Adolescent stress-induced epigenetic control of dopaminergic neurons via glucocorticoids

Abstract

Environmental stressors during childhood and adolescence influence postnatal brain maturation and human behavioral patterns in adulthood. Accordingly, excess stressors result in adult-onset neuropsychiatric disorders. We describe an underlying mechanism in which glucocorticoids link adolescent stressors to epigenetic controls in neurons. In a mouse model of this phenomenon, a mild isolation stress affects the mesocortical projection of dopaminergic neurons in which DNA hypermethylation of the tyrosine hydroxylase gene is elicited, but only when combined with a relevant genetic risk for neuropsychiatric disorders. These molecular changes are associated with several neurochemical and behavioral deficits that occur in this mouse model, all of which are blocked by a glucocorticoid receptor antagonist. The biology and phenotypes of the mouse models resemble those of psychotic depression, a common and debilitating psychiatric disease.

Fig. 1

The GXE mouse model: Behavioral abnormalities in DISC1-DN-Tg-PrP after exposure to adolescent isolation stress for 3 weeks. (A) Deficits in PPI. (B) Impaired performance in the forced swim test. (C) Aberrant locomotor activity. CTL, wild type without isolation; E, wild type with isolation; G, DISC1-DN-Tg-PrP without isolation; GXE, DISC1-DN-Tg-PrP with isolation. Values are means ± SE; **P < 0.01, *P < 0.05. Numbers of animals and statistical information are described in tables S1 and S2.

Fig. 2

Dopaminergic disturbances in the GXE model. (A) Levels of total content of monoamines [dopamine (DA), norepinephrine (NE), and serotonin (5-HT)]. (B) Levels of extracellular basal DA in the Fc. (C) Levels of total content of monoamines in the CPu. (D) Levels of TH in the Fc. (E) Levels of TH in the NAc. (F) Extracellular DA levels upon METH challenge in the Fc. (G) Extracellular DA levels upon METH challenge in the NAc. Total and extracellular levels of neurotransmitters were measured by high-performance liquid chromatography and in vivo microdialysis, respectively. Values are means ± SE; **P < 0.01, *P < 0.05.

Fig. 3

Influence of glucocorticoids on neurochemical and behavioral abnormalities in the GXE model. (A) Levels of plasma corticosterone after behavioral tests. (B) Effects of the GR antagonist RU38486 on levels of extracellular basal DA in the Fc. (C) Effects of RU38486 on levels of extracellular DA upon METH challenge in the NAc. (D to F) Effects of RU38486 on performance of PPI (D), forced swim test (E), and locomotor activity (F). Veh, treated with vehicle; RU, treated with RU38486. Values are means ± SE; **P < 0.01, *P < 0.05.

Fig. 4

Distinct influence of glucocorticoids on epigenetic modification of the Th genes between mesocortical and mesolimbic dopaminergic projections in the GXE model. (A) Confocal images of TH-immunopositive cells in the VTA (blue), which are also labeled with retrogradely transported beads in mesocortical neurons (green) and those in mesolimbic neurons (red), respectively. Scale bars, 20 and 10 µm for upper and lower panels, respectively. (B) Graphic representation of the bisulfite-sequenced region in the promoter of the Th gene. The 11 CpG sites inside the island are indicated by open circles. The transcription start site (arrow), first exon (white box), and translation start site (ATG) are shown. (C) DNA methylation pattern of the Th promoter in the VTA neurons projected to the Fc. (D) DNA methylation pattern of the Th promoter in the VTA neurons projected to the NAc. (E) Effects of RU38486 on increased DNA methylation of the Th promoter in the VTA neurons projected to the Fc. (F) Long-lasting change in the DNA methylation of the Th promoter in the VTA neurons projected to the Fc. GXE-G, GXE returned to group housing from 8 to 20 weeks. The columns and rows represent the 11 CpG sites and the sequenced clones, respectively. Black and white squares indicate methylated and unmethylated CpG sites, respectively. Results were obtained from at least three independent experiments. In right panels of (C) to (F), values are means ± SE; **P < 0.01, *P < 0.05.