CSF-1 expression is upregulated in astrocyte cultures by IL-1 and TNF and affects microglial proliferation and morphology in organotypic cultures

The Investigation into Neurotoxicity Mechanisms of Nonylphenol: A Narrative Review

BACKGROUND

Nonylphenol (NP), a chemical compound widely used in industry, is the result of the nonylphenol ethoxylate decomposition and it is known as an estrogen-like compound. Numerous studies and researches have shown that it has many destructive functions of various organs such as the brain. This toxicant causes oxidative stress in the cortex and hippocampus cells, which are two essential regions to preserve memory and learning in the brain.

METHODS

This review examines recent findings to better understanding the mechanisms of NP neurotoxicity. We used Scopus, Google Scholar, and PubMed databases to find articles focused on the destructive effects of NP on the oxidative stress pathway and its defense mechanisms.

RESULTS

NP has potential human health hazards associated with gestational, peri- and postnatal exposure. NP can disrupt brain homeostasis in different ways, such as activation of inflammatory factors in brain especially in hippocampus and cortex, disruption of the cell cycle, changes in neuron, dendrites and synapses morphology, disruption of extra and intracellular calcium ion balance and also memory and learning disorders.

The role of TLR4/NF-κB signaling pathway in activated microglia of rats with chronic high intraocular pressure and vitro scratch injury-induced microglia

Glaucoma is a kind of blind-causing disease with structural damages of optic nerve and defection of visual field. It is believed that the death of retinal ganglion cell (RGC) is a consequential event of over-reactive immune orchestral cells such as microglia. Previous evidences in animal and clinical studies show the innate immunity plays a pivotal role in neuro-inflammation of glaucoma. Toll-like receptor 4 (TLR4) is expressed on microglia and mediates many neuroinflammatory diseases. We aimed to explore the impacts of high intraocular pressure (IOP) on rat microglia in retina and the regulation of TLR4/NF-κB signaling pathway in scratched microglia cells. In our study, we successfully established chronic high IOP rat model by episcleral vein cauterization (EVC) which behaved like the chronic glaucoma. Besides, we set up an in vitro scratch-induced injury model in rat microglia cells. We found the level of activated microglia cells were significantly increased in the retina of chronic high IOP groups. Moreover, the inhibition of TLR4/NF-κB signaling pathway suppressed the expression of TLR4 protein and mRNA levels of P50, IL-6 and TNF-α. Our original study provided a theoretical basis on targeting TLR4/NF-κB to suppress pro-inflammatory factors releasing in activated microglia and it might be a good treatment target to prevent glaucoma from progressing.

IL-1β-driven amyloid plaque clearance is associated with an expansion of transcriptionally reprogrammed microglia

BACKGROUND

Neuroinflammation is thought to contribute to the pathogenesis of Alzheimer's disease (AD), yet numerous studies have demonstrated a beneficial role for neuroinflammation in amyloid plaque clearance. We have previously shown that sustained expression of IL-1β in the hippocampus of APP/PS1 mice decreases amyloid plaque burden independent of recruited CCR2+ myeloid cells, suggesting resident microglia as the main phagocytic effectors of IL-1β-induced plaque clearance. To date, however, the mechanisms of IL-1β-induced plaque clearance remain poorly understood.

METHODS

To determine whether microglia are involved in IL-1β-induced plaque clearance, APP/PS1 mice induced to express mature human IL-1β in the hippocampus via adenoviral transduction were treated with the Aβ fluorescent probe methoxy-X04 (MX04) and microglial internalization of fibrillar Aβ (fAβ) was analyzed by flow cytometry and immunohistochemistry. To assess microglial proliferation, APP/PS1 mice transduced with IL-1β or control were injected intraperitoneally with BrdU and hippocampal tissue was analyzed by flow cytometry. RNAseq analysis was conducted on microglia FACS sorted from the hippocampus of control or IL-1β-treated APP/PS1 mice. These microglia were also sorted based on MX04 labeling (MX04+ and MX04- microglia).

RESULTS

Resident microglia (CD45loCD11b+) constituted > 70% of the MX04+ cells in both Phe- and IL-1β-treated conditions, and < 15% of MX04+ cells were recruited myeloid cells (CD45hiCD11b+). However, IL-1β treatment did not augment the percentage of MX04+ microglia nor the quantity of fAβ internalized by individual microglia. Instead, IL-1β increased the total number of MX04+ microglia in the hippocampus due to IL-1β-induced proliferation. In addition, transcriptomic analyses revealed that IL-1β treatment was associated with large-scale changes in the expression of genes related to immune responses, proliferation, and cytokine signaling.

CONCLUSIONS

These studies show that IL-1β overexpression early in amyloid pathogenesis induces a change in the microglial gene expression profile and an expansion of microglial cells that facilitates Aβ plaque clearance.

