Peptide probes detect misfolded transthyretin oligomers in plasma of hereditary amyloidosis patients

Illuminating intercellular autophagy: A comprehensive review of cell non-autonomous autophagy

Macro-autophagy (autophagy hereafter) is an evolutionarily conserved cellular process that has long been recognized as an intracellular mechanism for maintaining cellular homeostasis. It involves the formation of a membraned structure called the autophagosome, which carries cargo that includes toxic protein aggregates and dysfunctional organelles to the lysosome for degradation and recycling. Autophagy is primarily considered and studied as a cell-autonomous mechanism. However, recent studies have illuminated an underappreciated facet of autophagy, i.e., non-autonomously regulated autophagy. Non-autonomously regulated autophagy involves the degradation of autophagic components, including organelles, cargo, and signaling molecules, and is induced in neighboring cells by signals from primary adjacent or distant cells/tissues/organs. This review provides insight into the complex molecular mechanisms governing non-autonomously regulated autophagy, highlighting the dynamic interplay between cells within tissue/organ or distinct cell types in different tissues/organs. Emphasis is placed on modes of intercellular communication that include secreted molecules, including microRNAs, and their regulatory roles in orchestrating this phenomenon. Furthermore, we explore the multidimensional roles of non-autonomously regulated autophagy in various physiological contexts, spanning tissue development and aging, as well as its importance in diverse pathological conditions, including cancer and neurodegeneration. By studying the complexities of non-autonomously regulated autophagy, we hope to gain insights into the sophisticated intercellular dynamics within multicellular organisms, including mammals. These studies will uncover novel avenues for therapeutic intervention to modulate intercellular autophagic pathways in altered human physiology.

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.

ATTRv-V30M Type A amyloid fibrils from heart and nerves exhibit structural homogeneity

ATTR amyloidosis is a systemic disease characterized by the deposition of amyloid fibrils made of transthyretin, a protein integral to transporting retinol and thyroid hormones. Transthyretin is primarily produced by the liver and circulates in blood as a tetramer. The retinal epithelium also secretes transthyretin, which is secreted to the vitreous humor of the eye. Because of mutations or aging, transthyretin can dissociate into amyloidogenic monomers triggering amyloid fibril formation. The deposition of transthyretin amyloid fibrils in the myocardium and peripheral nerves causes cardiomyopathies and neuropathies, respectively. Using cryo-electron microscopy, here we determined the structures of amyloid fibrils extracted from cardiac and nerve tissues of an ATTRv-V30M patient. We found that fibrils from both tissues share a consistent structural conformation, similar to the previously described structure of cardiac fibrils from an individual with the same genotype, but different from the fibril structure obtained from the vitreous humor. Our study hints to a uniform fibrillar architecture across different tissues within the same individual, only when the source of transthyretin is the liver. Moreover, this study provides the first description of ATTR fibrils from the nerves of a patient and enhances our understanding of the role of deposition site and protein production site in shaping the fibril structure in ATTRv-V30M amyloidosis.

Amyloid fibril polymorphism in the heart of an ATTR amyloidosis patient with polyneuropathy attributed to the V122Δ variant

ATTR amyloidosis is a phenotypically heterogeneous disease characterized by the pathological deposition of transthyretin in the form of amyloid fibrils into various organs. ATTR amyloidosis may stem from mutations in variant (ATTRv) amyloidosis, or aging in wild-type (ATTRwt) amyloidosis. ATTRwt generally manifests as a cardiomyopathy phenotype, whereas ATTRv may present as polyneuropathy, cardiomyopathy, or mixed, in combination with many other symptoms deriving from secondary organ involvement. Over 130 different mutational variants of transthyretin have been identified, many of them being linked to specific disease symptoms. Yet, the role of these mutations in the differential disease manifestation remains elusive. Using cryo-electron microscopy, here we structurally characterized fibrils from the heart of an ATTRv patient carrying the V122Δ mutation, predominantly associated with polyneuropathy. Our results show that these fibrils are polymorphic, presenting as both single and double filaments. Our study alludes to a structural connection contributing to phenotypic variation in ATTR amyloidosis, as polymorphism in ATTR fibrils may manifest in patients with predominantly polyneuropathic phenotypes.

Binding of a Pyrene-Based Fluorescent Amyloid Ligand to Transthyretin: A Combined Crystallographic and Molecular Dynamics Study

Misfolding and aggregation of transthyretin (TTR) cause several amyloid diseases. Besides being an amyloidogenic protein, TTR has an affinity for bicyclic small-molecule ligands in its thyroxine (T4) binding site. One class of TTR ligands are trans-stilbenes. The trans-stilbene scaffold is also widely applied for amyloid fibril-specific ligands used as fluorescence probes and as positron emission tomography tracers for amyloid detection and diagnosis of amyloidosis. We have shown that native tetrameric TTR binds to amyloid ligands based on the trans-stilbene scaffold providing a platform for the determination of high-resolution structures of these important molecules bound to protein. In this study, we provide spectroscopic evidence of binding and X-ray crystallographic structure data on tetrameric TTR complex with the fluorescent salicylic acid-based pyrene amyloid ligand (Py1SA), an analogue of the Congo red analogue X-34. The ambiguous electron density from the X-ray diffraction, however, did not permit Py1SA placement with enough confidence likely due to partial ligand occupancy. Instead, the preferred orientation of the Py1SA ligand in the binding pocket was determined by molecular dynamics and umbrella sampling approaches. We find a distinct preference for the binding modes with the salicylic acid group pointing into the pocket and the pyrene moiety outward to the opening of the T4 binding site. Our work provides insight into TTR binding mode preference for trans-stilbene salicylic acid derivatives as well as a framework for determining structures of TTR-ligand complexes.

