Abstract
Parkinson's disease is mainly a sporadic disorder in which both environmental and cellular factors play a major role in the initiation of this disease. Glycosaminoglycans (GAG) are integral components of the extracellular matrix and are known to influence amyloid aggregation of several proteins, including α-synuclein (α-Syn). However, the mechanism by which different GAGs and related biological polymers influence protein aggregation and the structure and intercellular spread of these aggregates remains elusive. In this study, we used three different GAGs and related charged polymers to establish their role in α-Syn aggregation and associated biological activities of these aggregates. Heparin, a representative GAG, affected α-Syn aggregation in a concentration-dependent manner, whereas biphasic α-Syn aggregation kinetics was observed in the presence of chondroitin sulfate B. Of note, as indicated by 2D NMR analysis, different GAGs uniquely modulated α-Syn aggregation because of the diversity of their interactions with soluble α-Syn. Moreover, subtle differences in the GAG backbone structure and charge density significantly altered the properties of the resulting amyloid fibrils. Each GAG/polymer facilitated the formation of morphologically and structurally distinct α-Syn amyloids, which not only displayed variable levels of cytotoxicity but also exhibited an altered ability to internalize into cells. Our study supports the role of GAGs as key modulators in α-Syn amyloid formation, and their distinct activities may regulate amyloidogenesis depending on the type of GAG being up- or down-regulated in vivo.
Highlights
Parkinson’s disease is mainly a sporadic disorder in which both environmental and cellular factors play a major role in the initiation of this disease
On comparing the amount of GAG incorporated in fibrils and the extent of fibril internalization, we found that less incorporation of Hep (30%) and dextran sulfate (Dext) (38%) in the fibrils resulted in negligible or no cellular internalization, whereas high incorporation of chondroitin sulfate A (CSA) (64%) and chondroitin sulfate B (CSB) (67.5%) in the fibrils exhibited more internalization
Glycosaminoglycans are important cellular components that have been reported to co-deposit with amyloids associated with various diseases including Parkinson’s [24, 25, 62]
Summary
To explore the interaction mechanism of GAGs with ␣-Syn and their role in aggregation, we used different GAGs and related polymers including heparin (Hep), chondroitin sulfate A (CSA), chondroitin sulfate B (CSB), dextran sulfate (Dext), chitosan, and polyvinyl sulfate (PVS) polymer. As ␣-Syn in the presence of chitosan formed a gel-like state upon incubation, it showed a very low soluble protein concentration in the supernatant. At 1:1 and 1:2 ratios of protein: GAG, with increasing polymer length, the lag phase of ␣-Syn aggregation is decreased (Fig. S9). The NMR data suggest that GAGs interact with a soluble form of protein through charge and/or hydrophobic interactions These interactions increase the local concentration of ␣-Syn (as a result of a crowding effect) that leads to accelerated aggregation kinetics. F, dynamic light scattering of the supernatant obtained after centrifugation of fibrils treated with various GAGs. fibrils in the presence of Hep, CSA, CSB, and Dext formed less or nontoxic fibrils, and cell viability was slightly increased with the increase in GAG:protein stoichiometry (Fig. 4C). In the case of PVS, the toxicity of the resultant ␣-Syn aggregates increased with an increase in PVS concentration
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