HOW A METABOLITE OF DOPAMINE CAN TRANSFORM ALPHA­SYNUCLEIN IN AN ENDOTOXIN

The dopamine metabolite 3,4­dihydroxyphenylacetaldehyde (DOPAL) is highly reactive aldehyde of great interest in neurodegeneration. DOPAL is typically processed by the enzyme aldehyde dehydrogenase that is able to detoxify neurons by conversion of the DOPAL to a non­toxic molecule, i.e. 3,4­dihydroxyphenylacetic acid. The toxicity ascribed to DOPAL acquires particular interest for Parkinson’s disease (PD), being the dopaminergic neurons primary affected in the disorder. In this frame, it was reported that DOPAL is accumulated in neurons in parkinsonian brains where it can chemically modify alpha­synuclein (aS), a protein strongly associated to familial and sporadic forms of PD. aS is a natively unfolded protein prone to form aggregates, which are found in parkinsonian brains. The goal of our study is the characterization of the synergistic toxic effect exerted by DOPAL and aS in PD, due to the formation of aS/DOPAL oligomeric species. To this aim, we used a broad range of biophysical and biochemical techniques to characterize the chemical modification of aS generated by the reaction with DOPAL and the heterogeneous ensemble of resulting oligomeric aggregated species. aS is modified by DOPAL mainly at lysine residues as verified by mass spectrometry and NMR. The aS modifications lead to the formation of oligomers, which were characterize by transmission electron microscopy, dynamic light scattering and atomic force microscopy. These DOPAL dependent aS oligomers can permeabilize artificial lipid membranes, when they contain cholesterol, and induce ions and dopamine leakage. The formation and the toxicity of these aS oligomers have been evaluate also in a cellular model, i.e. the dopaminergic neuroblastoma cell line BE(2)­M17.