Immortalized human microglial cell line: phenotypic expression

Human pluripotent stem cell (hPSC)-derived microglia for the study of brain disorders. A comprehensive review of existing protocols

Microglia, resident immune cells of the brain that originate from the yolk sac, play a critical role in maintaining brain homeostasis by monitoring and phagocytosing pathogens and cellular debris in the central nervous system (CNS). While they share characteristics with myeloid cells, they are distinct from macrophages. In response to injury, microglia release pro-inflammatory factors and contribute to brain homeostasis through activities such as synapse pruning and neurogenesis. To better understand their role in neurological disorders, the generation of in vitro models of human microglia has become essential. These models, derived from patient-specific induced pluripotent stem cells (iPSCs), provide a controlled environment to study the molecular and cellular mechanisms underlying microglia-mediated neuroinflammation and neurodegeneration. The incorporation or generation of microglia into three-dimensional (3D) organoid cultures provides a more physiologically relevant environment that offers further opportunities to study microglial dynamics and disease modeling. This review describes several protocols that have been recently developed for the generation of human-induced microglia. Importantly, it highlights the promise of these in vitro models in advancing our understanding of brain disorders and facilitating personalized drug screening.

Development and characterisation of mgTHP-1, a novel in vitro model for neural macrophages with microglial characteristics

Neuroinflammation is primarily characterised by activation of the brain's resident macrophages - the microglia. However, other central nervous system (CNS) cells also contribute to this response, including the astrocytes and endothelial cells. In addition, there is infiltration into the CNS of peripherally derived immune cells. Together these cells mediate inflammation by the production of cytokines, chemokines, reactive oxygen species, and secondary messengers, and enacting of the appropriate response to those signals. However, deciphering the specific contributions of each cell type has been challenging. Studying CNS cell biology is often challenging, as the isolation of primary cells is not always feasible, and differentiation towards microglia-like cells is complex. Here, we demonstrate a novel method whereby THP-1 monocytic cells are differentiated into neural macrophage cells with microglia-like cell characteristics. The cells, designated mgTHP-1, show typical morphological and gene expression patterns of resident CNS macrophages and functionally respond to inflammatory stimuli by producing inflammatory cytokines. Furthermore, with the addition of Vicenin-2 (an anti-inflammatory flavonoid) such responses can be reversed. This novel cell model will allow further investigations, and hence insights, into the neuroinflammatory mechanisms associated with CNS diseases.

PRMT3 drives glioblastoma progression by enhancing HIF1A and glycolytic metabolism

Glioblastoma (GBM) is the most common and aggressive primary brain tumor, but the mechanisms underlying tumor growth and progression remain unclear. The protein arginine methyltransferases (PRMTs) regulate a variety of biological processes, however, their roles in GBM growth and progression are not fully understood. In this study, our functional analysis of gene expression networks revealed that among the PRMT family expression of PRMT3 was most significantly enriched in both GBM and low-grade gliomas. Higher PRMT3 expression predicted poorer overall survival rate in patients with gliomas. Knockdown of PRMT3 markedly reduced the proliferation and migration of GBM cell lines and patient-derived glioblastoma stem cells (GSC) in cell culture, while its over-expression increased the proliferative capacity of GSC cells by promoting cell cycle progression. Consistently, stable PRMT3 knockdown strongly inhibited tumor growth in xenograft mouse models, along with a significant decrease in cell proliferation as well as an increase in apoptosis. We further found that PRMT3 reprogrammed metabolic pathways to promote GSC growth via increasing glycolysis and its critical transcriptional regulator HIF1α. In addition, pharmacological inhibition of PRMT3 with a PRMT3-specific inhibitor SGC707 impaired the growth of GBM cells. Thus, our study demonstrates that PRMT3 promotes GBM progression by enhancing HIF1A-mediated glycolysis and metabolic rewiring, presenting a point of metabolic vulnerability for therapeutic targeting in malignant gliomas.

