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Scientists Seek Keys to Muscle Loss in Space - and on Earth
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by KATHY MAJOR
Baylor College of Medicine
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Researchers tackling the problem of muscle loss in space hope to find solutions that also will benefit people with muscle-weakening conditions on Earth.
Dr. Robert Schwartz and laboratory technician
Kelly Cummings isolate DNA from transgenic
mice expressing growth hormone.
"In a weightless environment, astronauts quickly begin to lose muscle mass," says Dr. Robert Schwartz, muscle alterations and atrophy team leader for the National Space Biomedical Research Institute (NSBRI). "On Earth, similar muscle loss occurs in the elderly, in patients with nerve crush injuries or neuromuscular diseases, and in persons confined to their beds."
Astronauts lose 10 to 20 percent of their muscle mass on short missions. On long-term flights, like those on the Russian space station MIR or the proposed International Space Station, the muscle loss might rise to 50 percent without using countermeasures.
In addition to muscle loss, the fibers involved in muscle contractions change their contractile properties and are weakened. "Slow-twitch" muscles, which can influence posture and the ability to stand, are the most susceptible to weakening due to microgravity.
"Long-duration space travel and exploration will be risky without methods to control these muscle changes," says Dr. Schwartz, a professor of cell biology at Baylor College of Medicine. "The ability to escape after an emergency landing could be impaired."
The most likely solution will be a combination of resistance exercises, gene therapy and drug therapy. For Dr. Schwartz' team, the answers lie in a thorough examination of the mechanisms involved in muscle changes.
NSBRI muscle labs are studying changes during weightlessness that trigger muscle atrophy through protein breakdown and rapid changes in calcium. Another lab is determining if atrophy affects activity of motor neurons while others look for ways to control the loss of slow-twitch muscle through specific muscle genetic factors.
Potential drug therapies will initially be tested in healthy adults exposed to prolonged bed rest. Dr. Schwartz' team hopes to test a new drug produced by Merck that can increase growth hormone levels in the presence of high levels of glucocorticoids, hormones linked to muscle atrophy.
"We know that astronauts experience higher sustained glucocorticoid levels. In addition, while weightlessness is the major factor influencing muscle changes, sleep loss, poor light conditions and inadequate diet can add to the problem and depress growth hormone levels," he says. "Growth hormone, in combination with resistive exercise, is critical for maintenance of muscle."
The NSBRI muscle team's work is being complemented by NSBRI teams looking at other space health concerns such as bone loss, cardiovascular changes, balance disorders, sleep disturbances, radiation exposure, infections and immune response.
The NSBRI, a consortium headed by Baylor with Harvard Medical School, The Johns Hopkins University, Massachusetts Institute of Technology, Morehouse School of Medicine, Rice University and Texas A&M University, focuses on biomedical research related to the effects of long-term space flight on humans.
"As the NSBRI looks for ways to protect the health and safety of astronauts traveling to Mars or beyond, we expect to find solutions that will be equally applicable to health problems here on Earth," says Dr. Ronald White, NSBRI associate director.
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