Master of Science
Anatomy and Cell Biology
Whitehead, Shawn N.
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.
Summary for Lay Audience
Diseases of the brain, such as Alzheimer’s disease and stroke, represent a major cause of disability and death, yet many remain uncurable. This is partly due to a limited understanding of molecular changes that underlie diseases. Of the three categories of biological macromolecules, which are proteins, lipids, and carbohydrates, lipids are the most abundant in the brain, accounting for 60% of the dried mass. These lipids contribute to numerous aspects of cells in the brain including forming the structural walls of cells and influencing the behaviour of cells. Due to the abundance of lipids in the brain and their ability to influence cells, they are particularly likely to be altered in diseases of the brain. Previous studies have demonstrated that changes in lipids are part of many diseases of the brain, but our understanding still remains limited. This limited understanding is partially due to the difficulty of studying the enormous variety of lipids that occur in the brain. Recent improvements in mass spectrometry, a technique for studying lipids, have opened a door for investigating changes in lipids within diseased brains. In this thesis, we use this technique to identify lipid abnormalities within diseased post-mortem human brains. By doing so, we aim to establish a workflow that will allow others to study changes in lipids that are associated with clinically observable diseases. Research into these lipid changes may identify therapeutic targets to help manage or cure neurological diseases.
Pinsky, William J., "Regional lipid expression abnormalities identified using MALDI IMS correspond to MRI-defined white matter hyperintensities within post-mortem human brain tissue." (2021). Electronic Thesis and Dissertation Repository. 8185.
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