Mechanistic Insights into the Protective Roles of Polyphosphate Against Amyloid Cytotoxicity

The universally abundant polyphosphate (polyP) accelerates fibril formation of disease-related amyloids and protects against amyloid cytotoxicity. To gain insights into the mechanism(s) by which polyP exerts these effects, we focused on -synuclein, a well-studied amyloid protein, which constitutes the major component of Lewy bodies found in Parkinsons Disease. Here we demonstrate that polyP is unable to accelerate the rate-limiting step of -synuclein fibril formation but effectively nucleates fibril assembly once -synuclein oligomers are formed. Binding of polyP to -synuclein either during fibril formation or upon fibril maturation substantially alters fibril morphology, and effectively reduces the ability of -synuclein fibrils to interact with cell membranes. The effect of polyP appears to be -synuclein fibril specific, and successfully prevents the uptake of fibrils into neuronal cells. These results suggest that altering the polyP levels in the extracellular space might be a potential therapeutic strategy to prevent the spreading of the disease.