Transthyretin: the servant of many masters

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.

Usefulness of serum transthyretin for prediction of the 1-year outcome in idiopathic pulmonary fibrosis: An evaluation of sarcopenic and nutritional indicators

BACKGROUND

Patients with idiopathic pulmonary fibrosis (IPF) often experience sarcopenia and malnutrition. However, this has not been fully examined through longitudinal surveys. This study investigated whether sarcopenia and malnutrition were associated with 1-year outcomes in IPF.

METHODS

We evaluated sarcopenia and nutritional status in 64 outpatients with IPF. We assessed the time-to-event for respiratory-related hospitalizations or deaths 12 months after enrollment. Sarcopenia was diagnosed by the criteria of the Asian Working Group for Sarcopenia, 2019. Nutritional status was assessed by serum transthyretin and the Geriatric Nutritional Risk Index (GNRI).

RESULTS

The average age was 73.6 ± 7.9 years, and the percent predicted forced vital capacity (FVC) was 81.9 ± 15.7%. Of the 64 patients, 24 (37.5%) had sarcopenia. The median serum transthyretin level and mean GNRI were 23.8 mg/dL and 102, respectively. Eleven patients (17.2%) experienced respiratory-related hospitalization or death within the first year. Cox regression analysis showed that the % predicted diffusion capacity for carbon monoxide, lowest oxygen saturation in the 6-min walk test, serum transthyretin level, and GNRI were significant predictors of 1-year outcomes. The Kaplan-Meier method, which divided the patients into two groups based on a transthyretin level of 22.6 mg/dL, showed a significant difference (P < 0.001, log-rank test). Sarcopenia and the percent predicted FVC did not predict the 1-year outcomes.

CONCLUSIONS

This pilot study represents the first longitudinal survey assessing patients with IPF for sarcopenia and malnutrition. Serum transthyretin levels may predict respiratory-related hospitalization or death within 1 year in patients with IPF.

Cryo-EM confirms a common fibril fold in the heart of four patients with ATTRwt amyloidosis

ATTR amyloidosis results from the conversion of transthyretin into amyloid fibrils that deposit in tissues causing organ failure and death. This conversion is facilitated by mutations in ATTRv amyloidosis, or aging in ATTRwt amyloidosis. ATTRv amyloidosis exhibits extreme phenotypic variability, whereas ATTRwt amyloidosis presentation is consistent and predictable. Previously, we found unique structural variabilities in cardiac amyloid fibrils from polyneuropathic ATTRv-I84S patients. In contrast, cardiac fibrils from five genotypically different patients with cardiomyopathy or mixed phenotypes are structurally homogeneous. To understand fibril structure's impact on phenotype, it is necessary to study the fibrils from multiple patients sharing genotype and phenotype. Here we show the cryo-electron microscopy structures of fibrils extracted from four cardiomyopathic ATTRwt amyloidosis patients. Our study confirms that they share identical conformations with minimal structural variability, consistent with their homogenous clinical presentation. Our study contributes to the understanding of ATTR amyloidosis biopathology and calls for further studies.

Targeting TNF-α-induced expression of TTR and RAGE in rheumatoid arthritis: Apigenin's mediated therapeutic approach

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory disease induced by TNF-α, which increases fibroblast-like synoviocytes inflammation, resulting in cartilage destruction. The current work sought to comprehend the pathophysiological importance of TNF-α stimulation on differential protein expression and their regulation by apigenin using in-vitro and in-vivo models of RA.

METHODS

The human RA synovial fibroblast cells were stimulated with or without TNF-α (10 ng/ml) and treated with 40 μM apigenin. In-silico, in-vitro and in-vivo studies were performed to confirm the pathophysiological significance of apigenin on pro-inflammatory cytokines and on differential expression of TTR and RAGE proteins.

RESULTS

TNF-α induced inflammatory response in synoviocytes revealed higher levels of IL-6, IL-1β, and TNF-α cytokines and upregulated differential expression of TTR and RAGE. In-silico results demonstrated that apigenin has a binding affinity towards TNF-α, indicating its potential effect in the inflammatory process. Both in-vitro and in-vivo results obtained by Western Blot analysis suggested that apigenin reduced the level of p65 (p = 0.005), TTR (p = 0.002), and RAGE (p = 0.020).

CONCLUSION

The findings of this study suggested that TNF-α promotes the differential expression of pro-inflammatory cytokines, TTR, and RAGE via NF-kB pathways activation. Anti-inflammatory effect of apigenin impedes TNF-α mediated dysregulation or expression associated with RA pathogenesis.

Identification of isoaspartate-modified transthyretin as potential target for selective immunotherapy of transthyretin amyloidosis

BACKGROUND

Numerous studies suggest a progressive accumulation of post-translationally modified peptides within amyloid fibrils, including isoaspartate (isoD) modifications. Here, we generated and characterised novel monoclonal antibodies targeting isoD-modified transthyretin (TTR). The antibodies were used to investigate the presence of isoD-modified TTR in deposits from transthyretin amyloidosis patients and to mediate antibody-dependent phagocytosis of TTR fibrils.

METHODS

Monoclonal antibodies were generated by immunisation of mice using an isoD-modified peptide and subsequent hybridoma generation. The antibodies were characterised in terms of affinity and specificity to isoD-modified TTR using surface plasmon resonance, transmission electron microscopy and immunohistochemical staining of human cardiac tissue. The potential to elicit antibody-dependent phagocytosis of TTR fibrils was assessed using THP-1 cells.

RESULTS

We developed two mouse monoclonal antibodies, 2F2 and 4D4, with high nanomolar affinity for isoD-modified TTR and strong selectivity over the unmodified epitope. Both antibodies show presence of isoD-modified TTR in human cardiac tissue, but not in freshly purified recombinant TTR, suggesting isoD modification only present in aged fibrillar deposits. Likewise, the antibodies only facilitated phagocytosis of TTR fibrils and not TTR monomers by THP-1 cells.

CONCLUSIONS

These antibodies label aged, non-native TTR deposits, leaving native TTR unattended and thereby potentially enabling new therapeutic approaches.

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.

Cytosolic sulfotransferases in endocrine disruption

The mammalian cytosolic sulfotransferases (SULTs) catalyze the sulfation of endocrine hormones as well as a broad array of drugs, environmental chemicals, and other xenobiotics. Many endocrine-disrupting chemicals (EDCs) interact with these SULTs as substrates and inhibitors, and thereby alter sulfation reactions responsible for metabolism and regulation of endocrine hormones such as estrogens and thyroid hormones. EDCs or their metabolites may also regulate expression of SULTs through direct interaction with nuclear receptors and other transcription factors. Moreover, some sulfate esters derived from EDCs (EDC-sulfates) may serve as ligands for endocrine hormone receptors. While the sulfation of an EDC can lead to its excretion in the urine or bile, it may also result in retention of the EDC-sulfate through its reversible binding to serum proteins and thereby enable transport to other tissues for intracellular hydrolysis and subsequent endocrine disruption. This mini-review outlines the potential roles of SULTs and sulfation in the effects of EDCs and our evolving understanding of these processes.