The Bioactivities of Phycocyanobilin from Spirulina

Phycocyanobilin (PCB) is a linear open-chain tetrapyrrole chromophore that captures and senses light and a variety of biological activities, such as anti-oxidation, anti-cancer, and anti-inflammatory. In this paper, the biological activities of PCB are reviewed, and the related mechanism of PCB and its latest application in disease treatment are introduced. PCB can resist oxidation by scavenging free radicals, inhibiting the activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and delaying the activity of antioxidant enzymes. In addition, PCB can also be used as an excellent anti-inflammatory agent to reduce the proinflammatory factors IL-6 and IFN-γ and to up-regulate the production of anti-inflammatory cytokine IL-10 by inhibiting the inflammatory signal pathways NF-κB and mitogen-activated protein kinase (MAPK). Due to the above biological activities of phycocyanobilin PCB, it is expected to become a new effective drug for treating various diseases, such as COVID-19 complications, atherosclerosis, multiple sclerosis (MS), and ischaemic stroke (IS).

Evolving Models and Tools for Microglial Studies in the Central Nervous System

Microglia play multiple roles in such processes as brain development, homeostasis, and pathology. Due to their diverse mechanisms of functions, the complex sub-classifications, and the large differences between different species, especially compared with humans, very different or even opposite conclusions can be drawn from studies with different research models. The choice of appropriate research models and the associated tools are thus key ingredients of studies on microglia. Mice are the most commonly used animal models. In this review, we summarize in vitro and in vivo models of mouse and human-derived microglial research models, including microglial cell lines, primary microglia, induced microglia-like cells, transgenic mice, human-mouse chimeric models, and microglial replacement models. We also summarize recent developments in novel single-cell and in vivo imaging technologies. We hope our review can serve as an efficient reference for the future study of microglia.

Validation of Induced Microglia-Like Cells (iMG Cells) for Future Studies of Brain Diseases

Microglia are the primary resident immune cells of the central nervous system that maintain physiological homeostasis in the brain and contribute to the pathogenesis of many psychiatric disorders and neurodegenerative diseases. Due to the lack of appropriate human cellular models, it is difficult to study the basic pathophysiological processes linking microglia to brain diseases. In this study, we adopted a microglia-like cellular model derived from peripheral blood monocytes with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-34 (IL-34). We characterized and validated this in vitro cellular model by morphology, immunocytochemistry, gene expression profiles, and functional study. Our results indicated that the iMG cells developed typical microglial ramified morphology, expressed microglial specific surface markers (P2RY12 and TMEM119), and possessed phagocytic activity. Principal component analyses and multidimensional scaling analyses of RNA-seq data showed that iMG cells were distinct from monocytes and induced macrophages (iMacs) but clustered closer to human microglia and hiPSC-induced microglia. Heatmap analyses also found that iMG cells, but not monocytes, were closely clustered with human primary microglia. Further pathway and relative expression analysis indicated that unique genes from iMG cells were involved in the regulation of the complement system, especially in the synapse and ion transport. Overall, our data demonstrated that the iMG model mimicked many features of the brain resident microglia, highlighting its utility in the study of microglial function in many brain diseases, such as schizophrenia and Alzheimer's disease (AD).

Quantitative morphometric and cell-type-specific population analysis of microglia-enriched cultures subcloned to high purity from newborn rat brains

Morphological and functional characterizations of cultured microglia are essential for the improved understanding of their roles in neuronal health and disease. Although some studies (phenotype analysis, phagocytosis) can be carried out in mixed or microglia-enriched cultures, in others (gene expression) pure microglia must be used. If the use of genetically modified microglial cells is not feasible, isolation of resident microglia from nervous tissue must be carried out. In this study, mixed primary cultures were established from the forebrains of newborn rats. Secondary microglia-enriched cultures were then prepared by shaking off these cells from the primary cultures, which were subsequently used to establish tertiary cultures by further shaking off the easily detachable microglia. The composition of these cultures was quantitatively analyzed by immunocytochemistry of microglia-, astrocyte-, oligodendrocyte- and neuron-specific markers to determine yield and purity. Microglia were quantitatively characterized regarding morphological and proliferation aspects. Secondary and tertiary cultures typically exhibited 73.3% ± 17.8% and 93.1% ± 6.0% purity for microglia, respectively, although the total number of microglia in the latter was much smaller. One in seven attempts of culturing the tertiary cultures had ~99% purity for microglia. The overall yield from the number of cells plated at DIV0 to the Iba1-positive microglia in tertiary cultures was ~1%. Astrocytic and neuronal contamination progressively decreased during subcloning, while oligodendrocytes were found sporadically throughout culturing. Although the tertiary microglia cultures had a low yield, they produced consistently high purity for microglia; after validation, such cultures are suitable for purity-sensitive functional screenings (gene/protein expression).

