Stress or trigger a systemic immune response
September 21, 2018 Source: China Science News Author: Jin Nan
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Mitochondrial image source: Getty Images
Humans and other mammals adapt to stress and respond through a series of evolutions. In the face of predators hunting or losing their jobs, mammals and humans will release a series of stress hormones, rising heart rate, faster breathing, muscle tension, and sweating.
This “dry or run away†coping style is good for the ancestors, but it continues to be activated in today's modern life at a price. Scientists are beginning to realize that stress often exacerbates several diseases, including depression, diabetes, heart disease, AIDS and asthma. One of the theories that explain the relationship between stress and these extensive injuries points the finger at an unexpected source: a tiny "power generation room" within each cell.
Each cell of the human body contains tens of millions of "bean-shaped" tiny mitochondria, a secondary cell structure or organelle that provides energy for normal functioning. The mitochondria possess a circular genome of 37 genes. People only inherit this mitochondrial DNA from their mothers, so the composition of DNA coding tends to be consistent between generations.
But the human body's "dry or run away" mode will bring extreme demands to the mitochondria. Suddenly, they need to provide a lot of energy for faster heartbeats, dilated lungs, and tight muscles, which can make them vulnerable. Unlike DNA in the nucleus, mitochondria have only a limited repair mechanism. Recent animal studies have shown that chronic stress not only causes mitochondrial damage in the hippocampus, hypothalamus and frontal lobe, but also causes mitochondria to release DNA into the cytoplasm and eventually into the blood.
These genetic wastes are not just inert cell waste. "This flowing mitochondrial DNA is like a hormone," says Martin Picard, a psychobiologist who studies mitochondrial behavior and cellular free mitochondrial DNA at Columbia University. He said that cell mitochondrial DNA excretions are similar to cortisol released by the adrenal glands in response to stress. Certain cells produce flowing mitochondrial DNA, and like the adrenal glands, this effluent is also triggered by stress.
To demonstrate that psychological stress causes cells to release mitochondrial DNA, Picard and the team designed a rapid stress test. They asked 50 healthy men and women to quickly defend themselves against the wrong accusations in front of the camera. The researchers then collected blood samples from these participants and compared them to blood samples taken before they were stressed.
Although the stress task lasted only 5 minutes, the researchers found that the mitochondrial DNA levels in the serum of the participants were more than twice as high as 30 minutes after the test. These findings, which are in the review, provide the first direct evidence that mitochondrial DNA fragments drifting in the blood, like dominoes that fall one after another, transmit stress to other parts of the body. (Jin Nan)
Chinese Journal of Science and Technology (2018-09-20 2nd Edition International)
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