Istvan Horvath

Cross-talk between amyloidogenic proteins in type-2 diabetes and Parkinson’s disease

Significance Protein assembly into ordered so-called amyloid fibers is a process that promotes several neurodegenerative disorders, such as Alzheimer’s and Parkinson’s disease (PD). Also type-2 diabetes (T2D) is a disease involving amyloid formation, although it occurs in the pancreas. Since the protein that forms amyloids in PD, α-synuclein (aS), is also expressed in the pancreas, we investigated whether it could affect aggregation of the peptide involved in T2D, and vice versa. Using in vitro methods and purified proteins, we here demonstrate that the two proteins cross-react and, importantly, the T2D amyloid protein (both as monomer and amyloid seed) can accelerate aS aggregation. This result provides a possible explanation for why patients with T2D are more prone to getting PD. In type-2 diabetes (T2D) and Parkinson’s disease (PD), polypeptide assembly into amyloid fibers plays central roles: in PD, α-synuclein (aS) forms amyloids and in T2D, amylin [islet amyloid polypeptide (IAPP)] forms amyloids. Using a combination of biophysical methods in vitro we have investigated whether aS, IAPP, and unprocessed IAPP, pro-IAPP, polypeptides can cross-react. Whereas IAPP forms amyloids within minutes, aS takes many hours to assemble into amyloids and pro-IAPP aggregates even slower under the same conditions. We discovered that preformed amyloids of pro-IAPP inhibit, whereas IAPP amyloids promote, aS amyloid formation. Amyloids of aS promote pro-IAPP amyloid formation, whereas they inhibit IAPP amyloid formation. In contrast, mixing of IAPP and aS monomers results in coaggregation that is faster than either protein alone; moreover, pro-IAPP can incorporate aS monomers into its amyloid fibers. From this intricate network of cross-reactivity, it is clear that the presence of IAPP can accelerate aS amyloid formation. This observation may explain why T2D patients are susceptible to developing PD.

Direct Correlation Between Ligand-Induced α-Synuclein Oligomers and Amyloid-like Fibril Growth

Aggregation of proteins into amyloid deposits is the hallmark of several neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. The suggestion that intermediate oligomeric species may be cytotoxic has led to intensified investigations of pre-fibrillar oligomers, which are complicated by their transient nature and low population. Here we investigate alpha-synuclein oligomers, enriched by a 2-pyridone molecule (FN075), and the conversion of oligomers into fibrils. As probed by leakage assays, the FN075 induced oligomers potently disrupt vesicles in vitro, suggesting a potential link to disease related degenerative activity. Fibrils formed in the presence and absence of FN075 are indistinguishable on microscopic and macroscopic levels. Using small angle X-ray scattering, we reveal that FN075 induced oligomers are similar, but not identical, to oligomers previously observed during alpha-synuclein fibrillation. Since the levels of FN075 induced oligomers correlate with the amounts of fibrils among different FN075:protein ratios, the oligomers appear to be on-pathway and modeling supports an ‘oligomer stacking model’ for alpha-synuclein fibril elongation.

Immunochemical Detection of α-Synuclein Autoantibodies in Parkinson’s Disease: Correlation between Plasma and Cerebrospinal Fluid Levels

Autoantibodies to Parkinsons disease (PD) amyloidogenic protein, α-synuclein, were recognized as a prospective biomarker for early disease diagnostics, yet there is inconsistency in previous reports, potentially related to PD status. Therefore, plasma and cerebrospinal fluid (CSF) of the cross-sectional cohort of 60 individuals, including recently diagnosed PD patients with mild and moderate PD and age-matched controls, were examined by enzyme-linked immunosorbent assay (ELISA). Nonparametric statistics was used for data analysis. We found significantly elevated levels of α-synuclein autoantibodies in both plasma and CSF in mild PD compared to controls, followed by some decrease in moderate PD. Receiver operating characteristic and effect size analyses confirmed the diagnostic power of α-synuclein antibodies in both plasma and CSF. For the first time, we showed the correlation between plasma and CSF α-synuclein antibody levels for mild, moderate, and combined PD groups. This indicates the potentiality of α-synuclein antibodies as PD biomarker and the increased diagnostic power of their simultaneous analysis in plasma and CSF.

Extracellular vesicles from human pancreatic islets suppress human islet amyloid polypeptide amyloid formation

Significance Protein assembly into amyloid fibers underlies such neurodegenerative disorders as Alzheimer’s disease and Parkinson’s disease. Type 2 diabetes (T2D) also involves amyloid formation, although in the pancreas. Because there are no cures for amyloid diseases and T2D is on the rise due to an increasing prevalence of obesity, identifying involved mechanisms and control processes is of utmost importance. Extracellular vesicles (EVs) can mediate physiological and pathological communication both locally and at a distance. Here, we demonstrate that EVs secreted from healthy, but not from T2D, pancreatic cells slow amyloid formation of the major peptide found in amyloid deposits in T2D. We propose an EV-mediated process that tempers amyloid formation in the pancreas at normal conditions, which breaks down in T2D due to altered EV protein–lipid composition. Extracellular vesicles (EVs) are small vesicles released by cells to aid cell–cell communication and tissue homeostasis. Human islet amyloid polypeptide (IAPP) is the major component of amyloid deposits found in pancreatic islets of patients with type 2 diabetes (T2D). IAPP is secreted in conjunction with insulin from pancreatic β cells to regulate glucose metabolism. Here, using a combination of analytical and biophysical methods in vitro, we tested whether EVs isolated from pancreatic islets of healthy patients and patients with T2D modulate IAPP amyloid formation. We discovered that pancreatic EVs from healthy patients reduce IAPP amyloid formation by peptide scavenging, but T2D pancreatic and human serum EVs have no effect. In accordance with these differential effects, the insulin:C-peptide ratio and lipid composition differ between EVs from healthy pancreas and EVs from T2D pancreas and serum. It appears that healthy pancreatic EVs limit IAPP amyloid formation via direct binding as a tissue-specific control mechanism.