Design and Preclinical Evaluation of a Novel Prostate-Specific Membrane Antigen Radioligand Modified with a Transthyretin Binder

Transthyretin binders have previously been used to improve the pharmacokinetic properties of small-molecule drug conjugates and could, thus, be utilized for radiopharmaceuticals as an alternative to the widely explored "albumin binder concept". In this study, a novel PSMA ligand modified with a transthyretin-binding entity (TB-01) was synthesized and labeled with lutetium-177 to obtain [177Lu]Lu-PSMA-TB-01. A high and specific uptake of [177Lu]Lu-PSMA-TB-01 was found in PSMA-positive PC-3 PIP cells (69 ± 3% after 4 h incubation), while uptake in PSMA-negative PC-3 flu cells was negligible (<1%). In vitro binding studies showed a 174-fold stronger affinity of [177Lu]Lu-PSMA-TB-01 to transthyretin than to human serum albumin. Biodistribution studies in PC-3 PIP/flu tumor-bearing mice confirmed the enhanced blood retention of [177Lu]Lu-PSMA-TB-01 (16 ± 1% IA/g at 1 h p.i.), which translated to a high tumor uptake (69 ± 13% IA/g at 4 h p.i.) with only slow wash-out over time (31 ± 8% IA/g at 96 h p.i.), while accumulation in the PC-3 flu tumor and non-targeted normal tissue was reasonably low. Further optimization of the radioligand design would be necessary to fine-tune the biodistribution and enable its use for therapeutic purposes. This study was the first of this kind and could motivate the use of the "transthyretin binder concept" for the development of future radiopharmaceuticals.

Cryo-EM confirms a common fibril fold in the heart of four patients with ATTRwt amyloidosis

ATTR amyloidosis results from the conversion of transthyretin into amyloid fibrils that deposit in tissues causing organ failure and death. This conversion is facilitated by mutations in ATTRv amyloidosis, or aging in ATTRwt amyloidosis. ATTRv amyloidosis exhibits extreme phenotypic variability, whereas ATTRwt amyloidosis presentation is consistent and predictable. Previously, we found an unprecedented structural variability in cardiac amyloid fibrils from polyneuropathic ATTRv-I84S patients. In contrast, cardiac fibrils from five genotypically-different patients with cardiomyopathy or mixed phenotypes are structurally homogeneous. To understand fibril structure's impact on phenotype, it is necessary to study the fibrils from multiple patients sharing genotype and phenotype. Here we show the cryo-electron microscopy structures of fibrils extracted from four cardiomyopathic ATTRwt amyloidosis patients. Our study confirms that they share identical conformations with minimal structural variability, consistent with their homogenous clinical presentation. Our study contributes to the understanding of ATTR amyloidosis biopathology and calls for further studies.

Preclinical comparison of [177Lu]Lu-rhPSMA-10.1 and [177Lu]Lu-rhPSMA-10.2 for endoradiotherapy of prostate cancer: biodistribution and dosimetry studies

BACKGROUND

Radiohybrid PSMA-targeted ligands (rhPSMA) have been introduced as a novel platform for theranostic applications. Among a variety of rhPSMA-ligands developed for radioligand therapy, two stereoisomers [177Lu]Lu-rhPSMA-10.1 and -10.2 have been synthesized and initially characterized in preclinical experiments with the aim to provide an optimized binding profile to human serum albumin, a reduction of charge, and thus accelerated kidney excretion, and unaffected or even improved tumor uptake. As both isomers showed similar in vitro characteristics and tumor uptake at 24 h post injection in tumor bearing mice and in order to identify the isomer with the most favorable pharmacokinetics for radioligand therapy, we carried out in-depth biodistribution and dosimetry studies in tumor-bearing and healthy mice.

RESULTS

rhPSMA-10.1 and -10.2 were radiolabeled with lutetium-177 according to the established procedures of other DOTA-based PSMA ligands and displayed a high and comparable stability in all buffers and human serum (> 97%, 24 h). Biodistribution studies revealed fast clearance from the blood pool (0.3-0.6%ID/g at 1 h) and other background tissues within 48 h. Distinctive differences were found in the kidneys, where [177Lu]Lu-rhPSMA-10.1 displayed lower initial uptake and faster excretion kinetics compared to [177Lu]Lu-rhPSMA-10.2 expressed by a 1.5-fold and ninefold lower uptake value at 1 h and 24 h in healthy animals, respectively. Tumor uptake was comparable and in the range of 8.6-11.6%ID/g for both isomers over 24 h and was maintained up to 168 h at a level of 2.2 ± 0.8 and 4.1 ± 1.4%ID/g for [177Lu]Lu-rhPSMA-10.1 and [177Lu]Lu-rhPSMA-10.2, respectively.

CONCLUSION

Our preclinical data on biodistribution and dosimetry indicate a more favorable profile of [177Lu]Lu-rhPSMA-10.1 compared to [177Lu]Lu-rhPSMA-10.2 for PSMA-targeted radioligand therapy. [177Lu]Lu-rhPSMA-10.1 shows fast kidney clearance kinetics resulting in excellent tumor-to-organ ratios over a therapy relevant time course. Meanwhile, [177Lu]Lu-rhPSMA-10.1 is currently being investigated in clinical phase I/II studies in patients with mCRPC (NCT05413850), in patients with high-risk localized PC (NCT06066437, Nautilus Trial) and after external beam radiotherapy (NCT06105918).

Complex roles for sulfation in the toxicities of polychlorinated biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic toxicants derived from legacy pollution sources and their formation as inadvertent byproducts of some current manufacturing processes. Metabolism of PCBs is often a critical component in their toxicity, and relevant metabolic pathways usually include their initial oxidation to form hydroxylated polychlorinated biphenyls (OH-PCBs). Subsequent sulfation of OH-PCBs was originally thought to be primarily a means of detoxication; however, there is strong evidence that it may also contribute to toxicities associated with PCBs and OH-PCBs. These contributions include either the direct interaction of PCB sulfates with receptors or their serving as a localized precursor for OH-PCBs. The formation of PCB sulfates is catalyzed by cytosolic sulfotransferases, and, when transported into the serum, these metabolites may be retained, taken up by other tissues, and subjected to hydrolysis catalyzed by intracellular sulfatase(s) to regenerate OH-PCBs. Dynamic cycling between PCB sulfates and OH-PCBs may lead to further metabolic activation of the resulting OH-PCBs. Ultimate toxic endpoints of such processes may include endocrine disruption, neurotoxicities, and many others that are associated with exposures to PCBs and OH-PCBs. This review highlights the current understanding of the complex roles that PCB sulfates can have in the toxicities of PCBs and OH-PCBs and research on the varied mechanisms that control these roles.

The conformational landscape of human transthyretin revealed by cryo-EM

Transthyretin (TTR) is a natively tetrameric thyroxine transporter found in blood and cerebrospinal fluid whose misfolding and aggregation causes transthyretin amyloidosis. A rational drug design campaign identified the small molecule tafamidis (Vyndaqel/Vyndamax) as an effective stabilizer of the native TTR fold, and this aggregation inhibitor is regulatory agency-approved for the treatment of TTR amyloidosis. Despite 50 years of structural studies on TTR and this triumph of structure-based drug design, there remains a notable dearth of structural information available to understand ligand binding allostery and amyloidogenic TTR unfolding intermediates. We used single-particle cryo-electron microscopy (cryo-EM) to investigate the conformational landscape of this 55 kiloDalton tetramer in the absence and presence of one or two ligands, revealing inherent asymmetries in the tetrameric architecture and previously unobserved conformational states. These findings provide critical mechanistic insights into negatively cooperative ligand binding and the structural pathways responsible for TTR amyloidogenesis. This study underscores the capacity of cryo-EM to provide new insights into protein structures that have been historically considered too small to visualize and to identify pharmacological targets suppressed by the confines of the crystal lattice, opening uncharted territory in structure-based drug design.

