Regulation of astrocyte proliferation by prostaglandin E2 and the alpha subtype of protein kinase C

Prostaglandin synthesis in rat brain astrocytes is under the control of the n-3 docosahexaenoic acid, released by group VIB calcium-independent phospholipase A2

In the current study, we reveal that in astrocytes the VIB Ca(2+)-independent phospholipase A(2) is the enzyme responsible for the release of docosahexaenoic acid (22:6n-3). After pharmacological inhibition and siRNA silencing of VIB Ca(2+)-independent phospholipase A(2), docosahexaenoic acid release was strongly suppressed in astrocytes, which were acutely stimulated (30 min) with ATP and glutamate or after prolonged (6 h) stimulation with the endotoxin lipopolysaccharide. Docosahexaenoic acid release proceeds simultaneously with arachidonic acid (20:4n-6) release and prostaglandin liberation from astrocytes. We found that prostaglandin production is negatively controlled by endogenous docosahexaenoic acid, since pharmacological inhibition and siRNA silencing of VIB Ca(2+)-independent phospholipase A(2) significantly amplified the prostaglandin release by astrocytes stimulated with ATP, glutamate, and lipopolysaccharide. Addition of exogenous docosahexaenoic acid inhibited prostaglandin synthesis, which suggests that the negative control of prostaglandin synthesis observed here is likely due to competitive inhibition of cyclooxygenase-1/2 by free docosahexaenoic acid. Additionally, treatment of astrocytes with docosahexaenoic acid leads to the reduction in cyclooxygenase-1 expression, which also contributes to reduced prostaglandin production observed in lipopolysaccharide-stimulated cells. Thus, we identify a regulatory mechanism important for the brain, in which docosahexaenoic acid released from astrocytes by VIB Ca(2+)-independent phospholipase A(2) negatively controls prostaglandin production.

Microglia proliferation is regulated by hydrogen peroxide from NADPH oxidase

Microglia are resident brain macrophages that become activated and proliferate following brain damage or stimulation by immune mediators, such as IL-1beta or TNF-alpha. We investigated the mechanisms by which microglial proliferation is regulated in primary cultures of rat glia. We found that basal proliferation of microglia was stimulated by proinflammatory cytokines IL-1beta or TNF-alpha, and this proliferation was completely inhibited by catalase, implicating hydrogen peroxide as a mediator of proliferation. In addition, inhibitors of NADPH oxidase (diphenylene iodonium or apocynin) also prevented microglia proliferation, suggesting that this may be the source of hydrogen peroxide. IL-1beta and TNF-alpha rapidly stimulated the rate of hydrogen peroxide produced by isolated microglia, and this was inhibited by diphenylene iodonium, implying that the cytokines were acting directly on microglia to stimulate the NADPH oxidase. Low concentrations of PMA or arachidonic acid (known activators of NADPH oxidase) or xanthine/xanthine oxidase or glucose oxidase (generating hydrogen peroxide) also increased microglia proliferation and this was blocked by catalase, showing that NADPH oxidase activation or hydrogen peroxide was sufficient to stimulate microglia proliferation. In contrast to microglia, the proliferation of astrocytes was unaffected by the presence of catalase. In conclusion, these findings indicate that microglial proliferation in response to IL-1beta or TNF-alpha is mediated by hydrogen peroxide from NADPH oxidase.

Role of Ca2+-independent phospholipase A2 and n-3 polyunsaturated fatty acid docosahexaenoic acid in prostanoid production in brain: perspectives for protection in neuroinflammation

Various diseases of the central nervous system are characterized by induction of inflammatory events, which involve formation of prostaglandins. Production of prostaglandins is regulated by activity of phospholipases A(2) and cyclooxygenases. These enzymes release the prostaglandin precursor, the n-6 polyunsaturated fatty acid, arachidonic acid and oxidize it into prostaglandin H(2). Docosahexaenoic acid, which belongs to the n-3 class of polyunsaturated fatty acids, was shown to reduce production of prostaglandins after in vivo and in vitro administration. Nevertheless, the fact that in brain tissue cellular phospholipids naturally have a uniquely high content of docosahexaenoic acid was ignored so far in studies of prostaglandin formation in brain tissue. We consider the following possibilities: docosahexaenoic acid might attenuate production of prostaglandins by direct inhibition of cyclooxygenases. Such inhibition was found with the isolated enzyme. Another possibility, which has been already shown is reduction of expression of inducible cyclooxygenase-2. Additionally, we propose that docosahexaenoic acid could influence intracellular Ca(2+) signaling, which results in changes of activity of Ca(2+)-dependent phospholipase A(2), hence reducing the amount of arachidonic acid available for prostaglandin production. Astrocytes, the main type of glial cells in the brain control the release of arachidonic acid, docosahexaenoic acid and the formation of prostaglandins. Our recently obtained data revealed that the release of arachidonic and docosahexaenoic acids in astrocytes is controlled by different isoforms of phospholipase A(2), i.e. Ca(2+)-dependent phospholipase A(2) and Ca(2+)-independent phospholipase A(2), respectively. Moreover, the release of arachidonic and docosahexaenoic acids is differently regulated through Ca(2+)- and cAMP-dependent signal transduction pathways. Based on analysis of the current literature and our own data we put forward the hypothesis that Ca(2+)-independent phospholipase A(2) and docosahexaenoic acid are promising targets for treatment of inflammatory related disorders in brain. We suggest that Ca(2+)-independent phospholipase A(2) and docosahexaenoic acid might be crucially involved in brain-specific regulation of prostaglandins.

