Sex-related factors influence expression of mood-related genes in the basolateral amygdala differentially depending on age and stress exposure - PubMed (original) (raw)

Rachel Puralewski et al. Biol Sex Differ. 2016.

Abstract

Background: Women are twice as likely to be diagnosed with major depressive disorder (MDD) compared to men, but the molecular mechanisms underlying this sex difference are unclear. Previous studies in the human postmortem brain suggest dysfunction in basolateral amygdala (BLA) inhibitory gamma-aminobutyric acid (GABA) signaling and brain-derived neurotrophic factor (BDNF) function, specifically in females with MDD.

Methods: We investigated the effects of sex chromosome complement, developmental gonadal sex, and circulating testosterone on expression of 3 GABA-related and 2 BDNF-related genes in the BLA using three cohorts of four core genotypes (FCG) mice. Cohort 1 included gonadally intact pre-pubertal FCG mice; results were analyzed using two-way ANOVA (sex chromosome complement-by-gonadal sex). We examined the same genes under adult non-stressed (cohort 2) and chronically stressed conditions (cohort 3). The results for cohorts 2 and 3 were analyzed by three-way ANOVA (sex chromosome complement-by-gonadal sex-by-hormone). The use of heatmaps and Spearman correlation of BLA gene expression and anxiety-like behavior provides a global interpretation of gene expression patterns.

Results: In weanlings, we found an effect of sex chromosome complement, with lower expression of GABA/BDNF-related genes in XY mice. Most of these effects did not persist into adulthood, although a number of interesting interactions between organizational and activational effects of hormones emerged. In our adult cohorts, we found that testosterone had different effects depending on stress conditions and/or gonadal sex. Notably, in our chronically stressed adults, we found that the BLA pattern of gene expression for the GABA-related gene, somatostatin (Sst), matched the anxiety-like behavior pattern (i.e., lower Sst and higher anxiety-like behavior in XY mice, while testosterone increased Sst and decreased anxiety-like behavior). Additionally, increased Sst gene expression was correlated with decreased anxiety-like behavior.

Conclusions: Sex chromosome complement is an important factor modulating expression of mood-related genes during pre-pubertal development. The observed sex differences under chronically stressed conditions suggest that different molecular profiles may characterize male and female MDD. Our findings here for Sst are especially interesting, and suggest an underlying XY vulnerability that is typically compensated for by circulating testosterone in "normal" males. Without testosterone, women may have lower SST expression in the amygdala, resulting in increased MDD vulnerability.

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Figures

Fig. 1

Fig. 1

Experimental design for cohorts 1, 2, and 3. a Mice in cohort 1 were sacrificed at postnatal day 21 (P21; prior to the onset of puberty). b Mice in cohorts 2 and 3 were gonadectomized (GDX) at ~15 weeks of age and implanted subcutaneously with either a testosterone (T)-filled or blank capsule. After GDX, mice in cohort 2 were left unmanipulated until they were sacrificed at 24 weeks of age. After GDX, mice in cohort 3 were exposed to 8 weeks of unpredictable chronic mild stress (UCMS), and then sacrificed (same age as cohort 2). At the time of sacrifice for all cohorts, the brains were harvested for gene expression analyses and bloods were collected for hormone assays

Fig. 2

Fig. 2

The effects of sex-related factors on expression of GABA- and BDNF-related genes in the basolateral amygdala of weanling mice. Mice with male sex chromosome complement (XY) had significantly lower expression of Sst (a), Gad67 (b), Gad65 (c), and TrkB (d) compared to XX mice; there was no effect of sex chromosome complement on Bdnf expression (e). There were no organizational effects of hormones on expression of any gene investigated (a–e). For each gene, graphs on the left show results individually for all four experimental groups. Graphs on the right summarize the same data as shown on the left after collapsing across main effects. Numbers at base of bars indicate N. For main effect comparisons: **p < 0.01; *p < 0.05; # p < 0.1. F gonadal female, M gonadal male

