Neonatal rat primary microglia: isolation, culturing, and selected applications

Purine nucleoside phosphorylase inhibition is an effective approach for the treatment of chemical hemorrhagic cystitis

Hemorrhagic cystitis may be induced by infection, radiation therapy, or medications or may be idiopathic. Along with hemorrhagic features, symptoms include urinary urgency and frequency, dysuria (painful urination), and visceral pain. Cystitis-induced visceral pain is one of the most challenging types of pain to treat, and an effective treatment would address a major unmet medical need. We assessed the efficacy of a purine nucleoside phosphorylase inhibitor, 8-aminoguanine (8-AG), for the treatment of hemorrhagic/ulcerative cystitis. Lower urinary tract (LUT) function and structure were assessed in adult Sprague-Dawley rats, treated chronically with cyclophosphamide (CYP; sacrificed day 8) and randomized to daily oral treatment with 8-AG (begun 14 days prior to CYP induction) or its vehicle. CYP-treated rats exhibited multiple abnormalities, including increased urinary frequency and neural mechanosensitivity, reduced bladder levels of inosine, urothelial inflammation/damage, and activation of spinal cord microglia, which is associated with pain hypersensitivity. 8-AG treatment of CYP-treated rats normalized all observed histological, structural, biochemical, and physiological abnormalities. In cystitis 8-AG improved function and reduced both pain and inflammation likely by increasing inosine, a tissue-protective purine metabolite. These findings demonstrate that 8-AG has translational potential for reducing pain and preventing bladder damage in cystitis-associated LUT dysfunctions.

An LRP1-binding motif in cellular prion protein replicates cell-signaling activities of the full-length protein

Low-density lipoprotein receptor-related protein-1 (LRP1) functions as a receptor for nonpathogenic cellular prion protein (PrPC), which is released from cells by ADAM (a disintegrin and metalloproteinase domain) proteases or in extracellular vesicles. This interaction activates cell signaling and attenuates inflammatory responses. We screened 14-mer PrPC-derived peptides and identified a putative LRP1 recognition motif in the PrPC sequence spanning residues 98-111. A synthetic peptide (P3) corresponding to this region replicated the cell-signaling and biological activities of full-length shed PrPC. P3 blocked LPS-elicited cytokine expression in macrophages and microglia and rescued the heightened sensitivity to LPS in mice in which the PrPC gene (Prnp) had been deleted. P3 activated ERK1/2 and induced neurite outgrowth in PC12 cells. The response to P3 required LRP1 and the NMDA receptor and was blocked by the PrPC-specific antibody, POM2. P3 has Lys residues, which are typically necessary for LRP1 binding. Converting Lys100 and Lys103 into Ala eliminated the activity of P3, suggesting that these residues are essential in the LRP1-binding motif. A P3 derivative in which Lys105 and Lys109 were converted into Ala retained activity. We conclude that the biological activities of shed PrPC, attributed to interaction with LRP1, are retained in synthetic peptides, which may be templates for therapeutics development.

Microglia isolation from aging mice for cell culture: A beginner's guide

Microglia, the innate immune cell of the central nervous system, play significant roles in brain development, maintenance, homeostasis, and neuroinflammation. Although numerous methods have been developed to isolate microglia from embryonic or postnatal mouse brains, still major difficulties exist in isolating microglia from adult mice, often resulting in low yield and risk of cellular activation. Therefore, there is a need for a more efficient method to isolate pure and high-yield microglia from adult mice to study various neurodegenerative diseases. The aim of this study was to develop a fully functional protocol for the isolation of microglia by comparing different protocols. We investigated the efficacy of three protocols in terms of cell yield, purity, cellular activation, cellular aging, and migration properties and proposed the modified protocol (PROTOCOL 1), which provides an optimal yield of functional microglial cells with a minimum of material and equipment and allows young researchers with little experience to isolate microglia and helps them to delve deeper into the world of neuroscience.

Assessing the role of primary healthy microglia and gap junction blocker in hindering Alzheimer's disease neuroinflammatory type: Early approaches for therapeutic intervention

Alzheimer's disease (AD) is a predominantly heterogeneous disease with a highly complex pathobiology. The presence of amyloid-beta (Aβ) depositions and the accumulation of hyperphosphorylated tau protein remain the characteristic hallmarks of AD. These hallmarks can be detected throughout the brain and other regions, including cerebrospinal fluid (CSF) and the spinal cord. Microglia cells, the brain-resident macrophage type of the brain, are implicated in maintaining healthy brain homeostasis. The localized administration of primary healthy microglia (PHM) is suggested to play a role in mitigating AD hallmark depositions and associated cognitive dysfunction. Carbenoxolone (CBX) is the most common gap junction blocker. It cannot effectively cross the blood-brain barrier (BBB) under systemic administration. Therefore, localized administration of CBX may be a recommended intervention against AD by acting as an antioxidant and anti-inflammatory agent. This study aims to determine whether the localized intracerebroventricular (ICV) administration of PHM and CBX may act as an effective therapeutic intervention for AD neuroinflammatory type. In addition, this study also aims to reveal whether detecting AD hallmarks in the spinal cord and CSF can be considered functional and effective during AD early diagnosis. Male albino rats were divided into four groups: control (group 1), lipopolysaccharide (LPS)-induced AD neuroinflammatory type (group 2), ICV injection of LPS + isolated PHM (group 3), and ICV injection of LPS + CBX (group 4). Morris water maze (MWM) was conducted to evaluate spatial working memory. The brain and spinal cord were isolated from each rat with the collection of CSF. Our findings demonstrate that the localized administration of PHM and CBX can act as promising therapeutic approaches against AD. Additionally, Aβ and tau toxic aggregates were detected in the spinal cord and the CSF of the induced AD model concomitant with the brain tissues. Overall, it is suggested that the ICV administration of PHM and CBX can restore normal brain functions and alleviate AD hallmark depositions. Detecting these depositions in the spinal cord and CSF may be considered in AD early diagnosis. As such, conducting clinical research is recommended to reveal the benefits of related therapeutic approaches compared with preclinical findings.

Stable expression of a truncated TLX variant drives differentiation of induced pluripotent stem cells into self-renewing neural stem cells for production of extracellular vesicles

Background

Neural stem cells (NSCs)-derived extracellular vesicles (EVs) possess great potential in treating severe neurological and cerebrovascular diseases, as they carry the modulatory and regenerative ingredients of NSCs. Induced pluripotent stem cells (iPSCs)-derived NSCs culture represents a sustainable source of therapeutic EVs. However, there exist two major challenges in obtaining a scalable culture of NSCs for high-efficiency EVs production: (1) the heterogeneity of iPSC-derived NSCs culture impairs the production of high-quality EVs and (2) the intrinsic propensity of neuronal or astroglial differentiation of NSCs during prolonged culturing reduces the number of NSCs for preparing EVs. A NSCs strain that is amenable to stable self-renewal and proliferation is thus greatly needed for scalable and long-term culture.

Methods

Various constructs of the genes encoding the orphan nuclear receptor NR2E1 (TLX) were stably transfected in iPSCs, which were subsequently cultured in a variety of differentiation media for generation of iNSCs^TLX. Transcriptomic and biomarker profile of iNSCs^TLX were investigated. In particular, the positivity ratios of Sox2/Nestin and Musashi/Vimentin were used to gauge the homogeneity of the iNSCs^TLX culture. The iNSCs expressing a truncated version of TLX (TLX-TP) was expanded for up to 45 passages, after which its neuronal differentiation potential and EV activity were evaluated.

Results

Stable expression of TLX-TP could confer the iPSCs with rapid and self-driven differentiation into NSCs through stable passaging up to 225 days. The long-term culture of NSCs maintained the highly homogenous expression of NSC-specific biomarkers and potential of neuronal differentiation. EVs harvested from the TLX-expressing NSCs cultures exhibited anti-inflammatory and neuroprotective activities.

Conclusions

iPSC-derived NSCs stably expressing TLX-TP is a promising cell line for scalable production of EVs, which should be further exploited for therapeutic development in neurological treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03131-4.

Advances in microglia cellular models: focus on extracellular vesicle production

Microglia are the major component of the innate immune system in the central nervous system. They promote the maintenance of brain homeostasis as well as support inflammatory processes that are often related to pathological conditions such as neurodegenerative diseases. Depending on the stimulus received, microglia cells dynamically change their phenotype releasing specific soluble factors and largely modify the cargo of their secreted extracellular vesicles (EVs). Despite the mechanisms at the basis of microglia actions have not been completely clarified, the recognized functions exerted by their EVs in patho-physiological conditions represent the proof of the crucial role of these organelles in tuning cell-to-cell communication, promoting either protective or harmful effects. Consistently, in vitro cell models to better elucidate microglia EV production and mechanisms of their release have been increased in the last years. In this review, the main microglial cellular models that have been developed and validated will be described and discussed, with particular focus on those used to produce and derive EVs. The advantages and disadvantages of their use will be evidenced too. Finally, given the wide interest in applying EVs in diagnosis and therapy too, the heterogeneity of available models for producing microglia EVs is here underlined, to prompt a cross-check or comparison among them.

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).

Microglia Play an Essential Role in Synapse Development and Neuron Maturation in Tissue-Engineered Neural Tissues

In the process of constructing engineered neural tissues, we often use mixed primary neural cells, which contain microglia in the cell culture. However, the role that microglia play in the construction of engineered neural tissue has not been well studied. Here, we generated three-dimensional (3D) engineered neural tissues by silk fibroin/collagen composite scaffolds and primary mixed cortical cells. We depleted microglial cells by magnetic separation. Then, we analyzed the neural growth, development, mature and synapse-related gene, and protein expressions compared with the control engineered neural tissues with the microglia-depleted engineered neural tissues. We found that the engineered neural tissues constructed by magnetic separation to remove microglia showed a decrease in the number of synaptic proteins and mature neurons. These findings link microglia to neuron and synaptic maturation and suggest the importance of microglia in constructing engineered neural tissues in vitro.

