Fibril in senile systemic amyloidosis is derived from normal transthyretin

Transthyretin Amyloidosis: Role of oxidative stress and the beneficial implications of antioxidants and nutraceutical supplementation

Transthyretin (ATTR) amyloidosis constitutes a spectrum of debilitating neurodegenerative diseases instigated by systemic extracellular deposition of partially unfolded/aggregated aberrant transthyretin. The homotetrameric protein, TTR, is abundant in the plasma, and to a lesser extent the cerebrospinal fluid. Rate-limiting tetramer dissociation of the native protein is regarded as the critical step in the formation of morphologically heterogenous toxic aggregates and the onset of clinical manifestations such as polyneuropathy, cardiomyopathy, disturbances in motor and autonomic functions. Over the past few decades there has been increasing evidence suggesting that in addition to destabilization in TTR tetramer structure, oxidative stress may also play an important role in the pathogenesis of ATTR amyloidosis. In this review, an update on the impact of oxidative stress in TTR amyloidogenesis as well as TTR aggregate-mediated pathologies is discussed. The counteracting effects of antioxidants and nutraceutical agents explored in the treatment of ATTR amyloidosis based on recent evidence is also critically examined. The insights unveiled could further strengthen current understanding of the mechanisms underlying ATTR amyloidosis as well as extend the range of strategies for effective management of ATTR amyloidoses.

Assessment of transthyretin instability in patients with wild-type transthyretin amyloid cardiomyopathy

The pathophysiology of variant transthyretin (TTR) amyloidosis (ATTRv) is associated with destabilizing mutations in the TTR tetramer. However, why TTR with a wild-type genetic sequence misfolds and aggregates in wild-type transthyretin amyloidosis (ATTRwt) is unknown. Here, we evaluate kinetic TTR stability with a newly developed ELISA system in combination with urea-induced protein denaturation. Compared with that in control patients, endogenous TTR in patients with wild-type transthyretin amyloid cardiomyopathy (ATTRwt-CM) exhibited thermodynamic instability, indicating that circulating TTR instability may be associated with the pathogenesis of ATTRwt as well as ATTRv. Our findings provide new insight into the underlying mechanisms of ATTRwt.

Mispacking of the F87 sidechain drives aggregation-promoting conformational fluctuations in the subunit interfaces of the transthyretin tetramer

Aberrant formation and deposition of human transthyretin (TTR) aggregates causes transthyretin amyloidosis. To initialize aggregation, transthyretin tetramers must first dissociate into monomers that partially unfold to promote entry into the aggregation pathway. The native TTR tetramer (T) is stabilized by docking of the F87 sidechain into an interfacial cavity enclosed by several hydrophobic residues including A120. We have previously shown that an alternative tetramer (T*) with mispacked F87 sidechains is more prone to dissociation and aggregation than the native T state. However, the molecular basis for the reduced stability in T* remains unclear. Here we report characterization of the A120L mutant, where steric hindrance is introduced into the F87 binding site. The x-ray structure of A120L shows that the F87 sidechain is displaced from its docking site across the subunit interface. In A120S, a naturally occurring pathogenic mutant that is less aggregation-prone than A120L, the F87 sidechain is correctly docked, as in the native TTR tetramer. Nevertheless, 19F-NMR aggregation assays show an elevated population of a monomeric aggregation intermediate in A120S relative to a control containing the native A120, due to accelerated tetramer dissociation and slowed monomer tetramerization. The mispacking of the F87 sidechain is associated with enhanced exchange dynamics for interfacial residues. At 298 K, the T* populations of various naturally occurring mutants fall between 4% and 7% (ΔG ~ 1.5-1.9 kcal/mol), consistent with the free energy change expected for undocking and solvent exposure of one of the four F87 sidechains in the tetramer (ΔG ~ 1.6 kcal/mol). Our data provide a molecular-level picture of the likely universal F87 sidechain mispacking in tetrameric TTR that promotes interfacial conformational dynamics and increases aggregation propensity.

Identification of the interfacial regions in misfolded transthyretin oligomers

Misfolding and aggregation of transthyretin (TTR) is associated with numerous ATTR amyloidosis. TTR aggregates extracted from ATTR patients consist of not only full-length TTR, but also N-terminally truncated TTR fragments that can be produced by proteolytic cleavage, suggesting the presence of multiple misfolding pathways. Here, we report mechanistic studies of an early stage of TTR aggregation to probe the oligomerization process for the full-length as well as N-terminally truncated TTR. Our kinetic analyses using size exclusion chromatography revealed that amyloidogenic monomers dissociated from wild-type (WT) as well as pathogenic variants (V30M and L55P) form misfolded dimers, which self-assemble into oligomers, precursors of fibril formation. Dimeric interfaces in the full-length misfolded oligomers were investigated by examining the effect of single-point mutations on the two β-strands (F and H). The single-point mutations on the two β-strands (E92P on strand F and T119W on strand H) inhibited the dimerization of misfolded monomers, while the TTR variants can still form native dimers through the same F and H strands. These results suggest that the two strands are involved in intermolecular associations for both native and misfolded dimers, but detailed intermolecular interactions are different in the two forms of dimers. In the presence of a proteolytic enzyme, TTR aggregation is greatly accelerated. The two mutations on the two β-strands, however, inhibited TTR aggregation even in the presence of a proteolytic enzyme, trypsin. These results suggest that the two β-strands (F and H) play a critical role in aggregation of the N-terminally truncated TTR as well.

Successes in translation

Translational research is key in advancing the diagnosis and therapy of systemic amyloidoses. This paper summarises our presentations at the ISA Workshop on Translation in Systemic Amyloidoses held in Athens on September 25-26, 2023. The critical advances made by the pioneers in the field are reviewed, with particular attention to the discoveries and developments of utmost importance to our understanding of what amyloid is and how the substance affects functions. Examples of translational research regarding the mechanisms of cardiac damage in light chain amyloidosis, the role of biomarkers in improving our understanding of the biology of the disease and patients' management, and the molecular mechanisms involved in the cytotoxicity are described. Advances in basic research continue to open new therapeutic avenues.

Conformational Dynamics of an Amyloidogenic Intermediate of Transthyretin: Implications for Structural Remodeling and Amyloid Formation

The aggregation pathway of transthyretin (TTR) proceeds through rate-limiting dissociation of the tetramer (a dimer of dimers) and partial misfolding of the resulting monomer, which assembles into amyloid structures through a downhill polymerization mechanism. The structural features of the aggregation-prone monomeric intermediate are poorly understood. NMR relaxation dispersion offers a unique opportunity to characterize amyloidogenic intermediates when they exchange on favorable timescales with NMR-visible ground states. Here we use NMR to characterize the structure and conformational dynamics of the monomeric F87E mutant of human TTR. Chemical shifts derived from analysis of multinuclear relaxation dispersion data provide insights into the structure of a low-lying excited state that exchanges with the ground state of the F87E monomer at a rate of 3800 s-1. Disruption of the subunit interfaces of the TTR tetramer leads to destabilization of edge strands in both β-sheets of the F87E monomer. Conformational fluctuations are propagated through the entire hydrogen bonding network of the DAGH β-sheet, from the inner β-strand H, which forms the strong dimer-dimer interface in the TTR tetramer, to outer strand D which is unfolded in TTR fibrils. Fluctuations are also propagated from the AB loop in the weak dimer-dimer interface to the EF helix, which undergoes structural remodeling in fibrils. The conformational fluctuations in both regions are enhanced at acidic pH where amyloid formation is most favorable. The relaxation dispersion data provide insights into the conformational dynamics of the amyloidogenic state of monomeric TTR that predispose it for structural remodeling and progression to amyloid fibrils.

