Changes in lipid membranes may trigger amyloid toxicity in Alzheimer's disease

Amyloid beta peptides (A\b{eta}), implicated in Alzheimers disease (AD), interact with the cellular membrane and induce amyloid toxicity. The composition of cellular membranes changes in aging and AD. We designed multi component lipid models to mimic healthy and diseased states of the neuronal membrane. Using atomic force microscopy (AFM), Kelvin probe force microscopy (KPFM) and black lipid membrane (BLM) techniques, we demonstrated that these model membranes differ in their nanoscale structure and physical properties, and interact differently with A\b{eta}. Based on our data, we propose a new hypothesis that changes in lipid membrane due to aging and AD may trigger amyloid toxicity through electrostatic mechanisms, similar to the accepted mechanism of antimicrobial peptide action. Understanding the role of the membrane changes as a key activating amyloid toxicity may aid in the development of a new avenue for the prevention and treatment of AD

Effect of Surfaces on Amyloid Fibril Formation

Using atomic force microscopy (AFM) we investigated the interaction of amyloid beta (Aβ) (1–42) peptide with chemically modified surfaces in order to better understand the mechanism of amyloid toxicity, which involves interaction of amyloid with cell membrane surfaces. We compared the structure and density of Aβ fibrils on positively and negatively charged as well as hydrophobic chemically-modified surfaces at physiologically relevant conditions. We report that due to the complex distribution of charge and hydrophobicity amyloid oligomers bind to all types of surfaces investigated (CH3, COOH, and NH2) although the charge and hydrophobicity of surfaces affected the structure and size of amyloid deposits as well as surface coverage. Hydrophobic surfaces promote formation of spherical amorphous clusters, while charged surfaces promote protofibril formation. We used the nonlinear Poisson-Boltzmann equation (PBE) approach to analyze the electrostatic interactions of amyloid monomers and oligomers with modified surfaces to complement our AFM data

IL-8 as mediator in the microenvironment-leukaemia network in acute myeloid leukaemia

The bone marrow microenvironment is physiologically hypoxic with areas being as low as 1% O-2, e.g. the stem cell niche. Acute myeloid leukaemia (AML) blasts misuse these bone marrow niches for protection by the local microenvironment, but also might create their own microenvironment. Here we identify IL-8 as a hypoxia-regulated cytokine in both AML cell lines and primary AML samples that is induced within 48 hours of severe hypoxia (1% O2). IL-8 lacked effects on AML cells but induced migration in mesenchymal stromal cells (MSC),an integral part of the bone marrow. Accordingly, MSC were significantly increased in AML bone marrow as compared to healthy bone marrow. Interestingly, mononuclear cells obtained from healthy bone marrow displayed both significantly lower endogenous and hypoxia-induced production of IL-8. IL-8 mRNA expression in AML blasts from 533 patients differed between genetic subgroups with significantly lower expression of IL-8 in acute promyelocytic leukaemia (APL),while in non APL-AML patients with FLT ITD had the highest IL-8 expression. In this subgroup, high IL-8 expression was also prognostically unfavourable. In conclusion, hypoxia as encountered in the bone marrow specifically increases IL-8 expression of AML, which in turn impacts niche formation. High IL-8 expression might be correlated with poor prognosis in certain AML subsets

Significance of Frequencies, Compositions, and/or Antileukemic Activity of (DC-stimulated) Invariant NKT, NK and CIK Cells on the Outcome of Patients With AML, ALL and CLL