Therapeutic Targeting of Retinal Immune Microenvironment With CSF-1 Receptor Antibody Promotes Visual Function Recovery After Ischemic Optic Neuropathy

Retinal ischemia/reperfusion injury (RI) is a common cause of irreversible visual impairment and blindness in elderly and critical unmet medical need. While no effective treatment is available for RI, microglial activation and local immune responses in the retina are thought to play important roles in the pathophysiology of neurodegeneration. While survival and activation of microglia depend critically on colony-stimulating factor receptor (CSF-1R) signaling, it remains unclear if targeting the retinal immune microenvironments by CSF-1RAb after RI is sufficient to rescue vision and present a potentially effective therapy. Here we used rodent models of RI and showed that retinal ischemia induced by acute elevation of intraocular pressure triggered an early activation of microglia and macrophages in the retina within 12 h. This was followed by lymphocyte infiltration and increased production of pro-inflammatory cytokines. Intravitreal injection of CSF-1R neutralizing antibody (CSF-1RAb) after RI significantly blocked microglial activation and the subsequent T cell recruitment. This also led to improved retinal ganglion cell survival and function measured by cell quantification and electroretinogram positive scotopic threshold responses, as well as increased visual acuity and contrast sensitivity as assessed by optomotor reflex-based assays, when compared to the isotype-treated control group. Moreover, the administration of CSF-1RAb efficiently attenuated inflammatory responses and activation of human microglia in culture, suggesting a therapeutic target with human relevance. These results, together with the existing clinical safety profiles, support that CSF-1RAb may present a promising therapeutic avenue for RI, a currently untreatable condition, by targeting microglia and the immune microenvironment in the retina to facilitate neural survival and visual function recovery.

MiR-497 promotes microglia activation and proinflammatory cytokines production in chronic unpredictable stress-induced depression via targeting FGF2

Depression is one of important prevalent psychiatric disorders worldwide. MiR-497 is considered as a diagnostic biomarker and a promising therapeutic target in cancers. However, the role of miR-497 in depression remains unknown. In this study, we demonstrated that CUS induced depression-like behaviors and overexpression of miR-497 in rats. Interestingly, knockdown miR-497 ameliorated CUS-induced depressive-like behavior in rats. Moreover, knockdown of miR-497 inhibited the activation of microglia and the production of proinflammatory cytokines including IL-6, IL-1β, MCP-1 and TNF-α in CUS-induced rats. Luciferase activity assay proved that Fibroblast Growth Factor-2 (FGF2) was a direct target of miR-497 and modulated by miR-497 in microglia. In rescue experiments, overexpression of FGF2 inhibited miR-497-induced proinflammatory cytokines and iNOS expression. These results showed that miR-497 aggravated hippocampal microglial activation in CUS-induced depression in rat via targeting FGF2, providing a novel potential target for treatment of depression.

Impact of ambient temperature on inflammation-induced encephalopathy in endotoxemic mice-role of phosphoinositide 3-kinase gamma

BACKGROUND

Sepsis-associated encephalopathy (SAE) is an early and frequent event of infection-induced systemic inflammatory response syndrome. Phosphoinositide 3-kinase γ (PI3Kγ) is linked to neuroinflammation and inflammation-related microglial activity. In homeotherms, variations in ambient temperature (Ta) outside the thermoneutral zone lead to thermoregulatory responses, mainly driven by a gradually increasing sympathetic activity, and may affect disease severity. We hypothesized that thermoregulatory response to hypothermia (reduced Ta) aggravates SAE in PI3Kγ-dependent manner.

METHODS

Experiments were performed in wild-type, PI3Kγ knockout, and PI3Kγ kinase-dead mice, which were kept at neutral (30 ± 0.5 °C) or moderately lowered (26 ± 0.5 °C) Ta. Mice were exposed to lipopolysaccharide (LPS, 10 μg/g, from Escherichia coli serotype 055:B5, single intraperitoneal injection)-evoked systemic inflammatory response (SIR) and monitored 24 h for thermoregulatory response and blood-brain barrier integrity. Primary microglial cells and brain tissue derived from treated mice were analyzed for inflammatory responses and related cell functions. Comparisons between groups were made with one-way or two-way analysis of variance, as appropriate. Post hoc comparisons were made with the Holm-Sidak test or t tests with Bonferroni's correction for adjustments of multiple comparisons. Data not following normal distribution was tested with Kruskal-Wallis test followed by Dunn's multiple comparisons test.

RESULTS

We show that a moderate reduction of ambient temperature triggers enhanced hypothermia of mice undergoing LPS-induced systemic inflammation by aggravated SAE. PI3Kγ deficiency enhances blood-brain barrier injury and upregulation of matrix metalloproteinases (MMPs) as well as an impaired microglial phagocytic activity.

CONCLUSIONS

Thermoregulatory adaptation in response to ambient temperatures below the thermoneutral range exacerbates LPS-induced blood-brain barrier injury and neuroinflammation. PI3Kγ serves a protective role in suppressing release of MMPs, maintaining microglial motility and reinforcing phagocytosis leading to improved brain tissue integrity. Thus, preclinical research targeting severe brain inflammation responses is seriously biased when basic physiological prerequisites of mammal species such as preferred ambient temperature are ignored.

Chlorzoxazone exhibits neuroprotection against Alzheimer's disease by attenuating neuroinflammation and neurodegeneration in vitro and in vivo

Alzheimer's disease (AD), a complex and an age-related brain disease, is induced by the accumulation of amyloid beta (Aβ) and neuroinflammation. Chlorzoxazone (CZ) is a classical FDA-approved drug, and shows anti-inflammatory effects. However, up until now, its regulatory role in AD has not been investigated. Therefore, in this study we attempted to explore if CZ could be an effective therapeutic strategy for AD treatment. At first, the in vitro study was performed to mimic AD using Aβ. We found that Aβ caused p65 nuclear translocation in both primary microglial cells and astrocytes, which were, however, restrained by CZ treatments. Meanwhile, CZ incubation markedly decreased the expression of pro-inflammatory cytokines including tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β). Aβ deposition was also markedly reduced in glial cells treated with CZ. Importantly, we found that glial activation and its-related pro-inflammation induced by Aβ led to obvious neurodegeneration and neuroinflammation, which were effectively attenuated by CZ pre-treatment in the isolated primary cortical neurons. Then, the in vivo study was performed using APP/PS1 mice with AD. Behavior tests showed that CZ administration effectively improved cognitive deficits in AD mice. Neuron death in hippocampus of AD mice was also inhibited by CZ. Aβ accumulation in brain was markedly decreased in CZ-treated AD mice. We finally found that hippocampal glial activation in AD mice was obviously blocked by CZ supplementation, along with remarkable decreases in TNF-α, IL-1β and p65 nuclear translocation. Together, these findings above demonstrated that CZ could inhibit glial activation and inflammatory response, contributing to the suppression of neurodegeneration and neuroinflammation. Therefore, CZ may be an effective therapeutic strategy for AD treatment.

Nurr1 performs its anti-inflammatory function by regulating RasGRP1 expression in neuro-inflammation

Nurr1, a transcription factor belonging to the orphan nuclear receptor, has an essential role in the generation and maintenance of dopaminergic neurons and is important in the pathogenesis of Parkinson’ disease (PD). In addition, Nurr1 has a non-neuronal function, and it is especially well known that Nurr1 has an anti-inflammatory function in the Parkinson’s disease model. However, the molecular mechanisms of Nurr1 have not been elucidated. In this study, we describe a novel mechanism of Nurr1 function. To provide new insights into the molecular mechanisms of Nurr1 in the inflammatory response, we performed Chromatin immunoprecipitation sequencing (ChIP-Seq) on LPS-induced inflammation in BV2 cells and finally identified the RasGRP1 gene as a novel target of Nurr1. Here, we show that Nurr1 directly binds to the RasGRP1 intron to regulate its expression. Moreover, we also identified that RasGRP1 regulates the Ras-Raf-MEK-ERK signaling cascade in LPS-induced inflammation signaling. Finally, we conclude that RasGRP1 is a novel regulator of Nurr1’s mediated inflammation signaling.

Glutathione Depletion and Parkinsonian Neurotoxin MPP+-Induced TRPM2 Channel Activation Play Central Roles in Oxidative Cytotoxicity and Inflammation in Microglia

Parkinson's disease (PD) is one of most common neurodegenerative diseases. Environmental stressors such as oxidative stress (OS), calcium ion influx, apoptosis, and inflammation mechanisms are linked to activated microglia in patients with PD. The OS-dependent activated transient receptor potential melastatin 2 (TRPM2) channel is modulated in several neurons by glutathione (GSH). However, the cellular and molecular effects of GSH alteration on TRPM2 activation, OS, apoptosis, and inflammation in the microglia remain elusive. The microglia of TRPM2 wild-type (TRPM2-WT) and knockout (TRPM2-KO) mice were divided into control, PD model (MPP), L-buthionine sulfoximine (BSO), MPP + BSO and MPP + BSO + GSH groups. MPP-induced increases in apoptosis, death, OS, lipid peroxidation, PARP1, caspase-3 and caspase-9, inflammatory cytokines (IL-1β, TNF-α, IL-6), and intracellular free Zn²⁺ and Ca²⁺ levels in the microglia of TRPM2-WT mice were further increased by the BSO treatment, although they were diminished by the GSH treatment. Their levels were further reduced by PARP1 inhibitors (PJ34 and DPQ) and TRPM2 blockers (ACA and 2-APB). However, the effects of MPP and BSO were not observed in the microglia of TRPM2-KO mice. Taken together, our data demonstrate that maintaining GSH homeostasis is not only important for quenching OS in the microglia of patients with PD but also equally critical to modulating TRPM2, thus suppressing inflammatory responses elicited by environmental stressors.

