Imaging stable isotope labelling kinetics (iSILK) for following spatial Aβ plaque aggregation dynamics in evolving Alzheimers disease pathology

For our understanding of Alzheimers disease (AD) pathophysiology, it is of critical importance to determine how key pathological factors, specifically amyloid {beta} (A{beta}) plaque formation, are interconnected and implicated in neurodegeneration, disease progression and the development of clinical symptoms. Exactly how A{beta} plaque formation is initiated and how the ongoing plaque deposition proceeds is not well understood. This is partly because we can only examine details of the molecular pathology after death in humans, and in mice, we can only examine a particular point in time without any longitudinal information on the fate of individually formed deposits. Herein, we used metabolic labelling of proteins with stable isotopes, together with multimodal imaging mass spectrometry (IMS) for imaging stable isotope labelling kinetics (iSILK) in the APPNL-G-F knock-in mouse model of AD. The aim was to monitor the earliest seeds of A{beta} deposition through ongoing plaque development and track the deposition of A{beta} that is produced later in relation to already deposited plaques. This allowed us to visualize A{beta} peptide aggregation dynamics within individual deposits across different brain regions. We identified the cortex as a primary site of deposition in precipitating plaque pathology. Further, our data show that structural plaque heterogeneity is associated with differential peptide deposition. Specifically, A{beta}1-42 is forming an initial core seed followed by radial outgrowth and late secretion and deposition of A{beta}1-38. Together these data prove the potential of iSILK for probing amyloid protein secretion, processing and aggregation dynamics in AD pathology.