Structures and Dynamics of β-Rich Oligomers of ATTR (105-115) Assembly

Transthyretin (TTR) is a tetrameric homologous protein that can dissociate into monomers. Misfolding and aggregation of TTR can lead to amyloid transthyretin amyloidosis (ATTR), which can cause many diseases (e.g., senile systemic amyloidosis, familial amyloid cardiomyopathy, and familial amyloid polyneuropathy). Despite growing evidence indicating that small oligomers play a critical role in regulating cytotoxicity, the structures of these oligomeric intermediates and their conformational transformations are still unclear, impeding our understanding of neurodegenerative mechanisms and the development of therapeutics targeting early aggregation species. The TTR monomer protein consists of various fragments prone to self-aggregation, including the residue 105-115 sequence. Therefore, our study investigated the assembly progress of ATTR (105-115) peptides using all-atom molecular dynamics simulations. The findings indicate that the probability of β-sheet content increases with increasing numbers of peptides. Additionally, interactions between hydrophobic residues L110 and L111 are crucial for the formation of a β-rich oligomer formation. These β-rich oligomers may adopt β-barrel conformations, potentially toxic oligomer species. Free-energy analysis reveals that β-barrel conformations serve as intermediates for these β-rich oligomers. Our insights into the structural ensemble dynamics of ATTR (105-115) contribute to understanding the physical mechanisms underlying the β-barrel oligomers of ATTR. These findings may shed light on the pathological role of ATTR in neurodegenerative diseases and offer potential therapeutic targets.

Trypsin-induced aggregation of transthyretin Valine 30 variants associated with hereditary amyloidosis

Amyloid fibrils of transthyretin (TTR) consist of full-length TTR and C-terminal fragments starting near residue 50. However, the molecular mechanism underlying the production of the C-terminal fragment remains unclear. Here, we investigated trypsin-induced aggregation and urea-induced unfolding of TTR variants associated with hereditary amyloidosis. Trypsin strongly induced aggregation of variants V30G and V30A, in each of which Val30 in the hydrophobic core of the monomer was mutated to less-bulky amino acids. Variants V30L and V30M, in each of which Val30 was mutated to bulky amino acids, also exhibited trypsin-induced aggregation. On the other hand, pathogenic variant I68L as well as the nonpathogenic V30I did not exhibit trypsin-induced aggregation. The V30G variant was extremely unstable compared with the other variants. The V30G mutation caused the formation of a cavity and the rearrangement of Leu55 in the hydrophobic core of the monomer. These results suggest that highly destabilized transthyretin variants are more susceptible to trypsin digestion.

An ultra performance liquid chromatography method for transthyretin variants screening and heart failure assisting diagnosis

BACKGROUND

Transthyretin (TTR) gene mutations are associated with hereditary amyloidosis (ATTR) caused by mutant TTR protein dissociation, misfolding, aggregation, and insoluble fibrils deposition. Herein, we reported a chromatographic approach for quantification and identification of TTR tetramer in human blood serum by ultra performance liquid chromatography (UPLC).

METHODS

TTR proteins and serum were incubated with a fluorescent TTR tetramer sensor (A2). The A2 sensor specifically reacted with tetrameric TTR and released stoichiometric fluorescence that was detected by fluorescence detector coupled to UPLC. The external standard was used for quantification, the chromatographic peak parameters were used to identification certain mutation types.

RESULTS

UPLC correctly distinguished 18 types of mutant TTR proteins from wild type. The results were consistent with follow-up analysis of two ATTR patients' blood serum samples. In addition, the tetrameric TTR of 30 heart failure (HF) patients showed strongly correlation (r = -0.63, p < 0.00) with NT-proBNP, a HF clinical biomarker.

CONCLUSIONS

UPLC method has sufficient accuracy to eliminate the necessity of sequencing for certain types of TTR mutations and allows for facile initial screening of ATTR amyloidosis patients, carriers, and healthy individuals for time-saving and economical purposes. TTR tetramer may serve as a diagnostic biomarker to evaluate the risk of HF diseases.

PITB: A high affinity transthyretin aggregation inhibitor with optimal pharmacokinetic properties

The aggregation of wild-type transthyretin (TTR) and over 130 genetic TTR variants underlies a group of lethal disorders named TTR amyloidosis (ATTR). TTR chemical chaperones are molecules that hold great promise to modify the course of ATTR progression. In previous studies, we combined rational design and molecular dynamics simulations to generate a series of TTR selective kinetic stabilizers displaying exceptionally high affinities. In an effort to endorse the previously developed molecules with optimal pharmacokinetic properties, we conducted structural design optimization, leading to the development of PITB. PITB binds with high affinity to TTR, effectively inhibiting tetramer dissociation and aggregation of both the wild-type protein and the two most prevalent disease-associated TTR variants. Importantly, PITB selectively binds and stabilizes TTR in plasma, outperforming tolcapone, a drug currently undergoing clinical trials for ATTR. Pharmacokinetic studies conducted on mice confirmed that PITB exhibits encouraging pharmacokinetic properties, as originally intended. Furthermore, PITB demonstrates excellent oral bioavailability and lack of toxicity. These combined attributes position PITB as a lead compound for future clinical trials as a disease-modifying therapy for ATTR.

Hydrogen bonds connecting the N-terminal region and the DE loop stabilize the monomeric structure of transthyretin

Transthyretin (TTR) is a homo-tetrameric serum protein associated with sporadic and hereditary systemic amyloidosis. TTR amyloid formation proceeds by the dissociation of the TTR tetramer and the subsequent partial unfolding of the TTR monomer into an aggregation-prone conformation. Although TTR kinetic stabilizers suppress tetramer dissociation, a strategy for stabilizing monomers has not yet been developed. Here, we show that an N-terminal C10S mutation increases the thermodynamic stability of the TTR monomer by forming new hydrogen bond networks through the side chain hydroxyl group of Ser10. Nuclear magnetic resonance spectrometry and molecular dynamics simulation revealed that the Ser10 hydroxyl group forms hydrogen bonds with the main chain amide group of either Gly57 or Thr59 on the DE loop. These hydrogen bonds prevent the dissociation of edge strands in the DAGH and CBEF β-sheets during the unfolding of the TTR monomer by stabilizing the interaction between β-strands A and D and the quasi-helical structure in the DE loop. We propose that introducing hydrogen bonds to connect the N-terminal region to the DE loop reduces the amyloidogenic potential of TTR by stabilizing the monomer.

Thyroxine metabolite-derived 3-iodothyronamine (T1AM) and synthetic analogs as efficient suppressors of transthyretin amyloidosis

Aggregation and fibrillization of transthyretin (TTR) is a fatal pathogenic process that can cause cardiomyopathic and polyneuropathic diseases in humans. Although several therapeutic strategies have been designed to prevent and treat related pathological events, there is still an urgent need to develop better strategies to improve potency and wider applicability. Here, we present our study demonstrating that 3-iodothyronamine (T1AM) and selected thyronamine-like compounds can effectively prevent TTR aggregation. T1AM is one of the thyroid hormone (TH) metabolites, and T1AM and its analogs, such as SG2, SG6, and SG12, are notable molecules for their beneficial activities against metabolic disorders and neurodegeneration. Using nuclear magnetic resonance (NMR) spectroscopy and biochemical analysis, we confirmed that T1AM analogs could bind to and suppress acid-induced aggregation of TTR. In addition, we employed computational approaches to further understand the detailed mechanisms of the interaction between T1AM analogs and TTR. This study demonstrates that T1AM analogs, whose beneficial effects against several pathological processes have already been proven, may have additional benefits against TTR aggregation and fibrillization. Moreover, we believe that our work provides invaluable insights to enhance the pleiotropic activity of T1AM and structurally related analogs, relevant for their therapeutic potential, with particular reference to the ability to prevent TTR aggregation.

Tafamidis concentration required for transthyretin stabilisation in cerebrospinal fluid

BACKGROUND

Hereditary transthyretin (TTR) amyloidosis (ATTRv) initially presents as a polyneuropathy and/or a cardiomyopathy. Central nervous system (CNS) pathology in ATTRv amyloidosis, including focal neurological episodes, dementia, cerebrovascular bleeding, and seizures, appears around a decade later. Wild-type (WT) TTR amyloidosis (ATTRwt) causes a cardiomyopathy. CNS pathology risk likely also increases in these patients as cardiomyopathy progresses. Herein, we study tafamidis-mediated TTR kinetic stabilisation in cerebrospinal fluid (CSF).