Neural In Vitro Models for Studying Substances Acting on the Central Nervous System

Animal models have been greatly contributing to our understanding of physiology, mechanisms of diseases, and toxicity. Yet, their limitations due to, e.g., interspecies variation are reflected in the high number of drug attrition rates, especially in central nervous system (CNS) diseases. Therefore, human-based neural in vitro models for studying safety and efficacy of substances acting on the CNS are needed. Human iPSC-derived cells offer such a platform with the unique advantage of reproducing the "human context" in vitro by preserving the genetic and molecular phenotype of their donors. Guiding the differentiation of hiPSC into cells of the nervous system and combining them in a 2D or 3D format allows to obtain complex models suitable for investigating neurotoxicity or brain-related diseases with patient-derived cells. This chapter will give an overview over stem cell-based human 2D neuronal and mixed neuronal/astrocyte models, in vitro cultures of microglia, as well as CNS disease models and considers new developments in the field, more specifically the use of brain organoids and 3D bioprinted in vitro models for safety and efficacy evaluation.

Alzheimer's Disease Research Using Human Microglia

Experimental studies of neuroinflammation in Alzheimer's disease (AD) have mostly investigated microglia, the brain-resident macrophages. This review focused on human microglia obtained at rapid autopsies. Studies employing methods to isolate and culture human brain microglia in high purity for experimental studies were discussed. These methods were employed to isolate human microglia for investigation of a number of features of neuroinflammation, including activation phenotypes, neurotoxicity, responses to abnormal aggregated proteins such as amyloid beta, phagocytosis, and the effects of aging and disease on microglia cellular properties. In recent years, interest in human microglia and neuroinflammation has been renewed due to the identification of inflammation-related AD genetic risk factors, in particular the triggering receptor expressed on myeloid cells (TREM)-2. Because of the difficulties in developing effective treatments for AD, there has been a general need for greater understanding of the functions of microglia in normal and AD brains. While most experimental studies on neuroinflammation have employed rodent microglia, this review considered the role of human microglia in experimental studies. This review focused on the development of in vitro methodology for the culture of postmortem human microglia and the key findings obtained from experimental studies with these cells.

Interaction between microglia and retinal pigment epithelial cells determines the integrity of outer blood-retinal barrier in diabetic retinopathy

Inner and outer blood-retinal barriers (BRBs), mainly composed of retinal endothelial cells and retinal pigment epithelial (RPE) cells, respectively, maintain the integrity of the retinal tissues. In this study, we aimed to investigate the mechanisms of the outer BRB disruption regarding the interaction between RPE and microglia. In mice with high-fat diet-induced obesity and streptozotocin-induced hyperglycemia, microglia accumulated on the RPE layer, as in those after intravitreal injection of interleukin (IL)-6, which is elevated in ocular fluids of patients with diabetic retinopathy. Although IL-6 did not directly affect the levels of zonula occludens (ZO)-1 and occludin in RPE cells, IL-6 increased VEGFA mRNA in RPE cells to recruit microglial cells. In microglial cells, IL-6 upregulated the mRNA levels of MCP1, MIP1A, and MIP1B, to amplify the recruitment of microglial cells. In this manner, IL-6 modulated RPE and microglial cells to attract microglial cells on RPE cells. Furthermore, IL-6-treated microglial cells produced and secreted tumor necrosis factor (TNF)-α, which activated NF-κB and decreased the levels of ZO-1 in RPE cells. As STAT3 inhibition reversed the effects of IL-6-treated microglial cells on the RPE monolayer in vitro, it reduced the recruitment of microglial cells and the production of TNF-α in RPE tissues in streptozotocin-treated mice. Taken together, IL-6-treated RPE and microglial cells amplified the recruitment of microglial cells and IL-6-treated microglial cells produced TNF-α to disrupt the outer BRB in diabetic retinopathy.

