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Enhanced in vitro production of amyloid-like fibrils from mutant (S20G) islet amyloid polypeptide
Linköping University, Department of Molecular and Clinical Medicine, Molecular and Immunological Pathology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
First Department of Medicine, Wakayama University of Medical Science, Kagawa Medical University, Japan.
First Department of Medicine, Wakayama University of Medical Science, Kagawa Medical University, Japan.
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2001 (English)In: Amyloid: Journal of Protein Folding Disorders, ISSN 1350-6129, E-ISSN 1744-2818, Vol. 8, no 4, 242-249 p.Article in journal (Refereed) Published
Abstract [en]

Islet amyloid polypeptide (IAPP, “amylin”) is the amyloid-fibril-forming polypeptide in the islets of Langerhans associated with type 2 diabetes mellitus. A missense mutation in the IAPP gene associated with early-onset type 2 diabetes has been identified in the Japanese population. This mutation results in a glycine for serine substitution at position 20 of the mature IAPP molecule. Whether or not formation of islet amyloid with resulting destruction of islet tissue is the cause of this diabetes is yet not known. The present in vitro study was performed in order to investigate any influence of the amino acid substitution on the fibril formation capacity. Synthetic full-length wild type (lAPPwt) and mutant (IAPPS20G) as well as corresponding truncated peptides (position 18-29) were dissolved in dimethylsulfoxide (DMSO) or in 10% acetic acid at a concentration of 10 mg/mL and their fibril forming capacity was checked by Congo red staining, electron microscopy, a Congo red affinity assay and Thioflavine T fluorometric assay. It was found that full-length and truncated IAPPS20G both formed more amyloid-like fibrils and did this faster compared to IAPPwt. The fibril morphology differed slightly between the preparations. Conclusion: The amino acid substitution (S20G) is situated close to the region of the IAPP molecule implicated in the IAPP fibrillogenesis. The significantly increased formation of amyloid-like fibrils by IAPPS20G is highly interesting and may be associated with an increased islet amyloid formation in vivo and of fundamental importance in the pathogenesis of this specific form of diabetes.

Place, publisher, year, edition, pages
2001. Vol. 8, no 4, 242-249 p.
Keyword [en]
Islet amyloid polypeptide, fibrillogenesis, mutation, dye fluorescence, type 2 diabetes
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-25451DOI: 10.3109/13506120108993820Local ID: 9897OAI: oai:DiVA.org:liu-25451DiVA: diva2:245780
Note
On the day of the defence day the status of this article was submittedAvailable from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Islet amyloid polypeptide (IAPP): Mechanisms of Amyloidogenesis in the Pancreatic Islets and Potential Roles in Diabetes Mellitus
Open this publication in new window or tab >>Islet amyloid polypeptide (IAPP): Mechanisms of Amyloidogenesis in the Pancreatic Islets and Potential Roles in Diabetes Mellitus
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Islet amyloid is the most common characteristic feature of the islets in type 2 diabetes, being found in up to 90% of diabetic patients at post-mortem. lt has as its unique component the islet beta-cell peptide islet amyloid polypeptide (IAPP), which is eo-secreted with insulin. Because all human subjects produce and secrete the amyloidogenic form of IAPP, yet not all develop islet amyloid, some other factors must be involved in islet amyloid formation. The aim of the research presented in this thesis was to study factors of importance for the IAPP amyloidogenesis in type 2 diabetes. We developed a mouse monoclonal antibody to raVmouse IAPP (MAb4A5). MAb4A5 shows reactivity with IAPP in different species without detecting its close relative CGRP. In the pancreatic islets from patients with type 2 diabetes and diabetic cat, MAb4A5 labels immunohistochemically cellular IAPP but not IAPP in islet amyloid deposits. In contrast to MAb4A5 polyclonal rabbitiAPP antisera label beta cells close to amyloid only weakly, but label strongly IAPP in its amyloid form. The varying findings of IAPP immunoreactivity in pancreatic islets indicate that IAPP undergoes structural changes (impaired cleavage of proiAPP, conformational change, or post-transitional modifications) during the amyloidogenesis. A potentially important finding was the increased IAPP immunoreactivity in beta cells in islets of impaired glucose tolerant cats, irrespective of presence of amyloid in these islets. The finding may indicate that the formation of first islet amyloid occurs before Type 2 diabetes is manifest. Given the immunohistochemical results with MAb 4A5, we investigated whether the altered immunoreactivity of IAPP in association with the amyloidogenesis is due to a modification of IAPP (e.g. non-enzymatic glycation). We used synthetic IAPP fibrils glycated in vitro to study if non-enzymatic glycation may result in loss of an antigenic epitope. The results showed that a possible explanation of the lack of immunoreactivity of islet amyloid with MAb 4A5 actually is an nonenzymatic glycation. Association of an IAPP gene mutation with Type 2 diabetes has been found in the Japanese and Chinese population. We studied the possible enhanced fibril formation capacity of the mutant IAPP in vitro. Full-length and truncated IAPPS20G can form more amyloid-like fibrils and do this faster compared to wild type IAPP in vitro. We concluded that mutant (S20G) IAPP is a more amyloidogenic IAPP molecule and may be associated with an increased islet amyloid formation in vivo.

Based on the reports on the occurrence of islet amyloid in transgenic mice fed high fat diet, we investigated effects of free fatty acids on IAPP amyloid formation in isolated islets from transgenic mice expressing the gene for human IAPP but deficient of endogenous murine IAPP, and effects of FFAs on polymerization of IAPP in vitro. We found free fatty acids accelerate and increase polymerization of IAPP in vitro and promote amyloid like aggregation occurring in cultivated transgenic mouse isolated islets. All these results indicate that the pathogenesis of the islet amyloid may be a complex process involving many different mechanisms.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 70 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 655
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-28607 (URN)13762 (Local ID)91-7219-756-0 (ISBN)13762 (Archive number)13762 (OAI)
Public defence
2001-01-12, Berzeliussalen, Universitetssjukhuset, Linköping, 13:30 (Swedish)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-08-17Bibliographically approved

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Westermark, Gunilla

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