were 31.07 and 7.362 μg/mL, respectively. Exposure to a subtoxic concentration of TAE or F32 (0.3-3 μg/mL) induced vacuolation and disruption of the astrocyte monolayer and neurite network, ultrastructural changes, characterized by formation of double-membrane vacuoles, and mitochondrial damage, associated with changes in β-tubulin III and glial fibrillary acidic protein expression. Microglial proliferation was also observed in cultures exposed to TAE or F32, with increasing levels of OX-42-positive cells. Considering that F32 was more cytotoxic than TAE and that F32 reproduced in vitro the main morphologic and ultrastructural changes of "cara torta" disease, we can also suggest that piperidine alkaloids juliprosopine and juliprosine are primarily responsible for the neurotoxic damage observed in animals after they have consumed the plant.

Neuronal influence behind the central nervous system regulation of the immune cells

Central nervous system (CNS) has a highly specialized microenvironment, and despite being initially considered an immune privileged site, this immune status is far from absolute because it varies with age and brain topography. The brain monitors immune responses by several means that act in parallel; one pathway involves afferent nerves (vagal nerve) and the other resident cells (neurons and glia). These cell populations exert a strong role in the regulation of the immune system, favoring an immune-modulatory environment in the CNS. Neurons control glial cell and infiltrated T-cells by contact-dependent and -independent mechanisms. Contact-dependent mechanisms are provided by several membrane immune modulating molecules such as Sema-7A, CD95L, CD22, CD200, CD47, NCAM, ICAM-5, and cadherins; which can inhibit the expression of microglial inflammatory cytokines, induce apoptosis or inactivate infiltrated T-cells. On the other hand, soluble neuronal factors like Sema-3A, cytokines, neurotrophins, neuropeptides, and neurotransmitters attenuate microglial and/or T-cell activation. In this review, we focused on all known mechanism driven only by neurons in order to control the local immune cells.

Cellular and molecular mediators of neuroinflammation in the pathogenesis of Parkinson's disease

Neuroinflammation is a host-defense mechanism associated with restoration of normal structure and function of the brain and neutralization of an insult. Increasing neuropathological and biochemical evidence from the brains of individuals with Parkinson's disease (PD) provides strong evidence for activation of neuroinflammatory pathways. Microglia, the resident innate immune cells, may play a major role in the inflammatory process of the diseased brain of patients with PD. Although microglia forms the first line of defense for the neural parenchyma, uncontrolled activation of microglia may directly affect neurons by releasing various molecular mediators such as inflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β), nitric oxide, prostaglandin E2, and reactive oxygen and nitrogen species. Moreover, recent studies have reported that activated microglia phagocytose not only damaged cell debris but also intact neighboring cells. This phenomenon further supports their active participation in self-enduring neuronal damage cycles. As the relationship between PD and neuroinflammation is being studied, there is a realization that both cellular and molecular mediators are most likely assisting pathological processes leading to disease progression. Here, we discuss mediators of neuroinflammation, which are known activators released from damaged parenchyma of the brain and result in neuronal degeneration in patients with PD.

Human marrow stromal cells reduce microglial activation to protect motor neurons in a transgenic mouse model of amyotrophic lateral sclerosis

Background

Human marrow stromal cells (hMSCs) injected intrathecally can effectively increase the lifespan and protect motor neurons in a transgenic mouse model of amyotrophic lateral sclerosis. However, how the transplanted cells exert a neuroprotective effect is still unclear. More recently, the anti-inflammation effect of marrow stromal cells has generated a great deal of interest. In the present study, we sought to investigate whether intrathecally injected hMSCs protect motor neurons through attenuating microglial activation and the secretion of inflammatory factors in Cu/Zn superoxide dismutase 1 (SOD1) transgenic mice. In addition, we also focused on the mode of hMSCs inhibiting microglial activation.

Methods

We transplanted hMSCs into the cisterna magna of SOD1 mice at the age of 8, 10 and 12 weeks. At sacrifice, tissues were harvested for analysis of neuron counts, microglial activation, TNFα secretion and inducible nitric oxide synthase (iNOS) protein expression. In vitro, microglial cells were treated with hMSC co-culture, hMSC transwell culture or hMSC conditioned medium to investigate the mode of hMSCs exerting an anti-inflammation effect.

