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Islet amyloid polypeptide triggers limited complement activation and binds complement inhibitor C4b-binding protein, which enhances fibril formation.

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Author

Summary, in English

Islet amyloid polypeptide (IAPP) is synthesized in pancreatic β-cells and co-secreted with insulin. Aggregation and formation of IAPP-amyloid plays a critical role in β-cell death in type 2 diabetic patients. Since Aβ-fibrils in Alzheimer's disease activate the complement system, we have here investigated specific interactions between IAPP and complement factors. IAPP fibrils triggered limited activation of complement in vitro, involving both the classical and the alternative pathways. Direct binding assays confirmed that IAPP fibrils interact with globular head domains of complement initiator C1q. Furthermore, IAPP also bound complement inhibitors factor H and C4b-binding protein (C4BP). Recombinant C4BP mutants were used to show that complement control protein (CCP) domains 8 and 2 of the α-chain were responsible for the strong, hydrophobic binding of C4BP to IAPP. Immunostaining of pancreatic sections from type 2 diabetic patients revealed the presence of complement factors in the islets and varying degree of co-localization between IAPP fibrils and C1q, C3d as well as C4BP and FH but not membrane attack complex. Furthermore, C4BP enhanced formation of IAPP fibrils in vitro. We conclude that C4BP binds to IAPP thereby limiting complement activation and may be enhancing formation of IAPP fibrils from cytotoxic oligomers.

Publishing year

2012

Language

English

Pages

10824-10833

Publication/Series

Journal of Biological Chemistry

Volume

287

Issue

14

Document type

Journal article

Publisher

American Society for Biochemistry and Molecular Biology

Topic

  • Other Basic Medicine
  • Endocrinology and Diabetes

Status

Published

Research group

  • Protein Chemistry, Malmö
  • Diabetes - Islet Patophysiology

ISBN/ISSN/Other

  • ISSN: 1083-351X