Possible involvement of ER chaperone Grp78 on reduced formation of amyloid-beta deposits.
Explore the source record for details and available documents.
Alzheimer Disease↗
Biomedical subjects
P J Gebicke-Haerter
Publications and source records attributed to P J Gebicke-Haerter.
Possible protective mechanisms of heme oxygenase-1 in the brain.
Explore the source record for details and available documents.
Alzheimer Disease↗
Microglia in neurodegeneration: molecular aspects.
Inflammatory events in the CNS are associated with injuries as well as with well-known chronic degenerative diseases, such as Multiple Sclerosis, Parkinson's, or Alzheimer's disease. Compared to inflammation in peripheral tissues, inflammation in brain appears to follow distinct pathways and time-courses, which likely has to do with a relatively strong immunosuppression in that organ. For this reason, it is of great importance to get insights into the molecular mechanism governing immune reactions in brain tissue. This task is hard to achieve in vivo, but can be approached by studying the major cell type responsible for brain inflammation, the microglia, in culture. Since these cells are the only professional antigen-presenting cells resident in brain parenchyma, molecular mechanisms of antigen presentation are being discussed first. After covering the expression and regulation of anti- and proinflammatory cytokines, induction and regulation of two key enzymes and their products-COX-2 and iNOS-are summarized. Possibly, pivotal molecular targets for drug therapies of brain disorders will be discovered in intracellular signaling pathways leading to activation of transcription factors. Finally, the impact of growth factors, of neurotrophins in particular, is highlighted. It is concluded that the presently available data on the molecular level is far from being statisfying, but that only from better insights into molecular events will we obtain the information required for more specific therapies.
Animals↗
Lipopolysaccharide-induced switch between retinoid receptor (RXR) alpha and glucocorticoid attenuated response gene (GARG)-16 messenger RNAs in cultured rat microglia.
Glucocorticoid-attenuated response genes (GARG) belong to a recently described family of genes responsive to the action of dexamethasone. Full-length cDNA of one member of this family, GARG16, has been cloned from rat microglia and regulation of its mRNA expression has been studied. Moreover, regulation of retinoid/retinoic acid activated transcription factor (RXR/RAR) mRNAs in mixed astrocyte and in purified microglia cultures has been investigated. RARbeta mRNA was undetectable in microglia by RT-PCR, whereas clearly present in the mixed cultures. RXRalpha, RARgamma, and GARG16 mRNAs were found in both culture systems. RXRalpha mRNA was strongly expressed in control microglia but rapidly declined upon treatment with LPS. Conversely, GARG16 mRNA was almost untraceable in control microglia but rapidly increased by LPS. Time-course studies revealed an oscillating behavior of expression of both mRNAs during the first 6 hr, which receded to control levels (RXRalpha high, GARG16 low) at 72 hr of LPS-treatment. Additionally, p38 MAPK and SEK phosphorylations peaked at 1 hr followed by steady declines, whereas MEK and c-Jun showed double peaks at 1+4 hr and 1+6 hr, respectively, before subsiding to control levels. This behavior was not observed in comparative studies with TNF-alpha, interleukin-10 (IL-10), or interferon-gamma inducible protein 10 (IP-10). Finally, inhibitors of p38 MAPK, p42/p44 ERK, and PKCalpha as well as the use of dexamethasone revealed major influences of the p38 MAPK-c-Jun-AP-1 signaling pathway on RXRalpha and GARG16 mRNA expressions. The counter regulatory control of GARG16 and RXRalpha mRNA expression is believed to be an example of a fine-tuned cellular mechanism to react to inflammatory stimuli.
Animals↗
Bip/GRP78-induced production of cytokines and uptake of amyloid-beta(1-42) peptide in microglia.
In the brains of Alzheimer's disease (AD) patients, fibrillar amyloid-beta peptides (Abeta) are markedly accumulated and the microglia associate with the amyloid plaques. However, the regulation of Abeta clearance is still unclear. In the present study, we examined the effect of a chaperone protein BiP/GRP78 on the microglial function. Exogenous addition of recombinant BiP/GRP78 induced the production of cytokines such as interleukin-6 and tumor necrosis factor-alpha, but heat treatment of this protein abolished the activity. Although Abeta(1-42) did not induce cytokine production, it was taken up by the microglia. In addition, the amount of Abeta(1-42) uptake and the number of microglia that phagocytosed Abeta(1-42) were markedly increased by BiP/GRP78. Exogenous BiP/GRP78 also translocated to the endoplasmic reticulum (ER). These results suggest that BiP/GRP78 stimulates Abeta clearance in the microglia, and that dysfunction in the ER may cause the accumulation of extracellular Abeta(1-42).