Results

Intrathecally transplanted hMSCs inhibited inflammatory response in SOD1 transgenic mice, which was evidenced by the decreases in microglial activation, TNFα secretion and iNOS protein expression. In addition, the inhibitory effect on microglial activation of hMSCs was through secretion of diffusible molecules adjusted to environmental cues.

Conclusion

Intrathecally injected hMSCs can attenuate microglial activation through secretion of diffusible molecules to exert a therapeutic effect in SOD1 transgenic mice. Further studies are needed to explore the exact mechanisms by which hMSCs inhibit inflammation for facilitating the therapeutic effect.

Enhanced prostacyclin synthesis by adenoviral gene transfer reduced glial activation and ameliorated dopaminergic dysfunction in hemiparkinsonian rats

Prostacyclin (PGI₂), a potent vasodilator and platelet antiaggregatory eicosanoid, is cytoprotective in cerebral circulation. It is synthesized from arachidonic acid (AA) by the sequential action of cyclooxygenase- (COX-) 1 or 2 and prostacyclin synthase (PGIS). Because prostacyclin is unstable in vivo, PGI₂ analogs have been developed and demonstrated to protect against brain ischemia. This work attempts to selectively augment PGI₂ synthesis in mixed glial culture or in a model of Parkinson's disease (PD) by direct adenoviral gene transfer of prostacyclin biosynthetic enzymes and examines whether it confers protection in cultures or in vivo. Confluent mixed glial cultures actively metabolized exogenous AA into PGE₂ and PGD₂. These PGs were largely NS398 sensitive and considered as COX-2 products. Gene transfer of AdPGIS to the cultures effectively shunted the AA catabolism to prostacyclin synthesis and concurrently reduced cell proliferation. Furthermore, PGIS overexpression significantly reduced LPS stimulation in cultures. In vivo, adenoviral gene transfer of bicistronic COX-1/PGIS to substantia nigra protected 6-OHDA- induced dopamine depletion and ameliorated behavioral deficits. Taken together, this study shows that enhanced prostacyclin synthesis reduced glial activation and ameliorated motor dysfunction in hemiparkinsonian rats. Prostacyclin may have a neuroprotective role in modulating the inflammatory response in degenerating nigra-striatal pathway.

Time-dependent effects of hypothermia on microglial activation and migration

Background

Therapeutic hypothermia is one of the neuroprotective strategies that improve neurological outcomes after brain damage in ischemic stroke and traumatic brain injury. Microglial cells become activated following brain injury and play an important role in neuroinflammation and subsequent brain damage. The aim of this study was to determine the time-dependent effects of hypothermia on microglial cell activation and migration, which are accompanied by neuroinflammation.

Methods

Microglial cells in culture were subjected to mild (33 °C) or moderate (29 °C) hypothermic conditions before, during, or after lipopolysaccharide (LPS) or hypoxic stimulation, and the production of nitric oxide (NO), proinflammatory cytokines, reactive oxygen species, and neurotoxicity was evaluated. Effects of hypothermia on microglial migration were also determined in in vitro as well as in vivo settings.

Results

Early-, co-, and delayed-hypothermic treatments inhibited microglial production of inflammatory mediators to varying degrees: early treatment was the most efficient, and delayed treatment showed time-dependent effects. Delayed hypothermia also suppressed the mRNA levels of proinflammatory cytokines and iNOS, and attenuated microglial neurotoxicity in microglia-neuron co-cultures. Furthermore, delayed hypothermia reduced microglial migration in the Boyden chamber assay and wound healing assay. In a stab injury model, delayed local hypothermia reduced migration of microglia toward the injury site in the rat brain.

Conclusion

Taken together, our results indicate that delayed hypothermia is sufficient to attenuate microglial activation and migration, and provide the basis of determining the optimal time window for therapeutic hypothermia. Delayed hypothermia may be neuroprotective by inhibiting microglia-mediated neuroinflammation, indicating the therapeutic potential of post-injury hypothermia for patients with brain damages exhibiting some of the inflammatory components.

