Prolonged maternal exposure to glucocorticoids alters selenoprotein expression in the developing brain

Abstract

Aberrant activation of the stress-response system in early life can alter neurodevelopment and cause long-term neurological changes. Activation of the hypothalamic-pituitary-adrenal axis releases glucocorticoids into the bloodstream, to help the organism adapt to the stressful stimulus. Elevated glucocorticoid levels can promote the accumulation of reactive oxygen species, and the brain is highly susceptible to oxidative stress. The essential trace element selenium is obtained through diet, is used to synthesize antioxidant selenoproteins, and can mitigate glucocorticoid-mediated oxidative damage. Glucocorticoids can impair antioxidant enzymes in the brain, and could potentially influence selenoprotein expression. We hypothesized that exposure to high levels of glucocorticoids would disrupt selenoprotein expression in the developing brain. C57 wild-type dams of recently birthed litters were fed either a moderate (0.25 ppm) or high (1 ppm) selenium diet and administered corticosterone (75 μg/ml) via drinking water during postnatal days 1 to 15, after which the brains of the offspring were collected for western blot analysis. Glutathione peroxidase 1 and 4 levels were increased by maternal corticosterone exposure within the prefrontal cortex, hippocampus, and hypothalamus of offspring. Additionally, levels of the glucocorticoid receptor were decreased in the hippocampus and selenoprotein W was elevated in the hypothalamus by corticosterone. Maternal consumption of a high selenium diet independently decreased glucocorticoid receptor levels in the hippocampus of offspring of both sexes, as well as in the prefrontal cortex of female offspring. This study demonstrates that early life exposure to excess glucocorticoid levels can alter selenoprotein levels in the developing brain.

Keywords: corticosterone; glucocorticoid; neurodevelopment; selenium; selenoprotein.

Figure 1

Summary of experimental design. Wild-type C57BL/6 N mice were mated while being fed chow that contained either a moderate selenium (ModSe, 0.25 ppm) or high selenium (HiSe, 1 ppm) content. Following the birth of a litter, on postnatal day 1 (PND1), either corticosterone (CORT, 75 μg/ml), or vehicle control (1% grain alcohol) were added to the drinking water, and replaced twice weekly. On PND15, the entire litter was sacrificed and brain regions were harvested for western blot analysis.

Figure 2

Western blot analysis of the prefrontal cortex (PFC), hypothalamus (HYP), and hippocampus (HPC) of male mice on either a moderate (ModSe) or high selenium (HiSe) diet being treated with either CORT or vehicle control (VEH). (A) Percentage change in glucocorticoid receptor (GCR) protein levels. HPC: CORT and HiSe consumption both independently decreased GCR levels [p_CORT = 0.0018, F_(1,9) = 15.15. p_SeDiet = 0.0077, F_(1,9) = 11.68]. HiSe diet without CORT decreased GCR to the level of CORT-exposed ModSe mice, and GCR expression in both groups was significantly lower than the ModSe/VEH group (B) Percentage change in SELENOW protein levels. HYP: CORT increased SELENOW levels [p_CORT = 0.0178, F_(1,9) = 8.378], particularly within HiSe offspring. (C) Percentage change in GPX1 protein levels. CORT significantly increased GPX1 levels in the PFC [p_CORT = 0.0060, F_(1,9) = 12.79], HYP [p_CORT = 0.0015, F_(1,9) = 20.28] and HPC [p_CORT = <0.0001, F_(1,9) = 63.59]. HiSe diet consumption increased GPX1 in the HPC: p_SeDiet = 0.0147, F_(1,9) = 9.052. GPX1 reached the highest levels within the HiSe/CORT condition as this group was significantly higher than the ModSe/CORT group. (D) Percentage change in GPX4 protein levels. GPX4 was elevated in response to CORT in all brain regions: PFC [p_CORT = 0.0238, F_(1,9) = 7.372], HYP [p_CORT = 0.0045, F_(1,9) = 14.08], and HPC [p_CORT = 0.0037, F_(1,9) = 15.15]. Unexpectedly, maternal Se intake negatively impacted GPX4 levels in the PFC: p_SeDiet = 0.0253, F_(1,9) = 7.171. Individual data points are shown and bars indicate the mean ± standard error of the mean. All comparisons were made within each brain region for each protein via 2-way ANOVA, where # indicates a significant effect of CORT and % a significant effect of Se diet, with Tukey’s multiple comparisons used as a post-hoc test: *p < 0.05, **p < 0.01, ***p < 0.001. N = 3, 3, 3, 4 indicated in graph.

Figure 3

Western blot analysis in the prefrontal cortex (PFC), hypothalamus (HYP), and hippocampus (HPC) of female mice on a moderate (ModSe) or high selenium (HiSe) diet being treated with either CORT or vehicle control (VEH). (A) Percentage change in glucocorticoid receptor (GCR) protein levels. CORT significantly reduced GCR in the HPC [p_CORT = 0.0002, F_(1,11) = 28.70]. As with male offspring, maternal consumption of HiSe decreased GCR levels in the HPC [p_SeDiet = 0.0040, F_(1,11) = 13.14], however this effect was also observed in the PFC[p_SeDiet = 0.0269, F_(1,11) = 6.514]. (B) Percentage change in SELENOW protein levels. CORT significantly increased SELENOW levels in the HYP: p_CORT = 0.0118, F_(1,11) = 9.075. HiSe also increased SELENOW in the PFC: p_SeDiet = 0.0415, F_(1,11) = 5.322. (C) Percentage change in GPX1 protein levels. CORT increased GPX1 levels in all three brain regions: PFC [p_CORT = 0.0022, F_(1,10) = 16.68], HYP [p_CORT = 0.0010, F_(1,11) = 19.78], and HPC [p_CORT = 0.0032, F_(1,11) = 14.02]. HiSe increased GPX1 in both the PFC [p_SeDiet = 0.0244, F_(1,10) = 7.009] and the HPC [p_SeDiet = 0.0094, F_(1,11) = 9.852]. (D) Percentage change in GPX4 protein levels. CORT elevated GPX4 levels in all brain regions: PFC[p_CORT = 0.0170, F_(1,10) = 8.175], HYP[p_CORT = 0.0001, F_(1,11) = 34.09], and HPC[p_CORT = 0.0032, F_(1,11) = 14.03]. All comparisons were made within each brain region for each protein via 2-way ANOVA, where # indicates a significant effect of CORT and % a significant effect of Se diet, with Tukey’s multiple comparisons used as a post-hoc test: *p < 0.05, **p < 0.01, ***p < 0.001. N = 4, 4, 3, 4 indicated in graph.