Protease resistance of ex vivo amyloid fibrils implies the proteolytic selection of disease-associated fibril morphologies

Abstract

Several studies recently showed that ex vivo fibrils from patient or animal tissue were structurally different from in vitro formed fibrils from the same polypeptide chain. Analysis of serum amyloid A (SAA) and Ab-derived amyloid fibrils additionally revealed that ex vivo fibrils were more protease stable than in vitro fibrils. These observations gave rise to the proteolytic selection hypothesis that suggested that disease-associated amyloid fibrils were selected inside the body by their ability to resist endogenous clearance mechanisms. We here show, for more than twenty different fibril samples, that ex vivo fibrils are more protease stable than in vitro fibrils. These data support the idea of a proteolytic selection of pathogenic amyloid fibril morphologies and help to explain why only few amino acid sequences lead to amyloid diseases, although many, if not all, polypeptide chains can form amyloid fibrils in vitro.

Linking hIAPP misfolding and aggregation with type 2 diabetes mellitus: a structural perspective

“…Perlecan is thought to provide further stability to IAPP fibrils by assisting binding to membranes of islet capillaries. Like other amyloidogenic proteins, hIAPP amyloids are stable structures that are resistant to proteolysis [ 90 ] and hence can accumulate easily within the body and are difficult to remove. The stability of IAPP (28−33) polar fibrils is attributed to van der Waals and electrostatic bonds including hydrogen bonds [ 91 ].…”

“…The structures also explain one reason why the S20G hereditary mutation may facilitate hIAPP fibrillisation since glycine residues allow a more kinked conformation that in turn may allow the peptide chain to adopt a fibril-forming fold thus more easily forming a stable fibril structure. Since three of the polymorphs do not resemble any structures produced in vitro it suggests in vitro structures may differ from those in vivo as previously summarised for other amyloidogenic proteins [ 90 ] due to ex-vivo fibrils being more stable and protease-resistant which has important consequences for therapeutic design [ 139 ].…”

Role of the MBP protein in myelin formation and degradation in the brain

“…It is still not completely known whether this is a consequence of the senescence of microglia itself or if the accumulation of MBP aggregates is caused by the overloading of myelin debris in the cellular environment, which normal cells cannot cope with utilizing. In some ways this impaired microglial degradative capacity is reminiscent of aberrant accumulation of amyloid proteins in microglial cells during amyloid-induced neurodegenerative disorders, such as Alzheimer's (Paresce, Chung and Maxfield, 1997) or Huntington diseases (Franklin, Clarke and Patani, 2021), which can be explained by the high stability and resistance of amyloid fibrils to enzymatic proteolysis (Kushnirov, Dergalev and Alexandrov, 2020;Schönfelder et al, 2021).…”

SAA fibrils involved in AA amyloidosis are similar in bulk and by single particle reconstitution: A MAS solid-state NMR study

“…It has been found that in-vitro and ex-vivo SAA fibril structures are distinct ( Bansal et al, 2021 ) and that the ex-vivo amyloid fibril morphology can be propagated into an in-vitro formed structure by seeding ( Heerde et al, 2022 ). Ex-vivo and in-vitro SAA amyloid fibrils differ not only by their structure, but ex-vivo fibrils are also more protease stable ( Schönfelder et al, 2021 ), suggesting that disease associated fibril polymorphs could potentially be selected inside the body by their ability to resist endogenous clearance mechanisms.…”