Distribution by Scientific Domains

Kinds of Microglia

  • activated microglia
  • brain microglia
  • cortical microglia
  • primary microglia
  • rat microglia
  • reactive microglia

  • Terms modified by Microglia

  • microglia activation
  • microglia cell
  • microglia isolated

  • Selected Abstracts

    Microglia and inflammation: Impact on developmental brain injuries

    Li-Jin Chew
    Abstract Inflammation during the perinatal period has become a recognized risk factor for developmental brain injuries over the past decade or more. To fully understand the relationship between inflammation and brain development, a comprehensive knowledge about the immune system within the brain is essential. Microglia are resident immune cells within the central nervous system and play a critical role in the development of an inflammatory response within the brain. Microglia are critically involved with both the innate and adaptive immune system, regulating inflammation and cell damage within the brain via activation of Toll-like receptors, production of cytokines, and a myriad of other intracellular and intercellular processes. In this article, microglial physiology is reviewed along with the role of microglia in developmental brain injuries in humans and animal models. Last, microglial functions within the innate and adaptive immune system will be summarized. Understanding the processes of inflammation and microglial activation is critical for formulating effective preventative and therapeutic strategies for developmental brain injuries. MRDD Research Reviews 2006;12:105,112. © 2006 Wiley-Liss, Inc. [source]

    In vitro differentiation of lineage-negative bone marrow cells into microglia-like cells

    Daisuke Noto
    Abstract Microglia are believed to be the only resident immune cells in the CNS, originating from hematopoietic-derived myeloid cells and invading the CNS during development. However, the detailed mechanisms of differentiation and transformation of microglial cells are not fully understood. Here, we demonstrate that murine microglial cells show two morphological forms in vitro, namely, small round cells expressing CD11b, Iba1, triggering receptor expressing on myeloid cells-2 (TREM2), and weakly expressing major histocompatibility complex class II and large flat cells expressing only CD11b and Iba1. Moreover, lineage-negative bone marrow (LN) cells cultured with primary mixed glial culture cells could differentiate into only the small round microglia-like cells, despite the absence of CCR2 and Gr-1 expression. Addition of macrophage colony stimulating factor (M-CSF) to LN cell culture allowed the proliferation and expression of TREM2 in LN cells, and the addition of neutralizing anti-M-CSF antibodies suppressed the proliferation of LN cells despite the expression of TREM2. When LN cells were cultured with M-CSF, the number of small round cells in the culture was considerably low, indicating that the small round morphology of the immature cells is not maintained in the presence of only M-CSF. On the other hand, when LN cells were grown in the presence of astrocytes, the small round cells were maintained at a concentration of approximately 30% of the total population. Therefore, cell,cell contact with glial cells, especially astrocytes, may be necessary to maintain the small round shape of the immature cells expressing TREM2. [source]

    Microglia express functional 11,-hydroxysteroid dehydrogenase type 1,

    GLIA, Issue 10 2010
    Andres Gottfried-Blackmore
    Abstract Glucocorticoids are potent regulators of inflammation exerting permissive, stimulatory, and suppressive effects. Glucocorticoid access to intracellular receptors is regulated by the activity of two distinct enzymes known as 11,-hydroxysteroid dehydrogenase (11,HSD) Type 1 and Type 2, which catalyze the activation or deactivation of glucocorticoids. Although expression of these enzymes in major organ systems and their roles in the metabolic effects of glucocorticoids have been described, their role in the inflammatory response has only recently started to be addressed. In this report, we have studied the expression and activity of 11,HSD Type 1 and Type 2 in microglia cells. Microglia, the brain's resident macrophages, initiate and orchestrate CNS inflammatory responses. Importantly, activated microglia are implicated in most neurodegenerative conditions, making them key subjects of study. We found that microglia expressed 11,HSD-1, but not 11,HSD-2, both in ex vivo FACS-sorted adult cells and in vitro primary cultures. 11,HSD-1 expression was increased in LPS-activated microglia. Moreover, 11,HSD-1 catalyzed the metabolic conversion of 11-dehydro-corticosterone into corticosterone (CORT), which potently reduced cytokine production in activated microglia. We propose that 11,HSD-1 may provide microglia with an intrinsic mechanism to autoregulate and inhibit proinflammatory mediator production through CORT formation. © 2010 Wiley-Liss, Inc. [source]

    Inhibition of Rho-dependent pathways by Clostridium botulinum C3 protein induces a proinflammatory profile in microglia

    GLIA, Issue 11 2008
    Anja Hoffmann
    Abstract Successful regeneration in the central nervous system crucially depends on the adequate environment. Microglia as brain immune-competent cells importantly contribute to this task by producing pro- and anti-inflammatory mediators. Any environmental change transforms these cells towards an activated phenotype, leading to major morphological, transcriptional and functional alterations. Rho GTPases affect multiple cellular properties, including the cytoskeleton, and C3 proteins are widely used to study their involvement. Especially C3bot from Clostridium botulinum has been considered to promote neuronal regeneration by changing Rho activity. Yet C3bot may exert cellular influences through alternative mechanisms. To determine the role of Rho-dependent pathways in microglia we investigated the influence of C3bot on functional properties of cultivated primary mouse microglial cells. Nanomolar concentrations of C3bot transformed microglia towards an activated phenotype and triggered the release of nitric oxide and several proinflammatory cyto- and chemokines. These inductions were not mediated by the ROCK-kinase pathway, since its selective inhibitors Y27632 and H1152 had no effect. C3-induced and Rho-mediated NO release was instead found to be under the control of NF,B, as revealed by treatment with the NF,B inhibitor PDTC. Thus, C3bot induces a proinflammatory response in microglia resembling the classical proinflammatory phenotype elicited by bacterial LPS. The findings are relevant for the use of C3bot in regenerative approaches. © 2008 Wiley-Liss, Inc. [source]

