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

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.

Acute stress and hippocampal histone H3 lysine 9 trimethylation, a retrotransposon silencing response.

The hippocampus is a highly plastic brain region particularly susceptible to the effects of environmental stress; it also shows dynamic changes in epigenetic marks in response to stress and learning. We have previously shown that, in the rat, acute (30 min) restraint stress induces a substantial, regionally specific, increase in hippocampal levels of the repressive histone H3 lysine 9 trimethylation (H3K9me3). Because of the large magnitude of this effect and the fact that stress can induce the expression of endogenous retroviruses and transposable elements in many systems, we hypothesized that the H3K9me3 response was targeted to these elements as a means of containing potential genomic instability.