Podium Presentation in Room 2 on Wednesday at 11:20 (Chair: Elizabeth Want)
Authors: Melanie T. Odenkirk (1), Jeremy Ash (1,2), Denis Fourches (1,2), Kristin E. Burnum-Johnson (3), Kelly Stratton (3), Blaine R. Roberts (4), Erin S. Baker (1)
Introduction. Alzheimer’s disease (AD) is an increasingly common neurodegenerative disease that affects 47 million people worldwide. Despite efforts by many researchers, AD neuropathology has yet to be fully elucidated due to effects of other underlying factors such as ApoE genotype influencing AD progression and differentiating disease mechanisms.
Objective. The primary objective of this study was to characterize the neuropathology of AD with emphasis on unique mechanisms reflective of ApoE genotype effects.
Methods. In our molecular analyses, brain tissue samples from the cerebellum (CBM) and frontal cortex (FCX) were acquired from 62 patients post-mortem with various ApoE genotypes ε2/ε3, ε3/ε3, ε3/ε4, and ε4/ε4. In the study, the 29 healthy controls (HC) and 33 AD patients were split and present in all ApoE genotypes except ε4/ε4 where only AD patients were represented. Therefore, no HC to AD comparisons could be made. Proteomic and lipidomic analyses were performed using both LC-MS/MS and LC-IMS-MS with positive electrospray ionization (ESI) for proteomic assays while lipidomic studies utilized both positive and negative ESI. The resulting proteomic and lipidomic datasets were matched to an accurate time and tag database for identification and assessed for biological outliers or inadequate entries for statistics, of which all instances were removed. Mean centered normalization yielded 294 lipids and 3,768 proteins each having at least 2 peptides and one unique peptide per protein. Metallomic evaluations of 15 metals were also performed for the FCX tissue which was fractionated into total, vesicular, membrane and insoluble fractions and subsequently analyzed by ICP-MS.
Results. In our assessment of FCX and CBM tissues, the most molecular dysregulation was noted in the FCX due to its association with memory functions. Analysis of proteins associated with the AD pathway in the FCX presented the most significant dysregulation in AD versus HC comparisons within ε3/ε4 whereas the least dysregulation occurred within ε2/ε3 corresponding to potential links with the ApoE genotype. Lipidomics analysis revealed similar dysregulation between ε3/ε3 and ε3/ε4 genotypes with both exhibiting significant dysregulation within the FCX. Again, the ε2/ε3 AD group showed little dysregulation relative to the ε2/ε3 HC group with the exception of lysolipids within the CBM being significantly downregulated. Metallomics elucidated significant differences in AD and HC comparisons for Zn66, Cu63 and Fe56 all being significantly upregulated in the vesicular fraction of FCX tissue. Further evaluation of the enzymes, lipids, metals and their respective associations to ApoE genotype on AD progression are still undergoing.
Conclusions. Distinct molecular changes were observed in AD and HC comparisons with increased diversity between different ApoE genotypes. Taken together, these results reflect distinct AD progression mechanisms reflective of genotypic differences.
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