Venturing into space is no easy feat. If the extreme cold doesn’t make you sick, the intense heat might. Your suit could leak, or your ship could be vaporized in a high-speed collision with a meteoroid or a piece of space junk. Sounds pretty rough, doesn’t it?
But the risks don’t end when the astronauts are docked safely back at their NASA headquarters: Human bodies change in extreme ways during long periods outside the protection of Earth’s magnetic and gravitational fields.
“Once you get out of that protective shield of the planet, you are going to be exposed to different types of radiation,” says Nukhet Aykin-Burns, who studies the risks of radiation at the University of Arkansas for Medical Sciences.
Cancer, neurological problems and heart abnormalities can all result from the one-two punch of high radiation and weightlessness, but it is difficult to gauge the risks that they cause to astronauts. Now, though, researchers think they’ve found a useful way to indicate when an astronaut may be in trouble: by counting their mitochondria.
As you might remember from high school biology class, mitochondria are tiny structures less than three micrometers long found in nearly all types of human cells. Their primary role is to synthesize energy from nutrients, earning them the familiar nickname: “powerhouses of the cell.”
As it turns out, mitochondria levels in human blood soar during space missions and stay high upon return: A new study found mitochondrial concentrations up to 355 times higher in astronauts three days after they had landed back on Earth.
Because high mitochondria counts are a sign that the body’s immune system is responding to a threat, researchers like Aykin-Burns think that measuring mitochondria may be a good way to identify whether an astronaut is getting too much radiation.
Aykin-Burns and other experts in the field spoke recently at a virtual event organized by the National Center for Advancing Translational Sciences.
Attendees at this early December conference learned about the role mitochondria can play in identifying health risks from COVID-19 infection to harsh environmental conditions like space, the focus of Aykin-Burns’ work.
As astronauts start gearing up to try to set foot on Mars, it is critical to think about every molecule that can be measured to indicate stress or disease, says Christopher Mason, one of the panel members and a physiologist at New York’s Weill Cornell Medical College.
Because humans aren’t used to being in space, the weightlessness and high radiation trigger our immune systems, explains Mason, who has worked with NASA’s twin study that compared the changes in the body of identical twins, one on Earth and the other in space. Their results were published in 2019.
Because the body is not quite sure what to do with the lack of gravity in space, it produces more mitochondria as a way to prime the immune system, says Mason. The mitochondrial spike is neither good nor bad; it’s just an indicator, according to Mason. He compares this spike with having a cough. “The cough itself is not necessarily good or bad for you, it means you’re trying to get rid of phlegm.”
This triggering of the immune system by cosmic rays and weightlessness initiates a damaging chain reaction, addressed Aykin-Burns to the audience. It sparks more mitochondrial activity in the astronaut’s bones. This, in turn, stimulates a type of bone cell that breaks down tissues and leads to bone loss, according to another new study, by Aykin-Burns and her team.
“This is an important reason for the astronauts to have severe bone loss in space,” she says, adding that it may also be possible to develop new therapies to reprogram mitochondria and avoid bone loss.
However, the increase in mitochondria levels is short-lived and goes away once the astronauts come back to Earth, says Mason. “[It] did not last that long, which is a good thing”.
Although researchers are clear that the soaring mitochondria levels in space are a part of the body’s stress response, they are conducting studies to find out if this spike is so harmful that it should be prevented from happening to astronauts or if it is just a harmless byproduct of space travel, since it’s a part of the body’s normal response. It’s possible, says Mason, that the increase in mitochondrial numbers is a key bodily adaptation. Perhaps, he says, “This is how the body is restructuring itself to get used to gravity again.”