A novel mechano-enzymatic cleavage mechanism underlies transthyretin amyloidogenesis.

Julien Marcoux,Graham W Taylor,Philip N Hawkins,Guglielmo Verona,Mark B Pepys,Sofia Giorgetti,Mohsin M Naqvi,Justin Lp Benesch,Sarah Sanglier‐Cianférani,Julian D Gillmore,Ciro Cecconi,Sara Raimondi,Matteo T Degiacomi,P Patrizia Mangione,Carol V Robinson,Monica Stoppini,Vittorio Bellotti,Riccardo Porcari

doi:10.15252/emmm.201505357

Abstract

The mechanisms underlying transthyretin-related amyloidosis in vivo remain unclear. The abundance of the 49–127 transthyretin fragment in ex vivo deposits suggests that a proteolytic cleavage has a crucial role in destabilizing the tetramer and releasing the highly amyloidogenic 49–127 truncated protomer. Here, we investigate the mechanism of cleavage and release of the 49–127 fragment from the prototypic S52P variant, and we show that the proteolysis/fibrillogenesis pathway is common to several amyloidogenic variants of transthyretin and requires the action of biomechanical forces provided by the shear stress of physiological fluid flow. Crucially, the non-amyloidogenic and protective T119M variant is neither cleaved nor generates fibrils under these conditions. We propose that a mechano-enzymatic mechanism mediates transthyretin amyloid fibrillogenesis in vivo. This may be particularly important in the heart where shear stress is greatest; indeed, the 49–127 transthyretin fragment is particularly abundant in cardiac amyloid. Finally, we show that existing transthyretin stabilizers, including tafamidis, inhibit proteolysis-mediated transthyretin fibrillogenesis with different efficiency in different variants; however, inhibition is complete only when both binding sites are occupied.

Highlights

IntroductionThe abundance of the 49–127 transthyretin fragment in ex vivo deposits suggests that a proteolytic cleavage has a crucial role in destabilizing the tetramer and releasing the highly amyloidogenic 49–127 truncated protomer
The mechanisms underlying transthyretin-related amyloidosis in vivo remain unclear
Under the mild shear force conditions of low-pressure size-exclusion chromatography (SEC), the cleaved protein eluted as a single peak with the same Ve as native undigested tetrameric TTR (Fig 1A), and with both full-length protomer and the truncated residue 49–127 fragment detected by SDS–PAGE of the chromatographic peak (Fig 1A, inset)

Summary

Introduction

The abundance of the 49–127 transthyretin fragment in ex vivo deposits suggests that a proteolytic cleavage has a crucial role in destabilizing the tetramer and releasing the highly amyloidogenic 49–127 truncated protomer. We investigate the mechanism of cleavage and release of the 49–127 fragment from the prototypic S52P variant, and we show that the proteolysis/fibrillogenesis pathway is common to several amyloidogenic variants of transthyretin and requires the action of biomechanical forces provided by the shear stress of physiological fluid flow. We propose that a mechano-enzymatic mechanism mediates transthyretin amyloid fibrillogenesis in vivo. This may be important in the heart where shear stress is greatest; the 49–127 transthyretin fragment is abundant in cardiac amyloid. We show that existing transthyretin stabilizers, including tafamidis, inhibit proteolysis-mediated transthyretin fibrillogenesis with different efficiency in different variants; inhibition is complete only when both binding sites are occupied

Methods

Results

Conclusion