Amorphous protein aggregates stimulate plasminogen activation, leading to release of cytotoxic fragments that are clients for extracellular chaperones

Constantinescu, Patrick; Brown, Rebecca; Wyatt, Amy R.; Ranson, Marie; Wilson, Mark R.

doi:10.1074/jbc.m117.786657

Cited by 25 publications

(23 citation statements)

References 55 publications

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“…The plasminogen activation system may work synergistically with other chaperones such as clusterin and α2M, which are involved in the neutralization and clearance of soluble and potentially cytotoxic fragments of protein aggregates. 23 It is interesting that a 420-kDa isoform of fibrinogen (fibrinogen-420), but not the predominant 340 kDa form, shows chaperone-like activity. 24 This holds true, in particular, for the additional 236-residue carboxyl terminus globular domain of fibrinogen-420 (α E C) in isolated form, which might be produced in vivo by proteolysis of fibrinogen-420.…”

Section: Extracellular Chaperonesmentioning

confidence: 99%

Decoration of Fibrin with Extracellular Chaperones

et al. 2019

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Background Many proteins bind to fibrin during clot formation in plasma. We previously identified by mass spectrometry the most abundant proteins that noncovalently bind to fibrin clots. Several of these proteins (e.g., apolipoprotein J/clusterin, haptoglobin, α2-macroglobulin, α1-antitrypsin) can act as extracellular chaperones. Objective We hypothesize that clot-binding proteins may interact with fibrin as chaperones. The goal of this study is to test this hypothesis and to investigate the origin of the cross-β or amyloid structures in fibrin clots, which are associated with protein unfolding. Methods and Results A thioflavin T assay was used to detect cross-β structures. A steadily increasing amount was measured in the fibrinogen fraction of plasma during heat stress, a standard treatment to induce unfolding of proteins. Heat-stressed plasma was clotted and clot-bound proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The results showed that the amounts of the clot-bound proteins were related to the duration of the heat stress. This indicates that cross-β structures in unfolded fibrin(ogen) are involved in clot binding of the proteins, which supports our chaperone hypothesis. A contributing role of fibrin formation itself was studied by clotting purified fibrinogen with thrombin in the presence of thioflavin T. The fluorescence intensity increased in time in the presence of thrombin, but did not increase in its absence. This provides evidence for the generation of cross-β structures during fibrin formation. Conclusion Fibrin clots generated in plasma are decorated with extracellular chaperones. The binding of these chaperones involves cross-β structures originating both from unfolded fibrinogen and from fibrin formation.

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Section: Extracellular Chaperonesmentioning

confidence: 99%

Decoration of Fibrin with Extracellular Chaperones

et al. 2019

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“…This result is similar to prior findings in a clusterin knockout mouse model which found no change in cleavage of brain hAPP to amyloidogenic species 11 ; in another study, reduced rather than increased production of brain Aβ40 and 42 was observed in clusterin-deficient mice 12 . Second, 7B2 expression might negatively impact the degradation of amyloid aggregates, either by hindering their extracellular proteolytic clearance 39 ; or, less likely, by blocking amyloid degradation after reuptake into an intracellular degradative compartment. We explored the possibility that 7B2 loss might impact clusterin levels, thus indirectly reducing plaque burden; but no such association was found.…”

Section: Discussionmentioning

confidence: 99%

“…Frozen hemi-brains were sonicated in 1 ml of ice-cold 0.1 N HCl, frozen and thawed, centrifuged in the cold, and 0.5 ml of the clear supernatant lyophilized. After resolubilization and clarification of the dried extracts in RIA buffer, triplicate samples were subjected to RIA for 7B2 using iodinated peptide 7B2 23 – 39 and rabbit antiserum 13B6 (1:50,000 final dilution), as previously described 46 . Cross-reaction with the 21 kDa form of 7B2, the major form in brain tissue, was estimated to be approximately 30% using recombinant His-tagged 7B2 as a standard.…”

