Mice that spent three months aboard the International Space Station returned to Earth with thinning skin and surprising changes in hair follicles, a finding that may have implications for understanding the scope of physiological changes long-duration spaceflight has on humans, as well.
"There has been anecdotal evidence of skin problems in astronauts on orbit, including slow healing of scratches, and some crew members have had nonspecific rashes," NASA's lead space station scientist Julie Robinson told Discovery News.
In general, those skin problems have been considered nuisance medical issues, though the skin may be part of broader changes in the immune system, she added.
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The new mouse study hints that genetic changes are involved, with researchers reporting "significant modulation of 434 genes" in the space-flown mice, compared to ground-based subjects, Betty Nusgens, with the University of Liege in Belgium, and colleagues write in this week's Microgravity, a new journal by Nature Publishing.
"We have no clear answer. We have shown in several publications that fibroblasts, the cells populating the dermis, react to stress relaxation and microgravity by a disorganization of their cytoskeleton. That fibroblasts sense the loss of gravity within the dermal tissue is an open issue," Nusgens wrote in an email to Discovery News.
"The results on hair follicles were unexpected," she added. "Our hypothesis is that the stem cells involved in the hair follicle cycle .... are disturbed by microgravity."
The new findings are limited by the small sample size. Three of six mice flown for a 91-day stay aboard the station in 2009 died during the flight and were not viable for post-landing tissue analysis. (One mouse died from a major spinal cord injury that likely occurred when the space shuttle blasted off; the second mouse appears to have died from a liver disease; and the third due to a failure of its automated food-delivery system aboard the station, the authors note.)
The surviving trio, euthanized after landing, all showed "a significant reduction of dermal thickness" and numerous hair follicles in unexpected active, growing phases, the researchers wrote.
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They also noted changes in the muscles underlying the skin.
"This suggests that the skin of astronauts may be affected by pathophysiological alterations that could be detrimental during long trips in space," the study concludes.
"These results can be considered as a warning signal to space program policymakers to perform clinical investigations on the astronauts' skin to evaluate a potential thinning" making it more fragile, Nusgens wrote in an email.
So far, scientists have studied skin changes in just one astronaut, Europe's Thomas Reiter.
Additional insight may come from an ongoing European Space Agency space station study called SKIN-B and a Japanese investigation called HAIR.