Journal
JOURNAL OF NEUROSCIENCE
Volume 37, Issue 1, Pages 152-163Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.1698-16.2016
Keywords
beta 2-adrenergic receptor; A beta aggregation; Alzheimer's; long-term potentiation; microglia activation; size-exclusion chromatography
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Funding
- National Institute on Aging [AG006173, AG015379, AG046275]
- Marr Family Fund at Brigham and Women's Hospital
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Soluble oligomers of amyloid beta-protein (oA beta) isolated from the brains of Alzheimer's disease (AD) patients have been shown experimentally (in the absence of amyloid plaques) to impair hippocampal synaptic plasticity, decrease synapses, induce tau hyperphosphorylation and neuritic dystrophy, activate microglial inflammation, and impair memory in normal adult rodents. Nevertheless, there has been controversy about what types of oligomers actually confer these AD-like phenotypes. Here, we show that the vast majority of soluble A beta species obtained from brains of humans who died with confirmed AD elute at high molecular weight (HMW) on nondenaturing size-exclusion chromatography. These species have little or no cytotoxic activity in several bioassays. However, incubation of HMW oA beta in mildly alkaline buffer led to their quantitative dissociation into low molecular weight oligomers (similar to 8-70 kDa), and these were now far more bioactive: they impaired hippocampal LTP, decreased neuronal levels of beta 2-adrenergic receptors, and activated microglia in wt mice in vivo. Thus, most soluble A beta assemblies in AD cortex are large and inactive but under certain circumstances can dissociate into smaller, highly bioactive species. Insoluble amyloid plaques likely sequester soluble HMW oligomers, limiting their potential to dissociate. We conclude that conditions that destabilize HMW oligomers or retard the sequestration of their smaller, more bioactive components are important drivers of A beta toxicity. Selectively targeting these small, cytotoxic forms should be therapeutically beneficial.
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