METHODS

Varying tafamidis concentrations (50-1000 nM) were added to CSF from healthy donors or ATTRv patients, and TTR stabilisation was measured via the decrease in dissociation rate.

RESULTS

Tafamidis meglumine (Vyndaqel) can be dosed at 20 or 80 mg QD. The latter dose is bioequivalent to a 61 mg QD dose of tafamidis free acid (Vyndamax). The tafamidis CSF concentration in ATTRv patients on 20 mg Vyndaqel is ∼125 nM. By linear extrapolation, we expect a CSF concentration of ∼500 nM at the higher dose. When tafamidis is added to healthy donor CSF at 125 or 500 nM, the WT TTR dissociation rate decreases by 42% or 87%, respectively.

CONCLUSIONS

Tafamidis stabilises TTR in CSF to what is likely a clinically meaningful extent at CSF concentrations achieved by the normal tafamidis dosing regimen.

Arabidopsis metacaspase MC1 localizes in stress granules, clears protein aggregates, and delays senescence

Stress granules (SGs) are highly conserved cytoplasmic condensates that assemble in response to stress and contribute to maintaining protein homeostasis. These membraneless organelles are dynamic, disassembling once the stress is no longer present. Persistence of SGs due to mutations or chronic stress has been often related to age-dependent protein-misfolding diseases in animals. Here, we find that the metacaspase MC1 is dynamically recruited into SGs upon proteotoxic stress in Arabidopsis (Arabidopsis thaliana). Two predicted disordered regions, the prodomain and the 360 loop, mediate MC1 recruitment to and release from SGs. Importantly, we show that MC1 has the capacity to clear toxic protein aggregates in vivo and in vitro, acting as a disaggregase. Finally, we demonstrate that overexpressing MC1 delays senescence and this phenotype is dependent on the presence of the 360 loop and an intact catalytic domain. Together, our data indicate that MC1 regulates senescence through its recruitment into SGs and this function could potentially be linked to its remarkable protein aggregate-clearing activity.

Cardiac amyloidosis: evolving pathogenesis, multimodal diagnostics, and principles of treatment

Amyloidosis is a protein deposition disorder in which insoluble fibril structures accumulate in the bodily tissues damaging the organ function. Cardiac amyloidosis is a severe but under-reported medical condition characterized by the accumulation of amyloid in the extracellular area of the myocardium, which results in thickening and stiffening of ventricular walls. Cardiac amyloidosis has recently gained much attention with its slowly surging incidence. With this study, we seek to comprehensively compile the pathophysiology and clinical picture of cardiac amyloidosis subtypes, extending a clinically oriented, up-to-date clinical approach to diagnosis and therapy. Cardiac amyloidosis can be caused by rare genetic mutations which may be inherited or acquired. The growing incidence can be attributed to advancements in imaging methods and other diagnostic modalities. Most occurrences of cardiac amyloidosis result from two forms of precursor protein: transthyretin [TTR] amyloid and immunoglobulin-derived light-chain amyloid. Prompt identification of cardiac amyloidosis can facilitate the implementation of evolving therapeutic interventions to enhance the outcomes. The modalities for the management of CA have evolved significantly in the last ten years. Apart from therapies for modifying disease and heart failure, a myriad of novel therapeutic approaches that target specific aspects of the disease, including gene therapies, are being researched. These aim at impeding its progression and improving clinical outcomes. See also Figure 1(Fig. 1).

Cardiac DPD-uptake time dependency in ATTR patients verified by quantitative SPECT/CT and semiquantitative planar parameters

BACKGROUND

Bone scintigraphy plays an important role in the diagnosis of cardiac Transthyretin-Related Amyloidosis (ATTR). The mechanism of myocardial tracer accumulation and its dependence over time are not fully understood. Recently, a scintigraphic quantification of the cardiac amyloid deposition has been discussed. Nevertheless, little is known regarding the right time of quantitative imaging.

METHODS

The geometrical mean of decay corrected total counts over the heart and the heart/whole-body ratio (H/WB) were evaluated in 23 patients undergoing DPD-bone scan with planar whole-body images 1 and 3 hours post injection (p.i.). Myocardial standard uptake values (SUV)peak were assessed in another 15 patients with quantitative SPECT/CT imaging 1 hours and 3 hours p.i..

RESULTS

Total counts over the heart (1 hours p.i.: 81,676 cts, range 69,887 to 93,091 cts and 3 hours p.i.: 64,819 cts, range 52,048 to 86,123 cts, P = .0005) and H/WB ratio (1 hours p.i.:0.076 ± 0.020 and 3 hours p.i. 0.070 ± 0.022; P = .0003) were significantly increased 1 hours p.i.. Furthermore median myocardial SUVpeak (1 hours p.i.:12.2, range 9.6 to 18.9 and 3 hours p.i.: 9.6, range 8.2 to 15.0, P = 0.0012) was also significantly higher after 1 hours p.i. compared to 3 hours p.i..

CONCLUSION

Cardiac DPD activity and myocardial SUVpeak are time-dependent, which should be considered when using quantitative bone scintigraphy in ATTR patients.

Benziodarone and 6-hydroxybenziodarone are potent and selective inhibitors of transthyretin amyloidogenesis

Transthyretin amyloidosis is a progressive systemic disorder that is caused by the amyloid deposition of transthyretin in various organs. Stabilization of the native transthyretin is an effective strategy for the treatment of transthyretin amyloidosis. In this study we demonstrate that the clinically used uricosuric agent benziodarone is highly effective to stabilize the tetrameric structure of transthyretin. An acid-induced aggregation assay showed that benziodarone had strong inhibitory activity similar to that of tafamidis, which is currently used as a therapeutic agent for transthyretin amyloidosis. Moreover, a possible metabolite, 6-hydroxybenziodarone, retained the strong amyloid inhibitory activity of benziodarone. An ex vivo competitive binding assay using a fluorogenic probe showed that benziodarone and 6-hydroxybenziodarone were highly potent for selective binding to transthyretin in human plasma. An X-ray crystal structure analysis revealed that the halogenated hydroxyphenyl ring was located at the entrance of the thyroxine binding channel of transthyretin and that the benzofuran ring was located in the inner channel. These studies suggest that benziodarone and 6-hydroxybenziodarone would potentially be effective against transthyretin amyloidosis.

The flutemetamol analogue cyano-flutemetamol detects myocardial AL and ATTR amyloid deposits: a post-mortem histofluorescence analysis

BACKGROUND

[18F]flutemetamol is a PET radioligand used to image brain amyloid, but its detection of myocardial amyloid is not well-characterized. This histological study characterized binding of fluorescently labeled flutemetamol (cyano-flutemetamol) to amyloid deposits in myocardium.

METHODS

Myocardial tissue was obtained post-mortem from 29 subjects with cardiac amyloidosis including transthyretin wild-type (ATTRwt), hereditary/variant transthyretin (ATTRv) and immunoglobulin light-chain (AL) types, and from 10 cardiac amyloid-free controls. Most subjects had antemortem electrocardiography, echocardiography, SPECT and cardiac MRI. Cyano-flutemetamol labeling patterns and integrated density values were evaluated relative to fluorescent derivatives of Congo red (X-34) and Pittsburgh compound-B (cyano-PiB).

RESULTS

Cyano-flutemetamol labeling was not detectable in control subjects. In subjects with cardiac amyloidosis, cyano-flutemetamol labeling matched X-34- and cyano-PiB-labeled, and transthyretin- or lambda light chain-immunoreactive, amyloid deposits and was prevented by formic acid pre-treatment of myocardial sections. Cyano-flutemetamol mean fluorescence intensity, when adjusted for X-34 signal, was higher in the ATTRwt than the AL group. Cyano-flutemetamol integrated density correlated strongly with echocardiography measures of ventricular septal thickness and posterior wall thickness, and with heart mass.

