Synucleinophaties are progressive neurodegenerative disorders with no cure to date. An attractive strategy to tackle this problem is repurposing already tested safe drugs against novel targets. In this way, doxycycline prevents neurodegeneration in Parkinson models by modulating neuroinflammation. However, anti-inflammatory therapy per se is insufficient to account for neuroprotection. Herein we characterise novel targets of doxycycline describing the structural background supporting its effectiveness as a neuroprotector at subantibiotic doses. Our results show that doxycycline reshapes α-synuclein oligomers into off-pathway, high-molecular-weight species that do not evolve into fibrils. Off-pathway species present less hydrophobic surface than on-pathway oligomers and display different β-sheet structural arrangement. These structural changes affect the α-synuclein ability to destabilize biological membranes, cell viability, and formation of additional toxic species. Altogether, these mechanisms could act synergically giving novel targets for repurposing this drug.

Background: Although glycosaminoglycan-induced GAPDH prefibrillar species accelerates ␣-synuclein aggregation, its role in toxicity remains unclear. Results: The toxic effect exerted by ␣-synuclein oligomers on cell culture was abolished by GAPDH protofibril, which was identified and structurally characterized. Conclusion: GAPDH protofibrils can efficiently sequester ␣-synuclein toxic oligomers. Significance: GAPDH protofibrils may play an important role in neuronal proteostasis and could open a novel therapeutic strategy for synucleinopathies.

Background: GAPDH and glycosaminoglycans (GAGs) have been routinely found in Parkinson disease amyloid aggregates. Results: Heparin and heparan sulfate induce the formation of GAPDH amyloid-like oligomers, which were characterized by using biophysical techniques. Conclusion: Heparin-induced GAPDH early oligomeric species are able to reduce the amount of ␣-synuclein (AS) prefibrillar species. Significance: GAPDH oligomeric species might be taken into account in recruiting of AS toxic species.