Cyclooxygenase-2 inhibition improves amyloid-β-mediated suppression of memory and synaptic plasticity
1Department of Neurology, University of Minnesota, Minneapolis, MN 55455, USA, 2Department of Physiology, Trinity College, Dublin, Republic of Ireland, 3Departments of Medicine and Neurology, UCLA &GLAS, GRECC, VA Hospital, Sepulveda, CA 91343, USA, 4Neuroscience Department, University of Wales College of Cardiff, Cardiff CF1 3US, UK, 5Biochemistry Department, University of Missouri, Columbia, MO 65212, 6Mayo Clinic Jacksonville, Jacksonville FL 32224 and 7GRECC, Minneapolis VA Hospital, Minneapolis, MN 55417, USA
Correspondence to: Karen H. Ashe, MD, PhD, Department of Neurology, MMC 295, 420 Delaware Street SE, University of Minnesota, Minneapolis, MN 55455, USA E-mail: hsiao005{at}umn.edu
Non-steroidal anti-inflammatory agents (NSAIDs) are associated with a marked reduction in the risk of developing Alzheimer's disease, a form of dementia characterized by the accumulation of amyloid plaques containing the amyloid-β protein (Aβ). Studies of the effects of NSAIDs upon the inflammatory response surrounding amyloid plaques and upon the generation of Aβ from the amyloid precursor protein (APP) have led to two proposed mechanisms by which NSAIDs may protect against Alzheimer's disease: one, the selective lowering of Aβ42 by a subset of NSAIDs; and two, the reduction of inflammation. Although Alzheimer's disease is a disorder of brain and synaptic function, the effects of NSAIDs on Aβ-mediated suppression of synaptic plasticity and memory function have never been reported. We therefore investigated how three different NSAIDs, chosen for their distinct effects on Aβ42 production and the inhibition of the cyclooxygenase (COX) isoenzymes, COX-1 and COX-2, affect memory function and synaptic plasticity. By focusing upon brain and synapse function, we made novel observations about the effects of NSAIDs on Aβ-mediated neural processes. Here we report that the selective inhibition of COX-2, but not COX-1, acutely prevented the suppression of hippocampal long-term plasticity (LTP) by Aβ. The non-selective NSAIDs, ibuprofen and naproxen, and a selective COX-2 inhibitor, MF-tricyclic, each restored memory function in Tg2576 mice over-expressing APP, and also blocked Aβ-mediated inhibition of LTP. There was no advantage of ibuprofen, a selective Aβ42-lowering agent (SALA), over the non-SALAs, naproxen and MF-tricyclic. The beneficial effects on memory did not depend upon lowered levels of Aβ42 or the inflammatory cytokines, tumour necrosis factor 
(TNF-) and interleukin 1β (IL-1β). Intriguingly, improved memory function was inversely related to prostaglandin E2 (PGE2) levels. Conversely, exogenous PGE2 prevented the restorative effects of COX-2 inhibitors on LTP. The data indicate that the inhibition of COX-2 blocks Aβ-mediated suppression of LTP and memory function, and that this block occurs independently of reductions in Aβ42 or decreases in inflammation. The results lead us to propose a third possible mechanism by which NSAIDs may protect against Alzheimer's disease, involving the blockade of a COX-2-mediated PGE2 response at synapses.
Key Words: NSAIDs; inflammation; transgenic; memory; synaptic plasticity
Abbreviations:
APP, amyloid precursor protein; Aβ, amyloid-β protein; COX-1 and COX-2, cyclooxygenase isoenzymes; IL-1β, interleukin 1β; LTP, long-term plasticity; MPS, mean probe score; NSAIDs, Non-steroidal anti-inflammatory agents; PGE2, prostaglandin E2; SALA, selective Aβ42-lowering agent; TNF-, tumour necrosis factor .
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Received May 17, 2007. Revised October 31, 2007. Accepted January 10, 2008.
*These authors contributed equally to this work.
Present Address: Department of Physiology, Medical School, Ningbo University, Ningbo 315211, China