Mesenchymal transition and increased therapy resistance of glioblastoma cells is related to astrocyte reactivity

Grade IV astrocytoma/glioblastoma multiforme (GBM) is essentially incurable, partly due to its heterogenous nature, demonstrated even within the glioma-initiating cell (GIC) population. Increased therapy resistance of GICs is coupled to transition into a mesenchymal (MES) cell state. The GBM MES molecular signature displays a pronounced inflammatory character and its expression vary within and between tumors. Herein, we investigate how MES transition of GBM cells relates to inflammatory responses of normal astroglia. In response to CNS insults astrocytes enter a reactive cell state and participate in directing neuroinflammation and subsequent healing processes. We found that the MES signature show strong resemblance to gene programs induced in reactive astrocytes. Likewise, astrocyte reactivity gene signatures were enriched in therapy-resistant MES-like GIC clones. Variable expression of astrocyte reactivity related genes also largely defined intratumoral GBM cell heterogeneity at the single-cell level and strongly correlated with our previously defined therapy-resistance signature (based on linked molecular and functional characterization of GIC clones). In line with this, therapy-resistant MES-like GIC secreted immunoregulatory and tissue repair related proteins characteristic of astrocyte reactivity. Moreover, sensitive GIC clones could be made reactive through long-term exposure to the proinflammatory cytokine interleukin 1 beta (IL1β). IL1β induced a slow MES transition, increased therapy resistance, and a shift in DNA methylation profile towards that of resistant clones, which confirmed a slow reprogramming process. In summary, GICs enter through MES transition a reactive-astrocyte-like cell state, connected to therapy resistance. Thus, from a biological point of view, MES GICs would preferably be called 'reactive GICs'. The ability of GBM cells to mimic astroglial reactivity contextualizes the immunomodulatory and microenvironment reshaping abilities of GBM cells that generate a tumor-promoting milieu. This insight will be important to guide the development of future sensitizing therapies targeting treatment-resistant relapse-driving cell populations as well as enhancing the efficiency of immunotherapies in GBM. © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Hyperexcitability in Spinal WDR Neurons following Experimental Disc Herniation Is Associated with Upregulation of Fractalkine and Its Receptor in Nucleus Pulposus and the Dorsal Root Ganglion

Introduction. Lumbar radicular pain following intervertebral disc herniation may be associated with a local inflammatory response induced by nucleus pulposus (NP) cells. Methods. In anaesthetized Lewis rats, extracellular single unit recordings of wide dynamic range (WDR) neurons in the dorsal horn and qPCR were used to explore the effect of NP application onto the dorsal nerve roots (L3-L5). Results. A clear increase in C-fiber response was observed following NP conditioning. In the NP tissue, the expression of interleukin-1β (IL-1β), colony stimulating factor 1 (Csf1), fractalkine (CX3CL1), and the fractalkine receptor CX3CR1 was increased. Minocycline, an inhibitor of microglial activation, inhibited the increase in neuronal activity and attenuated the increase in IL-1β, Csf1, CX3L1, and CX3CR1 expression in NP tissue. In addition, the results demonstrated an increase in the expression of TNF, CX3CL1, and CX3CR1 in the dorsal root ganglions (DRGs). Conclusion. Hyperexcitability in the pain pathways and the local inflammation after disc herniation may involve upregulation of CX3CL1 signaling in both the NP and the DRG.

A comparative transcriptomic analysis of astrocytes differentiation from human neural progenitor cells

Astrocytes are a morphologically and functionally heterogeneous population of cells that play critical roles in neurodevelopment and in the regulation of central nervous system homeostasis. Studies of human astrocytes have been hampered by the lack of specific molecular markers and by the difficulties associated with purifying and culturing astrocytes from adult human brains. Human neural progenitor cells (NPCs) with self-renewal and multipotent properties represent an appealing model system to gain insight into the developmental genetics and function of human astrocytes, but a comprehensive molecular characterization that confirms the validity of this cellular system is still missing. Here we used an unbiased transcriptomic analysis to characterize in vitro culture of human NPCs and to define the gene expression programs activated during the differentiation of these cells into astrocytes using FBS or the combination of CNTF and BMP4. Our results demonstrate that in vitro cultures of human NPCs isolated during the gliogenic phase of neurodevelopment mainly consist of radial glial cells (RGCs) and glia-restricted progenitor cells. In these cells the combination of CNTF and BMP4 activates the JAK/STAT and SMAD signaling cascades, leading to the inhibition of oligodendrocytes lineage commitment and activation of astrocytes differentiation. On the other hand, FBS-derived astrocytes have properties of reactive astrocytes. Our work suggests that in vitro culture of human NPCs represents a valuable cellular system to study human disorders characterized by impairment of astrocytes development and function. Our datasets represent an important resource for researchers studying human astrocytes development and might set the basis for the discovery of novel human-specific astrocyte markers.

