Dissecting the Interactions between Human Serum Albumin and α-Synuclein: New Insights on the Factors Influencing α-Synuclein Aggregation in Biological Fluids

Thermal effects and drugs competition on the palmitate binding capacity of human serum albumin

Human serum albumin (HSA) is the most abundant plasma protein of the circulatory system. It is a multidomain, multifunctional protein that, combining diverse affinities and wide specificity, binds, stores, and transports a variety of biological compounds, pharmacores, and fatty acids. HSA is finding increasing uses in drug-delivery due to its ability to carry functionalized ligands and prodrugs. All this raises the question of competition for binding sites occupancy in case of multiple ligands, which in turn influences the protein structure/dynamic/function relationship and also has an impact on the biomedical applications. In this work, the effects of interactive binding of palmitic acid (PA), warfarin (War) and ibuprofen (Ibu) on the thermal stability of HSA were studied using DSC, ATR-FTIR, and EPR. PA is a high-affinity physiological ligand, while the two drugs are widely used for their anticoagulant (War) and anti-inflammatory (Ibu) efficacy, and are exogenous compounds that accommodate in the deputed drug site DS1 and DS2, respectively overlapping with some of the fatty acid binding sites. The results indicate that HSA acquires the highest thermal stability when it is fully saturated with PA. The binding of this physiological ligand does not hamper the binding of War or Ibu to the native state of the protein. In addition, the three ligands bind simultaneously, suggesting a synergic cooperative influence due to allosteric effects. The increased thermal stability subsequent to binary and multiple ligands binding moderates protein aggregation propensity and restricts protein dynamics. The biophysics findings provide interesting features about protein stability, aggregation, and dynamics in interaction with multiple ligands and are relevant in drug-delivery.

Aggregation-resistant alpha-synuclein tetramers are reduced in the blood of Parkinson's patients

Synucleinopathies such as Parkinson's disease (PD) are defined by the accumulation and aggregation of the α-synuclein protein in neurons, glia and other tissues. We have previously shown that destabilization of α-synuclein tetramers is associated with familial PD due to SNCA mutations and demonstrated brain-region specific alterations of α-synuclein multimers in sporadic PD patients following the classical Braak spreading theory. In this study, we assessed relative levels of disordered and higher-ordered multimeric forms of cytosolic α-synuclein in blood from familial PD with G51D mutations and sporadic PD patients. We used an adapted in vitro-cross-linking protocol for human EDTA-whole blood. The relative levels of higher-ordered α-synuclein tetramers were diminished in blood from familial PD and sporadic PD patients compared to controls. Interestingly, the relative amount of α-synuclein tetramers was already decreased in asymptomatic G51D carriers, supporting the hypothesis that α-synuclein multimer destabilization precedes the development of clinical PD. Our data, therefore suggest that measuring α-synuclein tetramers in blood may have potential as a facile biomarker assay for early detection and quantitative tracking of PD progression.

Cerebrospinal fluid/serum albumin ratio in patients with Lewy body disease: a systematic review and meta-analysis

Background

Abnormal cerebrospinal fluid (CSF)/serum albumin ratio (Qalb) levels have been observed in patients with cognitive impairment. Few studies have specifically focused on Lewy Body Disease (LBD), and the results were controversial. Thus, we conducted this systematic review and meta-analysis to investigate Qalb levels in patients with LBD by including data from different studies.

Method

We systematically searched PubMed, Embase, Cochrane Library, and Web of Science databases for a collection of studies containing studies comparing Qalb levels in patients with LBD and healthy controls (including healthy controls and other dementia subtypes). In the initial search, 86 relevant papers were retrieved. Standardized mean differences (SMD) in Qalb levels were calculated using a random effects model.

Results

A total of 13 eligible studies were included. Mean Qalb levels were significantly higher in patients with LBD compared to healthy older adults [standardized mean difference (SMD): 2.95, 95% confidence interval (CI): 0.89-5.00, Z = 2.81, p = 0.005]; and were significantly higher in patients with LBD than in patients with Alzheimer's disease (AD) (SMD: 1.13, 95% CI: 0.42-1.83, Z = 3.15, p = 0.002);whereas mean Qalb levels were significantly higher in patients with frontotemporal lobar degeneration (FTLD) compared to those with AD (SMD: 1.13, 95% CI,0.14-2.13, Z = 2.24, p = 0.03).