Amyloid beta-Peptides↗
Effects of 15-deoxy-delta(12,14) prostaglandin J(2) and interleukin-4 in Toll-like receptor-4-mutant glial cells.
15-Deoxy-Delta(12,14) prostaglandin J(2) and interleukin-4 are endogenous anti-inflammatory substances. In this study, we examined the effects of 15-deoxy-Delta(12,14) prostaglandin J(2) and interleukin-4 in glial cells from the Toll-like receptor-4-mutant (C3H/HeJ) and wild-type (C3H/HeN) mouse brains. The lipopolysaccharide-induced expression of inducible nitric oxide (NO) synthase and cyclooxygenase-2 in the Toll-like receptor-4-mutant glial cells have significantly lower levels (about half and quarter, respectively) than those in the wild-type cells. Treatment with both interleukin-4 (at 10 ng/ml, for 48 h) and 15-deoxy-Delta(12,14) prostaglandin J(2) (at 3 microM, for 30 min) completely inhibited the lipopolysaccharide-induced expression of inducible NO synthase and cyclooxygenase-2. In contrast, heme oxygenase-1 was induced by 15-deoxy-Delta(12,14) prostaglandin J(2) alone, but was not changed by interleukin-4 or lipopolysaccharide. The inhibitory protein of nuclear factor-kappa B was degraded by lipopolysaccharide in both mutant and wild-type glial cells, and this degradation was not inhibited by either 15-deoxy-Delta(12,14) prostaglandin J(2) or interleukin-4. These results suggest that the response to lipopolysaccharide is partially dependent on Toll-like receptor-4 in mouse glial cells, and that 15-deoxy-Delta(12,14) prostaglandin J(2) and interleukin-4 differently regulate the expression of inducible NO synthase and cyclooxygenase-2, and heme oxygenase-1.
Animals↗
Microglial chemokines and chemokine receptors.
Explore the source record for details and available documents.
AIDS Dementia Complex↗
Expression and function of adenosine receptors in human dendritic cells.
Dendritic cells (DCs) are specialized antigen-presenting cells characterized by their ability to migrate into target sites, process antigens, and activate naive T cells. In this study, we analyzed the biological activity and intracellular signaling of adenosine by using reverse transcriptase-polymerase chain reaction assays to investigate mRNA expression of A(1), A(2a) and A(3) adenosine receptors in immature and mature human DCs. Functional experiments on adenosine stimulation showed chemotaxis, intracellular calcium transients, and actin polymerization, but no activation of adenylate cyclase in immature DCs. Experiments with receptor isotype-selective agonists and antagonists as well as pertussis toxin revealed that chemotaxis, calcium transients, and actin polymerization were mediated via G(i-) or G(0-)protein-coupled A(1) and A(3) receptors. Maturation of DCs induced by lipopolysaccharide (LPS) resulted in down-regulation of A(1) and A(3) receptor mRNAs, although A(2a) receptor mRNA was still expressed. However, in LPS-differentiated DCs, adenosine and an A(2a) receptor agonist stimulated adenylate cyclase activity, enhanced intracellular cAMP levels, and inhibited interleukin 12 (IL-12) production. These effects could be completely prevented by pretreatment with A(2) receptor antagonist. These findings strongly suggest that adenosine has important but distinct biological effects in DCs activity as a chemotaxin for immature DCs and as a modulator of IL-12 production in mature DCs. These effects can be explained by differential expression of adenosine receptor subtypes.
Actins↗
Interleukin-4-inhibited mRNA expression in mixed rat glial and in isolated microglial cultures.
Interleukin-4 (IL-4) likely is one of the key players in the concert of immunosuppressive factors in brain. Therefore, influences of the cytokine on mRNA expression of endogenous mediators of inflammation, such as cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-alpha), interferon-inducible protein 10 (IP-10), interleukin-3 receptor-beta (IL-3R-beta), and of another antiinflammatory cytokine, IL-10, have been evaluated in the present study by semi-quantitative RT-PCR. Primary rat mixed glial cultures and isolated microglial cells, the resident immunocytes of the brain, have been used as rich sources of these mRNAs in response to the bacterial cell wall component lipopolysaccharide (LPS). Time-course studies showed peak levels of LPS-increased mRNAs at approximately 4 h. Interestingly, IL-10 mRNA was elevated also upon the LPS-stimulus. IL-4, given 30 min before LPS, inhibited increases of all mRNAs significantly, including IL-10 mRNA. IL-4, however, induced peroxisome proliferator-activated receptor (PPAR)-gamma in cultured microglia. This induction was completely inhibited by simultaneous administration of LPS. The data confirms IL-4 as an important antiinflammatory cytokine and gives some idea of cross-talk between intracellular signaling evoked by pro- and antiinflammatory substances.
