Increased cholesterol in Aβ-positive nerve terminals from Alzheimer's disease cortex

Synapse loss in Alzheimer's disease (AD) is poorly understood but evidence suggests it is a key pathological event. In order to precisely detect stable synaptic changes, we have developed methods for flow cytometry analysis of synaptosomes prepared from cryopreserved AD samples, and have previously shown that amyloid-β (Aβ) accumulates in surviving presynaptic terminals in AD cortex. In the present experiments we have examined amyloid-containing terminals in more detail, first dual labeling synaptosomes from AD cortex for Aβ and a series of markers, and then using quadrant analysis to compare amyloid-positive and amyloid-negative terminals. Amyloid-positive synaptosomes were larger in size than amyloid-negatives (p < 0.007), and significant increases were observed in mean fluorescence for the lipid raft markers cholesterol (27%; p < 0.0005) and GM1 ganglioside (24%; p < 0.005). SNAP-25 immunofluorescence was increased by 31% (p < 0.0001) in amyloid-bearing terminals, consistent with a sprouting response to amyloid accumulation. These results suggest that Aβ accumulation in synaptic terminals may underly dysfunction prior to or independent of extracellular amyloid deposition.