Neuroimmune crosstalk in the central nervous system and its significance for neurological diseases

The central nervous system (CNS) is now known to actively communicate with the immune system to control immune responses both centrally and peripherally. Within the CNS, while studies on glial cells, especially microglia, have highlighted the importance of this cell type in innate immune responses of the CNS, the immune regulatory functions of other cell types, especially neurons, are largely unknown. How neuroimmune cross-talk is homeostatically maintained in neurodevelopment and adult plasticity is even more elusive. Inspiringly, accumulating evidence suggests that neurons may also actively participate in immune responses by controlling glial cells and infiltrated T cells. The potential clinical application of this knowledge warrants a deeper understanding of the mutual interactions between neurons and other types of cells during neurological and immunological processes within the CNS, which will help advance diagnosis, prevention, and intervention of various neurological diseases. The aim of this review is to address the immune function of both glial cells and neurons, and the roles they play in regulating inflammatory processes and maintaining homeostasis of the CNS.

Adhesion molecules as potential targets for neuroprotection in a rodent model of Parkinson's disease

Cell adhesion molecules might play an important role in the inflammatory mechanisms associated with neurodegeneration. We have previously observed, in rats, that subcutaneous injection of complete Freund's adjuvant (CFA), a pro-inflammatory agent that induces a peripheral inflammatory stimulus, reduces the nigrostriatal degeneration and microglial activation caused by stereotaxic injection of 6-hydroxydopamine (6-OHDA). Here we further investigated the effects of CFA in 6-OHDA-lesioned rats by evaluating the expression of selected adhesion molecules, both at central and peripheral levels. Male, Sprague-Dawley rats received a subcutaneous injection of CFA followed, 10 days later, by intrastriatal injection of 6-OHDA. Animals were sacrificed at various time points and changes affecting intercellular (ICAM-1), vascular (VCAM-1), platelet endothelial (PECAM-1) and neural (NCAM-1) cell adhesion molecules were analyzed in striatum, ventral midbrain (containing the substantia nigra) and sera. Our results confirmed the protective effect of systemic CFA on 6-OHDA-induced nigrostriatal degeneration. Injection of 6-OHDA increased striatal ICAM-1 and PECAM-1 expression, while opposite changes (decreased expression) were detected in the ventral midbrain, particularly for VCAM-1 and NCAM-1. Pretreatment with CFA counteracted these changes. Nigrostriatal degeneration also affected peripheral immune function, with lesioned animals showing increased sPECAM levels with respect to intact animals. Also in this case, CFA pretreatment blocked the 6-OHDA induced increase of sPECAM. Our findings confirm that a pre-existing, peripheral pro-inflammatory condition reduces the neuroinflammatory response and associated neurodegeneration provoked by centrally-administered 6-OHDA, with a mechanism that seems to involve selected adhesion molecules. The link between peripheral and central immune responses may, therefore, represent a target for new therapeutic strategies aimed at reducing the neuroinflammatory component associated with neurodegeneration.

Erratum: Modulation of microglia by Wolfberry on the survival of retinal ganglion cells in a rat ocular hypertension model

The active component of Wolfberry (Lycium barbarum), lycium barbarum polysaccharides (LBP), has been shown to be neuroprotective to retinal ganglion cells (RGCs) against ocular hypertension (OH). Aiming to study whether this neuroprotection is mediated via modulating immune cells in the retina, we used multiphoton confocal microscopy to investigate morphological changes of microglia in whole-mounted retinas. Retinas under OH displayed slightly activated microglia. One to 100 mg/kg LBP exerted the best neuroprotection and elicited moderately activated microglia in the inner retina with ramified appearance but thicker and focally enlarged processes. Intravitreous injection of bacterial endotoxin lipopolysaccharide (LPS) decreased the survival of RGCs at 4 weeks, and the activated microglia exhibited amoeboid appearance as fully activated phenotype. When activation of microglia was attenuated by intravitreous injection of macrophage/microglia inhibitory factor, protective effect of 10 mg/kg LBP was attenuated. The results implicated that neuroprotective effects of LBP were partly due to modulating the activation of microglia.[This corrects the article on p. in vol. .].

