Abstract 9749: High-Avidity Binding Drives Nucleation of Amyloidogenic Transthyretin Monomer in Cardiac Amyloidosis

Abstract

Amyloidosis involves stepwise growth of fibrils assembled from soluble precursor proteins. Mutations of plasma carrier protein transthyretin (TTR) are associated with hereditary transthyretin amyloidosis (ATTR). TTR naturally folds into a stable tetramer for its function, whereas conditions and mutations that foster aberrant monomer formation facilitate TTR oligomeric aggregation and subsequent fibril extension. We investigated the dynamics of early assembly of oligomers by wild-type TTR, in comparison to its TTR V30M and TTR V122I disease mutants. We selected buffer conditions for monitoring time-dependent redistribution among monomer, dimer, tetramer, and oligomer contents in the presence and absence of multimeric TTR seeds. The seeds were artificially constructed recombinant multimers that contained 20-40 TTR subunits via engineered biotin-streptavidin interactions. As expected, these multimer seeds rapidly nucleated TTR monomers and dimers into larger complexes, while having no effect on tetramers. In vivo , streptavidin-induced multimers formed ATTR-like deposits in the heart and the kidney following i.v. injection in mice. While all three variants prominently deposited in the kidney glomerulus, only TTR V30M resulted in extensive deposition in the heart. The cardiac TTR deposits varied in size and shape and were localized to the intermyofibrillar space along the capillaries. These results are consistent with the notion of monomeric TTR to engage high-avidity interactions with tissue amyloids. Our multimeric induction approach therefore provides a new model for studying the initiation of TTR deposition in the heart.