Soluble oligomers of the amyloid β-protein impair synaptic plasticity and behavior

During the last 25 years, neuropathological, biochemical, genetic, cell biological and even therapeutic studies in humans have all supported the hypothesis that the gradual cerebral accumulation of soluble and insoluble assemblies of the amyloid beta-protein (A beta) in limbic and association cortices triggers a cascade of biochemical and cellular alterations that produce the clinical phenotype of Alzheimer's disease (AD). The reasons for elevated cortical A beta 42 levels in most patients with typical, late-onset AD are unknown, but based on recent work, these could turn out to include augmented neuronal release of A beta during some kinds of synaptic activity. Elevated levels of soluble A beta 42 monomers enable formation of soluble oligomers that can diffuse into synaptic clefts. We have identified certain APP-expressing cultured cell lines that form low-n oligomers intracellularly and release a portion of them into the medium. We find that these naturally secreted soluble oligomers - at picomolar concentrations - can disrupt hippocampal UP in slices and in vivo and can also impair the memory of a complex learned behavior in rats. A beta trimers appear to be more potent in disrupting UP than are dimers. The cell-derived oligomers also decrease dendritic spine density in organotypic hippocampal slice cultures, and this decrease can be prevented by administration of A beta antibodies or small-molecule modulators of A beta aggregation. This therapeutic progress has been accompanied by advances in imaging the A beta deposits non-invasively in humans. A new diagnostic-therapeutic paradigm to successfully address AD and its harbinger, mild cognitive impairment-amnestic type, is emerging. (C) 2008 Elsevier B.V. All rights reserved.