The level of serum retinol-binding protein is associated with diabetic mild cognitive impairment

BACKGROUND

Several studies have shown that retinol-binding protein (RBP) is linked to diabetes and neurodegenerative diseases. However, no studies have elucidated the relationship between RBP and diabetic cognitive disorders.

OBJECTIVE

To determine whether the change characteristics of serum RBP are associated with alterations in cognitive functioning in type 2 diabetes mellitus (T2DM).

METHODS

In this study, 252 patients with T2DM and 34 people as healthy controls were included. According to the Montreal Cognitive Assessment (MoCA), the diabetic subjects were divided into the mild cognitive impairment (MCI) group and the Non-MCI group. Demographic characteristics and clinical indicators as well as serum RBP levels were analyzed.

RESULTS

The serum RBP levels in the MCI group were lower compared with the Non-MCI group (P = 0.02). The level of RBP was higher in the diabetes without MCI group than in the healthy control (P < 0.001). Serum RBP levels were positively correlated with MoCA scores (r = 0.178, P = 0.003). Binary Logistic regression model analysis showed that low RBP [odds ratio (OR) = 0.936], old age (OR = 1.074), high fasting blood glucose (OR = 1.164), and low fasting C-peptide (OR = 0.722) may be independent risk factors for diabetic MCI. The ROC curve of serum RBP for predicting diabetic MCI showed that the area under the curve was 0.630.

CONCLUSIONS

Our study revealed an association between serum RBP and diabetic MCI. Serum RBP levels in diabetic MCI are lower and correlated with cognitive function.

Ophthalmological involvement in wild-type transthyretin amyloidosis: A multimodal imaging study

BACKGROUND AND AIMS

Ophthalmological abnormalities have been reported in hereditary transthyretin-related amyloidosis (ATTRv, v for variant) but not in wild-type transthyretin-related amyloidosis (ATTRwt).

METHODS

Patients with ATTRwt, ATTRv, and light chain amyloidosis (AL) and healthy subjects (controls) underwent complete eye examination, including optical coherence tomography (OCT), OCT angiography (OCTA), and in vivo corneal confocal microscopy (CCM).

RESULTS

Seventeen ATTRwt, nine ATTRv, two ATTRv carriers, and seven AL patients were enrolled. Compared with other groups, ATTRwt patients had 10 letters lower visual acuity and a higher prevalence of glaucoma, cataract, and retinal pigment epithelium alterations. In the whole group of patients, especially in ATTRwt, we observed (1) a reduced corneal nerve fiber length and more tortuous stromal nerves at CCM, (2) a reduced macular volume and peripapillary nerve fiber layer thickness at OCT, and (3) impairment of peripapillary and macular vascularization at OCTA.

INTERPRETATION

Ophthalmological abnormalities are common in ATTRwt, significantly impairing visual acuity. Noninvasive imaging modalities allow for the identification of small nerve fibers and small vessel damage, which may represent further warning signs for early diagnosis of ATTRwt.

Current Evidence Supporting the Role of Immune Response in ATTRv Amyloidosis

Hereditary transthyretin (ATTRv) amyloidosis with polyneuropathy, also known as familial amyloid polyneuropathy (FAP), represents a progressive, heterogeneous, severe, and multisystemic disease caused by pathogenic variants in the TTR gene. This autosomal-dominant neurogenetic disorder has an adult onset with variable penetrance and an inconstant phenotype, even among subjects carrying the same mutation. Historically, ATTRv amyloidosis has been viewed as a non-inflammatory disease, mainly due to the absence of any mononuclear cell infiltration in ex vivo tissues; nevertheless, a role of inflammation in its pathogenesis has been recently highlighted. The immune response may be involved in the development and progression of the disease. Fibrillary TTR species bind to the receptor for advanced glycation end products (RAGE), probably activating the nuclear factor κB (NF-κB) pathway. Moreover, peripheral blood levels of several cytokines, including interferon (IFN)-gamma, IFN-alpha, IL-6, IL-7, and IL-33, are altered in the course of the disease. This review summarizes the current evidence supporting the role of the immune response in ATTRv amyloidosis, from the pathological mechanisms to the possible therapeutic implications.

Defining diurnal fluctuations in mouse choroid plexus and CSF at high molecular, spatial, and temporal resolution

Transmission and secretion of signals via the choroid plexus (ChP) brain barrier can modulate brain states via regulation of cerebrospinal fluid (CSF) composition. Here, we developed a platform to analyze diurnal variations in male mouse ChP and CSF. Ribosome profiling of ChP epithelial cells revealed diurnal translatome differences in metabolic machinery, secreted proteins, and barrier components. Using ChP and CSF metabolomics and blood-CSF barrier analyses, we observed diurnal changes in metabolites and cellular junctions. We then focused on transthyretin (TTR), a diurnally regulated thyroid hormone chaperone secreted by the ChP. Diurnal variation in ChP TTR depended on Bmal1 clock gene expression. We achieved real-time tracking of CSF-TTR in awake TtrmNeonGreen mice via multi-day intracerebroventricular fiber photometry. Diurnal changes in ChP and CSF TTR levels correlated with CSF thyroid hormone levels. These datasets highlight an integrated platform for investigating diurnal control of brain states by the ChP and CSF.

Updated Evaluation of the Safety, Efficacy and Tolerability of Tafamidis in the Treatment of Hereditary Transthyretin Amyloid Polyneuropathy

Hereditary amyloid transthyretin (ATTRv) amyloidosis is a devastating hereditary multisystemic disease affecting predominantly the peripheral and autonomic nervous systems and the heart. ATTRv is caused by mutations in the transthyretin (TTR) gene, leading to extracellular deposition of amyloid fibrils in multiple organs including the peripheral nervous system. If untreated, it is associated with a fatal outcome 10-12 years after disease onset. Different treatments are available for patients with ATTRv polyneuropathy. Tafamidis 20 mg is approved in Europe since 2011 for early stages of ATTRv polyneuropathy (stage I - able to walk without support) and it is recommended as first-line therapy in these patients. Tafamidis is a TTR stabilizer that selectively binds to TTR and kinetically stabilizes both wild-type native TTR and mutant TTR. Consequently, it has the potential to prevent the amyloidogenic cascade initiated by TTR tetramer dissociation into its monomers and subsequent misfolding and aggregation. Tafamidis is an oral drug, taken once per day, with proved efficacy, safety and tolerability in ATTRv-PN patients as demonstrated in different clinical trials and open-label extension studies as well in clinical practice setting with around 10 years of experience. Tafamidis treatment started in the earliest stages of the disease is associated with better neurological outcomes. A multidisciplinary approach in referral centres is also fundamental for monitoring patients to assess individual response to treatment.

Transthyretin binds soluble endoglin and increases its uptake by hepatocytes: A possible role for transthyretin in preeclampsia?

BACKGROUND

Preeclampsia is a common but life-threatening condition of pregnancy. It is caused by poor placentation resulting in release of trophoblast material (including soluble endoglin (sEng)) into the maternal circulation leading to maternal vascular dysfunction and to the life-threatening condition of eclampsia. The only cure is early delivery, which can have lifelong consequences for the premature child. The thyroid hormone binding protein transthyretin is dysregulated in preeclampsia, however it is not known if this plays a role in disease pathology. We hypothesised that transthyretin may bind sEng and abrogate its negative effects by removing it from the maternal serum.

METHODS

The effect of transthyretin on hepatocyte uptake of Alexa-labelled sEng was measured using live cell imaging. Interactions between transthyretin, and sEng were investigated using molecular modelling, direct binding on CnBr Sepharose columns, confocal imaging, and measurement of fluorescence resonance energy transfer.

