Hippocampal lipid differences in Alzheimer's disease: a human brain study using matrix‐assisted laser desorption/ionization‐imaging mass spectrometry

INTRODUCTION: Alzheimer's disease (AD), the leading cause of dementia, is pathologically characterized by β‐amyloid plaques and tau tangles. However, there is also evidence of lipid dyshomeostasis‐mediated AD pathology. Given the structural diversity of lipids, mass spectrometry is a useful tool for studying lipid changes in AD. Although there have been a few studies investigating lipid changes in the human hippocampus in particular, there are few reports on how lipids change in each hippocampal subfield (e.g., Cornu Ammonis [CA] 1–4, dentate gyrus [DG] etc.). Since each subfield has its own function, we postulated that there could be lipid changes that are unique to each. METHODS: We used matrix‐assisted laser desorption/ionization‐imaging mass spectrometry to investigate specific lipid changes in each subfield in AD. Data from the hippocampus region of six age‐ and gender‐matched normal and AD pairs were analyzed with SCiLS lab 2015b software (SCiLS GmbH, Germany; RRID:SCR_014426), using an analysis workflow developed in‐house. Hematoxylin, eosin, and luxol fast blue staining were used to precisely delineate each anatomical hippocampal subfield. Putative lipid identities, which were consistent with published data, were assigned using MS/MS. RESULTS: Both positively and negatively charged lipid ion species were abundantly detected in normal and AD tissue. While the distribution pattern of lipids did not change in AD, the abundance of some lipids changed, consistent with trends that have been previously reported. However, our results indicated that the majority of these lipid changes specifically occur in the CA1 region. Additionally, there were many lipid changes that were specific to the DG. CONCLUSIONS: Matrix‐assisted laser desorption/ionization‐imaging mass spectrometry and our analysis workflow provide a novel method to investigate specific lipid changes in hippocampal subfields. Future work will focus on elucidating the role that specific lipid differences in each subfield play in AD pathogenesis.