Divalent and Trivalent Metallic Ions Differentially Affect Alpha-Synuclein Aggregation

Alpha-synuclein (αSyn) is the constituent protein associated with neurodegenerative synucleinopathies such as Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Recent studies have highlighted the potential role of altered metal ion homeostasis in influencing the aggregation and pathological behavior of αSyn, thereby affecting disease progression. We examined αSyn aggregation propensity in the presence of calcium (Ca²⁺), magnesium (Mg²⁺), copper (Cu²⁺), zinc (Zn²⁺), iron (Fe³⁺), and aluminum (Al³⁺). Recombinant αSyn was subjected to in vitro aggregation assays at varying metal ion concentrations. Our findings revealed distinct effects of metal ions on the aggregation kinetics of αSyn: most divalent cations seemed to have little effect on αSyn aggregation kinetics compared to the control, with zinc exhibiting a concentration-dependent acceleration of de novo αSyn aggregation. The trivalent cations, iron and aluminum, exhibited dual effects, promoting fibril elongation at lower concentrations, while inhibiting aggregation at higher ionic concentrations. Limited proteolysis, single molecule fingerprinting, and transmission electron microscopy imaging of the resulting aggregates indicated that Al³⁺-associated αSyn strains have different structural properties and enhanced cellular toxicity compared to the metal-free and Fe³⁺-associated fibrils. Our research highlights the relationship between metal ions and varied αSyn strain formation, contributing new insights into the impact of metal ion dyshomeostasis in αSyn pathologies.