Structural Dynamics of Amyloid-β Protofibrils and Actions of Anti-Amyloid-β Antibodies as Observed by High-Speed Atomic Force Microscopy

Lecanemab-Associated Amyloid-β Protofibril in Cerebrospinal Fluid Correlates with Biomarkers of Neurodegeneration in Alzheimer's Disease

OBJECTIVE

The Clarity AD phase III trial showed that lecanemab reduced amyloid markers in early Alzheimer's disease (AD) and resulted in less decline on measures of cognition and function than placebo. Herein, we aimed to characterize amyloid-β (Aβ) protofibril (PF) captured by lecanemab in human cerebrospinal fluid (CSF) from living participants with different stages in AD, which enable an enhanced understanding of the dynamic changes of lecanemab-associated Aβ-PF (Lec-PF) in vivo.

METHODS

We newly developed a unique and highly sensitive immunoassay method using lecanemab that selectively captures Lec-PF. The CSF level of Lec-PF, Aβ42, Aβ40, p-tau181, p-tau 217, total tau, and neurogranin were measured in Japanese participants (n = 163). The participants in this study consisted of 48 cognitively unimpaired Aβ-negative (CU-), 8 cognitively impaired diagnosed as suspected non-Alzheimer's disease pathophysiology, 9 cognitively unimpaired Aβ-positive (CU+), 34 Aβ-positive with mild cognitive impairment (MCI+), and 64 Aβ-positive with AD dementia (AD+).

RESULTS

The CSF Lec-PF levels significantly increased in the groups of MCI+ and AD+ compared with CU- group. Notably, CSF Lec-PF showed modest correlation with plaque-associated biomarkers in Aβ-positive participants and stronger correlation with neurodegeneration biomarkers, such as CSF total tau and neurogranin, suggesting that CSF Lec-PF levels proximally reflect neurodegeneration as well as the amount of senile amyloid plaques.

INTERPRETATION

This is the first report describing Aβ-PF species captured by lecanemab in human CSF and supporting that Lec-PF is correlated with neurodegeneration in AD and may explain the mechanism of the clinical effect of lecanemab. ANN NEUROL 2025;97:993-1006.

Nano-Scale Video Imaging of Motility Machinery by High-Speed Atomic Force Microscopy

Motility is a vital aspect of many forms of life, with a wide range of highly conserved as well as highly unique systems adapted to the needs of various organisms and environments. While many motility systems are well studied using structural techniques like X-ray crystallography and electron microscopy, as well as fluorescence microscopy methodologies, it is difficult to directly determine the relationship between the shape and movement of a motility system due to a notable gap in spatiotemporal resolution. Bridging this gap as well as understanding the dynamic molecular movements that underpin motility mechanisms has been challenging. The advent of high-speed atomic force microscopy (HS-AFM) has provided a new window into understanding these nano-scale machines and the dynamic processes underlying motility. In this review, we highlight some of the advances in this field, ranging from reconstituted systems and purified higher-order supramolecular complexes to live cells, in both prokaryotic and eukaryotic contexts.

Globular-shaped Aβ oligomers have diverse mechanisms for promoting Aβ aggregations with the facilitation of fibril elongation

The accumulation of amyloid β-proteins (Aβ) in the extracellular space, forming insoluble plaques, is a primary pathological process underlying Alzheimer's disease (AD). Among the various Aβ species that appear during Aβ aggregation, Aβ oligomers are considered the most neurotoxic form. However, the precise mechanisms of their molecular functions within the Aβ aggregation cascade have not been clarified so far. This research aimed to uncover the structural and functional characteristics of globular-shaped Aβ oligomers (gAβO) under in vitro conditions. We performed thioflavin T (ThT) assays on low-molecular-weight (LMW) Aβ42, testing different concentrations of Aβ42 mature fibril (MF) seeds and gAβO. Fibril formation was continuously observed using high-speed atomic force microscopy (HS-AFM) in LMW Aβ42 with different sample conditions. Conformational changes of Aβ42 aggregates in the presence of gAβO was also evaluated using circular dichroism spectroscopy. The results of the ThT analysis and HS-AFM observation indicated that gAβO promoted fibril formation of LMW Aβ42 while gAβO itself did not form fibrous aggregates, indicating that gAβO would have a catalytic effects on LMW Aβ42 aggregation. We also showed that the molecular interaction of gAβO was altered by the presence and amount of MF seeds in the reaction buffers, indicating that complex interactions would exist among different Aβ species. The results of our present research demonstrated that gAβO would have significant roles to accelerate Aβ aggregation in AD pathogenesis. 225 < 250 words.

The basis of anti-Aβ antibody therapy: The toxicity of Aβ aggregates and the mechanism of action of anti-Aβ antibodies

In the pathophysiology of Alzheimer's disease (AD), the amyloid hypothesis, which posits that amyloid β-protein (Aβ) abnormally aggregates and damages neurons with tau, has been proposed. It was originally thought that the accumulation of insoluble amyloid fibrils in the brain leads to AD-inducing neurotoxicity; however, in recent years, the positioning of early and intermediate aggregates has also been emphasized. In particular, following the positive results of phase 3 clinical trials of lecanemab and its approval in Japan and the United States, the pathology of protofibrils, which are the target molecules of lecanemab, has attracted attention. Using high-speed atomic force microscopy, we have previously reported that lecanemab, which has a high affinity for protofibrils, binds to and surrounds them. Donanemab, a recombinant monoclonal antibody that primarily targets fibrils composed of N3pG Aβ, has also attracted attention because of its efficacy in phase 3 clinical trials in patients with early stage AD.