Genetic and Histological Alterations Reveal Key Role of Prostaglandin Synthase and Cyclooxygenase 1 and 2 in Traumatic Brain Injury-Induced Neuroinflammation in the Cerebral Cortex of Rats Exposed to Moderate Fluid Percussion Injury

After the initial insult in traumatic brain injury (TBI), secondary neurodegeneration occurs that is intimately associated with neuroinflammation. Prostaglandin (PG) synthases and cyclooxygenase (COX) 1 and 2 may contribute to inflammation in the brain. Temporal and spatial expression features of PG and COX1 and 2 following trauma may guide the development of antineuroinflammation strategies. Here, we examined PG synthase signaling and COX1 and 2 gene expression levels and COX-1- and 2-positive cell types and their temporal localization in TBI-induced brain in an effort to reveal their participation in the disease’s evolving neuroinflammation. Using brain samples from the cerebral cortex of rats subjected to TBI model of lateral moderate fluid percussion injury (FPI), we sought to characterize the temporal (subacute TBI) and spatial (lateral cortical lesion) brain alterations accompanying the disease progression. Temporal gene expression changes of PG synthase signaling were compared between sham-operated and TBI-treated rats using microarray pathway analysis. Moreover, we examined COX1 and 2 expression patterns and their intracellular distribution in sham-operated and TBI-treated rats by immunohistochemistry. After FPI, COX1 and 2 gene expression levels, and PGE₂ synthase increased while PGD₂ synthase decreased, suggesting that PGE₂ and PGD₂ afforded contraindicative effects of inflammation and anti-inflammation, respectively. Immunohistochemical analyses showed that both COX1 and COX2 increased in a time-dependent manner in the brain, specifically in degenerating neurons of the cortex. Interestingly, the expression of COX cell type was cell-specific, in that COX1 was particularly increased in degenerating neurons while COX2 was expressed in macrophages. In view of the dynamic temporal and spatial expression of PG, COX1 and 2 gene expression and localization in the injured brain regulating PG synthase and COX1 and 2 activity will require a careful disease-specific tailoring of treatments to abrogate the neuroinflammation-plagued secondary cell death due to TBI.

Immortalization of primary microglia: a new platform to study HIV regulation in the central nervous system

The major reservoirs for HIV in the CNS are in the microglia, perivascular macrophages, and to a lesser extent, astrocytes. To study the molecular events controlling HIV expression in the microglia, we developed a reliable and robust method to immortalize microglial cells from primary glia from fresh CNS tissues and commercially available frozen glial cells. Primary human cells, including cells obtained from adult brain tissue, were transformed with lentiviral vectors expressing SV40 T antigen or a combination of SVR40 T antigen and hTERT. The immortalized cells have microglia-like morphology and express key microglial surface markers including CD11b, TGFβR, and P2RY12. Importantly, these cells were confirmed to be of human origin by sequencing. The RNA expression profiles identified by RNA-seq are also characteristic of microglial cells. Furthermore, the cells demonstrate the expected migratory and phagocytic activity, and the capacity to mount an inflammatory response characteristic of primary microglia. The immortalization method has also been successfully applied to a wide range of microglia from other species (macaque, rat, and mouse). To investigate different aspects of HIV molecular regulation in CNS, the cells have been superinfected with HIV reporter viruses and latently infected clones have been selected that reactive HIV in response to inflammatory signals. The cell lines we have developed and rigorously characterized will provide an invaluable resource for the study of HIV infection in microglial cells as well as studies of microglial cell function.

Endothelial STAT3 Activation Increases Vascular Leakage Through Downregulating Tight Junction Proteins: Implications for Diabetic Retinopathy

Vascular inflammation is characteristic feature of diabetic retinopathy. In diabetic retina, a variety of the pro-inflammatory cytokines are elevated and involved in endothelial dysfunction. STAT3 transcription factor has been implicated in mediating cytokine signaling during vascular inflammation. However, whether and how STAT3 is involved in the direct regulation of the endothelial permeability is currently undefined. Our studies revealed that IL-6-induced STAT3 activation increases retinal endothelial permeability and vascular leakage in retinas of mice through the reduced expression of the tight junction proteins ZO-1 and occludin. In a co-culture model with microglia and endothelial cells under a high glucose condition, the microglia-derived IL-6 induced STAT3 activation in the retinal endothelial cells, leading to increasing endothelial permeability. In addition, IL-6-induced STAT3 activation was independent of ROS generation in the retinal endothelial cells. Moreover, we demonstrated that STAT3 activation downregulates the ZO-1 and occludin levels and increases the endothelial permeability through the induction of VEGF production in retinal endothelial cells. These results suggest the potential importance of IL-6/STAT3 signaling in regulating endothelial permeability and provide a therapeutic target to prevent the pathology of diabetic retinopathy. J. Cell. Physiol. 232: 1123-1134, 2017. © 2016 Wiley Periodicals, Inc.

