α-synuclein fibril and synaptic vesicle interactions lead to vesicle destruction and increased uptake into neurons

Abstract

Monomeric alpha-synuclein (aSyn) is a well characterised as a lipid binding protein. aSyn is known to form amyloid fibrils which are also localised with lipids and organelles in so called Lewy bodies, insoluble structures found in Parkinson s disease patient s brains. It is still unclear under which conditions the aSyn-lipid interaction can start to become pathological. Previous work to address pathological interactions has focused on using synthetic lipid membranes, which lack the complexity of physiological lipid membranes which not only have a more complex lipid composition, but also contain lipid interacting proteins. Here, we investigate how either monomeric or fibrillar aSyn interact with physiological synaptic vesicles (SV) isolated from rodent brain. Using small angle neutron scattering and high-resolution imaging we observe that aSyn fibrils disintegrate SV, whereas aSyn monomers cause clustering of SV. Furthermore, SV enhance the aggregation rate of aSyn, however increasing the SV:aSyn ratio causes a reduction in aggregation propensity. SV lipids appear as an integrated part of aSyn fibrils and while the fibril morphology differs to aSyn fibrils alone, the core fibril structure remains the same. We finally demonstrate that lipid-associated aSyn fibrils are more easily taken up into cortical i3Neurons derived from induced pluripotent stem cells. Our study sheds light on differences between interactions of aSyn with synthetic lipid vesicles and physiological SV. We show how aSyn fibrils may enhance pathology by disintegrating SV, which in turn may have fatal consequences for neurons. Furthermore, disease burden may additionally be impacted by an increased uptake of lipid-associated aSyn by neurons, leading to more SV damage and enhancing aSyn aggregation.

Residues 2-7 of α-synuclein regulate amyloid formation via lipid-dependent and -independent pathways

“…We have shown that amyloid formation of αSynΔN7 is not stimulated by liposome binding (Fig. 4), in marked contrast to αSynWT, wherein lipid acts as a substrate for its assembly into amyloid, with the fibril yield and rate of assembly depending on the LPR (33–35). Lipids can become integrated into the core of the cross-β amyloid fold (33), being clearly observed in the cryo-EM structures of the resulting fibrils (36).…”

“…Binding of αSyn to membranes is not only important for its physiological function, but may also be critical in terms of the pathological mechanism of aggregation and Lewy body formation. Lipid membranes can trigger αSyn amyloid fibril formation (32–35), and lipids are incorporated into the fibril structures (35, 36). Together with evidence that lipids are a major component of Lewy bodies (37), this suggests that lipid-catalysed amyloid fibril formation may be involved in the aetiology of synucleinopathies.…”

α-Synuclein propagation leads to synaptic abnormalities in the cortex through microglial synapse phagocytosis

“…These studies have revealed that exogenous α-synuclein induces Lewy body pathology and lead to a decrease in synaptic protein, reduced synaptic activity, and altered spine dynamics prior to neuron loss [11,12,24]. Some studies have shown that α-synuclein PFFs and oligomers directly interact with membranes and synaptic vesicles, modulating calcium transients and vesicle homeostasis [25][26][27]. Here, we assessed the synaptic changes that occur during the propagation of α-synuclein in a neural network by measuring sEPSCs in the somatosensory cortex after PFF injection into the striatum, finding a decrease in the frequency of spontaneous events and a concomitant decrease in synapse density.…”