Tafamidis polyneuropathy amelioration requires modest increases in transthyretin stability even though increases in plasma native TTR and decreases in non-native TTR do not predict response

BACKGROUND

TTR aggregation causes hereditary transthyretin (TTR) polyneuropathy (ATTRv-PN) in individuals with destabilised TTR variants. ATTRv-PN can be treated with ligands that bind TTR and prevent aggregation. One such ligand, tafamidis, is widely approved to treat ATTRv-PN. We explore how TTR stabilisation markers relate to clinical efficacy in 210 ATTRv-PN patients taking tafamidis.

METHODS

TTR concentration in patient plasma was measured before and after tafamidis treatment using assays for native or combined native + non-native TTR. TTR tetramer dissociation kinetics, which are slowed by tafamidis binding, were also measured.

RESULTS

Native TTR levels increased by 56.8% while combined native + non-native TTR levels increased by 3.1% after 24 months of tafamidis treatment, implying that non-native TTR decreased. Accordingly, the fraction of native TTR increased from 0.54 to 0.71 with tafamidis administration. Changes in native and non-native TTR levels were uncorrelated with clinical response to tafamidis. TTR tetramer dissociation generally slowed to an extent consistent with ∼40% of TTR being tafamidis-bound. Male non-responders had a lower extent of binding.

CONCLUSIONS

Native and non-native TTR concentration changes cannot be used as surrogate measures for therapeutic efficacy. Also, successful tafamidis therapy requires only moderate TTR stabilisation. Male patients may benefit from higher tafamidis doses.

The Protein Network in Subcutaneous Fat Biopsies from Patients with AL Amyloidosis: More Than Diagnosis?

AL amyloidosis is caused by the misfolding of immunoglobulin light chains leading to an impaired function of tissues and organs in which they accumulate. Due to the paucity of -omics profiles from undissected samples, few studies have addressed amyloid-related damage system wide. To fill this gap, we evaluated proteome changes in the abdominal subcutaneous adipose tissue of patients affected by the AL isotypes κ and λ. Through our retrospective analysis based on graph theory, we have herein deduced new insights representing a step forward from the pioneering proteomic investigations previously published by our group. ECM/cytoskeleton, oxidative stress and proteostasis were confirmed as leading processes. In this scenario, some proteins, including glutathione peroxidase 1 (GPX1), tubulins and the TRiC complex, were classified as biologically and topologically relevant. These and other results overlap with those already reported for other amyloidoses, supporting the hypothesis that amyloidogenic proteins could induce similar mechanisms independently of the main fibril precursor and of the target tissues/organs. Of course, further studies based on larger patient cohorts and different tissues/organs will be essential, which would be a key point that would allow for a more robust selection of the main molecular players and a more accurate correlation with clinical aspects.

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.

Update on Disease-Specific Biomarkers in Transthyretin Cardiac Amyloidosis

PURPOSE OF REVIEW

Transthyretin cardiac amyloidosis (ATTR-CM) is an infiltrative cardiomyopathy and an increasingly recognized cause of morbidity and mortality. There remains substantial delay between initial symptoms and diagnosis. With the recent emergence of various targeted therapies proven to reduce morbidity and mortality, there is an imperative to diagnose subclinical disease. Biomarkers may be well-suited for this role.

RECENT FINDINGS

Conventional markers of heart failure, such as natriuretic peptides and cardiac troponins, and estimated glomerular filtration rate are associated with risk in ATTR-CM. Circulating transthyretin (TTR) levels parallel TTR kinetic stability, correlate with disease severity, and may serve as indirect markers of ATTR-CM disease activity and response to targeted treatment. There is also growing evidence for the correlation of TTR to retinol-binding protein 4, a biomarker which independently associates with this disease. The rate-limiting step for ATTR pathogenesis is dissociation of the TTR homotetramer, which may be quantified using subunit exchange to allow for early risk assessment, prognostication, and assessment of treatment response. The protein species that result from the dissociation and misfolding of TTR are known as nonnative transthyretin (NNTTR). NNTTR is quantifiable via peptide probes and is a specific biomarker whose reduction is positively correlated with improvement in neuropathic ATTR amyloidosis. Neurofilament light chain (NfL) is released into the blood after axonal damage and correlates with neuropathic ATTR amyloidosis, but its clinical use in ATTR-CM is uncertain. Conventional markers of heart failure, transthyretin, retinol-binding protein 4, transthyretin kinetic stability, nonnative transthyretin, peptide probes, and neurofilament light chain have potential as biomarkers to enable early, subclinical diagnosis in patients with transthyretin cardiac amyloidosis.