Circumdatin D Exerts Neuroprotective Effects by Attenuating LPS-Induced Pro-Inflammatory Responses and Downregulating Acetylcholinesterase Activity In Vitro and In Vivo

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder with multifactorial causes, of which systemic inflammation may play a key role to promote neurodegeneration, and acetylcholinesterase (AChE) is a target protein to induce cholinergic transmission. Inhibitors toward inflammation and targeting AChE are regarded to promote cholinergic signaling of the central nervous system in AD therapy. During the search for neuroprotection agents from marine-derived compounds, seven circumdatin-type alkaloids from a coral-associated fungus Aspergillus ochraceus LZDX-32-15 showed potent inhibition against lipopolysaccharide (LPS)-induced nitric oxide (NO) production and activation of NF-κB report gene along with anti-AChE activities. Among the tested compounds, circumdatin D showed the most potent inhibitory effect against AChE activity and NO production. In vivo experiments using AD-like nematode models demonstrated that circumdatin D effectively delayed paralysis of CL4176 worms upon temperature up-shift via suppression of AChE activity and inflammatory-related gene expression. Moreover, circumdatin D interfered with inflammatory response by inhibiting the secretion of pro-inflammatory cytokines in LPS-induced BV-2 and primary microglia cells. Mechanistically, circumdatin D modulated Toll-like receptor 4 (TLR4)-mediated NF-κB, MAPKs and JAK/STAT inflammatory pathways in LPS-stimulated BV-2 cells, and protected primary neurons cells from LPS-induced neurotoxicity. Thus, circumdatin D is a potential agent for neuroprotective effects by the multi-target strategy.

Idebenone attenuates cerebral inflammatory injury in ischemia and reperfusion via dampening NLRP3 inflammasome activity

BACKGROUND

Idebenone is a well-appreciated mitochondrial protectant while the mechanisms underlying the neuroprotection in cerebral ischemia and reperfusion (I/R) remain elusive. It has been manifested NLRP3 inflammasom activation contributed to I/R induced damage. It raises questions how exactly NLRP3 inflammasom was activated in microglia and neuron and whether idebenone reverses the process in I/R.

METHODS

I/R rat model was utilized and BV2, primary microglia and PC12 cells were subjected to oxygen-glucose deprivation (OGD). Then, western-blotting, q-PCR, immunofluorescence staining, ELISA, flow cytometry and immunoprecipitation analysis were performed.

RESULTS

We found ROS-NLRP3 singaling was activated in BV2 cells at OGD/R 24 h. Importantly, microglial NLRP3 activation was essential for NLRP3 activation in PC12 cells under microglial-neuronal co-culture circumstance, which has been confirmed to induced neuronal apoptosis. Further, we found mitochondrial dysfunction in OGD/R led to mt-DNA translocation as well as generation of mt-ROS, resulting cytosolic accumulation of oxidized mt-DNA. Ultimately, oxidized mt-DNA binding to NLRP3 contributed to further activation of NLRP3 and dramatically augmented inflammation in BV2 and PC12 cells. Furthermore, idebenone treatment inhibited the process, thus suppressing the NLRP3-mediated inflammatory injury after OGD/R. In vivo, NLRP3 was activated in microglia of I/R rats and inhibition of NLRP3 was observed in idebenone treatment group, which had less neurological deficit and less infarct volume.

INTERPRETATION

Our data revealed the anti-inflammatory effects of idebenone via suppressing activation of NLRP3 and ameliorating NLRP3-mediating damage in I/R, which may provide new insight in therapeutic strategy for ischemic stroke.

Ethanol Stimulation of Microglia Release Increases ERK1/2-Dependent Neuronal cPLA2 Activity in Immature Cultured Cortical Preparations

Ethanol consumption typically begins during adolescence and is associated with age-dependent responses and maladaptive neuronal consequences. Our previous work established the role of a putative signaling cascade involving cytoplasmic phospholipase A₂ (cPLA₂), arachidonic acid (AA) and novel protein kinase C isoforms in adolescent hypnotic sensitivity. The current study aimed to further delineate this pathway by ascertaining the cellular specificity as well as the upstream activators of cPLA₂ using an immature cultured cortical preparation. A threefold increase in cPLA₂ was detected within 2 min of 100 mM ethanol exposure as measured by phosphorylation of serine 505 (Ser505). Increases in cPLA₂ activity were further observed to be primarily confined to neuronal cells. Increases in the number of neurons co-expressing cPLA2 Ser505 phosphorylation were prevented by preincubation with an ERK1/2 inhibitor, but not P38 MAPK inhibition. Finally, conditioned media studies were used to determine whether glial cells were involved in the ethanol-induced neuronal cPLA₂ activity. Rapid increases in neuronal cPLA2 activity appears to be initiated through ethanol stimulated microglial, but not astrocytic releasable factors. Taken together, these data extend the proposed signaling cascade involved in developmental ethanol responding.

CSF-1 receptor inhibition as a highly effective tool for depletion of microglia in mixed glial cultures

BACKGROUND

A breakthrough in the microglia and macrophages field was the identification of the macrophage colony stimulating factor-1 (CSF-1) as a pro-survival factor. Its pharmacological inhibition in animals depletes rapidly all microglia and macrophages. Microglial depletion in mixed glial cultures has always represented a challenge and none of the existing approaches delivers satisfactory results.

NEW METHOD

We applied a CSF-1R inhibitor (PLX5622) in primary mouse glial cultures, analyzing microglial dose-responses, starting at different time-points and incubating for various periods of time.

RESULTS

We used two treatment modalities with 10 μM PLX5622 to deplete microglia: i) immediately after brain homogenization and ii) at day in vitro 12. The application of the inhibitor immediately after cell preparation depleted microglia to 8% at 1 week, to 2% at 4 weeks and to 0.5% at 6 weeks (half-time 3.5 days). When mixed glial cultures were treated starting at day in vitro 12, microglia depletion was slower (half-time 6 days) and not complete, indicating a decreased sensitivity to CSF-1. The remaining astrocytes preserved their proliferation ability, their migration in a scratch wound assay, and their pro-inflammatory (IL-6) response towards lipopolysaccharide.

COMPARISON TO EXISTING METHODS

The proposed approach for microglial depletion in mixed glial cultures is more effective than other existing methods and is non-toxic to non-microglial cells.

CONCLUSIONS

CSF-1R inhibitors are effective tools for depleting microglia in mixed glial cultures. Longer maturation of the cultures leads to a diminished sensitivity of microglia towards CSF-1. Thus, the treatment should start as early as possible after glial culture preparation.

Dissociation of neonatal and adult mice brain for simultaneous analysis of microglia, astrocytes and infiltrating lymphocytes by flow cytometry

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Recovery of neural cells is higher with 30 % Percoll gradient than 30–70 %.

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Papain enhances combined extraction of microglia, astrocytes and lymphocytes.

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Dispase II potentiates papain action only in adult brain.

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Mechanical dissociation isolates neonatal and adult astrocytes better than enzymes.

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Papain + dispase II alows cell cytometry quantification of glial activation by LPS.

The technical difficulty to isolate microglia, astrocytes and infiltrating immune cells from mouse brain is nowadays a limiting factor in the study of neuroinflammation. Brain isolation requirements are cell-type and animal-age dependent, but current brain dissociation procedures are poorly standardized. This lack of comprehensive studies hampers the selection of optimized methodologies. Thus, we present here a comparative analysis of dissociation methods and Percoll-based separation to identify the most efficient procedure for the combined isolation of healthy microglia, astrocytes and infiltrated leukocytes; distinguishing neonatal and adult mouse brain. Gentle mechanical dissociation and DNase I incubation was supplemented with papain or collagenase II. Dispase II digestion was also used alone or in combination. In addition, cell separation efficiency of 30 % and 30–70 % Percoll gradients was compared. In these experiments, cell yield and integrity of freshly dissociated cells was measured by flow cytometry. We found that papain digestion in combination with dispase II followed by 30 % Percoll separation is the most balanced method to obtain a mixture of microglia, astrocytes and infiltrated immune cells; while addition of dispase II was not an advantage for neonatal brain. These dissociation conditions allowed flow cytometry detection of a slight glial activation triggered by sublethal LPS injection. In conclusion, the enzymes and Percoll density gradients tested here affected differently resting microglia, activated microglia/macrophages, astrocytes and infiltrated lymphocytes. Also, newborn and adult brain showed contrasting reactions to digestion. Our study highlights the strength of flow cytometry for the simultaneous analysis of neuroimmune cell populations once extraction is optimized.

Fibrinolysis protease receptors promote activation of astrocytes to express pro-inflammatory cytokines

Background

Astrocytes contribute to the crosstalk that generates chronic neuro-inflammation in neurological diseases; however, compared with microglia, astrocytes respond to a more limited continuum of innate immune system stimulants. Recent studies suggest that the fibrinolysis system may regulate inflammation. The goal of this study was to test whether fibrinolysis system components activate astrocytes and if so, elucidate the responsible biochemical pathway.

Methods

Primary cultures of astrocytes and microglia were prepared from neonatal mouse brains. The ability of purified fibrinolysis system proteins to elicit a pro-inflammatory response was determined by measuring expression of the mRNAs encoding tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and chemokine (C-C motif) ligand 2 (CCL2). IκBα phosphorylation also was measured. Plasminogen activation in association with cells was detected by chromogenic substrate hydrolysis. The activity of specific receptors was tested using neutralizing antibodies and reagents.

