Abstract
The accumulation of aggregated α-synuclein (αSyn) is a hallmark of Parkinson’s disease (PD). Current evidence indicates that small soluble αSyn oligomers (αSynOs) are the most toxic species among the forms of αSyn aggregates, and that size and topological structural properties are crucial factors for αSynOs-mediated toxicity, involving the interaction with either neurons or glial cells. We previously characterized a human αSynO (H-αSynO) with specific structural properties promoting toxicity against neuronal membranes. Here, we tested the neurotoxic potential of these H-αSynOs in vivo, in relation to the neuropathological and symptomatic features of PD. The H-αSynOs were unilaterally infused into the rat substantia nigra pars compacta (SNpc). Phosphorylated αSyn (p129-αSyn), reactive microglia, and cytokine levels were measured at progressive time points. Additionally, a phagocytosis assay in vitro was performed after microglia pre-exposure to αsynOs. Dopaminergic loss, motor, and cognitive performances were assessed. H-αSynOs triggered p129-αSyn deposition in SNpc neurons and microglia and spread to the striatum. Early and persistent neuroinflammatory responses were induced in the SNpc. In vitro, H-αSynOs inhibited the phagocytic function of microglia. H-αsynOs-infused rats displayed early mitochondrial loss and abnormalities in SNpc neurons, followed by a gradual nigrostriatal dopaminergic loss, associated with motor and cognitive impairment. The intracerebral inoculation of structurally characterized H-αSynOs provides a model of progressive PD neuropathology in rats, which will be helpful for testing neuroprotective therapies.
Highlights
Parkinson’s disease (PD) belongs to the family of synucleinopathies, whose hallmark is the accumulation of misfolded aggregates of the protein alpha-synuclein in neuronal and non-neuronal brain cells [1]
The results indicated the concentration of 0.5 mg/mL in 5 μL volume as the best combination, since it was not associated with any evident mechanical damage of the infused tissue, as confirmed by hematoxylin and eosin (H&E) staining, nor induced the deposition of local large aggregates, or diffused excessively in the infused area or along the injector trace (Figure 2A,B)
We evaluated whether the infusion of H-αsynOs into the substantia nigra pars compacta (SNpc) induced the formation of pathological p129-αSyn within microglia and neurons in the infused SNpc, and whether the p129-αSyn pathology spread via dopaminergic fibers to the striatum; as this is the main SNpc projection area. p129-αSyn was analyzed as a frequently used marker for the pathological form of αSyn highly represented in protein aggregates
Summary
Parkinson’s disease (PD) belongs to the family of synucleinopathies, whose hallmark is the accumulation of misfolded aggregates of the protein alpha-synuclein (αSyn) in neuronal and non-neuronal brain cells [1]. In particular two essential elements of H-αSynOs were found in this mechanism, an N-terminal region acting as the membrane anchor [16,17,18,19,20,21,22,23,24], and a fibrillar core that effectively inserts into the hydrophobic layer of the membrane, and disrupts its integrity These findings indicate that, in addition to size, topological properties such as secondary structure and tertiary structural elements are pivotal for gains in cellular toxicity by H-αsynOs [3,7,16,17,25,26]. In a previous study the toxicity in vivo of H-αSynOs was demonstrated in the C. elegans over-expressing αSyn, where the incubation with antibodies targeting the N-terminal region of the protein reduced the toxicity of the aggregated species [24]
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