Abstract
The deposition of fibrillar alpha-synuclein (α-syn) within inclusions (Lewy bodies and Lewy neurites) in neurons and glial cells is a hallmark of synucleinopathies. α-syn populates a variety of assemblies ranging from prefibrillar oligomeric species to fibrils whose specific contribution to neurodegeneration is still unclear. Here, we compare the specific structural and biological properties of distinct soluble prefibrillar α-syn oligomers formed either spontaneously or in the presence of dopamine and glutaraldehyde. We show that both on-fibrillar assembly pathway and distinct dopamine-mediated and glutaraldehyde-cross-linked α-syn oligomers are only slightly effective in perturbing cell membrane integrity and inducing cytotoxicity, while mature fibrils exhibit the highest toxicity. In contrast to low-molecular weight and unstable oligomers, large stable α-syn oligomers seed the aggregation of soluble α-syn within reporter cells although to a lesser extent than mature α-syn fibrils. These oligomers appear elongated in shape. Our findings suggest that α-syn oligomers represent a continuum of species ranging from unstable low molecular weight particles to mature fibrils via stable elongated oligomers composed of more than 15 α-syn monomers that possess seeding capacity.
Highlights
When α -syn was incubated for 7 days at 4 °C in assembly buffer (50 mM Tris-HCl, pH 7.5, 150 mM KCl) without shaking, a peak emerging from the column with an apparent molecular weight >2200 kDa, representing 25% of total α -syn based on the peak area was observed beside the peak corresponding to monomeric α -syn (Fig. 1a, black solid line)
The observations that α -syn assemblies can be released into the extracellular medium and traffic between neurons[11,39,40] and that α -syn assemblies are detectable in body fluids such as serum and the cerebrospinal fluid of patients developing synucleinopathies[41,42] support the growing idea that extracellular α -syn assemblies play a role in synucleinopathies[43]
For more than a decade, prefibrillar oligomers formed at early stages of α -syn assembly into fibrils have been proposed to be involved in neurodegeneration[44,45,46,47]
Summary
A plethora of studies have described on- or off-fibrillar assembly pathway, toxic or harmless, α -syn oligomeric species (reviewed in34) whose respective contributions to the onset and progression of synucleinopathies have not yet been elucidated. Such information is urgently needed to design therapeutic strategies able to target pathogenic α -syn species slowing down disease progression. We determined the molecular mass of each type of oligomer that we purified to homogeneity by analytical ultracentrifugation (AUC) This allowed us to compare the specific toxicity and seeding properties of distinct α -syn oligomeric species at identical particle concentrations using cultured neuroblastoma SH-SY5Y and Neuro2A cells. This suggests that large soluble α -syn oligomers composed of more than 15–30 molecules arising spontaneously or in the presence of agents such as DA constitute a continuum with fibrillar α -syn and may contribute to some extent to the deleterious processes triggered by fibrillar α -syn
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
