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In the most recent of a series of studies conducted at the California National Primate Research Center (CNPRC), Hong Ji, Ph.D. along with colleagues examined a possible mechanism through which wildfire exposure during early life causes altered immune response and decreased lung capacity in adulthood. The study involved collecting cells lining the inside of the nose in a group of adult monkeys that were born during an intense wildfire season and comparing the molecular aspects of those cells to a group of monkeys born during an average year (see the graph below).
Figure from: https://doi.org/10.1016/j.envint.2021.106993
Intense wildfire seasons create high levels of pollution in the air which can have long term effects on health depending on the developmental period when the exposure occurs. For example, adults may experience acute effects of the exposure such as coughing, headaches, etc., but young children are at a greater risk of developing lifelong disorders such as asthma, high blood pressure, and even stunted growth. These adverse effects of PM2.5 exposure are becoming increasingly known, but the mechanisms through which these changes persist in the body is still unknown.
Through studying the molecular changes occurring in the cells of young monkeys exposed to wildfire smoke Ji and her colleagues hope to better understand the processes responsible for the detrimental long-term effects on adult immune response and lung function. Their findings indicate that this process might be occurring through epigenetic mechanisms. Epigenetics are changes to genes and gene expression that do not alter the inherited DNA directly but alter what the body does with the inherited DNA. 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.
Interestingly, the current study revealed drastic differences between the epigenomes of monkeys born during the 2008 wildfire season, when levels of PM2.5 were extraordinarily high, and monkeys 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. While the authors expected differences between the groups of monkeys, they were surprised by the sheer quantity of their findings. Ji and her coauthors were even more surprised to find that these molecular differences did not appear to correlate with obvious differences in gene expression between the animals. In other words, although the epigenomes of the groups were different, the genome still appeared to be expressed similarly across all study subjects.
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.
This study was conducted in nasal epithelial cells, a layer of cells coating the inside of your nose, in adult animals. Although the epigenome still appears different, gene expression may only change through a period of development or between difference cells, or perhaps when the animal is undergoing another exposure to high levels of PM2.5.
Future studies will look for examine mechanisms other than epigenetics that could be contributing to the long-lasting changes in immune response and lung function as well as look for similar epigenetic profiles in humans exposed to high levels of wildfire. There are still a lot of questions about how exposure to abnormally high PM2.5 levels will affect the human population, but 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
Citations
Brown, A.P., Cai, L., Laufer, B.I., Miller, L.A., LaSalle, J.M. & Ji, H. Long-term effects of wildfire smoke exposure during early life on the nasal epigenome in rhesus macaques. 2021.Environmental international, 158.
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