The interplay between dopamine and a-synuclein in the early pathogenesis of Parkinson’s disease

Accumulation of alpha-synuclein (a-syn) and alteration of dopamine (DA) homeostasis are both recognized as early pathogenic hallmarks of Parkinson’s disease (PD) in dopaminergic neurons. Alpha-synuclein is well known to initiate a multistep nucleation-oligomerization process, from monomers to oligomers, thereby forming mature fibrils. Toxic oligomers and protofibrils may interact with DA storage vesicles leading to their permeabilization and DA release. Free cytosolic DA undergoes auto-oxidation with the concurrent formation of reactive intermediates and products. These latter were recognized to covalently modify a-syn, thus stabilizing toxic oligomers and affecting its physiological function as soluble NSF attachment protein receptor (SNARE) chaperone. The aim of the present project is to elucidate the relationship between generation of toxic DA-derived products and formation of a-syn adducts with modified structural properties and their interplay in the early pathogenesis of PD. To fulfill this aim we plan to adopt a multidisciplinary approach based on combined biophysical and biochemical experiments at different levels of complexity, which will eventually lead us to: i) characterize the a-syn reactivity with DA and DA oxidation products; ii) evaluate the conformational distribution and aggregation dynamics of DA-modified Vs native a-syn; iii) evaluate the intracellular toxic effects of DA-modified a-syn upon its liposome-mediated delivery into differentiated neurons; iv) test the effects of DA-induced modifications on a-syn seeding and spreading properties using trans-well co-cultures; v) assess the non cell-autonomous effects of DA-modified a-syn upon targeted delivery by means of suitably decorated liposomes to specific cell types in 3D midbrain organoids. The results achieved through completion of the present project will provide us with a detailed picture of the causal relationship between alterations of DA homeostasis and the onset of pathogenic a-syn modifications, thus unravelling novel molecular mechanisms in the early pathogenesis of PD. More specifically, seeding and spreading properties of DA-modified a-syn will be deeply investigated in experimental models of increasing complexity, from the single molecule to the three-dimensional organ-like level, with a particular focus on the non cell-autonomous toxic effects of a-syn in the cell types affected by PD. Accordingly, our research is expected to open new avenues towards the development of therapeutic strategies (e.g., proteolytic enzymes) to specifically target detrimental a-syn without affecting the functional protein. Moreover, novel biological pathways mainly affected by DA/a-syn interplay will emerge, representing alternative and/or additional candidates for targeting with new-conception drugs.