Results

Astrocytes expressed pro-inflammatory cytokines when treated with plasminogen but not when treated with agonists for Toll-like Receptor-4 (TLR4), TLR2, or TLR9. Microglia also expressed pro-inflammatory cytokines in response to plasminogen; however, in these cells, the response was observed only when tissue-type plasminogen activator (tPA) was added to activate plasminogen. In astrocytes, endogenously produced urokinase-type plasminogen activator (uPA) converted plasminogen into plasmin in the absence of tPA. Plasminogen activation was dependent on the plasminogen receptor, α-enolase, and the uPA receptor, uPAR. Although uPAR is capable of directly activating cell-signaling, the receptor responsible for cytokine expression and IκBα phosphorylation response to plasmin was Protease-activated Receptor-1 (PAR-1). The pathway, by which plasminogen induced astrocyte activation, was blocked by inhibiting any one of the three receptors implicated in this pathway with reagents such as εACA, α-enolase-specific antibody, uPAR-specific antibody, the uPA amino terminal fragment, or a pharmacologic PAR-1 inhibitor.

Conclusions

Plasminogen may activate astrocytes for pro-inflammatory cytokine expression through the concerted action of at least three distinct fibrinolysis protease receptors. The pathway is dependent on uPA to activate plasminogen, which is expressed endogenously by astrocytes in culture but also may be provided by other cells in the astrocytic cell microenvironment in the CNS.

Protective Effect of Semisynthetic and Natural Flavonoid on Aged Rat Microglia-enriched Cultures

The ROS-mediated lysosomal dysfunction and coinciding deterioration of mitochondrial function are thought to be the prominent mechanisms responsible for aging. Microglia, the resident macrophages in the central nervous system, were postulated to belong to the major targets vulnerable to these detrimental processes, acting as principal drivers in brain aging. The present study investigated the potential protective effect of the semisynthetic flavonoid 3'-O-(3-chloropivaloyl) quercetin (CPQ) and quercetin (Q) on microglia-enriched mixed brain cultures (MBCs) established from aged Wistar rats. Both flavonoids tested suppressed the development of lipofuscin-related autofluorescence in aged cells. Further ensuing protective effects included reduction of protein oxidation markers in aged cells. Moreover, unlike Q, CPQ significantly suppressed sensitivity of aged cells to stimulation of superoxide burst. Other activation markers, cellular hypertrophy and isolectin B4 binding, were also downregulated by treatment with both CPQ and Q. In conclusion, results of our study suggest that both flavonoids tested may protect microglia with a quite comparable efficacy against aging-related accumulated alterations. The protective mechanism can include interference with the ROS-mediated vicious cycles involving lysosomal dysfunction. Nevertheless, the lipophilized quercetin, CPQ, a compound with proposed enhanced biological availability compared to parent molecule, can represent an agent potentially useful for new effective pharmaceutical intervention against brain aging, overcoming the limitations of clinical applicability of quercetin.

Memantine prodrug as a new agent for Alzheimer's Disease

Hydrogen sulphide has recently drawn much attention due to its potent anti-inflammatory and neuroprotective roles in brain functions. The purpose of the current study was to exploit these beneficial properties of H₂S to design a new agent for the treatment of Alzheimer's disease (AD). To pursue our aims, we replaced the free amine group of memantine with an isothiocyanate functionality as a putative H₂S-donor moiety. The new chemical entity, named memit, was then tested in vitro to determine whether it retains the pharmacological profile of the "native drug", while also providing a source of H₂S in the CNS. Indeed, Memit showed the ability to release H₂S through a cysteine-mediated mechanism, thus generating memantine. Moreover, the new hybrid molecule exerts protective effects against neuronal inflammation and induces a drastic fall in ROS production. In addition, memit was also able to reduce the Aβ(1-42) self-induced aggregation and exerted cytoprotective effect against Aβ oligomers-induced damage in both human neurons and rat microglia cells. Finally, similarly to memantine, the new compound promotes autophagy, a complex process required for cellular homeostasis in cell survival that results to be altered in neurodegenerative diseases. In conclusion, our study revealed that memit is a prodrug of memantine. Further in vivo studies will be necessary to fully investigate the synergic or cumulative effects due to the H₂S-releasing moiety and the native drug.

Loss of Par1b/MARK2 primes microglia during brain development and enhances their sensitivity to injury

Background

Microglia, the resident immune cells of the brain, exhibit various morphologies that correlate with their functions under physiological and pathological conditions. In conditions such as aging and stress, microglia priming occurs, which leads to altered morphology and lower threshold for activation upon further insult. However, the molecular mechanisms that lead to microglia priming are unclear.

Methods

To understand the role of Par1b/MARK2 in microglia, we first expressed shRNA targeting luciferase or Par1b/MARK2 in primary microglial cells and imaged the cells using fluorescent microscopy to analyze for morphological changes. A phagocytosis assay was then used to assess functional changes. We then moved in vivo and used a Par1b/MARK2 knockout mouse model to assess for changes in microglia density, morphology, and phagocytosis using immunohistochemistry, confocal imaging, and 3D image reconstruction. Next, we used two-photon in vivo imaging in live Par1b/MARK2 deficient mice to examine microglia dynamics. In addition, a controlled-cortical impact injury was performed on wild-type and Par1b/MARK2-deficient mice and microglial response was determined by confocal imaging. Finally, to help rule out non-cell autonomous effects, we analyzed apoptosis by confocal imaging, cytokine levels by multiplex ELISA, and blood-brain barrier permeability using Evans Blue assay.

Results

Here, we show that loss of the cell polarity protein Par1b/MARK2 facilitates the activation of primary microglia in culture. We next found that microglia in Par1b/MARK2 deficient mice show increased density and a hypertrophic morphology. These morphological changes are accompanied with alterations in microglia functional responses including increased phagocytosis of neuronal particles early in development and decreased surveillance of the brain parenchyma, all reminiscent of a primed phenotype. Consistent with this, we found that microglia in Par1b/MARK2 deficient mice have a significantly lower threshold for activation upon injury.

Conclusions

Together, our studies show that loss of Par1b/MARK2 switches microglia from a surveillant to a primed state during development, resulting in an increased neuroinflammatory response to insults.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1390-3) contains supplementary material, which is available to authorized users.

Lipid transporter Spns2 promotes microglia pro-inflammatory activation in response to amyloid-beta peptide

Accumulating evidence indicates that neuroinflammation contributes to the pathogenesis and exacerbation of neurodegenerative disorders, such as Alzheimer's disease (AD). Sphingosine-1-phosphate (S1P) is a pleiotropic bioactive lipid that regulates many pathophysiological processes including inflammation. We present evidence here that the spinster homolog 2 (Spns2), a S1P transporter, promotes microglia pro-inflammatory activation in vitro and in vivo. Spns2 knockout (Spns2KO) in primary cultured microglia resulted in significantly reduced levels of pro-inflammatory cytokines induced by lipopolysaccharide (LPS) and amyloid-beta peptide 1-42 oligomers (Aβ42) when compared with littermate controls. Fingolimod (FTY720), a S1P receptor 1 (S1PR1) functional antagonist and FDA approved drug for relapsing-remitting multiple sclerosis, partially blunted Aβ42-induced pro-inflammatory cytokine generation, suggesting that Spns2 promotes microglia pro-inflammatory activation through S1P-signaling. Spns2KO significantly reduced Aβ42-induced nuclear factor kappa B (NFκB) activity. S1P increased, while FTY720 dampened, Aβ42-induced NFκB activity, suggesting that Spns2 activates microglia inflammation through, at least partially, NFκB pathway. Spns2KO mouse brains showed significantly reduced Aβ42-induced microglia activation/accumulation and reduced levels of pro-inflammatory cytokines when compared with age-matched controls. More interestingly, Spns2KO ameliorated Aβ42-induced working memory deficit detected by Y-Maze. In summary, these results suggest that Spns2 promotes pro-inflammatory polarization of microglia and may play a crucial role in AD pathogenesis.

Oxidative stress induces release of 2'-AMP from microglia

BACKGROUND

Microglia metabolize exogenous 2'-AMP and 3'-AMP (non-canonical nucleotides) to adenosine and exogenous 2'-AMP and 3'-AMP (via conversion to adenosine) inhibit the production of inflammatory cytokines by microglia. This suggests that if microglia release endogenous 2'-AMP and/or 3'-AMP in response to injurious stimuli, this would complete an autocrine/paracrine mechanism that attenuates the over-activation of microglia during brain injury. Here we investigated in microglia (and for comparison astrocytes and neurons) the effects of injurious stimuli on extracellular and intracellular levels of 2',3'-cAMP (2'-AMP and 3'-AMP precursor), 2'-AMP, and 3'-AMP.

METHODS

Experiments were conducted in primary cultures of rat microglia, astrocytes, and neurons. Cells were exposed to oxygen/glucose deprivation, iodoacetate plus 2,4-dinitrophenol (metabolic inhibitors), glutamate, or H₂O₂ for one hour, and extracellular and intracellular 2',3'-cAMP, 2'-AMP, and 3'-AMP were measured by UPLC-MS/MS.

KEY RESULTS

In microglia, H₂O₂ increased extracellular levels of 2'-AMP, but not 3'-AMP, by ∼16-fold (from 0.17 ± 0.11 to 2.78 ± 0.27 ng/10⁶ cells; n = 13; mean ± SEM; P < 0.000005). H₂O₂ also induced oxidative changes in cellular proteins as detected by an increased number of carbonyl groups in protein side chains. In contrast, oxygen/glucose deprivation, metabolic inhibitors, or glutamate had no effect on either extracellular 2'-AMP or 3'-AMP levels. In astrocytes and neurons, none of the injurious stimuli increased extracellular 2'-AMP or 3'-AMP.