Serum Amyloid A Protein–Associated Kidney Disease: Presentation, Diagnosis, and Management

Serum amyloid A protein (AA) amyloidosis, also known as secondary amyloidosis, is a known consequence of chronic inflammation and results from several conditions including inflammatory arthritis, periodic fever syndromes, and chronic infection. AA amyloidosis can lead to multiorgan dysfunction, including changes in glomerular filtration rate and proteinuria. Definitive diagnosis requires tissue biopsy, and management of AA amyloid kidney disease is primarily focused on treating the underlying inflammatory condition to stabilize glomerular filtration rate, reduce proteinuria, and slow potential progression to kidney failure. In this narrative review, we describe the causes, pathophysiology, presentation, and pathologic diagnosis of AA amyloid kidney disease using an illustrative case of biopsy-proven AA amyloid kidney disease in a patient with long-standing rheumatoid arthritis who had a favorable response to interleukin 6 inhibition. We conclude the review with a description of established and more novel therapies for AA amyloidosis including published cases of use of tocilizumab (an interleukin 6 inhibitor) in biopsy-proven AA amyloid kidney disease.

The revolution of ATTR amyloidosis in cardiology: certainties, gray zones and perspectives

Transthyretin (TTR) is a tetrameric protein synthesized mostly by the liver. As a result of gene mutations or as an ageing-related phenomenon, TTR molecules may misfold and deposit in the heart and in other organs as amyloid fibrils. Amyloid transthyretin cardiac amyloidosis (ATTR-CA) manifests typically as left ventricular pseudohypertrophy and/or heart failure with preserved ejection fraction and is an underdiagnosed disorder affecting quality of life and prognosis. This justifies the current search for novel tools for early diagnosis and accurate risk prediction, as well as for safe and effective therapies. In this review we will provide an overview of the main unsolved issues and the most promising research lines on ATTR-CA, ranging from the mechanisms of amyloid formation to therapies.

Stress-responsive regulation of extracellular proteostasis

Genetic, environmental, and aging-related insults can promote the misfolding and subsequent aggregation of secreted proteins implicated in the pathogenesis of numerous diseases. This has led to considerable interest in understanding the molecular mechanisms responsible for regulating proteostasis in extracellular environments such as the blood and cerebrospinal fluid (CSF). Extracellular proteostasis is largely dictated by biological pathways comprising chaperones, folding enzymes, and degradation factors localized to the ER and extracellular space. These pathways limit the accumulation of nonnative, potentially aggregation-prone proteins in extracellular environments. Many reviews discuss the molecular mechanisms by which these pathways impact the conformational integrity of the secreted proteome. Here, we instead focus on describing the stress-responsive mechanisms responsible for adapting ER and extracellular proteostasis pathways to protect the secreted proteome from pathologic insults that challenge these environments. Further, we highlight new strategies to identify stress-responsive pathways involved in regulating extracellular proteostasis and describe the pathologic and therapeutic implications for these pathways in human disease.

Cu(II) Binding Increases the Soluble Toxicity of Amyloidogenic Light Chains

Light chain amyloidosis (AL) is caused by the aberrant overproduction of immunoglobulin light chains (LCs). The resulting abnormally high LC concentrations in blood lead to deposit formation in the heart and other target organs. Organ damage is caused not only by the accumulation of bulky amyloid deposits, but extensive clinical data indicate that circulating soluble LCs also exert cardiotoxic effects. The nematode C. elegans has been validated to recapitulate LC soluble toxicity in vivo, and in such a model a role for copper ions in increasing LC soluble toxicity has been reported. Here, we applied microscale thermophoresis, isothermal calorimetry and thermal melting to demonstrate the specific binding of Cu²⁺ to the variable domain of amyloidogenic H7 with a sub-micromolar affinity. Histidine residues present in the LC sequence are not involved in the binding, and yet their mutation to Ala reduces the soluble toxicity of H7. Copper ions bind to and destabilize the variable domains and induce a limited stabilization in this domain. In summary, the data reported here, elucidate the biochemical bases of the Cu²⁺-induced toxicity; moreover, they also show that copper binding is just one of the several biochemical traits contributing to LC soluble in vivo toxicity.

Synthetic Pept-Ins as a Generic Amyloid-Like Aggregation-Based Platform for In Vivo PET Imaging of Intracellular Targets

Amyloid-like aggregation of proteins is induced by short amyloidogenic sequence segments within a specific protein sequence resulting in self-assembly into β-sheets. We recently validated a technology platform in which synthetic amyloid peptides ("Pept-ins") containing a specific aggregation-prone region (APR) are used to induce specific functional knockdown of the target protein from which the APR was derived, including bacterial, viral, and mammalian cell proteins. In this work, we investigated if Pept-ins can be used as vector probes for in vivo Positron Emission Tomography (PET) imaging of intracellular targets. The radiolabeled Pept-ins [⁶⁸Ga]Ga-NODAGA-PEG₄-vascin (targeting VEGFR2) and [⁶⁸Ga]Ga-NODAGA-PEG₂-P2 (targeting E. coli) were evaluated as PET probes. The Pept-in based radiotracers were cross-validated in a murine tumor and muscle infection model, respectively, and were found to combine target specificity with favorable in vivo pharmacokinetics. When the amyloidogenicity of the interacting region of the peptide is suppressed by mutation, cellular uptake and in vivo accumulation are abolished, highlighting the importance of the specific design of synthetic Pept-ins. The ubiquity of target-specific amyloidogenic sequence segments in natural proteins, the straightforward sequence-based design of the Pept-in probes, and their spontaneous internalization by cells suggest that Pept-ins may constitute a generic platform for in vivo PET imaging of intracellular targets.