Translocation of protein kinase C-betaII in astrocytes requires organized actin cytoskeleton and is not accompanied by synchronous RACK1 relocation

Protein kinase C (PKC)-betaII is the most abundant PKC isoform in astrocytes. Upon activation, this isoform of PKC translocates from the cytosol to the plasma membrane (PM). In this study, we investigated in astrocytes the modality of PKC-betaII translocation as far as the participation of the receptor for activated C kinase-1 (RACK1) and the requirement for intact cytoskeleton in the process. In astrocytes, Western blots and immunocytochemistry coupled to confocal microscopic quantitative analysis showed that after 5 min of phorbol-12-myristate-13-acetate (PMA) exposure, native PKC-betaII, but not PKC-betaI, is relocated efficiently from the cytosol to the PM. Translocation of PKC-betaII was not associated with synchronous RACK1 relocation. Furthermore, the quantity of PM-associated PKC-betaII that co-immunoprecipitated with PM-bound RACK1 increased following PMA exposure, indicating a post activation binding of the two proteins in the PM. Because RACK1 and PKC-betaII relocation seemed not to be synchronous, we hypothesized that an intermediate interaction with the cytoskeleton was taking place. In fact, we were able to show that pharmacological disruption of actin-based cytoskeleton greatly deranged PKC-betaII translocation to the PM. The requirement for intact actin cytoskeleton was specific, because depolymerization of tubulin had no effect on the ability of the kinase to translocate to the PM. These results indicate that in astrocytes, RACK1 and PKC-betaII synchronous relocation is not essential for relocation of PKC-betaII to the PM. In addition, we show for the first time that the integrity of the actin cytoskeleton plays a specific role in PKC-betaII movements in these cells. We hypothesize that in glial cells, rapidly occurring changes of actin cytoskeleton arrangement may be involved in the fast reprogramming of PKC targeting to specific PM location to phosphorylate substrates in different cellular locations.

Prostaglandin E2 is increased in amyotrophic lateral sclerosis patients

OBJECTIVES

Oxidative stress and glutamate-mediated excitotoxicity may play an important role in the etiopathogenesis of amyotrophic lateral sclerosis (ALS). Prostaglandin E2 (PGE2) activity can be associated with motor neuron death by inducing free radical formation and glutamate release from astrocytes. The aim of this study was to determine PGE2 concentration in the serum and cerebrospinal fluid (CSF) of ALS patients.

MATERIAL AND METHODS

PGE2 concentration was measured by the enzyme-linked immunosorbent method in the serum and CSF from ALS and control group patients.

RESULTS

Serum and CSF PGE2 concentration was significantly higher in the whole group of ALS patients compared with the control group patients (P < 0.05). There was no relationship between PGE2 concentration and clinical parameters of the disease, such as clinical state, type of ALS onset, and duration of the disease (P > 0.05). A significant correlation between CSF PGE2 concentration and age of control group patients was found (P < 0.05).

CONCLUSIONS

A significant increase in serum and CSF PGE2 concentration, in ALS patients observed in this study, indicates that PGE2 may play a role in neurodegeneration of ALS through oxidative damage of neurons and glutamate-mediated excitotoxicity. It suggests that inhibition of PGE2 synthesis could prevent motor neuron death. However, serum and CSF PGE2 cannot be a marker of the type of ALS onset, clinical state of patients, or the duration of the disease.

Activated microglia in the human glaucomatous optic nerve head

To investigate the distribution and potential participation of microglia, the resident defense cells of the central nervous system, in the optic nerve head (ONH) in glaucoma, histological paraffin sections of optic nerves from normal and glaucoma patients with mild to advanced nerve damage were studied using double labeling immunohistofluorescence. A monoclonal antibody for HLA-DR, indicating activated microglia, was colocalized with antibodies for functional proteins. In normal ONHs, microglia do not contain TGF-beta2, COX-2, or TNF-alpha and are not positive for PCNA; however, in glaucomatous ONHs, microglia contain abundant TGF-beta2, TNF-alpha, and PCNA. In glaucomatous eyes, a few microglia are usually positive for COX-2. In normal ONHs, there are rarely microglia containing TGF-beta1, NOS-2, TSP, TIMP-2, and CD68, but, in glaucomatous tissue, a few microglia are positive from the prelaminar to the postlaminar regions. MMP-1, MMP-2, MMP-3, and MMP-14 are constitutively present in the perivascular microglia in normal ONHs and appear to be more abundant in glaucomatous tissue. COX-1, TNF-R1, TIMP-1, and c-fms are constitutively present in normal tissues and appear to be increased in microglia in the glaucomatous ONHs. HSP27 is not present in microglia. In glaucomatous ONHs, microglia become activated and phagocytic and produce cytokines, mediators, and enzymes that can alter the extracellular matrix. Our findings suggest that activated microglia may participate in stabilizing the tissue early in the disease process, but, as the severity of the glaucomatous damage increases, the activities of microglia may have detrimental consequences for the pathological course of glaucomatous optic neuropathy.

