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Aberrant processing of human proislet amyloid polypeptide results in increased amyloid formation
Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Division of cell biology.
Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Division of cell biology.
2005 (English)In: Diabetes, ISSN 0012-1797, Vol. 54, no 7, 2117-2125 p.Article in journal (Refereed) Published
Abstract [en]

The amyloid present in the islets of Langerhans in type 2 diabetes is polymerized islet amyloid polypeptide (IAPP). The precursor protein proIAPP is posttranslationally modified, a process involving the removal of NH2- and COOH-terminal flanking peptides. This step is performed by the prohormone convertases PC2 and PC1/3. PC2 processes proIAPP preferably at the NH 2-terminal processing site, and PC1/3 processes proIAPP exclusively at the COOH-terminal site. Little is known regarding the exact circumstances leading to islet amyloid formation. In this study, we have examined the possible significance of aberrant processing of proIAPP on amyloid formation in several in vitro cellular systems. In our studies, human (h)-proIAPP was transfected into β-TC-6 cells expressing both prohormone convertases and in which proIAPP is processed into IAPP. Additionally, h-proIAPP was transfected into three different pituitary-derived cell lines with different prohormone convertase profiles: AtT-20 cells (deficient in PC2), GH3 cells (deficient in PC1/3), and GH4C1 cells (deficient in both convertases). We followed the processing of h-proIAPP with antibodies specific for the respective cleavage sites and stained the cells with Congo red to verify the accumulation of amyloid. Incomplete processing of h-proIAPP that occurs in AtT-20 and GH4C1 cells resulted in the formation of intracellular amyloid. No amyloid developed in β-TC-6 and GH3 cells lines with full processing of proIAPP. An intracellular increase in proIAPP and/or its metabolic products may thus promote intracellular amyloid formation, thereby causing cell death. When extracellularly exposed, this amyloid might act as template for continuing amyloid formation from processed IAPP released from the surrounding β-cells. © 2005 by the American Diabetes Association.

Place, publisher, year, edition, pages
2005. Vol. 54, no 7, 2117-2125 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-30444DOI: 10.2337/diabetes.54.7.2117Local ID: 16007OAI: diva2:251266
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-01-03
In thesis
1. Proislet Amyloid Polypeptide (proIAPP): Impaired Processing is an Important Factor in Early Amyloidogenesis in Type 2 Diabetes
Open this publication in new window or tab >>Proislet Amyloid Polypeptide (proIAPP): Impaired Processing is an Important Factor in Early Amyloidogenesis in Type 2 Diabetes
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amyloid is defined as extracellular protein aggregates with a characteristic fibrillar ultra-structure, Congo red affinity and a unique x-ray diffraction pattern. At present, 25 different human amyloid fibril proteins have been identified, and amyloid aggregation is associated with pathological manifestations such as Alzheimer’s disease, spongiform encephalopathy and type 2 diabetes. Amyloid aggregation triggers apoptosis by incorporation of early oligomers in cellular membranes, causing influx of ions. Amyloid is the only visible pathological islet alteration in subjects with type 2 diabetes, and islet amyloid polypeptide (IAPP) is the major islet amyloid fibril component. IAPP is produced by beta-cells and co-localized with insulin in the secretory granules. Both peptides are synthesised as pro-molecules and undergo proteolytic cleavage by the prohormone convertase 1/3 and 2. Although IAPP is the main amyloid constituent, both proIAPP and proIAPP processing intermediates have been identified in islet amyloid.

The aim of this thesis was to study the role of impaired processing of human proIAPP in early islet amyloidogenesis. Five cell lines with individual processing properties were transfected with human proIAPP and expression, aggregation and viability were studied. Cells unable to process proIAPP into IAPP or to process proIAPP at the N-terminal processing site accumulated intracellular amyloid-like aggregates and underwent apoptosis. Further, proIAPP immunoreactivity was detected in intracellular amyloid-like aggregates in betacells from transgenic mice expressing human IAPP and in transplanted human beta-cells. ProIAPP was hypothesized to act as a nidus for further islet amyloid deposition, and to investigate this theory, amyloid-like fibrils produced from recombinant IAPP, proIAPP and insulin C-peptide/A-chain were injected in the tail vein of transgenic mice expressing the gene for human IAPP. Pancreata were recovered after 10 months and analysed for the presence of amyloid. Both IAPP and proIAPP fibrils but not des-31,32 proinsulin fibrils, caused an increase in affected islets and also an increase of the amyloid amount. This finding demonstrates a seeding capacity of proIAPP on IAPP fibrillogenesis. IAPP has been known for some time to trigger apoptosis in cultured cells, and a novel method for real time detection of apoptosis in beta-cells was developed. Aggregation of recombinant proIAPP and proIAPP processing intermediates were concluded to be inducers of apoptosis as potent as IAPP fibril formation.

From the results of this study, a scenario for initial islet amyloidogenesis is proposed. Initial amyloid formation occurs intracellularly as a result of alterations in beta-cell processing capacity. When the host cell undergoes apoptosis intracellular proIAPP amyloid becomes extracellular and can act as seed for further islet amyloid deposition.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2006. 74 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 967
Biosynthesis amyloid, Genetics amyloid, Metabolism amyloid, Islets of Langerhans, Proprotein convertases, Posttranslation protein processing
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
urn:nbn:se:liu:diva-8243 (URN)91-85643-59-9 (ISBN)
Public defence
2006-11-24, Berzeliussalen, Campus US, Linköpings Universitet, Linköping, 13:15 (English)
Available from: 2007-02-01 Created: 2007-02-01 Last updated: 2012-01-04Bibliographically approved

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Paulsson, JohanWestermark, Gunilla
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