Spatial Neurolipidomics at the Single Amyloid- Plaque Level in Postmortem Human Alzheimer's Disease Brain

Lipid dysregulations have been critically implicated in Alzheimer's disease (AD) pathology. Chemical analysis of amyloid-beta (A beta) plaque pathology in transgenic AD mouse models has demonstrated alterations in the microenvironment in the direct proximity of A beta plaque pathology. In mouse studies, differences in lipid patterns linked to structural polymorphism among A beta pathology, such as diffuse, immature, and mature fibrillary aggregates, have also been reported. To date, no comprehensive analysis of neuronal lipid microenvironment changes in human AD tissue has been performed. Here, for the first time, we leverage matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) through a high-speed and spatial resolution commercial time-of-light instrument, as well as a high-mass-resolution in-house-developed orbitrap system to characterize the lipid microenvironment in postmortem human brain tissue from AD patients carrying Presenilin 1 mutations (PSEN1) that lead to familial forms of AD (fAD). Interrogation of the spatially resolved MSI data on a single A beta plaque allowed us to verify nearly 40 sphingolipid and phospholipid species from diverse subclasses being enriched and depleted, in relation to the A beta deposits. This included monosialo-gangliosides (GM), ceramide monohexosides (HexCer), ceramide-1-phosphates (CerP), ceramide phosphoethanolamine conjugates (PE-Cer), sulfatides (ST), as well as phosphatidylinositols (PI), phosphatidylethanolamines (PE), and phosphatidic acid (PA) species (including Lyso-forms). Indeed, many of the sphingolipid species overlap with the species previously seen in transgenic AD mouse models. Interestingly, in comparison to the animal studies, we observed an increased level of localization of PE and PI species containing arachidonic acid (AA). These findings are highly relevant, demonstrating for the first time A beta plaque pathology-related alteration in the lipid microenvironment in humans. They provide a basis for the development of potential lipid biomarkers for AD characterization and insight into human-specific molecular pathway alterations.