    Differential regulation of trophic and proinflammatory microglial effectors is dependent on severity of neuronal injury

    GLIA, Issue 3 2008
    Aaron Y. Lai
    Abstract Microglial activation has been reported to promote neurotoxicity and also neuroprotective effects. A possible contributor to this dichotomy of responses may be the degree to which proximal neurons are injured. The aim of this study was to determine whether varying the severity of neuronal injury influenced whether microglia were neuroprotective or neurotoxic. We exposed cortical neuronal cultures to varying degrees of hypoxia thereby generating mild (<20% death, 30min hypoxia), moderate (40,60% death, 2 h hypoxia), or severe (>70% death, 6 h hypoxia) injuries. Twenty-four hours after hypoxia, the media from the neuronal cultures was collected and incubated with primary microglial cultures for 24 h. Results showed that the classic microglial proinflammatory mediators including inducible nitric oxide synthase, tumor necrosis factor ,, and interleukin-1-, were upregulated only in response to mild neuronal injuries, while the trophic microglial effectors brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor were upregulated in response to all degrees of neuronal injury. Microglia stimulated with media from damaged neurons were co-cultured with hypoxic neurons. Microglia stimulated by moderate, but not mild or severe damage were neuroprotective in these co-cultures. We also showed that the severity-dependent phenomenon was not related to autocrine microglial signaling and was dependent on the neurotransmitters released by neurons after injury, namely glutamate and adenosine 5,-triphosphate. Together our results show that severity of neuronal injury is an important factor in determining microglial release of "toxic" versus "protective" effectors and the resulting neurotoxicity versus neuroprotection. © 2007 Wiley-Liss, Inc. [source]

    Involvement of ,1 integrin in microglial chemotaxis and proliferation on fibronectin: Different regulations by ADP through PKA

    GLIA, Issue 2 2005
    Kaoru Nasu-Tada
    Abstract Microglia are immune cells in the brain; their activation, migration, and proliferation have pivotal roles in brain injuries and diseases. Microglia are known to attach firmly to fibronectin, the upregulation of which is associated with several pathological conditions in the CNS, through ,1 integrin and become activated. Extracellular nucleotides can serve as potent signaling molecules. Recently, ATP and ADP were revealed to possess chemoattractive properties to microglia via Gi-coupled P2Y receptors. In the present study, we report that the ADP-induced chemotaxis of microglia is mediated by P2Y12/13 receptors and is ,1 integrin-dependent in the presence of fibronectin. Signals from P2Y12/13 receptors also cause ,1 integrin translocation to the membrane ruffle regions, but this redistribution was lost when the intracellular cyclic AMP (cAMP) was increased by forskolin or dibutyryl cAMP. This inhibitory effect of cAMP-elevating agents did not appear when microglia were co-incubated with a protein kinase A (PKA) inhibitor, KT-5720, suggesting that PKA is a negative regulator of the ,1 integrin translocation. We also show that the engagement of ,1 integrin enhanced microglial proliferation. Signals from P2Y12/13 receptors attenuated the proliferation, whereas ADP itself had no effect on microglial growth. Furthermore, ,1 integrin-induced proliferation is positively regulated by the cAMP-dependent PKA. Together, these results indicate the involvement of ,1 integrin in microglial proliferation and chemotaxis, both of which have clinical importance. The data also suggest that PKA is inversely involved in these two cellular functions. © 2005 Wiley-Liss, Inc. [source]

    Gangliosides activate microglia via protein kinase C and NADPH oxidase

    GLIA, Issue 3 2004
    Kyoung-Jin Min
    Abstract Microglia, the major immune effector cells in the central nervous system, are activated when the brain suffers injury. A number of studies indicate that gangliosides activate microglia. However, the signaling mechanisms involved in microglial activation are not yet to be elucidated. Our results show that gangliosides induce the expression of interleukin (IL)-1,, tumor necrosis factor-, (TNF-,), and inducible nitric oxide synthase (iNOS) in rat brain microglia and BV2 murine microglia via protein kinase C (PKC) and NADPH oxidase. Expression of IL-1,, TNF-,, and iNOS in ganglioside-treated cells was significantly reduced in the presence of inhibitors of PKC (GF109203X, Gö6976, Ro31-8220, and rottlerin) and NADPH oxidase (diphenyleneiodonium chloride [DPI]). In response to gangliosides, PKC-,, ,II, and , and NADPH oxidase p67phox translocated from the cytosol to the membrane. ROS generation was also activated within 5 min of ganglioside treatment. Ganglioside-induced ROS generation was blocked by PKC inhibitors. Furthermore, ganglioside-induced activation of NF-,B, an essential transcription factor that mediates the expression of IL-1,, TNF-,, and iNOS, was reduced in the presence of GF109203X and DPI. Our results collectively suggest that gangliosides activate microglia via PKC and NADPH oxidase, which regulate activation of NF-,B. © 2004 Wiley-Liss, Inc. [source]

    Downregulation of inducible nitric oxide synthetase by neurotrophin-3 in microglia