A circulating, disease-specific, mechanism-linked biomarker for ATTR polyneuropathy diagnosis and response to therapy prediction

The transthyretin (TTR) amyloidoses (ATTR) are progressive, degenerative diseases resulting from dissociation of the TTR tetramer to monomers, which subsequently misfold and aggregate, forming a spectrum of aggregate structures including oligomers and amyloid fibrils. To determine whether circulating nonnative TTR (NNTTR) levels correlate with the clinical status of patients with V30M TTR familial amyloid polyneuropathy (FAP), we quantified plasma NNTTR using a newly developed sandwich enzyme-linked immunosorbent assay. The assay detected significant plasma levels of NNTTR in most presymptomatic V30M TTR carriers and in all FAP patients. NNTTR was not detected in age-matched control plasmas or in subjects with other peripheral neuropathies, suggesting NNTTR can be useful in diagnosing FAP. NNTTR levels were substantially reduced in patients receiving approved FAP disease-modifying therapies (e.g., the TTR stabilizer tafamidis, 20 mg once daily). This NNTTR decrease was seen in both the responders (average reduction 56.4 ± 4.2%; n = 49) and nonresponders (average reduction of 63.3 ± 4.8%; n = 32) at 12 mo posttreatment. Notably, high pretreatment NNTTR levels were associated with a significantly lower likelihood of clinical response to tafamidis. Our data suggest that NNTTR is a disease driver whose reduction is sufficient to ameliorate FAP so long as pretreatment NNTTR levels are below a critical clinical threshold.

Does protein aggregation drive postmitotic tissue degeneration?

Pharmacological evidence, from clinical trials where patients with systemic amyloid diseases are treated with disease-modifying therapies, supports the notion that protein aggregation drives tissue degeneration in these disorders. The protein aggregate structures driving tissue pathology and the commonalities in etiology between these diseases and Alzheimer's disease are under investigation.

Dissecting the role of glutamine in seeding peptide aggregation

Poly glutamine and glutamine-rich peptides play a central role in a plethora of pathological aggregation events. However, biophysical characterization of soluble oligomers -the most toxic species involved in these processes- remains elusive due to their structural heterogeneity and dynamical nature. Here, we exploit the high spatio-temporal resolution of coarse-grained simulations as a computational microscope to characterize the aggregation propensity and morphology of a series of polyglutamine and glutamine-rich peptides. Comparative analysis of ab-initio aggregation pinpointed a double role for glutamines. In the first phase, glutamines mediate seeding by pairing monomeric peptides, which serve as primers for higher-order nucleation. According to the glutamine content, these low molecular-weight oligomers may then proceed to create larger aggregates. Once within the aggregates, buried glutamines continue to play a role in their maturation by optimizing solvent-protected hydrogen bonds networks.

Blinded potency comparison of transthyretin kinetic stabilisers by subunit exchange in human plasma

Transthyretin (TTR) tetramer dissociation is rate limiting for aggregation and subunit exchange. Slowing of TTR tetramer dissociation via kinetic stabiliser binding slows cardiomyopathy progression. Quadruplicate subunit exchange comparisons of the drug candidate AG10, and the drugs tolcapone, diflunisal, and tafamidis were carried out at 1, 5, 10, 20 and 30 µM concentrations in 4 distinct pooled wild type TTR (TTRwt) human plasma samples. These experiments reveal that the concentration dependence of the efficacy of each compound at inhibiting TTR dissociation was primarily determined by the ratio between the stabiliser's dissociation constants from TTR and albumin, which competes with TTR to bind kinetic stabilisers. The best stabilisers, tafamidis (80 mg QD), AG10 (800 mg BID), and tolcapone (3 x 100 mg over 12 h), exhibit very similar kinetic stabilisation at the plasma concentrations resulting from these doses. At a 10 µM plasma concentration, AG10 is slightly more potent as a kinetic stabiliser vs. tolcapone and tafamidis (which are similar), which are substantially more potent than diflunisal. Dissociation of TTR can be limited to 10% of its normal rate at concentrations of 5.7 µM AG10, 10.3 µM tolcapone, 12.0 µM tafamidis, and 188 µM diflunisal. The potency similarities revealed by our study suggest that differences in safety, adsorption and metabolism, pharmacokinetics, and tissue distribution become important for kinetic stabiliser clinical use decisions.

