1,721,074 research outputs found
Microglia: active sensor and versatile effector cells in the normal and pathologic brain
No full textMicroglial cells constitute the resident macrophage population of the CNS. Recent in vivo studies have shown that microglia carry out active tissue scanning, which challenges the traditional notion of 'resting' microglia in the normal brain. Transformation of microglia to reactive states in response to pathology has been known for decades as microglial activation, but seems to be more diverse and dynamic than ever anticipated-in both transcriptional and nontranscriptional features and functional consequences. This may help to explain why engagement of microglia can be either neuroprotective or neurotoxic, resulting in containment or aggravation of disease progression. Moreover, little is known about the heterogeneity of microglial responses in different pathologic contexts that results from regional adaptations or from the progression of a disease. In this review, we focus on several key observations that illustrate the multi-faceted activities of microglia in the normal and pathologic brain
Physiology of microglia
No full textMicroglial cells are the resident macrophages in the central nervous system. These cells of mesodermal/mesenchymal origin migrate into all regions of the central nervous system, disseminate through the brain parenchyma, and acquire a specific ramified morphological phenotype termed "resting microglia. " Recent studies indicate that even in the normal brain, microglia have highly motile processes by which they scan their territorial domains. By a large number of signaling pathways they can communicate with macroglial cells and neurons and with cells of the immune system. Likewise, microglial cells express receptors classically described for brain-specific communication such as neurotransmitter receptors and those first discovered as immune cell-specific such as for cytokines. Microglial cells are considered the most susceptible sensors of brain pathology. Upon any detection of signs for brain lesions or nervous system dysfunction, microglial cells undergo a complex, multistage activation process that converts them into the "activated microglial cell." This cell form has the capacity to release a large number of substances that can act detrimental or beneficial for the surrounding cells. Activated microglial cells can migrate to the site of injury, proliferate, and phagocytose cells and cellular compartments
The tyrosine kinase inhibitor AG126 restores receptor signaling and blocks release functions in activated microglia (brain macrophages) by preventing a chronic rise in the intracellular calcium level
No full textWe recently reported that lasting activation of mouse microglial cells with bacterial lipopolysaccharide (LPS) chronically elevated the basal intracellular calcium concentration ([Ca 2+] i). This correlated to an attenuated calcium signaling of complement (C5a) and purinergic (UTP) receptors as well as to the capacity for effective production of cytokines-chemokines. Here, we demonstrate that these adjustments in the [Ca 2+] i regulation require a critical protein tyrosine kinase (PTK) function - even in varying stimulation scenarios. Changes in basal [Ca 2+] i and calcium signaling are not restricted to Gram-negative bacterial confrontation. Pneumococcal cell wall (PCW) modelling Gram-positive infection causes virtually the same effects. Moreover, decreases in calcium signaling efficacy are neither associated with altered receptor expression, nor mediated by autocrine loops. Administration of microglial release products, transfer of conditioned supernatant or presence of a radical scavenger during LPS or PCW treatments have no consequence. However, both the elevation in basal [Ca 2+] i as well as the suppression of C5a- and UTP-evoked calcium signals are selectively and dose-dependently reversed by tyrphostin AG126, a PTK inhibitor that, moreover, blocks inducible nitric oxide and cytokine-chemokine release. The findings suggest that the AG126-sensitive PTK critically controls both sensory and executive features of the microglial activation process via sustained up-regulation of basal [Ca 2+] i
Glial cells and the supply of substrates of energy metabolism to neurons
No full textNo abstract available
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Novel Mechanisms to Modulate Microglial Functional Phenotypes in Health and Disease
No full textMicroglia are resident innate immune cells that maintain homeostasis and sense a range of pathophysiological impairments within the central nervous system (CNS). Based on their involvement in brain disease progression, microglia-targeted therapy has emerged as a potential approach for reducing the burden of CNS disease. Microglia activation requires the activation of different signal pathways via neurotransmitters, neuropeptides and/ or other extracellular molecules, which each can be targeted. The neuropeptide VGF (non-acronym) is secreted by neurons and hydrolysed into biologically active peptides. One of these peptides is TLQP21, which binds to the complement receptors C1qbp and C3aR1. Although both receptors are expressed in microglia, the effect of TLQP21 on microglial cells has not been elucidated. The goal of the first study in the present dissertation was to determine whether TLQP21 might be a useful target in modulating microglial function. I demonstrate that exogenous application of TLQP21 stimulates microglial outward rectifying potassium (K+) currents, intracellular calcium (Ca2+) release, phagocytosis, and migration in C3aR-dependent manner. Interestingly, C3aR1 receptors were only expressed in microglia in vitro, but not in situ; suggesting that their expression might vary between different microglial activation states. Furthermore, in vitro and in situ activation of C1qbp leads to TLQP21 interference with metabotropic purinergic signalling (P2Y) in microglia, thereby, decreasing P2Y12-mediated activation of K+ conductance, microglia migration and laser lesion-induced processes outgrowth, as well as P2Y6-mediated phagocytic activity.
