Single-Molecular Heteroamyloidosis of Human Islet Amyloid Polypeptide

Human amyloids and plaques uncovered post mortem are highly heterogeneous in structure and composition, yet literature concerning the hetero-aggregation of amyloid proteins is extremely scarce. This knowledge deficiency is further exacerbated by the fact that peptide delivery is a major therapeutic strategy for targeting their full-length counterparts associated with the pathologies of a range of human diseases, including dementia and type 2 diabetes (T2D). Accordingly, here we examined the co-aggregation of full-length human islet amyloid polypeptide (IAPP), a peptide associated with type 2 diabetes, with its primary and secondary amyloidogenic fragments 19–29 S20G and 8–20. Single-molecular aggregation dynamics was obtained by high-speed atomic force microscopy, augmented by transmission electron microscopy, X-ray diffraction and super-resolution stimulated emission depletion microscopy. The co-aggregation significantly prolonged the pause phase of fibril elongation, increasing its dwell time by threefold. Surprisingly, unidirectional elongation of mature fibrils, instead of protofilaments, was observed for the co-aggregation, indicating a new form of tertiary protein aggregation unknown to existing theoretical models. Further in vivo zebrafish embryonic assay indicated improved survival and hatching, as well as decreased frequency and severity of developmental abnormalities for embryos treated with the hetero-aggregates of IAPP with 19–29 S20G, but not with 8–20, compared to the control, indicating the therapeutic potential of 19–29 S20G against T2D.