A
transparent roundworm could reveal the biological effects of microgravity and space
radiation, and perhaps provide clues on how to protect future human astronauts
headed for the moon, Mars and beyond.
The C.
elegans worm's biological responses proved eerily similar to those
of humans during a series of experiments aboard the International Space
Station in 2004. Now researchers have published a review of their findings in
the journal Advances in Space Research.
"At
least at face value, this validates that you can use C. elegans to look
at mechanisms of muscle
atrophy in spaceflight," said Nathaniel Szewczyk, a biomedical
researcher at the University of Nottingham in the UK and member of the research
team.
Szewczyk
said that the worms allow researchers to study both radiation and muscle health
problems facing human astronauts, which remain poorly understood. Researchers
could even launch the worms on unmanned missions to future human destinations
such as Mars, and remotely study the effects of long-term
spaceflight.
Why
muscles get weaker
Researchers
have long tried to figure out why long-term spaceflight can lead to weakened
muscles in human astronauts. Many agree that microgravity conditions somehow reduce
the rate at which new muscle proteins and fibers are created or synthesized.
"Rate
of synthesis is down across all species [in spaceflight]," Szewczyk
explained. "It doesn't matter if you're a worm, rat or human."
C.
elegans already
represents a model
organism for study among biologists, along with other creatures such as the
Drosophila fly. So it was an obvious choice when researchers from
Canada, France, Japan and the United States decided to combine forces for the
International C. elegans Experiment, also known as ICE-FIRST.
A Russian
Soyuz spacecraft launched 53 specimens to the space station in 2004. A
matching set of roundworms stayed on Earth to act as the lab control.
ICE-FIRST
showed a connection between weakened muscles and a reduced amount of a gene
transcription factor which helps manufacture new muscle proteins. The
transcription factor changes could in turn come from disruptions further up the
molecular command chain, such as altered Insulin or TGF-beta signaling during
spaceflight.
This
strongly suggests that spaceflight affects the usual gene transcription process
in which new proteins are made. However, researchers can't confirm a cause until
they run more experiments where they actively block the transcription process
to produce weakened muscles.
Besides,
spaceflight may not only affect new muscle creation - it might also degrade or
weaken existing muscle. There's less evidence for this, but it's a main focus
for Szewczyk. He wants to continue studying how typical muscle degradation
occurs on Earth, and also use future space experiments to examine the activity
of enzymes called proteases, which degrade proteins.
Other space
experiments done by the Japanese and Chinese space agencies have since
replicated and confirmed the muscle atrophy results from ICE-FIRST.
A living
radiation dosimeter
Another
health challenge which ICE-FIRST addressed was the problem of harmful
radiation in space. Astronauts in low Earth orbit still get some protection
from the planet's magnetic field, but they are nonetheless exposed to increased
amounts of radiation.
The
roundworms showed that they could normally repair their radiation damaged cells
in spaceflight by using apoptosis, or the programmed cell death which can also
be triggered by unusual amounts of damage. Researchers say that this makes them
ideal "living dosimeters" to track accumulated radiation damage over
time.
Since
ICE-FIRST, another space station experiment successfully tested a fully
automated culturing system which maintained the roundworms for six months
without human intervention. That could pave the way for future radiation
studies.
"With
the radiation aspect, there's the idea of automating experiments and putting
them on unmanned platform," Szewczyk explained. "We could actually
put worms on an unmanned mission to Mars."
Still, a
shift toward human rather than animal spaceflight experiments has squeezed the C.
elegans studies. The original NASA program under which ICE-FIRST operated
has been cancelled, although the U.S. space agency may once again be looking
for "model organism" experiments, Szewczyk noted.
So just as flies
and monkeys once preceded man's first step into an unknown space environment, perhaps
creatures such as C. elegans could once again blaze a path to more
distant planetary bodies in the solar system.
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