Gene expression fails to adapt in night shift workers

Working the night shift is not a prospect that a whole lot of people relish, but that doesn’t stop the positions from being filled. Statistics indicate that there were about 1.7 million Australians doing some kind of shift work as part of their main occupation in 2015, with 204,000 regularly working night and evening shifts that year.

The problem is that the typical biological clock is tuned to be most active in the daytime, so not only are shift workers’ bodies fighting against the dark and cold of the night — they’re also fighting their own circadian rhythms. But have you ever wondered whether you could overcome these natural urges if you did shift work for long enough? Might you even be able to change your body at a genetic level?

Investigating the molecular mechanisms associated with shift work-related health problems, researchers from the Douglas Mental Health University Institute (a teaching hospital affiliated with McGill University) recently revealed the impact that a four-day simulation of night shift work had on the expression of 20,000 genes. The results of their study were published in the Proceedings of the National Academy of Sciences.

The research saw eight healthy volunteers artificially subjected to a five-day schedule simulating night shift work. Living in a time-isolation room, they were deprived of any light or sound cues characteristic of the time of day, and were not allowed to use their phones or laptops. After sleeping during their normal bedtimes at the end of the first day, the volunteers spent the next four days working ‘night shifts’ — remaining awake during the night and sleeping during the day.

On the first day and after the last night shift, the team collected blood samples at different times for a period of 24 hours. Postdoctoral fellow Laura Kervezee then measured the expression of more than 20,000 genes using a technique called transcriptomic analysis and assessed which of these genes presented a variation over the day-night cycle.

“We now better understand the molecular changes that take place inside the human body when sleeping and eating behaviours are in sync with our biological clock,” said Dr Diane B Boivin, one of the authors on the study. “For example, we found that the expression of genes related to the immune system and metabolic processes did not adapt to the new behaviours.”

The expression of many of the genes analysed in the study varies over the course of the day and night, their repetitive rhythms important for the regulation of many physiological and behavioural processes. The study found that these rhythms did not successfully adapt to life during the night shifts.

“Almost 25% of the rhythmic genes lost their biological rhythm after our volunteers were exposed to our night shift simulation,” said Dr Nicolas Cermakian. “73% did not adapt to the night shift and stayed tuned to their daytime rhythm. And less than 3% partly adapted to the night shift schedule.”

So what do these observations mean for shift workers’ health? Dr Boivin stated, “We think the molecular changes we observed potentially contribute to the development of health problems like diabetes, obesity [and] cardiovascular diseases more frequently seen in night shift workers in the long term.” She did, however, note that this will require further investigations.

The researchers emphasised that their study was conducted under highly controlled conditions in the laboratory, so any future research should extend these findings by studying the gene expression of actual night shift workers whose physical activity, food intake and timing of sleep might differ from one another. This could also be applied to other people that are at risk of experiencing biological clock misalignment, such as travellers crossing time zones on a frequent basis.

Image credit: ©stock.adobe.com/au/vchalup