Aged↗
Differential expression, activity and regulation of the sodium/myo-inositol cotransporter in astrocyte cultures from different regions of the rat brain.
The high-affinity sodium/myo-inositol cotransporter (SMIT) is involved in osmoregulation in several cells and tissues. In the CNS the activity of SMIT also determines the individual susceptibility of neural cells to the inositol depleting effect of lithium, which is considered to be important in lithium's therapeutic effects in manic-depressive illness. Among neural cells SMIT is particularly active in astrocytes. In the present work we have cloned the cDNA of SMIT of the rat and assessed its activity, expression and regulation in primary astroglia cultures derived from five different rat brain regions: cerebellum, cortex, diencephalon, hippocampus and tegmentum. After an incubation period of 24 h in medium containing 3[H]labeled myo-inositol different steady-state concentrations were detected which were dependent on the brain region from which the astrocytes were cultured. In addition, myo-inositol uptake in astrocytes from different areas was characterized by two different Km values (27 microM for cerebellum and diencephalon, 50 microM for cortex, hippocampus and tegmentum) and by three different v(max) values (approx. 200 pmol/mg protein/min for astrocytes from cerebellum and tegmentum, 298 for hippocampus and 465 for cortex), indicating that the active myo-inositol uptake into astroglial cells is distinct in the various brain regions. The efficacy of uptake as determined by v(max) values of 3[H]myo-inositol uptake correlated with the level of mRNA of SMIT in the astrocyte cultures from the various brain regions as determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Both 3[H]myo-inositol uptake and SMIT mRNA content was upregulated by incubation of astrocytes in medium of increased osmolarity. In astrocytes from cerebellum, cortex, hippocampus and tegmentum 3[H]myo-inositol uptake was downregulated by chronic incubation with 400 microM inositol. This effect was not observed in astrocytes from diencephalon. Furthermore, in astrocytes from cortex and hippocampus but not from cerebellum, diencephalon and tegmentum incubation with corticosterone for three days upregulated 3[H]myo-inositol uptake. It is concluded that SMIT is differentially expressed and regulated in astrocytes from distinct brain regions. These regional differences suggest particular consideration of localized effects in investigations of the role of myo-inositol in the mechanism of action of antibipolar drugs.
Animals↗
Downregulation of platelet-activating factor responsiveness during maturation of human dendritic cells.
Dendritic cells (DCs) are specialized antigen-presenting cells characterized by their ability to migrate into target sites, process antigens, and activate naive T-cells. Biological activities of platelet-activating factor (PAF) and the cytokine macrophage inflammatory protein-3beta (MIP-3beta) as well as the mRNA expression of their receptors were characterized in human DCs during lipopolysaccharide (LPS)-promoted maturation. Platelet-activating factor induced calcium transients, migration-associated actin polymerization response, and chemotaxis in immature human dendritic cells differentiated in vitro from monocytes with interleukin-4 and granulocyte macrophage colony stimulating factor. In addition, RT-PCR experiments indicated mRNA expression of the PAF receptor in these immature DCs. Cell studies and mRNA analyses further revealed that immature DCs neither respond to MIP-3beta nor express its specific receptor, CCR7. Induction of cell differentiation by LPS led to the loss of the mRNA expression of the PAF receptor, accompanied by decreasing intracellular calcium release, actin polymerization, and migration after stimulation with PAF. In contrast, LPS treatment induced increasing responsiveness toward MIP-3beta and mRNA expression of CCR7. Comparable data regarding mRNA expression of PAF receptor and PAF responsiveness were also obtained with another maturation protocol using TNFalpha instead of LPS. The direct comparison between the two different protocols showed a slower decrease of PAF responsiveness induced by TNFalpha than by LPS. These results show the loss of PAF responsiveness associated with downregulation of PAF receptor mRNA expression during LPS- and TNFalpha-induced maturation in human DCs. Therefore, these findings point to a functional relevance of PAF in recruiting immature DCs, whereas MIP-3beta might regulate the migration of DCs at a later stage of maturation.
Antigen Presentation↗
Differential expression of inflammatory mediators in rat microglia cultured from different brain regions.