Inflammation and the pathophysiology of Alzheimer's disease

There is increasing evidence that a chronic inflammatory response in the brain in Alzheimer's disease (AD) ultimately leads to neuronal injury and cognitive decline. Microglia, the primary immune effector cells of the brain, are thought to be key to this process. This paper discusses the evidence for inflammation in AD, and describes the mechanism whereby microglia generate neurotoxic cytokines, reactive oxygen species, and nitric oxide. Evidence that the cytokine macrophage colony-stimulating factor (M-CSF) is an important cofactor in microglial activation in AD is presented. Ongoing work using organotypic hippocampal expiant cultures to model the inflammatory process in the AD brain is also discussed. Potential avenues for therapeutic intervention are outlined.

Roles of activated microglia in hypoxia induced neuroinflammation in the developing brain and the retina

Amoeboid microglial cells (AMCs) in the developing brain display surface receptors and antigens shared by the monocyte-derived tissue macrophages. Activation of AMCs in the perinatal brain has been associated with periventricular white matter damage in hypoxic-ischemic conditions. The periventricular white matter, where the AMCs preponderate, is selectively vulnerable to hypoxia as manifested by death of premyelinating oligodendrocytes and degeneration of axons leading to neonatal mortality and long-term neurodevelopmental deficits. AMCs respond vigorously to hypoxia by producing excess amounts of inflammatory cytokines e.g. the tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) along with glutamate, nitric oxide (NO) and reactive oxygen species which collectively cause oligodendrocyte death, axonal degeneration as well as disruption of the immature blood brain barrier. A similar phenomenon is observed in the hypoxic developing cerebellum in which activated AMCs induced Purkinje neuronal death through production of TNF-α and IL-1β via their respective receptors. Hypoxia is also implicated in retinopathy of prematurity in which activation of AMCs has been shown to cause retinal ganglion cell death through production of TNF-α and IL-1β and NO. Because AMCs play a pivotal role in hypoxic injuries in the developing brain affecting both neurons and oligodendrocytes, a fuller understanding of the underlying molecular mechanisms of microglial activation under such conditions would be desirable for designing of a novel therapeutic strategy for management of hypoxic damage.

Macrophage colony-stimulating factor and its receptor signaling augment glycated albumin-induced retinal microglial inflammation in vitro

Background

Microglial activation and the proinflammatory response are controlled by a complex regulatory network. Among the various candidates, macrophage colony-stimulating factor (M-CSF) is considered an important cytokine. The up-regulation of M-CSF and its receptor CSF-1R has been reported in brain disease, as well as in diabetic complications; however, the mechanism is unclear. An elevated level of glycated albumin (GA) is a characteristic of diabetes; thus, it may be involved in monocyte/macrophage-associated diabetic complications.

Results

The basal level of expression of M-CSF/CSF-1R was examined in retinal microglial cells in vitro. Immunofluorescence, real-time PCR, immunoprecipitation, and Western blot analyses revealed the up-regulation of CSF-1R in GA-treated microglial cells. We also detected increased expression and release of M-CSF, suggesting that the cytokine is produced by activated microglia via autocrine signaling. Using an enzyme-linked immunosorbent assay, we found that GA affects microglial activation by stimulating the release of tumor necrosis factor-α and interleukin-1β. Furthermore, the neutralization of M-CSF or CSF-1R with antibodies suppressed the proinflammatory response. Conversely, this proinflammatory response was augmented by the administration of M-CSF.

Conclusions

We conclude that GA induces microglial activation via the release of proinflammatory cytokines, which may contribute to the inflammatory pathogenesis of diabetic retinopathy. The increased microglial expression of M-CSF/CSF-1R not only is a response to microglial activation in diabetic retinopathy but also augments the microglial inflammation responsible for the diabetic microenvironment.

Effects of a metalloporphyrinic peroxynitrite decomposition catalyst, ww-85, in a mouse model of spinal cord injury

The aim of the present study was to assess the effect of a metalloporphyrinic peroxynitrite decomposition catalyst, ww-85, in the pathophysiology of spinal cord injury (SCI) in mice. Spinal cord trauma was induced by the application of vascular clips to the dura via a four-level T5-T8 laminectomy. SCI in mice resulted in severe trauma characterized by oedema, neutrophil infiltration, production of inflammatory mediators, tissue damage and apoptosis. ww-85 treatment (30-300 microg/kg, i.p. 1 h after the SCI) significantly reduced in a dose-dependent manner: (1) the degree of spinal cord inflammation and tissue injury, (2) neutrophil infiltration (myeloperoxidase activity), (3) nitrotyrosine formation and PARP activation, (4) pro-inflammatory cytokines expression, (5) NF-kappaB activation and (6) apoptosis. Moreover, ww-85 significantly ameliorated the recovery of limb function (evaluated by motor recovery score) in a dose-dependent manner. The results demonstrate that ww-85 treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma.

Expression of macrophage colony-stimulating factor (M-CSF) and its receptor in streptozotocin-induced diabetic rats

PURPOSE

To demonstrate the expression and location of macrophage colony-stimulating factor (M-CSF) and its receptor (CSF-1R) in the retinas of diabetic rats, as well as in vitreous human proliferative diabetic retinopathy (PDR).

