Conformational transitions of islet amyloid polypeptide (IAPP) in amyloid formation in Vitro

Extracellular vesicles (EVs) are small vesicles released by cells to aid cell–cell communication and tissue homeostasis. Human islet amyloid polypeptide (IAPP) is the major component of amyloid deposits found in pancreatic islets of patients with type 2 diabetes (T2D). IAPP is secreted in conjunction with insulin from pancreatic β cells to regulate glucose metabolism. Here, using a combination of analytical and biophysical methods in vitro, we tested whether EVs isolated from pancreatic islets of healthy patients and patients with T2D modulate IAPP amyloid formation. We discovered that pancreatic EVs from healthy patients reduce IAPP amyloid formation by peptide scavenging, but T2D pancreatic and human serum EVs have no effect. In accordance with these differential effects, the insulin:C-peptide ratio and lipid composition differ between EVs from healthy pancreas and EVs from T2D pancreas and serum. It appears that healthy pancreatic EVs limit IAPP amyloid formation via direct binding as a tissue-specific control mechanism.

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The Effect of Cholesterol on Membrane-Bound Islet Amyloid Polypeptide

Frontiers in Molecular Biosciences ◽

10.3389/fmolb.2021.657946 ◽

2021 ◽

Vol 8 ◽

Author(s):

Mikkel Christensen ◽

Nils A. Berglund ◽

Birgit Schiøtt

Keyword(s):

Pancreatic Beta Cells ◽

Cell Mass ◽

Islet Amyloid Polypeptide ◽

Beta Cell Mass ◽

Helical Structure ◽

Amyloid Formation ◽

Islet Amyloid ◽

Insertion Depth ◽

Membrane Bound

Islet amyloid polypeptide (IAPP) is a proposed cause of the decreased beta-cell mass in patients with type-II diabetes. The molecular composition of the cell-membrane is important for regulating IAPP cytotoxicity and aggregation. Cholesterol is present at high concentrations in the pancreatic beta-cells, and in-vitro experiments have indicated that it affects the amyloid formation of IAPP either by direct interactions or by changing the properties of the membrane. In this study we apply atomistic, unbiased molecular dynamics simulations at a microsecond timescale to investigate the effect of cholesterol on membrane bound IAPP. Simulations were performed with various combinations of cholesterol, phosphatidylcholine (PC) and phosphatidylserine (PS) lipids. In all simulations, the helical structure of monomer IAPP was stabilized by the membrane. We found that cholesterol decreased the insertion depth of IAPP compared to pure phospholipid membranes, while PS lipids counteract the effect of cholesterol. The aggregation propensity has previously been proposed to correlate with the insertion depth of IAPP, which we found to decrease with the increased ordering of the lipids induced by cholesterol. Cholesterol is depleted in the vicinity of IAPP, and thus our results suggest that the effect of cholesterol is indirect.

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Islet Amyloid Polypeptide: Structure, Function, and Pathophysiology

Journal of Diabetes Research ◽

10.1155/2016/2798269 ◽

2016 ◽

Vol 2016 ◽

pp. 1-18 ◽

Cited By ~ 86

Author(s):

Rehana Akter ◽

Ping Cao ◽

Harris Noor ◽

Zachary Ridgway ◽

Ling-Hsien Tu ◽

...

Keyword(s):

Type 2 Diabetes ◽

Cell Death ◽

Type 1 Diabetes ◽

Islet Amyloid Polypeptide ◽

Amyloid Formation ◽

Islet Amyloid

The hormone islet amyloid polypeptide (IAPP, or amylin) plays a role in glucose homeostasis but aggregates to form islet amyloid in type-2 diabetes. Islet amyloid formation contributes toβ-cell dysfunction and death in the disease and to the failure of islet transplants. Recent work suggests a role for IAPP aggregation in cardiovascular complications of type-2 diabetes and hints at a possible role in type-1 diabetes. The mechanisms of IAPP amyloid formationin vivoorin vitroare not understood and the mechanisms of IAPP inducedβ-cell death are not fully defined. Activation of the inflammasome, defects in autophagy, ER stress, generation of reactive oxygen species, membrane disruption, and receptor mediated mechanisms have all been proposed to play a role. Open questions in the field include the relative importance of the various mechanisms ofβ-cell death, the relevance of reductionist biophysical studies to the situationin vivo, the molecular mechanism of amyloid formationin vitroandin vivo, the factors which trigger amyloid formation in type-2 diabetes, the potential role of IAPP in type-1 diabetes, the development of clinically relevant inhibitors of islet amyloidosis toxicity, and the design of soluble, bioactive variants of IAPP for use as adjuncts to insulin therapy.

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Amyloid Formation in Response to β Cell Stress Occurs In Vitro, but Not In Vivo, in Islets of Transgenic Mice Expressing Human Islet Amyloid Polypeptide

Molecular Medicine ◽

10.1007/bf03401591 ◽

1995 ◽

Vol 1 (5) ◽

pp. 542-553 ◽

Cited By ~ 27

Author(s):

Gunilla Westermark ◽

Michelle Benig Arora ◽

Niles Fox ◽

Raymond Carroll ◽

Shu Jin Chan ◽

...

Keyword(s):

Transgenic Mice ◽

Islet Amyloid Polypeptide ◽

Human Islet ◽

Cell Stress ◽

Amyloid Formation ◽

Β Cell ◽

Islet Amyloid ◽

Human Islet Amyloid Polypeptide

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Matrix Metalloproteinase-9 Reduces Islet Amyloid Formation by Degrading Islet Amyloid Polypeptide

Journal of Biological Chemistry ◽

10.1074/jbc.m112.438457 ◽

2012 ◽

Vol 288 (5) ◽

pp. 3553-3559 ◽

Cited By ~ 23

Author(s):

Kathryn Aston-Mourney ◽

Sakeneh Zraika ◽

Jayalakshmi Udayasankar ◽

Shoba L. Subramanian ◽

Pattie S. Green ◽

...

