Polymorphic α-Synuclein Strains Modified by Dopamine and Docosahexaenoic Acid Interact Differentially with Tau Protein

Abstract

The pathological hallmark of synucleinopathies, including Parkinson's disease (PD), is the aggregation of α-synuclein (α-Syn) protein. Even so, tau protein pathology is abundantly found in these diseases. Both α-Syn and tau can exist as polymorphic aggregates, a phenomenon that has been widely studied, mostly in their fibrillar assemblies. We have previously discovered that in addition to α-Syn oligomers, oligomeric tau is also present in the brain tissues of patients with PD and dementia with Lewy bodies (DLB). However, the effect of interaction between polymorphic α-Syn oligomers and tau has not been scrupulously studied. Here, we have explored the structural and functional diversity of distinct α-Syn oligomers, prepared by modifying the protein with dopamine (DA) and docosahexaenoic acid (DHA). The two α-Syn oligomers differed in aggregate size, conformation, sensitivity to proteinase K digestion, tryptic digestion, and toxicity, suggesting them as distinct α-Syn oligomeric strains. We examined their internalization mechanisms in primary neurons and seeding propensity in inducing α-Syn aggregation. Using a combined approach of molecular and cellular techniques, we observed that the tau aggregates cross-seeded with the individual α-Syn oligomeric strains differed in their biochemical and biological properties, suggesting two distinct tau strains. The tau aggregate cross-seeded with the DA-modified α-Syn oligomeric strain possessed a potent intracellular tau seeding propensity. This study provides a comprehensive analysis of unique strain-specific interaction between oligomeric α-Syn and tau. Furthermore, this study allows us to speculate that distinct α-Syn-tau interactions inducing tau aggregation might be an underlying mechanism of neurodegeneration in PD.

Modulating disease-relevant tau oligomeric strains by small molecules

“…Procedures for proteinase K digestion were described previously ( 49 , 51 , 56 , 91 ). Briefly, in an Eppendorf tube, molecular grade water, Tris-HCl, and sodium chloride were added so that the final concentrations for these two buffers became 100 and 5 m m , respectively, in the entire solution volume.…”

“…Primary cortical neurons from C57BL/6 mice (Jackson Laboratory, stock number 000664) were maintained as described previously ( 48 , 51 , 91 , 92 ). Briefly, cortical neurons were isolated from embryos at embryonic day 16–18 using Accutase solution (A6964, Sigma).…”

“…Tau RD P301S biosensor cells (ATCC, CRL-3275) were cultured in Dulbecco's modified Eagle's medium supplemented with 10% FBS, 100 μg/ml penicillin, and 100 μg/ml streptomycin as described previously ( 51 , 91 ). Cultures were maintained in a humidified atmosphere of 5% CO 2 at 37 °C.…”

The Effect of Oxidized Dopamine on the Structure and Molecular Chaperone Function of the Small Heat-Shock Proteins, αB-Crystallin and Hsp27

“…Most relevant to this study, αSyn forms unstructured adducts and oligomers upon the interaction with DA ox [ 32 , 33 , 65 , 66 , 67 ]. Recently, there has been evidence suggesting that, in comparison to its unmodified counterpart, these αSyn oligomers are more effective at cross-seeding with Tau, a protein whose aggregation to form intracellular tangles is associated with Alzheimer’s disease [ 68 ], a process which may further exacerbate the disease’s pathogenesis. In a neuroblastoma cell line, PD-related proteins such as ubiquitin carboxy-terminal hydrolase L1 and DJ-1 were found to be conjugated with DA o -quinone [ 69 ].…”

Distinct cryo-EM Structure of α-synuclein Filaments derived by Tau

“…14,15 Misfolding and aggregation of α-synuclein is also promoted by interactions with a variety of co-factors such as lipids, poly(ADP-ribose) (PAR), and other pathological aggregation-prone proteins such as tau and Aβ(1-42) peptides. 14,[24][25][26][27] The co-factors may interact with monomeric α-synuclein and lead to distinct misfolding pathways, resulting in different molecular conformations. Comparative structural analyses of in vitro α-synuclein filaments derived by co-factors and brain-derived ex vivo α-synuclein filaments are required to identify co-factors that promote α-synuclein aggregation in vivo.…”