Spirulina and C-phycocyanin reduce cytotoxicity and inflammation-related genes expression of microglial cells

OBJECTIVE

Our aim was to investigate the effects of Spirulina on BV-2 microglial cell cytotoxicity and inflammatory genes expression.

METHODS

BV-2 microglial cells were treated with lipopolysaccharide (LPS) (1 µg/ml) and various concentrations of Spirulina platensis water extract or its active component (C-phycocyanin (C-PC)) for 24 hours. Cytotoxicity (lactate dehydrogenase (LDH) release) and expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) mRNAs were assayed.

RESULTS

LPS increased LDH production and up-regulated expression of iNOS, COX-2, TNF-α, and IL-6 by BV-2 microglial cells. However, Spirulina platensis water extract and C-PC significantly reduced LPS-induced LDH release, and expression of iNOS, COX-2, TNF-α, and IL-6 mRNAs.

CONCLUSION

Spirulina can reduce the cytotoxicity and inhibit expression of inflammation-related genes of LPS-stimulated BV-2 microglial cells.

Glucosamine suppresses platelet-activating factor-induced activation of microglia through inhibition of store-operated calcium influx

Microglia activation and subsequent release of inflammatory mediators are implicated in the pathophysiology of neurodegenerative diseases. Platelet-activating factor (PAF), a potent lipid mediator synthesized by microglia, is known to stimulate microglia functional responses. In this study, we determined that endogenous PAF exert autocrine effects on microglia activation, as well as the underlying mechanism involved. We also investigated the effect of D-glucosamine (GlcN) on PAF-induced cellular activation in human HMO6 microglial cells. PAF induced sustained intracellular Ca(2+) ([Ca(2+)]i) increase through store-operated Ca(2+) channels (SOC) and reactive oxygen species (ROS) generation. PAF also induced pro-inflammatory markers through NFκB/COX-2 signaling. GlcN significantly inhibited PAF-induced Ca(2+) influx and ROS generation without significant cytotoxicity. GlcN downregulated excessive expression of pro-inflammatory markers and promoted filopodia formation through NFκB/COX-2 inhibition in PAF-stimulated HMO6 cells. Taken together, these data suggest that GlcN may offer substantial therapeutic potential for treating inflammatory and neurodegenerative diseases accompanied by microglial activation.

Alternatively activated microglia and macrophages in the central nervous system

Macrophages are important players in the fight against viral, bacterial, fungal and parasitic infections. From a resting state they may undertake two activation pathways, the classical known as M1, or the alternative known as M2. M1 markers are mostly mediators of pro-inflammatory responses whereas M2 markers emerge for resolution and cleanup. Microglia exerts in the central nervous system (CNS) a function similar to that of macrophages in the periphery. Microglia activation and proliferation occurs in almost any single pathology affecting the CNS. Often microglia activation has been considered detrimental and drugs able to stop microglia activation were considered for the treatment of a variety of diseases. Cumulative evidence shows that microglia may undergo the alternative activation pathway, express M2-type markers and contribute to neuroprotection. This review focuses on details about the role of M2 microglia and in the approaches available for its identification. Approaches to drive the M2 phenotype and data on its potential in CNS diseases are also reviewed.

How dependent is synaptic plasticity on microglial phenotype?

Microglia are particularly plastic cells which can be shifted from their resting state by numerous factors and adopt distinct phenotypes. The cells are multifunctional, though their main role is probably maintenance of homoeostasis. Resting cells are responsible for surveillance, whereas activation induces the cells to adopt neuroprotective or neurodetrimental roles, which are anti-inflammatory or pro-inflammatory respectively. The evidence indicates that activated cells with a pro-inflammatory phenotype predominate in neurodegenerative diseases and models of neurodegeneration and that this may significantly contribute to the deteriorating neuronal function. This question is considered in this review, in particular in the context of animal models of Alzheimer's disease (AD). This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Quantification of microglial phagocytosis by a flow cytometer-based assay

Microglia represent the largest population of phagocytes in the CNS and have a principal role in immune defense and inflammatory responses in the CNS. Their phagocytic activity can be studied by a variety of techniques, including a flow cytometry-based approach utilizing polystyrene latex beads. The flow cytometry-based microglial phagocytosis assay, which is presented here, offers the advantage of rapid and reliable analysis of thousands of cells in a quantitative fashion.

