title: cAMP-Inhibits Cytoplasmic Phospholipase A₂ and Protects Neurons against Amyloid-β-Induced Synapse Damage.
abstract: A key event in Alzheimer's disease (AD) is the production of amyloid-β (Aβ) peptides and the loss of synapses. In cultured neurons Aβ triggered synapse damage as measured by the loss of synaptic proteins. α-synuclein (αSN), aggregates of which accumulate in Parkinson's disease, also caused synapse damage. Synapse damage was associated with activation of cytoplasmic phospholipase A₂ (cPLA₂), an enzyme that regulates synapse function and structure, and the production of prostaglandin (PG) E₂. In synaptosomes PGE₂ increased concentrations of cyclic adenosine monophosphate (cAMP) which suppressed the activation of cPLA₂ demonstrating an inhibitory feedback system. Thus, Aβ/αSN-induced activated cPLA₂ produces PGE₂ which increases cAMP which in turn suppresses cPLA₂ and, hence, its own production. Neurons pre-treated with pentoxifylline and caffeine (broad spectrum phosphodiesterase (PDE) inhibitors) or the PDE4 specific inhibitor rolipram significantly increased the Aβ/αSN-induced increase in cAMP and consequently protected neurons against synapse damage. The addition of cAMP analogues also inhibited cPLA₂ and protected neurons against synapse damage. These results suggest that drugs that inhibit Aβ-induced activation of cPLA₂ and cross the blood-brain barrier may reduce synapse damage in AD.
authors.affiliation: Department of Pathology and Pathogen Biology, Royal Veterinary College, Hawkshead Lane, North Mymms, Herts AL9 7TA, UK. cbate@rvc.ac.uk.
authors.forename: Clive
authors.initials: C
authors.lastname: Bate
authors.affiliation: Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 OES, UK. aw510@cam.ac.uk.
authors.forename: Alun
authors.initials: A
authors.lastname: Williams
keywords: Alzheimer’s disease; amyloid; cAMP; phosphodiesterase; phospholipase A2; prostaglandin E2; synapses