Anticancer drug resistance in primary human brain tumors

The difficult clinical situation still associated with most types of primary human brain tumors has fostered significant interest in defining novel therapeutic modalities for this heterogeneous group of neoplasms. Beginning in the 1980s chemotherapy has been incorporated into the treatment protocol of a number of intractable brain tumors. However, it has predominantly failed to improve patient outcome. The unsatisfactory results with chemotherapeutic intervention have chiefly been attributed to tumor cell resistance. In recent years, there has been a literal explosion in our understanding about the mechanisms by which cancer cells become chemoresistant. During the course of their evolution (intrinsic resistance) or in response to chemotherapy (acquired resistance) these cells may follow a number of pathways of genetic alterations to possess a common (multidrug) or drug-specific (individual drug) resistant phenotype. Genomic aberrations, deregulation of membrane transporting proteins and cellular enzymes, and an altered susceptibility to commit to apoptosis are among the steps on the way that contribute to the genesis of chemotherapeutic treatment failure. Although, through the years we have come to yield information and inferences as to the roles that different molecular events may have in the resistance phenotype of cancer cells, the actual involvement of single genetic alterations in conferring drug resistance in primary brain tumors remains debatable. This uncertainty and, besides, the lack of proper drug resistance diagnostics, in a vicious circle, hinder the development of effective resistance-modulation strategies. Clinical non-responsiveness to chemotherapy remains a formidable obstacle to the successful treatment of brain tumors and one of the most serious problems to be solved in the therapy of these lesions. Future advances in the chemotherapeutic management of these neoplasms will come with an improved understanding of the significance and interrelationship of the multiple biological systems operative in promoting resistance to this treatment modality. The focus of this review is to summarize current knowledge concerning major drug resistance-related markers, to describe their functional interaction en route to chemoresistance, and to discuss their implication in rendering human brain tumor cells resistant to chemotherapy.

Electrophysiological characteristics of reactive astrocytes in experimental cortical dysplasia

Neocortical freeze lesions have been widely used to study neuronal mechanisms underlying hyperexcitability in dysplastic cortex. Comparatively little attention has been given to biophysical changes in the surrounding astrocytes that show profound morphological and biochemical alterations, often referred to as reactive gliosis. Astrocytes are thought to aid normal neuronal function by buffering extracellular K(+). Compromised astrocytic K(+) buffering has been proposed to contribute to neuronal dysfunction. Astrocytic K(+) buffering is mediated, partially, by the activity of inwardly rectifying K(+) channels (K(IR)) and may involve intracellular redistribution of K(+) through gap-junctions. We characterized K(+) channel expression and gap-junction coupling between astrocytes in freeze-lesion-induced dysplastic neocortex. Whole cell patch-clamp recordings were obtained from astrocytes in slices from postnatal day (P) 16--P24 rats that had received a freeze-lesion on P1. A marked increase in glial fibrillary acidic protein immunoreactivity was observed along the entire length of the freeze lesion. Clusters of proliferative (bromo-deoxyuridine nuclear staining, BrdU+) astrocytes were seen near the depth of the microsulcus. Astrocytes in cortical layer I surrounding the lesion were characterized by a significant reduction in K(IR). BrdU-positive astrocytes near the depth of the microsulcus showed essentially no expression of K(IR) channels but markedly enhanced expression of delayed rectifier K(+) (K(DR)) channels. These proliferative cells showed virtually no dye coupling, whereas astrocytes in the hyperexcitable zone adjacent to the microsulcus displayed prominent dye-coupling as well as large K(IR) and outward K(+) currents. These findings suggest that reactive gliosis is accompanied by a loss of K(IR) currents and reduced gap junction coupling, which in turn suggests a compromised K(+) buffering capacity.

