Amyloid Plaque Polymorphism is Associated with Distinct Lipid Accumulations Revealed by Trapped Ion Mobility Mass Spectrometry Imaging (TIMS MSI)

Understanding of Alzheimer’s disease (AD) pathophysiology, requires molecular assessment of how key pathological factors, specifically amyloid β (Aβ) plaques, influence the surrounding microenvironment. Here, neuronal lipids are particularly of interest as these are implicated in pathological- and neurodegenerative processes in AD. The exact molecular characteristics of the cellular environment in direct proximity to Aβ plaques are however still not known, not in the least due to high molecular complexity of lipid species but also due to the lacking spatial resolution, sensitivity, and specificity of analytical approaches. Likewise, how such micro environmental changes differ, across structurally polymorphic Aβ features - such as diffuse, immature and mature, fibrillary structures - has been a challenge, requiring complemental, multimodal imaging approaches. Herein, we used matrix assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) trapped ion mobility spectrometry Time-of-Flight (TIMS TOF) in combination with hyperspectral microscopy to probe lipidomic microenvironment associated with structural polymorphism of Aβ plaque in transgenic mouse model of Alzheimer’s disease (tgAPPSWE).Integrated multivariate imaging data analysis revealed alteration of multiple lipid species showing a general, Aβ associated enrichment/depletion patterns. The hyperspectral imaging strategy further delineated unique distribution of PA, PE-Cer and PI lipids to more/less aggregated Aβ fibrillary structures present within individual Aβ plaques at different timepoints of progressing plaque pathology. Using an elaborate on tissue and ex situ validation approach, the unique possibility to obtain gas-phase isobar and isomer separations through TIMS TOF, facilitated unambiguous identification of lipid isomers that showed plaque pathology associated localizations. Finally, we followed AD pathology associated lipid changes over time, identifying plaque growth and maturation to be characterized by peripheral accumulation of PI (40:6). Together, these data demonstrate the potential of multimodal imaging approaches to overcome limitations associated with conventional advanced MS imaging applications. This allowed for differentiation of both distinct lipid components in a complex micro environment, as well as their correlation to disease relevant amyloid plaque polymorphs.