Use of biomarkers to diagnose and manage cardiac amyloidosis

Amyloidoses are characterized by the tissue accumulation of misfolded proteins into insoluble fibrils. The two most common types of systemic amyloidosis result from the deposition of immunoglobulin light chains (AL) and wild-type or variant transthyretin (ATTRwt/ATTRv). Cardiac involvement is the main determinant of outcome in both AL and ATTR, and cardiac amyloidosis (CA) is increasingly recognized as a cause of heart failure. In CA, circulating biomarkers are important diagnostic tools, allow to refine risk stratification at baseline and during follow-up, help to tailor the therapeutic strategy and monitor the response to treatment. Among amyloid precursors, free light chains are established biomarkers in AL amyloidosis, while the plasma transthyretin assay is currently being investigated as a tool for supporting the diagnosis of ATTRv amyloidosis, predicting outcome and monitor response to novel tetramer stabilizers or small interfering RNA drugs in ATTR CA. Natriuretic peptides (NPs) and troponins are consistently elevated in patients with AL and ATTR CA. Plasma NPs, troponins and free light chains hold prognostic significance in AL amyloidosis, and are evaluated for therapy decision-making and follow-up, while the value of NPs and troponins in ATTR is less well established. Biomarkers can be usefully integrated with clinical and imaging variables at all levels of the clinical algorithm of systemic amyloidosis, from screening to diagnosis and prognosis, and treatment tailoring.

Screening for ATTR amyloidosis in the clinic: overlapping disorders, misdiagnosis, and multiorgan awareness

Amyloid transthyretin (ATTR) amyloidosis is a clinically heterogeneous and fatal disease that results from deposition of insoluble amyloid fibrils in various organs and tissues, causing progressive loss of function. The objective of this review is to increase awareness and diagnosis of ATTR amyloidosis by improving recognition of its overlapping conditions, misdiagnosis, and multiorgan presentation. Cardiac manifestations include heart failure, atrial fibrillation, intolerance to previously prescribed antihypertensives, sinus node dysfunction, and atrioventricular block, resulting in the need for permanent pacing. Neurologic manifestations include progressive sensorimotor neuropathy (e.g., pain, weakness) and autonomic dysfunction (e.g., erectile dysfunction, chronic diarrhea, orthostatic hypotension). Non-cardiac red flags often precede the diagnosis of ATTR amyloidosis and include musculoskeletal manifestations (e.g., carpal tunnel syndrome, lumbar spinal stenosis, spontaneous rupture of the distal tendon biceps, shoulder and knee surgery). Awareness and recognition of the constellation of symptoms, including cardiac, neurologic, and musculoskeletal manifestations, will help with early diagnosis of ATTR amyloidosis and faster access to therapies, thereby slowing the progression of this debilitating disease.

Monitoring the formation of insulin oligomers using a NIR emitting glucose-conjugated BODIPY dye

Protein oligomers, which are formed due to the aggregation of protein molecules under physiological stress, are neurotoxic and responsible for several neurological diseases. Early detection of protein oligomers is essential for the timely intervention in the associated diseases. Although several probes have been developed for the detection of insoluble matured protein fibrils, fluorescent probes with emission in the near infrared (NIR) region for probing protein oligomers are very rare. In the present study we have designed and synthesized a glucose-conjugated BODIPY dye with emission in the NIR spectral range. Our detailed studies show that the new probe is not only capable of detecting matured fibrils but can also probe the formation of oligomers from the native protein. The new probe shows a large increase in its emission intensity upon association with oligomers and matured fibrils. Hence, the present probe has a great potential for the in vivo imaging of protein oligomers and matured fibrils. Detailed spectroscopic properties of the new probes in molecular solvents have been performed to understand its oligomers- and fibril- sensing mechanism.

Insights Into Peptide Inhibition of Alpha-Synuclein Aggregation

α-Synuclein (aSyn) aggregation is an attractive target for therapeutic development for a range of neurodegenerative conditions, collectively termed synucleinopathies. Here, we probe the mechanism of action of a peptide 4554W, (KDGIVNGVKA), previously identified through intracellular library screening, to prevent aSyn aggregation and associated toxicity. We utilize NMR to probe association and identify that 4554W associates with a "partially aggregated" form of aSyn, with enhanced association occurring over time. We also report the ability of 4554W to undergo modification through deamidation of the central asparagine residue, occurring on the same timescale as aSyn aggregation in vitro, with peptide modification enhancing its association with aSyn. Additionally, we report that 4554W can act to reduce fibril formation of five Parkinson's disease associated aSyn mutants. Inhibitory peptide binding to partially aggregated forms of aSyn, as identified here, is particularly attractive from a therapeutic perspective, as it would eliminate the need to administer the therapy at pre-aggregation stages, which are difficult to diagnose. Taken together the data suggest that 4554W could be a suitable candidate for future therapeutic development against wild-type, and most mutant aSyn aggregation.

