Isolation of synaptic terminals from Alzheimer's disease cortex

Amyloid beta (A beta) oligomers and phosphorylated tau (p-tau) aggregates are increasingly identified as potential toxic intermediates in Alzheimer's disease (AD). In cortical AD synapses, p-tau co-localizes with A beta, but the A beta and p-tau peptide species responsible for synaptic dysfunction and demise remains unclear. The present experiments were designed to use high-speed cell sorting techniques to purify synaptosome population based on size, and then extend the method to physically isolate A beta-positive synaptosomes with the goal of understanding the nature of A beta and tau pathology in AD synapses. To examine the purity of size-gated synaptosomes, samples were first gated on size; particles with sizes between 0.5 and 1.5 microns were collected. Electron microscopy documented a homogenous population of spherical particles with internal vesicles and synaptic densities. Next, size-gated synaptosomes positive for A beta were collected by fluorescence activated sorting and then analyzed by immunoblotting techniques. Sorted A beta-positive synaptosomes were enriched for amyloid precursor protein (APP) and for A beta oligomers and aggregates; immunolabeling for p-tau showed a striking accumulation of p-tau aggregates compared to the original homogenate and purified synaptosomes. These results confirm co-localization of A beta and p-tau within individual synaptic terminals and provide proof of concept for the utility of flow sorting synaptosomes. (C) 2011 International Society for Advancement of Cytometry