CONCLUSIONS

Oxidative stress (but not oxygen/glucose deprivation, energy deprivation, or excitotoxicity) induces microglia (but not astrocytes or neurons) to release 2'-AMP, but not 3'-AMP. The 2',3'-cAMP/2'-AMP/adenosine pathway mechanism may serve to prevent over-activation of microglia in response to oxidative stress.

GPR17 mediates ischemia-like neuronal injury via microglial activation

GPR17 is a G (i)-coupled dual receptor, linked to P2Y and CysLT receptors stimulated by uracil nucleotides and cysteinyl leukotrienes, respectively. Recent evidence has demonstrated that GPR17 inhibition ameliorates the progression of cerebral ischemic injury by regulating neuronal death and microglial activation. The present study aimed to assess the detailed regulatory roles of this receptor in oxygen-glucose deprivation/recovery (OGD/R)-induced ischemia-like injury in vitro and explore the underlying mechanism. The results demonstrated that OGD/R induced ischemic neuronal injury and microglial activation, including enhanced phagocytosis and increased inflammatory cytokine release in neuron‑glial mixed cultures of cortical cells. GPR17 upregulation during OGD/R was spatially and temporally correlated with neuronal injury and microglial activation. In addition, GPR17 knockdown inhibited OGD/R-induced responses in neuron-glial mixed cultures. GPR17 knockdown also attenuated cell injury induced by the agonist leukotriene D₄ (LTD₄) or uridine 5′-diphosphate (UDP) in neuron-glial mixed cultures. However, GPR17 knockdown did not affect OGD/R-induced ischemic neuronal injury in primary cultures of neurons. In primary astrocyte cultures, neither GPR17 nor OGD/R induced injury. By contrast, GPR17 knockdown ameliorated OGD/R-induced microglial activation, boosting phagocytosis and inflammatory cytokine release in primary microglia cultures. Finally, the results demonstrated that the conditioned medium of microglia pretreated with OGD/R induced neuronal death, and the neuronal injury was significantly inhibited by GPR17 knockdown. These findings suggested that GPR17 may mediate ischemia-like neuronal injury and microglial activation in vitro; however, the protective effects on ischemic neuronal injury might depend upon microglial activation. Whether GPR17 regulates neuronal injury mediated by oligodendrocyte linkage remains to be investigated.

Mitochondrial dysfunction induces NLRP3 inflammasome activation during cerebral ischemia/reperfusion injury

BACKGROUND

Nod-like receptor protein 3 (NLRP3) inflammasome is a crucial factor in mediating inflammatory responses after cerebral ischemia/reperfusion (I/R), but the cellular location of NLRP3 inflammasome in cerebral I/R has yet come to a conclusion, and there is still no specific evidence to state the relationship between mitochondria and the NLRP3 inflammasome in cerebral I/R.

METHODS

In the present study, we detected the cellular localization of NLRP3 inflammasomes in a transient middle cerebral artery occlusion (tMCAO) rat model and a transwell co-culture cell system under oxygen-glucose deprivation/reoxygenation (OGD/R) conditions. Then, we investigated the relationship between mitochondrial dysfunction and the activation of NLRP3 inflammasomes in different cell types after OGD/R and cerebral I/R injury.

RESULTS

Our results showed that NLRP3 inflammasomes were first activated in microglia soon after cerebral I/R injury onset and then were expressed in neurons and microvascular endothelial cells later, but they were mainly in neurons. Furthermore, mitochondrial dysfunction played an important role in activating NLRP3 inflammasomes in microglia after OGD/R, and mitochondrial protector could inhibit the activation of NLRP3 inflammasomes in cerebral I/R rats.

CONCLUSION

Our findings may provide novel insights into the cell type-dependent activation of NLRP3 inflammasomes at different stages of cerebral I/R injury and the role of mitochondrial dysfunction in activating the NLRP3 inflammasome pathway.

Cytosolic Phospholipase A2 Facilitates Oligomeric Amyloid-β Peptide Association with Microglia via Regulation of Membrane-Cytoskeleton Connectivity

Cytosolic phospholipase A₂ (cPLA₂) mediates oligomeric amyloid-β peptide (oAβ)-induced oxidative and inflammatory responses in glial cells. Increased activity of cPLA₂ has been implicated in the neuropathology of Alzheimer's disease (AD), suggesting that cPLA₂ regulation of oAβ-induced microglial activation may play a role in the AD pathology. We demonstrate that LPS, IFNγ, and oAβ increased phosphorylated cPLA₂ (p-cPLA₂) in immortalized mouse microglia (BV2). Aβ association with primary rat microglia and BV2 cells, possibly via membrane-binding and/or intracellular deposition, presumably indicative of microglia-mediated clearance of the peptide, was reduced by inhibition of cPLA₂. However, cPLA₂ inhibition did not affect the depletion of this associated Aβ when cells were washed and incubated in a fresh medium after oAβ treatment. Since the depletion was abrogated by NH₄Cl, a lysosomal inhibitor, these results suggested that cPLA₂ was not involved in the degradation of the associated Aβ. To further dissect the effects of cPLA₂ on microglia cell membranes, atomic force microscopy (AFM) was used to determine endocytic activity. The force for membrane tether formation (F_mtf) is a measure of membrane-cytoskeleton connectivity and represents a mechanical barrier to endocytic vesicle formation. Inhibition of cPLA₂ increased F_mtf in both unstimulated BV2 cells and cells stimulated with LPS + IFNγ. Thus, increasing p-cPLA₂ would decrease F_mtf, thereby increasing endocytosis. These results suggest a role of cPLA₂ activation in facilitating oAβ endocytosis by microglial cells through regulation of the membrane-cytoskeleton connectivity.

An Overview of in vitro Methods to Study Microglia

Neuroinflammation is a common feature in neurodegenerative diseases and strategies to modulate neuroinflammatory processes are increasingly considered as therapeutic options. In such strategies, glia cells rather than neurons represent the cellular targets. Microglia, the resident macrophages of the central nervous system, are principal players in neuroinflammation and detailed cellular biological knowledge of this particular cell type is therefore of pivotal importance. The last decade has shed new light on the origin, characteristics and functions of microglia, underlining the need for specific in vitro methodology to study these cells in detail. In this review we provide a comprehensive overview of existing methodology such as cell lines, stem cell-derived microglia and primary dissociated cell cultures, as well as discuss recent developments. As there is no in vitro method available yet that recapitulates all hallmarks of adult homeostatic microglia, we also discuss the advantages and limitations of existing models across different species.

Microglia P2Y13 Receptors Prevent Astrocyte Proliferation Mediated by P2Y1 Receptors

Cerebral inflammation is a common feature of several neurodegenerative diseases that requires a fine interplay between astrocytes and microglia to acquire appropriate phenotypes for an efficient response to neuronal damage. During brain inflammation, ATP is massively released into the extracellular medium and converted into ADP. Both nucleotides acting on P2 receptors, modulate astrogliosis through mechanisms involving microglia-astrocytes communication. In previous studies, primary cultures of astrocytes and co-cultures of astrocytes and microglia were used to investigate the influence of microglia on astroglial proliferation induced by ADPβS, a stable ADP analog. In astrocyte cultures, ADPβS increased cell proliferation through activation of P2Y₁ and P2Y₁₂ receptors, an effect abolished in co-cultures (of astrocytes with ∼12.5% microglia). The possibility that the loss of the ADPβS-mediated effect could have been caused by a microglia-induced degradation of ADPβS or by a preferential microglial localization of P2Y₁ or P2Y₁₂ receptors was excluded. Since ADPβS also activates P2Y₁₃ receptors, the contribution of microglial P2Y₁₃ receptors to prevent the proliferative effect of ADPβS in co-cultures was investigated. The results obtained indicate that P2Y₁₃ receptors are low expressed in astrocytes and mainly expressed in microglia. Furthermore, in co-cultures, ADPβS induced astroglial proliferation in the presence of the selective P2Y₁₃ antagonist MRS 2211 (3 μM) and of the selective P2Y₁₂ antagonist AR-C66096 (0.1 μM), suggesting that activation of microglial P2Y₁₂ and P2Y₁₃ receptors may induce the release of messengers that inhibit astroglial proliferation mediated by P2Y_1,12 receptors. In this microglia-astrocyte paracrine communication, P2Y₁₂ receptors exert opposite effects in astroglial proliferation as a result of its cellular localization: cooperating in astrocytes with P2Y₁ receptors to directly stimulate proliferation and in microglia with P2Y₁₃ receptors to prevent proliferation. IL-1β also attenuated the proliferative effect of ADPβS in astrocyte cultures. However, in co-cultures, the anti-IL-1β antibody was unable to recover the ADPβS-proliferative effect, an effect that was achieved by the anti-IL-1α and anti-TNF-α antibodies. It is concluded that microglia control the P2Y_1,12 receptor-mediated astroglial proliferation through a P2Y_12,13 receptor-mediated mechanism alternative to the IL-1β suppressive pathway that may involve the contribution of the cytokines IL-1α and TNF-α.

A refined rat primary neonatal microglial culture method that reduces time, cost and animal use

BACKGROUND

Primary microglial cultures have been used extensively to facilitate the development of therapeutic strategies for a variety of CNS disorders including neurodegeneration and neuropathic pain. However, existing techniques for culturing these cells are slow and costly.