RESULTS

Transthyretin directly bound to sEng and increased its uptake by hepatocytes. This uptake was altered in the presence of transforming growth factor-β1 (TGF-β1). Molecular modelling predicted that transthyretin and TGF-β1 bind at the same site in sEng and may compete for binding. Endocytosed transthyretin and endoglin entered cells together and co-localised inside hepatocyte cells.

CONCLUSION

Transthyretin can bind sEng and increase its uptake from the extracellular medium. This suggests that increasing transthyretin levels or developing drugs that normalise or mimic transthyretin, may provide treatment options to reduce sEng induced vascular dysfunction.

Transthyretin Is Commonly Upregulated in the Hippocampus of Two Stress-Induced Depression Mouse Models

Chronic stress can affect gene expression in the hippocampus, which alters neural and cerebrovascular functions, thereby contributing to the development of mental disorders such as depression. Although several differentially expressed genes in the depressed brain have been reported, gene expression changes in the stressed brain remain underexplored. Therefore, this study examines hippocampal gene expression in two mouse models of depression induced by forced swim stress (FSS) and repeated social defeat stress (R-SDS). Transthyretin (Ttr) was commonly upregulated in the hippocampus of both mouse models, as determined by microarray, RT-qPCR, and Western blot analyses. Evaluation of the effects of overexpressed Ttr in the hippocampus using adeno-associated virus-mediated gene transfer revealed that TTR overexpression induced depression-like behavior and upregulation of Lcn2 and several proinflammatory genes (Icam1 and Vcam1) in the hippocampus. Upregulation of these inflammation-related genes was confirmed in the hippocampus obtained from mice vulnerable to R-SDS. These results suggest that chronic stress upregulates Ttr expression in the hippocampus and that Ttr upregulation may be involved in the induction of depression-like behavior.

Omega-3 PUFAs as a Dietary Supplement in Senile Systemic Amyloidosis

Eicosapentaenoic acid (EPA; 20:5) and docosahexaenoic acid (DHA; 22:6), two omega-3 poly-unsaturated fatty acids (PUFAs), are the main components in oil derived from fish and other marine organisms. EPA and DHA are commercially available as dietary supplements and are considered to be very safe and contribute to guaranteeing human health. Studies report that PUFAs have a role in contrasting neurodegenerative processes related to amyloidogenic proteins, such as β-amyloid for AD, α-synuclein in PD, and transthyretin (TTR) in TTR amyloidosis. In this context, we investigated if EPA and DHA can interact directly with TTR, binding inside the thyroxin-binding pockets (T₄BP) that contribute to the tetramer stabilization. The data obtained showed that EPA and DHA can contribute to stabilizing the TTR tetramer through interactions with T₄BP.

Nutritional indices may have prognostic value in elderly critically ill patients with sepsis

Aim: Nutritional indicators are associated with adverse outcomes in critically ill elderly patients. In this study, we aimed to evaluate the prognostic potential of prealbumin and albumin in the prediction of mortality in elderly patients with sepsis. Material and Method: A total of 108 patients who developed intensive care unit-acquired sepsis were divided into two groups: Survivors (n=72) and Non-survivors (n=36). Results: Patients in the Non-survivors group were often older (68 vs 74) and presented lower prealbumin (15.1 vs 11), and higher Charlson index (4 vs 6), Sequential Organ Failure Assessment (SOFA) score (8.5 vs 10), C-reactive protein (CRP) (68.8 vs 91) and procalcitonin (PCT) (6 vs 8.4) (p< 0.05). The area under the curve of PCT was the highest at 0.74. Prealbumin presented the best sensitivity (75%) and 12 mg/dL cut-off value, while PCT had the best specificity (75%) and a cut-off value of 7 ng/mL. Although prealbumin was negatively correlated to SOFA score in a significant way (r=-0.226, p=0.019), White blood cells, CRP, and PCT were positively correlated to SOFA score (r=0.198, p=0.040; r=0.233, p=0.015; r=0.286, p=0.003, respectively). In addition, a weak negative correlation was observed between prealbumin and CRP and PCT (r=-0.203, p=0.037; r=-0.215, p=0.026, respectively). Multivariate analysis showed that a reduction in serum prealbumin levels compared to steady prealbumin greater than 4 mg/dL increased the risk of death by 85% (aHR: 1.85, 95% CI: 1.05-2.56, p=0.029). Conclusion: Changes in serum prealbumin in the acute phase of sepsis may assist in determining the risk of mortality and in the administration of specific treatment in critically ill elderly patients.

OPHTHALMOLOGIC INVOLVEMENT IN PATIENTS WITH HEREDITARY TRANSTHYRETIN AMYLOIDOSIS

PURPOSE

The aim of this study was to determine the ophthalmologic involvement in patients with hereditary transthyretin amyloidosis and its correlation with the mutations described in the literature.

METHODS

Cross-sectional, noninterventional study. Fifty-two eyes of 26 consecutive patients diagnosed with hereditary transthyretin amyloidosis who visited the Puerta de Hierro-Majadahonda University Hospital from September 2019 to March 2022. All patients underwent complete ophthalmologic examination and multimodal imaging. Cardiologic, neurologic, digestive, and renal examinations were also recorded.

RESULTS

Eighteen eyes of the total (34.61%) showed amyloid-related ocular involvement, vitreous amyloid deposits being the most common ocular manifestation (18/52). Statistically significant differences were found for the presence of vitreous amyloid deposits ( P < 0.01), crystalline amyloid deposits ( P < 0.05), parenchymal amyloid deposits ( P < 0.01), and vascular alterations ( P < 0.01) when comparing affected and unaffected eyes. Moreover, affected eyes showed worse best-corrected visual acuity ( P < 0.01).

CONCLUSION

Ocular manifestations are present in a substantial number of patients with ATTR that could potentially lead to devastating consequences to patients' best-corrected visual acuity and quality of life. Therefore, it is important to emphasize the importance of multidisciplinary management and ophthalmologic assessment, follow-up and surgical treatment when necessary. To the best of our knowledge, this represents the largest series in Spain of amyloidosis' ophthalmologic involvement.

Liver-directed drugs for transthyretin-mediated amyloidosis

Transthyretin-mediated amyloidosis (ATTR) is a rare, under-recognized, progressively debilitating, fatal disease caused by the aggregation and extracellular deposition of amyloid transthyretin (TTR) fibrils in multiple organs and tissues throughout the body. TTR is predominantly synthesized by the liver and normally circulates as a homotetramer, while misfolded monomers aggregate to form amyloid fibrils. One strategy to treat ATTR amyloidosis is to reduce the amount of TTR produced by the liver using drugs that directly target the TTR mRNA or gene. This narrative review focuses on how TTR gene silencing tools act to reduce TTR production, describing strategies for improved targeted delivery of these agents to hepatocytes where TTR is preferentially expressed. Antisense oligonucleotides (ASOs) and small interfering RNAs (siRNAs), termed RNA silencers, cause selective degradation of TTR mRNA, while a TTR gene editing tool reduces TTR expression by introducing nonsense mutations into the TTR gene. Two strategies to facilitate tissue-specific delivery of these nucleic acid-based drugs employ endogenous receptors expressed by hepatocytes. Lipid nanoparticles (LNPs) that recruit apolipoprotein E support low-density lipoprotein receptor-mediated uptake of unconjugated siRNA and are now used for CRISPR gene editing tools. Additionally, conjugating N-acetylgalactosamine (GalNAc) moieties to ASOs or siRNAs facilitates receptor-mediated uptake by the asialoglycoprotein receptor. In summary, ATTR is a progressive disease with various clinical manifestations due to TTR aggregation, deposition, and amyloid formation. Receptor-targeted ligands (eg, GalNAc) and nanoparticle encapsulation (eg, LNPs) are technologies to deliver ASOs, siRNAs, and gene editing tools to hepatocytes, the primary location of TTR synthesis.

