Effects of different amyloid β-protein analogues on synaptic function

Perisynaptic accumulations of amyloid beta-protein (A beta) play a critical role in the synaptic dysfunction underlying the cognitive impairment observed in Alzheimer's disease. The methionine residue at position 35 (Met35) in A beta is highly subject to oxidation in Alzheimer's disease brains. In hippocampal brain slices we found that long-term potentiation at CA3-CA1 synapses was significantly inhibited by wild type A beta 42 in which Met35 is reduced, but not by A beta 42 harboring Met35 sulfoxide. Similar differences were observed when basal synaptic transmission was investigated in autaptic hippocampal neurons. The significant decreases in excitatory postsynaptic current amplitude, vesicle release probability and miniature excitatory postsynaptic current frequency caused by 20-minute exposure to wild type A beta 42 were not observed after exposure to A beta 42 harboring Met35 sulfoxide. With longer (24-hour) A beta treatments, this early impairment of the presynaptic terminal function extended to involve the postsynaptic side as well. The Met35 oxidation also affected A beta 42 negative impact on dendritic spine density and expression of pre- and postsynaptic proteins (synaptophysin and postsynaptic density protein-95). Our findings suggest that oxidation of Met35 is critical for molecular, structural, and functional determinants of A beta 42 synaptotoxicity. (C) 2013 Elsevier Inc. All rights reserved.