Nucleation of α-Synuclein Amyloid Fibrils Induced by Cross-Interaction with ß-Hairpin Peptides Derived from Immunoglobulin Light Chains.

Heterologous interactions between different amyloid-forming proteins, also called cross-interactions, may have a critical impact on disease-related amyloid formation. ß-hairpin conformers of amyloid-forming proteins have been shown to affect homologous interactions in the amyloid self-assembly process. Here, we applied two ß-hairpin-forming peptides derived from immunoglobulin light chains as models to test how heterologous ß-hairpins modulate the fibril formation of Parkinson's disease-associated protein α-synuclein (αSyn). The peptides SMAhp and LENhp comprise ß-strands C and C' of the κ4 antibodies SMA and LEN, which are associated with light chain amyloidosis and multiple myeloma, respectively. SMAhp and LENhp bind with high affinity to the ß-hairpin-binding protein ß-wrapin AS10 according to isothermal titration calorimetry and NMR spectroscopy. The addition of SMAhp and LENhp affects the kinetics of αSyn aggregation monitored by Thioflavin T (ThT) fluorescence, with the effect depending on assay conditions, salt concentration, and the applied ß-hairpin peptide. In the absence of agitation, substoichiometric concentrations of the hairpin peptides strongly reduce the lag time of αSyn aggregation, suggesting that they support the nucleation of αSyn amyloid fibrils. The effect is also observed for the aggregation of αSyn fragments lacking the N-terminus or the C-terminus, indicating that the promotion of nucleation involves the interaction of hairpin peptides with the hydrophobic non-amyloid-ß component (NAC) region.

Endo-lysosomal Aß concentration and pH trigger formation of Aß oligomers that potently induce Tau missorting.

Amyloid-ß peptide (Aß) forms metastable oligomers >50 kDa, termed AßOs, that are more effective than Aß amyloid fibrils at triggering Alzheimer's disease-related processes such as synaptic dysfunction and Tau pathology, including Tau mislocalization. In neurons, Aß accumulates in endo-lysosomal vesicles at low pH. Here, we show that the rate of AßO assembly is accelerated 8,000-fold upon pH reduction from extracellular to endo-lysosomal pH, at the expense of amyloid fibril formation. The pH-induced promotion of AßO formation and the high endo-lysosomal Aß concentration together enable extensive AßO formation of Aß42 under physiological conditions. Exploiting the enhanced AßO formation of the dimeric Aß variant dimAß we furthermore demonstrate targeting of AßOs to dendritic spines, potent induction of Tau missorting, a key factor in tauopathies, and impaired neuronal activity. The results suggest that the endosomal/lysosomal system is a major site for the assembly of pathomechanistically relevant AßOs.