Synthesis of symmetrical and unsymmetrical tetrahydroxybiphenyls and their evaluation as amyloid-β aggregation inhibitors

Our group recently reported that the polyhydroxy aromatic compound 3,3',4,4'-biphenyltetrol (2a) is a successful inhibitor of amyloid-β peptide (Aβ) aggregation, decreasing Aβ aggregation by 50 % when present in equimolar concentrations. In the present study, several additional biphenyltetrols were prepared and examined for their in vitro activity against aggregation of Aβ, to investigate the effect of the relative positions of hydrogen-bond donors on the aggregation process. Congo red spectral shift assays have shown that, of the eight (8) additional biphenyltetrol compounds prepared, three (3) successfully inhibit association of Aβ monomers - two symmetrical isomers, 2,2',5,5'-biphenyltetrol (2c), and 2,2',3,3'-biphenyltetrol (2d), along with one unsymmetrical isomer, 2,3',4',5-biphenyltetrol (2g). These results, along with previously reported results of 2a, strongly suggest that hydroxyl group position affects the ability of the inhibitor to bind to Aβ assemblies, thus impacting inhibitory efficacy.

Molecular Dynamics Mappings of the CCT/TRiC Complex-Mediated Protein Folding Cycle Using Diffracted X-ray Tracking

The CCT/TRiC complex is a type II chaperonin that undergoes ATP-driven conformational changes during its functional cycle. Structural studies have provided valuable insights into the mechanism of this process, but real-time dynamics analyses of mammalian type II chaperonins are still scarce. We used diffracted X-ray tracking (DXT) to investigate the intramolecular dynamics of the CCT complex. We focused on three surface-exposed loop regions of the CCT1 subunit: the loop regions of the equatorial domain (E domain), the E and intermediate domain (I domain) juncture near the ATP-binding region, and the apical domain (A domain). Our results showed that the CCT1 subunit predominantly displayed rotational motion, with larger mean square displacement (MSD) values for twist (χ) angles compared with tilt (θ) angles. Nucleotide binding had a significant impact on the dynamics. In the absence of nucleotides, the region between the E and I domain juncture could act as a pivotal axis, allowing for greater motion of the E domain and A domain. In the presence of nucleotides, the nucleotides could wedge into the ATP-binding region, weakening the role of the region between the E and I domain juncture as the rotational axis and causing the CCT complex to adopt a more compact structure. This led to less expanded MSD curves for the E domain and A domain compared with nucleotide-absent conditions. This change may help to stabilize the functional conformation during substrate binding. This study is the first to use DXT to probe the real-time molecular dynamics of mammalian type II chaperonins at the millisecond level. Our findings provide new insights into the complex dynamics of chaperonins and their role in the functional folding cycle.

Neuroprotective Potential of Raloxifene via G-Protein-Coupled Estrogen Receptors in Aβ-Oligomer-Induced Neuronal Injury

Amyloid-β (Aβ) is one of the causes of Alzheimer's disease (AD), damaging nerve membranes and inducing neurotoxicity. AD is more prevalent in female patients than in male patients, and women are more susceptible to developing AD due to the decline in estrogen levels around menopause. Raloxifene, a selective estrogen receptor modulator, exhibits protective effects by activating the transmembrane G-protein-coupled estrogen receptor (GPER). Additionally, raloxifene prevents mild cognitive impairment and restores cognition. However, the influence of raloxifene via GPER on highly toxic Aβ-oligomers (Aβo)-induced neurotoxicity remains uncertain. In this study, we investigated the GPER-mediated neuroprotective effects of raloxifene against the neurotoxicity caused by Aβo-induced cytotoxicity. The impact of raloxifene on Aβo-induced cell damage was evaluated using measures such as cell viability, production of reactive oxygen species (ROS) and mitochondrial ROS, peroxidation of cell-membrane phospholipids, and changes in intracellular calcium ion concentration ([Ca2+]i) levels. Raloxifene hindered Aβo-induced oxidative stress and reduced excessive [Ca2+]i, resulting in improved cell viability. Furthermore, these effects of raloxifene were inhibited with pretreatment with a GPER antagonist. Our findings suggest that raloxifene safeguards against Aβo-induced neurotoxicity by modifying oxidative parameters and maintaining [Ca2+]i homeostasis. Raloxifene may prove effective in preventing and inhibiting the progression of AD.

The Mechanisms of the Roles of α-Synuclein, Amyloid-β, and Tau Protein in the Lewy Body Diseases: Pathogenesis, Early Detection, and Therapeutics

Lewy body diseases (LBD) are pathologically defined as the accumulation of Lewy bodies composed of an aggregation of α-synuclein (αSyn). In LBD, not only the sole aggregation of αSyn but also the co-aggregation of amyloidogenic proteins, such as amyloid-β (Aβ) and tau, has been reported. In this review, the pathophysiology of co-aggregation of αSyn, Aβ, and tau protein and the advancement in imaging and fluid biomarkers that can detect αSyn and co-occurring Aβ and/or tau pathologies are discussed. Additionally, the αSyn-targeted disease-modifying therapies in clinical trials are summarized.