Conclusion

Qalb levels were significantly elevated in LBD patients compared with normal older adults and were higher than those in AD patients and FTLD patients, which helped in the differential diagnosis of LBD from other neurodegenerative diseases.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42024496616.

Peripheral Upregulation of Parkinson's Disease-Associated Genes Encoding α-Synuclein, β-Glucocerebrosidase, and Ceramide Glucosyltransferase in Major Depression

Due to the high comorbidity of Parkinson's disease (PD) with major depressive disorder (MDD) and the involvement of sphingolipids in both conditions, we investigated the peripheral expression levels of three primarily PD-associated genes: α-synuclein (SNCA), lysosomal enzyme β-glucocerebrosidase (GBA1), and UDP-glucose ceramide glucosyltransferase (UGCG) in a sex-balanced MDD cohort. Normalized gene expression was determined by quantitative PCR in patients suffering from MDD (unmedicated n = 63, medicated n = 66) and controls (remitted MDD n = 39, healthy subjects n = 61). We observed that expression levels of SNCA (p = 0.036), GBA1 (p = 0.014), and UGCG (p = 0.0002) were higher in currently depressed patients compared to controls and remitted patients, and expression of GBA1 and UGCG decreased in medicated patients during three weeks of therapy. Additionally, in subgroups, expression was positively correlated with the severity of depression and anxiety. Furthermore, we identified correlations between the gene expression levels and PD-related laboratory parameters. Our findings suggest that SNCA, GBA1, and UGCG analysis could be instrumental in the search for biomarkers of MDD and in understanding the overlapping pathological mechanisms underlying neuro-psychiatric diseases.

Inhibition of toxic metal-alpha synuclein interactions by human serum albumin

Human serum albumin (HSA), the most abundant protein in plasma and cerebrospinal fluid, not only serves as a crucial carrier of various exogenous and endogenous ligands but also modulates the aggregation of amyloidogenic proteins, including alpha synuclein (αSyn), which is associated with Parkinson's disease and other α-synucleinopathies. HSA decreases αSyn toxicity through the direct binding to monomeric and oligomeric αSyn species. However, it is possible that HSA also sequesters metal ions that otherwise promote aggregation. Cu(ii) ions, for example, enhance αSyn fibrillization in vitro, while also leading to neurotoxicity by generating reactive oxygen species (ROS). However, it is currently unclear if and how HSA affects Cu(ii)-binding to αSyn. Using an integrated set of NMR experiments, we show that HSA is able to chelate Cu(ii) ions from αSyn more efficiently than standard chelators such as EDTA, revealing an unexpected cooperativity between the HSA metal-binding sites. Notably, fatty acid binding to HSA perturbs this cooperativity, thus interfering with the sequestration of Cu(ii) ions from αSyn. We also observed that glycation of HSA diminished Cu(ii)-binding affinity, while largely preserving the degree of cooperativity between the HSA metal-binding sites. Additionally, our results show that Cu(ii)-binding to HSA stabilizes the interactions of HSA with αSyn primarily at two different regions, i.e. the N-terminus, Tyr 39 and the majority of the C-terminus. Our study not only unveils the effect of fatty acid binding and age-related posttranslational modifications, such as glycation, on the neuroprotective mechanisms of HSA, but also highlights the potential of αSyn as a viable NMR-based sensor to investigate HSA-metal interactions.

Cerebrospinal fluid lipoproteins inhibit α-synuclein aggregation by interacting with oligomeric species in seed amplification assays

BACKGROUND

Aggregation of α-synuclein (α-syn) is a prominent feature of Parkinson's disease (PD) and other synucleinopathies. Currently, α-syn seed amplification assays (SAAs) using cerebrospinal fluid (CSF) represent the most promising diagnostic tools for synucleinopathies. However, CSF itself contains several compounds that can modulate the aggregation of α-syn in a patient-dependent manner, potentially undermining unoptimized α-syn SAAs and preventing seed quantification.

