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Synapse-Binding Subpopulations of Aβ Oligomers Sensitive to Peptide Assembly Blockers and scFv Antibodies
journal contribution
posted on 2012-11-21, 00:00 authored by Pauline
T. Velasco, Marie C. Heffern, Adriano Sebollela, Izolda A. Popova, Pascale
N. Lacor, Kevin B. Lee, Xiaoxia Sun, Benjamin N. Tiano, Kirsten L. Viola, Amanda L. Eckermann, Thomas
J. Meade, William L. KleinAmyloid β42 self-assembly is complex, with multiple
pathways
leading to large insoluble fibrils or soluble oligomers. Oligomers
are now regarded as most germane to Alzheimer’s pathogenesis.
We have investigated the hypothesis that oligomer formation itself
occurs through alternative pathways, with some leading to synapse-binding
toxins. Immediately after adding synthetic peptide to buffer, solutions
of Aβ42 were separated by a 50 kDa filter and fractions assessed
by SDS-PAGE silver stain, Western blot, immunoprecipitation, and capacity
for synaptic binding. Aβ42 rapidly assembled into aqueous-stable
oligomers, with similar protein abundance in small (<50 kDa) and
large (>50 kDa) oligomer fractions. Initially, both fractions were
SDS-labile and resolved into tetramers, trimers, and monomers by SDS-PAGE.
Upon continued incubation, the larger oligomers developed a small
population of SDS-stable 10–16mers, and the smaller oligomers
generated gel-impermeant complexes. The two fractions associated differently
with neurons, with prominent synaptic binding limited to larger oligomers.
Even within the family of larger oligomers, synaptic binding was associated
with only a subset of these species, as a new scFv antibody (NUsc1)
immunoprecipitated only a small portion of the oligomers while eliminating
synaptic binding. Interestingly, low doses of the peptide KLVFFA blocked
assembly of the 10–16mers, and this result was associated with
loss of the smaller clusters of oligomers observed at synaptic sites.
What distinguishes these smaller clusters from the unaffected larger
clusters is not yet known. Results indicate that distinct species
of Aβ oligomers are generated by alternative assembly pathways
and that synapse-binding subpopulations of Aβ oligomers could
be specifically targeted for Alzheimer’s therapeutics.