Islet amyloid polypeptide triggers α-synuclein pathology in Parkinson’s disease

Pathologic aggregation and prion-like propagation of α-synuclein (α-syn) are the hallmarks of Parkinson’s disease (PD). Emerging evidence shows that type 2 diabetes mellitus (T2DM) is a risk factor for PD. Interestingly, T2DM is characterized by the amyloid deposition of islet amyloid polypeptide (IAPP) in the pancreas. Although T2DM and PD share pathological similarities, the underlying molecular mechanisms bridging these two diseases remain unknown. Here, we report that IAPP co-deposits with α-syn in the brains of PD patients. IAPP interacts with α-syn and accelerates its aggregation. In addition, the IAPP-seeded α-syn fibrils show enhanced seeding activity and neurotoxicity compared with pure α-syn fibrils in vitro and in vivo. Strikingly, intravenous injection of IAPP fibrils into α-syn A53T transgenic mice or human SNCA transgenic mice accelerated the aggregation of α-syn and PD-like motor deficits. Taken together, these findings support that IAPP acts as a trigger of α-syn pathology in PD, and provide a mechanistic explanation for the increased risk and faster progression of PD in patients with T2DM.