METHODS

In this study, we characterized the inhibitory effect of CSF milieu on detection of α-syn aggregates by means of CSF fractionation, mass spectrometry, immunoassays, transmission electron microscopy, solution nuclear magnetic resonance spectroscopy, a highly accurate and standardized diagnostic SAA, and different in vitro aggregation conditions to evaluate spontaneous aggregation of α-syn.

RESULTS

We found the high-molecular weight fraction of CSF (> 100,000 Da) to be highly inhibitory on α-syn aggregation and identified lipoproteins to be the main drivers of this effect. Direct interaction between lipoproteins and monomeric α-syn was not detected by solution nuclear magnetic resonance spectroscopy, on the other hand we observed lipoprotein-α-syn complexes by transmission electron microscopy. These observations are compatible with hypothesizing an interaction between lipoproteins and oligomeric/proto-fibrillary α-syn intermediates. We observed significantly slower amplification of α-syn seeds in PD CSF when lipoproteins were added to the reaction mix of diagnostic SAA. Additionally, we observed a decreased inhibition capacity of CSF on α-syn aggregation after immunodepleting ApoA1 and ApoE. Finally, we observed that CSF ApoA1 and ApoE levels significantly correlated with SAA kinetic parameters in n = 31 SAA-negative control CSF samples spiked with preformed α-syn aggregates.

CONCLUSIONS

Our results describe a novel interaction between lipoproteins and α-syn aggregates that inhibits the formation of α-syn fibrils and could have relevant implications. Indeed, the donor-specific inhibition of CSF on α-syn aggregation explains the lack of quantitative results from analysis of SAA-derived kinetic parameters to date. Furthermore, our data show that lipoproteins are the main inhibitory components of CSF, suggesting that lipoprotein concentration measurements could be incorporated into data analysis models to eliminate the confounding effects of CSF milieu on α-syn quantification efforts.

Pyrogallol, Corilagin and Chebulagic acid target the "fuzzy coat" of alpha-synuclein to inhibit the fibrillization of the protein

The accumulation of the intrinsically disordered protein alpha-synuclein (αSyn) in the form of insoluble fibrillar aggregates in the central nervous system is linked to a variety of neurodegenerative disorders such as Parkinson's disease, Lewy body dementia, and multiple system atrophy. Here we show that Pyrogallol, Corilagin and Chebulagic acid, compounds containing a different number of catechol rings, are independently capable of delaying and reducing the extent of αSyn fibrillization. The efficiency of inhibition was found to correlate with the number of catechol rings. Further, our NMR studies reveal that these compounds interact with the N-terminal region of αSyn which is unstructured even in the fibrillar form of the protein and is known as the "fuzzy coat" of fibrils. Thus, Corilagin and Chebulagic acid target the fuzzy coat of αSyn and not the amyloid core which is a common target for the inhibition of protein fibrillization. Our results indicate that the N-terminus also plays a key role in the fibrillization of αSyn.

In Vitro Interaction of a C-Terminal Fragment of TDP-43 Protein with Human Serum Albumin Modulates Its Aggregation

An increased level of naturally occurring anti-TDP-43 antibodies was observed in the serum and cerebrospinal fluid (CSF) of amyotrophic lateral sclerosis patients. Human serum albumin (HSA), the most abundant protein in blood plasma and CSF, is found to interact with pathological proteins like Aβ and α-synuclein. Therefore, we examined the effect on the in vitro aggregation of a C-terminal fragment of TDP-43 in the presence of HSA. We found that the lag phase in TDP-43^2C aggregation is abrogated in the presence of HSA, but there is an overall decreased aggregation as examined by thioflavin-T fluorescence spectroscopy and microscopy. An early onset of TDP-43^2C oligomer formation in the presence of HSA was observed using atomic force microscopy and transmission electron microscopy. Also, a known chemical inhibitor of TDP-43^2Caggregation, AIM4, abolishes the HSA-induced early formation of TDP-43^2C oligomers. Notably, the aggregates of TDP-43^2C formed in the presence of HSA are more stable against sarkosyl detergent. Using affinity copurification, we observed that HSA can bind to TDP-43^2C, and biolayer interferometry further supported their physical interaction and suggested the binding affinity to be in sub-micromolar range. Taken together, the data support that HSA can interact with TDP-43^2C in vitro and affect its aggregation.

