Exposure to stress has a number of psycho- and physiological consequences, including the activation of epigenetic mechanisms (histone modifications, methylation of DNA bases and the action of micro RNA). They do not alter the nucleotide sequence in DNA, but rather affect the level of expression of target genes. Brain area that is particularly affected is the hippocampus. In the hippocampus, the epigenetic mechanisms alter the level of expression of glucocorticoid receptors (GR), which may increase the risk for developing anxious and depressive-like behaviour, decrease hippocampal volume and the connections between its sub-regions. Stress can also trigger epigenetic mechanisms that decrease the expression of brain-derived neurotrophic factor (BDNF), thereby diminishing its positive effects on cell growth and hippocampal development. As stress-related mental illnesses are becoming more prevalent, research of epigenetic mechanisms in the hippocampus may lead to many promising findings, especially those in the field of epigenetic drug development.
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