Modulation of microglia by Wolfberry on the survival of retinal ganglion cells in a rat ocular hypertension model

The active component of Wolfberry (Lycium barbarum), lycium barbarum polysaccharides (LBP), has been shown to be neuroprotective to retinal ganglion cells (RGCs) against ocular hypertension (OH). Aiming to study whether this neuroprotection is mediated via modulating immune cells in the retina, we used multiphoton confocal microscopy to investigate morphological changes of microglia in whole-mounted retinas. Retinas under OH displayed slightly activated microglia. One to 100 mg/kg LBP exerted the best neuroprotection and elicited moderately activated microglia in the inner retina with ramified appearance but thicker and focally enlarged processes. Intravitreous injection of lipopolysaccharide decreased the survival of RGCs at 4 weeks, and the activated microglia exhibited amoeboid appearance as fully activated phenotype. When activation of microglia was attenuated by intravitreous injection of macrophage/microglia inhibitory factor, protective effect of 10 mg/kg LBP was attenuated. The results implicated that neuroprotective effects of LBP were partly due to modulating the activation of microglia.

Neuronal regulation of immune responses in the central nervous system

The central nervous system (CNS) has traditionally been considered to be immunologically privileged, but over the years there has been a re-evaluation of this dogma. To date, studies have tended to focus on the immune functions of glial cells, whereas the roles of neurons have been regarded as passive and their immune-regulatory properties have been less examined. However, recent findings indicate that CNS neurons actively participate in immune regulation by controlling their glial cell counterparts and infiltrated T cells. Here, we describe the immune-regulatory roles of CNS neurons by both contact-dependent and contact-independent mechanisms. In addition, we specifically deal with the immune functions of neuronal cell adhesion molecules, many of which are key modulators of neuronal synaptic formation and plasticity.

The NADPH oxidase is involved in lipopolysaccharide-mediated motor neuron injury

Recent evidence indicates that neuroinflammation is a key event in amyotrophic lateral sclerosis (ALS). However, the precise impact of inflammation on motor neurons remains elusive. By using organotypic spinal cord slice cultures, we demonstrate that exposure to lipopolysaccharide (LPS) led to the demise of motor neurons in a dose- and time- dependent manner, whereas interneurons were impaired relatively mildly. The ultrastructure of motor neurons showed extensive vacuolation and swollen mitochondria. Motor neurons lacked the expression of calretinin, and BAPTA-AM, an intracellular calcium chelator, ameliorated motor neuron injury, indicating that the low capacity of calcium buffering may partially account for the vulnerability of motor neurons. NADPH oxidase was activated upon LPS challenge, and apocynin, the selective inhibitor of this enzyme, prevented inflammation-mediated toxicity to motor neurons, suggesting that NADPH oxidase may play a critical role in motor neuron death caused by LPS-induced inflammation.

Chronic microglial activation and progressive dopaminergic neurotoxicity

PD (Parkinson's disease) is characterized by the selective and progressive loss of DA neurons (dopaminergic neurons) in the substantia nigra. Inflammation and activation of microglia, the resident innate immune cell in the brain, have been strongly linked to neurodegenerative diseases, such as PD. Microglia can respond to immunological stimuli and neuronal death to produce a host of toxic factors, including cytokines and ROS (reactive oxygen species). Microglia can also become persistently activated after a single stimulus and maintain the elevated production of both cytokines and ROS, long after the instigating stimulus is gone. Current reports suggest that this chronic microglial activation may be fuelled by either dying/damaged neurons or autocrine and paracrine signals from local glial cells, such as cytokines. Here, we review proposed mechanisms responsible for chronic neuroinflammation and explain the interconnected relationship between deleterious microglial activation, DA neuron damage and neurodegenerative disease.

Microglia and inflammation-mediated neurodegeneration: multiple triggers with a common mechanism

Inflammation, a common denominator among the diverse list of neurodegenerative diseases, has recently been implicated as a critical mechanism responsible for the progressive nature of neurodegeneration. Microglia are the resident innate immune cells in the central nervous system and produce a barrage of factors (IL-1, TNFalpha, NO, PGE2, superoxide) that are toxic to neurons. Evidence supports that the unregulated activation of microglia in response to environmental toxins, endogenous proteins, and neuronal death results in the production of toxic factors that propagate neuronal injury. In the following review, we discuss the common thread of microglial activation across numerous neurodegenerative diseases, define current perceptions of how microglia are damaging neurons, and explain how the microglial response to neuronal damage results in a self-propelling cycle of neuron death.