Differential effects of ethanol on the expression of cyclo-oxygenase in cultured cortical astrocytes and neurons

The developing central nervous system is a primary target of ethanol toxicity. The teratogenic effect of ethanol may result from its action on prostaglandins. Prostaglandins are generated through the release of arachidonic acid (AA) by the action of cytosolic phospholipase A(2) (cPLA(2)) on membrane-bound phospholipids and the catalytic conversion of AA to prostaglandin E(2) (PGE(2)) by cyclo-oxygenase (COX). COX is expressed in two isoforms, constitutive COX1 and inducible COX2. Cultured astrocytes and neurons from immature cerebral cortex were used as in vitro models to investigate the effect of ethanol on PGE(2) synthesis. In both cell types, neither the activity nor the expression of cPLA(2) was affected by ethanol. PGE(2) was synthesized by astrocytes and neurons. Ethanol (200-400 mg/dL for 24 h) significantly increased PGE(2) production in both cell types and the ethanol-induced increase in PGE(2) accumulation in astrocytes was significantly greater than in neurons. These increases resulted from the effects of ethanol on COX. Overall COX activity was up-regulated by ethanol in astrocytes and neurons, and indomethacin, a nonselective blocker for COX, eliminated the ethanol-induced increases of COX activity in both cell types. Increased COX activity in astrocytes resulted from an increase in COX2 expression. NS-398, a selective COX2 blocker, completely inhibited ethanol-induced alterations in COX activity. In neurons, however, ethanol had a direct effect on COX activity in the absence of a change in COX expression. NS-398 only partially blocked ethanol-induced increases in neuronal COX activity. Thus, astrocytes are a primary target of ethanol and ethanol-induced increases in glial PGE(2) synthesis are mediated by COX, principally COX2. Ethanol toxicity may be mediated through PGE(2) in immature cortical cells.

Cyclopentenone prostaglandin 15-deoxy-Delta(12,14)-prostaglandin J(2) acts as a general inhibitor of inflammatory responses in activated BV-2 microglial cells

15-deoxy-Delta(12,14)-PGJ(2), a cyclopentenone derivative of PGD(2), was recently reported [Petrova et al., Proc. Natl. Acad. Sci. USA 96 (1999) 4668-4673] to suppress inducible nitric oxide synthase (iNOS) production in microglia and mixed glial cultures stimulated with lipopolysaccharide (LPS). We report here that in addition to suppressing iNOS production, 15d-PGJ(2) also decreases the production of tumor necrosis factor alpha (TNFalpha), interleukin-1 beta (IL-1beta) and cyclooxygenase-2 (COX-2) in LPS-stimulated BV-2 microglial cells, thereby acting as a general inhibitor of microglial activation. Concomitantly, 15d-PGJ(2) itself up-regulates the production of the antioxidant enzyme heme oxygenase-1 (HO-1) and increases intracellular total glutathione levels. To test if increased HO-1 levels were involved in the ability of 15d-PGJ(2) to block microglial activation, we used a HO-1 inhibitor that could block the activity of HO-1. The presence of the HO-1 inhibitor did not alter the 15d-PGJ(2)-induced inhibition of LPS-stimulated iNOS and TNFalpha protein levels, and led to only a partial reduction in the protection offered by 15d-PGJ(2) against LPS-induced nitrite production. These results suggest that HO-1 upregulation by 15d-PGJ(2) is not the primary pathway responsible for the anti-inflammatory action of 15d-PGJ(2) in microglial cells.

Eicosanoids and the large intestine

During the past three decades, many studies have been conducted to determine the precise role of eicosanoids in colorectal physiology and pathophysiology. This research has increased our understanding of bioactive lipid signaling, and may contribute to the development of more effective therapeutic modalities for digestive diseases in the future. The purpose of this report is to provide a brief overview of the role of eicosanoids in the colon and rectum. This information has been organized according to both functional and disease-related categories. The role of eicosanoids in colonic secretion, motility, inflammatory bowel disease, and colorectal neoplasia will be discussed.

Endothelins stimulate expression of cyclooxygenase 2 in rat cultured astrocytes

Endothelin (ET) is one of the active endogenous substances regulating the functions of astrocytes. In the present study, we examined effects of ET on cyclooxygenase (COX) expression in cultured astrocytes. ET-3 (100 nM) caused transient increases in the expression of both COX2 mRNA and protein, but not those of COX1, in cultured astrocytes. ET-induced COX2 mRNA expression was suppressed by 5 microg/ml actinomycin D, 30 microM BAPTA/AM, inhibitors of protein kinase C (1-100 nM staurosporin and 100 microM H-7), 2 microM dexamethasone, and prolonged treatment with 100 nM phorbol 12-myristate 13-acetate. ET-3 stimulated production of prostaglandin (PG) E2 in cultured astrocytes. The effect of ET-3 on the PGE2 production was diminished by actinomycin D. Indomethacin and NS398, a selective COX2 inhibitor, comparably decreased both the basal and the ET-stimulated PGE2 production. Proliferation of cultured astrocytes was stimulated by 100 nM ET-3, and the increased proliferation was reduced by co-addition of 1 microM PGE2. Treatment with 1 microM PGE2 caused astrocytic morphological changes accompanied by disappearance of stress fibers, a prominent structure of organized cytoskeletal actin in cultured astrocytes. In the presence of 10 nM ET-3, PGE2 did not show an effect on astrocytic actin organization. The present study shows that ET is an inducer of astrocytic COX2 and suggests that ET-induced PGE2 production through COX2 may be involved in the regulation of astrocytic functions.

