Human heart cells are altered by spaceflight but return mostly to normal when back on Earth. The findings could help scientists understand why astronauts’ hearts change and how to prevent it.
Previous studies of astronauts have found that spaceflight reduces both heart rate and blood pressure and increases the amount of blood pumped by the heart. But most research on how this happens has been done either on animals or on whole human tissues or organs.
To gain further insights, Alexa Wnorowski at Stanford University in California and her colleagues performed experiments using human heart cells.
First, they took blood from three people with no history of heart disease. They then reprogrammed some of the blood cells into stem cells that were then coaxed to form heart muscle cells.
Half of the heart muscle cells were put on a SpaceX spacecraft travelling to the International Space Station for a resupply mission. The other half were kept on Earth for comparison.
After five and a half weeks, the cells in orbit were returned to the ground and the scientists examined the effects of microgravity on them.
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The team found differences in the way that 3000 genes were expressed in these cells. The most notable changes were to genes responsible for metabolism and the functioning of mitochondria, which are the energy powerhouses of cells.
Around 1000 of these genes were still different after 10 days back on Earth, which is equivalent to roughly 4 to 5 per cent of all known human genes. But most of the genes responsible for the changes to the cells’ mitochondria and metabolism had returned to normal.
It isn’t clear from this study what effects the changes might have on astronauts. A previous study looked at two people who were twins: one went to space for a year and the other remained on Earth. It found changes to genes associated with cell mitochondria and metabolism in blood cells in the twin who had been to space. These weren’t seen in the other twin.
This raises the possibility that spaceflight has similar effects on multiple cell types, including heart and blood cells, says Wnorowski. “But it’s also not quite enough data to draw that large of a conclusion,” she says.
The team plans to send 3D tissue structures with multiple different cells types on an upcoming trip to the International Space Station to see how they are affected.
Journal reference: Stem Cell Reports, DOI: 10.1016/j.stemcr.2019.10.006
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