A team of US researchers have genetically modified a lettuce to grow a protein that will help to strengthen astronauts’ bones. While the lettuce isn’t ready for eating on the ISS yet, the researchers say it’s an important preparation for longer-term missions, like heading to Mars.
Bone density drops quickly in zero gravity. Astronauts can lose more than 1% of bone mass per month.
“Right now, astronauts on the International Space Station have certain exercise regimens to try to maintain bone mass,” says Kevin Yates, a graduate student in the Department of Chemical Engineering at the University of California, Davis, US.
“But they’re not typically on the International Space Station for more than six months.”
A Mars mission would take several years to complete.
Currently, bone mass can be restored with an injectable medication: a fragment of human parathyroid hormone (PTH). But it needs to be injected daily, so isn’t feasible for a long-term mission.
Instead, Yates and colleagues decided to see if they could genetically modify a lettuce to grow the hormone instead.
“Astronauts can carry transgenic seeds, which are very tiny — you can have a few thousand seeds in a vial about the size of your thumb — and grow them just like regular lettuce,” says collaborator Dr Somen Nandi, also at UC Davis.
“They could use the plants to synthesise pharmaceuticals, such as PTH, on an as-required basis and then eat the plants.”
The researchers identified a gene encoding for a slightly modified version of PTH: PTH-Fc, which includes a section of another protein to make it work more effectively in the human body.
They then transferred this gene to lettuce plants using a bacteria called Agrobacterium tumefaciens.
Once they’d grown the lettuce, they screened the plants for PTH-Fc, finding that the lettuce produced about 10-12 milligrams of the protein per kilogram.
Yates says that, in order to get enough PTH-Fc, astronauts would need to eat 380 grams, or eight cups, of lettuce per day – a “pretty big salad”.
But the researchers are working on improving the hormone content, as well as hoping to see how the lettuce grows on the International Space Station.
They’re also going to take the lettuce through animal and human clinical trials before digging in, so that they can ensure it’s safe to eat and actually stimulates bone growth.
“I would be very surprised if, by the time we send astronauts to Mars, plants aren’t being used to produce pharmaceuticals and other beneficial compounds,” says Yates.
The researchers have presented their findings at a meeting of the American Chemical Society.
Ellen Phiddian is a science journalist at Cosmos. She has a BSc (Honours) in chemistry and science communication, and an MSc in science communication, both from the Australian National University.
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