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Copper is one of the metals described to bind the Parkinson disease-related protein α-synuclein (aSyn), and to promote its aggregation. Although histidine at position 50 in the aSyn sequence is one of the most studied copper-anchoring sites, its precise role in copper binding and aSyn aggregation is still unclear. Previous studies suggested that this residue does not significantly affect copper-mediated aSyn aggregation. However, our findings showed that the aggregation of the pathological H50Q aSyn mutant is enhanced by copper hints otherwise. Despite the inexistence of a model for aSyn H50Q-copper complexation, we discuss possible mechanisms by which this metal contributes to the misfolding and self-assembly of this particular aSyn mutant. Considering the genetic association of the H50Q mutation with familial forms of Parkinson disease, and the fact that copper homeostasis is deregulated in this disorder, understanding the interplay between both factors will shed light into the molecular and cellular mechanisms triggering the development and spreading of the aSyn pathology.

Synucleinopathies are a group of progressive disorders characterized by the abnormal aggregation and accumulation of α-synuclein (aSyn), an abundant neuronal protein that can adopt different conformations and biological properties. Recently, aSyn pathology was shown to spread between neurons in a prion-like manner. Proteins like aSyn that exhibit self-propagating capacity appear to be able to adopt different stable conformational states, known as protein strains, which can be modulated both by environmental and by protein-intrinsic factors. Here, we analyzed these factors and found that the unique combination of the neurodegeneration-related metal copper and the pathological H50Q aSyn mutation induces a significant alteration in the aggregation properties of aSyn. We compared the aggregation ofWT and H50Q aSyn with andwithout copper, and assessed the effects of the resultant protein species when applied to primary neuronal cultures. The presence of copper induces the formation of structurally different and less-damaging aSyn aggregates. Interestingly, these aggregates exhibit a stronger capacity to induce aSyn inclusion formation in recipient cells, which demonstrates that the structural features of aSyn species determine their effect in neuronal cells and supports a lack of correlation between toxicity and inclusion formation. In total, our study provides strong support in favor of the hypothesis that protein aggregation is not a primary cause of cytotoxicity. [ABSTRACT FROM AUTHOR]

Background: Aggregation and aggregation-mediated formation of toxic alpha synuclein (aSyn) species have been linked to the pathogenesis of sporadic and monogenic Parkinson's disease (PD). A novel H50Q mutation of aSyn, resulting in the substitution of histidine by glutamine, has recently been identified in PD patients. We have previously shown that the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) induces the formation of HNE-aSyn adducts, thereby promoting aSyn oligomerization and increasing its extracellular toxicity to human dopaminergic neurons. Intriguingly, we identified histidine 50 (H50) of aSyn as one of the HNE modification target residues. These converging lines of evidence support the hypothesis that changes in H50 via posttranslational modification (PTM) and mutation trigger the formation of aggregated, toxic aSyn species, which interfere with cellular homeostasis. In the present study, we aim to elucidate 1) the role of H50 in HNE-mediated aSyn aggregation and toxicity, and 2) the impact of H50 mutation on aSyn pathology. Besides the PD-related H50Q, we analyze a PD-unrelated control mutation, in which H50 is replaced by an arginine residue (H50R). Results: Analysis of HNE-treated aSyn revealed that H50 is the most susceptible residue of aSyn to HNE modification and is crucial for HNE-mediated aSyn oligomerization. Overexpression of aSyn with substituted H50 in H4 neuroglioma cells reduced HNE-induced cell damage, indicating a pivotal role of H50 in HNE modification-induced aSyn toxicity. Furthermore, we showed in vitro that H50Q/R mutations substantially increase the formation of high density and fibrillar aSyn species, and potentiate the oligomerization propensity of aSyn in the presence of a nitrating agent. Cell-based experiments also revealed that overexpression of H50Q aSyn in H4 cells promotes aSyn oligomerization. Importantly, overexpression of both H50Q/R aSyn mutants in H4 cells significantly increased cell death when compared to wild type aSyn. This increase in cell death was further exacerbated by the application of H2O2. Conclusion: A dual approach addressing alterations of H50 showed that either H50 PTM or mutation trigger aSyn aggregation and toxicity, suggesting an important role of aSyn H50 in the pathogenesis of both sporadic and monogenic PD. [ABSTRACT FROM AUTHOR]

Copper is one of the metals described to bind the Parkinson disease-related protein α-synuclein (aSyn), and to promote its aggregation. Although histidine at position 50 in the aSyn sequence is one of the most studied copper-anchoring sites, its precise role in copper binding and aSyn aggregation is still unclear. Previous studies suggested that this residue does not significantly affect copper-mediated aSyn aggregation. However, our findings showed that the aggregation of the pathological H50Q aSyn mutant is enhanced by copper hints otherwise. Despite the inexistence of a model for aSyn H50Q-copper complexation, we discuss possible mechanisms by which this metal contributes to the misfolding and self-assembly of this particular aSyn mutant. Considering the genetic association of the H50Q mutation with familial forms of Parkinson disease, and the fact that copper homeostasis is deregulated in this disorder, understanding the interplay between both factors will shed light into the molecular and cellular mechanisms triggering the development and spreading of the aSyn pathology. [ABSTRACT FROM PUBLISHER]