Microglial cells show a rather uniform distribution of cell numbers throughout the brain with only minor prevalences in some brain regions. Their in situ morphologies, however, may vary markedly from elongated forms observed in apposition with neuronal fibers to spherical cell bodies with sometimes extremely elaborated branching. This heterogeneity gave rise to the hypothesis that these cells are differentially conditioned by their microenvironment and, therefore, also display specific patterns of differential gene expression. In this study, microglia were isolated from 2-4 week-old mixed CNS cultures that had been prepared from neonatal rat diencephalon, tegmentum, hippocampus, cerebellum and cerebral cortex, and were investigated 24 h later. Messenger RNA levels of proteins involved in crucial immune functions of this cell type (TNF-alpha, CD4, Fcgamma receptor II, and IL-3 receptor beta-subunit) have been determined by semi-quantitative RT-PCR. The results clearly show, that three of these mRNAs (TNF-alpha, CD4, Fcgamma receptor II) are differentially expressed in microglia with hippocampal microglia displaying the highest levels of these mRNAs. The data strongly support the notion that the status of microglial gene expression depends on their localization in brain and on specific interactions with other neural cell types. Consequently, it is hypothesized that their responsiveness to signals arising in injury or disease may vary from one brain region to another.
Animals↗
Activators of peroxisome proliferator-activated receptor-gamma (PPARgamma) inhibit inducible nitric oxide synthase expression but increase heme oxygenase-1 expression in rat glial cells.
The peroxisome proliferator-activated receptor-gamma (PPARgamma) is activated by 15-deoxy-delta(12,14) prostaglandin J2 (15d-PGJ2), anti-diabetic thiazolidinediones and several non-steroidal anti-inflammatory drugs (NSAIDs). In rat glial cells, lipopolysaccharide and interferon-gamma (LPS/IFN-gamma) induced expression of both inducible nitric oxide synthase (iNOS) and heme oxygenase-1 (HO-1). PPARgamma activators inhibited iNOS expression by LPS and IFN-gamma. However, PPARgamma activator alone induced HO-1 expression and further enhanced LPS/IFN-gamma-induced HO-1 expression. These results suggest that activation of PPARgamma negatively regulate iNOS expression and positively regulates HO-1 expression in glial cells.
Alitretinoin↗
Increased expression of cyclooxygenases and peroxisome proliferator-activated receptor-gamma in Alzheimer's disease brains.
Recent studies suggest that inflammatory events are associated with plaque formation in the brains of patients with Alzheimer's disease (AD). Treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) of these patients appears to slow the progression of disease. We assessed the occurrence of cyclooxygenases (COX-1 and -2) and peroxisome proliferator-activated receptor-gamma (PPARgamma) in temporal cortex from normal and AD brains using specific antibodies. In AD brains, protein levels of COX-1 were increased in both cytosolic and particulate fractions, and COX-2 protein was also increased in the particulate fraction. On the other hand, PPARgamma level was increased in the cytosolic fraction but not in the particulate fraction. Thus, expression levels of COX-1, COX-2, and PPARgamma may change in AD brains. In addition, several NSAIDs which are also PPARgamma activators, such as indomethacin, inhibited COX-2 expression in glial cells. These results suggest that PPARgamma activators have inhibitory effects on inflammatory events in AD brains.
Aged↗
Regulation of K+ channel mRNA expression by stimulation of adenosine A2a-receptors in cultured rat microglia.
Previous investigations suggest that the expression of K+ channels in cultured rat microglia is related to the activation status of these cells. Both, lipopolysaccharide (LPS) and agents that raise intracellular cyclic AMP have been shown to inhibit microglial proliferation. LPS also regulates the mRNA expression levels of K+ channels in cultured microglia, which led us to investigate possible regulatory interactions between K+ channels and adenosine A2a-receptors, which are coupled to the cAMP-signal transduction pathway. The selective adenosine A2a-receptor agonist CGS 21680 induced enhanced mRNA expression of both Kv1.3 and ROMK1, as well as an elevation of Kv1.3 protein. The selective adenosine A2a-receptor antagonist aminophenol (ZM 241385) and the nonselective antagonist 8-phenyltheophylline (8-PT) inhibited these effects. Elevations of cyclic AMP by use of dibutyryl cyclic AMP (dbcAMP), phosphodiesterase-inhibitor (RO 20-1724), forskolin, or cholera toxin (CTX), strongly enhanced Kv1.3-mRNA expression, but decreased ROMK1-mRNA levels. Results from experiments with actinomycin D suggest that K+ channel mRNA levels in cultured microglia were regulated by altered mRNA synthesis. Evidently, the CGS 21680-induced effects upon Kv1.3 were mediated via an increase in intracellular cyclic AMP, whereas ROMK1-mRNA expression appeared to be regulated by coupling of adenosine A2a-receptors to an alternative pathway, which involves activation of protein kinase C (PKC). It is concluded that the cyclic AMP second messenger system in microglia is not only involved in regulation of K+ channel activity, but also in regulation of de novo K+ channel synthesis.
