Stability of the Transthyretin Molecule as a Key Factor in the Interaction with A-Beta Peptide - Relevance in Alzheimer's Disease

Abstract

Transthyretin (TTR) protects against A-Beta toxicity by binding the peptide thus inhibiting its aggregation. Previous work showed different TTR mutations interact differently with A-Beta, with increasing affinities correlating with decreasing amyloidogenecity of the TTR mutant; this did not impact on the levels of inhibition of A-Beta aggregation, as assessed by transmission electron microscopy. Our work aimed at probing differences in binding to A-Beta by WT, T119M and L55P TTR using quantitative assays, and at identifying factors affecting this interaction. We addressed the impact of such factors in TTR ability to degrade A-Beta. Using a dot blot approach with the anti-oligomeric antibody A11, we showed that A-Beta formed oligomers transiently, indicating aggregation and fibril formation, whereas in the presence of WT and T119M TTR the oligomers persisted longer, indicative that these variants avoided further aggregation into fibrils. In contrast, L55PTTR was not able to inhibit oligomerization or to prevent evolution to aggregates and fibrils. Furthermore, apoptosis assessment showed WT and T119M TTR were able to protect against A-Beta toxicity. Because the amyloidogenic potential of TTR is inversely correlated with its stability, the use of drugs able to stabilize TTR tetrameric fold could result in increased TTR/A-Beta binding. Here we showed that iododiflunisal, 3-dinitrophenol, resveratrol, [2-(3,5-dichlorophenyl)amino] (DCPA) and [4-(3,5-difluorophenyl)] (DFPB) were able to increase TTR binding to A-Beta; however only DCPA and DFPB improved TTR proteolytic activity. Thyroxine, a TTR ligand, did not influence TTR/A-Beta interaction and A-Beta degradation by TTR, whereas RBP, another TTR ligand, not only obstructed the interaction but also inhibited TTR proteolytic activity. Our results showed differences between WT and T119M TTR, and L55PTTR mutant regarding their interaction with A-Beta and prompt the stability of TTR as a key factor in this interaction, which may be relevant in AD pathogenesis and for the design of therapeutic TTR-based therapies.

The Effect of (−)-Epigallo-catechin-(3)-gallate on Amyloidogenic Proteins Suggests a Common Mechanism

“…The anti-oligomer antibody A11 recognizes a common intermediate oligomeric structure in Aβ40 and Aβ42 (Kayed et al 2003), Sup35 (Shorter and Lindquist 2004), β2m (Ribeiro et al 2012), α-Syn (Ehrnhoefer et al 2008) and tau (Flach et al 2012; Wobst et al 2015). EGCG prevented the binding of A11 to Aβ (Sinha et al 2012), α-Syn (Ehrnhoefer et al 2008) and tau (Wobst et al 2015) indicating that either structural changes in the protein aggregates or EGCG binding obscured the antibody binding sites.…”

Transthyretin stability is critical in assisting beta amyloid clearance– Relevance of transthyretin stabilization in Alzheimer's disease

“…As previously reported, the effect of TTR stabilizers on the TTR/Aβ interaction is best observed when using unstable TTR mutants . To study the importance of TTR stabilization in Aβ clearance, FAM‐Aβ internalization was assessed in the absence or presence of L55P TTR preincubated with or without IDIF or resveratrol.…”

“…Most importantly, small compounds known to stabilize TTR tetrameric fold have been demonstrated to improve TTR–Aβ interaction, in vitro . One of such stabilizers, iododiflunisal (IDIF), when administrated to AD transgenic mice ameliorates AD features, such as cognitive function, brain Aβ deposition, and plasma Aβ levels .…”

Resveratrol Administration Increases Transthyretin Protein Levels, Ameliorating AD Features: The Importance of Transthyretin Tetrameric Stability

“…Interestingly, also using an AD transgenic mice model, it was shown that resveratrol intake increased TTR levels (30). Previous work in our laboratory indicated that resveratrol increases TTR affinity to Aβ (31), probably by stabilizing the TTR native tetramer conformation. It has been described that the binding of resveratrol to TTR is at the T 4 binding pocket, although the exact binding site still generates some controversy.…”