Expression of Amyloidogenic Transthyretin Drives Hepatic Proteostasis Remodeling in an Induced Pluripotent Stem Cell Model of Systemic Amyloid Disease

The systemic amyloidoses are diverse disorders in which misfolded proteins are secreted by effector organs and deposited as proteotoxic aggregates at downstream tissues. Although well described clinically, the contribution of synthesizing organs to amyloid disease pathogenesis is unknown. Here, we utilize hereditary transthyretin amyloidosis (ATTR amyloidosis) induced pluripotent stem cells (iPSCs) to define the contribution of hepatocyte-like cells (HLCs) to the proteotoxicity of secreted transthyretin (TTR). To this end, we generated isogenic, patient-specific iPSCs expressing either amyloidogenic or wild-type TTR. We combined this tool with single-cell RNA sequencing to identify hepatic proteostasis factors correlating with destabilized TTR production in iPSC-derived HLCs. By generating an ATF6 inducible patient-specific iPSC line, we demonstrated that enhancing hepatic ER proteostasis preferentially reduces the secretion of amyloidogenic TTR. These data highlight the liver's capacity to chaperone misfolded TTR prior to deposition, and moreover suggest the potential for unfolded protein response modulating therapeutics in the treatment of diverse systemic amyloidoses.

Cardiac Amyloidosis: Evolving Diagnosis and Management: A Scientific Statement From the American Heart Association

Transthyretin amyloid cardiomyopathy (ATTR-CM) results in a restrictive cardiomyopathy caused by extracellular deposition of transthyretin, normally involved in the transportation of the hormone thyroxine and retinol-binding protein, in the myocardium. Enthusiasm about ATTR-CM has grown as a result of 3 simultaneous areas of advancement: Imaging techniques allow accurate noninvasive diagnosis of ATTR-CM without the need for confirmatory endomyocardial biopsies; observational studies indicate that the diagnosis of ATTR-CM may be underrecognized in a significant proportion of patients with heart failure; and on the basis of elucidation of the mechanisms of amyloid formation, therapies are now approved for treatment of ATTR-CM. Because therapy for ATTR-CM may be most effective when administered before significant cardiac dysfunction, early identification of affected individuals with readily available noninvasive tests is essential. This scientific statement is intended to guide clinical practice and to facilitate management conformity by covering current diagnostic and treatment strategies, as well as unmet needs and areas of active investigation in ATTR-CM.

TTRMDB: A database for structural and functional analysis on the impact of SNPs over transthyretin (TTR) using bioinformatic tools

Hereditary Transthyretin-associated amyloidosis (ATTR) is an autosomal dominant protein-folding disorder with adult-onset caused by mutation of transthyretin (TTR). TTR is characterized by extracellular deposition of amyloid, leading to loss of autonomy and finally, death. More than 100 distinct mutations in TTR gene have been reported from variable age of onset, clinical expression and penetrance data. Besides, the cure for the disease remains still obscure. Further, the prioritizing of mutations concerning the characteristic features governing the stability and pathogenicity of TTR mutant proteins remains unanswered, to date and thus, a complex state of study for researchers. Herein, we provide a full report encompassing the effects of every reported mutant model of TTR protein about the stability, functionality and pathogenicity using various computational tools. In addition, the results obtained from our study were used to create TTRMDB (Transthyretin mutant database), which could be easy access to researchers at http://vit.ac.in/ttrmdb.

Inherent Biophysical Properties Modulate the Toxicity of Soluble Amyloidogenic Light Chains

In light chain amyloidosis (AL), fibrillar deposition of monoclonal immunoglobulin light chains (LCs) in vital organs, such as heart, is associated with their severe dysfunction. In addition to the cellular damage caused by fibril deposition, direct toxicity of soluble prefibrillar amyloidogenic proteins has been reported, in particular, for cardiotoxicity. However, the molecular bases of proteotoxicity by soluble LCs have not been clarified. Here, to address this issue, we rationally engineered the amino acid sequence of the highly cardiotoxic LC H6 by introducing three residue mutations, designed to reduce the dynamics of its native state. The resulting mutant (mH6) is less toxic than its parent H6 to human cardiac fibroblasts and C. elegans. The high sequence and structural similarity, together with the different toxicity, make H6 and its non-toxic designed variant mH6 a test case to shed light on the molecular properties underlying soluble toxicity. Our comparative structural and biochemical study of H6 and mH6 shows closely matching crystal structures, whereas spectroscopic data and limited proteolysis indicate that H6 displays poorly cooperative fold, higher flexibility, and kinetic instability, and a higher dynamic state in its native fold. Taken together, the results of this study show a strong correlation between the overall conformational properties of the native fold and the proteotoxicity of cardiotropic LCs.

Diagnostic and Treatment Approaches Involving Transthyretin in Amyloidogenic Diseases

Transthyretin (TTR) is a thyroid hormone-binding protein which transports thyroxinefrom the bloodstream to the brain. The structural stability of TTR in tetrameric form is crucial for maintaining its original functions in blood or cerebrospinal fluid (CSF). The altered structure of TTR due to genetic mutations or its deposits due to aggregation could cause several deadly diseases such as cardiomyopathy and neuropathy in autonomic, motor, and sensory systems. The early diagnoses for hereditary amyloid TTR with cardiomyopathy (ATTR-CM) and wild-type amyloid TTR (ATTRwt) amyloidosis, which result from amyloid TTR (ATTR) deposition, are difficult to distinguish due to the close similarities of symptoms. Thus, many researchers investigated the role of ATTR as a biomarker, especially its potential for differential diagnosis due to its varying pathogenic involvement in hereditary ATTR-CM and ATTRwt amyloidosis. As a result, the detection of ATTR became valuable in the diagnosis and determination of the best course of treatment for ATTR amyloidoses. Assessing the extent of ATTR deposition and genetic analysis could help in determining disease progression, and thus survival rate could be improved following the determination of the appropriate course of treatment for the patient. Here, the perspectives of ATTR in various diseases were presented.