Generation and characterization of immortalized rat retinal microglial cell lines

Retinal microglia play an important role as resident immunocompetent and phagocytic cells in the event of injury and disease. Retinal microglia and microglia precursor transplantation show a rescue effect in ischemic retina and retinal degeneration. However, studies of retinal microglia have been hampered by the difficulty of obtaining sufficient numbers of microglia. One way to circumvent this difficulty is to establish permanent retinal microglia cell lines. In the present study, we report the generation of immortalized retinal microglia, T-MG cells, from postnatal day 3 rat retinal tissue using a lentiviral vector encoding SV40 large T antigen. The T-MG cells exhibited cell-type-specific antigens for monocyte/macrophage lineage cells, including CD11b (OX42), ED1 (OX6), and Iba1, and actively phagocytosed latex beads. In addition to primary retinal microglia, T-MG cells also have the ability to recruit into chemokines. Treatment of T-MG cells with lipopolysaccharide (LPS) led to increased levels of tumor necrosis factor-α, interleukin-1β, and inducible nitric oxide synthase. Genome-wide microarray analysis showed a less than 1% difference in the genes between the T-MG cells and the control primary retinal microglia. The T-MG cells exhibited properties similar to those of the primary retinal microglia and should have considerable utility as an in vitro model for the study of retinal microglia in health and as a curative therapy and an in vivo model for the study of retinal microglia in disease.

Inhibition of microglia activation as a phenotypic assay in early drug discovery

Complex biological processes such as inflammation, cell death, migration, proliferation, and the release of biologically active molecules can be used as outcomes in phenotypic assays during early stages of drug discovery. Although target-based approaches have been widely used over the past decades, a disproportionate number of first-in-class drugs have been identified using phenotypic screening. This review details phenotypic assays based on inhibition of microglial activation and their utility in primary and secondary screening, target validation, and pathway elucidation. The role of microglia, both in normal as well as in pathological conditions such as chronic neurodegenerative diseases, is reviewed. Methodologies to assess microglia activation in vitro are discussed in detail, and classes of therapeutic drugs known to decrease the proinflammatory and cytotoxic responses of activated microglia are appraised, including inhibitors of glutaminase, cystine/glutamate antiporter, nuclear factor κB, and mitogen-activated protein kinases.

The B1-cell subpopulation is diminished in patients with relapsing-remitting multiple sclerosis

B cell subsets in newly diagnosed untreated, relapsing-remitting multiple sclerosis (MS) patients were examined. The fraction of CD20(+) B cells was significantly increased in MS. Among subsets of B cells, MS patients had increased frequency of naïve cells, but reduced frequency of memory and B1 cells. The frequencies of B1 cells were inversely correlated with the time since last attack. B1 cells resembled the phenotype of either lymphocytes (CD11b(-) B1 cells) or monocytes (CD11b(+) B1 cells) and a small fraction of cells was CD3(+)CD20(+) by confocal microscopy.

SN79, a sigma receptor ligand, blocks methamphetamine-induced microglial activation and cytokine upregulation

Methamphetamine (METH) abuse is associated with several negative side effects including neurotoxicity in specific brain regions such as the striatum. The precise molecular mechanisms by which METH usage results in neurotoxicity remain to be fully elucidated, with recent evidence implicating the importance of microglial activation and neuroinflammation in damaged brain regions. METH interacts with sigma receptors which are found in glial cells in addition to neurons. Moreover, sigma receptor antagonists have been shown to block METH-induced neurotoxicity in rodents although the cellular mechanisms underlying their neuroprotection remain unknown. The purpose of the current study was to determine if the prototypic sigma receptor antagonist, SN79, mitigates METH-induced microglial activation and associated increases in cytokine expression in a rodent model of METH-induced neurotoxicity. METH increased striatal mRNA and protein levels of cluster of differentiation 68 (CD68), indicative of microglial activation. METH also increased ionized calcium binding adapter molecule 1 (IBA-1) protein expression, further confirming the activation of microglia. Along with microglial activation, METH increased striatal mRNA expression levels of IL-6 family pro-inflammatory cytokines, leukemia inhibitory factor (lif), oncostatin m (osm), and interleukin-6 (il-6). Pretreatment with SN79 reduced METH-induced increases in CD68 and IBA-1 expression, demonstrating its ability to prevent microglial activation. SN79 also attenuated METH-induced mRNA increases in IL-6 pro-inflammatory cytokine family members. The ability of a sigma receptor antagonist to block METH-induced microglial activation and cytokine production provides a novel mechanism through which the neurotoxic effects of METH may be mitigated.