Single Nucleus Transcriptome Data from Alzheimer’s Disease Mouse Models Yield New Insight into Pathophysiology

Background: 5XFAD humanized mutant mice and Trem2 knockout (T2KO) mice are two mouse models relevant to the study of Alzheimer’s disease (AD)-related pathology. Objective: To determine hippocampal transcriptomic and polyadenylation site usage alterations caused by genetic mutations engineered in 5XFAD and T2KO mice. Methods: Employing a publicly available single-nucleus RNA sequencing dataset, we used Seurat and Sierra analytic programs to identify differentially expressed genes (DEGs) and differential transcript usage (DTU), respectively, in hippocampal cell types from each of the two mouse models. We analyzed cell type-specific DEGs further using Ingenuity Pathway Analysis (IPA). Results: We identified several DEGs in both neuronal and glial cell subtypes in comparisons of wild type (WT) versus 5XFAD and WT versus T2KO mice, including Ttr, Fth1, Pcsk1n, Malat1, Rpl37, Rtn1, Sepw1, Uba52, Mbp, Arl6ip5, Gm26917, Vwa1, and Pgrmc1. We also observed DTU in common between the two comparisons in neuronal and glial subtypes, specifically in the genes Prnp, Rbm4b, Pnisr, Opcml, Cpne7, Adgrb1, Gabarapl2, Ubb, Ndfip1, Car11, and Stmn4. IPA identified three statistically significant canonical pathways that appeared in multiple cell types and that overlapped between 5XFAD and T2KO comparisons to WT, including ‘FXR/RXR Activation’, ‘LXR/RXR Activation’, and ‘Acute Phase Response Signaling’. Conclusion: DEG, DTU, and IPA findings, derived from two different mouse models of AD, highlight the importance of energy imbalance and inflammatory processes in specific hippocampal cell types, including subtypes of neurons and glial cells, in the development of AD-related pathology. Additional studies are needed to further characterize these findings.

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.

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

Transthyretin amyloidosis (ATTR) is a group of fatal diseases described by the misfolding and amyloid deposition of transthyretin (TTR). Discovering small molecules that bind and stabilize the TTR tetramer, preventing its dissociation and subsequent aggregation, is a therapeutic strategy for these pathologies. Departing from the crystal structure of TTR in complex with tolcapone, a potent binder in clinical trials for ATTR, we combined rational design and molecular dynamics (MD) simulations to generate a series of novel halogenated kinetic stabilizers. Among them, M-23 displays one of the highest affinities for TTR described so far. The TTR/M-23 crystal structure confirmed the formation of unprecedented protein–ligand contacts, as predicted by MD simulations, leading to an enhanced tetramer stability both in vitro and in whole serum. We demonstrate that MD-assisted design of TTR ligands constitutes a new avenue for discovering molecules that, like M-23, hold the potential to become highly potent drugs to treat ATTR.

Deep blue autofluorescence reflects the oxidation state of human transthyretin

Human transthyretin (TTR) is a tetrameric protein transporting thyroid hormones and retinol. TTR is a neuroprotective factor and sensor of oxidative stress which stability is diminished due to mutations and aging, leading to amyloid deposition. Adverse environmental conditions, such as redox and metal ion imbalances, induce destabilization of the TTR structure. We have previously shown that the stability of TTR was disturbed by Ca²⁺ and other factors, including DTT, and led to the formation of an intrinsic fluorophore(s) emitting blue light, termed deep blue autofluorescence (dbAF). Here, we show that the redox state of TTR affects the formation dynamics and properties of dbAF. Free thiols lead to highly unstable subpopulations of TTR and the frequent ocurrence of dbAF. Oxidative conditions counteracted the destabilizing effects of free thiols to some extent. However, strong oxidative conditions led to modifications of TTR, which altered the stability of TTR and resulted in unique dbAF spectra. Riboflavin and/or riboflavin photoproducts bound to TTR and crosslinked TTR subunits. Riboflavin-sensitized photooxidation increased TTR unfolding, while photooxidation, either in the absence or presence of riboflavin, increased proteolysis and resulted in multiple oxidative modifications and dityrosine formation in TTR molecules. Therefore, oxidation can switch the role of TTR from a protective to pathogenic factor.

Transthyretin proteoforms of intraocular origin in human subretinal fluid

Understanding the molecular composition of ocular tissues and fluids could inform new approaches to prevalent causes of blindness. Subretinal fluid accumulating between the photoreceptor outer segments and retinal pigment epithelium (RPE) is potentially a rich source of proteins and lipids normally cycling among outer retinal cells and choroid. Herein, intact post-translationally modified proteins (proteoforms) were extracted from subretinal fluids of five patients with rhegmatogenous retinal detachment (RRD), analyzed by tandem mass spectrometry, and compared to published data on these same proteins as synthesized by other organs. Single-nuclei transcriptomic data from non-diseased human retina/RPE were used to identify whether proteins in subretinal fluid were of potential ocular origin. Two human donor eyes with normal maculas were immunoprobed for transthyretin (TTR) with appropriate controls. The three most abundant proteins detected in subretinal fluid were albumin, TTR, and apolipoprotein A-I. Remarkably, TTR relative to the other proteins was more abundant than its serum counterpart, suggestive of TTR being synthesized predominantly locally. Six post-translationally modified protein forms (proteoforms) of TTR were detected, with the relative amount of glutathionylated TTR being much higher in the subretinal fluid (12-43%) than values reported for serum (<5%) and cerebrospinal fluid (0.4-13%). Moreover, a putative glycosylated TTR dimer of 32,428 Da was detected as the fourth most abundant protein. The high abundance of TTR and putative TTR dimer in subretinal fluid was supported by analysis of available single-nuclei transcriptomic data, which showed strong and specific signal for TTR in RPE. Immunohistochemistry further showed strong diffuse TTR immunoreactivity in choroidal stroma that contrasted with vertically aligned signal in the outer segment zone of the subretinal space and negligible signal in RPE cell bodies. These results suggest that TTR in the retina is synthesized intraocularly, and glutathionylation is crucial for its normal function. Further studies on the composition, function, and quantities of TTR and other proteoforms in subretinal fluid could inform mechanisms, diagnostic methods, and treatment strategies for age-related macular degeneration, familial amyloidosis, and other retinal diseases involving dysregulation of physiologic lipid transfer and oxidative stress.

Single-Cell Transcriptomic Analysis of the Mouse Pancreas: Characteristic Features of Pancreatic Ductal Cells in Chronic Pancreatitis

Chronic pancreatitis (CP) is a fibroinflammatory disorder of the pancreas. Our understanding of CP pathogenesis is partly limited by the incomplete characterization of pancreatic cell types. Here, we performed single-cell RNA sequencing on 3825 cells from the pancreas of one control mouse and mice with caerulein-induced CP. An analysis of the single-cell transcriptomes revealed 16 unique clusters and cell type-specific gene expression patterns in the mouse pancreas. Sub-clustering of the pancreatic mesenchymal cells from the control mouse revealed four clusters of cells with specific gene expression profiles (combinatorial expressions of Smoc2, Cxcl14, Tnfaip6, and Fn1). We observed that immune cells in the pancreas of the CP mice were abundant and diverse in cellular type. Compared to the control, 547 upregulated genes (including Mmp7, Ttr, Rgs5, Adh1, and Cldn2) and 257 downregulated genes were identified in ductal cells from the CP group. The elevated expression levels of MMP7 and TTR were further verified in the pancreatic ducts of CP patients. This study provides a preliminary description of the single-cell transcriptome profiles of mouse pancreata and accurately demonstrates the characteristics of pancreatic ductal cells in CP. The findings provide insight into novel disease-specific biomarkers and potential therapeutic targets of CP.

