Amyloid beta (Abeta) has been strongly implicated in inducing neurotoxicity in the pathology of Alzheimer's disease (AD). However, the underlying mechanisms remain unknown. In this study, we examined, in real-time, the spatio-temporal changes in individual model membranes induced by the presence of different Abeta-40 molecular assemblies (species). We used cell-sized lipid vesicles to enable the direct observation of these changes. We found three significantly different membrane-transformation pathways. We characterized the biophysical mechanisms behind these transformations in terms of the change in inner vesicle volume and surface area. Oligomeric Abeta exhibited the highest tendency to cause membrane fluctuation and transformations. Interestingly, mature fibrils, which are often considered inert species, also induced profound membrane changes. Furthermore, we imaged the localization of pre-fibrillar species on membranes. The real-time observation of these morphological transformations, which can be missed in a discretised analysis, may help to unlock the mechanisms of AD's Abeta-induced neuro-degeneration.
" to GUVs in the form of fluctuations , tubular and bead protrusions , release of intravesicular GUVs and formation of sphero - stomatocytes , which previous studies attributed to increased membrane fluidity in the case of stilbenes , octaethyleneglycol dodecylether , and amyloid beta peptides in the presence of oxysterols ( Mavcic et al . , 2004 ; Morita et al . , 2010 ; Phan et al . , 2013 ) ( Figure 6 and Supporting Video ) . Structural changes of GUVs in the presence of isoeugenol therefore contradicts structural changes of GUVs exposed to rigidifying molecules like flavonoids , which cause aggregation , endo - budding , and bursting with subsequent release of daughter vesicles or release of small "
[Show abstract][Hide abstract] ABSTRACT: Isoeugenol is an essential oil constituent of nutmeg, clove, and cinnamon. Despite isoeugenol's promising antimicrobial activity, no studies have yet investigated its mode of antibacterial action at the molecular level. The aim of this study is to clarify isoeugenol's antibacterial mode of action using the Gram-negative and Gram-positive model organisms Escherichia coli and Listeria innocua, respectively. We determined the antimicrobial activity of isoeugenol against the model organisms, and examined how isoeugenol affects cell morphology, cell membrane permeabilization, and how isoeugenol interacts with phospholipid membranes using vesicle and supported lipid bilayer models. Isoeugenol demonstrated a bactericidal activity against E. coli and L. innocua that did not affect cell morphology, although the cell membrane was permeabilized. We hypothesized that the cell membrane was the primary site of action, and studied this interaction in further detail using purified membrane model systems. Isoeugenol's permeabilization of calcein-encapsulated vesicles was concentration dependent, and isoeugenol's interaction with giant unilamellar vesicles indicated increased membrane fluidity and a non-disruptive permeabilization mechanism. This contradicted membrane fluidity measurements on supported lipid bilayers (SLBs), which indicated decreased membrane fluidity. However, further investigations demonstrated that the interaction between isoeugenol and bilayers was reversible, and caused membranes to display heterogeneous topography, an increased mass, and a higher degree of hydration. In conclusion, we propose that isoeugenol interacts with membranes in a reversible non-disruptive detergent-like manner, which causes membrane destabilization. Furthermore, we argue that isoeugenol increases membrane fluidity. Our work contributes to the understanding of how essential oil constituents interact with cell components.
Frontiers in Microbiology 08/2015; 6:754. DOI:10.3389/fmicb.2015.00754 · 3.99 Impact Factor
"Aβ was introduced into liposome-containing solution at the final concentration of 1 μM dissolved in Tris buffer (0.5 mM). This concentration of Tris buffer has been shown not to influence membrane stability . 5 μL of liposome solution and Aβ solution was mixed, then transferred immediately in a circular silicone well (0.1 mm) placed on a glass slide, and covered with a glass cover. "
[Show abstract][Hide abstract] ABSTRACT: The interaction of amyloid beta (Aβ) peptide with cell membranes has been shown to be influenced by Aβ conformation, membrane physicochemical properties and lipid composition. However, the effect of cholesterol and its oxidized derivatives, oxysterols, on Aβ-induced neurotoxicity to membranes is not fully understood. We employed here model membranes to investigate the localization of Aβ in membranes and the peptide-induced membrane dynamics in the presence of cholesterol and 7-ketocholesterol (7keto) or 25-hydroxycholesterol (25OH). Our results have indicated that oxysterols rendered membranes more sensitive to Aβ, in contrast to role of cholesterol in inhibiting Aβ/membranes interaction. We have demonstrated that two oxysterols had different impacts owing to distinct positions of the additional oxygen group in their structures. 7keto-containing cell-sized liposomes exhibited a high propensity toward association with Aβ, while 25OH systems were more capable of morphological changes in response to the peptide. Furthermore, we have shown that 42 amino acid Aβ (Aβ-42) pre-fibril species had higher association with membranes, and caused membrane fluctuation faster than 40 residue isoform (Aβ-40). These findings suggest the enhancing effect of oxysterols on interaction of Aβ with membranes and contribute to clarify the harmful impact of cholesterol on Aβ-induced neurotoxicity by means of its oxidation.
"Aβ-peptides were added to lipid vesicles to a final concentration of 2 μM, and visualized using a phase-contrast microscopy (Olympus BX-51, Japan). Membrane vesicular responses were captured in real-time at 30 frames/s . Using an oil-in-water micro-droplet system , lipid organization in the droplet section were observed using a laser confocal microscopy (Olympus FV-1000, Japan) at RT. Diodelasers (473 nm) were used to excite fluorescence labeled Aβ, 488-Aβ, respectively. "
[Show abstract][Hide abstract] ABSTRACT: Amyloid beta (Aβ) peptides, produced through endo-proteolytic cleavage of amyloid precursor protein, are thought to be involved in the death of neural cells in Alzheimer's disease (AD). Although the mechanisms are not full known, it has been suggested that disruption of cellular activity due to Aβ interactions with the cell membrane may be one of the underlying causes. Here in, we have investigated the interaction between Aβ-42 and biomimetic lipid membranes and the resulting perturbations in the lipid vesicles. We have shown that Aβ oligomeric species localized closer to the membrane surface. Localization of the fibrillar species of Aβ-42, although varied, was not as closely associated with the membrane surface was varied. We have demonstrated that the presence of Aβ-42 lead to an increase in membrane surface area, inducing lipid temporal vesicular transformation. Furthermore, we have unequivocally shown revealed that Aβ-peptides mediate membrane fusion. Although membrane fusion induced by Aβ has been hypothesized/proposed, this is the first time it has been visually captured. This fusion may be one of the mechanisms behind the membrane increase is surface area and the resulting vesicular transformation. We have shown that the longer more 'amyloidogenic' isoform causes vesicular transformation more readily, and has a higher membrane fusogenic potential than Aβ-40. Although not core to this study, it is hugely interesting to observe the high agreement between membrane dynamics and the reported amyloidogenicity of the peptides and aggregation species _opening up the potential role of vesicular dynamics for profiling and biosensing of Aβ-induced neuro-toxicity.
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