METHODS

The retinas of streptozotocin-induced diabetic rat were studied. Real-time PCR was applied to evaluate M-CSF and its receptor CSF-1R mRNA expression in the retinas. The protein levels of M-CSF and CSF-1R were evaluated by Western blot analysis. Cellular sources of M-CSF and CSF-1R were determined by double-immunofluorescence staining. M-CSF levels in vitreous samples from patients with PDR were measured by ELISA.

RESULTS

M-CSF and CSF-1R mRNA were upregulated in the retinas as early as two weeks after the onset of diabetes and increased over time. A similar pattern was observed for M-CSF/CSF-1R protein expression levels. Double-immunofluorescence staining revealed that increased M-CSF immunoreactivity occurred mainly in the nerve fiber layer in diabetic retinas, co-localizing with glial fibrillary acidic protein. Increased CSF-1R immunoreactivity was observed in OX-42-labeled microglia and ganglion cells in the ganglion cell layer. The vitreous level of M-CSF was elevated in patients with PDR compared to control subjects.

CONCLUSIONS

The early upregulation of MCSF/CSF-1R signaling may be an important regulatory pathway among neurons, microglia, and glia in diabetic retinopathy.

Melatonin regulates matrix metalloproteinases after traumatic experimental spinal cord injury

The matrix metalloproteinases (MMPs) are important enzymes that regulate developmental processes, maintain normal physiology in adulthood and have reparative roles at specific stages after an insult to the nervous system. MMPs, particularly MMP-9/gelatinase B, promote early inflammation and barrier disruption after spinal cord injury (SCI). Recently, we have reported that the pineal secretory product melatonin exerts important anti-inflammatory effects in an experimental model of SCI induced by the application of vascular clips (force of 24 g) to the dura after a four-level T5-T8 laminectomy. However, no reports are available on the relationship between the activity of MMPs and melatonin's anti-inflammatory effects. The aim of the present study was to evaluate whether the protective effect of melatonin observed in SCI is related to the regulation of MMP-9 and MMP-2 in mice. Biochemical and zymographic methods were used to analyze MMP-9 and -2 expression and activities in spinal cord tissue from SCI-treated mice at 24 hr after the trauma. Our studies reveal that melatonin reduced SCI and lipid peroxidation in spinal cord at 24 hr after SCI. Melatonin also diminished proMMP-9 and -2 activities that were induced in the spinal cord tissues at 24 hr after SCI. The reduced activities of MMP-9 and -2 were associated with depressed expression of TNF-alpha. We propose that melatonin's ability to reduce SCI in mice is also related to a reduction in MMP-9 and MMP-2 activity and expression.

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".

Beneficial effects of FeTSPP, a peroxynitrite decomposition catalyst, in a mouse model of spinal cord injury

The aim of the present study was to assess the contribution of peroxynitrite formation in the pathophysiology of spinal cord injury (SCI) in mice. To this purpose, we used a peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron III chloride (FeTSPP). Spinal cord trauma was induced by the application of vascular clips (force of 24g) to the dura via a four-level T5-T8 laminectomy. SCI in mice resulted in severe trauma characterized by edema, neutrophil infiltration, production of inflammatory mediators, tissue damage, and apoptosis. FeTSPP treatment (10-100 mg/kg, i.p.) significantly reduced in dose-dependent manner 1 and 4 h after the SCI (1) the degree of spinal cord inflammation and tissue injury (histological score), (2) neutrophil infiltration (myeloperoxidase activity), (3) nitrotyrosine formation and poly-(ADP-ribose) polymerase activation, (4) proinflammmaory cytokines expression, (5) NF-kappaB activation, and (6) apoptosis (TUNEL staining, Bax and Bcl-2 expression). Moreover, FeTSPP significantly ameliorated the recovery of limb function (evaluated by motor recovery score) in a dose-dependent manner. Taken together, our results clearly demonstrate that FeTSPP treatment reduces the development of inflammation and tissue injury associated with spinal cord trauma similarly to dexamethasone, a well-known antiinflammatory agent which we have used as positive control.

Role of interleukin-1beta in the control of neuroepithelial proliferation and differentiation of the spinal cord during development

Interleukin-1beta (IL-1beta) is an important trophic factor in the nervous system (NS). IL-1beta is ubiquitously expressed from very early stages during the development of the amphibian NS and its action has been demonstrated in vitro on survival, proliferation and differentiation in mammalian embryos. In this report, we show that IL-1beta is immunocytochemically expressed in embryonic spinal cord from early stages, both in rat (embryonic day 12) and in chicken (stage 17-HH), in neuroepithelial cells and nerve fibres, dorsal root ganglia, anterior and posterior roots of the spinal nerves, and in the fibres of these nerves. Our in vivo experiments on chick embryos, with microbeads impregnated with IL-1beta implanted laterally to the spinal cord at the level of the wing anlage, demonstrate that this cytokine produces a statistically significant increase in nuclear incorporation of BrdU at the dorsal level and a reduction of this at the ventral level, whereas local immunoblocking with anti-IL-1beta antibodies causes a dorsal reduction of BrdU incorporation and alters ventral differentiation. These data demonstrate that IL-1beta plays a part in controlling proliferation and early differentiation during the development of the spinal cord in chick embryos.