CONCLUSION

The high selectivity of cyano-flutemetamol binding to myocardial amyloid supports the diagnostic utility of [18F]flutemetamol PET imaging in patients with ATTR and AL types of cardiac amyloidosis.

Emerging Therapies for Transthyretin Amyloidosis

PURPOSE OF REVIEW

This review provides an overview of the available therapies for treating neuropathic and/or cardiac manifestations of transthyretin amyloidosis (ATTR), as well as investigational therapeutic agents in ongoing clinical trials. We discuss additional emergent approaches towards thwarting this life-threatening disease that until recently was considered virtually untreatable.

RECENT FINDINGS

Advances in noninvasive diagnostic methods for detecting ATTR have facilitated easier diagnosis and detection at an earlier stage of disease when therapeutic interventions are likely to be more effective. There are now several ATTR-directed treatments that are clinically available, as well as investigational agents that are being studied in clinical trials. Therapeutic strategies include tetramer stabilization, gene silencing, and fibril disruption. ATTR has been historically underdiagnosed. With advances in diagnostic methods and the advent of disease-modifying treatments, early diagnosis and initiation of treatment is revolutionizing management of this disease.

Transthyretin Binding Mode Dichotomy of Fluorescent trans-Stilbene Ligands

The orientations of ligands bound to the transthyretin (TTR) thyroxine (T4) binding site are difficult to predict. Conflicting binding modes of resveratrol have been reported. We previously reported two resveratrol based trans-stilbene fluorescent ligands, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (SB-11) and (E)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol (SB-14), that bind native and misfolded protofibrillar TTR. The binding orientations of these two analogous ligands to native tetrameric TTR were predicted to be opposite. Herein we report the crystal structures of these TTR:ligand complexes. Opposite binding modes were verified but were different than predicted. The reverse binding mode (SB-14) placing the naphthalene moiety toward the opening of the binding pocket renders the fluorescent ligand pH sensitive due to changes in Lys15 amine protonation. Conversely, the forward binding mode (SB-11) placing the naphthalene inward mediates a stabilizing conformational change, allowing intersubunit H-bonding between Ser117 of different monomers across the dimer interface. Our structures of TTR complexes answer important questions in ligand design and interpretation of trans-stilbene binding modes to the TTR T4 binding site.

Hint approach on Transthyretin folding/unfolding mechanism comprehension

Non-covalent intramolecular interactions play a key role in the protein folding process. Aminoacidic mutations or changes in physiological conditions such as pH and/or temperature variations can compromise intramolecular stability generating misfolding or unfolding proteins with consequent impairment of functionality and the triggering of pathological states. The intramolecular HINT scoring function recently implemented and validated, is proposed as a rapid and sensitive method for the evaluation of different conformational states characterizing destabilization processes. In this work, the stability of Transthyretin, whose denaturation is related to amyloid fibril formation, is evaluated by generating multiple structural mutated models under different pH conditions in comparison with experimental data. These results suggest that the HINT scoring function can be used for an accurate and rapid evaluation and computational prediction of the effects of structural changes on any protein system.

The Regulatory Mechanism of Transthyretin Irreversible Aggregation through Liquid-to-Solid Phase Transition

Transthyretin (TTR) aggregation and amyloid formation are associated with several ATTR diseases, such as senile systemic amyloidosis (SSA) and familial amyloid polyneuropathy (FAP). However, the mechanism that triggers the initial pathologic aggregation process of TTR remains largely elusive. Lately, increasing evidence has suggested that many proteins associated with neurodegenerative diseases undergo liquid-liquid phase separation (LLPS) and subsequent liquid-to-solid phase transition before the formation of amyloid fibrils. Here, we demonstrate that electrostatic interactions mediate LLPS of TTR, followed by a liquid-solid phase transition, and eventually the formation of amyloid fibrils under a mildly acidic pH in vitro. Furthermore, pathogenic mutations (V30M, R34T, and K35T) of TTR and heparin promote the process of phase transition and facilitate the formation of fibrillar aggregates. In addition, S-cysteinylation, which is a kind of post-translational modification of TTR, reduces the kinetic stability of TTR and increases the propensity for aggregation, while another modification, S-sulfonation, stabilizes the TTR tetramer and reduces the aggregation rate. Once TTR was S-cysteinylated or S-sulfonated, they dramatically underwent the process of phase transition, providing a foundation for post-translational modifications that could modulate TTR LLPS in the context of pathological interactions. These novel findings reveal molecular insights into the mechanism of TTR from initial LLPS and subsequent liquid-to-solid phase transition to amyloid fibrils, providing a new dimension for ATTR therapy.

Chlorinated Naringenin Analogues as Potential Inhibitors of Transthyretin Amyloidogenesis

Misfolding and aggregation of transthyretin are implicated in the fatal systemic disease known as transthyretin amyloidosis. Here, we report the development of a naringenin derivative bearing two chlorine atoms that will be efficacious for preventing aggregation of transthyretin in the eye. The amyloid inhibitory activity of the naringenin derivative was as strong as that of tafamidis, which is the first therapeutic agent targeting transthyretin in the plasma. X-ray crystal structures of the compounds in complex with transthyretin demonstrated that the naringenin derivative with one chlorine bound to the thyroxine-binding site of transthyretin in the forward mode and that the derivative with two chlorines bound to it in the reverse mode. An ex vivo competitive binding assay showed that naringenin derivatives exhibited more potent binding than tafamidis in the plasma. Furthermore, an in vivo pharmacokinetic study demonstrated that the dichlorinated derivative was significantly delivered to the eye.

Overview of Current and Emerging Therapies for Amyloid Transthyretin Cardiomyopathy

Recent efforts in basic science have elucidated the pathobiology of amyloid transthyretin (ATTR) amyloidosis, leading to the development of the first generation of transthyretin (TTR)-targeted therapies for this disease. Along with tafamidis, the first approved therapy for ATTR-cardiomyopathy (CM), several other agents are in late-stage clinical development for ATTR-CM. TTR-stabilizing and -silencing agents with various mechanisms target TTR, preventing disaggregation of tetrameric TTR, and subsequent misfolding of TTR and formation of amyloid fibrils in the myocardium. These agents, including the TTR-super-stabilizing agent acoramidis, TTR-silencing agents patisiran, vutrisiran, and eplontersen, and TTR gene silencing with clustered, regularly interspaced, short palindromic repeats and associated Cas9 endonuclease-based therapy NTLA-2001, are in varying stages of development. The nonsteroidal anti-inflammatory diflunisal has been shown to have TTR-stabilizing properties and may play a role off-label as treatment in selected patients, particularly allele carriers of TTR variants and patients unable to afford current therapies. Anti-amyloid treatments represent another strategy for treating patients with advanced ATTR amyloidosis. These agents are designed to bind to epitopes on amyloid fibril and extract amyloid by activation of macrophage-mediated phagocytosis addressing amyloid already deposited in organs and tissues. Since many patients with ATTR-CM present with advanced disease and the presence of significant amyloid burden in the heart, anti-amyloid therapy represents an important area of unmet treatment need. Various investigational anti-amyloid therapies are in early-stage clinical development.

