Astronaut looking at cell growth

Microbiologist and astronaut Kate Rubins examines stem cell–derived heart muscle cells aboard the International Space Station.


Why are scientists shooting stem cells into space?

WEST PALM BEACH, FLORIDA—The near-weightless conditions of flying in space can wreak havoc on your hairdo and your sense of direction. And as it turns out, they can also do some pretty weird things to cells in a dish. During a session here yesterday at the World Stem Cell Summit (WSCS), an annual gathering of scientists and advocates organized by the nonprofit Regenerative Medicine Foundation, researchers described their forays into stem cell research in microgravity.

It’s possible to simulate weightless conditions on Earth, but there’s one way to get the real thing: Send cells on a 400-kilometer vertical journey to a U.S. national lab stationed on the International Space Station (ISS). Here are three questions scientists hope to answer by shooting their precious experiments into low-Earth orbit.

What’s going on in an astronaut’s body?

Among the many risks of leaving Earth are changes to the human cardiovascular system; some evidence suggests astronauts are prone to arrhythmia and atrophy of the heart (not to mention other space hazards). Cell biologist Arun Sharma explained to the WSCS audience how he and his team at Stanford University in Palo Alto, California, want to use the ISS to get a detailed look at what microgravity does to heart muscle.

Because cells from a real human heart are in short supply for research and are hard to maintain, the team created new ones from stem cells. They reprogrammed adult skin and blood cells from three people into so-called induced pluripotent stem cells, which are able to develop into many different types of cells in the body, including heart cells. This July, the SpaceX CRS-9 mission brought vials of these heart muscle cells, known as cardiomyocytes, for a monthlong stay on the ISS. (A second set of cardiomyocytes from the same people stayed on Earth as controls.)

Now that the cells have returned to Earth, the team is beginning to analyze data collected during and after the trip, including which genes were turned on or off and the cells' structure and ability to contract. Sharma says that from preliminary observations, the cells took on a slightly irregular rhythm while they flew, but returned to a normal rhythm back on Earth. Explaining microgravity’s effects might have implications beyond astronauts, he notes, because some changes to their bodies seem to mimic the natural aging process on fast-forward.

Why does microgravity make stem cells more “stemmy”?

Long missions in space might cause the body to deteriorate, but it seems to have a different effect on some types of stem cells. Transplant immunologist Mary Kearns-Jonker of Loma Linda University in California has been experimenting with simulated microgravity by sticking cardiac progenitor cells—tissue-specific stem cells that can develop into heart muscle—into a device called a clinostat, which rotates them constantly to minimize gravitational force.

Her team has discovered that cardiac progenitors from neonates, but not adults, seem to proliferate better under these microgravity conditions, and that they show signs of dedifferentiation—reverting back to a more primitive, unspecialized state. “They back up a little bit to go forward more efficiently,” she explained. In fact, she has found that microgravity can activate certain genetic pathways that kick into gear when damaged tissue regenerates.

But “it’s generally agreed that there’s no perfect [microgravity] system on Earth,” she says. So in March 2017, cells from her lab are slated to start a monthlong stay on the ISS, to find out whether the age-dependent effects she has seen also occur in space.

Can cells grown in microgravity make better therapies?

Kearns-Jonker’s team is already testing the potential therapeutic effects of plain old Earth-bound cardiac progenitor cells. In yet-unpublished research, she induced heart attacks in adult sheep and then injected them with progenitor cells isolated from the hearts of neonatal sheep. But if those cells prove effective at healing the heart, she is hoping to test whether microgravity—even just a weeklong spin in the clinostat—could boost their powers further.

Abba Zubair, a stem cell researcher at the Mayo Clinic in Jacksonville, Florida, has an even grander vision of future therapy: stem cell treatments grown aboard the ISS. His work focuses on hemorrhagic stroke, bleeding caused by ruptured blood vessels in the brain. He is preparing clinical trials to test another cell type, known as mesenchymal stem cells (MSCs), to rescue injured neurons.

But he estimates it will take 100 million to 200 million such cells to treat a human, and they are difficult and time-consuming to grow. Based on earlier evidence that stem cells proliferate happily in microgravity, Zubair plans to test whether a trip to space will coax his MSC populations to expand. If so, his research will tackle an ever bigger question: Can sterile, clinical-grade cells be grown in the orbiting lab? And after their space odyssey, would they still be safe to inject into people?

For more of our related coverage on stem cells, visit our topic page.