Next, I examined other possible P2Y regulators in microglia. Neurofibromin is a known downstream effector of tyrosine kinase receptors and G protein-coupled receptors that indirectly regulates cyclic AMP (cAMP) levels through purinergic receptors. Mutations on this protein results in Neurofibromatosis type 1 disease (NF1). In the second study, a mouse model of NF1 with heterozygous neurofibromin knockout (Nf1 +/-) was employed. Interestingly, only male Nf1 +/- microglia showed impaired ATP-induced P2Y-mediated membrane currents and P2Y-dependent laser lesion-induced process movement in situ. Moreover, I found that the P2Y-control of microglial phagocytosis was only affected in male Nf1 +/- mice. In contrast, basal phagocytic activity was reduced in both male and female Nf1 +/- mice. Studying the neurofibromin downstream signaling intermediate, cAMP, revealed that male Nf1 +/- mice exhibited defects in cAMP regulation. Pharmacological blockade of phosphodiesterase III enzyme rescued these defects.
The extracellular matrix (ECM) contains other factors that likely regulate the activity of microglia. In my third project, I studied Tenascin C (TNC), an ECM glycoprotein that activates Toll-like receptor 4 (Tlr4) expressed in microglia using TNC KO and Tlr4 KO mice. I found that TNC regulates microglial phagocytic activity in situ at an early postnatal age (P4) partially via Tlr4 activation. Furthermore, TNC regulates pro-inflammatory cytokine/chemokine production, chemotaxis and phagocytosis in Tlr4-dependent manner in vitro. Interestingly, the effect of TNC on microglia was linked to the expression of histone-deacetylase 1 (HDAC1) in microglia, which itself was induced by TNC. The use of MS-275 (HDAC1 inhibitor) attenuated TNC-induced microglia proinflammatory cytokines.
In summary, the present dissertation demonstrates that TLQP21, NF1, and TNC are critical modulators of microglial function, suggesting that they might serve as promising targets to correct microglial dysfunction in the setting of CNS diseaseAls residente angeborene Immunzellen des ZNS sind Mikroglia wichtig für die Gewebehomöostase und erkennen jede Art von pathologischer Dysfunktion. Die zielgerichtete Mikroglia-Therapie hat sich zu einem viel versprechenden Ansatz entwickelt. Für die Aktivierung der Mikroglia über extrazelluläre Moleküle wie Pathogene, Neurotransmitter oder Neuropeptide sind verschiedene Signalwege erforderlich. Das Neuropeptid VGF wird von Neuronen sezerniert und im Golgi-Apparat zu biologisch aktiven Peptiden hydrolysiert. TLQP21 ist ein von VGF abgeleitetes Peptid, das mit metabolischen und neurologischen Störungen assoziiert ist, und die Komplementrezeptoren C1qbp und C3aR bindet, die von Mikrogliazellen exprimiert werden. Die Wirkung von TLQP21 auf Mikroglia ist jedoch noch unbekannt. In der vorgestellten Dissertation demonstriere ich, dass die exogene Anwendung von TLQP21 auswärts rektifizierende Kalium(K+)-Ströme, intrazelluläre Calcium(Ca2+)-Freisetzung, Phagozytose und Migration in Abhängigkeit von C3aR stimuliert. C3aRs werden von Mikroglia nur in vitro was darauf hindeutet, dass ihre Expression zwischen verschiedenen mikroglialen Zuständen variieren. Durch die Aktivierung von C1qbp in vitro und in situ interferierte TLQP21 mit den metabotropen purinergen Signalen (P2Y) in Mikroglia und verringerte die P2Y12-vermittelte Aktivierung der K+-Leitfähigkeit, die Migration, die durch Laserläsion Prozessauswüchse sowie die P2Y6-vermittelte phagozytische Aktivität induzierten.
