An islet amyloid polypeptide oligomer model inhibits fibril formation

Type 2 diabetes mellitus (T2DM) is a multifactorial metabolic and widespread disease. In patients' pancreas, islet amyloid polypeptide (IAPP) is found as aggregates. As for other disease-related amyloidogenic proteins, oligomeric species of IAPP have been suggested to exhibit cytotoxic activity. Here, we developed an IAPP model, denoted dimIAPP, which assembles into curvilinear oligomers that persist over extended periods of time. DimIAPP is an engineered dimer of a cysteine-free IAPP mutant (C2S, C7S), with the two dimer subunits linked by a flexible (G₄S)₄ linker on one polypeptide chain. In contrast to IAPP, dimIAPP did not form Thioflavin T-positive amyloid fibrils, but assembled into oligomers (dimIAPP-O) which tended to coalesce into larger clusters. IAPP fibril formation was slowed down by addition of dimIAPP-O, a finding that extends previous studies demonstrating an intrinsic inhibitory activity of off-pathway oligomers on amyloid fibril formation. Exposure of pancreatic RIN-m5f cells to dimIAPP-O and IAPP fibrils differentially activated cellular stress response. We conclude that the dimIAPP model is a useful tool to gain further insights into IAPP aggregation and to characterize the effects of off-pathway oligomers of amyloidogenic proteins.