Treatment of hereditary and acquired forms of transthyretin amyloidosis in the era of personalized medicine: the role of randomized controlled trials

There have now been randomized controlled trials of four different therapeutics for hereditary amyloid polyneuropathy related to transthyretin (TTR) deposition and one for amyloidotic cardiomyopathy of both genetic and sporadic origin. It is likely that in the next few months those not already approved by either the US Food and Drug Administration (FDA) and/or the European Medicines Authority (EMA) will receive similar approvals for treatment for all or particular groups of patients. This is a far cry from circumstances less than 10 years ago when the only available therapy was gene replacement by liver transplant. The randomized controlled trials have shown that all the treatments (tafamidis, diflunisal, patisiran, and inotersen) are effective in the context of a clinical trial. However, we have very little idea of whether individual patients will respond in an equally positive way to all the drugs or whether there will be some who respond better to one or another or not respond at all, nor do we know whether combinations will be additive or synergistic. We lack validated markers of clinical response. While the small molecule TTR stabilizers increase serum TTR levels, the RNA-based drugs lower serum TTR. In the latter case, it is not clear that the reduction in serum TTR is related to the clinical response in a 1:1 fashion. Pharmaceutical companies have made substantial investments in the development of these agents and will clearly attempt to recoup those investments quickly. It is incumbent upon those of us who care for these patients to develop ways to assess the effects of therapy in the shortest possible time at the lowest possible cost. The better we are able to accomplish this the more likely it is that we will be able to treat the most patients in the most clinically efficient fashion regardless of their economic status. We now have the drugs we just have to figure out who should get them and when.

Brazilian consensus for diagnosis, management and treatment of transthyretin familial amyloid polyneuropathy

Transthyretin familial amyloid polyneuropathy is an autosomal dominant inherited sensorimotor and autonomic polyneuropathy, which if untreated, leads to death in approximately 10 years. In Brazil, liver transplant and tafamidis are the only disease-modifying treatments available. This review consists of a consensus for the diagnosis, management and treatment for transthyretin familial amyloid polyneuropathy from the Peripheral Neuropathy Scientific Department of the Brazilian Academy of Neurology. The first and last authors produced a draft summarizing the main views on the subject and emailed the text to 10 other specialists. Relevant literature on this subject was reviewed by each participant and used for the individual review of the whole text. Each participant was expected to review the text and send a feedback review by e-mail. Thereafter, the 12 panelists got together at the city of Fortaleza, discussed the controversial points, and reached a consensus for the final text.

Cellular clearance of circulating transthyretin decreases cell-nonautonomous proteotoxicity in Caenorhabditis elegans

Cell-autonomous and cell-nonautonomous mechanisms of neurodegeneration appear to occur in the proteinopathies, including Alzheimer's and Parkinson's diseases. However, how neuronal toxicity is generated from misfolding-prone proteins secreted by nonneuronal tissues and whether modulating protein aggregate levels at distal locales affects the degeneration of postmitotic neurons remains unknown. We generated and characterized animal models of the transthyretin (TTR) amyloidoses that faithfully recapitulate cell-nonautonomous neuronal proteotoxicity by expressing human TTR in the Caenorhabditis elegans muscle. We identified sensory neurons with affected morphological and behavioral nociception-sensing impairments. Nonnative TTR oligomer load and neurotoxicity increased following inhibition of TTR degradation in distal macrophage-like nonaffected cells. Moreover, reducing TTR levels by RNAi or by kinetically stabilizing natively folded TTR pharmacologically decreased TTR aggregate load and attenuated neuronal dysfunction. These findings reveal a critical role for in trans modulation of aggregation-prone degradation that directly affects postmitotic tissue degeneration observed in the proteinopathies.

Crystal structures of amyloidogenic segments of human transthyretin

Amyloid diseases are characterized by the deposition of proteins in the form of amyloid fibrils, in organs that eventually fail. The development of effective drug candidates follows from the understanding of the molecular processes that lead to protein aggregation. Here, we study amyloidogenic segments of transthyretin (TTR). TTR is a transporter of thyroxine and retinol in the blood and cerebrospinal fluid. When mutated and/or as a result of aging, TTR aggregates into amyloid fibrils that accumulate in organs such as the heart. Recently, we reported two amyloidogenic segments that drive amyloid aggregation. Here, we report the crystal structure of another six amyloidogenic segments of TTR. We found that the segments from the C-terminal region of TTR form in-register steric-zippers with highly-interdigitated, wet interfaces, whereas the β-strand B from the N-terminal region of TTR forms an out-of-register assembly, previously associated with oligomeric formation. Our results contribute fundamental information for understanding the mechanism of aggregation of TTR.