Adenosine↗
Hydrogen peroxide-induced apoptosis mediated by p53 protein in glial cells.
It is now generally accepted that massive neuronal death due to oxidative stress is a regular feature of brains in neurodegenerative diseases. However, much less attention has been given to the death of glial cells. In this study, we examined p53-sensitive apoptosis of cells by using human glioblastoma A172 cells and p53-deficient mouse astrocytes. In human A172 cells, hydrogen peroxide (H2O2) caused cell death in a time- and concentration-dependent manner, accompanied by nucleosomal DNA fragmentation and chromatin condensation. After treatment with H2O2, p53 protein was highly expressed and protein levels of Bak, p21WAF1/CIP1 and GADD45 were also enhanced. However, the protein levels of Bcl-2 and Bax did not change. On the other hand, primary cultured astrocytes from p53-deficient mouse brain grew faster than wild-type and heterozygous astrocytes. In addition, p53-deficient astrocytes were more resistant to H2O2-induced apoptosis than wild-type and heterozygous astrocytes. These results suggest that glial proliferation and the repair of damaged DNA may be regulated by p53-induced p21WAF1/CIP1 and GADD45, and that glial apoptosis caused by oxidative stress may be mediated by p53-induced Bak.
Animals↗
Interferon-gamma plus lipopolysaccharide induction of delayed neuronal apoptosis in rat hippocampus.
Interferon-gamma and lipopolysaccharide (IFN-gamma/LPS) induce expression of inducible nitric oxide synthase (iNOS) protein both in cells in vitro and in the brain in vivo. In cultured cells, excessive production of nitric oxide (NO) induces neuronal cell death. However, it is still unclear whether IFN-gamma and LPS might induce neuronal cell death in vivo. In this study, we examined the neuronal cell death and induction of major histocompatibility complex (MHC) antigens after microinjection of IFN-gamma/LPS into the rat hippocampus. Although microglia appeared morphologically ramified in the normal and vehicle-injected hippocampus, microinjection of IFN-gamma/LPS immediately induced the ameboid type. From days 1-7, iNOS was expressed in ameboid microglia surrounding the site of the microinjection. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells appeared among the granular neurons of the dentate gyrus on day 3 and peaked about 7 days after microinjection. When the NOS inhibitor N(G)-nitro-L-arginine (L-NA) was intraperitoneally administered prior to the microinjection, the number of TUNEL-positive neurons decreased in a L-NA dose-dependent manner. These results suggest that IFN-gamma/LPS induces delayed neuronal apoptosis in the hippocampus in vivo, and it possibly involves excessive NO production by iNOS. Thus, this animal model may be one of neurodegenerative with extensive inflammatory activation in the hippocampus.
Animals↗
Protein kinase C-mediated regulation of inducible nitric oxide synthase expression in cultured microglial cells.
Nitric oxide (NO) has been implicated in a number of important brain functions, such as long-term potentiation (LTP) and long-term depression (LTD), and in events associated with neurodegeneration and neuroprotection. In response to brain injury or disease NO production is increased by an inducible enzyme (iNOS), which is only expressed under these conditions. Activated microglia are a major cellular source of iNOS in brain. Due to the important role of iNOS in brain injury and disease, a detailed understanding of intracellular events triggering the expression of iNOS in microglia would facilitate pharmacotherapeutic approaches. It is shown here, that iNOS mRNA, protein and NO product are induced in cultured microglia by lipopolysaccharide (LPS). This induction is reduced by a number of substances elevating intracellular cyclic AMP levels. It is unabated, however, in the presence of substances inhibiting cyclooxygenase-1 and/or cyclooxygenase-2 (e.g., acetyl salicylic acid, SC 58125, L 745337), but is decreased by approx. 50% with PDTC, a scavenger of reactive oxygen intermediates (ROI) that inhibits nuclear factor kappaB (NF-kappaB) activation. Furthermore, inhibitors of protein kinase C (PKC) strongly inhibit iNOS mRNA and protein induction. PKC, therefore, constitutes a major second messenger component (besides NF-kappaB) in the signaling pathway regulating iNOS expression in microglia.
Animals↗