Brain activation of monocyte lineage cells: brain-derived soluble factors differentially regulate BV2 microglia and peripheral macrophage immune functions

Brain injury and subsequent neurodegeneration are often associated with infiltrating leukocytes and the activation of microglia as well as other infiltrating cells. However, the characteristics of activation are poorly understood. The objective of this study was to further the understanding of brain regulation of microglial activation. We used an organotypic coculture paradigm to assess how brain-derived soluble factors modulate microglia and peripheral macrophage activation through microscopy and flow cytometry techniques. In the presence of brain-derived soluble factors, the BV2 microglia cell line increased MHC II and phagocytic receptor (Fcgamma II/III) expression. The increased expression correlated with a functional increase in phagocytic activity, but did not correlate with an increase in allostimulation ability. Furthermore, this interaction was selective to an interaction between brain-derived soluble factor(s) and BV2 microglia, since it was not observed in the ANA1 macrophage cell line or in primary peritoneal macrophages. The results indicated that brain-derived soluble factor(s) modulate microglial activation in a manner that is distinct from the effects on peripheral macrophages. Moreover, our results suggest that inflammatory events associated with some types of brain injury may be induced by the brain without dependence on infiltrating peripheral macrophages or T lymphocytes.

Brain activation of monocyte-lineage cells: involvement of interleukin-6

Immune processes such as phagocytosis of debris and antigen presentation can be damaging to the function and survival of brain cells. Understanding what conditions and factors mediate immune processes in the brain is central to ameliorating the pathology associated with brain injury and disease. The elevation of secreted interleukin (IL)-6 is a common feature of brain injury and neurodegenerative pathology. Using organotypic brain slice coculture, the effects of brain-derived soluble factors on immune functions in the BV2 microglial cell line were studied. We have previously shown that brain-derived soluble factors upregulated phagocytic activity and class II major histocompatibility complex (MHC II) expression and altered BV2 morphology in a manner selective for microglia and not peripheral macrophages. The present study used IL-6-neutralizing antibody to show that brain-derived IL-6 was at least partially responsible for the brain coculture-induced upregulation of MHC II expression in the BV2 microglia. Additionally, IL-6 upregulated phagocytic activity and induced morphological changes in the BV2 cells similar to brain coculture. These effects were selective for microglia, as they were not observed in peripheral macrophage cell types. The ability of IL-6-neutralizing antibody to downregulate MHC II expression while maintaining enhanced phagocytic activity could potentially evade an antagonizing immune response associated with brain injury or disease.

Microglia as potential contributors to motor neuron injury in amyotrophic lateral sclerosis

The central nervous system (CNS) is equipped with a variety of cell types, all of which are assigned particular roles during the development, maintenance, function and repair of neural tissue. One glial cell type, microglia, deserves particular attention, as its role in the healthy or injured CNS is incompletely understood. Evidence exists for both regenerative and degenerative functions of these glial cells during neuronal injury. This review integrates the current knowledge of the role of microglia in an adult-onset neurodegenerative disease, amyotrophic lateral sclerosis (ALS), and pays particular attention to the possible mechanisms of initiation and propagation of neuronal damage during disease onset and progression. Microglial cell properties, behavior and detected inflammatory reactions during the course of the disease are described. The neuroinflammatory changes that occur in a mouse model of ALS are summarized. The understanding of microglial function in the healthy and injured CNS could offer better diagnostic as well as therapeutic approaches for prevention, retardation, or repair of neural tissue degeneration.