Serum albumin, cognitive function, motor impairment, and survival prognosis in Parkinson disease

The role of albumin in Parkinson disease (PD) is not well understood, our study will investigate the association between the serum albumin level and risk of dementia, motor impairment, as well as survival outcome in PD. Data were obtained from the publicly available dataset in the DRYAD database (https://datadryad.org/). The original prospective study enrolled patients with PD from a single center in Japan between March 2004 and November 2007. Due to missing values, 242 and 274 participants were included in the study, in which we aimed to, respectively, analyze the relationship between serum albumin and cognitive function as well as motor impairment; additionally, 264 participants were included to assess the association between baseline serum albumin levels and risk of PD-related death with a median follow-up of 5.24 years. Compared to patients of the low tertile of albumin levels, Mini-Mental State Examination (MMSE) of patients of middle tertile increased 2.09 [95% confidence interval (CI) (0.45, 3.73), P = .013], independent of age, sex, PD duration, modified Hoehn-Yahr (mHY) stage, C-reactive protein (CRP) level, and use of nonsteroidal anti-inflammatory drugs (NSAIDs). Further analysis revealed a positive curvilinear association between albumin and MMSE, with cutoff values of 3.9. As concentration serum albumin increased, the risk of severe motor impairment was grown [odds ratio (OR) 0.34 (95% CI 0.14,0.8), P = .013] after adjustment by age, sex, PD duration, MMSE scores, CRP level, and use of NSAIDs. Albumin levels increased per unit of mg/dL, and the risk of PD-related death reduced 0.74-fold with 95% CI (0.15, 0.86) (P = .021), independent of age, sex, PD disease duration, mHY stage, CRP levels, use of NSAIDs, and MMSE. Higher serum albumin levels were significantly association with the better cognitive function when albumin was <3.9 mg/dL, and played a protective role in severe motor impairment and PD-related death.

Interactions between S100A9 and Alpha-Synuclein: Insight from NMR Spectroscopy

S100A9 is a pro-inflammatory protein that co-aggregates with other proteins in amyloid fibril plaques. S100A9 can influence the aggregation kinetics and amyloid fibril structure of alpha-synuclein (α-syn), which is involved in Parkinson's disease. Currently, there are limited data regarding their cross-interaction and how it influences the aggregation process. In this work, we analyzed this interaction using solution 19F and 2D ¹⁵N-¹H HSQC NMR spectroscopy and studied the aggregation properties of these two proteins. Here, we show that α-syn interacts with S100A9 at specific regions, which are also essential in the first step of aggregation. We also demonstrate that the 4-fluorophenylalanine label in alpha-synuclein is a sensitive probe to study interaction and aggregation using 19F NMR spectroscopy.

Human serum albumin in neurodegeneration

Serum albumin (SA) exists in relatively high concentrations, in close contact with most cells. However, in the adult brain, except for cerebrospinal fluid (CSF), SA concentration is relatively low. It is mainly produced in the liver to serve as the main protein of the blood plasma. In the plasma, it functions as a carrier, chaperon, antioxidant, source of amino acids, osmoregulator, etc. As a carrier, it facilitates the stable presence and transport of the hydrophobic and hydrophilic molecules, including free fatty acids, steroid hormones, medicines, and metal ions. As a chaperon, SA binds to and protects other proteins. As an antioxidant, thanks to a free sulfhydryl group (-SH), albumin is responsible for most antioxidant properties of plasma. These functions qualify SA as a major player in, and a mirror of, overall health status, aging, and neurodegeneration. The low concentration of SA is associated with cognitive deterioration in the elderly and negative prognosis in multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). SA has been shown to be structurally modified in neurological conditions such as Alzheimer's disease (AD). During blood-brain barrier damage albumin enters the brain tissue and could trigger epilepsy and neurodegeneration. SA is able to bind to the precursor agent of the AD, amyloid-beta (Aβ), preventing its toxic effects in the periphery, and is being tested for treating this disease. SA therapy may also be effective in brain rejuvenation. In the current review, we will bring forward the prominent properties and roles of SA in neurodegeneration.

