Amyloid seeding of transthyretin by ex vivo cardiac fibrils and its inhibition

Abstract

Each of the 30 human amyloid diseases is associated with the aggregation of a particular precursor protein into amyloid fibrils. In transthyretin amyloidosis (ATTR), mutant or wild-type forms of the serum carrier protein transthyretin (TTR), synthesized and secreted by the liver, convert to amyloid fibrils deposited in the heart and other organs. The current standard of care for hereditary ATTR is liver transplantation, which replaces the mutant gene with the wild-type gene. However, the procedure is often followed by cardiac deposition of wild-type TTR secreted by the new liver. Here we find that amyloid fibrils extracted from autopsied and explanted hearts of ATTR patients robustly seed wild-type TTR into amyloid fibrils in vitro. Cardiac-derived ATTR seeds can accelerate fibril formation of wild-type and monomeric TTR at acidic pH and under physiological conditions, respectively. We show that this seeding is inhibited by peptides designed to complement structures of TTR fibrils. These inhibitors cap fibril growth, suggesting an approach for halting progression of ATTR.

Exploring Mechanisms of Inhibition of Amyloid Seeding of Transthyretin

“…Tetramer stabilization by ligands does not inhibit TTR amyloid formation induced by ATTR-D38A exvivo seeds. We previously found that the presence of tafamidis or diflunisal at 180 µM is not sufficient to prevent amyloid seeding of wild-type TTR catalyzed by ATTR fibrils extracted from an ATTR-D38A patient (3). Here we expand the study by evaluating the effect of these ligands at various concentrations.…”

“…For instance, inhibiting amyloid seeding may potentially hinder post-surgical ATTR cardiac deposition after liver transplantation. In our previous study, we found that tetramer stabilizers do not inhibit amyloid seeding catalyzed by amyloid fibrils extracted from an ATTR-D38A patient (3). In contrast, peptide inhibitors halted this process.…”

“…However, this extreme surgery is not sufficient to stop amyloid cardiac deposition in many patients that end up requiring secondary heart transplantation a few years later. Our recent studies have shown that pre-formed TTR fibrils present in the heart of ATTR patients by the time of surgery have the capacity to catalyze or seed fibril polymerization of wild-type TTR that is secreted by the implanted liver (3).…”

“…In our recent studies, we have developed and optimized peptide inhibitors that are designed to cap the tip of TTR fibrils and block further polymerization (3,10). This structure-based drug design strategy started with the identification of two amyloid-driving segments of transthyretin that comprise the βstrands F and H (10).…”

The inhibition of cellular toxicity of amyloid-beta by dissociated transthyretin

“…What makes the pair of TTR and Aβ42 particularly interesting is the amyloid nature of the two elements. In transthyretin amyloidosis patients, dissociation of tetrameric TTR leads to amyloid fibril formation and systemic TTR amyloid deposition [10][11][12]. Whether the amyloidogenicity of TTR is linked to its interaction to Aβ42 is still under debate.…”