    Shun-Fen Tzeng
    Abstract Microglia activated after many neurological degeneration of the central nervous system (CNS) act as important regulators for neuropathogenesis in the injured CNS via producing proinflammatory mediators, such as nitric oxide (NO), TNF-,, and IL-1,. Neurotrophin-3 (NT-3) is a well-known trophic factor for neural survival, development, and plasticity. Activated microglia are NT-3-producing cells in the injured CNS, and express its receptor-TrkC. However, little is known about the effect of NT-3 on activated microglia. In this study, pre-treatment of a mouse microglial cell line, BV2, with NT-3 for 24 h indicated that NT-3 reduced the inducible form of NO synthase (iNOS), NO, and TNF-, in BV2 stimulated with lipopolysaccharide (LPS). NT-3 exerted less effect on the reduction of these proinflammatory mediators when it was added to BV2 cultures either simultaneously with LPS or post LPS treatment. These findings indicate that NT-3 may serve as an anti-inflammatory factor to suppress microglial activation. J. Cell. Biochem. 90: 227,233, 2003. © 2003 Wiley-Liss, Inc. [source]

    Tumor necrosis factor-alpha (TNF-,) regulates Toll-like receptor 2 (TLR2) expression in microglia

    Mohsin Md.
    Abstract Microglia represent one effector arm of CNS innate immunity as evident by their role in pathogen recognition. We previously reported that exposure of microglia to Staphylococcus aureus (S. aureus), a prevalent CNS pathogen, led to elevated Toll-like receptor 2 (TLR2) expression, a pattern recognition receptor capable of recognizing conserved structural motifs associated with gram-positive bacteria such as S. aureus. In this study, we demonstrate that the proinflammatory cytokine tumor necrosis factor-, (TNF-,) enhances TLR2 expression in microglia, whereas interleukin-1, has no significant effect. To determine the downstream signaling events responsible for elevated microglial TLR2 expression in response to TNF-,, a series of signal transduction inhibitors were employed. Treatment with caffeic acid phenethyl ester, an inhibitor of redox-mediated nuclear factor-kappa B activation, significantly attenuated TNF-,-induced TLR2 expression. Similar results were observed with the IKK-2 and I,B-, inhibitors SC-514 and BAY 11-7082, respectively. In contrast, no significant alterations in TLR2 expression were observed with protein kinase C or p38 mitogen-activated protein kinase inhibitors. A definitive role for TNF-, was demonstrated by the inability of S. aureus to augment TLR2 expression in microglia isolated from TNF-, knockout mice. In addition, TLR2 expression was significantly attenuated in brain abscesses of TNF-, knockout mice. Collectively, these results indicate that in response to S. aureus, TNF-, acts in an autocrine/paracrine manner to enhance TLR2 expression in microglia and that this effect is mediated, in part, by activation of the nuclear factor-kappa B pathway. [source]

    Nitric oxide-producing microglia mediate thrombin-induced degeneration of dopaminergic neurons in rat midbrain slice culture

    Hiroshi Katsuki
    Abstract Activated microglia are considered to play important roles in degenerative processes of midbrain dopaminergic neurons. Here we examined mechanisms of neurotoxicity of thrombin, a protease known to trigger microglial activation, in organotypic midbrain slice cultures. Thrombin induced a progressive decline in the number of dopaminergic neurons, an increase in nitric oxide (NO) production, and whole tissue injury indicated by lactate dehydrogenase release and propidium iodide uptake. Microglia expressed inducible NO synthase (iNOS) in response to thrombin, and inhibition of iNOS rescued dopaminergic neurons without affecting whole tissue injury. Inhibitors of mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun N-terminal kinase (JNK) attenuated thrombin-induced iNOS induction and dopaminergic cell death. Whole tissue injury was also attenuated by inhibition of ERK and p38 MAPK. Moreover, depletion of resident microglia from midbrain slices abrogated thrombin-induced NO production and dopaminergic cell death, but did not inhibit tissue injury. Finally, antioxidative drugs prevented thrombin-induced dopaminergic cell death without affecting whole tissue injury. Hence, NO production resulting from MAPK-dependent microglial iNOS induction is a crucial event in thrombin-induced dopaminergic neurodegeneration, whereas damage of other midbrain cells is MAPK-dependent but is NO-independent. [source]

    Identification of a Peptide Sequence in Albumin that Potentiates Superoxide Production by Microglia

    Yoichi Nakamura
    Abstract: Microglial activation has recently been recognized as acause of damage in various neurodegenerative diseases. A possible mechanismunderlying this damage is the activation of microglia by serum factors leakedthrough a disruption of the blood,brain barrier, which in turn triggermicroglial cell proliferation and the release of various substances toxic toneurons, such as superoxide (O2 - ). We recently reportedthat serum albumin enhanced O2 - producation in culturedrat microglia stimulated by phorbol ester. In the present report, we identifythe active site of this enhancement within the albumin molecule. We purifiedan active subfragment from trypsin-treated bovine serum albumin that wascomposed of 12-mer and 33-mer peptides connected by a disulfide bond. Thechemically synthesized 12-mer peptide showed activity within a concentrationrange (,10 -7M) equivalent to that of albumin. Theactivities of a series of synthesized peptides conclusively indicated that theminimum active sequence was Leu-His-Thr-Leu. The present study may shed lighton the mechanism of neuronal cell damage in various neurodegenerativediseases. [source]

    IL-1,, an immediate early protein secreted by activated microglia, induces iNOS/NO in C6 astrocytoma cells through p38 MAPK and NF-,B pathways

