Emilie Cerf

Antiparallel beta-sheet: a signature structure of the oligomeric amyloid beta-peptide

AD (Alzheimers disease) is linked to Abeta (amyloid beta-peptide) misfolding. Studies demonstrate that the level of soluble Abeta oligomeric forms correlates better with the progression of the disease than the level of fibrillar forms. Conformation-dependent antibodies have been developed to detect either Abeta oligomers or fibrils, suggesting that structural differences between these forms of Abeta exist. Using conditions which yield well-defined Abeta-(1-42) oligomers or fibrils, we studied the secondary structure of these species by ATR (attenuated total reflection)-FTIR (Fourier-transform infrared) spectroscopy. Whereas fibrillar Abeta was organized in a parallel beta-sheet conformation, oligomeric Abeta displayed distinct spectral features, which were attributed to an antiparallel beta-sheet structure. We also noted striking similarities between Abeta oligomers spectra and those of bacterial outer membrane porins. We discuss our results in terms of a possible organization of the antiparallel beta-sheets in Abeta oligomers, which may be related to reported effects of these highly toxic species in the amyloid pathogenesis associated with AD.

Transformation of amyloid β(1-40) oligomers into fibrils is characterized by a major change in secondary structure.

Alzheimer’s disease (AD) is a neurodegenerative disorder occurring in the elderly. It is widely accepted that the amyloid beta peptide (Aβ) aggregation and especially the oligomeric states rather than fibrils are involved in AD onset. We used infrared spectroscopy to provide structural information on the entire aggregation pathway of Aβ(1–40), starting from monomeric Aβ to the end of the process, fibrils. Our structural study suggests that conversion of oligomers into fibrils results from a transition from antiparallel to parallel β-sheet. These structural changes are described in terms of H-bonding rupture/formation, β-strands reorientation and β-sheet elongation. As antiparallel β-sheet structure is also observed for other amyloidogenic proteins forming oligomers, reorganization of the β-sheet implicating a reorientation of β-strands could be a generic mechanism determining the kinetics of protein misfolding. Elucidation of the process driving aggregation, including structural transitions, could be essential in a search for therapies inhibiting aggregation or disrupting aggregates.

High ability of apolipoprotein E4 to stabilize amyloid-β peptide oligomers, the pathological entities responsible for Alzheimer's disease

Nowadays, the emerging role of amyloid‐β peptide (Aβ) oligomers in Alzheimers disease (AD) is widely accepted, putting aside the old idea that fibrils are the primary entities responsible for the onset of the disease. Besides, carrying the E4 isoform of apolipoprotein E (apoE) represents the highest risk of developing AD. Nevertheless, the involvement of apoE4 in AD remains confusing. The goal of this study was to bring new insights into the role of apoE4 in Aβ aggregation. We used infrared spectroscopy, thioflavin T fluorescence, and Western blots to evaluate the influence of apoE isoforms on Aβ aggregation in vitro. Comparing Aβ controls with Aβ incubated either with the apoE3 or apoE4 isoform, we report a 30% reduction of the Aβ fibrillar content, whereas the oligomeric content is 2 times higher on incubation with the pathological isoform apoE4. ApoE4 would bind and block Aβ in its oligomeric conformation, inhibiting further formation of less toxic fibrillar forms of Aβ. While previous studies mostly correlated E4 with fibrils, our report underlines a link between apoE4 and Aβ oligomers and therefore reconciles apoE4 with the new amyloid cascade hypothesis. Our observations suggest that apoE4 strongly stabilizes Aβ oligomers, the pathological species responsible for Alzheimers disease.—Cerf, E., Gustot, A., Goormaghtigh, E., Ruysschaert, J.‐M., Raussens, V. High ability of apolipoprotein E4 to stabilize amyloid‐β peptide oligomers, the pathological entities responsible for Alzheimers disease. FASEB J. 25, 1585–1595 (2011). www.fasebj.org

ATR–FTIR, a new tool to analyze the oligomeric content of Aβ samples in the presence of apolipoprotein E isoforms

