Regional lipid expression abnormalities identified using MALDI IMS correspond to MRI-defined white matter hyperintensities within post-mortem human brain tissue.
Abstract
Periventricular white matter hyperintensities (pvWMHs) are a neurological feature detected with magnetic resonance imaging (MRI) and are clinically associated with an increased risk of stroke and dementia. pvWMHs are characterized by white matter lesions with myelin and axon rarefaction, and as such likely involve changes in lipid composition, however these alterations remain unknown. Lipids are critical in determining cell function and survival, although their detection within tissue, until recently has been challenging. Perturbations in lipid expression have previously been associated with neurological disorders. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) is an emerging technique for untargeted, high-throughput investigation of lipid expression and spatial distribution in situ, however the use of MALDI IMS has been previously been limited by the need for non-embedded, non-fixed, fresh-frozen samples. Work within this thesis demonstrates the novel use of MALDI IMS to distinguish regional lipid abnormalities that correlate with MRI defined pvWMHs within ammonium formate washed, formalin-fixed human archival samples. MALDI IMS scans were conducted in positive or negative ion detection mode on tissue sublimated with 2,5-dihydroxybenzoic acid or 1,5- diaminonaphthalene matrices, respectively. Using a broad, untargeted approach to lipid analysis we consistently detected 116 lipid ion species in 21 tissue blocks from 11 different post-mortem formalin-fixed human brains. Comparing the monoisotopic mass peaks of these lipid ions elucidated significant differences in lipid expression between pvWMHs and NAWM for 31 lipid ion species. Expanding our understanding of alterations in lipid composition will provide greater knowledge of molecular mechanisms underpinning ischemic white matter lesions and provides the potential for novel therapeutic interventions targeting lipid composition abnormalities.