    Yun-Jung Kim
    Abstract In the present study we sought to examine cell,cell interactions by investigating the effects of factors released by stimulated microglia on inducible nitric oxide (NO) synthase (iNOS) induction in astrocytoma cells. After examining the temporal profiles of proinflammatory molecules induced by lipopolysaccharide (LPS) stimulation in BV2 microglial cells, iNOS and IL-1, were observed to be the first immediate-response molecules. Removal of LPS after 3 hr stimulation abrogated NO release, whereas a full induction of IL-1, was retained in BV2 cells. We observed consistently that conditioned medium (CM) from activated microglia resulted in the induction of iNOS in C6 cells, and IL-1, was shown to be a key regulator of iNOS induction. An IL-1,-neutralizing antibody diminished NO induction. Incubation with recombinant IL-1, stimulated NO release to a lesser extent compared to microglial CM; co-treatment of LPS and IL-1, had a potent, synergistic effect on NO release from C6 cells. Transient transfection with MEK kinase 1 (MEKK1) or nuclear factor-kappa B (NF-,B) expression plasmids induced iNOS, and IL-1, further enhanced the MEKK1 response. Furthermore, IL-1,-mediated NO release from C6 cells was significantly suppressed by inhibition of p38 mitogen activated protein kinase (MAPK) or NF-,B by specific chemical inhibitors. Both IL-1, and MEKK1 stimulated p38 and JNK MAPKs, as well as the NF-,B pathway, to induce iNOS in C6 cells. Microglia may represent an anti-tumor response in the central nervous system, which is potentiated by the local secretion of immunomodulatory factors that in turn affects astrocytoma (glioma) cells. A better understanding of microglia,glioma or microglia,astrocyte interactions will help in the design of novel immune-based therapies for brain tumors or neuronal diseases. © 2006 Wiley-Liss, Inc. [source]

    Human and mouse microglia express connexin36, and functional gap junctions are formed between rodent microglia and neurons

    K. Dobrenis
    Abstract Microglia, the tissue macrophages of the central nervous system (CNS), intimately interact with neurons physically and through soluble factors that can affect microglial activation state and neuronal survival and physiology. We report here a new mechanism of interaction between these cells, provided by the formation of gap junctions composed of connexin (Cx) 36. Among eight Cxs tested, expression of Cx36 mRNA and protein was found in microglial cultures prepared from human and mouse, and Cx45 mRNA was found in mouse microglial cultures. Electrophysiological measurements found coupling between one-third of human or mouse microglial pairs that averaged below 30 pico-Siemens and displayed electrical properties consistent with Cx36 gap junctions. Importantly, similar frequency of low-strength electrical coupling was also obtained between microglia and neurons in cocultures prepared from neocortical or hippocampal rodent tissue. Lucifer yellow dye coupling between neurons and microglia was observed in 4% of pairs tested, consistent with the low strength and incidence of electrical coupling. Cx36 expression level and/or the degree of coupling between microglia did not significantly change in the presence of activating agents, including lipopolysaccharide, granulocyte-macrophage colony-stimulating factor, interferon-,, and tumor necrosis factor-,, except for some reduction of Cx36 protein when exposed to the latter two agents. Our findings that intercellular coupling occurs between neuronal and microglial populations through Cx36 gap junctions have potentially important implications for normal neural physiology and microglial responses in neuronopathology in the mammalian CNS. © 2005 Wiley-Liss, Inc. [source]

    Glial reactions in Parkinson's disease

    MOVEMENT DISORDERS, Issue 4 2008
    Patrick L. McGeer MD
    Abstract Dopaminergic neurons of the substantia nigra are particularly vulnerable to oxidative and inflammatory attack. Such processes may play a crucial role in the etiology of Parkinson disease (PD). Since glia are the main generators of these processes, the possibility that PD may be caused by glial dysfunction needs to be considered. This review concentrates on glial reactions in PD. Reactive astrocytes and reactive microglia are abundant in the substantia nigra (SN) of PD cases indicating a robust inflammatory state. Glia normally serve neuroprotective roles but, given adverse stimulation, they may contribute to damaging chronic inflammation. Microglia, the phagocytes of brain, may be the main contributors since they can produce large numbers of superoxide anions and other neurotoxins. Their toxicity towards dopaminergic neurons has been demonstrated in tissue culture and various animal models of PD. The MPTP and ,-synuclein models are of particular interest. Years after exposure to MPTP, inflammation has been observed in the SN. This has established that an acute insult to the SN can result in a sustained local inflammation. The ,-synuclein model indicates that an endogenous protein can induce inflammation, and, when overexpressed, can lead to autosomal dominant PD. Less is known about the role of astrocytes than microglia, but they are known to secrete both inflammatory and anti-inflammatory molecules and may play a role in modulating microglial activity. Oligodendrocytes do not seem to play a role in promoting inflammation although, like neurons, they may be damaged by inflammatory processes. Further research concerning glial reactions in PD may lead to disease-modifying therapeutic approaches. © 2007 Movement Disorder Society [source]

    Microglial colonization of the developing mouse brain: the effect of CD11b deletion