Toxic Misfolded Transthyretin Oligomers with Different Molecular Conformations Formed through Distinct Oligomerization Pathways

Protein aggregation is initiated by structural changes from native polypeptides to cytotoxic oligomers, which form cross-β structured amyloid. Identification and characterization of oligomeric intermediates are critically important for understanding not only the molecular mechanism of aggregation but also the cytotoxic nature of amyloid oligomers. Preparation of misfolded oligomers for structural characterization is, however, challenging because of their transient, heterogeneous nature. Here, we report two distinct misfolded transthyretin (TTR) oligomers formed through different oligomerization pathways. A pathogenic TTR variant with a strong aggregation propensity (L55P) was used to prepare misfolded oligomers at physiological pH. Our mechanistic studies showed that the full-length TTR initially forms small oligomers, which self-assemble into short protofibrils at later stages. Enzymatic cleavage of the CD loop was also used to induce the formation of N-terminally truncated oligomers, which was detected in ex vivo cardiac TTR aggregates extracted from the tissues of patients. Structural characterization of the oligomers using solid-state nuclear magnetic resonance and circular dichroism revealed that the two TTR misfolded oligomers have distinct molecular conformations. In addition, the proteolytically cleaved TTR oligomers exhibit a higher surface hydrophobicity, suggesting the presence of distinct oligomerization pathways for TTR oligomer formation. Cytotoxicity assays also revealed that the cytotoxicity of cleaved oligomers is stronger than that of the full-length TTR oligomers, indicating that hydrophobicity might be an important property of toxic oligomers. These comparative biophysical analyses suggest that the toxic cleaved TTR oligomers formed through a different misfoling pathway may adopt distinct structural features that produce higher surface hydrophobicity, leading to the stronger cytotoxic activities.

Cryo-EM structure of an ATTRwt amyloid fibril from systemic non-hereditary transthyretin amyloidosis

Wild type transthyretin-derived amyloid (ATTRwt) is the major component of non-hereditary transthyretin amyloidosis. Its accumulation in the heart of elderly patients is life threatening. A variety of genetic variants of transthyretin can lead to hereditary transthyretin amyloidosis, which shows different clinical symptoms, like age of onset and pattern of organ involvement. However, in the case of non-hereditary transthyretin amyloidosis ATTRwt fibril deposits are located primarily in heart tissue. In this structural study we analyzed ATTRwt amyloid fibrils from the heart of a patient with non-hereditary transthyretin amyloidosis. We present a 2.78 Å reconstructed density map of these ATTRwt fibrils using cryo electron microscopy and compare it with previously published V30M variants of ATTR fibrils extracted from heart and eye of different patients. All structures show a remarkably similar spearhead like shape in their cross section, formed by the same N- and C-terminal fragments of transthyretin with some minor differences. This demonstrates common features for ATTR fibrils despite differences in mutations and patients.

Evaluation of strain echocardiography and atrial electromechanical delay in patients with idiopathic carpal tunnel syndrome

Aim: Carpal tunnel syndrome (CTS) could be an early marker for amyloidosis before developing of overt symptoms of cardiac amyloidosis (CA). CA characterized with left ventricular (LV) diastolic dysfunction and impairment of LV deformation-based parameters. There is limited data about echocardiographic parameters such as strain value of LV, diastolic parameters and atrial EMD in patients with idiopathic CTS. In this study, we investigated LV strain values, diastolic parameters of LV and atrial EMD in patients with idiopathic CTS. Then, we compared these parameters in CTS patients to control group. Material and Method: Thirty-four patients with idiopathic CTS and twenty-four aged and sex matched volunteers were enrolled to study. Patients with known amyloidosis, heart failure, diabetes mellitus and secondary etiologic states for CTS such as trauma or rheumatologic disease were excluded from the study. ECG and echocardiographic examination of each patient were performed and recorded by cardiology specialist. Conventional and strain imaging echocardiography were performed. Atrial electromechanical delays (EMD) were measured. Results: Baseline characteristics features were not different in groups. Mitral inflow velocities (mitral E and A wave), mitral E wave deceleration time, tissue Doppler velocities (lateral annular E’ and A wave), E/A and E/E’ ratios were similar in two groups. Septal basal strain values increased in CTS group (-21.3±4.83% vs -25.7±2.96%, p&lt;0.001). Septal apical to base ratio (SAB) and relative apical sparing (RELAPS) were increased in CTS group compared to control group (0.94±0.43 vs 0.66±0.12, 0.90±0.31 vs 0.73±0.08, p=0.004, p=0.013, respectively). PA lateral, PA septal, inter-atrial EMD and intra-atrial EMD were significantly higher in CTS group compared to control group (78.2±12.3 ms vs 70.6±9.9 ms, 64.1±8.42 ms vs 58.3±10.1 ms, 25.8±9.09 ms vs 20.7±5.31 ms, 11.68±5.11 ms vs 8.46±3.02 ms, p=0.015, p=0.023, p=0.009 and p=.008, respectively). Conclusion: In CTS group, mean basal strain decreased compared to control group. SAB and RELAPS which associate with CA, decreased in CTS group. Atrial EMD prolonged in CTS group. These changes may associate with increased risk of CA and AF in patients with CTS.

The hydrophobic residue Leu73 is crucial for the high stability and low aggregation properties of murine transthyretin

Destabilization of human transthyretin leads to its aggregation into amyloid fibrils, which causes a rare, progressive and fatal systemic disorder called ATTR amyloidosis. By contrast, murine transthyretin is known to be very stable and therefore does not aggregate into amyloid fibrils in vivo or in vitro. We examined the hydrophobic residues responsible for the high-stability and low-aggregation properties of murine transthyretin using site-directed mutagenesis. Urea-induced unfolding and thioflavin T fluorescence aggregation assay revealed that Leu73 of murine transthyretin largely contributes to its high stability and low aggregation properties: the I73L mutation stabilized human transthyretin, while the L73I mutation destabilized murine transthyretin. In addition, the I26V/I73L mutation stabilized the amyloidogenic V30M mutant of human transthyretin to the same degree as the suppressor mutation T119M, which protects transthyretin against amyloid fibril aggregation. The I73L mutation resulted in no significant differences in the overall structure of the transthyretin tetramer or the contacts of side-chains in the hydrophobic core of the monomer. We also found that Leu73 of murine transthyretin is conserved in many mammals, while Ile73 of human transthyretin is conserved in monkeys and cats. These studies will provide new insights into the stability and aggregation properties of transthyretin from various mammals.

Transthyretin cardiac amyloidosis

Transthyretin cardiac amyloidosis (ATTR-CA) is an increasingly recognized cause of heart failure (HF) and mortality worldwide. Advances in non-invasive diagnosis, coupled with the development of effective treatments, have shifted ATTR-CA from a rare and untreatable disease to a relatively prevalent condition that clinicians should consider on a daily basis. Amyloid fibril formation results from age-related failure of homoeostatic mechanisms in wild-type ATTR (ATTRwt) amyloidosis (non-hereditary form) or destabilizing mutations in variant ATTR (ATTRv) amyloidosis (hereditary form). Longitudinal large-scale studies in the United States suggest an incidence of cardiac amyloidosis in the contemporary era of 17 per 100 000, which has increased from a previous estimate of 0.5 per 100 000, which was almost certainly due to misdiagnosis and underestimated. The presence and degree of cardiac involvement is the leading cause of mortality both in ATTRwt and ATTRv amyloidosis, and can be identified in up to 15% of patients hospitalized for HF with preserved ejection fraction. Associated features, such as carpal tunnel syndrome, can preceed by several years the development of symptomatic HF and may serve as early disease markers. Echocardiography and cardiac magnetic resonance raise suspicion of disease and might offer markers of treatment response at a myocardial level, such as extracellular volume quantification. Radionuclide scintigraphy with 'bone' tracers coupled with biochemical tests may differentiate ATTR from light chain amyloidosis. Therapies able to slow or halt ATTR-CA progression and increase survival are now available. In this evolving scenario, early disease recognition is paramount to derive the greatest benefit from treatment.

