Stress and corticosteroids regulate rat hippocampal mitochondrial DNA gene expression via the glucocorticoid receptor

Abstract

Glucocorticoids (GCs) are involved in stress and circadian regulation, and produce many actions via the GC receptor (GR), which is classically understood to function as a nuclear transcription factor. However, the nuclear genome is not the only genome in eukaryotic cells. The mitochondria also contain a small circular genome, the mitochondrial DNA (mtDNA), that encodes 13 polypeptides. Recent work has established that, in the brain and other systems, the GR is translocated from the cytosol to the mitochondria and that stress and corticosteroids have a direct influence on mtDNA transcription and mitochondrial physiology. To determine if stress affects mitochondrially transcribed mRNA (mtRNA) expression, we exposed adult male rats to both acute and chronic immobilization stress and examined mtRNA expression using quantitative RT-PCR. We found that acute stress had a main effect on mtRNA expression and that expression of NADH dehydrogenase 1, 3, and 6 (ND-1, ND-3, ND-6) and ATP synthase 6 (ATP-6) genes was significantly down-regulated. Chronic stress induced a significant up-regulation of ND-6 expression. Adrenalectomy abolished acute stress-induced mtRNA regulation, demonstrating GC dependence. ChIP sequencing of GR showed that corticosterone treatment induced a dose-dependent association of the GR with the control region of the mitochondrial genome. These findings demonstrate GR and stress-dependent transcriptional regulation of the mitochondrial genome in vivo and are consistent with previous work linking stress and GCs with changes in the function of brain mitochondria.

Keywords: allostasis; brain metabolism; mitochondrial plasticity; mitochondrial transcription; nuclear receptors.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Change in the expression of mitochondrial mRNA after acute immobilization stress and brief (1-h) recovery. There was a main effect of stress on mtRNA expression (n = 8, F = 40.3, P < 0.0001) and were significant decreases in ND-1 (*P < 0.05) and ND-3, ND-6, and ATP-6 expression (**P < 0.001).

Fig. S1.

Acute administration of 300 μg corticosterone to adrenalectomized rats recapitulates the effects of acute stress on the expression of the mitochondrial genes ND-6 (A) and ATP-6 (B) (n = 6; *P < 0.03).

Fig. 2.

Chronic (21-d) immobilization stress increased the expression of the mitochondrial ND-6 gene (n = 8; *P < 0.05) but had no significant effect on the expression of other mitochondrial genes.

Fig. 3.

Acute immobilization stress in adrenalectomized rats did not have an effect on the expression of mtRNA (n = 5–8; *P < 0.05 versus sham controls; +P < 0.05 versus sham stress, no difference from sham control). ADX, adrenalectomized.

Fig. 4.

(A) GR interaction with the mitochondrial chromosome after a dose of either 300 μg/kg (green) or 3,000 μg/kg (blue) [n = 6; *P < 1 × 10−9; FDR < 0.001%; visualization produced using IGV (48)]. The yellow bar denotes the location of the D-loop control region. (B) Representative Bamtools image of mt-mRNA RNA-seq reads from vehicle-treated adrenalectomized rat hippocampus. (C) mt-mRNA RNA-seq reads from acute (300 μg/kg) corticosterone-treated adrenalectomized rat hippocampus. Corticosterone treatment resulted in significantly higher expression of 10 of 13 mtDNA genes (n = 6; P < 0.00005; q < 0.0008).

Fig. 5.

Relation of corticosterone-induced GR binding in rat hippocampus to the structure of the rat mitochondrial genome. Heavy-strand mitochondrial genes are shown in blue, light-strand genes are shown in green, and the two mt-rRNA genes are shown in yellow. The D-loop binding site observed at both 300-μg and 3-mg doses of corticosterone is shown as a red box in the D-loop control region.