Time-resolved studies define the nature of toxic IAPP intermediates, providing insight for anti-amyloidosis therapeutics

Abstract

Islet amyloidosis by IAPP contributes to pancreatic β-cell death in diabetes, but the nature of toxic IAPP species remains elusive. Using concurrent time-resolved biophysical and biological measurements, we define the toxic species produced during IAPP amyloid formation and link their properties to induction of rat INS-1 β-cell and murine islet toxicity. These globally flexible, low order oligomers upregulate pro-inflammatory markers and induce reactive oxygen species. They do not bind 1-anilnonaphthalene-8-sulphonic acid and lack extensive β-sheet structure. Aromatic interactions modulate, but are not required for toxicity. Not all IAPP oligomers are toxic; toxicity depends on their partially structured conformational states. Some anti-amyloid agents paradoxically prolong cytotoxicity by prolonging the lifetime of the toxic species. The data highlight the distinguishing properties of toxic IAPP oligomers and the common features that they share with toxic species reported for other amyloidogenic polypeptides, providing information for rational drug design to treat IAPP induced β-cell death.DOI: http://dx.doi.org/10.7554/eLife.12977.001

RAGE binds preamyloid IAPP intermediates and mediates pancreatic β cell proteotoxicity

“…We have shown that toxic h-IAPP LP intermediates, but not nontoxic h-IAPP amyloid fibrils, induce the production of ROS in INS-1 β cells and that this event precedes the detection of metabolic dysfunction (19). If RAGE is a mediator of h-IAPP-induced β cell toxicity, then we would expect that toxic h-IAPP LP intermediates would likewise upregulate RAGE expression before detectable loss of β cell viability.…”

“…Amyloidogenic h-IAPP induces β cell apoptosis in vitro, in rodent models in vivo, and in human T2D (10,19,26,34,35,37,38). Multiple mechanisms of toxicity have been proposed, but there is no consensus about how h-IAPP causes β cell damage (6,17,39).…”

“…Mice that overexpress h-IAPP demonstrate intracellular oligomer formation and defects in autophagy and/or ER stress (27)(28)(29)(30), while cultured Tg murine islets expressing physiological levels of h-IAPP do not display ER stress during islet amyloidosis (31). Extracellular h-IAPP oligomers are toxic (6,19,(32)(33)(34)(35). Findings that h-IAPP secretion is necessary for β cell proteotoxicity and amyloid formation (32), studies that show extracellular h-IAPP oligomers can be translocated into β cells (36), and receptor-mediated mechanisms of cytotoxicity (33) all support a role for extracellular oligomers in h-IAPP-induced β cell and islet pathogenesis.…”

“…Aggregation of h-IAPP into amyloid fibrils involves 3 observable stages: Preamyloid oligomers (or prefibrillar intermediates) formed in the lag phase (LP) (first phase) assemble into amyloid fibrils in the growth phase (GP) (second phase), leading to an equilibrium between amyloid fibrils and residual soluble peptide in the saturation phase (SP) (third phase) (Supplemental Figure 1, A and B; supplemental material available online with this article; https:// doi.org/10.1172/JCI85210DS1). Toxic h-IAPP aggregates cause pancreatic β cell and islet dysfunction and death, contributing to T2D, islet transplant failure, and, ultimately, cardiovascular and microvascular complications (19)(20)(21)(22)(23).…”

IAPP and type 1 diabetes: implications for immunity, metabolism and islet transplants

“…Since aggregation of hIAPP progresses in vitro from monomeric through to pre-fibrillar aggregates and subsequently fibrillar forms over the course of minutes to hours (depending on the concentration and solvent used), application of freshly dissolved hIAPP to macrophages will expose these cells to a range of hIAPP aggregate species. Early, pre-fibrillar hIAPP species are the most pro-inflammatory (Masters et al 2010, Westwell-Roper et al 2011 and most toxic to INS1 cells (Abedini et al 2016). It should be noted that fibrillar hIAPP species can, however, activate the inflammasome in LPS-primed macrophages, though to a lesser extent than freshly dissolved hIAPP (Westwell-Roper et al 2016).…”