Calcium Binds to Transthyretin with Low Affinity

The plasma protein transthyretin (TTR), a transporter for thyroid hormones and retinol in plasma and cerebrospinal fluid, is responsible for the second most common type of systemic (ATTR) amyloidosis either in its wild type form or as a result of destabilizing genetic mutations that increase its aggregation propensity. The association between free calcium ions (Ca²⁺) and TTR is still debated, although recent work seems to suggest that calcium induces structural destabilization of TTR and promotes its aggregation at non-physiological low pH in vitro. We apply high-resolution NMR spectroscopy to investigate calcium binding to TTR showing the formation of labile interactions, which leave the native structure of TTR substantially unaltered. The effect of calcium binding on TTR-enhanced aggregation is also assessed at physiological pH through the mechano-enzymatic mechanism. Our results indicate that, even if the binding is weak, about 7% of TTR is likely to be Ca²⁺-bound in vivo and therefore more aggregation prone as we have shown that this interaction is able to increase the protein susceptibility to the proteolytic cleavage that leads to aggregation at physiological pH. These events, even if involving a minority of circulating TTR, may be relevant for ATTR, a pathology that takes several decades to develop.

Analysis of amyloidogenic transthyretin mutations using continuum solvent free energy calculations

Many proteins can undergo pathological conformational changes that result in the formation of amyloidogenic fibril structures. Various neurodegenerative diseases are associated with such pathological fibril formation of specific proteins. Transthyretin (TTR) is a tetrameric globular transport protein in the blood plasma that can dissociate, unfold, and form long and stable fibrils. Many TTR mutations are known that promote (TTR) amyloidosis and cause severe diseases. TTR amyloidosis has been studied extensively using biochemical methods and structures of various mutations in the globular form have been characterized. Recently, also the structure of a TTR fibril has been determined. In an effort to better understand why some mutations increase or decrease the tendency of amyloid formation, we have applied a combined molecular dynamics and continuum solvent approach to calculate the energetic influence of residue changes in the globular versus fibril form. For 29 out of 36 tested TTR single residue mutations, the approach correctly predicts the increased or decreased tendency for amyloidosis allowing us also to elucidate the origins of the tendency. We find that indeed the destabilization of the globular monomer or changes in dimer and tetramer stability due to mutation has a dominant influence on the amyloidogenic tendency. The continuum solvent model predicts a significantly more favorable mean energy per residue of the fibril form compared to the globular form. This effect is only slightly modulated by single-point mutations preserving the energetic preference for fibril formation upon protein unfolding. It explains why no correlation between experimental amyloidosis and calculated change in fibril stability was observed.

Surface-induced Dissociation Mass Spectrometry as a Structural Biology Tool

Native mass spectrometry (nMS) is evolving into a workhorse for structural biology. The plethora of online and offline preparation, separation, and purification methods as well as numerous ionization techniques combined with powerful new hybrid ion mobility and mass spectrometry systems has illustrated the great potential of nMS for structural biology. Fundamental to the progression of nMS has been the development of novel activation methods for dissociating proteins and protein complexes to deduce primary, secondary, tertiary, and quaternary structure through the combined use of multiple MS/MS technologies. This review highlights the key features and advantages of surface collisions (surface-induced dissociation, SID) for probing the connectivity of subunits within protein and nucleoprotein complexes and, in particular, for solving protein structure in conjunction with complementary techniques such as cryo-EM and computational modeling. Several case studies highlight the significant role SID, and more generally nMS, will play in structural elucidation of biological assemblies in the future as the technology becomes more widely adopted. Cases are presented where SID agrees with solved crystal or cryoEM structures or provides connectivity maps that are otherwise inaccessible by "gold standard" structural biology techniques.

Treatment of Transthyretin Amyloid Cardiomyopathy: The Current Options, the Future, and the Challenges

Transthyretin amyloid cardiomyopathy (ATTR-CM) is a progressively debilitating, rare disease associated with high mortality. ATTR-CM occurs when TTR amyloid protein builds up in the myocardium along with different organs, most commonly the peripheral and the autonomic nervous systems. Managing the cardiac complications with standard heart failure medications is difficult due to the challenge to maintain a balance between the high filling pressure associated with restricted ventricular volume and the low cardiac output. To date, tafamidis is the only agent approved for ATTR-CM treatment. Besides, several agents, including green tea, tolcapone, and diflunisal, are used off-label in ATTR-CM patients. Novel therapies using RNA interference also offer clinical promise. Patisiran and inotersen are currently approved for ATTR-polyneuropathy of hereditary origin and are under investigation for ATTR-CM. Monoclonal antibodies in the early development phases carry hope for amyloid deposit clearance. Despite several drug candidates in the clinical development pipeline, the small ATTR-CM patient population raises several challenges. This review describes current and future therapies for ATTR-CM and sheds light on the clinical development hurdles facing them.

High-avidity binding drives nucleation of amyloidogenic transthyretin monomer

Amyloidosis involves stepwise growth of fibrils assembled from soluble precursors. Transthyretin (TTR) naturally folds into a stable tetramer, whereas conditions and mutations that foster aberrant monomer formations facilitate TTR oligomeric aggregation and subsequent fibril extension. We investigated the early assembly of oligomers by WT TTR compared with its V30M and V122I variants. We monitored 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 (SA) interactions. As expected, these multimer seeds rapidly nucleated TTR monomers into larger complexes, while having less effect on dimers and tetramers. In vivo, SA-induced multimers formed TTR-like deposits in the heart and the kidney following i.v. injection in mice. While all 3 variants prominently deposited glomerulus in the kidney, only V30M resulted in extensive deposition in the heart. The cardiac TTR deposits varied in size and shape and were localized in the intermyofibrillar space along the capillaries. These results are consistent with the notion of monomeric TTR engaging in high-avidity interactions with tissue amyloids. Our multimeric induction approach provides a model for studying the initiation of TTR deposition in the heart.

Amyloid fibril composition type is consistent over time in patients with Val30Met (p.Val50Met) transthyretin amyloidosis

Background

We have previously shown that transthyretin (TTR) amyloidosis patients have amyloid fibrils of either of two compositions; type A fibrils consisting of large amounts of C-terminal TTR fragments in addition to full-length TTR, or type B fibrils consisting of only full-length TTR. Since type A fibrils are associated with an older age in ATTRVal30Met (p.Val50Met) amyloidosis patients, it has been discussed if the TTR fragments are derived from degradation of the amyloid deposits as the patients are aging. The present study aimed to investigate if the fibril composition type changes over time, especially if type B fibrils can shift to type A fibrils as the disease progresses.

Material and methods

Abdominal adipose tissue biopsies from 29 Swedish ATTRVal30Met amyloidosis patients were investigated. The fibril type in the patients´ initial biopsy taken for diagnostic purposes was compared to a biopsy taken several years later (ranging between 2 and 13 years). The fibril composition type was determined by western blot.

Results

All 29 patients had the same fibril composition type in both the initial and the follow-up biopsy (8 type A and 21 type B). Even patients with a disease duration of more than 12 years and an age over 75 years at the time of the follow-up biopsy had type B fibrils in both biopsies.

Discussion

The result clearly shows that the amyloid fibril composition containing large amounts of C-terminal fragments (fibril type A) is a consequence of other factors than a slow degradation process occurring over time.

Endogenous Human Proteins Interfering with Amyloid Formation

Amyloid formation is a pathological process associated with a wide range of degenerative disorders, including Alzheimer’s disease, Parkinson’s disease, and diabetes mellitus type 2. During disease progression, abnormal accumulation and deposition of proteinaceous material are accompanied by tissue degradation, inflammation, and dysfunction. Agents that can interfere with the process of amyloid formation or target already formed amyloid assemblies are consequently of therapeutic interest. In this context, a few endogenous proteins have been associated with an anti-amyloidogenic activity. Here, we review the properties of transthyretin, apolipoprotein E, clusterin, and BRICHOS protein domain which all effectively interfere with amyloid in vitro, as well as displaying a clinical impact in humans or animal models. Their involvement in the amyloid formation process is discussed, which may aid and inspire new strategies for therapeutic interventions.