Fig. 3

Fig. 3

The effects of sex-related factors on expression of GABA- and BDNF-related genes in the basolateral amygdala of non-stressed adult mice. There was no effect of sex chromosome complement on expression of Sst (a), Gad67 (b), Gad65 (c), or Bdnf (e). However, mice with male sex chromosome complement (XY) had significantly lower expression of TrkB (d). e Mice with male developmental gonadal sex had lower Bdnf expression compared to mice with female developmental gonadal sex. Testosterone significantly increased expression of Bdnf. For each gene, graphs on the left show results individually for all eight experimental groups. Graphs on the right summarize the same data as shown on the left after collapsing across main effects. Numbers at the base of bars indicate N. For main effect comparisons: *p < 0.05. T testosterone, B blank, F gonadal female, M gonadal male

Fig. 4

Fig. 4

Interactions of sex-related factors on expression of GABA- and BDNF-related genes in the basolateral amygdala of non-stressed adult mice. There was a significant gonadal sex by hormone interaction on expression of Gad67 (a) and Gad65 (b), with testosterone significantly increasing gene expression only in gonadal males. c There was a significant gonadal sex by hormone interaction for Bdnf, with testosterone significantly increasing expression only in gonadal females. Numbers at the base of bars indicate N. For post hoc two-group comparisons: $ p < 0.05. T testosterone, B blank, F gonadal female, M gonadal male

Fig. 5

Fig. 5

The effects of sex-related factors on expression of GABA- and BDNF-related genes in the basolateral amygdala of stressed adult mice. a Mice with male sex chromosome complement (XY) had lower expression of Sst. Additionally, mice treated with testosterone had higher Sst expression. There were no main effects of sex chromosome complement on expression of Gad67 (b), Gad65 (c), TrkB (d), or Bdnf (e). There were no main effects of gonadal sex on gene expression (a–e). Testosterone significantly decreased expression of Bdnf (e), but did not affect expression of Gad67 (b), Gad65 (c), or TrkB (d). There was a significant three-way sex chromosome complement × gonadal sex × hormone interaction on expression of Gad67 (b, left) and Gad65 (c, left). Specifically, the post hoc analyses revealed a significant interaction of gonadal sex and hormone only in XY mice. Graphs on the left show results individually for all eight experimental groups. For each gene, graphs on the right summarize the same data as shown on the left after collapsing across main effects. Numbers at the base of the bars indicate N. For main effect comparisons: *p < 0.05. For interaction between gonadal sex and hormone: δ p < 0.05. T testosterone, B blank, F gonadal female, M gonadal male

Fig. 6

Fig. 6

Interactions of sex-related factors on expression of GABA- and BDNF-related genes in the basolateral amygdala of stressed adult mice. a There was a significant sex chromosome complement by gonadal sex interaction for Sst, with a pattern for an increase in expression in gonadal males compared to gonadal females for XX mice and a pattern of a decrease in expression in gonadal males compared to gonadal females for XY mice. b There was a trend for an interaction of gonadal sex and hormone on Bdnf expression, with exploratory analysis revealing that testosterone decreased Bdnf expression only in gonadal females. Numbers at the base of the bars indicate N. For post hoc two-group comparisons: $$ p < 0.01. T testosterone, B blank, F gonadal female, M gonadal male

Fig. 7

Fig. 7

Heatmap representation of basolateral amygdala gene expression results. Expression for each main factor is expressed as the “male” phenotype divided by the “female” phenotype (i.e., sex chromosome complement, XY/XX; organizational, male gonads/female gonads; activational, testosterone/blank). Red is indicative of higher levels of expression in male phenotypes; blue is indicative of higher levels of expression in female phenotypes. Heatmap representation was done for a weanlings, b adult non-stressed, and c adult stressed. For main effect comparisons: **p < 0.01; *p < 0.05; # p < 0.1

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