Intraparenchymal administration of interleukin-1β induces cyclooxygenase-2-mediated expression of membrane- and cytosolic-associated prostaglandin E synthases in mouse brain

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Abstract

Interleukin (IL)-1β is a proinflammatory cytokine expressed in neural tissue following injury and in neurodegenerative states. To understand the consequences of its presence in brain, we carried out intraparenchymal IL-1β injections and found significant increases in prostaglandin (PG)E2, a critical factor in inflammatory and physiological processes. Elevated mRNA and protein expression of the PGE2-synthetic-related enzymes cyclooxygenase (COX)-2 and membrane-associated PGE synthase (PGES) accompanied local PGE2 production. In addition, IL-1β stimulated protein expression of cytosolic PGES. Finally, we showed attenuation of these IL-1β-inductions by COX-2 inhibition, suggesting in vivo regulation of both PGE synthase isoforms in the brain.

Introduction

Inflammation-related changes are a prominent part of the CNS response to acute injury, infection, and disease. A variety of studies indicate that attenuation of CNS inflammation may be beneficial in the treatment of ischemic injury (Danton and Dietrich, 2003), traumatic injury (Hurley et al., 2002), and certain neurodegenerative disorders (Maida and O'Banion, 2001), including Alzheimer's disease (AD) (Moore and O'Banion, 2002). Among numerous molecules upregulated in the AD brain, proinflammatory cytokine interleukin (IL)-1β is recognized as a significant factor in the initiation and propagation of neuroinflammation (Mrak and Griffin, 2001).

IL-1β stimulates expression of several inflammation-related molecules, including cyclooxygenase (COX)-2, one of two isoforms of the obligate enzyme for prostaglandin biosynthesis (O'Banion et al., 1992). COX-2 is recognized as a major contributor to peripheral inflammatory processes and its selective inhibition has become a mainstay therapy for rheumatoid and osteo-arthritis FitzGerald and Patrono, 2001, Mitka, 2002. Of the prostaglandins generated by COX-2 activity, prostaglandin (PG)E2 appears to be the principal mediator of peripheral inflammation (Portanova et al., 1996). We now know that COX-2 is produced in brain and is induced by IL-1β and other proinflammatory cytokines in astrocytes, microglia and endothelial cells in the central nervous system (CNS) Minghetti et al., 1999, Cao et al., 1996, O'Banion et al., 1996. Moreover, we have recently found that selective inhibition of COX-2 attenuates the expression of inflammation-related genes and the acute synthesis of PGE2 following whole brain irradiation and stab injury Kyrkanides et al., 2002, O'Banion et al., 2002.

Tissue-specific isomerases convert PGH2, the immediate product of COX activity, to terminal prostanoids, providing a critical point of regulation downstream from COX. Interest in selectively inhibiting production of PGE2, the principle inflammatory prostanoid, has been heightened by recognition of at least two PGE2 synthase (PGES) isoforms that are reportedly coupled to distinct COX isoforms in vitro. More specifically, a membrane-associated isoform (mPGES-1) is functionally coupled to COX-2, whereas a cytosolic enzyme (cPGES/p23) appears to be linked to COX-1-dependent PGE2 production Jakobsson et al., 1999, Murakami et al., 2000, Tanioka et al., 2000. In vivo studies support the inducible nature of COX-2 and mPGES-1 by demonstrating co-localization of these enzymes in IL-1β-stimulated endothelial cells (Ek et al., 2001) and lipopolysaccharide (LPS)-induced peritoneal macrophages (Lazarus et al., 2002). Furthermore, mPGES-1-null mice show decreased PGE2 production in LPS-stimulated peritoneal macrophages Trebino et al., 2003, Uematsu et al., 2002 and reduced paw edema formation and white blood cell infiltration following antigen injection (Trebino et al., 2003), confirming the role of this enzyme in inflammatory responses. Recently, Claveau et al. (2003) reported increased protein expression of both mPGES-1 and cPGES/p23 in a rat model of adjuvant-induced arthritis. This evidence of PGE synthase regulation suggests potential therapeutic targets that would not interfere with the production of other COX-related products that are necessary for recovery-related and homeostatic processes.

To determine the consequence of IL-1β on members of the PGE2 synthesizing pathway, we administered murine recombinant IL-1β into the mouse cortex via intraparenchymal microinjection. We observed a robust increase in PGE2 tissue concentration that correlated with an increase in enzyme gene and protein expression. Using pharmacological inhibition of COX-2 activity, we found modulation of cPGES/p23 protein expression that has not been previously reported, suggesting a novel level of regulation following pro-inflammatory stimuli in the central nervous system.

Section snippets

Subjects and surgical procedures

Male C57/BL6 mice, 6–8 weeks of age (Jackson Laboratories) were used for this study (n=108). Surgical anesthesia was induced in mice by means of intraperitoneal (i.p.) injection of Avertin (300 mg/kg of the active agent 2,2,2-tribromoethanol). Under a surgical plane of anesthesia, mice were placed in a David Kopf stereotaxic apparatus and a longitudinal incision of the soft skull tissues was made to expose bregma and lambda sutures that served as landmarks. Under visualization with a Nikon

Intracerebral administration of IL-1β stimulates acute PGE2 production

To determine if intraparenchymal delivery of murine recombinant IL-1β affected local prostaglandin synthesis, PGE2 was measured at 6 and 24 h post-microinjection in cortical tissue surrounding the injection site using enzyme immunoassay. PGE2 levels in sham animals (n=6) ranged from 3.4 to 8.5 pg/mg with a mean of 7.0±0.6 pg/mg. Vehicle-injected animals at 6 h (n=6; 7.0±0.5 pg/mg) and at 24 h (n=6; 7.4±2.2 pg/mg) post-injection were not significantly different from sham animals. However, IL-1β

Discussion

IL-1β is a proinflammatory cytokine that is produced by activated resident glia and implicated in numerous pathological and neurodegenerative states such as brain injury, fever and Alzheimer's disease. For instance, elevated IL-1β expression is found in activated microglia associated with beta-amyloid (Aβ) plaques (for review, see Moore and O'Banion, 2002) and brain injury (Wang and Schuaib, 2002). Local elevation of IL-1β initiates a cascade of events through activation of IL-1R1 as well as

Acknowledgments

The authors would like to thank Dr. Mary Maida, Sharon Paige and Joanna Daeschner for their scientific efforts and support. This research was funded by NIH NS33553.

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    Current address: Department of Biology, Santa Clara University, 500 El Camino Real, Santa Clara, CA 95053, USA.

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