NEW METHOD

Here, we report a refined protocol based on our previously published methods described by Clark et al., which reduces in the time, reagents and the number of animals used for each culture whilst yielding high number and excellent quality microglial cells.

RESULTS

Our refined protocol offers an isolation of >96% microglia from a mixed glial culture after only four days of incubation. It results in a high yield of microglia, in excess of one million cells per cortex with predominantly resting morphology and a low level of cell activation.

COMPARISON WITH EXISTING METHOD(S)

Compared to conventional procedures our refined protocol requires only one third of the time to prepare high quality microglial cultures, cuts the cost more than four-fold, and significantly reduces the number of animals used per culture.

CONCLUSION

Our consistent, reliable, and time/cost effective microglial culture protocol is crucial for efficient in vitro screening of potential therapeutics. By dramatically reducing the culture time from 2 weeks to just 4 days and increasing the laboratory research output it has implications for the Reduction, Refinement and Replacement policies endorsed by many government funding agencies and animal research regulatory bodies.

Primary microglia isolation from mixed cell cultures of neonatal mouse brain tissue

BACKGROUND

Microglia are the main resident immunological cells of the central nervous system (CNS) that are functionally equivalent to macrophages. However, due to the cellular heterogeneity of the brain, it is technically challenging to obtain highly specific, healthy microglia with the desired phenotype in sufficient yield for in vivo experiments.

NEW METHOD

This study presents a new and easy method for the isolation of microglia cells from mouse pups (P1-P3). This method consists of a 20-day protocol, divided in three sections: mixed cell culture, culture maintaining (astrocytes growing), and isolation after astrocytes confluence.

RESULTS

This procedure produces microglia with no astrocyte, neuron and oligodendrocyte precursors cells contamination that are functionally active to answer inflammatory responses based on the measurement of cell and inflammatory markers. This technique requires approximately three hours for the isolation of neonatal mixed cell culture, 20 to 22 days for microglia growing and two days before starting experiments from pure and healthy microglia.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

This study presents an isolation protocol that is adapted from existing methods and is economic, rapid, not tedious, with little manipulation time and work. This method also allows to isolate large amount of high specific microglia cells with no specific phenotype and with great reproducibility and efficiently. This study provides a detailed description of the methods that is routinely used in our laboratory for the isolation and the culture of microglia, with emphasis on the steps that are deemed most critical for obtaining large amount of pure and healthy cultures.

Microglia: Housekeeper of the Central Nervous System

Microglia, of myeloid origin, play fundamental roles in the control of immune responses and the maintenance of central nervous system homeostasis. These cells, just like peripheral macrophages, may be activated into M1 pro-inflammatory or M2 anti-inflammatory phenotypes by appropriate stimuli. Microglia do not respond in isolation, but form part of complex networks of cells influencing each other. This review addresses the complex interaction of microglia with each cell type in the brain: neurons, astrocytes, cerebrovascular endothelial cells, and oligodendrocytes. We also highlight the participation of microglia in the maintenance of homeostasis in the brain, and their roles in the development and progression of age-related neurodegenerative disorders.

Oncolytic Virotherapy Blockade by Microglia and Macrophages Requires STAT1/3

The first oncolytic virotherapy employing HSV-1 (oHSV-1) was approved recently by the FDA to treat cancer, but further improvements in efficacy are needed to eradicate challenging refractory tumors, such as glioblastomas (GBM). Microglia/macrophages comprising approximately 40% of a GBM tumor may limit virotherapeutic efficacy. Here, we show these cells suppress oHSV-1 growth in gliomas by internalizing the virus through phagocytosis. Internalized virus remained capable of expressing reporter genes while viral replication was blocked. Macrophage/microglia formed a nonpermissive OV barrier, preventing dissemination of oHSV-1 in the glioma mass. The deficiency in viral replication in microglial cells was associated with silencing of particular viral genes. Phosphorylation of STAT1/3 was determined to be responsible for suppressing oHSV-1 replication in macrophages/microglia. Treatment with the oxindole/imidazole derivative C16 rescued oHSV-1 replication in microglia/macrophages by inhibiting STAT1/3 activity. In the U87 xenograft model of GBM, C16 treatment overcame the microglia/macrophage barrier, thereby facilitating tumor regression without causing a spread of the virus to normal organs. Collectively, our results suggest a strategy to relieve a STAT1/3-dependent therapeutic barrier and enhance oHSV-1 oncolytic activity in GBM.Significance: These findings suggest a strategy to enhance the therapeutic efficacy of oncolytic virotherapy in glioblastoma. Cancer Res; 78(3); 718-30. ©2017 AACR.

Co-Culture of Neurons and Microglia

Microglia, the resident immune cells of the brain, have been implicated in numerous neurodegenerative and neurodevelopmental diseases. Activation of microglia by a variety of stimuli induces the release of factors, including pro- and anti-inflammatory cytokines and reactive oxygen species, that contribute to modulating neuro-inflammation and oxidative stress, two crucial processes linked to disorders of the central nervous system. The in vitro techniques described here will provide a set of protocols for the isolation and plating of primary cerebellar granule neurons, primary cortical microglia from a mixed glia culture, and methods for co-culturing both cell types. These methods allow the study of how microglia and the factors they release in this shared environment mediate the effects of toxicants on neuronal function and survival. The protocols presented here allow for flexibility in experimental design, the study of numerous toxicological endpoints, and the opportunity to explore neuroprotective strategies. © 2017 by John Wiley & Sons, Inc.

Shedding of membrane-associated LDL receptor-related protein-1 from microglia amplifies and sustains neuroinflammation

In the CNS, microglia are activated in response to injury or infection and in neurodegenerative diseases. The endocytic and cell signaling receptor, LDL receptor-related protein-1 (LRP1), is reported to suppress innate immunity in macrophages and oppose microglial activation. The goal of this study was to identify novel mechanisms by which LRP1 may regulate microglial activation. Using primary cultures of microglia isolated from mouse brains, we demonstrated that LRP1 gene silencing increases expression of proinflammatory mediators; however, the observed response was modest. By contrast, the LRP1 ligand, receptor-associated protein (RAP), robustly activated microglia, and its activity was attenuated in LRP1-deficient cells. An important element of the mechanism by which RAP activated microglia was its ability to cause LRP1 shedding from the plasma membrane. This process eliminated cellular LRP1, which is anti-inflammatory, and generated a soluble product, shed LRP1 (sLRP1), which is potently proinflammatory. Purified sLRP1 induced expression of multiple proinflammatory cytokines and the mRNA encoding inducible nitric-oxide synthase in both LRP1-expressing and -deficient microglia. LPS also stimulated LRP1 shedding, as did the heat-shock protein and LRP1 ligand, calreticulin. Other LRP1 ligands, including α₂-macroglobulin and tissue-type plasminogen activator, failed to cause LRP1 shedding. Treatment of microglia with a metalloproteinase inhibitor inhibited LRP1 shedding and significantly attenuated RAP-induced cytokine expression. RAP and sLRP1 both caused neuroinflammation in vivo when administered by stereotaxic injection into mouse spinal cords. Collectively, these results suggest that LRP1 shedding from microglia may amplify and sustain neuroinflammation in response to proinflammatory stimuli.

P2Y12 and P2Y13 receptors involved in ADPβs induced the release of IL-1β, IL-6 and TNF-α from cultured dorsal horn microglia

Objective

P2 receptors have been implicated in the release of neurotransmitter and pro-inflammatory cytokines due to their response to neuroexcitatory substances in the microglia. Dorsal horn P2Y₁₂ and P2Y₁₃ receptors are involved in the development of pain behavior induced by peripheral nerve injury. However, it is not known whether P2Y₁₂ and P2Y₁₃ receptors activation is associated with the expression and the release of interleukin-1B (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) in cultured dorsal spinal cord microglia. For this reason, we examined the effects of ADPβs (ADP analog) on the expression and the release of IL-1β, IL-6, and TNF-α.

Methods and results

In this study, we observed the effect of P2Y receptor agonist ADPβs on the expression and release of IL-1β, IL-6 and TNF-α by using real-time fluorescence quantitative polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). ADPβs induced the increased expression of Iba-1, IL-1β, IL-6 and TNF-α at the level of messenger RNA (mRNA). ADPβs-evoked increase in Iba-1, IL-1β, IL-6 and TNF-α mRNA expression was inhibited only partially by P2Y₁₂ receptor antagonist MRS2395 or P2Y₁₃ receptor antagonist MRS2211, respectively. Similarly, ADPβs-evoked release of IL-1β, IL-6 and TNF-α was inhibited only partially by MRS2395 or MRS2211. Furthermore, ADPβs-evoked increased expression of Iba-1, IL-1β, IL-6 and TNF-α mRNA, and release of IL-1β, IL-6 and TNF-α were nearly all blocked after co-administration of MRS2395 plus MRS2179. Further evidence indicated that P2Y₁₂ and P2Y₁₃ receptor-evoked increased gene expression of IL-1β, IL-6 and TNF-α were inhibited by Y-27632 (ROCK inhibitor), SB203580 (P38MAPK inhibitor) and PDTC (NF-κb inhibitor), respectively. Subsequently, P2Y₁₂ and P2Y₁₃ receptor-evoked release of IL-1β, IL-6 and TNF-α, were also inhibited by Y-27632, SB203580 and PDTC, respectively.

Conclusion

These observations suggest that P2Y₁₂ and P2Y₁₃ receptor-evoked gene expression and release of IL-1β, IL-6 and TNF-α are associated with ROCK/P38MAPK/NF-κb signaling pathway.

