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Background: L-Homocysteine (Hcy) is a non-proteinogenic α-amino acid synthesized from dietary methionine. In healthy humans, high Hcy levels are a risk factor for cardiovascular diseases, stroke and type 2 diabetes. A recent study reports that Hcy reacts with Cys 10 of transthyretin (TTR), generating a stable covalent adduct. However, to date the effect of S-homocysteinylation on TTR conformational stability remains unknown., Methods: The effect of Hcy on the conformational properties of wt- and L55P-TTR were analysed using a set of biophysical techniques. The cytotoxicity of S-homocysteinylated L55P-TTR was also evaluated in the HL-1 cardiomyocyte cell line, while the effects of the assemblies on kinematic and dynamics properties of cardiac muscle cells were analysed in cardiomyocyte syncytia., Results: We found that Hcy stabilizes tetrameric wt-TTR, while it destabilizes the tetrameric structure of the L55P mutant, promoting the accumulation of self-assembly-prone monomeric species., Conclusions: Our study demonstrated that S-homocysteinylation of the L55P-TTR mutant impairs protein stability, favouring the appearance of toxic monomers. Interestingly, S-homocysteinylation affected only mutant, not wt-TTR. Moreover, we also show that assemblies of S-homocysteinylated L55P-TTR impair cardiomyocytes functional parameters., General Significance: Our study offers new insights on the negative impact of S-homocysteinylation on L55P-TTR stability, whose aggregation is considered the causative agent of a form of early-onset familial amyloid polyneuropathy and cardiomyopathy. Our results suggest that high homocysteine levels are a further risk factor for TTR cardiomyopathy in patients harbouring the L55P-TTR mutation., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Protein misfolding and aggregation are associated with a number of human degenerative diseases. In spite of the enormous research efforts to develop effective strategies aimed at interfering with the pathogenic cascades induced by misfolded/aggregated peptides/proteins, the necessary detailed understanding of the molecular bases of amyloid formation and toxicity is still lacking. To this aim, approaches able to provide a global insight in amyloid-mediated physiological alterations are of importance. In this study, we exploited Fourier transform infrared microspectroscopy, supported by multivariate analysis, to investigate in situ the spectral changes occurring in cultured intact HL-1 cardiomyocytes exposed to wild type (WT) or mutant (L55P) transthyretin (TTR) in native, or amyloid conformation. The presence of extracellular deposits of amyloid aggregates of WT or L55P TTR, respectively, is a key hallmark of two pathological conditions, known as senile systemic amyloidosis and familial amyloid polyneuropathy. We found that the major effects, associated with modifications in lipid properties and in the cell metabolic/phosphorylation status, were observed when natively folded WT or L55P TTR was administered to the cells. The effects induced by aggregates of TTR were milder and in some cases displayed a different timing compared to those elicited by the natively folded protein.

Transthyretin (TTR) amyloidoses are familial or sporadic degenerative conditions that often feature heavy cardiac involvement. Presently, no effective pharmacological therapy for TTR amyloidoses is available, mostly due to a substantial lack of knowledge about both the molecular mechanisms of TTR aggregation in tissue and the ensuing functional and viability modifications that occur in aggregate-exposed cells. TTR amyloidoses are of particular interest regarding the relation between functional and viability impairment in aggregate-exposed excitable cells such as peripheral neurons and cardiomyocytes. In particular, the latter cells provide an opportunity to investigate in parallel the electrophysiological and biochemical modifications that take place when the cells are exposed for various lengths of time to variously aggregated wild-type TTR, a condition that characterizes senile systemic amyloidosis. In this study, we investigated biochemical and electrophysiological modifications in cardiomyocytes exposed to amyloid oligomers or fibrils of wild-type TTR or to its T4-stabilized form, which resists tetramer disassembly, misfolding, and aggregation. Amyloid TTR cytotoxicity results in mitochondrial potential modification, oxidative stress, deregulation of cytoplasmic Ca 2+ levels, and Ca 2+ cycling. The altered intracellular Ca 2+ cycling causes a prolongation of the action potential, as determined by whole-cell recordings of action potentials on isolated mouse ventricular myocytes, which may contribute to the development of cellular arrhythmias and conduction alterations often seen in patients with TTR amyloidosis. Our data add information about the biochemical, functional, and viability alterations that occur in cardiomyocytes exposed to aggregated TTR, and provide clues as to the molecular and physiological basis of heart dysfunction in sporadic senile systemic amyloidosis and familial amyloid cardiomyopathy forms of TTR amyloidoses., (Copyright © 2016. Published by Elsevier Inc.)

Transthyretin (TTR) is involved in a subset of familial or sporadic amyloid diseases including senile systemic amyloidosis (SSA), familial amyloid polyneuropathy and cardiomyopathy (FAP/FAC) for which no effective therapy has been found yet. These conditions are characterized by extracellular deposits primarily found in the heart parenchyma and in peripheral nerves whose main component are amyloid fibrils, presently considered the main culprits of cell sufferance. The latter are polymeric assemblies grown from misfolded TTR, either wt or carrying one out of many identified mutations. The recent introduction in the clinical practice of synthetic TTR-stabilizing molecules that reduce protein aggregation provides the rationale to search natural effective molecules able to interfere with TTR amyloid aggregation by hindering the appearance of toxic species or by favoring the growth of harmless aggregates. Here we carried out an in depth biophysical and morphological study on the molecular features of the aggregation of wt- and L55P-TTR involved in SSA or FAP/FAC, respectively, and on the interference with fibril aggregation, stability and toxicity to cardiac HL-1 cells to demonstrate the ability of Oleuropein aglycone (OleA), the main phenolic component of the extra virgin olive oil. We describe the molecular basis of such interference and the resulting reduction of TTR amyloid aggregate cytotoxicity. Our data offer the possibility to validate and optimize the use of OleA or its molecular scaffold to rationally design promising drugs against TTR-related pathologies that could enter a clinical experimental phase., (Copyright © 2016 Elsevier Inc. All rights reserved.)