Single molecule imaging of protein aggregation in Dementia: Methods, insights and prospects

Detection of p53 aggregates in plasma of glioma patients

BACKGROUND

The tumour-suppressor protein p53 can form amyloid aggregates resulting in loss of tumour-suppressing functions and leading to tumour formation. The detection of p53 aggregates in cancer cells has been demonstrated but these aggregates have not been detected in liquid biopsies to date, due to the lack of sufficiently sensitive methods.

METHODS

We developed an ultrasensitive immunoassay based on the single-molecule array (SiMoA) technology to detect p53 aggregates in plasma, based on antibody capture of the aggregates. We confirmed that the assay detects p53 aggregates using super-resolution imaging. We then investigated the p53 aggregate concentrations in the plasma of 190 pre-surgery glioblastoma (GB) patients and 22 controls using this assay.

RESULTS

We found that the plasma p53 aggregate levels are significantly elevated in pre-surgery GB patients' plasma compared to controls. Longitudinal study further reveals that p53 aggregate levels may increase before GB recurrence and decrease following treatment. We also observed raised p53 aggregate concentrations in the plasma of cancer patients with brain metastases.

CONCLUSIONS

This study demonstrates the detection of p53 aggregates in liquid biopsies. Our findings highlight the potential of p53 aggregates as a novel biomarker for glioblastoma.

Lecanemab preferentially binds to smaller aggregates present at early Alzheimer's disease

INTRODUCTION

The monoclonal antibodies Aducanumab, Lecanemab, Gantenerumab, and Donanemab were developed for the treatment of Alzheimer's disease (AD).

METHODS

We used single-molecule detection and super-resolution imaging to characterize the binding of these antibodies to diffusible amyloid beta (Aβ) aggregates generated in-vitro and harvested from human brains.

RESULTS

Lecanemab showed the best performance in terms of binding to the small-diffusible Aβ aggregates, affinity, aggregate coating, and the ability to bind to post-translationally modified species, providing an explanation for its therapeutic success. We observed a Braak stage-dependent increase in small-diffusible aggregate quantity and size, which was detectable with Aducanumab and Gantenerumab, but not Lecanemab, showing that the diffusible Aβ aggregates change with disease progression and the smaller aggregates to which Lecanemab preferably binds exist at higher quantities during earlier stages.

DISCUSSION

These findings provide an explanation for the success of Lecanemab in clinical trials and suggests that Lecanemab will be more effective when used in early-stage AD.

HIGHLIGHTS

Anti amyloid beta therapeutics are compared by their diffusible aggregate binding characteristics. In-vitro and brain-derived aggregates are tested using single-molecule detection. Lecanemab shows therapeutic success by binding to aggregates formed in early disease. Lecanemab binds to these aggregates with high affinity and coats them better.

SynPull: An advanced method for studying neurodegeneration-related aggregates in synaptosomes using super-resolution microscopy

Synaptic dysfunction is a primary hallmark of both Alzheimer's and Parkinson's disease, leading to cognitive and behavioral decline. While alpha-synuclein, beta-amyloid, and tau are involved in the physiological functioning of synapses, their pathological aggregation has been linked to synaptopathology. The methodology for studying the small-soluble protein aggregates formed by these proteins is limited. Here we describe SynPull, a method combining single-molecule pull-down, super-resolution microscopy, and advanced computational analyses to characterize the protein aggregates in human and mouse synaptosomes. We show that AT8-positive tau aggregates are the predominant aggregate type in synaptosomes from postmortem Alzheimer's disease brain, although the aggregate size does not change in disease. Meanwhile, the relatively smaller amount of alpha-synuclein and beta-amyloid aggregates found in the synapses are larger than the extra-synaptic ones. Collectively, these results show the utility of SynPull to study pathological aggregates in neurodegeneration, elucidating the disease mechanisms causing synaptic dysfunction.

