Abstract
Many protein misfolding diseases (e.g. type II diabetes and Alzheimer's disease) are characterised by amyloid deposition. Human islet amyloid polypeptide (hIAPP, involved in type II diabetes) spontaneously undergoes liquid–liquid phase separation (LLPS) and a kinetically complex hydrogelation, both catalysed by hydrophobic–hydrophilic interfaces (e.g. air–water interface and/or phospholipids–water interfaces). Gelation of hIAPP phase-separated liquid droplets initiates amyloid aggregation and the formation of clusters of interconnected aggregates, which grow and fuse to eventually percolate the whole system. Droplet maturation into irreversible hydrogels via amyloid aggregation is thought to be behind the pathology of several diseases. Biological fluids contain a high volume fraction of macromolecules, leading to macromolecular crowding. Despite crowding agent addition in in vitro studies playing a significant role in changing protein phase diagrams, the mechanism underlying enhanced LLPS, and the effect(s) on stages beyond LLPS remain poorly or not characterised.We investigated the effect of macromolecular crowding and increased viscosity on the kinetics of hIAPP hydrogelation using rheology and the evolution of the system beyond LLPS by microscopy. We demonstrate that increased viscosity exacerbated the kinetic variability of hydrogelation and of the phase separated-aggregated system, whereas macromolecular crowding abolished heterogeneity. Increased viscosity also strengthened the gel meshwork and accelerated aggregate cluster fusion. In contrast, crowding either delayed cluster fusion onset (dextran) or promoted it (Ficoll). Our study highlights that an in vivo crowded environment would critically influence amyloid stages beyond LLPS and pathogenesis.
Highlights
The pathology of many degenerative diseases, such as Alzheimer’s disease and type 2 diabetes mellitus (D2M), is strongly associated with the deposition of insoluble proteinaceous aggregates termed amyloids [1]
We previously demonstrated by rheology the formation of a 3D hydrogel by full-length nonmutated human islet amyloid polypeptide (IAPP), consisting of a 3D supramolecular network of condensed fibrils, which was initially catalysed by the air–water interface (AWI) or phospholipids [32]
We showed that IAPP, without any added triggers, can spontaneously undergo an AWI-catalysed liquid–liquid phase separation (LLPS), with the initial liquid droplets maturing into a hydrogel-state followed by amyloid aggregation at the droplet surface
Summary
The pathology of many degenerative diseases, such as Alzheimer’s disease and type 2 diabetes mellitus (D2M), is strongly associated with the deposition of insoluble proteinaceous aggregates termed amyloids [1]. The burden of these diseases on human health is far-reaching, which has triggered a great deal of research into the understanding of the complexity of amyloid formation. Adsorption to HHIs allows amyloid polypeptides to spatially concentrate, to align their side chains, to promote β-sheet formation and to assemble into amyloid species [10,11,12,13,14,15]. IAPP interacts with β cell membranes, which leads to a concomitant increase in membrane permeability and calcium dysregulation [18,19]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