Invariant natural killer T (iNKT)/natural killer (NK)/cytokine-induced killer (CIK) cells are important for immune surveillance. (I) Novel combinations of antibody 6B11 (targeting the V alpha 24-J alpha 18-invariant T-cell receptor) with CD4/CD8/CD1d/V alpha 24 for iNKT subset detection and "T/NK cell-like"-iNKT subsets were defined. Compared with healthy peripheral blood mononuclear cells (MNC) (significantly) lower proportions of iNKT cells (6B11 (+)/6B11 (+)CD3 (+)/6B11 (+)CD161(+)), NK cells (CD3(-)CD56(+)/CD3(-)CD161(+)), and CIK cells (CD3(+)CD56(+)/CD3(+)CD161(+)) were found in peripheral blood MNC from acute myeloid (AML)/acute myeloid, lymphoid (ALL)/chronic lymphoid leukemia (CLL) patients in acute disease stages. Subtyping of iNKT cells revealed (significantly) higher proportions of CD3(+) T cells and CD161(+) NK cells in AML/ALL/CLL expressing 6B11 compared with healthy MNC. Prognostic evaluations showed higher proportions of iNKT/NK/CIK cells in favorable AML subgroups (younger age, primary, no extramedullary disease, achievement/maintenance of complete remission) or adult ALL and CLL patients. (II) iNKT/NK/CIK cell frequencies increased after (vs. before) mixed lymphocyte cultures of T-cell-enriched immune reactive cells stimulated with MNC/whole blood with or without pretreatment with "cocktails" (dendritic cells generating methods/kits inducing blasts' conversion to leukemia-derived dendritic cells from AML patients). Individual "cocktails" leading to "highest" iNKT cell frequencies could be defined. Antileukemic blast lytic activity correlated significantly with frequencies of iNKT/NK/CIK cells. In summary healthy MNC show significantly more iNKT/NK/CIK cells compared with AML/ALL/CLL MNC, a shift in the iNKT cell composition is seen in healthy versus leukemic samples and iNKT/NK/CIK cell-proportions in AML/ALL/CLL MNC samples correlate with prognosis. "Cocktail"-treated AML blasts lead to higher iNKT/NK/CIK cell frequencies and samples with antileukemic activity show significantly higher frequencies of iNKT/NK/CIK cells. Proportions of iNKT/NK/CIK cells should regularly be evaluated in AML/ALL/CLL diagnosis panels for quantitative/prognostic estimation of individual patients' anti leukemic potential and their role in dendritic cells/leukemia-derived dendritic cells triggered immune surveillance

Biophysical Studies of Lipid Membranes and their Interactions with Amyloid Peptides

Amyloid beta peptides are known to form amyloid fibrils which are implicated in more than 20 currently incurable neurodegenerative diseases, including Alzheimer’s, Huntington’s and Parkinson’s. The proposed mechanism of amyloid fibril formation involves protein unfolding and formation of amyloid β-sheet aggregates. Although fibril plaque formation is associated with biological membranes in vivo, the role of membrane heterogeneity - and especially the effect of cholesterol and lipid rafts - in the process of amyloid fibril formation and toxicity is not well understood. Therefore, research in this area is of great interest and necessity. Cholesterol is a well-known sterol, which is found in eukaryotic membranes and is important for membrane structure and function. It has been shown that an increased level of cholesterol may lead to various disorders. It is my hypothesis that cholesterol may alter the interaction of plasma membrane with membrane-interacting biomolecules such as amyloid beta and may play an important role in amyloid toxicity. In this thesis, I used multiple methods of investigation, including neutron scattering, atomic force microscopy, the Langmuir-Blodgett trough, and frequency modulated-Kelvin probe force microscopy, to study both simple and complex lipid systems. The thesis is organized in such a way that it begins with looking at the simple systems of a single to a few lipids and proceed to examine more complex systems, with multiple constituents. Through these methods, it was found that cholesterol and melatonin have opposite effects on altering membrane thickness. Lipid properties like head group charge and lipid phase were shown to define the size and the amount of amyloid clusters when incubated on single lipid systems, and the presence of cholesterol resulted in cholesterol-induced electrostatic domains that can cause targeted binding of amyloid. It was also shown that cholesterol has measureable effects on membrane properties even in systems more complex than just a single lipid. Finally, through the development of specific membrane models, it was shown that the models differed in properties and also had differential interactions with amyloid in terms of electrophysiology and amyloid accumulation. The goal of this thesis is to investigate the nanoscale effects of both cholesterol, and the interactions of lipids in complex mixtures on the physical and electrical properties of model lipid membranes, especially nanoscale heterogeneity of the membrane and membrane domains, and how these altered properties affect binding of Aβ and amyloid fibril formation on the surface of lipid membranes. The results will help to understand the role of membrane nanoscale heterogeneity in the molecular mechanism of amyloid toxicity and therefore will help towards the development of new approaches for the prevention and treatment of neurodegenerative diseases.1 yea