Clearance of beta-amyloid and tau aggregates is size dependent and altered by an inflammatory challenge

Extracellular beta-amyloid aggregation and inflammation are in a complex and not fully understood interplay during hyperphosphorylated tau aggregation and pathogenesis of Alzheimer's disease. Our group has previously shown that an immune challenge with tumour necrosis factor alpha can alter extracellular beta-sheet containing aggregates in human-induced pluripotent stem cell-derived cortical neurons carrying familial Alzheimer's disease-related presenilin 1 mutations. Here, using single-molecule detection and super-resolution imaging techniques, we quantified and characterized the intra- and extracellular beta-amyloid and AT8-positive tau aggregates. Our results indicate a pre-existing Alzheimer's disease-like pathology caused by the presenilin 1 mutation, with increased beta-amyloid aggregates in both the cell lysate and conditioned media compared to isogenic controls and also increased intracellular tau aggregates. The main effect of tumour necrosis factor alpha treatment on presenilin 1 neurons was the formation of larger intracellular beta-amyloid aggregates. In contrast, isogenic controls showed more significant changes with tumour necrosis factor alpha treatment with an increase in beta-amyloid aggregates in the media but not intracellularly and an increase in tau aggregates in both the media and cell lysate, suggesting a chronic inflammation-driven mechanism for the development of sporadic Alzheimer's disease. Remarkably, we also found significant morphological differences between intra- and extracellular beta-amyloid and tau aggregates in human-induced pluripotent stem cell-derived cortical neurons, suggesting these neurons can only clear aggregates when small, and that larger aggregates stay inside the neurons. While majority of the beta-amyloid aggregates were cleared into the media, a greater portion of the tau aggregates remained intracellular. This size-dependent aggregate clearance was also shown to be conserved in vivo, using soaked and homogenized mouse and human post-mortem Alzheimer's disease brain samples. As such, our results are proposing a previously unknown, size-dependent aggregate clearance mechanism, which can possibly explain the intracellular aggregation of tau and extracellular aggregation of beta-amyloid.

The thermodynamics of neurodegenerative disease

The formation of protein aggregates in the brain is a central aspect of the pathology of many neurodegenerative diseases. This self-assembly of specific proteins into filamentous aggregates, or fibrils, is a fundamental biophysical process that can easily be reproduced in the test tube. However, it has been difficult to obtain a clear picture of how the biophysical insights thus obtained can be applied to the complex, multi-factorial diseases and what this means for therapeutic strategies. While new, disease-modifying therapies are now emerging, for the most devastating disorders, such as Alzheimer's and Parkinson's disease, they still fall well short of offering a cure, and few drug design approaches fully exploit the wealth of mechanistic insights that has been obtained in biophysical studies. Here, I attempt to provide a new perspective on the role of protein aggregation in disease, by phrasing the problem in terms of a system that, under constant energy consumption, attempts to maintain a healthy, aggregate-free state against the thermodynamic driving forces that inexorably push it toward pathological aggregation.

Advances in the study of organelle interactions and their role in neurodegenerative diseases enabled by super-resolution microscopy

From the first illustrations of neuronal morphology by Ramón y Cajal to the recent three-dimensional reconstruction of synaptic connections, the development of modern neuroscience has greatly benefited from breakthroughs in imaging technology. This also applies specifically to the study of neurodegenerative diseases. Much of the research into these diseases relies on the direct visualisation of intracellular structures and their dynamics in degenerating neural cells, which cannot be fully resolved by diffraction-limited microscopes. Progress in the field has therefore been closely linked to the development of super-resolution imaging methods. Their application has greatly advanced our understanding of disease mechanisms, ranging from the structural progression of protein aggregates to defects in organelle morphology. Recent super-resolution studies have specifically implicated the disruption of inter-organelle interactions in multiple neurodegenerative diseases. In this article, we describe some of the key super-resolution techniques that have contributed to this field. We then discuss work to visualise changes in the structure and dynamics of organelles and associated dysfunctions. Finally, we consider what future developments in imaging technology may further our knowledge of these processes.