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Prefibrillar oligomeric Transthyretin mutants - amyloid conformation, toxicity and association with Serum amyloid P component
Umeå University, Faculty of Medicine, Molecular Biology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Amyloidoses represent a heterogeneous group of diseases characterized by abnormal protein metabolism leading to extracellular deposition of fibrillar, proteinaceous amyloid in various tissues and organs of the body. To date more than 20 different proteins have been linked to diseases with amyloid depositions, of which Alzheimer’s disease and the prion-associated diseases are the most well known. Despite the origin of protein in the amyloid, the fibrils share some common biochemical and biophysical properties such as a diameter of 8-13 nm, a β-pleated sheet secondary structure packed in an ordered crystal-like way, Congo red and thioflavin binding with characteristic spectroscopic patterns and decoration of the fibrils with Serum amyloid P component and glycoseaminoglycans.

The plasma protein transthyretin (TTR) is associated with familial amyloidosis with polyneuropathy (FAP) and senile systemic amyloidosis (SSA). FAP is a lethal, autosomal inherited disorder caused by point mutations in the TTR-gene. More than 80 different mutations have been associated with amyloid formation and linked to FAP. The interpretation is that amino acid replacements at different sites of the polypeptide lead to reduced stability. Mutant TTR were constructed that have a strong tendency to self-aggregate under physiological conditions. The precipitates were shown to be amyloid by staining with thioflavin T and Congo red. As the mutants were sensitive to trypsin cleavage compared to plasma TTR, we suggest that the mutants represent amyloid precursors or that they may share structural properties with intermediates on a pathway leading to amyloid deposition. Monoclonal antibodies were generated that exclusively recognize the amyloidogenic folding of TTR providing direct biochemical evidence for a structural change in amyloidogenic intermediates. Two cryptic epitopes were mapped to a domain of TTR, where most mutations associated with amyloidosis occur and is proposed to be displaced at the initial phase of amyloid formation. Amyloidogenic intermediates of TTR were shown to induce a toxic, free radical dependent, response in cultured neuroblastoma cells. Morphological studies revealed a correlation between toxicity (apoptosis) and the presence of immature amyloid suggesting that mature full-length fibrils represent an inert end stage, which might serve as a rescue mechanism.

Serum amyloid P component (SAP) is a highly conserved plasma glycoprotein universally found associated with amyloid depositions independently of protein origin. SAP’s role in amyloid formation is contradictory since both inhibition and promotion of aggregation have been shown in the case of fibril formation from the Aβ peptide of Alzheimer’s disease. Amyloidogenic prefibrils of TTR were shown to bind SAP and no interference with aggregation was detected. SAP co-localize in patches with mutant TTR on the surface of neuroblastoma cells and prevent apoptosis induced by mutant TTR and Aβ peptide, while several other molecules known to decorate amyloid fibrils were without effect.

Place, publisher, year, edition, pages
2005. , 47 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 958
Keyword [en]
Cell and molecular biology
Keyword [sv]
Cell- och molekylärbiologi
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-494ISBN: 91-7305-862-9 (print)OAI: oai:DiVA.org:umu-494DiVA: diva2:143599
Public defence
2005-04-29, Major Groove, 6L, Inst f Molekylärbiologi, Umeå, 13:00
Opponent
Supervisors
Available from: 2005-04-08 Created: 2005-04-08Bibliographically approved
List of papers
1. Characterisation of two highly amyloidogenic mutants of transthyretin.
Open this publication in new window or tab >>Characterisation of two highly amyloidogenic mutants of transthyretin.
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1997 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 36, no 18, 5346-5352 p.Article in journal (Refereed) Published
Abstract [en]