Interactions of intrinsically disordered proteins with the unconventional chaperone human serum albumin: From mechanisms of amyloid inhibition to therapeutic opportunities

Human Serum Albumin (HSA), the most abundant protein in plasma, serves a diverse repertoire of biological functions including regulation of oncotic pressure and redox potential, transport of serum solutes, but also chaperoning of misfolded proteins. Here we review how HSA interacts with a wide spectrum of client proteins including intrinsically disordered proteins (IDPs) such as Aβ, the islet amyloid peptide (IAPP), alpha synuclein and stressed globular proteins such as insulin. The comparative analysis of the HSA chaperone - client interactions reveals that the amyloid-inhibitory function of HSA arises from at least four emerging mechanisms. Two mechanisms (the monomer stabilizer model and the monomer competitor model) involve the direct binding of HSA to either IDP monomers or oligomers, while other mechanisms (metal chelation and membrane protection) rely on the indirect modulation by HSA of other factors that drive IDP aggregation. While HSA is not the only extracellular chaperone, given its abundance, HSA is likely to account for a significant fraction of the chaperoning effects in plasma, thus opening new therapeutic opportunities in the context of the peripheral sink hypothesis.

Alpha and Beta Synucleins: From Pathophysiology to Clinical Application as Biomarkers

The synuclein family includes three neuronal proteins, named α‐synuclein, β‐synuclein, and γ‐synuclein, that have peculiar structural features. α‐synuclein is largely known for being a key protein in the pathophysiology of Parkinson's disease (PD) and other synucleinopathies, namely, dementia with Lewy bodies and multisystem atrophy. The role of β‐synuclein and γ‐synuclein is less well understood in terms of physiological functions and potential contribution to human diseases. α‐synuclein has been investigated extensively in both cerebrospinal fluid (CSF) and blood as a potential biomarker for synucleinopathies. Recently, great attention has been also paid to β‐synuclein, whose CSF and blood levels seem to reflect synaptic damage and neurodegeneration independent of the presence of synucleinopathy. In this review, we aim to provide an overview on the pathophysiological roles of the synucleins. Because γ‐synuclein has been poorly investigated in the field of synucleinopathy and its pathophysiological roles are far from being clear, we focus on the interactions between α‐synuclein and β‐synuclein in PD. We also discuss the role of α‐synuclein and β‐synuclein as potential biomarkers to improve the diagnostic characterization of synucleinopathies, thus highlighting their potential application in clinical trials for disease‐modifying therapies. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society

S100A9 Alters the Pathway of Alpha-Synuclein Amyloid Aggregation

The formation of amyloid fibril plaques in the brain creates inflammation and neuron death. This process is observed in neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. Alpha-synuclein is the main protein found in neuronal inclusions of patients who have suffered from Parkinson's disease. S100A9 is a calcium-binding, pro-inflammation protein, which is also found in such amyloid plaques. To understand the influence of S100A9 on the aggregation of α-synuclein, we analyzed their co-aggregation kinetics and the resulting amyloid fibril structure by Fourier-transform infrared spectroscopy and atomic force microscopy. We found that the presence of S100A9 alters the aggregation kinetics of α-synuclein and stabilizes the formation of a particular amyloid fibril structure. We also show that the solution's ionic strength influences the interplay between S100A9 and α-synuclein, stabilizing a different structure of α-synuclein fibrils.

Interfacing aptamers, nanoparticles and graphene in a hierarchical structure for highly selective detection of biomolecules in OECT devices

In several biomedical applications, the detection of biomarkers demands high sensitivity, selectivity and easy-to-use devices. Organic electrochemical transistors (OECTs) represent a promising class of devices combining a minimal invasiveness and good signal transduction. However, OECTs lack of intrinsic selectivity that should be implemented by specific approaches to make them well suitable for biomedical applications. Here, we report on a biosensor in which selectivity and a high sensitivity are achieved by interfacing, in an OECT architecture, a novel gate electrode based on aptamers, Au nanoparticles and graphene hierarchically organized to optimize the final response. The fabricated biosensor performs state of the art limit of detection monitoring biomolecules, such as thrombin-with a limit of detection in the picomolar range (≤ 5 pM) and a very good selectivity even in presence of supraphysiological concentrations of Bovine Serum Albumin (BSA-1mM). These accomplishments are the final result of the gate hierarchic structure that reduces sterich indrance that could contrast the recognition events and minimizes false positive, because of the low affinity of graphene towards the physiological environment. Since our approach can be easily applied to a large variety of different biomarkers, we envisage a relevant potential for a large series of different biomedical applications.

