The rigors of space travel could accelerate changes in the human body usually associated with aging.
According to a new study of human tissues sent into low-Earth orbit, time in space reduces cell production, exacerbates DNA damage, and increases the signs of aging in the telomeres that cap the ends of the chromosomes.
"Space is the ultimate stress test for the human body," says physician Catriona Jamieson of the University of California, San Diego School of Medicine.
"These findings are critically important because they show that the stressors of space – like microgravity and cosmic galactic radiation – can accelerate the molecular aging of blood stem cells.
"Understanding these changes not only informs how we protect astronauts during long-duration missions but also helps us model human aging and diseases like cancer here on Earth. This is essential knowledge as we enter a new era of commercial space travel and research in low Earth orbit."
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Led by biochemist Jessica Pham of UC San Diego, a team of researchers developed a bioreactor system to cultivate and monitor human hematopoietic stem and progenitor cells (HSPCs) in microgravity.
A close examination of the HSPCs – which are involved in the production and maintenance of the blood – could provide a better understanding of the aging effects of spaceflight on a molecular level, the researchers reasoned.
The experimental platforms were then placed on SpaceX's International Space Station resupply missions, which spent between 32 and 45 days in low-Earth orbit. The effects on the cells were remarkable, with several key findings.
In a microgravity environment, the rate at which the blood-forming stem cells produce inflammatory proteins increases, resulting in a higher workload with less time to recover. The result of this was an increase in several markers generally associated with aging.
The cells became less able to produce healthy new cells over time and showed signs of wear and tear. Of particular note was a shortening of the telomeres. These are the protective caps at the ends of our chromosomes, and typically, they grow shorter over time with each cell division, until they're so short they can't divide anymore. Short telomeres are also strongly associated with aging.
Interestingly, some of the cells grew so stressed that they were unable to express proteins that suppress activation of the 'dark genome' – the so-called junk DNA that normally resides dormant in our cells, suppressed to maintain stability. This meant that these sections of the genome started waking up, which in turn can impair immune function.
It's not all doom and gloom. The researchers found that once the cells had been returned to Earth and were placed on young, healthy bone marrow substrates, some of the damage reversed. This suggests that spaceflight-related damage is repairable, and further research efforts in this direction may aid astronaut recovery in the future, as well as offer insights into aging here on Earth.
"These short-duration spaceflight models of accelerated HSPC aging may provide insights into terrestrial human aging and age-related malignancies," the researchers write in their paper.
"Ultimately, these studies may provide guidance for therapeutic strategies to mitigate space-specific changes in the expanding space economy, as well as space-accelerated models of aging and age-related diseases, such as cancer."
The research has been published in Cell Stem Cell.