Section: Methodsmentioning

confidence: 99%

7B2 chaperone knockout in APP model mice results in reduced plaque burden

Jarvela

Womack

Georgiou

et al. 2018

Sci Rep

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Impairment of neuronal proteostasis is a hallmark of Alzheimer’s and other neurodegenerative diseases. However, the underlying molecular mechanisms leading to pathogenic protein aggregation, and the role of secretory chaperone proteins in this process, are poorly understood. We have previously shown that the neural-and endocrine-specific secretory chaperone 7B2 potently blocks in vitro fibrillation of Aβ42. To determine whether 7B2 can function as a chaperone in vivo, we measured plaque formation and performed behavioral assays in 7B2-deficient mice in an hAPPswe/PS1dE9 Alzheimer’s model mouse background. Surprisingly, immunocytochemical analysis of cortical levels of thioflavin S- and Aβ-reactive plaques showed that APP mice with a partial or complete lack of 7B2 expression exhibited a significantly lower number and burden of thioflavin S-reactive, as well as Aβ-immunoreactive, plaques. However, 7B2 knockout did not affect total brain levels of either soluble or insoluble Aβ. While hAPP model mice performed poorly in the Morris water maze, their brain 7B2 levels did not impact performance. Since 7B2 loss reduced amyloid plaque burden, we conclude that brain 7B2 can impact Aβ disposition in a manner that facilitates plaque formation. These results are reminiscent of prior findings in hAPP model mice lacking the ubiquitous secretory chaperone clusterin.

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“…Recent studies showed that amorphous protein aggregates are degraded by plasmin, releasing smaller soluble protein fragments, which are cytotoxic in vitro for both endothelial and microglial cells (Constantinescu et al, 2017).…”

Section: Contribution Of Ttr Proteolysis To Amyloid Formationmentioning

confidence: 99%

Modulation of the Mechanisms Driving Transthyretin Amyloidosis

Bezerra

Saraiva

Almeida

2020

Front. Mol. Neurosci.

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Transthyretin (TTR) amyloidoses are systemic diseases associated with TTR aggregation and extracellular deposition in tissues as amyloid. The most frequent and severe forms of the disease are hereditary and associated with amino acid substitutions in the protein due to single point mutations in the TTR gene (ATTRv amyloidosis). However, the wild type TTR (TTR wt) has an intrinsic amyloidogenic potential that, in particular altered physiologic conditions and aging, leads to TTR aggregation in people over 80 years old being responsible for the non-hereditary ATTRwt amyloidosis. In normal physiologic conditions TTR wt occurs as a tetramer of identical subunits forming a central hydrophobic channel where small molecules can bind as is the case of the natural ligand thyroxine (T4). However, the TTR amyloidogenic variants present decreased stability, and in particular conditions, dissociate into partially misfolded monomers that aggregate and polymerize as amyloid fibrils. Therefore, therapeutic strategies for these amyloidoses may target different steps in the disease process such as decrease of variant TTR (TTRv) in plasma, stabilization of TTR, inhibition of TTR aggregation and polymerization or disruption of the preformed fibrils. While strategies aiming decrease of the mutated TTR involve mainly genetic approaches, either by liver transplant or the more recent technologies using specific oligonucleotides or silencing RNA, the other steps of the amyloidogenic cascade might be impaired by pharmacologic compounds, namely, TTR stabilizers, inhibitors of aggregation and amyloid disruptors. Modulation of different steps involved in the mechanism of ATTR amyloidosis and compounds proposed as pharmacologic agents to treat TTR amyloidosis will be reviewed and discussed.

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Amorphous protein aggregates stimulate plasminogen activation, leading to release of cytotoxic fragments that are clients for extracellular chaperones

Cited by 25 publications

References 55 publications

Decoration of Fibrin with Extracellular Chaperones

Decoration of Fibrin with Extracellular Chaperones

7B2 chaperone knockout in APP model mice results in reduced plaque burden

Modulation of the Mechanisms Driving Transthyretin Amyloidosis

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