Amyloid Plaques Beyond Aβ: A Survey of the Diverse Modulators of Amyloid Aggregation

Aggregation of the amyloid-β (Aβ) peptide is strongly correlated with Alzheimer’s disease (AD). Recent research has improved our understanding of the kinetics of amyloid fibril assembly and revealed new details regarding different stages in plaque formation. Presently, interest is turning toward studying this process in a holistic context, focusing on cellular components which interact with the Aβ peptide at various junctures during aggregation, from monomer to cross-β amyloid fibrils. However, even in isolation, a multitude of factors including protein purity, pH, salt content, and agitation affect Aβ fibril formation and deposition, often producing complicated and conflicting results. The failure of numerous inhibitors in clinical trials for AD suggests that a detailed examination of the complex interactions that occur during plaque formation, including binding of carbohydrates, lipids, nucleic acids, and metal ions, is important for understanding the diversity of manifestations of the disease. Unraveling how a variety of key macromolecular modulators interact with the Aβ peptide and change its aggregation properties may provide opportunities for developing therapies. Since no protein acts in isolation, the interplay of these diverse molecules may differentiate disease onset, progression, and severity, and thus are worth careful consideration

The hairpin conformation of the Amyloid β peptide is a common structural motif along the aggregation pathway

Biophysical Structural Chemistr

Expression and Purification of Intrinsically Disordered Aβ Peptide and Setup of Reproducible Aggregation Kinetics Experiment

High purity and sequence homogeneity of intrinsically disordered proteins are prerequisites for reproducible studies of the kinetics and equilibrium of their self-assembly reactions. Starting from the pure state enables quantitative studies of intrinsic and extrinsic factors in the process to understand its molecular determinants. Here we outline detailed protocols for recombinant expression and purification of ultra-pure amyloid β peptide (Aβ) in sequence homogeneous form, which allows for the setup of reproducible kinetic self-assembly experiments

Spacecraft dynamic analysis and correlation with test results : Shock environment analysis of LISA Pathfinder at VESTA test bed

The particular study case in this thesis is the shock test performed on the LISA Pathfinder satellite conducted in a laboratory environment on a dedicated test bed: Vega Shock Test Apparatus (VESTA). This test is considered fully representative to study shock levels produced by fairing jettisoning event at Vega Launcher Vehicle, which induces high shock loads towards the satellite. In the frame of this thesis, some transient response analyses have been conducted in MSC Nastran, and a shock simulation tool for the VESTA test configuration has been developed. The simulation tool is based on Nastran Direct Transient Response Analysis solver (SOL 109), and is representative of the upper composite of Vega with the LISA Pathfinder coupled to it. Post-processing routines of transient response signals were conducted in Dynaworks which served to calculate Shock Response Spectra (SRS). The simulation tool is a model of forcing function parameters for transient analysis which adequately correlates with the shock real test data, in order to understand how the effect of shock generated by the launcher is seen in the satellite and its sub-systems. Since available computation resources are limited the parameters for analysis were optimised for computation time, file size, memory capacity,  and model complexity. The forcing function represents a release of the HSS clamp band which is responsible for fairing jettisoning, thus the parameters which were studied are mostly concerning the modelling of this event. Among many investigated, those which visibly improved SRS correlation are radial forcing function shape, implementation of axial impulse, clamp band loading geometry and refined loading scheme. Integration time step duration and analysis duration were also studied and found to improve correlation.  From each analysis, the qualifying shock environment was then derived by linear scaling in proportion of the applied preload, and considering a qualification margin of 3dB. Consecutive tracking of structural responses along shock propagation path exposed gradual changes in responses pattern and revealed an important property that a breathing mode (n = 0) at the base of a conical Adapter translates into an axial input to the spacecraft. The parametrisation itself was based on responses registered at interfaces located in near-field (where the clamp band is located and forcing function is applied) and medium-field with respect to the shock event location. Following shock propagation path, the final step was the analysis of shock responses inside the satellite located in a far-field region, which still revealed a very good correlation of results. Thus, it can be said that parametrisation process was adequate, and the developed shock simulation tool can be qualified. However, due to the nature of shock, the tool cannot fully replace VESTA laboratory test, but can support shock assessment process and preparation to such test. In the last part of the thesis, the implementation of some finite element model improvements is investigated. Majority of the panels in spacecraft interior exhibited shock over-prediction due to finite element model limitation. Equipment units modelled as lump masses rigidly attached with RBE2 elements to the panel surface are a source of such local over-predictions. Thus, some of the units were remodelled and transient responses were reinvestigated. It was found that remodelling with either solid elements, or lump mass connected to RBE3 element and reinforced by RBE2 element, can significantly improve local transient responses. This conclusion is in line with conclusions found in ECSS Shock Handbook

Characterization of Mn(II) ion binding to the amyloid-ß peptide in Alzheimer’s disease

Growing evidence links neurodegenerative diseases to metal exposure. Aberrant metal ion concentrationshave been noted in Alzheimer’s disease (AD) brains, yet the role of metals in AD pathogenesis remainsunresolved. A major factor in AD pathogenesis is considered to be aggregation of and amyloid formationby amyloid-ß (Aß) peptides. Previous studies have shown that Aß displays specific binding to Cu(II)and Zn(II) ions, and such binding has been shown to modulate Aß aggregation. Here, we use nuclearmagnetic resonance (NMR) spectroscopy to show that Mn(II) ions also bind to the N-terminal part ofthe Aß(1–40) peptide, with a weak binding affinity in the milli- to micromolar range. Circular dichroism(CD) spectroscopy, solid state atomic force microscopy (AFM), fluorescence spectroscopy, and molecularmodeling suggest that the weak binding of Mn(II) to Aß may not have a large effect on the peptide’saggregation into amyloid fibrils. However, identification of an additional metal ion displaying Aß bindingreveals more complex AD metal chemistry than has been previously considered in the literature