A novel in vitro human microglia model: characterization of human monocyte-derived microglia

Microglia are the innate immune cells of the central nervous system. They help maintaining physiological homeostasis and contribute significantly to inflammatory responses in the course of infection, injury and degenerative processes. To date, there is no standardized simple model available to investigate the biology of human microglia. The aim of this study was to establish a new human microglia model. For that purpose, human peripheral blood monocytes were cultured in serum free medium in the presence of M-CSF, GM-CSF, NGF and CCL2 to generate monocyte-derived microglia (M-MG). M-MG were clearly different in morphology, phenotype and function from freshly isolated monocytes, cultured monocytes in the absence of the cytokines and monocyte-derived dendritic cells (M-DC) cultured in the presence of GM-CSF and IL-4. M-MG acquired a ramified morphology with primary and secondary processes. M-MG displayed a comparable phenotype to the human microglia cell line HMC3, expressing very low levels of CD45, CD14 and HLA-DR, CD11b and CD11c; and undetectable levels of CD40, CD80 and CD83, and a distinct pattern of chemokine receptors (positive for CCR1, CCR2, CCR4, CCR5, CXCR1, CXCR3, CX3CR1; negative for CCR6 and CCR7). In comparison with M-DC, M-MG displayed lower T-lymphocyte stimulatory capacity, as well as lower phagocytosis activity. The described protocol for the generation of human monocyte-derived microglia is feasible, well standardized and reliable, as it uses well defined culture medium and recombinant cytokines, but no serum or conditioned medium. This protocol will certainly be very helpful for future studies investigating the biology and pathology of human microglia.

Human microglia transplanted in rat focal ischemia brain induce neuroprotection and behavioral improvement

Background and Purpose

Microglia are resident immunocompenent and phagocytic cells of central nervous system (CNS), which produce various cytokines and growth factors in response to injury and thereby regulate disease pathology. The purpose of this study is to investigate the effects of microglial transplantation on focal cerebral ischemia model in rat.

Methods

Transient middle cerebral artery occlusion (MCAO) in rats was induced by the intraluminal filament technique. HMO6 cells, human microglial cell line, were transplanted intravenously at 48 hours after MCAO. Functional tests were performed and the infarct volume was measured at 7 and 14 days after MCAO. Migration and cell survival of transplanted microglial cells and host glial reaction in the brain were studied by immunohistochemistry. Gene expression of neurotrophic factors, cytokines and chemokines in transplanted cells and host rat glial cells was determined by laser capture microdissection (LCM) and quantitative real time-PCR.

Results

HMO6 human microglial cells transplantion group demonstrated significant functional recovery compared with control group. At 7 and 14 days after MCAO, infarct volume was significantly reduced in the HMO group. In the HMO6 group, number of apoptotic cells was time-dependently reduced in the infarct core and penumbra. In addition, number of host rat microglia/macrophages and reactive astrocytes was significantly decreased at 7 and 14 days after MCAO in the penumbra. Gene expression of various neurotrophic factors (GDNF, BDNF, VEGF and BMP7) and anti-inflammatory cytokines (IL4 and IL5) was up-regulated in transplanted HMO6 cells of brain tissue compared with those in culture. The expression of GDNF and VEGF in astrocytes in penumbra was significantly up-regulated in the HMO6 group.

Conclusions

Our results indicate that transplantation of HMO6 human microglial cells reduces ischemic deficits and apoptotic events in stroke animals. The results were mediated by modulation of gliosis and neuroinflammation, and neuroprotection provided by neurotrophic factors of endogenous and transplanted cells-origin.