    J. K. Jeetle
    Introduction:, Microglia are resident mononuclear phagocytes of the central nervous system, which colonize the brain both prenatally and after birth. It is proposed that they enter the brain initially via the surrounding mesenchyme, via ventricles and later through blood vessels, but the mechanisms of entry and signals used for migration are still to be established. Previous studies have shown that ligands for some integrin adhesion molecules expressed on blood vessels in the developing nervous system (particularly ICAM-1 and ICAM-2 which bind CD11a/LFA-1 and CD11b/Mac-1), may act as potential recruiting signals for microglial precursors. This study addressed whether CD11b is influential on the migration of microglial precursors into the developing CNS. Material and methods:,Ricinus communis agglutinin-1 (RCA-1) lectin histochemistry was employed to anatomically map the distribution of amoeboid and ramified microglia from embryonic day 15 (E15) to birth. Embryonic mouse brains from CD11b knockout (,/,) (n = 42), and heterozygote (+/,) (n = 52) mice generated on a C57/BL6 background (Melo et al. Cell Immunol 2000; 205: 13,23) and wild-type (+/+) (n = 37) litter mates were fixed in Bouin's solution, processed to paraffin wax and serially sectioned at 15,40 µm. To investigate further potential signals for recruiting microglial precursors, brains were immunochemically screened for integrins CD11a, CD11b, CD18, ,X, VLA-4 and the chemokine MCP-1. Results:, Microscopic analysis revealed the morphological transition of microglia from predominantly amoeboid forms at E15,E16 to a flourishing population of ramified cells at E19,E20. RCA-1 histochemistry showed no clear differences in microglial distribution or timing of colonization between CD11b (,/,) and wild-type mice from E15 to birth. Although CD11b deletion did not influence the timing of microglial ramification, there appeared to be fewer ramified cells in (,/,) mice within comparative brain regions. This requires further quantitative morphometric analysis. Of the integrins investigated, none were restricted to microglia and only VLA-4 and ,X showed reactivity within the CNS. However, MCP-1 was notably localized to the cortical plate within all genotypes, consistent with previous findings in human foetal CNS (Rezaie & Male. Microsc Res Tech 1999; 45: 359,382). Conclusion:, The results suggest that CD11b has little influence on the timing or regional distribution of microglia in the developing murine CNS. It is more likely that CD11b is only one of several factors that influence the migration and differentiation of these cells. [source]

    The Role of Glia and the Immune System in the Development and Maintenance of Neuropathic Pain

    PAIN PRACTICE, Issue 3 2010
    Ricardo Vallejo MD
    Abstract Neuropathic pain refers to a variety of chronic pain conditions with differing underlying pathophysiologic mechanisms and origins. Recent studies indicate a communication between the immune system and the nervous system. A common underlying mechanism of neuropathic pain is the presence of inflammation at the site of the damaged or affected nerve(s). This inflammatory response initiates a cascade of events resulting in the concentration and activation of innate immune cells at the site of tissue injury. The release of immunoactive substances such as cytokines, neurotrophic factors, and chemokines initiate local actions and can result in a more generalized immune response. The resultant neuroinflammatory environment can cause activation of glial cells located in the spinal cord and the brain, which appear to play a prominent role in nociception. Glial cells, also known as neuroglia, are nonconducting cells that modulate neurotransmission at the synaptic level. Glial cells can be subdivided into two primary categories: microglia and macroglia, which include astrocytes and oligodendrocytes. Astrocytes and microglia are known to play a role in the development, spread, and potentiation of neuropathic pain. Following peripheral nociceptive activation via nerve injury, microglia become activated and release pro-inflammatory cytokines such as tumor necrosis factor-,, interleukin-1,, and interleukin-6, thereby initiating the pain process. Microglia propagate the neuroinflammation by recruiting other microglia and eventually activating nearby astrocytes, which prolongs the inflammatory state and leads to a chronic neuropathic pain condition. Our review focuses on the role of glia and the immune system in the development and maintenance of neuropathic pain. [source]

    Integration of K+ and Cl, currents regulate steady-state and dynamic membrane potentials in cultured rat microglia

    Evan W. Newell
    The role of ion channels and membrane potential (Vm) in non-excitable cells has recently come under increased scrutiny. Microglia, the brain's resident immune cells, express voltage-gated Kv1.3 channels, a Kir2.1-like inward rectifier, a swelling-activated Cl, current and several other channels. We previously showed that Kv1.3 and Cl, currents are needed for microglial cell proliferation and that Kv1.3 is important for the respiratory burst. Although their mechanisms of action are unknown, one general role for these channels is to maintain a negative Vm. An impediment to measuring Vm in non-excitable cells is that many have a very high electrical resistance, which makes them extremely susceptible to leak-induced depolarization. Using non-invasive Vm -sensitive dyes, we show for the first time that the membrane resistance of microglial cells is several gigaohms; much higher than the seal resistance during patch-clamp recordings. Surprisingly, we observed that small current injections can evoke large Vm oscillations in some microglial cells, and that injection of sinusoidal currents of varying frequency exposes a strong intrinsic electrical resonance in the 5- to 20-Hz frequency range in all microglial cells tested. Using a dynamic current clamp that we developed to actively compensate for the damage done by the patch-clamp electrode, we found that the Vm oscillations and resonance were more prevalent and larger. Both types of electrical behaviour required Kv1.3 channels, as they were eliminated by the Kv1.3 blocker, agitoxin-2. To further determine how the ion currents integrate in these cells, voltage-clamp recordings from microglial cells displaying these behaviours were used to analyse the biophysical properties of the Kv1.3, Kir and Cl, currents. A mathematical model that incorporated only these three currents reproduced the observed Vm oscillations and electrical resonance. Thus, the electrical behaviour of this ,non-excitable' cell type is much more complex than previously suspected, and might reflect a more common oversight in high resistance cells. [source]

    MHC Gene Related Effects on Microglia and Macrophages in Experimental Autoimmune Encephalomyelitis Determine the Extent of Axonal Injury

