Cellular prion protein and calcium ions trigger the neurotoxicity of α-synuclein aggregates

The aggregation of α-Synuclein (αS) into amyloid fibrils and their deposition in intraneuronal Lewy bodies are hallmark features of Parkinson's disease (PD) and other synucleinopathies. Among the molecular players implicated in αS toxicity, the cellular prion protein (PrP^C) has emerged as a potential modulator of αS-neuron interactions.

Using confocal microscopy, colocalization analysis and both siRNA-induced PrP^C silencing and antibody-based blockade, we investigated the contribution of PrP^C to αS-induced neurotoxicity in human iPSC-derived dopaminergic neurons, primary rat cortical neurons and human SH-SY5Y neuroblastoma cells. We show that PrP^C facilitated the early recruitment of αS prefibrillar type B* oligomers (OB*) and short fibrils (SF) to neuronal membranes, enhancing αS-induced Ca²⁺ influx and membrane permeabilization. However, PrP^C levels remained unchanged following prolonged exposure with OB* and SF, suggesting no feedback modulation of PrP^C expression. While PrP^C blockade partially inhibited the release of toxic soluble oligomers from αS fibrils, downstream cell death was only marginally reduced, indicating a limited contribution of PrP^C to the final neurotoxic outcome. By contrast, extracellular Ca²⁺ emerged as a major driver of αS toxicity, directly promoting the membrane recruitment, internalization and cytotoxic effects of αS aggregates.

Collectively, our findings indicate that while PrP^C facilitates early events in αS aggregate interaction with neurons, the sustained neurotoxicity induced by αS prefibrillar oligomers and fibrils is predominantly mediated by extracellular Ca²⁺. This promotes aggregate-membrane interactions, membrane permeabilization, and intracellular Ca²⁺ dyshomeostasis, thereby establishing a vicious cycle of neuronal dysfunction and death.