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Studies on Islet Amyloid Polypeptide Aggregation: From Model Organism to Molecular Mechanisms
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The proper folding of a protein into its defined three--‐dimensional structure is one of the many fundamental challenges a cell encounters. A number of tightly controlled pathways have evolved to assist in the proper folding of a protein, but also to aid in the removal of misfolded proteins. Despite the presence of these pathways accumulation of misfolded proteins can still occur. Amyloid deposits consist of misfolded proteins with a characteristic highly ordered fibrillar structure that will exert affinity for the amyloid dye Congo red and has a unique X-ray diffraction pattern. Currently 27 different proteins have been identified as amyloid forming proteins in human, however the exact role of amyloid in the pathogenesis of the connected disease is most often unclear.

Islet amyloid is made up of the beta cell derived hormone islet amyloid polypeptide (IAPP) and is associated with the development of type 2 diabetes. Propagation of IAPP-fibrils is believed to be one important cause of the pancreatic beta cell death detected in patients with type 2 diabetes. IAPP is a naturally occurring polypeptide hormone stored and secreted together with insulin. IAPP and insulin arise from posttranslational processing of their biological inactive precursors proIAPP and proinsulin. In addition to human, cat and monkey IAPP will form amyloid deposits in conditions resembling human type 2 diabetes. However, IAPP from mouse and rat do not form amyloid as a result of the differences in amino acid sequence.

My main research goal was to establish a unique model system suitable to study the effects of proIAPP and IAPP aggregation. I selected Drosophila melanogaster due to its many suitable characteristics as a model organism and its superior genetic toolbox. I have demonstrated that over--‐expression of hproIAPP and hIAPP in the central nervous system (CNS) results in aggregate formation in the brain and neighbouring fat body. Consistent with previous studies, expression of mIAPP does not result in the formation of aggregates. To investigate the intracellular effects of hproIAPP and hIAPP aggregation on a specific population of neurons, we targeted the expression of these peptides specifically to 16 neurons in the brain, the pdf- neurons. These pdf-neurons are divided into 2 clusters of 8 cells per brain hemisphere. First I showed that expression of aggregation prone hIAPP and hproIAPP resulted in significant death of the 8 cells, whereas expression of mIAPP had no such effect. In efforts to pinpoint the mechanisms behind the observed cell death I demonstrated that hproIAPP and hIAPP both pass the ERs quality control for protein folding and that the initiated cell death does not occur through classical apoptosis. Instead, selective autophagy is activated by hIAPP and hproIAPP. This activation counteracts the usually neuro-protective effects of autophagy and contributes to cell death. Strikingly, I also showed that Aâ, the amyloid protein implicated in Alzheimer’s disease, does not exhibit any intracellular toxicity when expressed in pdf-cells. This supports the existence of separate toxic pathways for different amyloid proteins.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2011. , 100 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1254
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-70094ISBN: 9789173930994 (print)OAI: oai:DiVA.org:liu-70094DiVA: diva2:435439
Public defence
2011-09-16, Berzeliussalen, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2011-08-18 Created: 2011-08-18 Last updated: 2017-12-12Bibliographically approved
List of papers
1. Real-Time Monitoring of Apoptosis by Caspase-3-Like Protease Induced FRET Reduction Triggered by Amyloid Aggregation
Open this publication in new window or tab >>Real-Time Monitoring of Apoptosis by Caspase-3-Like Protease Induced FRET Reduction Triggered by Amyloid Aggregation
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2008 (English)In: Experimental Diabetes Research, ISSN 1687-5214, E-ISSN 1687-5303, Vol. 2008, no 865850Article in journal (Refereed) Published
Abstract [en]

Amyloid formation is cytotoxic and can activate the caspase cascade. Here, we monitor caspase-3-like activity as reduction of fluorescence resonance energy transfer (FRET) using the contstruct pFRET2-DEVD containing enhanced cyan fluorescent protin (EYFP) linked by the caspase-3 specific cleavage site residues DEVD. Beta-TC-6 cells were transfected, and the fluoorescence was measured at 440 nm excitation and 535 nm (EYFP) and 480 nm (ECFP) emission wavelength. Cells were incubated with recombinant pro lset Amyloid Polypeptide (rec prolAPP) or the processing metabolites of prolAPP; the N-terminal flanking peptide withIAPP (recN+IAPP); IAPP with the C-terminal flanking peptied (recIAPP+C) and lslet Amyloid Polypeptide (recIAPP). Peptides were added in solubilized from (50 mu M) or as performed amyloid-like fibrils, or as a combination of these. FRET was measured and incubation with a mixture of solubilized peptide and performed fibrils resulted in loss of FRET and apoptosis was determined to occurein cells incubated with recproIAPP (49%), recN+IAPP (46%), recIAPP (72%) and recIAPP+C (59%). These results show that proIAPP and the processing intermediates reside the same cell toxic capacity as IAPP, and they can all have a central role in the reduction of beta-cell number in type 2 diabetes.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-19669 (URN)10.1155/2008/865850 (DOI)
Note
Original Publication: Johan F Paulsson, Sebastian Schultz, Martin Kohler, Ingo Leibiger, Per-Olof Berggren and Gunilla Westermark, Real-Time Monitoring of Apoptosis by Caspase-3-Like Protease Induced FRET Reduction Triggered by Amyloid Aggregation, 2008, EXPERIMENTAL DIABETES RESEARCH, (2008), 865850. http://dx.doi.org/10.1155/2008/865850 Copyright: Authors Available from: 2009-08-28 Created: 2009-07-10 Last updated: 2017-12-13Bibliographically approved
2. Drosophila Melanogaster as a Model System for Studies of Islet Amyloid Polypeptide Aggregation
Open this publication in new window or tab >>Drosophila Melanogaster as a Model System for Studies of Islet Amyloid Polypeptide Aggregation
2011 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 6Article in journal (Refereed) Published
Abstract [en]