Protein Aggregation and Self Assembly in Health and Disease

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Self-attachment of proteins leading to the formation of highly insoluble protein oligomers and aggregates has become an important focus of research owing to its diverse implications in pathophysiology and diseases. This has become a more frequent phenomenon in most neurological and neurodegenerative diseases as well as in dementia. In recent years such event of protein aggregation has linked to other disease conditions, disorders or adverse health conditions. Interestingly, aggregation of protein also plays role in development, growth or metabolism. Most often physiological proteins are initially bio-synthesised in native or nascent geometrical forms or conformations but later they undergo specific folding pattern and thereby acquire a stable configuration that is biologically relevant and active. It is highly important that these proteins remain in their biologically active configuration in order to exert their functional properties. Any alteration or change to this structural configuration can be detrimental to their specific functions and may cause pathological consequences leading to the onset of diseases or disorders. Several factors such as the action of chaperones, binding partners, physiological metal ions, pH level, temperature, ionic strength, interfacial exposure (solid-liquid, liquid-liquid, gas-liquid), mutation and post translational modification, chemical changes, interaction with small molecules such as lipids, hormones, etc. and solvent environment have been either identified or proposed as important factors in conferring the ultimate status of protein structure and configuration. Among many misfolding protein conformations, self-assembly or aggregation is the most significant. It leads to the formation of highly oligomeric self-aggregates that precipitate and interfere with many biochemical processes with serious pathological consequences. The most common implication of protein aggregation leading to the formation of deposits / plaques of various morphological types is the onset of neurological and neurodegenerative diseases that include Alzheimer’s, Parkinson’s, Huntington, ALS (Amyotrophic Lateral Sclerosis), CJD (Creutzfeldt Jakob Dementia), Prion diseases, Amyloidosis and other forms of dementia. However increasingly studies revealed that protein aggregation may also be associated with other diseases such as cancer, type 2 diabetes, renal, corneal and cardiovascular diseases. Protein aggregation diseases are now considered as part of “Proteinopathy” which refers to conditions where proteins become structurally abnormal or fail to fold into stable normal configurations. In this review, we reflect on various aspects of protein self-aggregation, potential underlying causes, mechanism, role of secondary structures, pathological consequences and possible intervention strategies as reported in published literatures.

Inhibiting mTTR Aggregation/Fibrillation by a Chaperone-like Hydrophobic Amino Acid-Conjugated SPION

Transthyretin (TTR) aggregation via misfolding of a mutant or wild-type protein leads to systemic or partial amyloidosis (ATTR). Here, we utilized variable biophysical assays to characterize two distinct aggregation pathways for mTTR (a synthesized monomer TTR incapable of association into a tetramer) at pH 4.3 and also pH 7.4 with agitation, referred to as mTTR aggregation and fibrillation, respectively. The findings suggest that early-stage conformational changes termed monomer activation here determine the aggregation pathway, resulting in developing either amorphous aggregates or well-organized fibrils. Less packed partially unfolded monomers consisting of more non-regular secondary structures that were rapidly produced via a mildly acidic condition form amorphous aggregates. Meanwhile, more hydrophobic and packed monomers consisting of rearranged β sheets and increased helical content developed well-organized fibrils. Conjugating superparamagnetic iron oxide nanoparticles (SPIONs) with leucine and glutamine (L-SPIONs and G-SPIONs in order) via a trimethoxysilane linker provided the chance to study the effect of hydrophobic/hydrophilic surfaces on mTTR aggregation. The results indicated a powerful inhibitory effect of hydrophobic L-SPIONs on both mTTR aggregation and fibrillation. Monomer depletion was introduced as the governing mechanism for inhibiting mTTR aggregation, while a chaperone-like property of L-SPIONs by maintaining an mTTR native structure and adsorbing oligomers suppressed the progression of further fibril formation.

Features and evolution of patients with systemic amyloidosis and cardiac involvement

Objective

To estimate the prevalence of cardiac amyloidosis in patients with systemic amyloidosis. Compare survival rates based on whether they show cardiac involvement.

Methods

A retrospective cohort study of patients with systemic amyloidosis from the Institutional Amyloidosis Registry of the Hospital Italian of Buenos Aires from 2010 to 2019. Heart involvement is considered to be the presence of symptoms and/or images consistent with amyloidosis, and there is no other reason to explain it. All deaths due to causes were evaluated. The survival rate was estimated by Kaplan-Meier. Cox regression model was used to evaluate factors related to mortality. Heart transplantation was evaluated in a competitive risk regression model.

Results

The prevalence of heart involvement is 63%. For the group with heart damage, the death rate was 14/1,000 person-months, and for patients without damage, the death rate was 5/1,000 person-months. The 5-year overall survival rate for patients with heart involvement was 44%, while that for patients without damage was 67% (p = 0.02). The original HR for heart involvement was 2.09 (p = 0.02). Age showed that HRa was 1.06 (p <0.01). The sub-HR estimated by the competitive risk regression model are 1.86 (95% CI 0.99-3.49) p = 0.05.

Conclusion

Cardiac involvement is an important prognostic factor in patients with amyloidosis.

Synthesis and biological evaluation of quinolone derivatives as transthyretin amyloidogenesis inhibitors and fluorescence sensors

Under certain conditions, numerous soluble proteins possess an inherent tendency to convert into insoluble amyloid aggregates, which are associated with several sporadic and genetic human diseases. Transthyretin (TTR) is one of the more than 30 human amyloidogenic proteins involved in conditions such as senile systemic amyloidosis, familial amyloid polyneuropathy, and familial amyloid cardiomyopathy. Considerable effort has been focused on identifying the native tetrameric TTR stabilizers to inhibit rate-limiting tetramer dissociation and, consequently, ameliorate TTR amyloidogenesis. Here, we describe the design and synthesis of quinolin-2(1H)-one derivatives that could be structurally complementary to the thyroxine-binding site within tetrameric TTR. Among these quinolin-2(1H)-one derivatives, compound 7a allowed 16.7% of V30M-TTR (3.6 μM) fibril formation at the same concentration and 49.6% at a concentration of 1.8 μM. Compound 7a exhibited much greater potency in complex biological samples like human plasma than that observed with tafamidis, the drug approved for the treatment of TTR amyloid cardiomyopathy for wild-type or hereditary TTR-mediated amyloidosis. Furthermore, the unique spectral properties of compound 7a demonstrated its high potential for TTR quantification, imaging sensors, and fluorescent tools to study the mechanism of TTR amyloidogenesis.

Wild-type Transthyretin Amyloidosis with Diffuse Alveolar-septal Amyloidosis Diagnosed by a Transbronchial Lung Biopsy

A 69-year-old man visited our pulmonary medicine department for dyspnea. Chest computed tomography (CT) revealed ground-glass opacity bilaterally in the lungs. Upon performing a transbronchial lung biopsy (TBLB), organizing pneumonia was diagnosed. His electrocardiogram revealed low voltage, and the cardiac ultrasound revealed hypertrophy of the interventricular septum. The patient had bilateral carpal tunnel syndrome, and amyloidosis was suspected. Congo red stain was added to the lung biopsy specimen. Amyloid deposition of transthyretin (ATTR) was positive, mutations with amino acid changes were not observed in the TTR gene. Wild-type ATTR Amyloidosis (ATTRwt amyloidosis) was diagnosed using a TBLB. Chest CT after treatment with steroids revealed diffuse alveolar-septal amyloidosis.

Molecular Mechanisms of Cardiac Amyloidosis

Cardiac involvement has a profound effect on the prognosis of patients with systemic amyloidosis. Therapeutic methods for suppressing the production of causative proteins have been developed for ATTR amyloidosis and AL amyloidosis, which show cardiac involvement, and the prognosis has been improved. However, a method for removing deposited amyloid has not been established. Methods for reducing cytotoxicity caused by amyloid deposition and amyloid precursor protein to protect cardiovascular cells are also needed. In this review, we outline the molecular mechanisms and treatments of cardiac amyloidosis.