ATF6 Activation Reduces Amyloidogenic Transthyretin Secretion through Increased Interactions with Endoplasmic Reticulum Proteostasis Factors

The extracellular aggregation of destabilized transthyretin (TTR) variants is implicated in the onset and pathogenesis of familial TTR-related amyloid diseases. One strategy to reduce the toxic, extracellular aggregation of TTR is to decrease the population of aggregation-prone proteins secreted from mammalian cells. The stress-independent activation of the unfolded protein response (UPR)-associated transcription factor ATF6 preferentially decreases the secretion and subsequent aggregation of destabilized, aggregation-prone TTR variants. However, the mechanism of this reduced secretion was previously undefined. Here, we implement a mass-spectrometry-based interactomics approach to identify endoplasmic reticulum (ER) proteostasis factors involved in ATF6-dependent reductions in destabilized TTR secretion. We show that ATF6 activation reduces amyloidogenic TTR secretion and subsequent aggregation through a mechanism involving ER retention that is mediated by increased interactions with ATF6-regulated ER proteostasis factors including BiP and PDIA4. Intriguingly, the PDIA4-dependent retention of TTR is independent of both the single TTR cysteine residue and the redox activity of PDIA4, indicating that PDIA4 retains destabilized TTR in the ER through a redox-independent mechanism. Our results define a mechanistic basis to explain the ATF6 activation-dependent reduction in destabilized, amyloidogenic TTR secretion that could be therapeutically accessed to improve treatments of TTR-related amyloid diseases.

Antioxidant Quercetin 3-O-Glycosylated Plant Flavonols Contribute to Transthyretin Stabilization

Plants are rich in secondary metabolites, which are often useful as a relevant source of nutraceuticals. Quercetin (QUE) is a flavonol aglycone able to bind Transthyretin (TTR), a plasma protein that under pathological conditions can lose its native structure leading to fibrils formation and amyloid diseases onset. Here, the dual nature of five quercetin 3-O-glycosylated flavonol derivatives, isolated from different plant species, such as possible binders of TTR and antioxidants, was investigated. The crystal structure of 3-O-β-D-galactopyranoside in complex with TTR was solved, suggesting that not only quercetin but also its metabolites can contribute to stabilizing the TTR tetramer.

Amyloid seeding as a disease mechanism and treatment target in transthyretin cardiac amyloidosis

Transthyretin (TTR) is a tetrameric transport protein mainly synthesized by the liver and choroid plexus. ATTR amyloidosis is characterized by the misfolding of TTR monomers and their accumulation within tissues as amyloid fibres. Current therapeutic options rely on the blockade of TTR production, TTR stabilization to maintain the native structure of TTR, amyloid degradation, or induction of amyloid removal from tissues. “Amyloid seeds” are defined as small fibril fragments that induce amyloid precursors to assume a structure rich in β-sheets, thus promoting fibrillogenesis. Amyloid seeds are important to promote the amplification and spread of amyloid deposits. Further studies are needed to better understand the molecular structure of ATTR seeds (i.e. the characteristics of the most amyloidogenic species), and the conditions that promote the formation and multiplication of seeds in vivo. The pathological cascade may begin months to years before symptom onset, suggesting that seeds in tissues might potentially be used as biomarkers for the early disease stages. Inhibition of amyloid aggregation by anti-seeding peptides may represent a disease mechanism and treatment target in ATTR amyloidosis, with an additional benefit over current therapies.

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.

Perfluorohexanoic acid caused disruption of the hypothalamus-pituitary-thyroid axis in zebrafish larvae

Perfluorohexanoic acid (PFHxA) has been recognized as an alternative to the wide usage of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in the fluoropolymer industry for years. PFHxA has been frequently detected in the environment due to its wide application. However, the ecological safety of PFHxA, especially its toxicological effects on aquatic organisms, remains obscure. In the present study, PFHxA at different concentrations (0, 0.48, 2.4, and 12 mg/L) was added to the culture medium for zebrafish embryo/larval exposure at 96 h postfertilization (hpf). Zebrafish larvae showed a slow body growth trend and changes in thyroid hormone levels (THs) upon PFHxA exposure, indicating the interference effect of PFHxA on fish larval development. Moreover, the transcription levels of genes related to the hypothalamic-pituitary-thyroid (HPT) axis were also analyzed. The gene expression level of thyroid hormone receptor β (trβ) was upregulated in a dose-dependent manner. Exposure to 0.48 mg/L PFHxA increased the expression levels of the thyrotrophic-releasing hormone (trh) and thyroid hormone receptor α (trα). Significant increases in corticotrophin-releasing hormone (crh) and transthyretin (ttr) gene expression were also observed when the zebrafish larvae were treated with 12 mg/L PFHxA, except iodothyronine deiodinases (dio1), which decreased obviously at that point. There were significant declines in the transcription of both thyroid-stimulating hormone β (tshβ) and uridinediphosphate-glucuronosyltransferase (ugt1ab) upon exposure to 2.4 mg/L PFHxA. In addition, PFHxA induced a dose-related inhibitory effect on the transcription of sodium/iodide symporter (nis). Finally, the thyroid status will be destroyed after exposure to PFHxA, thus leading to growth impairment in zebrafish larvae.

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

In the last twenty years, significant progress in understanding the pathophysiology of age-associated neurodegenerative diseases has been made. However, the prevention and treatment of these diseases remain without clinically significant therapeutic advancement. While we still hope for some potential genetic therapeutic approaches, the current reality is far from substantial progress. With this state of the issue, emphasis should be placed on early diagnosis and prompt intervention in patients with increased risk of neurodegenerative diseases to slow down their progression, poor prognosis, and decreasing quality of life. Accordingly, it is urgent to implement interventions addressing the psychosocial and biochemical disturbances we know are central in managing the evolution of these disorders. Genomic and proteomic studies have shown the high molecular intricacy in neurodegenerative diseases, involving a broad spectrum of cellular pathways underlying disease progression. Recent investigations indicate that the dysregulation of the sensitive-cysteine proteome may be a concurrent pathogenic mechanism contributing to the pathophysiology of major neurodegenerative diseases, opening new therapeutic opportunities. Considering the incidence and prevalence of these disorders and their already significant burden in Western societies, they will become a real pandemic in the following decades. Therefore, we propose large-scale investigations, in selected groups of people over 40 years of age with decreased blood glutathione levels, comorbidities, and/or mild cognitive impairment, to evaluate supplementation of the diet with low doses of N-acetyl-cysteine, a promising and well-tolerated therapeutic agent suitable for long-term use.

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.

Modern Approaches To Cardiovascular Amyloidosis Treatment

Cardiovascular (cardiac) amyloidosis (CA) is a clinical pathology, usually of a geneticallymediated nature, initiated by the precipitation process of the insoluble fibrous protein with β-pleated sheet secondary structure. Such anomalous changes lead to the formation of amyloid fibrils, which may give rise to various forms of amyloidosis. Amyloid formation can be found in various organs and systems, such as cardiovascular system, central and peripheral nervous systems, liver, urinary tract, etc. CA is a rare degenerative disease resulting in congestive cardiac failure and heart arrhythmia with subsequent untimely death. Unfortunately, up to date, the choice of medications for treating amyloidosis is very limited. In this paper, we review clinically used pharmaceutical drugs for CA treatment, along with some delivery systems for such compounds.

