In recent years, mounting evidence has backed up the profound idea that the legacy of trauma in childhood can be passed down to people's offspring, even affecting the mental and physical health of future generations. As one of the most jarring examples, studies have shown that the children of Holocaust survivors are more likely to experience severe schizophrenia and other health problems.
Although it’s known that this is guided by changes to the epigenome, a multitude of biological and chemical factors that affect how genes are expressed, it has never been crystal clear how the signals triggered by traumatic experience become “imprinted” in the reproductive cells.
Now, reporting in The EMBO Journal, scientists at the University of Zurich in Switzerland used mice to help explain how the impacts of trauma in early life might be passed down through generations via changes that occur in the blood. Their findings confirm the hypothesis that blood delivers stress signals to the reproductive cells, which thereby pass on the legacy of trauma to the next generation.
Firstly, they compared the blood of mice that experienced early life trauma with the blood of control mice and noted some significant differences in lipid metabolism, with the blood of traumatized mice showing way higher levels of certain polyunsaturated fatty acids metabolites. They then observed that these same changes were also found in the offspring of the traumatized mice. To further nail down the evidence, they infected the serum of traumatized male mice into non-traumatized male mice and found that these offspring also had these same metabolic changes, suggesting the changes in blood had affected their sperm cells and were being passed on to the next generation.
Next up, the researchers looked at 25 children from an orphanage in Pakistan who had lost their father and were separated from their mother. By comparing their blood and saliva samples to other kids, they found that the orphaned children had higher levels of several lipid metabolites, just like the traumatized mice.
The researchers then dug even deeper by trying to find the molecular mechanism that guides this process. They found that PPAR, a surface receptor on cells that helps to regulate gene expression in numerous tissues, becomes upregulated in the sperm of traumatized males. By artificially activating this receptor in male mice, it led to decreased body weight and changes in glucose metabolism. Once again, this effect was also seen in their offspring and even their grand-offspring.
Altogether, the study paints a clear picture of how trauma in childhood may become reflected in the reproductive cells and, as such, passed on to the offspring.
The researchers say they hope their findings will help to inform further research that looks at how tough childhoods and adverse life experiences can have a much-overlooked effect on peoples’ health in later life.
“These findings are extremely important for medicine, as this is the first time that a connection between early trauma and metabolic disorders in descendants is characterized," Isabelle Mansuy, a professor of neuroepigenetics at the University of Zurich’s Brain Research Institute and the ETH Zurich’s Institute for Neuroscience, said in a statement.
“Our findings demonstrate that early trauma influences both mental and physical health in adulthood and across generations, which can be seen in factors like lipid metabolism and glucose levels. This is rarely taken into consideration in clinical settings," they added.
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