Microglia-derived tumor necrosis factor-α exaggerates death of newborn hippocampal progenitor cells in vitro

Production of new hippocampal neurons continues in adult mammals and different brain insults can significantly increase this process. However, many hippocampal progenitor cells (HPC) die shortly after birth. Here we investigated the possibility that increased release of cytokines by activated microglia contributes to the death of HPC. We showed that addition of tumor necrosis factor-alpha (TNFalpha) to the medium of a cultured HPC line (HiB5) shortly after the cells stopped division causes significant apoptotic cell death. Conditioned medium from an activated microglial cell line (BV-2) had a similar effect, though conditioned medium from nonactivated microglia increased the survival of HPC. Reverse transcription-PCR indicated that HPC and microglial cells express both TNF receptors, TNF-R1 and TNF-R2. Coculturing of HPC with activated microglial cells aggravated death of hippocampal progenitors and also caused death of microglial cells themselves. Our data indicate that activated microglia-released TNFalpha might be an important contributor in inflammation-induced exaggeration of death of newly formed HPC in the adult brain after an insult.

Glial activation modulates glutamate neurotoxicity in cerebellar granule cell cultures

We studied the influence of glial cells on the neuronal response to glutamate toxicity in cerebellar granule cell cultures. We compared the effect of glutamate on neuronal viability in neuronal vs. neuronal-glial cultures and determined this effect after pretreating the cultures with the lipopolysaccharide (LPS) of Escherichia coli, agent widely used to induce glial activation. Morphological changes in glial cells and nitric oxide (NO) production were evaluated as indicators of glial activation. We observed that glutamate neurotoxicity in neuronal-glial cultures was attenuated in a certain range of glutamate concentration when compared to neuronal cultures, but it was enhanced at higher glutamate concentrations. This enhanced neurotoxicity was associated with morphological changes in astrocytes and microglial cells in the absence of NO production. LPS treatment induced morphological changes in glial cells in neuronal-glial cultures as well as NO production. These effects occurred in the absence of significant neuronal death. However, when LPS-pretreated cultures were treated with glutamate, the sensitivity of neuronal-glial cultures to glutamate neurotoxicity was increased. This was accompanied by additional morphological changes in glial cells in the absence of a further increase in NO production. These results suggest that quiescent glial cells protect neuronal cells from glutamate neurotoxicity, but reactive glial cells increase glutamate neurotoxicity. Therefore, glial cells play a key role in the neuronal response to a negative stimulus, suggesting that this response can be modified through an action on glial cells.

Regulation of microglial inflammatory response by histone deacetylase inhibitors

The activation of microglial cells is involved in the pathogenesis of a variety of neurodegenerative diseases, stroke and traumatic brain injuries. Recent studies suggest that protein acetylation can affect the extent of inflammatory responses. Our aim was to elucidate whether histone deacetylase inhibitors, inducers of protein hyperacetylation, regulate the inflammatory response in neural models of inflammation in vitro and whether neurone-glia interactions affect this regulation. Interestingly, we observed that histone deacetylase inhibitors, such as trichostatin A (TSA) and suberoylanilide hydroxamic acid, strongly potentiated the lipopolysaccharide (LPS)-induced inflammatory response in murine N9 and rat primary microglial cells as well in neural co-cultures and hippocampal slice cultures. TSA clearly potentiated the LPS-induced expression of interleukin (IL)-6 and inducible nitric oxide synthase mRNAs, as well as the secretion of cytokines IL-6, tumour necrosis factor-alpha and macrophage inflammatory protein (MIP)-2, and nitric oxide (NO). Co-culture and slice culture experiments showed that the presence of astrocytes and neurones did not stimulate or prevent the pro-inflammatory potentiation induced by histone deacetylase inhibitor in microglial cells. The potentiation of cytokine and NO responses was blocked by the nuclear factor kappa B (NF-kappa B) inhibitors caffeic acid phenethyl ester and helenalin, demonstrating that the NF-kappa B signalling pathway is involved. The DNA-binding activity of the NF-kappa B complex was strongly increased by LPS treatment but not enhanced by TSA. This suggests that potentiation of the inflammatory response is not dependent on the level of cytoplasmic NF-kappa B activation or DNA-binding activity but that site of action may be at the level of transcriptional regulation. Our results suggest that environmental stresses, ageing, diet and diseases that regulate protein acetylation status may also affect the inflammatory response.

