Effects of Transmitters and Amyloid-Beta Peptide on Calcium Signals in Rat Cortical Astrocytes: Fura-2AM Measurements and Stochastic Model Simulations

BACKGROUND: To better understand the complex molecular level interactions seen in the pathogenesis of Alzheimer's disease, the results of the wet-lab and clinical studies can be complemented by mathematical models. Astrocytes are known to become reactive in Alzheimer's disease and their ionic equilibrium can be disturbed by interaction of the released and accumulated transmitters, such as serotonin, and peptides, including amyloid- peptides (A). We have here studied the effects of small amounts of A25-35 fragments on the transmitter-induced calcium signals in astrocytes by Fura-2AM fluorescence measurements and running simulations of the detected calcium signals. METHODOLOGY/PRINCIPAL FINDINGS: Intracellular calcium signals were measured in cultured rat cortical astrocytes following additions of serotonin and glutamate, or either of these transmitters together with A25-35. A25-35 increased the number of astrocytes responding to glutamate and exceedingly increased the magnitude of the serotonin-induced calcium signals. In addition to A25-35-induced effects, the contribution of intracellular calcium stores to calcium signaling was tested. When using higher stimulus frequency, the subsequent calcium peaks after the initial peak were of lower amplitude. This may indicate inadequate filling of the intracellular calcium stores between the stimuli. In order to reproduce the experimental findings, a stochastic computational model was introduced. The model takes into account the major mechanisms known to be involved in calcium signaling in astrocytes. Model simulations confirm the principal experimental findings and show the variability typical for experimental measurements. CONCLUSIONS/SIGNIFICANCE: Nanomolar A25-35 alone does not cause persistent change in the basal level of calcium in astrocytes. However, even small amounts of A25-35, together with transmitters, can have substantial synergistic effects on intracellular calcium signals. Computational modeling further helps in understanding the mechanisms associated with intracellular calcium oscillations. Modeling the mechanisms is important, as astrocytes have an essential role in regulating the neuronal microenvironment of the central nervous system

Omega-3 Fatty Acids Regulate the Interaction of the Alzheimer’s Aβ(25–35) Peptide with Lipid Membranes

Poly-unsaturated omega-3 fatty acids are increasingly proposed as dietary supplements able to reduce the risk of development or progression of the Alzheimer's disease (AD). To date, the molecular mechanism through which these lipids act has not been yet univocally identified. In this work, we investigate whether omega-3 fatty acids could interfere with the fate of the Alzheimer-related amyloid peptide by tuning the microstructural and dynamical properties of the neuronal membrane. To this aim, the influence of the omega-3 lipid 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine (22:6(cis)PC) on the biophysical properties of lipid bilayers and on their interaction with the amyloid peptide fragment Aβ(25-35) has been investigated by Electron Spin resonance (ESR), using spin-labeled phospholipids. The results show that the peptide selectively interacts with bilayers enriched in cholesterol (Chol) and sphingomyelin (SM). (22:6(cis)PC) enhances the Aβ(25-35)/membrane interaction, favouring a deeper internalization of the peptide among the lipid acyl chains, and consequently hindering its pathogenic self-aggregation

Conformational analysis of a glycosylated human myelin oligodendrocyte glycoprotein peptide epitope able to detect antibody response in multiple sclerosis.

Myelin oligodendrocyte glycoprotein (MOG), a minor myelin component, is an important central nervous system specific target autoantigen for primary demyelination in autoimmune diseases such as multiple sclerosis (MS). The native structure of MOG presents a glycosylation site at position 31 (Asn(31)). It has been recently described that glycosylation of a MOG peptide epitope improved the detection of specific autoantibodies in sera of MS patients. The solution conformational behavior of two MOG derived peptides-hMOG(30-50) (1) and the glycosylated analogue [Asn(31)(N-beta -Glc)]hMOG(30-50) (2)-were investigated through NMR analysis in a water/HFA solution. Conformational studies revealed that peptides 1 and 2 adopted similar conformations in this environment. In particular, they showed strong propensity to assume a well-defined amphipatic structure encompassing residues 41-48. The N-terminal region resulted to be almost completely unstructured for both peptides. The presence in 1 of a low populated Asx-turn conformation characteristic of the Asn-Xaa-Thr glycosylation sites was the only conformational difference between peptides 1 and 2. Thus, the specific antibody recognition of peptide 2 is most likely driven by direct interactions of the antibody binding site with the Asn-linked sugar moiety

Solution structure of amyloid beta-peptide (25-35) in different media.

The design of molecules able to interact with the amyloid peptides either as inhibitors of fibril formation or as inhibitors of amyloid membrane pore formation represents one of the most relevant approaches in the development of anti-Alzheimer therapies. Aâ-(25-35), sequence GSNKGAIIGLM, is a highly toxic synthetic derivative of amyloid â-peptides (Aâ-peptides), which forms fibrillary aggregates. Here, we report the NMR and CD investigation of Aâ-(25-35) in a membrane-mimicking environment and in isotropic mixtures of water and fluoroalcohols to scan its conformational properties as a function of the medium. The analysis of the 3D structures in the mentioned conditions indicates a propensity of the peptide to behave as a typical transmembrane helix in the lipidic environment. In media characterized by different polarity, it loses the structural regularity at specific points of the sequence as a function of the environment. Furthermore, a comparison with the solution structure of full-length amyloid peptides suggests a role for the 25-27 kink region, which appears to be a general feature of all peptides under the solution conditions explored

Solution structure of the Alzheimer amyloid beta-peptide (1-42) in an apolar microenvironment - Similarity with a virus fusion domain

The major components of neuritic plaques found in Alzheimer disease (AD) are peptides known as amyloid b-peptides (Ab),whic h derive from the proteolitic cleavage of the amyloid precursor proteins. In vitroAb may undergo a conformational transition from a soluble form to aggregated, fibrillary b-sheet structures,which seem to be neurotoxic. Alternatively,it has been suggested that an a-helical form can be involved in a process of membrane poration, which would then trigger cellular death. Conformational studies on these peptides in aqueous solution are complicated by their tendency to aggregate, and only recently NMR structures of Ab-(1–40) and Ab-(1–42) have been determined in aqueous trifluoroethanol or in SDS micelles. All these studies hint to the presence of two helical regions,connected through a flexible kink,but it proved difficult to determine the length and position of the helical stretches with accuracy and, most of all,to ascertain whether the kink region has a preferred conformation. In the search for a medium which could allow a more accurate structure determination,we performed an exhaustive solvent scan that showed a high propensity of Ab-(1–42) to adopt helical conformations in aqueous solutions of fluorinated alcohols. The 3D NMR structure of Ab-(1–42) shows two helical regions encompassing residues 8–25 and 28–38,connected by a regular type I b-turn. The surprising similarity of this structure,as well as the sequence of the C-terminal moiety,with those of the fusion domain of influenza hemagglutinin suggests a direct mechanism of neurotoxicit