Epigenetics: Can Stress Influence Your Genes?
Epigenetics: Can Stress Influence Your
Genes?
By Salimot Ojerinde,
Geisinger Commonwealth School of Medicine, MBS 2018
Mentor: Dr. Gregory
Shanower, PhD
Is there a long-term
biological effect associated with severe stress, personal loss, and adverse
conditions? In 2015, Rachel Yehuda and her colleagues at Mount Sinai published
the results of their study examining the genes of 32 Jewish men and women that
survived the Holocaust along with genes of 22 children who were born to these Holocaust
survivors after the Second World War. Previous studies had indicated that
children of Holocaust survivors have a higher risk of developing post-traumatic
stress disorder, depression and anxiety, especially if the parents themselves
have PTSD (Trappler et al, 2007), but there was no explanation as to how this
could be possible. Yehuda’s research suggested that a genetic cause was
responsible for this unusual inheritance of trauma. They found chemical changes
in DNA of Holocaust survivors that were passed on to their progeny, suggesting
that traumatic experiences affect DNA heredity in ways that can be passed on to
children and grandchildren, a kind of “molecular scars”.
The phenomena that Yehuda
and her team described is referred to as epigenetic inheritance. What is
epigenetic inheritance, you ask? Before I can explain what epigenetics is, we
need to understand the structure of DNA. Of the 50 trillion or so cells in the human
body, each one contains about two meters of DNA (Science Focus, 2011). In order
to fit the entire human genome into the cell nucleus, DNA is wrapped around
clusters of proteins called histones forming a nucleoprotein conglomerate known
as chromatin (Nature Education, 2014). Chromatin acts to organize the human
genome within the nucleus. The functional units of DNA are genes that tell the
cell what to do and what to become (Nature Education, 2014). Epigenetics
involves chemical modifications to DNA and chromatin, which regulate whether or
not genes are on or off depending on the environment or developmental
circumstances. DNA methylation, for example, is associated with turning genes
off during development and during normal cell metabolism. Some epigenetic marks
such as histone methylation can help condense chromatin, preventing the cell
from being able to read the genes, and essentially turning “off” the genes.
Other epigenetic marks such as histone acetylation can help loosen the
chromatin, making the genes easily accessible to the cell and the genes are
turned “on”.
Epigenetic modifications
occur in cells during development, as part of normal metabolism, and in
response to different environmental conditions (both intracellular and
extracellular in origin). Interestingly, when you were first conceived and your
cells were becoming more specialized, your chromatin is thought to be a “blank
slate”. This means that there are no epigenetic marks on it. It is only as embryonic
cells began to divide and receive signals and information from surrounding
cells that the epigenetic marks began to accumulate. It is during this time
that epigenetic marks can be influenced by the environment outside of the
developing embryo. The stressors that the mother endures during pregnancy can
be transmitted through her blood stream to her developing fetus influencing the
epigenetic state of the developing embryo.
So, to answer the question
that was initially posed, “Is there a long-term biological effect associated
with severe stress, personal stress, and adverse conditions?”, the answer, is
well, possibly. A strong body of evidence suggests that epigenetic marks can
have impactful consequences on the health of an individual which could
subsequently impact the health and well-being of their future progeny. This can
be observed in the case of the holocaust survivors, there is now evidence
suggesting that the severe treatment they faced epigenetically changed a number
of their genes. These changes were subsequently passed onto the progeny long
after the stressor had been removed from the parents. What is also intriguing
about this is that epigenetic modifications are thought to be completely
removed in the developing human germline. So how were these epigenetic changes passed
on the progeny? This is an area of research that is still being studied. Something
is making it through this barrier, and that thing is DNA methylation and
histone modifications.
Watch this animation on the subject:
https://www.powtoon.com/c/e06nXQvlMoT/1/m .
References
Nature Education. (2014).
Histone/Histones. https://www.nature.com/scitable/definition/histone-histones-57
Trappler, Brian &
Cohen, Carl & Tulloo, Rajeshree. (2007). Impact of Early Lifetime Trauma in
Later Life: Depression Among Holocaust Survivors 60 Years After the Liberation
of Auschwitz. The American journal of geriatric psychiatry : official journal
of the American Association for Geriatric Psychiatry. 15. 79-83.
10.1097/01.JGP.0000229768.21406.a7.
Yehuda R, Daskalakis NP,
Bierer LM, Bader HN, Klengel T, Holsboer F, Binder EB.Biol Psychiatry. 2016 Sep
01; 80(5):372-80
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