Differentiation-specific mRNA expression of a mouse bipotential glial cell line

We have previously reported that a bipotential glial cell line from mouse cerebrum, designated OS3, phenotypically differentiates into oligodendrocytes and astrocytes both in vitro and in vivo. To study the potential mechanisms of differentiation, in this study we investigated mRNA expression of cytokines and developmentally regulated proteins in OS3 during differentiation into oligodendrocytes by semi-quantitative reverse transcription and polymerase chain reaction. In the presence of 10% calf serum OS3 cells expressed IL-1alpha and IL-1beta mRNA. However, when the cells were cultured in chemically defined medium or low serum-containing medium the expression of IL-1alpha and IL-1beta mRNA was down-regulated. Under stimulation of phorbol ester, expression of IL-6 and nerve growth factor mRNA was up-regulated. The capacity for differentiation of OS3 cells into oligodendrocytes in vitro was limited and most OS3 cells ceased their differentiation at the proligodendroblast stage. However, expression of proteolipid protein (PLP) and DM20 mRNA was detectable and was up-regulated in accordance with the differentiation into oligodendrocytes. As a control, primary astrocytes expressed DM20 mRNA but not PLP mRNA and the expression of DM20 mRNA was independent of culture condition. Therefore, OS3 cells will be of use for the study of differentiation of progenitor cells into type-2 astrocytes or oligodendrocytes at the molecular level.

Prostaglandin E2 increases proenkephalin mRNA level in rat astrocyte-enriched culture

The effect of prostaglandin E2 (PGE2) on proenkephalin (proENK) mRNA expression in primary cultured rat astrocytes was studied. The proENK mRNA level was significantly increased about 3.3-fold 4 h after PGE2 (10 microM) treatment and this increase was potentiated by the pre-treatment with cycloheximide (CHX; 15 microM) about 1.7-fold as much as PGE2 alone treated cells. The pretreatment with staurosporine (1 microM) completely inhibited the increase of PGE2-induced proENK mRNA level, although only a partial inhibition of PGE2-induced proENK mRNA level (approximately 1.5-fold) by H89 (10 microM) was observed. The increase of PGE2-induced proENK mRNA level was not affected by the pretreatment with PD98059 (1, 5, and 10 microM), omega-conotoxin GIVA (1 microM), nimodipine (1 microM), calmidazolium (1 microM), or KN-62 (1 microM). In addition to the proENK mRNA level, PGE2 also increased c-Fos (approximately 4.3-fold), Fra-1 ( approximately 3.8 fold), and Fra-2 (approximately 8.2-fold) protein levels at 4 h after drug treatment. However, c-Jun, JunB, and JunD protein levels were not affected by PGE2. Indeed, PGE2 failed to up-regulate c-jun mRNA expression as well as its protein product. Surprisingly, although three Jun proteins were not induced by PGE2, AP-1 and ENKCRE-2 DNA binding activities were increased by PGE2, (approximately 5 and approximately 2.8-fold, respectively) and which were effectively reduced by CHX (approximately 2.5 and 2-fold, respectively). In western blot analyses, PGE2 enhanced the phosphorylation of CREB (approximately 2.6-fold at 1 h), and CHX showed a potentiative effect on PGE2-induced CREB phosphorylation ( approximately 1.7 fold at 1 h) which is similar to the action on proENK mRNA regulation. Our results suggest that PGE2 increases proENK mRNA expression via activating serine/threonine protein kinase such as PKA, but not calcium/calmodulin dependent protein kinase and MAPK. In addition, phosphorylation of CREB rather than the increase of AP-1 may have a possible role at least early stage in PGE2-induced proENK mRNA level and CHX-evoked potentiation.

Tryptophan and its metabolite, kynurenine, stimulate expression of nerve growth factor in cultured mouse astroglial cells

Effects of L-tryptophan and its metabolites were evaluated on expression of nerve growth factor (NGF) in primary culture of mouse astroglial cells. L-Tryptophan produced concentration-dependent increases in accumulation of NGF transcripts in the cells. L-Kynurenine, a metabolite of the kynurenine pathway, markedly increased the levels of mRNAs for NGF, the maximal increases (4-5 fold) occurred at its dose of 1 microM. Kynurenine-induced increase in mRNA levels for NGF occurred as early as 1 h after the addition of the compound, peaked at 4 h and declined thereafter. In contrast to kynurenine, other tryptophan metabolites such as quinolinic acid, kynurenic acid and serotonin had little effect on the levels of NGF mRNA.

The role of protein kinase C (PKC) in the evolution and proliferation of malignant gliomas, and the application of PKC inhibition as a novel approach to anti-glioma therapy

The present article reviews the role of the second messenger enzyme protein kinase C (PKC) in the growth regulation of high-grade gliomas, and evaluates the efficacy of therapeutic strategies directed against PKC for blocking the proliferation of these malignancies in in vitro and in vivo models. The translation of such strategies to the treatment of patients with malignant gliomas may provide a novel approach for improving the otherwise grim outlook associated with these neoplasms.

