ABSTRACT
BACKGROUND AND PURPOSE: Although microsomal prostaglandin E synthase (mPGES)-1 is known to contribute to stroke injury, the underlying mechanisms remain poorly understood. This study examines the hypothesis that EP(3) receptors contribute to stroke injury as downstream effectors of mPGES-1 neurotoxicity through Rho kinase activation. EXPERIMENTAL APPROACH: We used a glutamate-induced excitotoxicity model in cultured rat and mouse hippocampal slices and a mouse middle cerebral artery occlusion-reperfusion model. Effects of an EP(3) receptor antagonist on neuronal damage in mPGES-1 knockout (KO) mice was compared with that in wild-type (WT) mice. KEY RESULTS: In cultures of rat hippocampal slices, the mRNAs of EP(1-4) receptors were constitutively expressed and only the EP(3) receptor antagonist ONO-AE3-240 attenuated and only the EP(3) receptor agonist ONO-AE-248 augmented glutamate-induced excitotoxicity in CA1 neurons. Hippocampal slices from mPGES-1 KO mice showed less excitotoxicity than those from WT mice and the EP(3) receptor antagonist did not attenuate the excitotoxicity. In transient focal ischaemia models, injection (i.p.) of an EP(3) antagonist reduced infarction, oedema and neurological dysfunction in WT mice, but not in mPGES-1 KO mice, which showed less injury than WT mice. EP(3) receptor agonist-induced augmentation of excitotoxicity in vitro was ameliorated by the Rho kinase inhibitor Y-27632 and Pertussis toxin. The Rho kinase inhibitor HA-1077 also ameliorated stroke injury in vivo. CONCLUSION AND IMPLICATIONS: Activity of mPGES-1 exacerbated stroke injury through EP(3) receptors and activation of Rho kinase and/or G(i). Thus, mPGES-1 and EP(3) receptors may be valuable therapeutic targets for treatment of human stroke.
Subject(s)
Brain Ischemia/physiopathology , Intramolecular Oxidoreductases/metabolism , Microsomes/enzymology , Receptors, Prostaglandin E/metabolism , Signal Transduction , Animals , Brain Edema/drug therapy , Brain Edema/prevention & control , Brain Ischemia/drug therapy , Brain Ischemia/metabolism , CA1 Region, Hippocampal/drug effects , CA1 Region, Hippocampal/metabolism , Excitatory Amino Acid Agents/agonists , Excitatory Amino Acid Agents/antagonists & inhibitors , Excitatory Amino Acid Agents/toxicity , Female , In Vitro Techniques , Infarction, Middle Cerebral Artery/drug therapy , Infarction, Middle Cerebral Artery/genetics , Infarction, Middle Cerebral Artery/metabolism , Infarction, Middle Cerebral Artery/physiopathology , Intramolecular Oxidoreductases/genetics , Ischemic Attack, Transient/drug therapy , Ischemic Attack, Transient/metabolism , Ischemic Attack, Transient/physiopathology , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Neurons/drug effects , Neurons/metabolism , Prostaglandin-E Synthases , RNA, Messenger/metabolism , Rats , Rats, Wistar , Receptors, Prostaglandin E/agonists , Receptors, Prostaglandin E/antagonists & inhibitors , Receptors, Prostaglandin E/genetics , Receptors, Prostaglandin E, EP3 Subtype , Reperfusion Injury/drug therapy , Reperfusion Injury/metabolism , Reperfusion Injury/physiopathology , Reperfusion Injury/prevention & control , Signal Transduction/drug effects , rho-Associated Kinases/antagonists & inhibitors , rho-Associated Kinases/metabolismABSTRACT
BACKGROUND AND PURPOSE: Although both microsomal prostaglandin E synthase (mPGES)-1 and cyclooxygenase (COX)-2 are critical factors in stroke injury, but the interactions between these enzymes in the ischaemic brain is still obscure. This study examines the hypothesis that mPGES-1 activity is required for COX-2 to cause neuronal damage in ischaemic injury. EXPERIMENTAL APPROACH: We used a glutamate-induced excitotoxicity model in cultures of rat or mouse hippocampal slices and a mouse middle cerebral artery occlusion-reperfusion model in vivo. The effect of a COX-2 inhibitor on neuronal damage in mPGES-1 knockout (KO) mice was compared with that in wild-type (WT) mice. KEY RESULTS: In rat hippocampal slices, glutamate-induced excitotoxicity, as well as prostaglandin (PG) E(2) production and PGES activation, was significantly attenuated by either MK-886 or NS-398, inhibitors of mPGES-1 and COX-2 respectively; however, co-application of these inhibitors had neither an additive nor a synergistic effect. The protective effect of NS-398 on the excitotoxicity observed in WT slices was completely abolished in mPGES-1 KO slices, which showed less excitotoxicity than WT slices. In the transient focal ischaemia model, mPGES-1 and COX-2 were co-localized in the infarct region of the cortex. Injection of NS-398 reduced not only ischaemic PGE(2) production, but also ischaemic injuries in WT mice, but not in mPGES-1 KO mice, which showed less dysfunction than WT mice. CONCLUSION AND IMPLICATIONS: Microsomal prostaglandin E synthase-1 and COX-2 are co-induced by excess glutamate in ischaemic brain. These enzymes are co-localized and act together to exacerbate stroke injury, by excessive PGE(2) production.
Subject(s)
Brain Ischemia/physiopathology , Cyclooxygenase 2/metabolism , Intramolecular Oxidoreductases/metabolism , Reperfusion Injury/physiopathology , Animals , Brain Ischemia/enzymology , Cyclooxygenase 2/drug effects , Cyclooxygenase 2 Inhibitors/pharmacology , Dinoprostone/metabolism , Disease Models, Animal , Female , Glutamic Acid/metabolism , Hippocampus/metabolism , Intramolecular Oxidoreductases/genetics , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Microsomes/metabolism , Neurons/drug effects , Neurons/pathology , Prostaglandin-E Synthases , Rats , Reperfusion Injury/enzymology , Stroke/enzymology , Stroke/physiopathologyABSTRACT
Hepatocyte growth factor (HGF) promotes the survival and migration of immature neurons, but its role in the mature brain has remained elusive. In the hippocampus of juvenile rats, we found that the HGF receptor c-Met was expressed in neurons. Furthermore, it was highly Tyr-phosphorylated, more so than in the liver under normal conditions, suggesting that the receptor is activated and that HGF may act continuously in the intact brain. Exogenously applied HGF enhanced synaptic long-term potentiation (LTP) in the CA1 region of hippocampus, but did not affect long-term depression. We further found that HGF augmented N-methyl-D-aspartate receptor-mediated currents in both slices and dissociated neurons. This augmentation is likely to underlie the enhancement of LTP. Considering that the expression of both HGF and c-Met are known to be induced by ischemic stimuli, this modulation would provide a novel understanding of a neuronal regulatory systems shared with pathogenic ischemic states.
