Probing Amyloid Aggregation Dynamics in vivo, Using SILK Imaging (iSILK) Jörg Hanrieder (Presenter) University of Gothenburg Presenter Bio: Jörg has been working with different modalities of imaging mass spectrometry over the last 10 years to understand biochemical processes underlying neurodegeneration. He has a background in chemistry and molecular neuroscience (MSc 2005, University of Leipzig; PhD 2011, Uppsala University). Following a Postdoc on SIMS imaging at Chalmers University of Technology he joined the University of Gothenburg as Assistant Professor in Neurochemistry. He was promoted to Associate Professor in 2017. Since 2017, he is establishing a second group at University College London, where he holds an honorary appointment at the Institute of neurology. The work of his group concerns the development and advancement of chemical imaging tools for probing neurodegenerative disease pathology, specifically amyloid plaque pathology in Alzheimer’s disease.

Authors: Jörg Hanrieder(1,2), Wojciech Michno (1), Henrik Zetterberg (1,2), Kaj Blennow (1)
(1) University of Gothenburg, Sweden, (2) University College London, UK

Although the importance of amyloid beta (Aβ) plaque deposition in Alzheimer’s disease (AD) has long been recognized, exactly how plaques develop over time and their neurotoxic potential is not clear. Recent advances in imaging technologies such as imaging mass spectrometry (IMS) greatly increase the resolution of such events and the advent of isotope labelling of proteins and high-resolution IMS opens up possibilities for measuring spatial protein turnover kinetics in tissue. The aim of this study is to take advantages of such advances by using IMS along with metabolic labeling to recently developed novel genetic mouse models of AD. The results show distinct rates of secretion and deposition for distinct Aβ peptides within different brain regions. These data allow us to understand the progression of plaque deposition from initial seeding through to later aggregation.

Introduction

It is of critical importance to our understanding of Alzheimer’s disease (AD) pathology, to determine how key pathological factors including beta-amyloid (Aβ) plaque formation are interconnected and implicated in nerve cell death, clinical symptoms and disease progression. Exactly how Aβ plaques begin and how the ongoing plaque deposition proceeds is not well understood (1). This is partly because in humans we can only look in detail after death and in mice we can only see a particular point in time without any longitudinal information on the fate of individually formed deposits.

We here report the application of a novel approach, iSILK, based on metabolic labelling of proteins with stable isotopes (2) together with ultrahigh resolution imaging mass spectrometry (3,4) for studying amyloid plaque formation dynamics in novel genetic mouse models of AD.

Methods

Imaging of stable isotope labelling kinetics (iSILK) was performed in recently developed knock in mice with familial mutations in Amyloid Precursor Protein (APP NL-F) (5). We fed mice a diet containing a stable isotope (15N) just prior to plaque onset (PNW12) until plaque pathology was prominently manifested (PNW16) followed by a 4 week chase. Metabolically incorporated 15N was afterwards be detected in the brain with high spatial and temporal resolution using a combination of MALDI imaging, and nanoSIMS along with transmission electron microscopy for ultrastructure imaging of protein turnover (3,4).

Results

The data reveal early formation of plaques consisting primarily of Aβ1-42 in cortical areas followed by later deposition within the hippocampus. NanoSIMS reveal that these plaques form first a core structure consisting of highly abundant,soluble Aβ1-42 secreted prior to plaque deposition. In addition, these plaques form radiating diffuse fibers that evolve at a later time from the core seed. Further, other C-terminal Aβ species, including Aβ1-38 and Aβ1-39 were found to be secreted at a later time during evolving plaque pathology and were processed prior to deposition to pre-exiting Aβ1-42 containing plaque structures.

Conclusions & Discussion

These data bring considerable novel information about the deposition mechanism of Aβ. In detail, our data show that plaque pathology is seeded by Aβ1-42, forming distinct amyloid structures that evolve into plaques. Further these data show us that the cortex is the first site of plaque deposition, something that is well in line with other mouse models (6). Further, we show that C-terminal Aβ processing is occurring prior to deposition and not associated with plaque specific mechanisms.

Taken together these results provide significant novel insight for understanding the earliest stages of Alzheimer’s disease and the ongoing progressive changes in amyloidosis.

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(6) Lord, A.; Philipson, O.; Klingstedt, T., et al. Am. J. Pathol. 2011, 178, 2286-2298.