Development of a culture system that supports adult microglial cell proliferation and maintenance in the resting state

Microglial cells constitute what is considered to be a fixed macrophage population in the central nervous system (CNS), which are broadly implicated in the regulation of neuroinflammation. In the normal adult CNS, microglial cells exist in a resting state characterized by a minimal or negative expression of MHC class II and the co-stimulatory molecules CD80, CD86 and CD40 and exhibit a unique ramified morphology. Microglial cell activation is associated with many inflammatory and neurogenerative CNS pathologies and is characterized by the transformation of resting microglia into cells with a macrophage morphology and up-regulation of MHC class II and co-stimulatory molecules. The cellular and molecular mechanisms required for microglial cell activation and their immunological functions in the adult brain still remain enigmatic, primarily due to the lack of an appropriate culture system that both facilitates microglial survival and expansion in the resting state. Here, we describe a new M-CSF-dependent culture system that overcomes these barriers and allows the long-term proliferation and maintenance of resting adult microglial cells isolated from the CNS. These cultured microglial cells retain their plasticity as indicated by their ability to up-regulate MHC class II and differentiate into cells with a macrophage morphology following the addition of IFN-gamma and GM-CSF, or activated T cells, which produce both cytokines. By measuring the proliferation of the T cells, we were also able to demonstrate that the microglial cells differentiated into fully functional antigen presenting cells. In addition, the replacement of the M-CSF with GM-CSF resulted in the differentiation of microglial cells into cells morphologically and phenotypically similar to dendritic cells. Our microglial cell culture system is the first described that allows the expansion of adult cells in the resting state and will facilitate studies examining the specific mechanisms of microglial cell activation and functions involved in a variety of CNS pathologies.

Cultured rat microglial cells synthesize the endocannabinoid 2-arachidonylglycerol, which increases proliferation via a CB2 receptor-dependent mechanism

Microglia, as phagocytes and antigen-presenting cells in the central nervous system, are activated in such disease processes as stroke and multiple sclerosis. Because peripheral macrophages are capable of producing endocannabinoids, we have examined endocannabinoid production in a macrophage-colony stimulating factor (M-CSF)-dependent rat microglial cell line (RTMGL1) using reversed phase high-pressure liquid chromatography and liquid chromatography-mass spectroscopy. We determined that cultured microglial cells produce the endocannabinoid 2-arachidonylglycerol (2-AG) as well as anandamide in smaller quantities. When 2-AG, but not anandamide, is added exogenously, RTMGL1 microglia increase their proliferation. This increased proliferation is blocked by an antagonist of the CB(2) receptor N-[(1S)endo-1,3,3-trimethyl bicyclo heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) and mimicked by the CB(2) receptor-specific agonist 1,1-dimethylbutyl-1-deoxy-Delta(9)-tetrahydrocannabinol (JWH133). Accompanying the increase in proliferation seen with 2-AG is an increase in active ERK1 that is also blocked with SR144528. The RTMGL1 microglial cells, which exist in a primed state, express the CB(1) and CB(2) receptors as demonstrated by reverse transcription-polymerase chain reaction and immunostaining. The CB(2) receptor in untreated cells is expressed both at the cell surface and internally, and exposure of the cells to 2-AG significantly increases receptor internalization. These data suggest that 2-AG activation of CB(2) receptors may contribute to the proliferative response of microglial cells, as occurs in neurodegenerative disorders.

The relative number of macrophages/microglia expressing macrophage colony-stimulating factor and its receptor decreases in multiple sclerosis lesions

The activation of macrophages/microglia in multiple sclerosis (MS) lesions plays a central role in the effector phase of myelin breakdown. The precise patterns of macrophage/microglia activation during demyelination have not yet been defined. The growth and activating factor macrophage-colony stimulating factor (M-CSF) and its specific receptor (M-CSFR) may be involved in this process. The present study investigated the expression of M-CSF and M-CSFR mRNA by in situ hybridization in 60 lesions from 32 MS patients. In the control and periplaque white matter, microglia was almost completely M-CSFR positive. Irrespective of the demyelinating activity, an increased number of cells expressed M-CSF or M-CSFR mRNA within the lesions. However, despite the tremendous increase in macrophages/microglia within the lesions, the relative number of these cells expressing M-CSF or M-CSFR decreased. There was no correlation of M-CSF or M-CSFR expression with active myelin breakdown. The correlation between the clinical course and the expression of M-CSF or M-CSFR mRNA revealed significant differences with the lowest expression in primary progressive MS. These results suggest a downregulation of M-CSF and M-CSFR inside the MS plaque probably due to the high amount of macrophage-derived cytokines or mediators. Nevertheless, the differences in the relative number of cells expressing the M-CSF/M-CSFR pathway implicate that this pathway may be an important contributory factor in different forms of MS pathology.