Fluorescence Lifetime and Intensity of Thioflavin T as Reporters of Different Fibrillation Stages: Insights Obtained from Fluorescence Up-Conversion and Particle Size Distribution Measurements

Thioflavin T (ThT) assay is extensively used for studying fibrillation kinetics in vitro. However, the differences in the time course of ThT fluorescence intensity and lifetime and other physical parameters of the system, such as particle size distribution, raise questions about the correct interpretation of the aggregation kinetics. In this work, we focused on the investigation of the mechanisms, which underlay the difference in sensitivity of ThT fluorescence intensity and lifetime to the formation of protein aggregates during fibrillation by the example of insulin and during binding to globular proteins. The assessment of aggregate sizes and heterogeneity was performed using dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). Using the sub-nanosecond resolution measurements, it was shown that the ThT lifetime is sensitive to the appearance of as much as a few percent of ThT bound to the high-affinity sites that occur simultaneously with an abrupt increase of the average particle size, particles concentration, and size heterogeneity. The discrepancy between ThT fluorescence intensity and a lifetime can be explained as the consequence of a ThT molecule fraction with ultrafast decay and weak fluorescence. These ThT molecules can only be detected using time-resolved fluorescence measurements in the sub-picosecond time domain. The presence of a bound ThT subpopulation with similar photophysical properties was also demonstrated for globular proteins that were attributed to non-specifically bound ThT molecules with a non-rigid microenvironment.

Molecular profiling in Parkinsonian syndromes: CSF biomarkers

An accurate and early diagnosis of degenerative parkinsonian syndromes is a major need for their correct and timely therapeutic management. The current diagnostic criteria are mostly based on clinical features and molecular imaging. However, diagnostic doubts often persist especially in the early stages of diseases when signs are slight, ambiguous and overlapping among different syndromes. Molecular imaging may not be altered in the early stages of diseases, also failing to discriminate among different syndromes. Cerebrospinal fluid (CSF) represents an ideal source of biomarkers reflecting different pathways of neuropathological changes taking place in the brain and preceding the clinical onset. The aim of this review is to provide un update on CSF biomarkers in parkinsonian disorders, discussing in detail their association with neuropathological correlates. Their potential contribution in differential diagnosis and prognostic assessment of different parkinsonian syndromes is also discussed. Before entering the clinical use both for diagnostic and prognostic purposes, these CSF biomarkers need to be thoroughly assessed in terms of pre-analytical and analytical variability, as well as to clinical validation in independent cohorts.

Differential Roles of Plasma Protein Corona on Immune Cell Association and Cytokine Secretion of Oligomeric and Fibrillar Beta-Amyloid

Alzheimer's disease (AD) is a primary neurological disease with no effective cure. A hallmark of AD is the presence of intracellular tangles and extracellular plaques derived from the aberrant aggregation of tau- and beta-amyloid (Aβ). Aβ presents in the brain as well as in cerebrospinal fluid and the circulation, and Aβ toxicity has been attributed to amyloidosis and inflammation, among other causes. In this study, the effects of the plasma protein corona have been investigated with regard to the blood cell association and cytokine secretion of oligomeric (Aβo) and fibrillar Aβ_1-42(Aβ_f), two major forms of the peptide aggregates. Aβo displayed little change in membrane association in whole blood or washed blood (i.e., cells in the absence of plasma proteins) at 37 °C, while Aβ_f showed a clear preference for binding with all cell types sans plasma proteins. Immune cells exposed to Aβo, but not to Aβ_f, resulted in significant expression of cytokines IL-6 and TNF measured in real-time by a localized surface plasmon resonance sensor. These observations indicate greater immune cell association and cytokine stimulation of Aβo than Aβ_f and shed new light on the contrasting toxicities of Aβo and Aβ_f resulting from their differential capacities in acquiring a plasma protein corona. These results further implicate a close connection between Aβ amyloidosis and immunopathology in AD.