Background: Recent research supports that aggregation of islet amyloid polypeptide (IAPP) leads to cell death and this makes islet amyloid a plausible cause for the reduction of beta cell mass, demonstrated in patients with type 2 diabetes. IAPP is produced by the beta cells as a prohormone, and proIAPP is processed into IAPP by the prohormone convertases PC1/3 and PC2 in the secretory granules. Little is known about the pathogenesis for islet amyloid and which intracellular mechanisms are involved in amyloidogenesis and induction of cell death.

Methodology/Principal Findings: We have established expression of human proIAPP (hproIAPP), human IAPP (hIAPP) and the non-amyloidogenic mouse IAPP (mIAPP) in Drosophila melanogaster, and compared survival of flies with the expression driven to different cell populations. Only flies expressing hproIAPP in neurons driven by the Gal4 driver elavC(155,Gal4) showed a reduction in lifespan whereas neither expression of hIAPP or mIAPP influenced survival. Both hIAPP and hproIAPP expression caused formation of aggregates in CNS and fat body region, and these aggregates were both stained by the dyes Congo red and pFTAA, both known to detect amyloid. Also, the morphology of the highly organized protein granules that developed in the fat body of the head in hIAPP and hproIAPP expressing flies was characterized, and determined to consist of 15.8 nm thick pentagonal rod-like structures.

Conclusions/Significance: These findings point to a potential for Drosophila melanogaster to serve as a model system for studies of hproIAPP and hIAPP expression with subsequent aggregation and developed pathology.

Place, publisher, year, edition, pages
Public Library of Science (PLoS), 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-69857 (URN)10.1371/journal.pone.0020221 (DOI)000291682300005 ()
Note

Original Publication: Sebastian Schultz, Peter Nilsson and Gunilla Torstensdotter Westermark, Drosophila Melanogaster as a Model System for Studies of Islet Amyloid Polypeptide Aggregation, 2011, PLoS ONE, (6), 6. http://dx.doi.org/10.1371/journal.pone.0020221 Copyright: Public Library of Science (PLoS) http://www.plos.org/

Available from: 2011-08-10 Created: 2011-08-08 Last updated: 2017-12-08Bibliographically approved
3. HIAPP and hproIAPP triggers elective autophagy and inhibit the neuro-­protective effect of autophagy
Open this publication in new window or tab >>HIAPP and hproIAPP triggers elective autophagy and inhibit the neuro-­protective effect of autophagy
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2010 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Introduction: Amyloid formation is associated with cell death and islet amyloid is thought to participate in the 50-60% β-cell reduction detected in patients with type 2 diabetes. Islet amyloid polypeptide (IAPP) is the main amyloid protein in the islets of Langerhans. Initial IAPP-amyloid formation is intracellular and part of this amyloid constitutes of proIAPP.

Material & methods: We have established a new model in Drosophila melanogaster where expression of hproIAPP and IAPP results in the formation of amyloid. With this model, we have investigated the effect of protein aggregation on pathways such as ER-stress, unfolded protein response (UPR), apoptosis and autophagy. Important steps in the different pathways were manipulated by RNAi-technique or over- expression of endogenous Drosophila proteins.

Results: Expression of hproIAPP and hIAPP driven to the pdf-neurons led to cell death, but this was without activation of ER-stress, UPR or apoptosis. Aggregated hproIAPP and IAPP, labeled with antibodies against ubiquitin and p62 were accumulated intracellular, a finding that points to an involvement of autophagy. HproIAPP and hIAPP were shown to exert their toxic activity by an intracellular mechanism in contrary to Aβ42 and Aβ42 E22G that exhibit an extracellular toxic activity.

Conclusion: Studies on toxicity suggest that hproIAPP and hIAPP aggregates can occupy the autophagy pathway and prevent maintenance of basal cellular homeostasis. Comparison of proIAPP/IAPP and Aβ42 toxicity shows that amyloid proteins of separate origin can exhibit different toxicity.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-70093 (URN)
Available from: 2011-08-18 Created: 2011-08-18 Last updated: 2011-08-18Bibliographically approved

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