Microglia transplantation attenuates white matter injury in rat chronic ischemia model via matrix metalloproteinase-2 inhibition

Chronic cerebral ischemia is thought to induce white matter lesions (WMLs), which contribute to subcortical vascular dementia. Although glial activation and protease upregulation are believed to modify WML pathology, effective therapy remains elusive. Here, we compare the efficacy of microglial cell transplantation and mesenchymal stem cell (MSC) transplantation in protecting against WML development in a chronic cerebral hypoperfusion rat model. A microglial cell line (HMO6), MSC cell line (B10) or vehicle (phosphate-buffered saline; PBS) was intravenously injected, and the appearance and severity of WMLs were evaluated. Transplanted HMO6 and B10 cells migrated to sites of WMLs, including the corpus callosum (CC) and caudoputamen (CP), reduced the severity of WMLs, and inhibited the accumulation and activation of microglia and astrocytes. Transplantation of both cell types reduced the level of matrix metalloproteinase (MMP)-2 mRNA in microglia of the CC. MMP-2 protein level and activity were also both greatly reduced in the same region. Our results indicate that transplantation of either microglial cells or mesenchymal stem cells could inhibit chronic cerebral ischemia-induced WML formation by decreasing MMP-2 expression in microglia and decreasing MMP-2 activity in the CC region.

The genome-wide expression profile of Nelumbinis semen on lipopolysaccharide-stimulated BV-2 microglial cells

This study was conducted to evaluate the protective mechanisms of Nelumbinis semen (NS) on lipopolysaccharide (LPS)-induced activation of BV-2 microglial cells. The anti-inflammatory effects of NS were determined by analyzing nitric oxide production and proinflammatory cytokines using enzyme-linked immunosorbent assay. The mechanism was evaluated in BV-2 cells with or without NS treated with LPS for various lengths of time using oligonucleotide microarray and real time reverse transcription-polymerase chain reaction. The oligonucleotide microarray analysis revealed that mitogen activated protein kinase (MAPK) signaling pathway-related genes such as Fgfr3, Fgf12, Rasal2, Nfkb2, Map2k5, Mapk1, Map3k7, and NFatc2 were down-regulated in LPS activated BV-2 cells by pretreatment with NS. In addition, significant decreases in Nos1ap gene expression were observed with NS pretreatment. Cluster linked pathway analysis using the Kyoto Encyclopedia of Genes and Genomes database revealed that the effects of NS were closely associated with the regulation of mitochondria functions. These results suggested that NS can affect the MAPK signaling pathway and mitochondrial functions in BV-2 cells activated with LPS.

The multifaceted profile of activated microglia

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

Inducible IL-23p19 expression in human microglia via p38 MAPK and NF-kappaB signal pathways

Activated microglia can release a variety of proinflammatory cytokines that play a crucial role in the pathogenesis of multiple sclerosis (MS). IL-23, a novel proinflammatory cytokine, is required for the induction of experimental autoimmune encephalomyelitis. Previously we demonstrated that IL-23 is expressed in MS lesions and that microglia are one cellular source of IL-23 in MS patients. In the present study we investigated the inducible expression and regulation of p19, a key subunit of IL-23, in human microglia. We demonstrated the inducible expression of IL-23p19 by lipopolysaccharide-stimulated microglial cells. Using signaling pathway-specific inhibitors, we showed that blocking p38 MAP kinase or NF-kappaB signaling pathway significantly reduced p19 expression in microglia. The regulatory role of p38 MAP kinase in p19 expression was further confirmed by decreased expression in microglia transduced with dominant-negative p38. We concluded that the p38 MAP kinase and NF-kappaB signaling pathways play an important role in regulation of IL-23p19 expression on human microglia, and are thus potential therapeutic targets in the treatment of MS.

Microglia activation in retinal degeneration

Microglia cells are phagocytic sentinels in the CNS and in the retina required for neuronal homeostasis and innate immune defense. Accumulating experimental evidence suggests that chronic microglia activation is associated with various neurodegenerative diseases including retinal dystrophies. Endogenous triggers alert microglia cells rapidly in the degenerating retina, leading to local proliferation, migration, enhanced phagocytosis, and secretion of cytokines, chemokines, and neurotoxins. This amplified, immunological cascade and the loss of limiting control mechanisms may contribute significantly to retinal tissue damage and proapoptotic events. This review summarizes the developmental and immune surveillance functions of microglia in the healthy retina and discusses early signaling events and transcriptional networks of microglia activation in retinal degeneration. The characterization of activation pathways at the molecular level may lead to innovative, therapeutic options in degenerative retinal diseases based on a selective, pharmacological interference with the neurotoxic activities of microglia cells, without compromising their homeostastic functions.