The aggregation of α-synuclein
(aSyn) is believed to be mechanistically
linked to the degeneration of dopamine (DA)-producing neurons in Parkinson’s
disease (PD). In this respect, one crucial question that yet remains
unsolved is whether aSyn aggregation is associated with either a gain-
or loss-of-function of the protein in neuronal cells. Herein, we investigated
the effect of monomeric versus fibrillar aSyn on mesencephalic dopaminergic
neurons in primary cultures challenged with the neurotoxic catechols:
salsolinol (SALSO; 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline)
and 3,4-dihydroxyphenylacetaldehyde (DOPAL). aSyn monomer protected
cells against either SALSO- or DOPAL-induced toxicity via inhibition
of caspase-3-mediated apoptosis. While fibrillar aSyn failed in attenuating
SALSO neurotoxicity, it increased the viability of DOPAL-treated cells,
which was apparently not associated with the inhibition of caspase-3
cleavage. The fact that DOPAL-derived aSyn adducts exhibit lower toxicity
compared with DOPAL itself raises the question of whether the generation
of these adducts could be part of or a collateral effect of aSyn-mediated
protection in neurons exposed to DOPAL. Overall, our work provides
important evidence on the impact of the fibrillation of aSyn on its
protective role in neuronal cells exposed to the toxic catechols SALSO
and DOPAL.