How genetically modified lettuce could help Mars-bound astronauts avoid bone loss

This genetically modified lettuce contains a fragment of a hormone that stimulates bone formation. (Kevin Yates)

As NASA prepares to send humans to Mars sometime in the 2030s, figuring out how to keep astronauts healthy during the three-year mission has been a challenge.

But researchers from the University of California, Davis say they've developed a genetically modified lettuce that could be grown in space and provide astronauts what they need to avoid bone loss.

"We decided to use lettuce because lettuce is a plant that has been grown on the International Space Station. It's also a plant that is very productive in terms of producing seeds," UC Davis professor Karen McDonald said in an online media briefing on Tuesday.

On Earth, the bones in your body constantly form microfractures due to gravity and constantly rebuild themselves while regulating the supply of calcium in the blood. But in space, this doesn't happen, resulting in a net loss of bone mineral density.

The modified lettuce contains a fragment of the parathyroid hormone (PTH), which stimulates bone formation. There already exists a medication that can supply the hormone, but it requires daily injections. On a three-year mission, it would be impractical to transport that much medication.

Using a plant that can be grown in space, like lettuce, solves this supply conundrum.

"If you grow that plant and harvest seeds, you can generate thousands of seeds. So, you get this biological amplification of the amount of material," McDonald said. "It's a very simple and cost-effective way to make a therapeutic."

The researchers were able to develop this lettuce by attaching the hormone to a piece of protein, resulting in a protein called PTH-Fc that makes the hormone more stable and effective. From there, they infected plant cells with a species of bacteria that can transfer genes to plants.

"From that we grew plants, harvested seeds from those plants, and we now just extract protein from the lettuce tissue and use analytical techniques to verify that they are producing PTH-Fc. We also looked at this over different generations of lettuce plants," UC Davis graduate student Kevin Yates said during the media briefing.

At its current state, astronauts would need to eat eight cups of the lettuce per day in order to get enough PTH. The researchers said they're working on trying to improve the amount of PTH-Fc that the lettuce generates so astronauts won't have to eat as much of it.

"We also want to look at the stability of the lettuce from one generation to the next, over many generations, to make sure it maintains its production level," McDonald said.

The researchers also said the lettuce could one day help treat or prevent osteoporosis and other bone conditions on Earth.

"Obviously, we need ways to produce therapeutics … in a lower cost manner and I think the use of plants to make therapeutics such as PTH-Fc would be very valuable here on Earth," said McDonald.