    BRAIN PATHOLOGY, Issue 3 2002
    Maria K. Storch
    Myelin-oligodendrocyte-glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) in rats is a chronic inflammatory demyelinating disease of the central nervous system (CNS) strongly mimicking multiple sclerosis (MS). We determined the involvement of macrophages and microglia in the lesions of MOG-EAE in relation to different major histocompatibility complex (MHC, RT1 in rat) haplotypes. We used intra-RT1 recombinant rat strains with recombinations between the RT1a and RT1u haplotypes on the disease permissive LEW non-MHC genome. Activated microglia and macrophages were identified morphologically and by expression of ED1 and allograft inhibitory factor-1 (AIF-1), and differentiated by their morphological phenotype. White matter lesions contained more macrophages and less microglia compared to grey matter lesions. Similarly active lesions were mainly infiltrated by macrophages, while microglia were abundant in inactive demyelinated plaques. In addition, we found a highly significant genetic association between a macrophage or microglia dominated lesional phenotype, which was independent from location and activity of the lesions. This was not only the case in demyelinating plaques of chronic EAE, but also in purely inflammatory lesions of acute passive transfer EAE. Rat strains with an u-haplotype in both the Class II and the telomeric non-classical Class I region revealed inflammatory and demyelinating lesions, which were dominated by activated microglia. The a-haplotype in any of these regions was associated with macrophage dominated lesions. A comparison of lesions, exactly matched for stages of demyelinating activity in these different rat strains, showed that in spite of a similar extent of demyelination, axonal injury was significantly less in microglia compared to macrophage dominated lesions. Thus, our studies document a genetic influence of the MHC-region on the relative contribution of macrophages versus microglia in the pathogenesis of EAE. [source]

    Microglia as immune effectors of the central nervous system: Expression of cytokines and chemokines

    Seung U. Kim
    Abstract Microglia, one of three glial cell types in the central nervous system (CNS), play an important role as resident immunocompetent and phagocytic cells in the CNS in the event of injury and disease. It was del Rio Hortega in 1927 who determined that microglia belong to a distinct glial cell type in the CNS, apart from astrocytes and oligodendrocytes. Since the 1970s, there has been wide recognition that microglia are immune effectors in the CNS that respond to pathological conditions and participate in the initiation and progression of neurological disorders including Alzheimer's disease, Parkinson's disease, multiple sclerosis and acquired immune deficiency syndrome dementia complex by releasing potentially cytotoxic molecules such as pro-inflammatory cytokines, reactive oxygen intermediates, proteinases and complement proteins. There is also evidence to suggest that the microglia are capable of secreting neurotrophic or neuron survival factors on activation through inflammation or injury. In the present review, the current status of knowledge on biology and immunology of microglia is reported. (Clin. Exp. Neuroimmunol. doi: 10.1111/j.1759-1961.2010.00007.x, 2010) [source]

    Radiation-induced morphologic changes in the rhesus monkey (Macaca mulatta) brain

    Roger E. Price
    The right cerebral hemisphere of 24 rhesus monkeys scheduled for necropsy at the completion of another project were studied histopathologically 1,30 days after a single dose of 60Co-irradiation. Histopathologically, inflammation and gliosis consistently occurred at specific time points but varied in severity between individuals. Multifocal hemorrhage, edema, and an acute neutrophilic inflammatory response were observed initially whereas perivascular accumulations of lymphocytes were observed in specimens at the end of the study. Microglia/macrophages were most prominent during the first week after irradiation, whereas astrocytes were reactive throughout the observation period. The early clinical manifestations of the central nervous system (CNS), because of brain irradiation in humans, correspond temporally with acute vascular responses, acute and subacute inflammatory cell responses, and subacute demyelination and reactive astrocytic and microglial responses observed in the rhesus monkey. Initial responses of the CNS to gamma-irradiation may have potential implications for the development of radiation-induced late injury of the CNS. [source]

    Estrogen attenuated markers of inflammation and decreased lesion volume in acute spinal cord injury in rats

    Eric Anthony Sribnick
    Abstract Spinal cord injury (SCI) is a devastating neurologic injury with functional deficits for which the only currently recommended pharmacotherapy is high-dose methylprednisolone, which has limited efficacy. Estrogen is a multiactive steroid that has shown antiinflammatory and antioxidant effects, and estrogen may modulate intracellular Ca2+ and attenuate apoptosis. For this study, male rats were divided into three groups. Sham group animals received a laminectomy at T12. Injured rats received both laminectomy and 40 g · cm force SCI. Estrogen-group rats received 4 mg/kg 17,-estradiol (estrogen) at 15 min and 24 hr post-injury, and vehicle-group rats received equal volumes of dimethyl sulfoxide (vehicle). Animals were sacrificed at 48 hr post-injury, and 1-cm-long segments of the lesion, rostral penumbra, and caudal penumbra were excised. Inflammation was assessed by examining tissue edema, infiltration of macrophages/microglia, and levels of cytosolic and nuclear NF,B and inhibitor of kappa B (I,B,). Myelin integrity was examined using Luxol fast blue staining. When compared to sham, vehicle-treated animals revealed increased tissue edema, increased infiltration of inflammatory cells, decreased cytosolic levels of NF,B and I,B,, increased levels of nuclear NF,B, and increased myelin loss. Treatment of SCI rats with estrogen reduced edema and decreased inflammation and myelin loss in the lesion and penumbral areas, suggesting its potential as a therapeutic agent. Further work needs to be done, however, to elucidate the neuroprotective mechanism of estrogen. © 2005 Wiley-Liss, Inc. [source]

    Magnetic resonance imaging of blood,spinal cord barrier disruption in mice with experimental autoimmune encephalomyelitis

