Large Fatty Acid-Derived Aβ42 Oligomers Form Ring-Like Assemblies

As the primary toxic species in the etiology of Alzheimer disease (AD) are low molecular weight oligomers of Aβ, it is crucial to understand the structure of Aβ oligomers for gaining molecular insights into AD pathology. We have earlier demonstrated that in the presence of fatty acids, Aβ42 peptides assemble as 12-24mer oligomers. These Large Fatty Acid-derived Oligomers (LFAOs) exist predominantly as 12mers at low and as 24mers at high concentrations. The 12mers are more neurotoxic than the 24mers and undergo self-replication, while the latter propagate to morphologically distinct fibrils with succinct pathological consequences. In order to glean into their functional differences and similarities, we have determined their structures in greater detail by combining molecular dynamic simulations with biophysical measurements. We conjecture that the LFAO are made of Aβ units in an S-shaped conformation, with the 12mers forming a double-layered hexamer ring (6 × 2) while the structure of 24mers is a double-layered dodecamer ring (12 × 2). A closer inspection of the (6 × 2) and (12 × 2) structures reveals a concentration and pH dependent molecular reorganization in the assembly of 12 to 24mers, which seems to be the underlying mechanism for the observed biophysical and cellular properties of LFAOs

Biophysical Characteristics of Lipid-Induced Aβ Oligomers Correlate to Distinctive Phenotypes In Transgenic Mice

Alzheimer\u27s disease (AD) is a progressive neurodegenerative disorder that affects cognition and memory. Recent advances have helped identify many clinical sub-types in AD. Mounting evidence point toward structural polymorphism among fibrillar aggregates of amyloid-β (Aβ) to being responsible for the phenotypes and clinical manifestations. In the emerging paradigm of polymorphism and prion-like propagation of aggregates in AD, the role of low molecular weight soluble oligomers, which are long known to be the primary toxic agents, in effecting phenotypes remains inconspicuous. In this study, we present the characterization of three soluble oligomers of Aβ42, namely 14LPOs, 16LPOs, and GM1Os with discreet biophysical and biochemical properties generated using lysophosphatidyl glycerols and GM1 gangliosides. The results indicate that the oligomers share some biophysical similarities but display distinctive differences with GM1Os. Unlike the other two, GM1Os were observed to be complexed with the lipid upon isolation. It also differs mainly in detection by conformation-sensitive dyes and conformation-specific antibodies, temperature and enzymatic stability, and in the ability to propagate morphologically-distinct fibrils. GM1Os also show distinguishable biochemical behavior with pronounced neuronal toxicity. Furthermore, all the oligomers induce cerebral amyloid angiopathy (CAA) and plaque burden in transgenic AD mice, which seems to be a consistent feature among all lipid-derived oligomers, but 16LPOs and GM1Os displayed significantly higher effect than the others. These results establish a correlation between molecular features of Aβ42 oligomers and their distinguishable effects in transgenic AD mice attuned by lipid characteristics, and therefore help bridge the knowledge gap in understanding how oligomer conformers could elicit AD phenotypes

Robust and ultrasensitive polymer membrane-based carbonate-selective electrodes

Quantitative analysis of the carbonate species within clinical and environmental samples is highly critical to the advancement of accurate environmental monitoring, disease screening, and personalized medicine. Herein we report the first example of carbonate detection using ultrasensitive ion selective electrodes (ISEs). The low detection limit (LDL) of these electrodes was at least 4 orders of magnitude lower than the best currently existing carbonate sensors. This was achieved by a simple alteration of the sensor's conditioning protocol. This resulted in the reduction of ion fluxes across the membrane interface consequently lowering the LDL to picomolar levels. The proposed ISEs exhibited near-Nernstian potentiometric responses to carbonate ions with a detection limit of 80 pmol L(-1) (5 ppt) and was utilized for direct determination of carbonate in seawater. Moreover, the new methodology has produced electrodes with excellent reproducibility, robustness, and durability. It is anticipated that this approach may form the basis for the development of highly sensitive and robust ion selective electrodes capable of in situ measurements

Architecture of Hydrated Multilayer Poly(methacrylic acid) Hydrogels: The Effect of Solution pH

We report on the evolution of the internal structure of dry and hydrated poly(methacrylic acid) (PMAA) hydrogels by quantifying the extent of layer interdiffusion in hydrogen-bonded (HB) films and upon subsequent cross-linking and hydration. These hydrogels are produced by ethylenediamine (EDA)-assisted cross-linking of PMAA in spin-assisted (SA) and dipped HB PMAA/poly(N-vinylpyrrolidone) (PVPON) multilayers followed by complete release of PVPON at pH 8 due to severing of hydrogen bonds with the PMAA network. Internal hydrogel architecture was monitored by neutron reflectometry using deuterated dPMAA marker layers. We found that even in the highly stratified SA HB films, layer interdiffusion extends over three (PMAA/PVPON) bilayers. Cross-linking of this film induces marker layer interpenetration more deeply into the surrounding material, extending over five layers. The volume fraction of dPMAA at the nominal center of a marker layer decreased from 0.65 to 0.51 after cross-linking. Hydrated SA hydrogels preserve well-organized layering and exhibit a persistent differential swelling with two distinct swelling ratios corresponding to MAA cross-link-rich and cross-link-poor strata. In contrast, layer organization in dipped films decays rapidly with distance from the silicon substrate. Both types of hydrogel swelled by factors of two and four times their dry total thicknesses at pH 5 and 7, respectively, and exhibited elevated surface roughness upon hydration. To fit the neutron reflectometry data, a self-consistent model was developed wherein the amount of PMAA initially deposited was preserved through subsequent chemical modification and hydration. Our results open opportunities for the development of thin hydrogels with a regulated structure, which can be utilized for efficient sensing, protection, activation, and rapid response in an aqueous environment. The internal morphological hierarchy of these multilayer hydrogels affords a means of fine-tuning their response to pH, temperature, or light to a degree rarely possible for randomly cross-linked responsive networks or brushes

Cationic Glycopolyelectrolytes for RNA Interference in Tick Cells

The black-legged tick (Ixodes scapularis) is the primary vector for bacteria that cause Lyme disease (Borrelia burgdorferi), where numerous glycosylated tick proteins are involved at the interface of vector–host–pathogen interactions. Reducing the expression of key tick proteins, such as selenoprotein K (SelK), through RNA interference is a promising approach to reduce pathogen transmission, but efficient delivery of nucleic acids to arthropods has proven challenging. While cationic glycopolymers have been used as nonviral gene delivery vehicles in mammalian cells, their use in arthropod or insect gene transfection has not been established. In this study, statistical acrylamide-based cationic glycopolymers with glucose or galactose pendant groups were synthesized by reversible addition–fragmentation chain transfer polymerization, and the effects of the saccharide pendant group and cationic monomer loading on polymer cytotoxicity, RNA complexation, and SelK gene knockdown in ISE6 cells were evaluated. All polymers exhibited low cytotoxicity, yet RNA/copolymer complex cell uptake and gene knockdown were highly dependent on the saccharide structure and the N:P (amino to phosphate groups) ratio