While your genes are more or less set in stone, the way they're expressed can be changed by environmental or lifestyle factors, and there's evidence that these changes can even be inherited from parents. A new study has found that male mice who spend time in cold environments may pass down this "experience" to their kids, in the form of higher levels of warming brown fat.

Our gene expression can be modified by what we eat or how much stress we're put under, which in turn can affect our lifespan, and risk of cancer or other illnesses. Last year, a NASA twin experiment examined how living in that most harsh of environments, space, can affect gene expression. By comparing the genes of an astronaut who'd recently spent a year on the International Space Station to those of his twin brother who didn't, the scientists spotted a large number of differences in expression.

But are these changes inheritable? Past research, such as a 2015 study that suggested Holocaust survivors could pass on lingering trauma to their children, has been controversial, but a recent epigenetics study found more concrete evidence. A team at DZNE had a group of mice undergo intense physical and mental training, and found that the offspring of these animals inherited the same benefits.

The new study, led by scientists at ETH Zurich, took a similar approach to determining whether ambient temperature would affect the gene expression of mice offspring. To do so, they kept one group of mice at a comfortable 23° C (73.4° F), while another group lived at a much more brisk 8° C (46.4° F). After a few days at those temperatures, the animals were allowed to mate and the resulting babies were then examined for any changes.

The specific change the team was looking for was levels of brown adipose. This "healthy" version of fat tissue is known to keep human babies warm, and was only very recently discovered in adults too. Unlike infamous white fat, brown fat burns more readily, helping people lose weight and avoid the metabolic issues of obesity.

The researchers found that the offspring of male mice kept in the cold prior to conception had higher levels of brown fat than those whose fathers had lived more comfortably. When the young mice were fed a high-fat diet, those with cool dads gained less weight than the control group.

Interestingly, the temperature that the mothers were kept at didn't seem to have any effect on the health of their offspring. Backing up the DZNE study, that seems to be because epigenetic changes affect the DNA methylation of sperm.

Of course, as a mouse study it's hard to know just how this might translate to humans, but the finding does seem to correlate with other observations. The researchers analyzed computer tomography images of 8,400 patients and found that in general, people conceived in the colder half of the year have more brown fat than those whose parents got frisky in the summertime.

"Until now, the assumption was that this had something to do with the temperatures people experienced during their lifetime," says Christian Wolfrum, lead researcher on the study. "But our observations suggest that temperatures prior to conception might also affect later levels of brown fat."

Next up, the team is planning to study how epigenetic changes in human sperm differ between summer and winter.

The research was published in the journal Nature Medicine.

Source: ETH Zurich