The International Space Station over Earth. Photo: NASA via Getty Images

Genetically enhanced mice retained or increased muscle mass after spending a month on the International Space Station.

Why it matters: The findings of the study, published Monday in the journal Proceedings of the National Academy of Sciences, suggest that muscle and bone loss could be mitigated for astronauts on space flights as well as for people on Earth who experience muscle degeneration.

What they did: The nonprofit Jackson Laboratory provided 40 black, female mice that were placed on a SpaceX rocket that traveled to the space station for the "Rodent Research-19" experiment.

What they found: 24 mice that were left untreated experienced muscle and bone mass loss of up to 18%.

  • But eight "mighty mice" lost none of their brawn after being modified to lack the protein myostatin, which blocks a molecular signaling pathway.
  • The muscles increased noticeably in eight other mice given the "mighty mouse" treatment in space after they returned to Earth in a SpaceX Dragon capsule on Jan. 7.

What they're saying: Lead researcher Se-Jin Lee, of the Jackson Laboratory, and wife Emily Germain-Lee, of Connecticut Children's Medical Center, who also took part in the study, told AP the results were encouraging.

  • But Germain-Lee added researchers were "years away" from testing the drug in people without concerns about "serious side effects."
  • Lee said they were looking at possibly sending more "mighty mice" to space for a longer duration.

Of note: NASA astronauts Andrew Morgan and Jessica Meir and Christina Koch — who made history with the first female spacewalk last October — cared for the mice on the ISS, and they're listed as study co-authors.

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