Quercetin Protects Obesity-Induced Hypothalamic Inflammation by Reducing Microglia-Mediated Inflammatory Responses via HO-1 Induction

Obesity-induced hypothalamic inflammation is characterized by activation of microglia, which are resident macrophages of the central nervous system, and is implicated in the derangement of energy homeostasis, metabolic complications, and neurodegenerative diseases. Quercetin, a naturally occurring flavonoid, is known to protect against oxidative stress and inflammation-related metabolic complications. Here, we demonstrate that quercetin reduces obesity-induced hypothalamic inflammation by inhibiting microglia-mediated inflammatory responses, and the beneficial action of quercetin is associated with heme oxygenase (HO-1) induction. Quercetin markedly reduced the production of inflammatory mediators (monocyte chemoattractant protein (MCP)-1, interleukin (IL-6), IL-1β, nitric oxide) by microglia stimulated with saturated fatty acid palmitate and/or lipid-laden microglia-conditioned medium. Quercetin also upregulated the expression of HO-1 in palmitate-treated lipid-laden microglia, and the actions of quercetin against microglia activation accompanied by IκBα degradation were abolished by a HO-1 inhibitor. Moreover, quercetin supplementation reduced the levels of inflammatory cytokines and microglia activation markers in the hypothalamus of high fat diet (HFD)-fed obese mice, which was accompanied by upregulation of HO-1. These findings indicate that quercetin suppresses microglia-mediated inflammatory responses via the induction of HO-1, and hence protects against obesity-induced hypothalamic inflammation.

Cocaine-Mediated Downregulation of miR-124 Activates Microglia by Targeting KLF4 and TLR4 Signaling

Cocaine is known to activate microglia both in vitro and in vivo. High expression of microglial Toll-like receptors (TLRs) and their downstream signal transducers play critical roles in determining microglial activation status. Emerging reports have also demonstrated that cocaine can enhance the strength of TLR signaling. Detailed molecular mechanisms underlying this phenomenon, however, remain elusive. In this study, we investigated the role(s) of miR-124 in regulating microglial TLR4 signaling in the context of cocaine. Herein, we found a dose- and time-dependent upregulation of KLF4 in cocaine-exposed BV-2 cells and rat primary microglial cells (rPMs). KLF4 also identified as a novel 3'-UTR target directly regulated by miR-124. In parallel, miR-124 regulated multiple TLR4 signaling molecules including TLR4, MyD88, TRAF6, and IRAK1. Repeated doses of cocaine (20 mg/kg; i.p.) administration in mice for 7 days further validated the in vitro key findings. Also, miR-124 overexpression significantly blocked the cocaine-mediated upregulation of pro-inflammatory cytokines. In contrast, miR-124 overexpression notably increased the expression of anti-inflammatory mediators in cocaine-exposed microglial cells. Intriguingly, stereotactic administration of lentivirus-miR-124 in the striatum significantly inhibited cocaine-mediated microglial activation and locomotor hyperactivity in vivo. In summary, these findings implicate the role of miR-124 in regulating TLR4 signaling, thereby indicating a new pathway responsible for cocaine-mediated microglial activation.

Adenosine production by brain cells

The early release of adenosine following traumatic brain injury (TBI) suppresses seizures and brain inflammation; thus, it is important to elucidate the cellular sources of adenosine following injurious stimuli triggered by TBI so that therapeutics for enhancing the early adenosine-release response can be optimized. Using mass spectrometry with ¹³ C-labeled standards, we investigated in cultured rat neurons, astrocytes, and microglia the effects of oxygen-glucose deprivation (OGD; models energy failure), H₂ O₂ (produces oxidative stress), and glutamate (induces excitotoxicity) on intracellular and extracellular levels of 5'-AMP (adenosine precursor), adenosine, and inosine and hypoxanthine (adenosine metabolites). In neurons, OGD triggered increases in intracellular 5'-AMP (2.8-fold), adenosine (2.6-fold), inosine (2.2-fold), and hypoxanthine (5.3-fold) and extracellular 5'-AMP (2.2-fold), adenosine (2.4-fold), and hypoxanthine (2.5-fold). In neurons, H₂ O₂ did not affect intracellular or extracellular purines; yet, glutamate increased intracellular adenosine, inosine, and hypoxanthine (1.7-fold, 1.7-fold, and 1.6-fold, respectively) and extracellular adenosine, inosine, and hypoxanthine (2.9-fold, 2.1-fold, and 1.6-fold, respectively). In astrocytes, neither H₂ O₂ nor glutamate affected intracellular or extracellular purines, and OGD only slightly increased intracellular and extracellular hypoxanthine. Microglia were unresponsive to OGD and glutamate, but were remarkably responsive to H₂ O₂ , which increased intracellular 5'-AMP (1.6-fold), adenosine (1.6-fold), inosine (2.1-fold), and hypoxanthine (1.6-fold) and extracellular 5'-AMP (5.9-fold), adenosine (4.0-fold), inosine (4.3-fold), and hypoxanthine (1.9-fold).

CONCLUSION

Under these particular experimental conditions, cultured neurons are the main contributors to adenosine production/release in response to OGD and glutamate, whereas cultured microglia are the main contributors upon oxidative stress. Developing therapeutics that recruit astrocytes to produce/release adenosine could have beneficial effects in TBI.

Leucine-rich repeat kinase 2 (LRRK2) regulates α-synuclein clearance in microglia

BACKGROUND

α-Synuclein (αSYN) has been genetically implicated in familial and sporadic Parkinson's disease (PD), and is associated with disease susceptibility, progression and pathology. Excess amounts of αSYN are toxic to neurons. In the brain, microglial αSYN clearance is closely related to neuronal survival. Leucine-rich repeat kinase 2 (LRRK2) is the one of the other genes implicated in familial and sporadic PD. While LRRK2 is known to be expressed in microglia, its true function remains to be elucidated. In this study, we investigated αSYN clearance by microglia isolated from LRRK2-knockout (KO) mice.

RESULTS

In LRRK2-KO microglia, αSYN was taken up in larger amounts and cleared from the supernatant more effectively than for microglia isolated from wild-type (WT) mice. This higher clearance ability of LRRK2-KO microglia was thought to be due to an increase of Rab5-positive endosomes, but not Rab7- or Rab11-positive endosomes. Increased engagement between Rab5 and dynamin 1 was also observed in LRRK2-KO microglia.

CONCLUSION

LRRK2 negatively regulates the clearance of αSYN accompanied by down-regulation of the endocytosis pathway. Our findings reveal a new functional role of LRRK2 in microglia and offer a new insight into the mechanism of PD pathogenesis.

Isolation and characterization of primary microglia from post-natal murine brain tissues: a comparison of two methods

Microglia are resident macrophages of the central nervous system (CNS). Apart from playing vital roles as sentinel cells, they are crucial in physiological processes such as synaptic pruning during brain development. CNS disorders require an understanding of the contribution of each cellular compartment to the pathogenesis. Elucidating the role of microglia in disease development and progression in the intricate CNS environment is technically challenging and requires the establishment of reliable, reproducible techniques to isolate and culture microglia. A number of different protocols have been developed for isolation of neonatal microglia and here we compare two widely used methods, namely, mild trypsinization and EasySep® magnetic separation. EasySep® magnetic separation provided higher microglia yield, and flow cytometric evaluation of CD11b and F4/80 markers revealed that EasySep® separation method also produced significantly higher purity compared to mild trypsinization. Microglia isolated using EasySep® separation method were functional, as demonstrated by the generation of nitric oxide, IL-6, TNF-α, and MCP-1 in response to lipopolysaccharide stimulation. In summary, this study has revealed that magnetic separation is superior to mild trypsinization in terms of yield and purity of microglia.

P2Y13 receptor-mediated rapid increase in intracellular calcium induced by ADP in cultured dorsal spinal cord microglia

P2Y receptors have been implicated in the calcium mobilization by the response to neuroexcitatory substances in neurons and astrocytes, but little is known about P2Y receptors in microglia cells. In the present study, the effects of ADP on the intracellular calcium concentration ([Ca(2+)]i) in cultured dorsal spinal cord microglia were detected with confocal laser scanning microscopy using fluo-4/AM as a calcium fluorescence indicator that could monitor real-time alterations of [Ca(2+)]i. Here we show that ADP (0.01-100 μM) causes a rapid increase in [Ca(2+)]i with a dose-dependent manner in cultured microglia. The action of ADP on [Ca(2+)]i was significantly blocked by MRS2211 (a selective P2Y13 receptor antagonist), but was unaffected by MRS2179 (a selective P2Y1 receptor antagonist) or MRS2395 (a selective P2Y12 receptor antagonist), which suggest that P2Y13 receptor may be responsible for ADP-evoked Ca(2+) mobilization in cultured microglia. P2Y13-evoked Ca(2+) response can be obviously inhibited by BAPTA-AM and U-73122, respectively. Moreover, removal of extracellular Ca(2+) (by EGTA) also can obvious suppress the Ca(2+) mobilization. These results means both intracellular calcium and extracellular calcium are potentially important mechanisms in P2Y13 receptor-evoked Ca(2+) mobilization. However, P2Y13 receptor-evoked Ca(2+) response was not impaired after CdCl2 and verapamil administration, which suggest that voltage-operated Ca(2+) channels may be not related with P2Y13-evoked Ca(2+) response. In addition, Ca(2+) mobilization induced by ADP was abolished by different store-operated Ca(2+) channels (SOCs) blocker, 2-APB (50 μM) and SKF-96365 (1 mM), respectively. These observations suggest that the activation of P2Y13 receptor might be involved in the effect of ADP on [Ca(2+)]i in cultured dorsal spinal cord microglia. Furthermore, our results raise a possibility that P2Y13 receptor activation causes Ca(2+) release from Ca(2+) store, which leads to the opening of SOCs.