Peptide-based nanoprobes for molecular imaging and disease diagnostics

Pathological changes in a diseased site are often accompanied by abnormal activities of various biomolecules in and around the involved cells. Identifying the location and expression levels of these biomolecules could enable early-stage diagnosis of the related disease, the design of an appropriate treatment strategy, and the accurate assessment of the treatment outcomes. Over the past two decades, a great diversity of peptide-based nanoprobes (PBNs) have been developed, aiming to improve the in vitro and in vivo performances of water-soluble molecular probes through engineering of their primary chemical structures as well as the physicochemical properties of their resultant assemblies. In this review, we introduce strategies and approaches adopted for the identification of functional peptides in the context of molecular imaging and disease diagnostics, and then focus our discussion on the design and construction of PBNs capable of navigating through physiological barriers for targeted delivery and improved specificity and sensitivity in recognizing target biomolecules. We highlight the biological and structural roles that low-molecular-weight peptides play in PBN design and provide our perspectives on the future development of PBNs for clinical translation.

Cerebrospinal fluid and vitreous body exposure to orally administered tafamidis in hereditary ATTRV30M (p.TTRV50M) amyloidosis patients

Hereditary transthyretin (TTR) amyloidosis associated with the TTRV30M (p.TTRV50M) mutation presents predominantly as an axonal polyneuropathy, with variable involvement of other organs. Serious central nervous system (CNS) and eye manifestations, including stroke, dementia, vitreous opacities and glaucoma, have been reported in untreated V30M TTR amyloidosis patients, and in these patients after treatment with liver transplantation (LT). Distinct therapies for V30M TTR amyloidosis developed during the last decade exhibit promising results in slowing the peripheral and autonomic nervous system pathology. However, the effect of these therapies on the CNS and eye manifestations of V30M TTR amyloidosis is not known. Herein, we show that in a small cohort of patients taking tafamidis orally (20 mg tafamidis meglumine daily) we could detect this small molecule in the cerebrospinal fluid (CSF) and the vitreous body. In the CSF, the ratio of TTR tetramer to tafamidis was ≈2:1, leading to a moderate kinetic stabilization of TTR in the CSF of these patients. Our data suggest that tafamidis can cross the CSF-blood and eye-blood barriers. Future studies comparing CNS and eye manifestations in patients treated with LT, kinetic stabilizers or TTR lowering drugs are essential to understand the clinical effect of our observations.

Amyloid assembly and disassembly

Amyloid fibrils are protein homopolymers that adopt diverse cross-β conformations. Some amyloid fibrils are associated with the pathogenesis of devastating neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Conversely, functional amyloids play beneficial roles in melanosome biogenesis, long-term memory formation and release of peptide hormones. Here, we showcase advances in our understanding of amyloid assembly and structure, and how distinct amyloid strains formed by the same protein can cause distinct neurodegenerative diseases. We discuss how mutant steric zippers promote deleterious amyloidogenesis and aberrant liquid-to-gel phase transitions. We also highlight effective strategies to combat amyloidogenesis and related toxicity, including: (1) small-molecule drugs (e.g. tafamidis) to inhibit amyloid formation or (2) stimulate amyloid degradation by the proteasome and autophagy, and (3) protein disaggregases that disassemble toxic amyloid and soluble oligomers. We anticipate that these advances will inspire therapeutics for several fatal neurodegenerative diseases.

Summary: This Review showcases important advances in our understanding of amyloid structure, assembly and disassembly, which are inspiring novel therapeutic strategies for amyloid disorders.

Amyloid fibril polymorphism: a challenge for molecular imaging and therapy

The accumulation of misfolded proteins (MPs), both unique and common, for different diseases is central for many chronic degenerative diseases. In certain patients, MP accumulation is systemic (e.g. TTR amyloid), and in others, this is localized to a specific cell type (e.g. Alzheimer's disease). In neurodegenerative diseases, NDs, it is noticeable that the accumulation of MP progressively spreads throughout the nervous system. Our main hypothesis of this article is that MPs are not only markers but also active carriers of pathogenicity. Here, we discuss studies from comprehensive molecular approaches aimed at understanding MP conformational variations (polymorphism) and their bearing on spreading of MPs, MP toxicity, as well as MP targeting in imaging and therapy. Neurodegenerative disease (ND) represents a major and growing societal challenge, with millions of people worldwide suffering from Alzheimer's or Parkinson's diseases alone. For all NDs, current treatment is palliative without addressing the primary cause and is not curative. Over recent years, particularly the shape-shifting properties of misfolded proteins and their spreading pathways have been intensively researched. The difficulty in addressing ND has prompted most major pharma companies to severely downsize their nervous system disorder research. Increased academic research is pivotal for filling this void and to translate basic research into tools for medical professionals. Recent discoveries of targeting drug design against MPs and improved model systems to study structure, pathology spreading and toxicity strongly encourage future studies along these lines to provide an opportunity for selective imaging, prognostic diagnosis and therapy.