Parkinson's disease and exposure to infectious agents and pesticides and the occurrence of brain injuries: role of neuroinflammation

Idiopathic Parkinson's disease (PD) is a devastating movement disorder characterized by selective degeneration of the nigrostriatal dopaminergic pathway. Neurodegeneration usually starts in the fifth decade of life and progresses over 5-10 years before reaching the fully symptomatic disease state. Despite decades of intense research, the etiology of sporadic PD and the mechanism underlying the selective neuronal loss remain unknown. However, the late onset and slow-progressing nature of the disease has prompted the consideration of environmental exposure to agrochemicals, including pesticides, as a risk factor. Moreover, increasing evidence suggests that early-life occurrence of inflammation in the brain, as a consequence of either brain injury or exposure to infectious agents, may play a role in the pathogenesis of PD. Most important, there may be a self-propelling cycle of inflammatory process involving brain immune cells (microglia and astrocytes) that drives the slow yet progressive neurodegenerative process. Deciphering the molecular and cellular mechanisms governing those intricate interactions would significantly advance our understanding of the etiology and pathogenesis of PD and aid the development of therapeutic strategies for the treatment of the disease.

Neuron-conditioned media differentially affect the survival of activated or unstimulated microglia: evidence for neuronal control on apoptotic elimination of activated microglia

It is presently unknown what types of neuronal signals maintain microglial cells resting in the normal brain or control their activation in neuropathology. Recent data suggest that microglia activation induces apoptosis and that healthy neurons are controllers of the activation state and immune functions of microglia. In the present study we have evaluated, on microglial cells in cultures, whether neurons are able to affect their survival in resting conditions or upon activation with the bacterial endotoxin, lipopolysaccharide (LPS). We report that neuron-conditioned culture media induced apoptosis of LPS-stimulated, but not of unstimulated, microglia. This effect was, however, only present when conditioned media had been exposed to differentiated neurons and not to immature ones, and was absent when glutamate receptors had been pharmacologically blocked in neuronal cultures. The effect was also blocked by heat-inactivation of the conditioned media. Media conditioned with either differentiated or undifferentiated cerebellar granule neurons positively affected the survival of unstimulated microglial cells when the standard concentration of fetal bovine serum (10%) was included in the culture media. Our results highlight the ability of differentiated neurons to maintain a controlled inflammatory state through production of factor(s) favoring the apoptotic elimination of activated microglia. They also suggest that immature neurons may, on the contrary, favor the survival of microglia during development.

Use of cocultured cell systems to elucidate chemokine-dependent neuronal/microglial interactions: control of microglial activation

In order to understand processes involved in central nervous system inflammatory diseases, a critical appreciation of mechanisms involved in the control of immune function in the brain is needed. Microglial cells are watchful eyes for unusual events and detecting the presence of pathogens but are also alert to signals emanating from damaged neurons. Fractalkine (CX3CL1) is a chemokine which is expressed predominantly in the central nervous system, being localized on neurons, while its receptor, CX3CR1, is found on microglial cells. We have developed a strategy to investigate the role of this chemokine in neuronal-microglia interactions. Because fractalkine is expressed both as a soluble and as a membrane-attached protein, we have established various protocols involving different levels of cell-to-cell communication. Three experimental systems were instituted, including (1) a conditioned medium transfer system in which no cell-cell communication or contact is possible, (2) a transwell system that permits cell-contact-independent communication through diffusible soluble factors only, and (3) a coculture system allowing cell-to-cell communication via direct microglial-neuronal contacts. Using these in vitro cocultured systems, we have investigated the role of a soluble and/or cell-associated chemokine, such as fractalkine, in order to obtain insights into the role of glia-neuron interactions in cerebral inflammation.