Alzheimers disease (AD) is a neurodegenerative disorder caused by the aggregation of the amyloid-beta peptide (Aβ), leading to amyloid plaques deposition in the brain. Although Aβ aggregation pathway still remains unclear, recent studies point out the enhanced toxicity of oligomers compared to fibrils. The E4 isoform of apolipoprotein E (ApoE) is the major risk factor in AD as people carrying one e4 allele have significantly higher chances to develop the disease. Nevertheless, this phenomenon is still poorly understood. Our group has shown that attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) could discriminate between Aβ42 oligomers and fibrils. Indeed, oligomers display anti-parallel β-sheet spectral components while fibrils are characterized by a parallel β-sheet organization. Using those spectral features to analyze the oligomeric content of our samples, we studied the influence of ApoE on Aβ42 aggregation. Our experiments demonstrated that ApoE3 increased the amount of Aβ42 oligomers in the sample. We can thus determine the proportion of Aβ oligomers in the presence of another compound in the sample. We plan to use ATR-FTIR to assess the effects of the other isoforms of ApoE on Aβ aggregation. Moreover, this could be extended to study the influence of other molecules or proteins on Aβ aggregation.

A low-cost timing device for increasing the versatility of physiological stimulators ☆

Abstract A versatile and inexpensive timing device suitable for driving standard stimulators and associated equipment used in neurophysiological experiments is described. Using this device as a building block, systems generating relatively complex stimulation patterns may easily be assembled. It delivers, as required, a square gate pulse of variable duration (1 msec-2 min), a brief trigger pulse with an adjustable delay (1 msec-2 min), or repetitive pulses at a variable frequency (0.005–600 Hz). The output voltage is adequate for triggering or modulating commercial stimulators, including older but still widely used vacuum-tube models. The device itself can be controlled by external signals.

A holder for rapid filling of micropipette electrodes by centrifugal action

SummaryA holder has been designed to house a glass micropipette for highspeed spinning in a centrifuge. Using this device, fine-tipped microelectrodes can be filled individually with the desired electrolyte, within minutes after their fabrication.

Aggregation of the Aβ(1-40) peptide: Secondary structure change from oligomers to fibrils

age matched controls) and individuals with TBI (survival time 0-24 hours n 1⁄4 18, 1-28 days, n 1⁄4 6, 1-32 years n 1⁄4 13) underwent 4G8 immunohistochemistry to detect amyloidb and AT8 immunostaining to detect neurofibrillary tangles. Sections underwent semi-quantitative assessment of intraneuronal amyloid and tau immunostaining using a scoring system of 0-3 in the dentate gyrus, CA4, CA3, CA1 and subiculum. Results: Intraneuronal amyloid was detected in both control cases and in response to mild brain injury. There was a significant increase in intraneuronal amyloid in all fields of the hippocampus in the TBI cases compared with controls (p1⁄4 0.0027 -0.0135). Intense immunostaining (grade 3) was present in 0-15% of control cases and 45-55% of TBI cases. Intraneuronal amyloid increased with increasing survival time following TBI and was most extensive in individuals who survived longest after injury (p 1⁄4 0.0035 0.0087 compared to controls). There was no evidence of increased neurofibrillary tangles in the head injury as compared to controls. Conclusions: This study indicates that mild brain injury is sufficient to induce alterations in amyloid and highlights the need to understand more about the mechanisms by which injury can lead to AD.

High Ability of ApoE4 to Interfere with Aβ Aggregation

Introduction: The aggregation of the amyloid-beta peptide (Aβ) is most probably the early event in Alzheimers disease (AD) that subsequently leads to amyloid plaques deposition in the brain. The ε4 allele of apolipoprotein E (ApoE) gene is the major known genetic risk factor associated with late onset AD. A few mechanisms underlying this pathogenic nature have been identified. Nevertheless, none of them have been completely elucidated.

A simple device for driving the Grass oscilloscope recording camera by electrical signals.

The device described is a simple circuit functioning as a normally open switch controllable by electrical signals. It has several modes of operation, permitting full use of the different capabilities of the C4 camera (single frames, repetitive frames, moving film). Depending on the mode, either short triggering pulses or rectangular gating signals of adjustable duration are needed for driving the circuit. A square wave stimulator, for instance, can be used to deliver the appropriate signals.