Um mögliche Regulatoren von P2Y in Mikroglia in einem Krankheitskontext zu untersuchen, verwendete ich in einem anderen Projekt ein transgenes Mausmodell für Neurofibromatose Typ 1 (Nf1+/-). Interessanterweise zeigten männliche Nf1+/- -Mikroglia eine Verringerung der ATP-induzierten P2Y-vermittelten Membranströme und P2Y-abhängige Laserläsion-induzierte Akkumulation mikroglialer Prozesse in situ, die weiblichen jedoch nicht. Darüber hinaus war die P2Y-Kontrolle der mikroglialen Phagozytose nur bei männlichen Nf1+/- Mäusen betroffen. Allerdings war die basale Phagozytoseaktivität sowohl bei männlichen als auch bei weiblichen Nf1+/- Mäusen reduziert. Durch Untersuchung des nachgeschalteten Botenstoffs, des zyklischen AMPs (cAMP), es wurde herausgefunden, dass männliche Nf1+/- Mäuse einen Defekt in der cAMP-Regulation aufweisen. Eine pharmakologische Blockade der Phosphodiesterase korrigierte die männlichen Nf1+/- Mikroglia-cAMP-Defekte.
Als nächsten Schritt wandte ich mich der Frage zu, wie die extrazelluläre Matrix (ECM) Mikroglia beeinflussen könnte. TNC ist ein ECM-Glykoprotein, das Toll-like-Rezeptor 4 (TLR4) aktiviert. Es wurden TNC KO und TLR4 KO Mausmodelle verwendet, aus denen entweder primäre Mikrogliakulturen oder akute Hirnschnitte generiert wurden, um die Unterscheide der mikroglialen Aktivitäten zu studieren. TNC reguliert die phagozytäre Aktivität der Mikroglia in situ in einem frühen postnatalen Alter (P4) teilweise über die TLR4-Aktivierung. Die proinflammatorische Zytokin-/Chemokin-Produktion, Chemotaxis und in-vitro-Phagozytose wird hingegen in TLR4-abhängiger Weise reguliert. Darüber hinaus ist die Wirkung von TNC auf Mikroglia mit der Expression der Histon-Deacetylase 1 (HDAC1) in Mikroglia verbunden. Durch Verwendung des HDAC1-Inhibitors MS-275 konnte die TNC-induzierte Freisetzung von pro-inflammatorischen Zytokinen in Mikrogliazellen reduziert werden.
Zusammengenommen zeige ich hier, dass TLQP21, NF1 und TNC Modulatoren der mikroglialen Funktionen sind und daher vielversprechende Ziele zur Korrektur mikroglialer Funktionsstörungen in Pathologien darstellen können
Cell Culture Models as Alternatives to Animal Experimentation for the Testing of Neuroprotective Compounds in Stroke Research
No full textThis handbook is the result of a projeet partly financed by the German Ministry for Education, Research, Science and Technlogy (BMBF) which ran for three years from 1995 to 1998 and involved several research groups in Germany. The statement of Lord Adrian, famous for his discovery that the frequency of firing in a nerve cell is a measure of the intensity of the stimulus, quoted above is a way of ethically justifying the use of animals in research. It also contains a very important caveat. It requires us to ask ourselves carefully whether there is really of conducting the research in questions. And this is the aim that we have set ourselves for our joint project. During the course of our work wo have developed and relined different cell assay techniques which can be used for investigating the effects of neuroprotective compounds in strake research. We thought it would be worthwhile to share some of the experimental details from our filldings with a wider audience. And we have therefore decided in association with the BMBF to print a handbook which summarizes these methods. But first, why have we chosen human strake as our research target? Thromboembolic stroke causes the death of nerve cells by depriving the brain of an adequate supply of oxygenated blood. The process is called cerebral ischaemia and is primarily a vascular event which leads to damage of brain tissue and impaired function. Strake is the third leading cause of death after coronary heart disease and cancer, and is an importatnt source of adult disability in industrialized nations (Bonita, 1992). Surprisingly, funding of stroke research per death by the National Institutes of Health in the United States falls well behind that of many other of these diseases (NIH, 1998). The brain depends on arterial blood for a continuous supply of oxygen and glucose. Even if blood flow is interrupted for only a few minutes, certain highly vulnerable neurons will degenerate. If the interruption is sustained, then all types of brain cells will eventually die. Fundamental to aur understanding of the pracess of cerebral ischaemia has been the presumption that brain cells do not simply die beeause of energy failure. The link betwecn ischaemia and neuronal death is considerably more complicated. Strake triggers a chain reaction of eleelrieal atld chemieal aetivity which is relatcd 10 ischaemic depolarization, the release of exeitatory amino acids and ehanges in calcium homeostasis (Matlson and Mark, 1996; Tymianski and Tator, 1996). These events act in concert to orchestrate cell death. [...
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