Effect of aspirin on cell proliferation and differentiation of colon adenocarcinoma Caco-2 cells

Several lines of evidence suggest that long-term treatment with non-steroidal anti-inflammatory drugs may reduce the risk of colon cancer and the size and number of colonic polyps in patients with familial adenomatous polyposis. Aspirin has also been shown to inhibit cell proliferation in human tumor cell lines and to induce apoptosis in colonic mucosa of familial polyposis patients. To elucidate the molecular mechanisms of the antiproliferative action of aspirin, we studied the effects of aspirin on cell growth and differentiation of the human colon carcinoma Caco-2 cell line. These cells represent a useful tool for studying the mechanisms involved in the regulation of cell growth and differentiation of intestinal epithelial cells since they spontaneously differentiate into polarized cells, expressing brush border enzymes. We show in this study that aspirin (0.1-10 mM) induces a profound inhibition of cell replication as assessed either by cell counts or thymidine incorporation. Moreover, aspirin concentrations of 5 and 10 mM induce apoptosis, whereas concentrations of 1 and 2 mM do not. The inhibition of growth is associated with a dose-dependent reduction in insulin-like growth factor II mRNA expression and with an increase in sucrase activity (a brush border enzyme) and apolipoprotein A-I mRNA expression, 2 specific markers of the differentiative status of this cell line. Our data thus show that aspirin-dependent inhibition of cell growth is associated with the enterocyte-like differentiation of Caco-2 cells.

GFAP expression induced by dopamine D(2) receptor agonists in the rat pituitary intermediate lobe

This study was conducted to determine if intermediate lobe glial-like cells are affected by compounds that regulate melanotrope biosynthetic activity via the dopamine D(2) receptor. Glial-like cells were stellate, and expressed glial fibrillary acidic protein (GFAP) and vimentin in cell bodies and processes as revealed by immunohistochemistry. Following bromocriptine and quinpirole treatments, the number of cell bodies and processes expressing vimentin did not change, whereas those expressing GFAP increased, although never to exceed the number of vimentin containing structures. The percent of cells and processes coexpressing GFAP and vimentin also increased. The GFAP response was reversible by haloperidol treatment following the agonist treatment. Haloperidol treatment alone did not change GFAP expression. Thus, following D(2) receptor agonist treatment, GFAP was induced in pre-existing vimentin-positive glial cells. Dopamine D(2) receptor mRNA and protein were detected in melanotropes, but not in cells expressing GFAP or vimentin. Although glial-like cells may express dopamine D(2) receptor mRNA and protein below the detection levels of our methods, the possibility of an indirect effect via dopamine D(2) receptor agonists acting on melanotropes needs to be considered.

Ethanol enhances the in situ phosphorylation of MARCKS and protein kinase C activity in primary cultures of astrocytes

Protein kinase C (PKC) plays an important regulatory role in astrocyte function. Chronic exposure to ethanol for 4 days resulted in an increase in Ca2+-dependent PKC activity in the supernatant fraction of astrocyte homogenates. Only Ca2+-independent PKC activity could be observed in the membrane fraction and this activity was unaffected by ethanol exposure. Chronic ethanol exposure also increased the in situ phosphorylation of MARCKS in permeabilized astrocytes both in the absence or presence of the PKC activator, phorbol 12 -myristate 13 -acetate (PMA). These results suggest an increase in the expression of one or more astrocytic PKC isoforms after chronic ethanol exposure.

Protein kinase C and growth regulation of malignant gliomas

This article reviews the role of the signal transduction enzyme protein kinase C in the regulation of growth of malignant gliomas, and describes how targetting this enzyme clinically can provide a novel approach to glioma therapy.

Reactive microglia in cerebral ischaemia: an early mediator of tissue damage?

Microglial cell activation is a rapidly occurring cellular response to cerebral ischaemia. Microglia proliferate, are recruited to the site of lesion, upregulate the expression of several surface molecules including major histocompatibility complex class I and II antigens, complement receptor and the amyloid precursor protein (APP) as well as newly expressed cytokines, e.g. interleukin-1 and transforming growth factor beta 1. The ischaemia-induced production of APP may contribute to amyloid deposition in the aged brain under conditions of hypofusion. Ultrastructurally, microglia transform into phagocytes removing necrotic neurons but still respecting the integrity of eventually surviving neurons even in the close vicinity of necrotic neurons. Microglial activation starts within a few minutes after ischaemia and thus precedes the morphologically detectable neuronal damage. It additionally involves a transient generalized response within the first 24 hours post-ischaemia even at sites without eventual neuronal cell death. In functional terms, the microglial reaction appears to be a double-edged sword in ischaemia. Activated microglia may exert a cytotoxic effector function by releasing reactive oxygen species, nitric oxide, proteinases or inflammatory cytokines. All of these cytotoxic compounds may cause bystander damage following ischaemia. Pharmacological suppression of microglial activation after ischaemia has accordingly attenuated the extent of cell death and tissue damage. However, activated microglia support tissue repair by secreting factors such as transforming growth factor beta 1 which may limit tissue damage as well as suppress astroglial scar formation. In line with ultrastructural observations microglial activation in ischaemia is a strictly controlled event. By secreting cytokines and growth factors activated microglia most likely serve seemingly opposed functions in ischaemia, i.e. maintenance as well as removal of injured neurons. Post-ischaemic pharmacological modulation of microglial intervention in the cascade of events that lead to neuronal necrosis may help to improve the structural and functional outcome following CNS ischaemia.

