Epigenetic effects of psychological stressors in humans
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The term epigenetics describes the machinery that acts over DNA and controls gene expression and cellular phenotype. With this mechanism, the epigenome controls gene expression by silencing or activating gene transcription. Epigenetics has been characterized as the mediator between environment and the genome. The genome of living eukaryotic organisms is influenced by external environmental cues which modify its functions. The occurring modifications, subsequently define the final phenotype and determine the behavior of the organisms. Stressful signs received from the environment can influence epigenetic mechanisms. These stressful cues can include psychosocial changes across the lifespan of an organism, implying that social environment is able to indirectly change phenotypic features through epigenetic mechanisms. Recently, research has been focused on the effect of psychological stressing cues on the epigenetic machinery, with most of the studies being focused on DNA methylation changes. Animal studies have shown that stressful events during different developmental stages of the organism, especially during early development, can have persistent effects on the epigenome and on the consequent phenotype. Although human studies concerning the effect of psychological stressors are relatively limited, there is growing evidence that similar phenomena with the ones obtained from animal studies, take place in humans too. All studies published so far regarding the effects of psychological stressors in the human epigenome in different developmental stages will be interpreted and discussed in this review, in an attempt to give an insight of the connection between environment and the epigenome.