Tyrosine Hydroxylase Binding to Phospholipid Membranes Prompts Its Amyloid Aggregation and Compromises Bilayer Integrity

Tyrosine hydroxylase (TH), a rate-limiting enzyme in the synthesis of catecholamine neurotransmitters and hormones, binds to negatively charged phospholipid membranes. Binding to both large and giant unilamellar vesicles causes membrane permeabilization, as observed by efflux and influx of fluorescence dyes. Whereas the initial protein-membrane interaction involves the N-terminal tail that constitutes an extension of the regulatory ACT-domain, prolonged membrane binding induces misfolding and self-oligomerization of TH over time as shown by circular dichroism and Thioflavin T fluorescence. The gradual amyloid-like aggregation likely occurs through cross-β interactions involving aggregation-prone motives in the catalytic domains, consistent with the formation of chain and ring-like protofilaments observed by atomic force microscopy in monolayer-bound TH. PC12 cells treated with the neurotoxin 6-hydroxydopamine displayed increased TH levels in the mitochondrial fraction, while incubation of isolated mitochondria with TH led to a decrease in the mitochondrial membrane potential. Furthermore, cell-substrate impedance and viability assays showed that supplementing the culture media with TH compromises cell viability over time. Our results revealed that the disruptive effect of TH on cell membranes may be a cytotoxic and pathogenic factor if the regulation and intracellular stability of TH is compromised.

Abundant fish protein inhibits α-synuclein amyloid formation

The most common allergen in fish, the highly-abundant protein β-parvalbumin, forms amyloid structures as a way to avoid gastrointestinal degradation and transit to the blood. In humans, the same amyloid structures are mostly associated with neurodegenerative disorders such as Alzheimer’s and Parkinson’s. We here assessed a putative connection between these amyloids using recombinant Atlantic cod β-parvalbumin and the key amyloidogenic protein in Parkinson’s disease, α-synuclein. Using a set of in vitro biophysical methods, we discovered that β-parvalbumin readily inhibits amyloid formation of α-synuclein. The underlying mechanism was found to involve α-synuclein binding to the surface of β-parvalbumin amyloid fibers. In addition to being a new amyloid inhibition mechanism, the data suggest that health benefits of fish may be explained in part by cross-reaction of β-parvalbumin with human amyloidogenic proteins.

In vitro analysis of α-synuclein amyloid formation and cross-reactivity

In vitro time-resolved characterization of protein aggregation into amyloid fibers and the effects of other proteins on the aggregation process are fundamentally important measurements to obtain a better understanding of the mechanisms contributing to neurodegeneration, as well as other diseases involving amyloid formation. Here, we describe how to perform in vitro aggregation experiments with α-synuclein, the amyloidogenic protein involved in Parkinsons disease, including how to assess the starting material, useful experimental/instrumental conditions, as well as how to set up cross-seeding and co-aggregation experiments. The high variability of data reported for in vitro α-synuclein amyloid formation may in part be explained by experimental differences.

In Vitro Interactions Between Model Proteins and Amyloid Inhibitors

Protein folding is an essential requirement for most biological functions. Therefore, if folding of proteins can be specifically modulated, we have the power to tune/inhibit protein function, disease progression, and create novel analytical tools. This is an inter-disciplinary research project that aims to find small molecules that selectively modulate protein-folding reactions. The small molecules used in the study are bicyclic 2-pyridone derivatives . These compounds were originally designed to inhibit the assembly of bacterial pili, and are peptidomimetics that were directed to block the periplasmic chaperone PapD required for pilus biogenesis. A subgroup of these compounds are designed to inhibit the formation of curlin-based bacterial biofilms. Curlicides and pilicides thus are potential new antibiotics to fight bacterial infections. The curlicides bind the major curlin protein CsgA inhibiting its oligomerization into amyloid fibrils Moreover, some of these compounds have been found to inhibit β-amyloid peptide fibrillization. During the project we studied the interactions of some selected compounds with Pseudomas aureginosa azurin (beta-sheet model protein), Borrelia burgdorferi Vlse and human alpha-synuclein. We have found that two of the compounds we have studied, namely FNO75 and its fluorescently labelled analogue CB84 are interacting with VlsE directly, while binding to azurin occurs upon refolding of the protein after heat denaturation. Moreover, weve tested the effect of the compounds on alpha synuclein fibrillization. Surprisingly, it was found that FNO75, which is known to inhibit curli and beta-fibrillization was speeding up the aggregation of alpha synuclein.