Reciprocal interactions between microglia and neurons: from survival to neuropathology

Microglia represent a major cellular component of the brain, where they constitute a widely distributed network of immunoprotective cells. During the last decades, it has become clear that the functions traditionally ascribed to microglia, i.e. to dispose of dead cells and debris and to mediate brain inflammatory states, are only a fraction of a much wider repertoire of functions spanning from brain development to aging and neuropathology. The aim of the present survey is to critically discuss some of these functions, focusing in particular on the reciprocal microglia-neuron interactions and on the complex signaling systems subserving them. We consider first some of the functional interactions dealing with invasion, proliferation and migration of microglia as well as with the establishment of the initial blueprint of neural circuits in the developing brain. The signals related to the suppression of immunological properties of microglia by neurons in the healthy brain, and the derangement from this physiological equilibrium in aging and diseases, are then examined. Finally, we make a closer examination of the reciprocal signaling between damaged neurons and microglia and, on these bases, we propose that microglial activation, consequent to neuronal injury, is primarily aimed at neuroprotection. The loss of specific communication between damaged neurons and microglia is viewed as responsible for the turning of microglia to a hyperactivated state, which allows them to escape neuronal control and to give rise to persistent inflammation, resulting in exacerbation of neuropathology. The data surveyed here point at microglial-neuron interactions as the basis of a complex network of signals conveying messages with high information content and regulating the most important aspects of brain function. This network shares similar features with some fundamental principles governing the activity of brain circuits: it is provided with memory and it continuously evolves in relation to the flow of time and information.

Evidence that toxicity of lipopolysaccharide upon cholinergic basal forebrain neurons requires the presence of glial cells in vitro

The cholinergic system of the basal forebrain is affected in brains of dementia patients and during neuroinflammation. The aim of this study was to establish a method to cultivate basal forebrain cholinergic neurons in dissociated, pure neuronal cultures and to apply this method to study the effect of acute and chronic experimentally-induced inflammation using lipopolysaccharide. Purity of the cultures, degrees of neuronal dissociation, connectivity and neuronal survival were investigated by immunocytochemistry for microtubule-associated protein-2 (neurons), glial fibrillary acidic protein (astroglia), complement receptor 3 (microglia), choline acetyltransferase and the neurotrophin receptor p75 (cholinergic neurons). Neuronal cultures only contained <7% astrocytes and <1% microglia when using a "sandwich-technique". Acute (1, 10 microg/ml) as well as chronic (0.1, 1 microg/ml) treatment with lipopolysaccharide did neither affect total number of neurons, nor number of p75-positive neurons or enhance expression of major histocompatibility complex I or II. Our results suggest that lipopolysaccharide-induced degeneration of both microtubule-associated protein-2-like immunoreactive as well as specific killing of cholinergic forebrain neurons in vitro are mediated by glial cells.

Neurons reduce glial responses to lipopolysaccharide (LPS) and prevent injury of microglial cells from over-activation by LPS

The microenvironment of the CNS has been considered to tonically inhibit glial activities. It has been shown that glia become activated where neuronal death occurs in the aging brain. We have previously demonstrated that neurons tonically inhibit glial activities including their responses to the bacterial endotoxin lipopolysaccharide (LPS). It is not clear whether activation of glia, especially microglia in the aging brain, is the consequence of disinhibition due to neuronal death. This study was designed to determine if glia regain their responsiveness to LPS once the neurons have died in aged cultures. When cultured alone, glia from postnatal day one rat mesencephalons stimulated with LPS (0.1-1000 ng/mL) produced both nitric oxide (NO) and tumor necrosis factor alpha (TNFalpha), yielding a sigmoid and a bell-shaped curve, respectively. When neuron-containing cultures were prepared from embryonic day 14/15 mesencephalons, the shape of the dose-response curve for NO was monotonic and the bell-shaped curve for TNFalpha production was shifted to the right. After 1 month of culture under conditions where neurons die, the production curves for NO and TNFalpha in LPS-stimulated glia shifted back to the left compared to mixed neuron-glia cultures. Immunostaining of rat microglia for the marker CR3 (the receptor for complement component C3) demonstrated that high concentrations of LPS (1 microg/mL) reduced the number of microglia in mixed-glial cultures. In contrast, reduction of CR3 immunostaining was not observed in LPS-stimulated mixed neuron-glia cultures. Taken together, the results demonstrate that disinhibition of the glial response to LPS occurs after neurons die in aged cultures. Once neurons have died, the responsiveness of glia to LPS is restored. Neurons prevented injury to microglia by reducing their responsiveness to LPS. This study broadens our understanding of the ways in which the CNS microenvironment affects cerebral inflammation.