Eicosanoids and the gastrointestinal tract

Determining the role of eicosanoids in gastrointestinal physiology and pathophysiology has been an active area of investigation over the past 20 years. The landmark discovery of prostaglandin endoperoxide synthase and other enzymes involved in the production of arachidonic acid products (lipoxygenases and epoxygenases) ushered in a new era of research. The goal of this review is to distill a large body of work pertaining to studies of eicosanoids in the gastrointestinal tract. This review has been organized according both to functional (secretion and motility) and disease-related (inflammation, mucosal injury, and neoplasia) effects. The aim of this article is to present a clear summary of this area of gastroenterology so that future research can be directed in a logical and productive manner.

Nonsteroidal anti-inflammatory drug use and sporadic colorectal adenomas

First, and most importantly, the standard of care for treating adenomatous polyps is polypectomy and not therapy with NSAIDs. The initial clinical observation by Waddell and Loughry in 1983 that sulindac treatment influenced rectal polyps in patients with FAP has led to a considerable amount of research, commentary, and discussion during the past decade. These original observations have been validated by controlled clinical trials. Work presented in this issue by Ladenheim et al. indicates that sulindac may not be effective therapy for sporadic polyps that are present before initiation of treatment (secondary prevention). Even though their study may have failed to show a small effect of NSAIDs on polyps, further investigation of the ability of NSAIDs to cause regression of established polyps is probably not warranted. A more clinically relevant question, whether or not these agents can be used in a primary prevention strategy to prevent the development of adenomas in a colon devoid of these lesions, is currently being addressed in a large trial with sufficient statistical power to render firm conclusions (personal communication, January 1995). The multiple reports that sulindac treatment causes regression of adenomas in patients with FAP has stimulated research directed at understanding the molecular basis for these effects. If we are able to understand the molecular mechanism by which NSAIDs decrease the risk of colorectal cancer, we might be able to design more effective drugs or other approaches that would be clinically useful in humans for colorectal cancer chemoprevention.

Nitric oxide modulates gamma-interferon-induced MHC class II antigen expression on rat astrocytes

Brain astroglial cells can be brought in vivo and in vitro to express an immunocompetent cell-like phenotype. We investigated the effect of the NO. releasing compound sodium nitroprusside (SNP) on Ia expression in rat astrocyte cultures. SNP down-regulates, in a concentration-dependent manner, the gamma-interferon-induced Ia expression. Inhibition of the NO. synthesis attenuates the glutamate mediated down-regulation of class II expression. Our results show that NO. is implicated in the immunomodulatory reactions in the brain parenchyma.

Protein kinase C isoform alpha overexpression in C6 glioma cells and its role in cell proliferation

Previous studies from this laboratory have demonstrated that protein kinase C (PKC) enzyme activity is highly correlated with the proliferation rate of glioma cells, and that glioma cells of both human and rat origin have very high PKC enzyme activity when compared to non-malignant glia including astrocytes, the antecedents of most gliomas. In the present study, by contrasting the rat C6 glioma cells with non-malignant rat astrocytes, we have sought to determine whether the high PKC enzyme activity of glioma cells was due to the overexpression of a specific isoform of PKC. By Western blot analyses, both C6 glioma cells and astrocytes were found to express PKC alpha, beta, delta, epsilon and zeta, but not gamma. Enzyme activity measurements revealed that the elevated PKC activity of glioma cells compared to glia was calcium-dependent, thereby implicating abnormal activity of the alpha or beta isoforms. On Western blots, when compared to astrocytes, glioma cells were determined to overexpress PKC alpha but not beta. An antisense oligonucleotide to PKC alpha, directed at the site of initiation of translation, inhibited the proliferation rate of glioma cells when compared to cells treated with control oligonucleotides; PKC enzyme activity and PKC alpha protein expression were significantly reduced by the antisense treatment. These results suggest that the high PKC enzyme activity of glioma cells, and its correspondence with proliferation rate, is the result of overexpression of isozyme alpha. Targetting PKC alpha in glioma cells may provide a refinement of therapy of glioma patients, some of which are already showing clinical stabilization when treated with drugs with PKC-inhibitory effects.