Regulatory Factors and Functions of Microglia during Development

This article reviews current knowledge on the origin and development of microglia as well as on regulatory factors that influence microglial development within the neural tube during embryogenesis. Ameboid microglia found in the developing neural tube originate from mesodermal precursors derived from the yolk sac. These microglial cells, which exhibit characteristic features of reactive microglia, undergo mitosis in situ in the nervous parenchyma and function as the full-blown phagocytes involved in the removal of cellular debris resulting from neural tube defect or normal cellular turnover. During embryogenesis, the microglia express various cytokines, growth factors and chemokines. Some of those factors together with other local factors may influence the proliferation and activation of microglia in the developing neural tube.

Overexpression of macrophage colony-stimulating factor receptor on microglial cells induces an inflammatory response

Microglia are important in the inflammatory response in Alzheimer's disease (AD). We showed previously that macrophage colony-stimulating factor receptor (M-CSFR), encoded by the c-fms protooncogene, is overexpressed on microglia surrounding amyloid beta (Abeta) deposits in the APP(V717F) mouse model for AD. The M-CSFR is also increased on microglia after experimental brain injury and in AD. To determine the relevance of these findings, we transiently expressed M-CSFR on murine BV-2 and human SV-A3 microglial cell lines using an SV40-promoted c-fms construct. M-CSFR overexpression resulted in microglial proliferation and increased expression of inducible nitric-oxide synthase, the proinflammatory cytokines interleukin-1alpha, macrophage inflammatory protein 1-alpha, and interleukin-6 and of macrophage colony-stimulating factor (M-CSF) itself. Antibody neutralization of M-CSF showed that the M-CSFR-induced proinflammatory response was dependent on M-CSF in the culture media. By using a co-culture of c-fms-transfected murine microglia and rat organotypic hippocampal slices and a species-specific real time reverse transcriptase-polymerase chain reaction assay and enzyme-linked immunosorbent assay, we showed that M-CSFR overexpression on exogenous microglia induced expression of interleukin-1alpha by the organotypic culture. These results show that increased M-CSFR expression induces microglial proliferation, cytokine expression, and a paracrine inflammatory response, suggesting that in APP(V717F) mice increased M-CSFR on microglia could be an important factor in Abeta-induced inflammatory response.

Spatiotemporal induction patterns of cytokine and related immune signal molecule mRNAs in response to intrastriatal injection of lipopolysaccharide

The brain's response to a direct immune challenge was examined by in situ hybridization histochemistry. Lipopolysaccharide (bacterial endotoxin) injected acutely into rat striatum induced mRNA expression for inhibitory factor kappaBalpha, interleukin (IL)-1beta, tumor necrosis factor-alpha, IL-6, IL-12 p35, inducible nitric oxide synthase, IL-1 receptor antagonist, and the type 1 IL-1 receptor. Expression patterns were evaluated at select time points ranging from 15 min to 3 days post-injection. Rats injected with vehicle alone were used to control for mechanical effects. Following lipopolysaccharide administration, a wave of mRNA induction within brain parenchyma radiated outward from the injection site, generally peaking in intensity at the 16-h time point. The individual profiles of cytokine mRNA induction patterns reveal that the brain's immune response to local inflammatory stimulation is quite elaborate and in many ways resembles the progression of cytokine induction customary of localized inflammation in peripheral tissues.

Entry, dispersion and differentiation of microglia in the developing central nervous system

Microglial cells within the developing central nervous system (CNS) originate from mesodermic precursors of hematopoietic lineage that enter the nervous parenchyma from the meninges, ventricular space and/or blood stream. Once in the nervous parenchyma, microglial cells increase in number and disperse throughout the CNS; these cells finally differentiate to become fully ramified microglial cells. In this article we review present knowledge on these phases of microglial development and the factors that probably influence them.

Spatiotemporal induction patterns of cytokine and related immune signal molecule mRNAs in response to intrastriatal injection of lipopolysaccharide

The brain's response to a direct immune challenge was examined by in situ hybridization histochemistry. Lipopolysaccharide (bacterial endotoxin) injected acutely into rat striatum induced mRNA expression for inhibitory factor kappaBalpha, interleukin (IL)-1beta, tumor necrosis factor-alpha, IL-6, IL-12 p35, inducible nitric oxide synthase, IL-1 receptor antagonist, and the type 1 IL-1 receptor. Expression patterns were evaluated at select time points ranging from 15 min to 3 days post-injection. Rats injected with vehicle alone were used to control for mechanical effects. Following lipopolysaccharide administration, a wave of mRNA induction within brain parenchyma radiated outward from the injection site, generally peaking in intensity at the 16-h time point. The individual profiles of cytokine mRNA induction patterns reveal that the brain's immune response to local inflammatory stimulation is quite elaborate and in many ways resembles the progression of cytokine induction customary of localized inflammation in peripheral tissues.

