Exposure to microgravity aboard the International Space Station causes mitochondria in human cells to produce fewer proteins, researchers have found — a discovery that could explain why astronauts experience muscle wasting, bone loss, and other physiological deterioration during spaceflight.
The study, published in Nature Communications on June 30, also identified a previously unknown molecular pathway that translates the effects of gravity on mitochondria through the mechanical action of cell adhesion.
"This could be used to understand how we should better prepare astronauts going into space," said Thomas Corydon, a space biologist at Aarhus University in Denmark.
Led by Shintaro Iwasaki, a molecular biologist at Japan's RIKEN research institute, the team worked with ISS astronauts to culture human cells in a laboratory module aboard the station for 24 or 48 hours, then froze them. Control samples were kept in a centrifuge that simulated Earth gravity.
Analysis revealed that cells exposed to microgravity for 24 hours had less mitochondrial mRNA, and their mitochondrial ribosomes made fewer proteins. Similar results were found in C. elegans worm larvae cultured in microgravity for four days.
In further Earth-based experiments using a clinostat — a tool that spins cells to mimic reduced gravity — mitochondrial protein synthesis continued to decrease over 72 hours. The research identified that the drop is driven by reduced mechanical force on cell adhesion receptors, which signals mitochondria to dial down protein production.
Previous studies had suggested spaceflight damages mitochondria, but the molecular mechanism was poorly understood. This work shifts focus from gene expression to the actual protein translation level — opening new avenues for potential countermeasures.
"It is well known that microgravity reduces or alters gene expression," Corydon said. This analysis provides evidence of how it affects cells "directly on the protein level."
The findings could inform the design of exercise regimens, pharmaceutical interventions, or genetic countermeasures for long-duration missions, including future trips to Mars.