Nitric oxide-mediated immunosuppressive effect of human amniotic membrane-derived mesenchymal stem cells on the viability and migration of microglia

Human amniotic membrane-derived mesenchymal stem cells (AMSCs) are considered a novel and promising source of stem cells for cell replacement-based therapy. Current research is mostly limited to investigating the cellular differentiation potential of AMSCs, while few have focused on their immunosuppressive properties. This study is aimed at exploring and evaluating the immunosuppressive effect of human AMSCs on the viability and migratory properties of microglia. We found, from results of cell viability assays, that AMSCs can reduce the activity of inflammatory cells by secreting nitric oxide (NO). Also, based on results from wound healing and transwell migration assays, we show that AMSCs can inhibit the migration of human microglia as well as the mouse microglial cell line BV2, suggesting that they have the ability to inhibit the recruitment of certain immune cells to injury sites. Furthermore, we found that NO contributes significantly to this inhibitory effect. Our study provides evidence that human AMSCs can have detrimental effects on the viability and migration of microglia, through secretion of NO. This mechanism may contribute to anti-inflammatory processes in the central nervous system.

Microglia change from a reactive to an age-like phenotype with the time in culture

Age-related neurodegenerative diseases have been associated with chronic neuroinflammation and microglia activation. However, cumulative evidence supports that inflammation only occurs at an early stage once microglia change the endogenous characteristics with aging and switch to irresponsive/senescent and dystrophic phenotypes with disease progression. Thus, it will be important to have the means to assess the role of reactive and aged microglia when studying advanced brain neurodegeneration processes and age-associated related disorders. Yet, most studies are done with microglia from neonates since there are no adequate means to isolate degenerating microglia for experimentation. Indeed, only a few studies report microglia isolation from aged animals, using either short-term cultures or high concentrations of mitogens in the medium, which trigger microglia reactivity. The purpose of this study was to develop an experimental process to naturally age microglia after isolation from neonatal mice and to characterize the cultured cells at 2 days in vitro (DIV), 10 DIV, and 16 DIV. We found that 2 DIV (young) microglia had predominant amoeboid morphology and markers of stressed/reactive phenotype. In contrast, 16 DIV (aged) microglia evidenced ramified morphology and increased matrix metalloproteinase (MMP)-2 activation, as well as reduced MMP-9, glutamate release and nuclear factor kappa-B activation, in parallel with decreased expression of Toll-like receptor (TLR)-2 and TLR-4, capacity to migrate and phagocytose. These findings together with the reduced expression of microRNA (miR)-124, and miR-155, decreased autophagy, enhanced senescence associated beta-galactosidase activity and elevated miR-146a expression, are suggestive that 16 DIV cells mainly correspond to irresponsive/senescent microglia. Data indicate that the model represent an opportunity to understand and control microglial aging, as well as to explore strategies to recover microglia surveillance function.

Methylmercury alters the activities of Hsp90 client proteins, prostaglandin E synthase/p23 (PGES/23) and nNOS

Methylmercury (MeHg) is a persistent pollutant with known neurotoxic effects. We have previously shown that astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS) by altering glutamate signaling, generating oxidative stress, depleting glutathione (GSH) and initiating lipid peroxidation. Interestingly, all of these pathways can be regulated by the constitutively expressed, 90-kDa heat shock protein, Hsp90. As Hsp90 function is regulated by oxidative stress, we hypothesized that MeHg disrupts Hsp90-client protein functions. Astrocytes were treated with MeHg and expression of Hsp90, as well as the abundance of complexes of Hsp90-neuronal nitric oxide synthase (nNOS) and Hsp90-prostaglandin E synthase/p23 (PGES/p23) were assessed. MeHg exposure decreased Hsp90 protein expression following 12 h of treatment while shorter exposures had no effect on Hsp90 protein expression. Interestingly, following 1 or 6 h of MeHg exposure, Hsp90 binding to PGES/p23 or nNOS was significantly increased, resulting in increased prostaglandin E₂ (PGE₂) synthesis from MeHg-treated astrocytes. These effects were attenuated by the Hsp90 antagonist, geldanmycin. NOS activity was increased following MeHg treatment while cGMP formation was decreased. This was accompanied by an increase in •O₂⁻ and H₂O₂ levels, suggesting that MeHg uncouples NO formation from NO-dependent signaling and increases oxidative stress. Altogether, our data demonstrates that Hsp90 interactions with client proteins are increased following MeHg exposure, but over time Hsp90 levels decline, contributing to oxidative stress and MeHg-dependent excitotoxicity.

Human amniotic epithelial stem cells inhibit microglia activation through downregulation of tumor necrosis factor-α, interleukin-1β and matrix metalloproteinase-12 in vitro and in a rat model of intracerebral hemorrhage

BACKGROUND AIMS

The molecular mechanisms by which stem cell transplantation improves functional recovery after intracerebral hemorrhage (ICH) are not well understood. Accumulating evidence suggests that microglia cells are activated shortly after ICH and that this activation contributes to secondary ICH-induced brain injury. We studied the effect of human amniotic epithelial stem cells (HAESCs) on microglia activation.

METHODS

To study the effect of HAESCs in vitro, we used thrombin to activate the microglia cells. Twenty-four hours after thrombin treatment, the levels of tumor necrosis factor-α and interleukin-1β were measured by enzyme-linked immunosorbent assay. In vivo, the HAESCs were transplanted into the rat striatum 1 day after collagenase-induced ICH. The expression levels of matrix metalloproteinase (MMP)-12 and microglia infiltration in the peri-hematoma tissues were determined 7 days after ICH through the use of reverse transcriptase-polymerase chain reaction and immunohistochemical analysis, respectively.

RESULTS

Thrombin-activated microglia expression of tumor necrosis factor-α, interleukin-1β and MMP-12 was significantly reduced through contact-dependent and paracrine mechanisms when the HAESCs were co-cultured with microglia cells. After transplantation of HAESCs in rat brains, the expression levels of MMP-12 and microglia infiltration in the peri-hematoma tissues were significantly reduced.

CONCLUSIONS

Our observations suggest that microglia activation could be inhibited by HAESCs both in vitro and in vivo, which may be an important mechanism by which the transplantation of HAESCs reduces brain edema and ameliorates the neurologic deficits after ICH. Therefore, we hypothesize that methods for suppressing the activation of microglia and reducing the inflammatory response can be used for designing effective treatment strategies for ICH.

Developmental onset of bilirubin-induced neurotoxicity involves Toll-like receptor 2-dependent signaling in humanized UDP-glucuronosyltransferase1 mice

Biological and signaling events that connect developmentally induced hyperbilirubinemia to bilirubin-induced neurological dysfunction (BIND) and CNS toxicity in humans are poorly understood. In mammals, UDP-glucuronosyltransferase 1A1 (UGT1A1) is the sole enzyme responsible for bilirubin glucuronidation, a rate-limiting step necessary for bilirubin metabolism and clearance. Humanized mice that express the entire UGT1 locus (hUGT1) and the UGT1A1 gene, develop neonatal hyperbilirubinemia, with 8-10% of hUGT1 mice succumbing to CNS damage, a phenotype that is presented by uncontrollable seizures. We demonstrate that neuroinflammation and reactive gliosis are prominent features of bilirubin brain toxicity, and a disturbed redox status resulting from activation of NADPH oxidase is an important contributing mechanism found in BIND. Using knock-out mice and primary brain cells, we connect a key pattern recognition receptor, Toll-like receptor 2 (TLR2), to hyperbilirubinemia-induced signaling. We illustrate a requirement for TLR2 signaling in regulating gliosis, proinflammatory mediators, and oxidative stress when neonatal mice encounter severe hyperbilirubinemia. TLR2-mediated gliosis strongly correlates with pronounced neuroinflammation in the CNS with up-regulation of TNFα, IL-1β, and IL-6, creating a pro-inflammatory CNS environment. Gene expression and immunohistochemistry staining show that hUGT1/Tlr2(-/-) mice fail to activate glial cells, proinflammatory cytokines, and stress response genes. In addition, bilirubin-induced apoptosis was significantly enhanced by blocking TLR2 signaling indicating its anti-apoptotic property. Consequently, a higher neonatal death rate (57.1%) in hUGT1/Tlr2(-/-) mice was observed when compared with hUGT1 mice (8.7%). These results suggest that TLR2 signaling and microglia neuroinflammation are linked to a repair and/or protection mode against BIND.

Advances in cellular models to explore the pathophysiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disorder, is fatal for most patients less than 3 years from when the first symptoms appear. The aetiologies for sporadic and most familial forms of ALS are unknown, but genetic factors are increasingly recognized as causal in a subset of patients. Studies of disease physiology suggest roles for oxidative stress, glutamate-mediated excitotoxicity or protein aggregation; how these pathways interact in the complex pathophysiology of ALS awaits elucidation. Cellular models are being used to examine disease mechanisms. Recent advances include the availability of expanded cell types, from neuronal or glial cell culture to motoneuron-astrocyte co-culture genetically or environmentally modified. Cell culture experiments confirmed the central role of glial cells in ALS. The recent adaptation of induced pluripotent stem cells (iPSC) for ALS modeling could allow a broader perspective and is expected to generate new hypotheses, related particularly to mechanisms underlying genetic factors. Cellular models have provided meaningful advances in the understanding of ALS, but, to date, complete characterization of in vitro models is only partially described. Consensus on methodological approaches, strategies for validation and techniques that allow rapid adaptation to new genetic or environmental influences is needed. In this article, we review the principal cellular models being employed in ALS and highlight their contribution to the understanding of disease mechanisms. We conclude with recommendations on means to enhance the robustness and generalizability of the different concepts for experimental ALS.