IFNgamma enhances microglial reactions to hippocampal axonal degeneration

Glial reactivity is implicated in CNS repair and regenerative responses. Microglia, the cells responding earliest to axonal injury, produce tumor necrosis factor-alpha (TNFalpha), a cytokine with both cytopathic and neuroprotective effects. We have studied activation of hippocampal microglia to produce TNFalpha in response to transection of perforant path axons in SJL/J mice. TNFalpha mRNA was produced in a transient manner, peaking at 2 d and falling again by 5 d after lesioning. This was unlike other markers of glial reactivity, such as Mac-1 upregulation, which were sustained over longer time periods. Message for the immune cytokine interferon-gamma (IFNgamma) was undetectable, and glial reactivity to axonal lesions occurred as normal in IFNgamma-deficient mice. Microglial responses to lesion-induced neuronal injury were markedly enhanced in myelin basic protein promoter-driven transgenic mice, in which IFNgamma was endogenously produced in hippocampus. The kinetics of TNFalpha downregulation 5 d after lesion was not affected by transgenic IFNgamma, indicating that IFNgamma acts as an amplifier and not an inducer of response. These results are discussed in the context of a regenerative role for TNFalpha in the CNS, which is innately regulated and potentiated by IFNgamma.

Estrogen and microglia: A regulatory system that affects the brain

Sex hormones are involved in the physiological regulation of several aspects of behavior and neuroendocrine events. It has been accepted that such effects are mediated directly by steroid actions on neurons; however, new studies have shown that the glial cells are also affected by gonadal steroids. The microglia are one specialized brain glial cell type, which is a target for estrogen actions. In fact, we believe that many of the immune and nonimmune regulatory functions of microglia in the brain are influenced directly by estrogen via expression and secretion of cytokines, and growth factors by the microglia. The present review details only a section of the known aspects of microglial function, focusing mainly on nonimmune regulatory actions in the brain and their functional relationship with sex hormones. Moreover, we present evidence for the presence of estrogen receptor-beta (ERbeta) in rat microglial cells.

Macrophage colony-stimulating factor augments beta-amyloid-induced interleukin-1, interleukin-6, and nitric oxide production by microglial cells

In Alzheimer's disease (AD), a chronic cerebral inflammatory state is thought to lead to neuronal injury. Microglia, intrinsic cerebral immune effector cells, are likely to be key in the pathophysiology of this inflammatory state. We showed that macrophage colony-stimulating factor, a microglial activator found at increased levels in the central nervous system in AD, dramatically augments beta-amyloid peptide (betaAP)-induced microglial production of interleukin-1, interleukin-6, and nitric oxide. In contrast, granulocyte macrophage colony-stimulating factor, another hematopoietic cytokine found in the AD brain, did not augment betaAP-induced microglial secretory activity. These results indicate that increased macrophage colony-stimulating factor levels in AD could magnify betaAP-induced microglial inflammatory cytokine and nitric oxide production, which in turn could intensify the cerebral inflammatory state by activating astrocytes and additional microglia, as well as directly injuring neurons.

Morphological features of the entorhinal-hippocampal connection

The goal of this review in an overview of the structural elements of the entorhinal-hippocampal connection. The development of the dendrites of hippocampal neurons will be outlined in relation to afferent pathway specificity and the mature dendritic structure compared. Interneurons will be contrasted to pyramidal cells in terms of processing of physiological signals and convergence and divergence in control of hippocampal circuits. Mechanisms of axonal guidance and target recognition, target structures, the involvement of receptor distribution on hippocampal dendrites and the involvement of non-neuronal cellular elements in the establishment of specific connections will be presented. Mechanisms relevant for the maintenance of shape and morphological specializations of hippocampal dendrites will be reviewed. One of the significant contexts in which to view these structural elements is the degree of plasticity in which they participate, during development and origination of dendrites, mature synaptic plasticity and after lesions, when the cells must continue to maintain and reconstitute function, to remain part of the circuitry in the hippocampus. This review will be presented in four main sections: (1) interneurons-development, role in synchronizing influence and hippocampal network functioning; (2) principal cells in CA1, CA3 and dentate gyrus regions-their development, function in terms of synaptic integration, differentiating structure and alterations with lesions; (3) glia and glia/neuronal interactions-response to lesions and developmental guidance mechanisms; and (4) network and circuit aspects of hippocampal morphology and functioning. Finally, the interwoven role of these various elements participating in hippocampal network function will be discussed.

