In the study of 28 Caucasian men, two sperm microRNAs – miRNA449 and miRNA34 – were expressed significantly less in those who had experienced abuse, neglect or other dysfunctional family experiences as a child. In men who had had gone through the most extensive childhood abuse, the reduction in the sperm microRNAs was as much as 300-fold.
Both miRNA449 and miRNA34 are expressed in sperm, but not eggs, meaning that only fathers can contribute these two microRNAs to the next generation.
In a second experiment, the researchers found that these differences were passed down to the offspring of male mice. Males going through chronic social stress had lowered levels of the same two microRNAs in their sperm. The embryos conceived with this sperm also had lower levels of those microRNAs, as did the sperm of the grown offspring.
'The study raises the possibility that some of the vulnerability of children is due to Lamarckian-type inheritance derived from their parents' experiences,' said Professor Larry Feig at Tufts University School of Medicine in Boston, Massachusetts, who led the study .
Some of the psychological disorders reported among the children of men exposed to early life stress could be explained by the regulation of specific sperm microRNAs, the authors suggest.
'Looking to the future, we may be able to figure out a way to restore the low miRNA levels found in men exposed to extreme trauma, because epigenetic changes, such as stress-induced decreases in sperm miRNA expression, are reversible, unlike genetic changes that alter the DNA sequence,' said David Dickson, a PhD student at Tufts and first author of the study.
The results are published in Translational Psychiatry. In their next study, the researchers are carrying out an investigation in a larger number of men, and more experiments in mice to explore these intergenerational effects further.