Pre-plaque conformational changes in Alzheimer’s disease-linked Aβ and APP

Abstract

Reducing levels of the aggregation-prone Aβ peptide that accumulates in the brain with Alzheimer's disease (AD) has been a major target of experimental therapies. An alternative approach may be to stabilize the physiological conformation of Aβ. To date, the physiological state of Aβ in brain remains unclear, since the available methods used to process brain tissue for determination of Aβ aggregate conformation can in themselves alter the structure and/or composition of the aggregates. Here, using synchrotron-based Fourier transform infrared micro-spectroscopy, non-denaturing gel electrophoresis and conformational specific antibodies we show that the physiological conformations of Aβ and amyloid precursor protein (APP) in brain of transgenic mouse models of AD are altered before formation of amyloid plaques. Furthermore, focal Aβ aggregates in brain that precede amyloid plaque formation localize to synaptic terminals. These changes in the states of Aβ and APP that occur prior to plaque formation may provide novel targets for AD therapy.

Super‐Resolution Infrared Imaging of Polymorphic Amyloid Aggregates Directly in Neurons

“…For the experiment, as a negative control for Aβ, we used APP knock‐out neurons derived from mice which lack the APP gene and therefore do not produce Aβ proteins 30. As another control, we used wild‐type mouse neurons which have the mouse APP gene and produce mouse Aβ which does not aggregate,22 these genetic modifications allowed us to study Aβ specific structural changes.…”

“…Primary neurons were seeded directly on 13 mm diameter and 1 mm thick CaF 2 spectrophotometric windows (Eksma Optics, Lithuania) and grown for 19 days. To avoid artificial β‐sheet formation, neurons were fixed with 4% paraformaldehyde in phosphate buffer saline for 15 min washed with 20 × 10 −3 m phosphate buffer (PB) and stored at −80 °C until measurements 22. µFTIR spectromicroscopy was performed at the SMIS beamline of the SOLEIL synchrotron (France) using a Thermo Fisher Scientific Continuum XL FTIR microscope through a 32× magnification, 0.65 NA Schwarzschild objective.…”

“…Another nondestructive, structure‐sensitive and, importantly, label‐free method that can be used for delineation of protein molecular structures in biological samples is Fourier‐transform infrared spectromicroscopy (μFTIR) 21. It has been shown that μFTIR can be used to detect β‐sheet structures in neurons thought to be associated with AD pathogenesis 22. µFTIR allows highly sensitive detection of β‐sheet structures,23 however, there are two main problems which limit its application for cellular studies.…”

Nanoscale Discrimination between Toxic and Nontoxic Protein Misfolded Oligomers with Tip‐Enhanced Raman Spectroscopy

“…Importantly, the molecular events leading to the formation of these species are supposed to appear 10–20 years before the symptoms become evident . Studies aimed at unraveling the relationship between structure and neurotoxicity of misfolded oligomers are thus pivotal in gaining insights into the pathological process, as well as in designing novel diagnostic and therapeutic strategies tuned toward the earliest and presymptomatic stages of the disease …”

Investigating Amyloid β toxicity in Drosophila melanogaste

“…demonstrated that the physiological conformation of Aβ is altered before the formation of amyloid plaques, and that the Aβ peptide initially exists as a β-sheet rich tetramer. These results suggests a novel therapeutic approach, where stabilization of the tetramer, similar to that of transthyretin (TTR) in transthyretin amyloidosis, could inhibit the oligomerization and toxic effects of Aβ [121].…”