Tumor necrosis factor-alpha: a neuromodulator in the CNS

In the central nervous system (CNS), the cytokine tumor necrosis factor-alpha (TNF alpha) is produced by both neurons and glial cells, participates in developmental modeling, and is involved in many pathophysiological conditions. There are activity-dependent expressions of TNF alpha as well as low levels of secretion in the resting state. In contrast to the conventional view of a cytotoxic effect of TNF alpha, accumulating evidence suggests a beneficial effect when TNF alpha is applied at optimal doses and at specific periods of time. The bimodal effect is related to subtypes of receptors, activation of different signal transduction pathways, and the presence of other molecules that alter the intracellular response elements such as immediate-early genes. TNF alpha may be an important neuromodulator in development of the CNS, diseases of demyelination and degeneration, and in the process of regeneration. It could induce growth-promoting cytokines and neurotrophins, or it could increase the production of antiproliferative cytokines, nitric oxide, and free radicals, thereby contributing to apoptosis.

Cytokines in inflammatory brain lesions: helpful and harmful

Multiple sclerosis (MS) is thought to be an autoimmune disease. In healthy individuals, the T cells of the immune system, when activated by an infectious agent, regularly traffic across an intact blood-brain barrier, survey the CNS and then leave. In MS, for reasons that are only gradually being understood, certain events in the peripheral immune response and in the brain cause some autoreactive T cells to stay in the CNS. Their presence initiates infiltration by other leukocytes and activation and recruitment of endogenous glia to the inflammatory process, ultimately leading to the destruction of myelin and the myelin-producing cell, the oligodendrocyte, and the dysfunction of axons. The key mediators in the subsequent cycles of histological damage and repair, and clinical relapse and remission are thought to be adhesion molecules, chemokines and cytokines.

Mitogenic effects of interleukin-5 on microglia

Interleukin-3 (IL-3), interleukin-5 (IL-5), and granulocyte macrophage-colony stimulating factor (GM-CSF) are cytokines that bind to receptor complexes comprised of unique alpha-receptor subunits specific for each ligand and a commonly shared beta-receptor subunit. Previous studies have shown that IL-3 and GM-CSF induce mitosis in microglia and macrophage cells, indicating the functional presence of their cognate receptors. In this study, it is shown that the third member of this cytokine group, IL-5, also serves as a microglia mitogen. Proliferative effects were seen in culture on both murine microglia and a murine macrophage cell line, RAW 264.7. Since IL-5 is known to be secreted by both microglia and astrocytes in response to inflammatory stimuli, these results indicate that IL-5 may be involved in the cytokine-immune cascades leading to microglia proliferation in areas affected by disease and tissue damage.

A qualitative and quantitative study of the glial cells in normal and athymic mice

A qualitative and quantitative light and electron microscopic analysis of the glial cells in the supraventricular part of the corpus callosum of the neonatal and adult homozygous athymic nude (nu/nu) and normal BALB/c (+/+) mice was carried out to determine the possible contribution of nude gene mutation to glial cell development. Quantitative cell counts using toluidine blue stained serial callosal sections of 0.5 micron thickness showed that the overall glial cell population was significantly reduced in both neonatal and adult athymic mice. The number of glioblasts, astrocytes and microglia of 5-day-old athymic mouse was reduced by 10%, 27%, and 39%, respectively, when compared to the 5-day-old normal mouse. The frequency of necrotic cells in the neonatal athymic mouse increased by 70% when compared with the normal mouse. In the 13-week-old adult athymic mouse, the number of oligodendrocytes, astrocytes, and microglia decreased by 19%, 31%, and 33%, respectively, when compared to normal mouse. There was no significant difference in the area covered by the corpus callosum in 5-day-old and adult nude mice versus the normal ones of corresponding ages. Except for microglia and astrocytes, the ultrastructural features of the other glial cell types in both strains were comparable. Most of the microglial cells of the neonatal normal mouse were round and were selectively marked by Mac-1 monoclonal antibody at their plasma membrane. The immunoreactivity appeared to be more intense in the normal than the athymic mouse, suggesting a down regulation of CR3 receptors and reduced phagocytic activity of this cell type in the athymic mouse. It is proposed that the increased number of necrotic cells in the neonatal athymic mouse may be attributed to the delay in the removal of dead cells normally phagocytosed by microglia. The microglia in both strains of mouse showed comparable lectin staining intensity at the plasma membrane, indicating that their glycoprotein binding receptors to lectin remained unchanged. Some astrocytes in the adult athymic mice showed hypertrophy. The reduced number of glial cells may be the direct result of genetic mutation or consequential to the lack of certain trophic factors arising from the genetic mutation. Thus, the reduction of microglial cells in both neonatal and adult athymic mice may be due to the lack of thymic hormones which, together with lymphokines have been shown to affect the maturation of bone marrow-derived cells including monocytes, the putative precursor cells of microglia. The reduction in the number of glioblasts and astrocytes may be attributed to the diminution of T lymphocytes or consequential to the reduction of microglia which are known to secrete interleukin-1 that would influence gliogenesis and produce specific growth factors for promoting astrocyte proliferation. Last, as interaction exists between astrocytes and oligodendrocytes, the products of astrocytes may affect the development of oligodendrocytes and vice vasa. The present findings point to a relation between glial cell development and immune network system.