Can Early Life Exposure to Wildfire Smoke Alter Our Genes?

Early life wildfire smoke exposure led to long-term changes in genes impacting nervous and immune systems in rhesus macaques, according to research from the California National Primate Research Center (CNPRC) at the University of California, Davis. The work was published in Environment International Nov. 4, 2021, and builds upon a series of studies conducted by the CNPRC.

Previous studies indicate that early life exposure to wildfire smoke is associated with adolescent immune and respiratory challenges. These adverse effects of wildfire exposure are increasingly recognized, the mechanisms through which these changes persist in the body are still unknown.

“Epigenetics may be a potential mechanism that explains this phenomenon,” said Hong Ji, Ph.D, lead researcher on the study.

Epigenetics refers to external modifications to DNA that turn genes “on” or “off.” These modifications do not change our inherited DNA sequence, but instead, they affect how cells “read” our genes. Unlike the genome, which is the entire set of DNA inherited at the point of conception, the epigenome is flexible and can change through a myriad of environmental impacts.

External factors, like what we eat, our habits, the places we live, the air we breathe, can result in epigenetic changes.

To evaluate if early-life exposure to wildfire smoke had an impact on the epigenome, Ji and colleagues compared molecular aspects of nasal epithelium samples from two groups of adult female rhesus macaques: one group born just before the 2008 California wildfire season and the other group born in 2009 with no wildfire smoke exposure during early-life.

Their data revealed drastic differences between the epigenomes of macaques born during the 2008 wildfire season, when levels of PM2.5 were extraordinarily high, and macaques born during the following year with average levels of PM2.5. In total, there were over 3000 sites along the epigenome with molecular differences capable of altering gene expression.

Most of the DNA methylation changes occurred near nervous and immune system genes. Additionally, genes involved in asthma, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis showed changes in DNA methylation.

While Ji and her coauthors expected differences between the groups of macaques, they were surprised by the sheer quantity of their findings. They were even more surprised to find that these molecular differences did not correlate with obvious differences in gene expression between the animals. In other words, although the epigenomes of the two groups were different, these differences were not associated with alterations of genes important for nervous and immune functions.

One possible reason for the perplexing similarity in gene expression despite epigenetic differences is the role those differences play in the body. Our genome is vast and complex, expressing genes differently depending on the stage in development, the type of cells they are expressed in, and the current demands on those cells. Think about the different demands of a blood cell carrying oxygen through the body might have from a nerve cell communicating sensory input to the brain. Alternatively, sex organs require specific cellular activity depending on the stage of development when the conditions are right to start producing more hormones.

“Although we did not see any differences in gene expression, this study opens the door to a lot of research on the epigenetic effects of wildfire,” says Ji. “We hypothesize that gene expression may only change when challenged with additional exposure to high levels of PM 2.5 or other disease associated risk factors such as bacterial infection or viral infection.”

Wildfire smoke is responsible for around 20% of all particulate emissions in the U.S. and affects millions of people worldwide. Children are especially vulnerable to exposure, making this type of research more critical now than ever. There are still a lot of questions about how exposure to wildfire will affect the human population. Still, the evidence so far continues to illustrate the importance of minimizing pollution as much as possible.

For recommendations on how to protect yourself and others from wildfire smoke please visit: https://www.cdc.gov/nceh/features/wildfires/index.html

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