Keyword(s):

Matrix Metalloproteinase ◽

Islet Amyloid Polypeptide ◽

Matrix Metalloproteinase 9 ◽

Amyloid Formation ◽

Islet Amyloid ◽

Metalloproteinase 9

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Pancreatic beta-cell granule peptides form heteromolecular complexes which inhibit islet amyloid polypeptide fibril formation

Biochemical Journal ◽

10.1042/bj20030852 ◽

2004 ◽

Vol 377 (3) ◽

pp. 709-716 ◽

Cited By ~ 67

Author(s):

Emma T. A. S. JAIKARAN ◽

Melanie R. NILSSON ◽

Anne CLARK

Keyword(s):

Type 2 Diabetes ◽

Amyloid Fibrils ◽

Secretory Granules ◽

Pancreatic Beta Cell ◽

Islet Amyloid Polypeptide ◽

Fibril Formation ◽

Islet Amyloid ◽

Β Sheet

Islet amyloid polypeptide (IAPP), or ‘amylin’, is co-stored with insulin in secretory granules of pancreatic islet β-cells. In Type 2 diabetes, IAPP converts into a β-sheet conformation and oligomerizes to form amyloid fibrils and islet deposits. Granule components, including insulin, inhibit spontaneous IAPP fibril formation in vitro. To determine the mechanism of this inhibition, molecular interactions of insulin with human IAPP (hIAPP), rat IAPP (rIAPP) and other peptides were examined using surface plasmon resonance (BIAcore), CD and transmission electron microscopy (EM). hIAPP and rIAPP complexed with insulin, and this reaction was concentration-dependent. rIAPP and insulin, but not pro-insulin, bound to hIAPP. Insulin with a truncated B-chain, to prevent dimerization, also bound hIAPP. In the presence of insulin, hIAPP did not spontaneously develop β-sheet secondary structure or form fibrils. Insulin interacted with pre-formed IAPP fibrils in a regular repeating pattern, as demonstrated by immunoEM, suggesting that the binding sites for insulin remain exposed in hIAPP fibrils. Since rIAPP and hIAPP form complexes with insulin (and each other), this could explain the lack of amyloid fibrils in transgenic mice expressing hIAPP. It is likely that IAPP fibrillogenesis is inhibited in secretory granules (where the hIAPP concentration is in the millimolar range) by heteromolecular complex formation with insulin. Alterations in the proportions of insulin and IAPP in granules could disrupt the stability of the peptide. The increase in the proportion of unprocessed pro-insulin produced in Type 2 diabetes could be a major factor in destabilization of hIAPP and induction of fibril formation.

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Inhibition of Glycosaminoglycan-Mediated Amyloid Formation by Islet Amyloid Polypeptide and proIAPP Processing Intermediates

Journal of Molecular Biology ◽

10.1016/j.jmb.2010.12.028 ◽

2011 ◽

Vol 406 (3) ◽

pp. 491-502 ◽

Cited By ~ 16

Author(s):

Fanling Meng ◽

Daniel P. Raleigh

Keyword(s):

Islet Amyloid Polypeptide ◽

Amyloid Formation ◽

Islet Amyloid

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Human Islet Amyloid Polypeptide Fibril Binding to Catalase: A Transmission Electron Microscopy and Microplate Study

The Scientific World JOURNAL ◽

10.1100/tsw.2010.73 ◽

2010 ◽

Vol 10 ◽

pp. 879-893 ◽

Cited By ~ 10

Author(s):

Nathaniel G. N. Milton ◽

J. Robin Harris

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Islet Amyloid Polypeptide ◽

Amyloid Β ◽

Human Islet ◽

Islet Amyloid ◽

Human Islet Amyloid Polypeptide ◽

Transmission Electron

The diabetes-associated human islet amyloid polypeptide (IAPP) is a 37-amino-acid peptide that forms fibrilsin vitroandin vivo. Human IAPP fibrils are toxic in a similar manner to Alzheimer's amyloid-β (Aβ) and prion protein (PrP) fibrils. Previous studies have shown that catalase binds to Aβ fibrils and appears to recognize a region containing the Gly-Ala-Ile-Ile sequence that is similar to the Gly-Ala-Ile-Leu sequence found in human IAPP residues 24-27. This study presents a transmission electron microscopy (TEM)—based analysis of fibril formation and the binding of human erythrocyte catalase to IAPP fibrils. The results show that human IAPP 1-37, 8-37, and 20-29 peptides form fibrils with diverse and polymorphic structures. All three forms of IAPP bound catalase, and complexes of IAPP 1-37 or 8-37 with catalase were identified by immunoassay. The binding of biotinylated IAPP to catalase was high affinity with a KDof 0.77nM, and could be inhibited by either human or rat IAPP 1-37 and 8-37 forms. Fibrils formed by the PrP 118-135 peptide with a Gly-Ala-Val-Val sequence also bound catalase. These results suggest that catalase recognizes a Gly-Ala-Ile-Leu—like sequence in amyloid fibril-forming peptides. For IAPP 1-37 and 8-37, the catalase binding was primarily directed towards fibrillar rather than ribbon-like structures, suggesting differences in the accessibility of the human IAPP 24-27 Gly-Ala-Ile-Leu region. This suggests that catalase may be able to discriminate between different structural forms of IAPP fibrils. The ability of catalase to bind IAPP, Aβ, and PrP fibrils demonstrates the presence of similar accessible structural motifs that may be targets for antiamyloid therapeutic development.

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