    Angela E. Schellenberg
    Abstract Inflammation, demyelination, and blood-spinal cord barrier (BSB) breakdown occur in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. The purpose of this study was to evaluate the utility of MRI for detecting lesions and BSB disruption in vivo during EAE in the mouse lumbar spinal cord, to determine how MR features of BSB disruption change during the course of disease, and to relate such changes to clinical signs and histological features of disease. Following induction of EAE in C57BL/6 mice, contrast-enhanced (CE) T1 -weighted MR images were acquired to detect BSB disruption in the lumbar spinal cord at the early stage of disease, at peak disease, and at remission, and T2 -weighted images were obtained to monitor spinal cord morphology. Following imaging the spinal cords were assessed in situ for general features of inflammation, BSB leakage, activated macrophages/microglia, and demyelination. No focal lesions were evident on T2 -weighted MR images. BSB disruption was greatest at the onset of signs of disease, and decreased progressively thereafter. Inflammation and demyelination were pronounced at the initial stage of disease and at peak disease, and were decreased at remission. Nonuniform contrast enhancement indicated that breakdown of the BSB occurred predominantly within the white matter (WM) of the spinal cord. Magn Reson Med 58:298,305, 2007. © 2007 Wiley-Liss, Inc. [source]

    Human Immunodeficiency Virus Infection of the Brain: Pitfalls in Evaluating Infected/Affected Cell Populations

    BRAIN PATHOLOGY, Issue 1 2004
    Stephanie J. Bissel
    Monocyte/macrophages and CD4 T-cells are the primary hematopoietic targets of productive HIV infection. In the brain, potential cellular targets for HIV infection include perivascular and parenchymal macrophages/microglia, oligodendrocytes, endothelia, neurons, and astrocytes. We examine evidence of productive and non-productive infection for each cell type in the brains of HIV-infected patients with and without HIV encephalitis. Despite the voluminous literature and substantial experimental effort over the past two decades, evidence for productive infection of any brain cell other than macrophages is left wanting. [source]

    Key Factors in Alzheimer's Disease: ,-amyloid Precursor Protein Processing, Metabolism and Intraneuronal Transport

    BRAIN PATHOLOGY, Issue 1 2001
    Thomas A. Bayer
    During the last years it has become evident that the ,-amyloid (A,) component of senile plaques may be the key molecule in the pathology of Alzheimer's disease (AD). The source and place of the neurotoxic action of A,, however, is still a matter of controversy. The precursor of the ,-amyloid peptide is the predominantly neuronal ,-amyloid precursor protein. We, and others, hypothesize that intraneuronal misregulation of APP leads to an accumulation of A, peptides in intracellular compartments. This accumulation impairs APP trafficking, which starts a cascade of pathological changes and causes the pyramidal neurons to degenerate. Enhanced A, secretion as a function of stressed neurons and remnants of degenerated neurons provide seeds for extracellular A, aggregates, which induce secondary degenerative events involving neighboring cells such as neurons, astroglia and macrophages/microglia. [source]

    Study of the MR relaxation of microglia cells labeled with Gd-DTPA-bearing nanoparticles

    Emeline Julie Ribot
    Abstract Therapies involving cells as vehicles need to visualize in situ the trafficking of the cells concerned. This cellular imaging can be driven by cell contrast agent-based nanoparticle internalization and non-invasive MRI (magnetic resonance imaging) detection. Here, microglial cells, that would transport a suicide gene to a glioma, were incubated for different times, with various concentrations of silica nanoparticles on which numerous Gd-DTPA were grafted. The goal of this study was to investigate the repartition of cell-associated particles. MRI was used to quantitatively follow the particle uptake process. Fluorescence microscopy images showed that, although most of the nanoparticles were internalized, some remained adsorbed on the extracellular membrane surface. The cells were then submitted to various treatments: glycine to release bound nanoparticles and/or ultrasound to destroy the cell membranes. The R1 relaxation rates were measured at 4.7 T. R1 was maximal for 4,h of incubation, decreased after 8,h and remained stable for the 24 following hours. The magnetic resonance signal of ultrasonicated and glycine-treated cells made it possible to quantify the loss of bound nanoparticles after 8,h. Nevertheless, this release did not prevent cell detection since the internalized nanoparticles are enough concentrated to visualize the labeled cells even after 4 days of cell growth. These results highlight the compartmentalization of nanoparticles in microglia and the evolution of the MR signal of the labeled cells. This study could be of importance to interpret in vivo the MR signal changes that could occur after administration of such nanoparticle-labeled cells in therapeutic strategies. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Could chronic pain and spread of pain sensation be induced and maintained by glial activation?

    ACTA PHYSIOLOGICA, Issue 1-2 2006
    E. Hansson
    Abstract An injury often starts with acute physiological pain, which becomes inflammatory or neuropathic, and may sometimes become chronic. It has been proposed recently that activated glial cells, astrocytes and microglia within the central nervous system could maintain the pain sensation even after the original injury or inflammation has healed, and convert it into chronic by altering neuronal excitability. Glial cell activation has also been proposed to be involved in the phenomenon of spread of pain sensation ipsilaterally or to the contralateral side (i.e. mirror image pain). Substance P and calcitonin gene-related peptide, released due to an inflammatory process, interact with the endothelial cells of the blood,spinal cord and blood,brain barriers. The barriers open partially and substances may influence adjacent glial cells. Such substances are also released from neurones carrying the ,pain message' all the way from the injury to the cerebral cortex. Pro-inflammatory cytokines may be released from the microglial cells, and astroglial Ca2+ -transients or oscillations may spread within the astroglial networks. One theory is that Ca2+ -oscillations could facilitate the formation of new synapses. These new synapses could establish neuronal contacts for maintaining and spreading the pain sensation. If this theory holds true, it is possible that Ca2+ waves, production of cytokines and growth factors could be modified by selective anti-inflammatory drugs to achieve a balance in the activities of the different intercellular and intracellular processes. This paper reviews current knowledge about glial mechanisms underlying the phenomena of chronic pain and spread of the pain sensation. [source]

