Spaceflight has a broad impact on the way our body functions — and that includes our reproductive systems. Indeed, to get a better idea of how future pregnancies and new generations born to humans beyond Earth will be affected, scientists need to examine how well our reproductive germ cells and stem cells respond to potentially harmful factors, like radiation and microgravity.
Researchers from Kyoto University in Japan did just this: They froze the spermatogonial stem cells of mice through a process called cryopreservation, then kept them on the International Space Station (ISS) for six months. Once back on Earth, researchers injected the same spermatogonial stem cells — which are cells located in the testes that play a crucial role in sperm production — back into the testes of mice. After a few months, following natural mating patterns, healthy mice babies were born with relatively normal gene expression.
Researchers were pleasantly surprised to find that spaceflight did not affect how well the germ cells sustained themselves through cryopreservation, underlining an important option for future human use.
“It is important to examine how long we can store germ cells in the ISS to better understand the limits of storage for future human spaceflight,” the study’s first author Mito Kanatsu-Shinohara of Kyoto University said in a statement.
Human reproduction in space is uncharted waters, though as the Kyoto University researchers pointed out in their paper, successful Earth-centered reproductive technology such as embryo freezing may currently have “limited applications,” as other research has found that embryonic cells may be “particularly sensitive to spaceflight,” and have problems developing properly. (Embryos are the youngest form of human offspring, representing the earliest days and weeks of development after an egg is fertilized. For reproductive technology procedures including in-vitro fertilization, embryos are created in a lab and frozen at days-old ages.)
Scientists of the study also pointed out that arguably more simple procedures such as freeze-drying sperm itself (rather than the cells that assist in healthy sperm production), may carry health risks for future offspring, making more research into germ cell preservation techniques crucial for safe long-haul space exploration.
In terms of humans actually reproducing in space, however, scientists may just be scratching the surface as studies of pregnancy in space are limited to animals — and also potentially more limited to men, as fewer women have traveled to space.
While research has found that menstruation itself (the bleeding portion of the menstrual cycle) is largely unaffected by spaceflight, how microgravity and radiation affects follicular development (the phase of the menstrual cycle where an egg is matured and selected for ovulation) and ovulation (the release of an egg for potential pregnancy) in humans requires further research. As space gynecologist Dr. Varsha Jain pointed out in an article for BBC’s Science Focus, reproductive health research on Earth itself is often lacking — the idea of space conception and birth is even more theoretical than that.
The results of the study were published in August in the journal Stem Cell Reports.