The role of TNF-α signaling pathway on COX-2 upregulation and cognitive decline induced by β-amyloid peptide

Alzheimer's disease (AD), a chronic degenerative and inflammatory brain disorder characterized by neuronal dysfunction and loss, is linked to accumulation of beta-amyloid (A beta) peptide. Tumor necrosis factor-alpha (TNF-alpha) and cyclooxygenase-2 (COX-2) are proteins that have key roles in immune cell activation, inflammation and cognitive function in the brain. Here, we evaluated the link between TNF-alpha and COX-2 on the acute responses elicited by A beta. Behavioral and molecular analyses were performed in mice after an intracerebroventricular (i.c.v.) injection of A beta(1-40). Genetic and/or pharmacological approaches were used to inhibit TNF-alpha and COX-2. i.c.v. A beta(1-40) injection in mice activates TNF-alpha signaling pathway resulting in COX-2 upregulation, synaptic loss and cognitive decline. Pharmacological studies revealed that COX-2 is involved in the cognitive impairment mediated by TNF-alpha. However, COX-2 inhibition failed in reducing the synaptophysin loss induced by A beta(1-40). The COX-2 upregulation induced by A beta(1-40) was attributed to activation of different protein kinases and transcriptional factors that are greatly regulated by TNF-alpha. Together, these results indicate that A beta(1-40) induces the activation of several TNF-alpha-dependent intracellular signaling pathways that play a key role in the control of COX-2 upregulation and activation, synaptic loss and cognitive decline in mice. Therefore, selective TNF-alpha inhibitors may be potentially interesting tools for AD drug development. (C) 2010 Elsevier B.V. All rights reserved.