Structural basis for transthyretin amyloid formation in vitreous body of the eye

Amyloid transthyretin (ATTR) amyloidosis is characterized by the abnormal accumulation of ATTR fibrils in multiple organs. However, the structure of ATTR fibrils from the eye is poorly understood. Here, we used cryo-EM to structurally characterize vitreous body ATTR fibrils. These structures were distinct from previously characterized heart fibrils, even though both have the same mutation and type A pathology. Differences were observed at several structural levels: in both the number and arrangement of protofilaments, and the conformation of the protein fibril in each layer of protofilaments. Thus, our results show that ATTR protein structure and its assembly into protofilaments in the type A fibrils can vary between patients carrying the same mutation. By analyzing and matching the interfaces between the amino acids in the ATTR fibril with those in the natively folded TTR, we are able to propose a mechanism for the structural conversion of TTR into a fibrillar form.

Multiple de novo gene variations in a progeroid phenotype case report: haploinsufficiency mechanisms

We are presenting the case of a 6-year-old male patient with progeroid phenotype and severe developmental delay referred to Genetic clinic. Given the complex phenotype an extensive metabolic and genetic evaluation was performed including a whole exome sequencing analysis that showed genetic variants in TTR, RELN, MYH6, PHIP, and SYNE2 genes. Patients' mother and brother were analyzed for the genetic variants in MYH6, PHIP and RELN. Both had same variants on PHIP and RELN as our patient, with no apparent phenotypical consequences. Physical examination was remarkable for dysmorphism including plagiocephaly, low set and abnormally shaped ears, up slanted palpebral fissures, hypoplastic alae nasi, and a head circumference two standard deviations below the 3^rd percentile (microcephaly). Other characteristics include wrinkled skin, a broad forehead, sparse eyelashes in lower eyelid, short palpebral fissures, upturned nares, thick lips, right occipital plagiocephaly, overfolded helix and prominent anti-helix, protuberant chest, scaphoid abdomen, digitalized thumbs, and kyphosis due to low muscle tone. The patient presented abnormal EEG with evidence of epileptic discharges. A temporal bone CT showed plagiocephaly with flattening of the right occipital bone. Brain MRI showed callosal agenesis with bilateral colpocephaly with temporal horn dilatation, parahippocampal atrophy, lissencephaly and midbrain hypoplasia. The combination of de novo gene variants mentioned above has never been reported nor correlated as the result of haploinsufficiency mechanisms. Thus, we propose haploinsufficiency and loss of heterozygosity as etiological reasons for this patient phenotype. Further proteomic studies are needed to allocate the extense of genetic influence within the clinical manifestations.

Haemonchus contortus Transthyretin-Like Protein TTR-31 Plays Roles in Post-Embryonic Larval Development and Potentially Apoptosis of Germ Cells

Transthyretin (TTR)-like proteins play multi-function roles in nematode and are important component of excretory/secretory product in Haemonchus contortus. In this study, we functionally characterised a secretory transthyretin-like protein in the barber's pole worm H. contortus. A full-length of transthyretin-like protein-coding gene (Hc-ttr-31) was identified in this parasitic nematode, representing a counterpart of Ce-ttr-31 in Caenorhabditis elegans. High transcriptional levels of Hc-ttr-31 were detected in the egg and early larval stages of H. contortus, with the lowest level measured in the adult stage, indicating a decreased transcriptional pattern of this gene during nematode development. Localisation analysis indicated a secretion of TTR-31 from the intestine to the gonad, suggesting additional roles of Hc-ttr-31 in nematode reproduction. Expression of Hc-ttr-31 and Ce-ttr-31 in C. elegans did not show marked influence on the nematode development and reproduction, whereas Hc-ttr-31 RNA interference-mediated gene knockdown of Ce-ttr-31 shortened the lifespan, decreased the brood size, slowed the pumping rate and inhibited the growth of treated worms. Particularly, gene knockdown of Hc-ttr-31 in C. elegans was linked to activated apoptosis signalling pathway, increased general reactive oxygen species (ROS) level, apoptotic germ cells and facultative vivipary phenotype, as well as suppressed germ cell removal signalling pathways. Taken together, Hc-ttr-31 appears to play roles in regulating post-embryonic larval development, and potentially in protecting gonad from oxidative stress and mediating engulfment of apoptotic germ cells. A better knowledge of these aspects should contribute to a better understanding of the developmental biology of H. contortus and a discovery of potential targets against this and related parasitic worms.

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).

Transthyretin and Receptor for Advanced Glycation End Product's Differential Levels Associated with the Pathogenesis of Rheumatoid Arthritis

Objective

Rheumatoid arthritis (RA) is a chronic autoimmune, inflammatory joint disease. The identification of multifaceted etiological changes at the protein level in RA remains an important need. We aimed to identify differential proteins (DPs) and gene profiles to uncover inflammatory indicators and their association to RA pathogenesis.

Methods

2-DE and SWATH-MS were used to identify DPs in RA and healthy control plasma. Fluorescence phenylboronate gel electrophoresis (Flu-PAGE) with mass spectrometry was used for protein glycation in RA plasma. Disease specificity of identified DPs was confirmed by ELISA and Western blot analysis. The gene expressions of selected DPs were evaluated by qRT-PCR in PBMCs of RA, systemic lupus erythematosus (SLE), spondyloarthritis (SpA), and osteoarthritis (OA). The functional implication of glycated protein was determined by in- silico and validated by in vitro analysis in fibroblast-like synoviocytes.

Results

A total of 150 DPs (127 increased and 23 decreased) were identified by 2-DE and SWATH-MS analysis in RA plasma compared to healthy control (HC). Nine proteins were identified as glycated by Flu-PAGE LC-MS/MS. Transthyretin (TTR), serotransferrin, and apolipoprotein-A1 (Apo-A1) were found to be differential and glycated. ELISA and Western blot results revealed the disease-specific increased expression of TTR and RAGE in RA. The qRT-PCR results signify the aberrant gene expression of TTR and RAGE, found to be associated with RA when compared with SLE, SpA, and OA PBMCs. TTR-RAGE interactions were predicted by in-silico and validated by in-vitro analysis using RA-FLS. The increased levels of pro-inflammatory cytokines IL-6, IL-1β, TNF-α, and differently expressed TTR and RAGE were confirmed in fibroblast-like synoviocytes under inflammatory conditions.

Conclusion

Our findings showed that the level of TTR was increased in RA plasma, along with an altered glycation rate. TTR and RAGE aberrant gene expression in PBMCs are the key events associated with RA, and TNF-α activates the NF-KB pathways and promote TTR and RAGE differential expressions that may have pathogenic/inflammatory significance.

Associations of serum transthyretin with triglyceride in non-obese elderly Japanese women independently of insulin resistance, HDL cholesterol, and adiponectin

Objective

Studies are limited on the association between serum transthyretin (TTR), a negative acute phase reactant, and triglyceride (TG).

Research design and methods

TG, TTR, and insulin resistance-related cardiometabolic variables were measured in 159 fasting and 185 nonfasting community-dwelling elderly women aged 50-96 years. Pearson correlation analysis and then stepwise multiple regression analyses were performed to further identify the most significant variables contributing to the variation of fasting and nonfasting TG.

