Acute Stress Leaves Epigenetic Marks on the Hippocampus
ScienceDaily (Jan. 4, 2010) — In trying to explain psychiatric disorders, genes simply cannot tell the whole story. The real answers are in the interaction of genes and the environment. Post-traumatic stress disorder requires some trauma, for instance, and people, for the most part, aren't born depressed. Now research has revealed one mechanism by which a stressful experience changes the way that genes are expressed in the rat brain. The discovery of "epigenetic" regulation of genes in the brain is helping change the way scientists think about psychiatric disorders and could open new avenues to treatment.
Richard Hunter, a postdoc in Rockefeller University's Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, found that a single 30-minute episode of acute stress causes a rapid chemical change in DNA packaging proteins called histones in the rat hippocampus, which is a brain region known to be especially susceptible to the effects of stress in both rodents and humans.
The chemical change Hunter examined, called methylation, can either increase or decrease the expression of genes that are packaged by the histones, depending on the location of the methylation. He looked for methylation on three regions of histone H3 that have been shown to actively regulate gene expression. In experiments published this month in Proceedings of the National Academy of Sciences, he shows that methylation of one mark, H3K9 trimethyl, roughly doubled in the hippocampus. Methylation of a second mark, H3K27 trimethyl, dropped by about 50 percent in the same area. Changes associated with the third mark were minor.
"The hippocampus is involved in episodic memory, so you would expect it to be sensitive to episodic experiments like this, more so than the motor regions, for instance," says Hunter, who worked on the project with Rockefeller scientists Bruce S. McEwen and Donald W. Pfaff. "But what is surprising is the magnitude and regional specificity of these patterns." The sheer size of the change in histone methylation suggests that it is important to the brain's response to acute stress, although its exact role remains a mystery. The two methyl marks that changed are both thought to repress gene expression usually, but methylation increased in one and decreased in the other.
http://www.sciencedaily.com/releases/2009/12/091231153341.htmI was not born depressed. I was not born as a computer geek who cannot find a job. My environment has had a lot to do with who and where I am - and there are some things in that I cannot change nor do I have control over. Those things I can control are on my shoulders and are my own fault, but I do not exist (nor do you) in a vacuum.
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