Plasmin activity promotes amyloid deposition in a transgenic model of human transthyretin amyloidosis

Abstract

Cardiac ATTR amyloidosis, a serious but much under-diagnosed form of cardiomyopathy, is caused by deposition of amyloid fibrils derived from the plasma protein transthyretin (TTR), but its pathogenesis is poorly understood and informative in vivo models have proved elusive. Here we report the generation of a mouse model of cardiac ATTR amyloidosis with transgenic expression of human TTRS52P. The model is characterised by substantial ATTR amyloid deposits in the heart and tongue. The amyloid fibrils contain both full-length human TTR protomers and the residue 49-127 cleavage fragment which are present in ATTR amyloidosis patients. Urokinase-type plasminogen activator (uPA) and plasmin are abundant within the cardiac and lingual amyloid deposits, which contain marked serine protease activity; knockout of α2-antiplasmin, the physiological inhibitor of plasmin, enhances amyloid formation. Together, these findings indicate that cardiac ATTR amyloid deposition involves local uPA-mediated generation of plasmin and cleavage of TTR, consistent with the previously described mechano-enzymatic hypothesis for cardiac ATTR amyloid formation. This experimental model of ATTR cardiomyopathy has potential to allow further investigations of the factors that influence human ATTR amyloid deposition and the development of new treatments.

Development of a Highly Potent Transthyretin Amyloidogenesis Inhibitor: Design, Synthesis, and Evaluation

“…An alternative pathway for TTR amyloid formation in vivo proposes that TTR aggregation is triggered by proteolytic cleavage. It is supported by the fact that the amyloid deposits formed by most TTR variants in vivo contain the truncated 49-127 polypeptide. , This mechanism might be especially relevant in organs with substantial shear stress, such as the heart, where the physiological fluid flow, together with the hydrophobic forces acting on the protein, might increase its susceptibility to proteolytic cleavage. , …”

Molecular Mechanism of Pathogenesis and Treatment Strategies for AL Amyloidosis

“…Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) are also highly expressed in tissues in AL [ 35 ], and the ratio of MMP-2, TIMP-1, and MMP-2/TIMP-2 is high in the serum of patients with AL [ 36 ]. It has also been reported that plasmin is required for amyloid formation in ATTR [ 37 ]; however, it conversely acts to degrade and eliminate amyloid β [ 38 ]. Hence, the role of plasmin in AL needs to be carefully evaluated.…”

Amyloid Formation by Globular Proteins: The Need to Narrow the Gap Between in Vitro and in Vivo Mechanisms

“…All those mouse models developed a very limited amount of amyloid in the heart in which non-fibrillar amorphous aggregates of TTR were mostly observed. The deposition in the heart has been very recently obtained in a new transgenic mouse strain expressing the human S52P TTR variant in which the formation of amyloid requires pre-inoculation with seeds of natural amyloid fibrils (Slamova From the first mouse model (Yi et al, 1991), several attempts were made to reproduce the disease in invertebrates (i.e., C. elegans, Drosophila melanogaster) before developing a novel transgenic mouse model reproducing amyloid in the heart and tongue (Slamova et al, 2021(Slamova et al, ). et al, 2021.…”

“…All those mouse models developed a very limited amount of amyloid in the heart in which non-fibrillar amorphous aggregates of TTR were mostly observed. The deposition in the heart has been very recently obtained in a new transgenic mouse strain expressing the human S52P TTR variant in which the formation of amyloid requires pre-inoculation with seeds of natural amyloid fibrils ( Slamova et al, 2021 ). Here, the time frame of the onset of amyloid deposition and the amount of deposits are strictly dependent on the plasma concentration of TTR and, the amyloid mainly affects the heart and tongue.…”

“… Development of animal models for ATTR in humans. From the first mouse model ( Yi et al, 1991 ), several attempts were made to reproduce the disease in invertebrates (i.e., C. elegans , Drosophila melanogaster ) before developing a novel transgenic mouse model reproducing amyloid in the heart and tongue ( Slamova et al, 2021 ). …”