Results

Multiple regression analysis for fasting TG as a dependent variable revealed that TTR (standardized β: 0.299) and HDL cholesterol (standardized β: -0.545) emerged as determinants of TG independently of percentage of body fat, homeostasis model assessment insulin resistance, serum leptin and adiponectin, and plasminogen activator inhibitor-1 (PAI-1) (R ² = 0.36). For nonfasting TG, HDL cholesterol (standardized β: - 0.461), TTR (standardized β: 0.231), nonfasting insulin, a marker of insulin resistance, (standardized β: 0.202), and PAI-1 (standardized β: 0.187) emerged as determinants independently of percentage of body fat, nonfasting glucose, serum leptin and adiponectin, and high-sensitivity C-reactive protein (R ² = 0.45).

Conclusions

Fasting and nonfasting TG showed positive association with TTR in community-dwelling elderly non-obese women independently of insulin resistance, HDL cholesterol, and adiponectin. These findings may provide a clue as to a physiological function of circulating TTR in human: an influence factor of TG-rich lipoproteins in the circulation.

Shotgun-based proteomics of extracellular vesicles in Alzheimer's disease reveals biomarkers involved in immunological and coagulation pathways

Alzheimer's disease (AD) is the most common form of dementia and without readily available clinical biomarkers. Blood-derived proteins are routinely used for diagnostics; however, comprehensive plasma profiling is challenging due to the dynamic range in protein concentrations. Extracellular vesicles (EVs) can cross the blood-brain barrier and may provide a source for AD biomarkers. We investigated plasma-derived EV proteins for AD biomarkers from 10 AD patients, 10 Mild Cognitive Impairment (MCI) patients, and 9 healthy controls (Con) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The ultracentrifuged EVs were washed and confirmed according to the MISEV2018 guidelines. Some AD patients presented with highly elevated FXIIIA1 (log₂ FC: 4.6, p-value: 0.005) and FXIIIB (log₂ FC: 4.9, p-value: 0.018). A panel of proteins was identified discriminating Con from AD (AUC: 0.91, CI: 0.67-1.00) with ORM2 (AUC: 1.00, CI: 1.00-1.00), RBP4 (AUC: 0.99, CI: 0.95-1.00), and HYDIN (AUC: 0.89, CI: 0.72-1.00) were found especially relevant for AD. This indicates that EVs provide an easily accessible matrix for possible AD biomarkers. Some of the MCI patients, with similar protein profiles as the AD group, progressed to AD within a 2-year timespan.

Transthyretin as a target of alkylation and a potential biomarker for sulfur mustard poisoning: Electrophoretic and mass spectrometric identification and characterization

For the verification of exposure to the banned blister agent sulfur mustard (SM) and the better understanding of its pathophysiology, protein adducts formed with endogenous proteins represent an important field of toxicological research. SM and its analogue 2-chloroethyl ethyl sulfide (CEES) are well known to alkylate nucleophilic amino acid side chains, for example, free-thiol groups of cysteine residues. The specific two-dimensional thiol difference gel electrophoresis (2D-thiol-DIGE) technique making use of maleimide dyes allows the staining of free cysteine residues in proteins. As a consequence of alkylation by, for example, SM or CEES, this staining intensity is reduced. 2D-thiol-DIGE analysis of human plasma incubated with CEES and subsequent matrix-assisted laser desorption/ionization time-of-flight (tandem) mass-spectrometry, MALDI-TOF MS(/MS), revealed transthyretin (TTR) as a target of alkylating agents. TTR was extracted from SM-treated plasma by immunomagnetic separation (IMS) and analyzed after tryptic cleavage by microbore liquid chromatography-electrospray ionization high-resolution tandem-mass spectrometry (μLC-ESI MS/HR MS). It was found that the Cys¹⁰ -residue of TTR present in the hexapeptide C(-HETE)PLMVK was alkylated by the hydroxyethylthioethyl (HETE)-moiety, which is characteristic for SM exposure. It was shown that alkylated TTR is stable in plasma in vitro at 37°C for at least 14 days. In addition, C(-HETE)PLMVK can be selectively detected, is stable in the autosampler over 24 h, and shows linearity in a broad concentration range from 15.63 μM to 2 mM SM in plasma in vitro. Accordingly, TTR might represent a complementary protein marker molecule for the verification of SM exposure.

Disease-associated mutations impacting BC-loop flexibility trigger long-range transthyretin tetramer destabilization and aggregation

Hereditary transthyretin amyloidosis (ATTR) is an autosomal dominant disease characterized by the extracellular deposition of the transport protein transthyretin (TTR) as amyloid fibrils. Despite the progress achieved in recent years, understanding why different TTR residue substitutions lead to different clinical manifestations remains elusive. Here, we studied the molecular basis of disease-causing missense mutations affecting residues R34 and K35. R34G and K35T variants cause vitreous amyloidosis, whereas R34T and K35N mutations result in amyloid polyneuropathy and restrictive cardiomyopathy. All variants are more sensitive to pH-induced dissociation and amyloid formation than the wild-type (WT)-TTR counterpart, specifically in the variants deposited in the eyes amyloid formation occurs close to physiological pHs. Chemical denaturation experiments indicate that all the mutants are less stable than WT-TTR, with the vitreous amyloidosis variants, R34G and K35T, being highly destabilized. Sequence-induced stabilization of the dimer–dimer interface with T119M rendered tetramers containing R34G or K35T mutations resistant to pH-induced aggregation. Because R34 and K35 are among the residues more distant to the TTR interface, their impact in this region is therefore theorized to occur at long range. The crystal structures of double mutants, R34G/T119M and K35T/T119M, together with molecular dynamics simulations indicate that their strong destabilizing effect is initiated locally at the BC loop, increasing its flexibility in a mutation-dependent manner. Overall, the present findings help us to understand the sequence-dynamic-structural mechanistic details of TTR amyloid aggregation triggered by R34 and K35 variants and to link the degree of mutation-induced conformational flexibility to protein aggregation propensity.

Juvenile Idiopathic Arthritis Associated Uveitis

Juvenile idiopathic arthritis (JIA) is the most common childhood rheumatic disease. The development of associated uveitis represents a significant risk for serious complications, including permanent loss of vision. Initiation of early treatment is important for controlling JIA-uveitis, but the disease can appear asymptomatically, making frequent screening procedures necessary for patients at risk. As our understanding of pathogenic drivers is currently incomplete, it is difficult to assess which JIA patients are at risk of developing uveitis. Identification of specific risk factors for JIA-associated uveitis is an important field of research, and in this review, we highlight the genomic, transcriptomic, and proteomic factors identified as potential uveitis risk factors in JIA, and discuss therapeutic strategies.

Transthyretin: From Structural Stability to Osteoarticular and Cardiovascular Diseases

Transthyretin (TTR) is a tetrameric protein transporting hormones in the plasma and brain, which has many other activities that have not been fully acknowledged. TTR is a positive indicator of nutrition status and is negatively correlated with inflammation. TTR is a neuroprotective and oxidative-stress-suppressing factor. The TTR structure is destabilized by mutations, oxidative modifications, aging, proteolysis, and metal cations, including Ca2+. Destabilized TTR molecules form amyloid deposits, resulting in senile and familial amyloidopathies. This review links structural stability of TTR with the environmental factors, particularly oxidative stress and Ca2+, and the processes involved in the pathogenesis of TTR-related diseases. The roles of TTR in biomineralization, calcification, and osteoarticular and cardiovascular diseases are broadly discussed. The association of TTR-related diseases and vascular and ligament tissue calcification with TTR levels and TTR structure is presented. It is indicated that unaggregated TTR and TTR amyloid are bound by vicious cycles, and that TTR may have an as yet undetermined role(s) at the crossroads of calcification, blood coagulation, and immune response.