Effects of Sex and Western Diet on Spatial Lipidomic Profiles for the Hippocampus, Cortex, and Corpus Callosum in Mice Using MALDI MSI

Abstract

Diet is inextricably linked to human health and biological functionality. Reduced cognitive function among other health issues has been correlated with a western diet (WD) in mouse models, indicating that increases in neurodegeneration could be fueled in part by a poor diet. In this study, we use matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) to spatially map the lipidomic profiles of male and female mice that were fed a high-fat, high-sucrose WD for a period of 7 weeks. Our findings concluded that the cortex and corpus callosum showed significant lipid variation by WD in female mice, while there was little to no variation in the hippocampus, regardless of sex. On the other hand, lipid profiles were significantly affected by sex in all regions. Overall, 83 lipids were putatively identified in the mouse brain; among them, HexCer(40:1;O3) and PE(34:0) were found to have the largest statistical difference based on diet for female mice in the cortex and corpus callosum, respectively. Additional lipid changes are noted and can serve as a metric for understanding the brain's metabolomic response to changes in diet, particularly as it relates to disease.

Figure 1

Overview of the experimental workflow. From left to right, workflow begins with 9-month-old mice fed either a WD or CD for 7 weeks, resulting in increased or normal weight gain, respectively. Cryosectioned tissues were thaw mounted onto ITO glass slides and subsequently coated with the MALDI matrix DAN. Data acquisition was performed on a MALDI mass spectrometer with data analysis completed through SCiLS software.

Figure 2

Weight gain for male and female mice fed WD and CD. Female and male mice gained 40% and 28% more weight, respectively, on WD in comparison to CD. N = 3 male and 3 female (total of six animals) per diet.

Figure 3

MALDI MS Images for five representative lipids; box plots show relative lipid intensity and statistical significance. Distribution and relative abundance of (A) PE(40:4), (B) HexCer(42:2;O3), (C) PI(38:4), (D) ShexCer(42:2;O2), and (E) PS(42:9) throughout the coronal section. MALDI MSI images are scaled from low abundance (dark blue) to high abundance (yellow). Stars indicate level of statistical significance; * = p < 0.1, ** = P < 0.05, *** = P < 0.01. N = 3 for all groups (Figures S1 and S2).

Figure 4

Variation in lipid abundance as a function of diet for different brain regions. The lipids selected have the highest ROC scores in the given brain region as a function of diet. (A) In female mice, HexCer(40:1;O3) and PE(34:0) show significant differences as a function of diet in the cortex and corpus callosum, respectively. Within the hippocampus, SHexCer(38:6;O5) is not statistically significant among the groups. (B) For male mice, none of the lipids were statistically significant. N = 3 male, 3 female per diet (six animals total).

Figure 5

Lipid abundances as a function of sex for different brain regions. (A) For mice fed CD, PS(42:9), PI(38:4), and PS(42:9) were the lipids with highest, significant variation in the cortex, corpus callosum, and hippocampus, respectively. (B) For mice given a western diet, PS(42:9), SHexCer(42:2;O2), and PS(42:9) were the lipids with the highest variation in the cortex, corpus callosum, and hippocampus, respectively. Only SHexCer(42:2;O2) did not show a statistical significance. N = 3 male, 3 female per diet (total of six mice).

Figure 6

Relative signal intensity and ROC scores for PE and PI lipids within all comparisons. Relative lipid abundance for (A) female CD vs WD (left half-circle = CD, right half circles = WD), (B) male CD vs WD (left half-circle = CD, right half circles = WD), (C) female CD vs male CD (left half-circle = female, right half circles = male), and (D) female WD vs male WD (left half-circle = female, right half circles = male). ROC score increases with color intensity. Darkened color shade represents increased ROC score, and increasing circle radius represents higher lipid ion signal. N = 3 male, 3 female per diet.