Sexually dimorphic brain fatty acid composition in low and high fat diet-fed mice

Abstract

Objective: In this study, we analyzed the fatty acid profile of brains and plasma from male and female mice fed chow or a western-style high fat diet (WD) for 16 weeks to determine if males and females process fatty acids differently. Based on the differences in fatty acids observed in vivo, we performed in vitro experiments on N43 hypothalamic neuronal cells to begin to elucidate how the fatty acid milieu may impact brain inflammation.

Methods: Using a comprehensive mass spectrometry fatty acid analysis, which includes a profile for 52 different fatty acid isomers, we assayed the plasma and brain fatty acid composition of age-matched male and female mice maintained on chow or a WD. Additionally, using the same techniques, we determined the fatty acid composition of N43 hypothalamic cells following exposure to palmitic and linoleic acid, alone or in combination.

Results: Our data demonstrate there is a sexual dimorphism in brain fatty acid content both following the consumption of the chow diet, as well as the WD, with males having an increased percentage of saturated fatty acids and reductions in ω6-polyunsaturated fatty acids when compared to females. Interestingly, we did not observe a sexual dimorphism in fatty acid content in the plasma of the same mice. Furthermore, exposure of N43 cells to the ω6-PUFA linoleic acid, which is higher in female brains when compared to males, reduces palmitic acid-induced inflammation.

Conclusions: Our data suggest male and female brains, and not plasma, differ in their fatty acid profile. This is the first time, to our knowledge, lipidomic analyses has been used to directly test the hypothesis there is a sexual dimorphism in brain and plasma fatty acid composition following consumption of the chow diet, as well as following exposure to the WD.

Keywords: AA, arachidonic acid; ACC, acetyl-CoA carboxylase; B2m, beta-2 microglobulin; BBB, blood brain barrier; BSA, bovine serum albumin; C, Chow diet; CNS, central nervous system; Central nervous system; DHA, docosahexaenoic acid; F, female; FABP, fatty acid binding protein; FAS, fatty acid synthase; FAT/CD36, fatty acid transporter; FATP1, fatty acid transport protein 1; FAs, fatty acids; FFAs, free fatty acids; IL6, interleukin 6; LA, linoleic acid; Linoleic acid; M, male; MCD, malonyl-CoA decarboxylase; MSFD2a, membrane protein major facilitator super family domain containing 2a; MUFAs, monounsaturated fatty acids; N43; NF-κB, Nuclear Factor-κ Beta; Obesity; PA, palmitic acid; PUFAs, polyunsaturated fatty acids; Palmitic acid; SatFAs, saturated fatty acids; TFAs, total fatty acids; TNFα, Tumor Necrosis Factor α; UnsatFAs, unsaturated fatty acids; WD, western diet; WT, wild-type; Western diet; ω6-fatty acids.

Figure 1

Mice Body Weight: (A) Animals body weight at time of sacrifice. (B) Body-weight gain in male and female mice following WD exposure. All data are presented as mean ± SEM, and ***p < 0.001. n = 4/group.

Figure 2

Brain Total Fatty Acid (TFA) composition: (A) Heat-map showing the concentration of the FAs in brains of male and female mice fed chow or WD. Levels expressed as a relative fold-change with the male chow condition used as the baseline. (B) Relative abundance (in %) of the different classes of TFAs in the brain of male and female mice fed chow or WD. (C) concentration levels (in ng of FA per mg of brain dry weight) of the eight most abundant fatty acids quantified in the brain. All data are presented as mean ± SEM, and *p < 0.05, **p < 0.01, ***p < 0.001. n = 4/group. Statistically significant differences in (B) found between M Chow and M WD SatFA* and ω6-PUFA***; between Male WH and Female WD SatFA*, ω3-PUFA*** and ω6-PUFA***.

Figure 3

Plasma Total Fatty Acid (TFA) composition: (A) Heat-map showing the concentration of the FAs in plasma of male and female mice fed chow or WD. Levels expressed as a relative fold-change with respect to the male chow concentration. (B) Relative abundance (in %) of the different classes of TFAs in the plasma of male and female mice fed chow or WD. (C) concentration levels (in ng of FA per μL of plasma) of the eight most abundant fatty acids quantified the plasma. All data are presented as mean ± SEM, and *p < 0.05, **p < 0.01, ***p < 0.001. n = 4/group. Statistically significant differences in (B) found between Male Chow and Male WD SatFA***, MUFA***, ω3-PUFA*** and ω6-PUFA***; between Female Chow and WD SatFA**, ω3-PUFA** and ω6-PUFA***; between Male WD and F WD SatFA**, ω3-PUFA*** and ω6-PUFA*.

Figure 4

The anti-inflammatory activity of LA correlates with increased ω6-PUFA concentration: N43 cells were pre-treated for 1 h with LA and then treated for 5 h as indicated. (A) mRNA levels of inflammatory markers in N43 cells following treatments. All data are presented as mean ± SEM, and *p < 0.05, *p < 0.01. n = 3. (B) Heat-map of the different FA isomers analyzed in N43 following treatments. (C–F) Graphs of the concentration (ng/mg) of the different classes of FAs in N43 cells following the aforementioned treatments. All data are presented as mean ± SEM, and *p < 0.05, ***p < 0.001. n.s. = not significant. n = 3.