The plasma protein transthyretin (TTR) has the potential to form amyloid under certain conditions. More than 50 different point mutations have been associated with amyloid formation that occurs only in adults. It is not known what structural changes are introduced into the structure of this otherwise stable molecule that results in its aggregation into insoluble amyloid fibrils. On the basis of calculations of the frequency of known mutations over the polypeptide, we have constructed two mutants in the D-strand of the polypeptide. These molecules, containing either a deletion or a substitution at amino acid positions 53−55, were unstable and spontaneously formed aggregates upon storage in TBS (pH 7.6). The precipitates were shown to be amyloid by staining with thioflavin T and Congo Red. Their ultrastructure was very similar to that of amyloid fibrils deposited in the vitreous body of patients with familial amyloidotic polyneuropathy type 1 with an amino acid replacement in position 30 (TTRmet30). Like amyloid isolated from the vitreous body of the eye, the amyloid precipitates generated from the TTR mutants exposed a trypsin cleavage site between amino acid residues 48 and 49, while plasma TTRmet30 isolated from amyloidosis patients as well as wild-type TTR only showed minor trypsin sensitivity. Our data indicate that the mutants we have constructed are similar to amyloid precursors or may share structural properties with intermediates on a pathway leading to amyloid deposits of plasma TTR.

Identifiers
urn:nbn:se:umu:diva-4474 (URN)10.1021/bi961649c (DOI)9154916 (PubMedID)
Available from: 2005-04-08 Created: 2005-04-08 Last updated: 2011-04-13Bibliographically approved
2. Exposure of cryptic epitopes on transthyretin only in amyloid and in amyloidogenic mutants
Open this publication in new window or tab >>Exposure of cryptic epitopes on transthyretin only in amyloid and in amyloidogenic mutants
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1999 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, Vol. 96, no 6, 3108-3113 p.Article in journal (Refereed) Published
Abstract [en]

The structural requirements for generation of amyloid from the plasma protein transthyretin (TTR) are not known, although it is assumed that TTR is partly misfolded in amyloid. In a search for structural determinants important for amyloid formation, we generated a TTR mutant with high potential to form amyloid. We demonstrated that the mutant represents an intermediate in a series of conformational changes leading to amyloid. Two monoclonal antibodies were generated against this mutant; each displayed affinity to ex vivo TTR and TTR mutants with amyloidogenic folding but not to wild-type TTR or mutants exhibiting the wild-type fold. Two cryptic epitopes were mapped to a domain of TTR, where most mutations associated with amyloidosis occur and which we propose is displaced at the initial phase of amyloid formation, opening up new surfaces necessary for autoaggregation of TTR monomers. The results provide direct biochemical evidence for structural changes in an amyloidogenic intermediate of TTR.

Identifiers
urn:nbn:se:umu:diva-4475 (URN)10077645 (PubMedID)
Available from: 2005-04-08 Created: 2005-04-08Bibliographically approved
3. Only amyloidogenic inermediates of transthyretin induce apoptosis
Open this publication in new window or tab >>Only amyloidogenic inermediates of transthyretin induce apoptosis
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2002 (English)In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, Vol. 294, no 2, 309-314 p.Article in journal (Refereed) Published
Abstract [en]

In diseases like Alzheimer's disease and familial amyloidotic polyneuropathy (FAP) amyloid deposits co-localize with areas of neurodegeneration. FAP is associated with mutations of the plasma protein transthyretin (TTR). We can here show an apoptotic effect of amyloidogenic mutants of TTR on a human neuroblastoma cell line. Toxicity could be blocked by catalase indicating a free oxygen radical dependent mechanism. The toxic effect was dependent on the state of aggregation and unexpectedly mature fibrils from FAP-patients who failed to exert an apoptotic response. Morphological studies revealed a correlation between toxicity and the presence of immature amyloid. Thus, we can show that toxicity is associated with early stages of fibril formation and propose that mature full-length fibrils represent an inert end stage, which might serve as a rescue mechanism. (c) 2002 Elsevier Science (USA).

Keyword
Amyloid, Transthyretin, Cytotoxicity, Apoptosis, Free radicals
Identifiers
urn:nbn:se:umu:diva-4476 (URN)10.1016/S0006-291X(02)00465-5 (DOI)12051711 (PubMedID)
Available from: 2005-04-08 Created: 2005-04-08Bibliographically approved
4. Inhibition of amyloid induced apoptosis - a new role for Serum amyloid P component
Open this publication in new window or tab >>Inhibition of amyloid induced apoptosis - a new role for Serum amyloid P component
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4477 (URN)
Available from: 2005-04-08 Created: 2005-04-08 Last updated: 2010-01-13Bibliographically approved

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