    Microglia and inflammation: Impact on developmental brain injuries

    Li-Jin Chew
    Abstract Inflammation during the perinatal period has become a recognized risk factor for developmental brain injuries over the past decade or more. To fully understand the relationship between inflammation and brain development, a comprehensive knowledge about the immune system within the brain is essential. Microglia are resident immune cells within the central nervous system and play a critical role in the development of an inflammatory response within the brain. Microglia are critically involved with both the innate and adaptive immune system, regulating inflammation and cell damage within the brain via activation of Toll-like receptors, production of cytokines, and a myriad of other intracellular and intercellular processes. In this article, microglial physiology is reviewed along with the role of microglia in developmental brain injuries in humans and animal models. Last, microglial functions within the innate and adaptive immune system will be summarized. Understanding the processes of inflammation and microglial activation is critical for formulating effective preventative and therapeutic strategies for developmental brain injuries. MRDD Research Reviews 2006;12:105,112. © 2006 Wiley-Liss, Inc. [source]

    SPARC is expressed by macroglia and microglia in the developing and mature nervous system

    Adele J. Vincent
    Abstract SPARC (secreted protein, acidic and rich in cysteine) is a matricellular protein that is highly expressed during development, tissue remodeling, and repair. SPARC produced by olfactory ensheathing cells (OECs) can promote axon sprouting in vitro and in vivo. Here, we show that in the developing nervous system of the mouse, SPARC is expressed by radial glia, blood vessels, and other pial-derived structures during embryogenesis and postnatal development. The rostral migratory stream contains SPARC that becomes progressively restricted to the SVZ in adulthood. In the adult CNS, SPARC is enriched in specialized radial glial derivatives (Müller and Bergmann glia), microglia, and brainstem astrocytes. The peripheral glia, Schwann cells, and OECs express SPARC throughout development and in maturity, although it appears to be down-regulated with maturation. These data suggest that SPARC may be expressed by glia in a spatiotemporal manner consistent with a role in cell migration, neurogenesis, synaptic plasticity, and angiogenesis. Developmental Dynamics 237:1449-1462, 2008. © 2008 Wiley-Liss, Inc. [source]

    Prospects for therapeutic vaccination with glatiramer acetate for neurodegenerative diseases such as Alzheimer's disease

    Michal Schwartz
    Abstract Neurodegenerative diseases, whatever their primary causes, are characterized by certain common features, one of which is their self-perpetuating nature. The ongoing progression of the disorder is due to the effects of destructive self-compounds, whose presence in the tissues is an outcome of the early phase of the disease and which gradually destroy remaining functional neurons. Studies in our laboratory have led to the recent formulation of a novel concept of protective autoimmunity as the body's mechanism of defense against these destructive self-compounds. This autoimmune response to central nervous system (CNS) insults is mediated by T-cells and presumably operates by activating and regulating local microglia and infiltrating macrophages (inflammatory response) to carry out their function of clearing destructive material from the tissue at risk. We suggest that a well-controlled autoimmunity counteracts and overcomes the destructive effects of the potentially harmful self-compounds, at the cost of some loss of tissue. An additional risk to the individual is the induction of an autoimmune disease, which is likely to occur if the autoimmune response is malfunctioning. An optimal balance of the various factors will lead to an outcome of maximal benefit at minimal cost to the tissue. A procedure for safely boosting the autoimmune response, by vaccination with a weak self-crossreactive antigen such as glatiramer acetate (also known as Cop-1) was found to protect rats from glutamate toxicity, a major mediator of the spread of damage and a well-known causative factor in neurodegenerative disorders. Cop-1, when administered according to a different regimen, is an FDA-approved drug for the treatment of multiple sclerosis. Different formulations of the same drug can therefore be used to treat two extreme manifestations of chronic degenerative diseases of the CNS. Drug Dev. Res. 56:143,149, 2002. © 2002 Wiley-Liss, Inc. [source]

    Independent signaling pathways in ATP-evoked secretion of plasminogen and cytokines from microglia

    *Article first published online: 28 AUG 200, Kazuhide Inoue
    Abstract We investigated the action of ATP on the secretion of plasminogen, TNF-,, and IL-6 from microglia. ATP (10,100 ,M) stimulated the release of plasminogen from rat cultured microglia in a concentration-dependent manner with a peak response at 5,10 min after the stimulation. The release was dependent on extracellular Ca2+ and was blocked by pretreatment with oxidized ATP, a blocker of P2X7. UTP, an agonist of P2Y2, also stimulated the release of plasminogen from a subpopulation (about 20% of total cells) of cultured microglia. The release was also dependent on extracellular Ca2+, suggesting a role of stocker-operated calcium entry (SOC). ATP potently stimulated TNF-, release from 2 h after the stimulation with TNF-, mRNA expression in primary cultures of rat brain microglia. The TNF-, release was maximally elicited by 1 mM ATP and 2,- and 3,-O-(4-benzoylbenzoyl)-adenosine 5,-triphosphate (BzATP), a P2X7 selective agonist, suggesting the involvement of P2X7. This TNF-, release was correlated with a sustained Ca2+ influx. The release was inhibited by PD98059, an inhibitor of MEK1 which activates extracellular signal-regulated protein kinase (ERK), and SB203580, an inhibitor of p38 MAP kinase. However, both ERK and p38 were rapidly activated by ATP even in the absence of extracellular Ca2+. These results indicate that extracellular ATP triggers TNF-, release in rat microglia via P2X7 in a manner dependent on the sustained Ca2+ influx and via the ERK/p38 cascade independently of Ca2+ influx. ATP caused the mRNA expression and release of IL-6 in a concentration-dependent manner in MG-5. The physiological meaning of these independent release mechanisms is also discussed. Drug Dev. Res. 53:166,171, 2001. © 2001 Wiley-Liss, Inc. [source]