Extracellular and intraneuronal HMW-AbetaOs represent a molecular basis of memory loss in Alzheimer's disease model mouse

Ayumi Takamura,Etsuro Matsubara,Naoki Yamamoto,Tsuneo Urisu,Akihiro Mouri,Takeshi Kawarabayashi,Toshitaka Nabeshima,Hui Sun,Masao Shibata,Yasuhide Okamoto,Tatsuki Yokoseki,Koji Abe,Mikio Shoji,Katsuhiko Yanagisawa,Makoto Michikawa

doi:10.1186/1750-1326-6-20

Abstract

BackgroundSeveral lines of evidence indicate that memory loss represents a synaptic failure caused by soluble amyloid β (Aβ) oligomers. However, the pathological relevance of Aβ oligomers (AβOs) as the trigger of synaptic or neuronal degeneration, and the possible mechanism underlying the neurotoxic action of endogenous AβOs remain to be determined.ResultsTo specifically target toxic AβOs in vivo, monoclonal antibodies (1A9 and 2C3) specific to them were generated using a novel design method. 1A9 and 2C3 specifically recognize soluble AβOs larger than 35-mers and pentamers on Blue native polyacrylamide gel electrophoresis, respectively. Biophysical and structural analysis by atomic force microscopy (AFM) revealed that neurotoxic 1A9 and 2C3 oligomeric conformers displayed non-fibrilar, relatively spherical structure. Of note, such AβOs were taken up by neuroblastoma (SH-SY5Y) cell, resulted in neuronal death. In humans, immunohistochemical analysis employing 1A9 or 2C3 revealed that 1A9 and 2C3 stain intraneuronal granules accumulated in the perikaryon of pyramidal neurons and some diffuse plaques. Fluoro Jade-B binding assay also revealed 1A9- or 2C3-stained neurons, indicating their impending degeneration. In a long-term low-dose prophylactic trial using active 1A9 or 2C3 antibody, we found that passive immunization protected a mouse model of Alzheimer's disease (AD) from memory deficits, synaptic degeneration, promotion of intraneuronal AβOs, and neuronal degeneration. Because the primary antitoxic action of 1A9 and 2C3 occurs outside neurons, our results suggest that extracellular AβOs initiate the AD toxic process and intraneuronal AβOs may worsen neuronal degeneration and memory loss.ConclusionNow, we have evidence that HMW-AβOs are among the earliest manifestation of the AD toxic process in mice and humans. We are certain that our studies move us closer to our goal of finding a therapeutic target and/or confirming the relevance of our therapeutic strategy.

Highlights

Several lines of evidence indicate that memory loss represents a synaptic failure caused by soluble amyloid b (Ab) oligomers
Generation of Ab oligomer-specific monoclonal antibodies Since the removal of AbMs is critical for the preparation of antigens to obtain Ab oligomers (AbOs)-specific antibodies, we isolated sodium dodecylsulphate (SDS)-stable Ab tetramers alone without any contamination of Ab trimers and AbMs by SDS-PAGE (Figure 1A)
Monoclonal 1A9 or 2C3 immunotherapy protects Tg2576 from memory impairment Using active 1A9 and 2C3 antibodies, we evaluated whether a specific control of endogenous AbOs in vivo would be sufficient to prevent the disruption of neuronal function leading to memory loss

Summary

Introduction

Several lines of evidence indicate that memory loss represents a synaptic failure caused by soluble amyloid b (Ab) oligomers. The steady-state level of Ab is controlled by the generation of Ab from its precursor, the degradation of Ab within the brain, and transport of Ab out of the form of Ab such as AbOs [9,10,11,12], rather than fibrillar Ab [7]. If this were the case, therapeutic intervention targeting AbOs may be effective in blocking this pathogenic cascade. A particular form of AbO, named the native amylospheroids [23], has been isolated from AD brains and found to induce neuronal loss through its binding to synaptic targets [24]

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Discussion

Conclusion