By studying mice that had become depressed, Chinese researchers found that they transmitted a stronger tendency to depression to their offspring, but not through the genes. How is this condition transmitted?
No embarrassment from depression?
Depression is a very common mental illness, but it should not be confused with depression, which is a passing state and not an illness.
If scientists have not yet understood all the contours of this disease, it was generally accepted that there could be genetic predispositions. Indeed, we know that depression often affects members of the same family. However, no gene for depression has been identified.
A new study, published in Science Advances, conducted at Nanjing University in China, brings new elements.
Depressed male mice
To carry out their research, the researchers made mice depressed. To do this, they subjected male mice to mild, but repeated, and unpredictable stress for five weeks. At the end of these five weeks, the mice lost weight and became listless and anhedonic compared to the other mice.
These depressed males then mated with healthy females. When their young pups reached adulthood, the researchers put them under two weeks of mild stress. Results? They developed the same symptoms as their parent.
Transmission by microRNAs from spermatozoa
According to the researchers, this hereditary depression is not caused by genes, but is transmitted via small RNAs. By examining the semen of male mice, they did indeed observe changes in the genetic content. They isolated all the non-coding RNAs from sperm and injected them into a healthy zygote. The latter was then implanted in a carrier mouse. The young pups born from the experiment also showed sensitivity to depression.
“We show that offspring of depressed fathers develop an increased susceptibility to depression when exposed to mild stress, and that sperm RNAs (especially microRNAs) play a causal role in the inheritance of depression. Such a mechanism of epigenetic inheritance of the germ line opens a new way to fill the void in our knowledge on the physiopathology of depression ”, explains Xi Chen, main author of the work.
According to him, this discovery could “Offer a new dimension for the development of new antidepressant treatments”.
