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Cyclooxygenases-1 and -2 are differentially localized to microglia and endothelium in rat EAE and glioma

https://doi.org/10.1016/S0165-5728(98)00257-4Get rights and content

Abstract

Cyclooxygenases (COX) mediate a wide variety of derangements observed during diseases of the brain. Their overexpression is involved in the mediation of inflammation, immunomodulation, blood flow, apoptosis and fever. Here, we have analyzed the localization of COX-1 and COX-2 in rat experimental autoimmune encephalomyelitis (EAE), C6 glioblastoma and 9L gliosarcoma by immunohistochemistry. In healthy brain, COX-1 was expressed in single macrophages/microglial cells. Neurons and few endothelial cells expressed COX-2. In EAE, we observed an increase in COX-1+ macrophages/microglial cells and COX-2+ endothelial cells that was closely linked to disease progression. Both COX-1+ macrophages/microglial cells and COX-2+ endothelial cells were abundant in areas of cellular infiltration. In C6 and 9L tumors, high numbers of COX-1+ macrophages/microglial cells and COX-2+ endothelial cells were found both in the tumor parenchyma and in areas of infiltrative tumor growth. Double labeling experiments confirmed expression of COX-2 in vWF+ (endothelial) cells and COX-1 in ED1+ (macophages), OX6+ (MHC class II) and in W3/13+ (lymphoblasts) cells. These data provide further evidence that expression of COX-1 in macrophages/microglial cells and COX-2 in endothelial cells might represent important regulatory mechanisms in inflammatory processes associated with autoimmunity and neoplasia of the rat brain.

Introduction

Cyclooxygenases (COX, prostaglandin endoperoxide synthases, PGG/H synthases) catalyze the synthesis of the eicosanoid prostaglandin metabolites PGG2 and PGH2 which are metabolized to PGE2, PGD2 and PGF, the thromboxane TXA2, or the functional antagonist of TXA2, PGI2 (prostacyclin) (Samuelsson, 1976; Funk et al., 1991). Two cyclooxygenase isoforms, COX-1 and COX-2, have been described (Hla and Neilson, 1992). While constitutive COX-1 expression is associated with physiological eicosanoid production, COX-2 is cytokine-inducible following proinflammatory stimuli. Constitutively expressed eicosanoids exert differerential housekeeping effects in hematopoiesis (Moore et al., 1990), the kidney (Yun et al., 1984), smooth muscle (Sanders, 1978) and the gut (Davies and Rampton, 1997). These include the regulation of blood perfusion (Gerritsen, 1996) and modulation of the immune system (Phipps et al., 1990).

In a wide variety of diseases of the brain, induction of COX-2 expression is associated with complex pathophysiological derangements. Cerebral ischemia causes upregulation of COX-2 message, protein and reaction products in the injured hemispheres (Nogawa et al., 1997) and prostaglandins contribute at least in part to the vascular damage evoked by brain trauma (Ellis et al., 1989). COX-2 modulates HIV-induced encephalitis (Bagetta et al., 1998), inflammation (Lacroix and Rivest, 1998) and Alzheimer's disease (Lukiw and Bazan, 1997), and inhibitors of cyclooxygenase function suppress the effector phase of active EAE (Simmons et al., 1992). Furthermore, COX-2 expression modulates tumor growth. In colorectal cancer, COX-2 regulates angiogenesis (Tsujii et al., 1998), apoptosis (Tsujii and DuBois, 1995) and cell adhesion (Tsujii et al., 1997). Inhibitors of eicosanoid biosynthesis suppress proliferation in glioblastoma cells (Wilson et al., 1990). Although more complex eicosanoid effects are described, evidence accumulates that induction of COX-2 expression in brain blood vessels following pyogenic stimuli predominantly constitutes a mechanism to promote the development of fever (Cao et al., 1995; Breder and Saper, 1996).

In order to provide a pathophysiological basis for the involvement of cyclooxygenases in autoimmunity and neoplasia of the rat brain, we analyzed COX-1 and COX-2 expression in EAE, C6 glioblastoma and 9L gliosarcoma by immunohistochemistry.

Section snippets

C6 and 9L cell culture and transplantation

Rat C6 glioblastoma and 9L gliosarcoma cell lines were obtained from the American Type Culture Collection (ATCC, Manassas, USA) and raised in RPMI 1640 medium with Glutamax II (Gibco BRL, Paisley, Great Britain) containing 10% fetal calf serum (FCS, Gibco BRL, Paisley, Great Britain) and 1.2% penicillin/streptomycin (Fluka, Buchs, Switzerland) at 37°C and 5% CO2. Cells were implanted intracranially as described (Deininger et al., 1998a). Briefly, cells were harvested and 5 μl of cell suspension

Healthy brain

In healthy rat brain, COX-1 was expressed in a minor subset of cells with morphological characteristics of macrophages/microglial cells like elongations and dendritic protrusions. Single COX-1+ cells were disseminated throughout the entire brain (Fig. 1A). Occasionally, COX-1 immunoreactivity was observed in neurons. COX-2 immunoreactivity was identified in clustered accumulations of neurons in the forebrain areas of all control rats and in single endothelial cells. COX-2+ neurons were

Discussion

In the healthy rat brains, we observed immunoreactivity of COX-1 in single disseminated macrophages/microglial cells and in few neurons. COX-2 expression was detected in grouped accumulations of neurons and single endothelial cells. In EAE, there was a marked increase of COX-1+ macrophages/microglial cells and of COX-2+ endothelial cells that paralleled the extent of perivascular cellular infiltration. In C6 glioblastomas and 9L gliosarcomas, a marked accumulation of COX-1+

Acknowledgements

Supported by a grant from the Federal Ministry of Education, Science, Research and Technology (Fö 01KS9602) and the Interdisciplinary Clinical Research Center (IKFZ) Tübingen. We wish to thank Thai Dung Nguyen for expert technical support.

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