Proteins in Wonderland: The Magical World of Pressure

Admitting the "Native", "Unfolded" and "Fibril" states as the three basic generic states of proteins in nature, each of which is characterized with its partial molar volume, here we predict that the interconversion among these generic states N, U, F may be performed simply by making a temporal excursion into the so called "the high-pressure regime", created artificially by putting the system under sufficiently high hydrostatic pressure, where we convert N to U and F to U, and then back to "the low-pressure regime" (the "Anfinsen regime"), where we convert U back to N (U→N). Provided that the solution conditions (temperature, pH, etc.) remain largely the same, the idea provides a general method for choosing N, U, or F of a protein, to a great extent at will, assisted by the proper use of the external perturbation pressure. A successful experiment is demonstrated for the case of hen lysozyme, for which the amyloid fibril state F prepared at 1 bar is turned almost fully back into its original native state N at 1 bar by going through the "the high-pressure regime". The outstanding simplicity and effectiveness of pressure in controlling the conformational state of a protein are expected to have a wide variety of applications both in basic and applied bioscience in the future.

A quinoline derived D-A-D type fluorescent probe for sensing tetrameric transthyretin

Nowadays, with an upward trend in the prevalence of intracerebral amyloidosis, it is of great significance to use fluorescent probes for early diagnosis in vitro. In this study, a quinoline-derived D-A-D type chemosensor was rationally designed and synthesized as a probe for the sensitive detection of tetrameric transthyretin (WT-TTR).

Aggregation-Prone Structural Ensembles of Transthyretin Collected With Regression Analysis for NMR Chemical Shift

Monomer dissociation and subsequent misfolding of the transthyretin (TTR) is one of the most critical causative factors of TTR amyloidosis. TTR amyloidosis causes several human diseases, such as senile systemic amyloidosis and familial amyloid cardiomyopathy/polyneuropathy; therefore, it is important to understand the molecular details of the structural deformation and aggregation mechanisms of TTR. However, such molecular characteristics are still elusive because of the complicated structural heterogeneity of TTR and its highly sensitive nature to various environmental factors. Several nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) studies of TTR variants have recently reported evidence of transient aggregation-prone structural states of TTR. According to these studies, the stability of the DAGH β-sheet, one of the two main β-sheets in TTR, is a crucial determinant of the TTR amyloidosis mechanism. In addition, its conformational perturbation and possible involvement of nearby structural motifs facilitates TTR aggregation. This study proposes aggregation-prone structural ensembles of TTR obtained by MD simulation with enhanced sampling and a multiple linear regression approach. This method provides plausible structural models that are composed of ensemble structures consistent with NMR chemical shift data. This study validated the ensemble models with experimental data obtained from circular dichroism (CD) spectroscopy and NMR order parameter analysis. In addition, our results suggest that the structural deformation of the DAGH β-sheet and the AB loop regions may correlate with the manifestation of the aggregation-prone conformational states of TTR. In summary, our method employing MD techniques to extend the structural ensembles from NMR experimental data analysis may provide new opportunities to investigate various transient yet important structural states of amyloidogenic proteins.

Are we creating a new phenotype? Physiological barriers and ethical considerations in the treatment of hereditary transthyretin-amyloidosis

Hereditary transthyretin (TTR) amyloidosis (ATTRv) is an autosomal dominant, systemic disease transmitted by amyloidogenic mutations in the TTR gene. To prevent the otherwise fatal disease course, TTR stabilizers and mRNA silencing antisense drugs are currently approved treatment options. With 90% of the amyloidogenic protein produced by the liver, disease progression including polyneuropathy and cardiomyopathy, the two most prominent manifestations, can successfully be halted by hepatic drug targeting or-formerly-liver transplantation. Certain TTR variants, however, favor disease manifestations in the central nervous system (CNS) or eyes, which is mostly associated with TTR production in the choroid plexus and retina. These compartments cannot be sufficiently reached by any of the approved medications. From liver-transplanted patients, we have learned that with longer lifespans, such CNS manifestations become more relevant over time, even if the underlying TTR mutation is not primarily associated with such. Are we therefore creating a new phenotype? Prolonging life will most likely lead to a shift in the phenotypic spectrum, enabling manifestations like blindness, dementia, and cerebral hemorrhage to come out of the disease background. To overcome the first therapeutic limitation, the blood-brain barrier, we might be able to learn from other antisense drugs currently being used in research or even being approved for primary neurodegenerative CNS diseases like spinal muscular atrophy or Alzheimer's disease. But what effects will unselective CNS TTR knock-down have considering its role in neuroprotection? A potential approach to overcome this second limitiation might be allele-specific targeting, which is, however, still far from clinical trials. Ethical standpoints underline the need for seamless data collection to enable more evidence-based decisions and for thoughtful consenting in research and clinical practice. We conclude that the current advances in treating ATTRv amyloidosis have become a meaningful example for mechanism-based treatment. With its great success in improving patient life spans, we will still have to face new challenges including shifts in the phenotype spectrum and the ongoing need for improved treatment precision. Further investigation is needed to address these closed barriers and open questions.

tipNrich: A Tip-Based N-Terminal Proteome Enrichment Method

The mass spectrometry-based analysis of protein post-translational modifications requires large amounts of sample, complicating the analysis of samples with limited amounts of proteins such as clinical biopsies. Here, we present a tip-based N-terminal analysis method, tipNrich. The entire procedure is processed in a single pipette tip to minimize sample loss, which is so highly optimized to analyze small amounts of proteins, even femtomole-scale of a single protein. With tipNrich, we investigated various single proteins purified from different organisms using a low-resolution mass spectrometer and identified several N-terminal peptides with different Nt-modifications such as ragged N-termini. Furthermore, we applied matrix-assisted laser desorption ionization time-of-flight mass spectrometry to our method for shortening the analysis time. Moreover, we showed that our method could be utilized in disease diagnosis as exemplified by the characterization of wild-type transthyretin amyloidosis patients compared to the healthy individuals based on N-terminome profiling. In summary, tipNrich will satisfy the need of identifying N-terminal peptides even with highly scarce amounts of proteins and of having faster processing time to check the quality of protein products or to characterize N-terminal proteoform-related diseases.

Man does not live by intrinsically unstructured proteins alone: The role of structured regions in aggregation

Protein misfolding is a topic that is of primary interest both in biology and medicine because of its impact on fundamental processes and disease. In this review, we revisit the concept of protein misfolding and discuss how the field has evolved from the study of globular folded proteins to focusing mainly on intrinsically unstructured and often disordered regions. We argue that this shift of paradigm reflects the more recent realisation that misfolding may not only be an adverse event, as originally considered, but also may fulfil a basic biological need to compartmentalise the cell with transient reversible granules. We nevertheless provide examples in which structure is an important component of a much more complex aggregation behaviour that involves both structured and unstructured regions of a protein. We thus suggest that a more comprehensive evaluation of the mechanisms that lead to aggregation might be necessary.

Age-related amyloidosis outside the brain: A state-of-the-art review

Inside and outside the brain, accumulation of amyloid fibrils plays key roles in the pathogenesis of fatal age-related diseases such as Alzheimer's and Parkinson's diseases and wild-type transthyretin amyloidosis. Although the incidence of all amyloidoses increases with age, for some types of amyloidosis aging is known as the main direct risk factor, and these types are typically diseases of elderly people. More than 10 different precursor proteins are known to cause age-associated amyloidosis; these proteins include amyloid β protein, α-synuclein, transthyretin, islet amyloid polypeptide, atrial natriuretic factor, and the newly discovered epidermal growth factor-containing fibulin-like extracellular matrix protein 1. Except for intracerebral amyloidoses, most age-related amyloidoses have been little studied. Indeed, in view of the increasing life expectancy in our societies, understanding how aging is involved in the process of amyloid fibril accumulation and the effects of amyloid deposits on the aging body is extremely important. In this review, we summarize current knowledge about the nature of amyloid precursor proteins, the prevalence, clinical manifestations, and pathogenesis of amyloidosis, and recent advances in our understanding of age-related amyloidoses outside the brain.