Cytokine network in the central nervous system and its roles in growth and differentiation of glial and neuronal cells

Cells resident within the central nervous system (CNS) can synthesize, secrete and respond to inflammatory cytokines not only contributing to the responses to injury or immunological challenge within the CNS, but also regulating their own growth and differentiation potential. The actions and cell communication via cytokines in the CNS are designated as the CNS cytokine network, in which microglia and astrocytes play the central roles. To further characterize the CNS cytokine network we investigated the differences in roles of these cells, and found that microglia might contribute to the early phase of cytokine production reaction and that astrocytes might contribute the late phase of the reaction. We also investigated roles of inhibitory cytokines such as TGF beta, IL-4, and IL-10, and showed that each might play a distinct role in the inhibitory regulation in the CNS. We summarized our previous report about cellular distribution of cytokine receptors in the CNS cells and discussed their roles in the CNS cytokine network. Finally, we investigated that expression of IL-6 and IL-2 receptors in neuronal and oligodendrocytic differentiation, respectively. From these results, we discussed the features of the CNS cytokine network.

Up-regulation of cyclooxygenase 2 gene expression in human colorectal adenomas and adenocarcinomas

BACKGROUND/AIMS

Several clinical, epidemiological, and animal studies indicate that nonsteroidal anti-inflammatory drugs (NSAIDs) may alter the incidence of colorectal cancer. A likely target for NSAIDs is cyclooxygenase, a key enzyme in arachidonic acid metabolism. Two isoforms of this enzyme have been identified; cyclooxygenase (COX) 1 and COX-2. The present study was undertaken to determine if there is differential expression of these isoforms in colorectal neoplasia, and, if so, at what stage in malignant transformation this occurs.

METHODS

COX-1 and COX-2 messenger RNA (mRNA) levels were determined by Northern blot analysis of poly(A)+ RNA isolated from human colorectal cancers, adenomas, and accompanying normal mucosa.

RESULTS

There was a marked increase in COX-2 mRNA levels in 12 of 14 carcinomas (86%) compared with paired normal mucosa. In contrast, there was equivalent intensity of the COX-1 mRNA transcript between the normal mucosa and cancer in all 14 cases. In six pairs of colorectal adenomas and normal mucosa, three showed up-regulation of COX-2 in the adenoma compared with the normal mucosa. Because COX-2 expression is low to undetectable in normal colorectal mucosa, 14 unpaired adenomas were examined for COX-2 expression; a clearly detectable transcript was identified in six (43%).

CONCLUSIONS

COX-2, but not COX-1, gene expression is markedly elevated in most human colorectal cancers compared with accompanying normal mucosa. Furthermore, COX-2 expression seems to be increased in a subset of adenomas. COX-2 may provide an attractive therapeutic target in colorectal neoplasia.

Immunohistochemical investigation of hypoxic/ischemic brain damage in forensic autopsy cases

A neuropathological study of 41 forensic autopsy cases of hypoxic/ischemic brain damage has been undertaken, using immunohistochemical staining to detect the 70-kDa heat shock protein (hsp70) and the status of the glial cells. In cases surviving 2-5 h after hypoxic/ischemic injury, ischemic cell changes were seen whereas glial reactions were not apparent. In cases of longer survival, neuronal necrosis and a loss of neurons were seen, and these changes were accompanied by proliferation of glial fibrillary acidic protein (GFAP), vimentin-positive astrocytes and microglia which transformed into rod cells or lipid-laden macrophages. In cases with a history of hypoxic attacks, GFAP-positive and vimentin-negative astrocytes had proliferated in the CA3 and CA4 regions of hippocampus. The cases of severe hypoxic injury, such as an asthmatic attack and choking, showed no ischemic changes in the hippocampal neurons. On the other hand, the CA1 pyramidal cells showed neuronal necrosis in a patient suffering from tetralogy of Fallot (TOF), who survived for 2 h after a traffic accident. Therefore, it is suggested that even moderate hypoxic injury induces astrocytosis in the CA3 and CA4 regions and may affect the neuronal proteins and the metabolism, and that in cases with a history of hypoxic attacks neuronal damage may be severe even several hours after ischemic injury. The protein hsp70 expression was found in the CA2, CA3 and CA4 regions in cases of long-term survival after severe hypoxic/ischemic injury and in cases of alcoholic intake or toluene abuse just before acute death.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of cytokine receptors in cultured neuronal and glial cells

We investigated mRNA expression of cytokine receptors in three different types of glial cells and two neuronal line cells by the RT-PCR method. Microglia expressed mRNA for receptors of IL-3, -4, -6, -7, GM-CSF, and M-CSF. Astrocytes were positive for receptors of IL-6, -7, GM-CSF, and M-CSF. Oligodendrocytes were positive for receptors of IL-3, -4, -7, GM-CSF, and M-CSF. Neuronal cells expressed receptors of IL-6 and GM-CSF with very low levels. This is the first demonstration of cytokine receptor mRNA expression in isolated glial and neuronal cells.