The Ability of Rodent Islet Amyloid Polypeptide To Inhibit Amyloid Formation by Human Islet Amyloid Polypeptide Has Important Implications for the Mechanism of Amyloid Formation and the Design of Inhibitors

Abstract

Islet amyloid polypeptide (IAPP) is a 37-residue polypeptide hormone which is responsible for islet amyloid formation in type II diabetes. Human IAPP is extremely amyloidogenic while rat and mouse IAPP do not form amyloid in vitro or in vivo. Rat and mouse IAPP have identical primary sequences, but differ from the human polypeptide at six positions, five of which are localized between residues 20 to 29. The ability of rat IAPP to inhibit amyloid formation by human IAPP was tested and the rat peptide was found to be an effective inhibitor. Thioflavin-T fluorescence monitored kinetic experiments, transmission electron microscopy and circular dichroism showed that rat IAPP lengthened the lag phase for amyloid formation by human IAPP, slowed the growth rate, reduced the amount of amyloid fibrils produced in a dose dependent manner, and altered the morphology of the fibrils. The inhibition of human IAPP amyloid formation by rat IAPP can be rationalized by a model which postulates formation of an early helical intermediate during amyloid formation where the helical region is localized to the N-terminal region of IAPP. The model predicts that proline mutations in the putative helical region should lead to ineffective inhibitors as should mutations which alter the peptide peptide interaction interface. This was confirmed by testing the ability of A13P and F15D point mutants of rat IAPP to inhibit amyloid formation by human IAPP. Both these mutants were noticeably less effective inhibitors than wild type rat IAPP. The implications for inhibitor design are discussed. + This work was supported by Grant NIH GM078114 to DPR.* Author to whom correspondence should be addressed: Daniel P. Raleigh: telephone, 631-632-9547; fax: 631-632-7960; draleigh@notes.cc.sunysb.edu. Supporting Information Available: The results of the sedimentation equilibrium studies of rat IAPP, plots of the derivative of the thioflavin-T fluorescence vs time, experimental CD spectra and calculated CD spectra of rat and human IAPP as well as 1:1, 2:1 and 5:1 mixtures of rat and human IAPP. The results of gel filtration experiments conducted on A13P-rat IAPP and F15D-rat IAPP. An AGADIR analysis of the helical propensity of rat IAPP, A13P rat IAPP, and F15D rat IAPP. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public Access Author ManuscriptBiochemistry. Author manuscript; available in PMC 2011 February 9. Published in final edited form as:Biochemistry. Amyloid formation plays an important role in a broad range of human diseases, including Alzheimer's disease, Parkinson's disease, and type II diabetes (1-3). Islet amyloid polypeptide (IAPP), also known as amylin, is a 37-residue polypeptide co-locally produced with insulin and co-secreted by the pancreatic β-cells as a soluble monomer (4-9). IAPP is the major protein component of the pancreatic islet amyloid deposits often associated with type II diabetes (4-5). Formation of islet amyloid is believed to contribute to the pathology of the disease by promoti...

Induction of de novo α-synuclein fibrillization in a neuronal model for Parkinson’s disease

“…Likewise, in transthyretin (TTR) amyloid diseases, murine/human TTR homologs form heterotetramers that impair amyloid formation (51,52), and aggregation in vivo was achieved mostly in Tg mice expressing TTR mutants on an endogenous TTR-KO background (52). Finally, the aggregation kinetics of the islet amyloid polypeptide (IAPP) in bulk solution was reduced dramatically by the presence of its rat homolog (53,54).…”

Matrix Metalloproteinase-9 Protects Islets from Amyloid-induced Toxicity

“…Hexapeptides derived from the amyloidogenic region 20 -29 as well as other hIAPP fragments and structurally related peptides have been shown to be modulators of hIAPP fibrillogenesis (31)(32)(33)(34). For MMP-9 cleavage of hIAPP to be a target to reduce amyloid formation and cytotoxicity, it is important that its cleavage products do not aggravate full-length hIAPP's toxicity.…”

“…Not-Some hIAPPderived fragments and structurally related peptides have been shown to be able to inhibit while others have been shown to be able to enhance fibril formation (31)(32)(33)(34). To test whether hIAPP 16 -37 is able to modulate the aggregation kinetics of full-length hIAPP, mixtures of full-length hIAPP and hIAPP 16 -37 at ratios of 1:0.5, 1:1, 1:5, and 1:10 were analyzed.…”

Stability Analysis of Human Islet Amyloid Polypeptide and Its Mutated Oligomeric Forms

“…This work provides a molecular basis for improving our understanding of interactions governing the self-assembly of amyloidogenichIAPP peptides and non-amyloidogenicrIAPP peptides. Therefore rIAPP peptides could be used as therapeutic agents for diabetes 2 patients [27].…”