Stem Cells Point to Space Ills

Sept. 28, 2009 -- Stem cells exposed to microgravity express different proteins than those grown in normal gravity, say Australian researchers.

The finding may explain why long-term exposure to microgravity causes astronaut health issues such as loss of bone density and muscle wasting.

The research, led by biologist Brendan Burns of the University of New South Wales in Sydney, will be presented this week at the 9th Australian Space Sciences Conference.

Burns, along with graduate researchers Elizabeth Blaber and Helder Marcal, used a NASA rotating-wall vessel to simulate microgravity, which is experienced by astronauts in low Earth orbit, to analyse its effect on human embryonic stem cells.

Stem cells are cells that have yet to differentiate into cells with specialized functions.

The researchers isolated and identified proteins expressed by the cells and compared these to proteins from cells grown under normal gravity conditions.

Their results showed 75 percent of the proteins from the cells exposed to microgravity were not found in those grown under normal gravity.

"A lot of work has been done on microgravity at a systemic level, such as the effects on the immune system. No one has really looked at the effect of microgravity at a cellular level and we think that is a huge gap," said Burns.

"What we've found is a range of different proteins that are potentially important for astronaut health were more or less predominant in terms of different gravity."

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In particular, cells exposed to microgravity produced more proteins that negatively regulate bone density. In the human body, these changes in bone tissue could result in decreases in bone density, leading to osteoporosis.

"Although it has long been known that microgravity affects bone density, what kinds of genes and proteins that are affected by microgravity to cause this condition isn't known," said Burns.

The microgravity-exposed cells also produced fewer proteins with antioxidant effects, he said. Antioxidants protect the body from reactive oxidants that can damage DNA.

"We're trying to get down to the nuts and bolts of what is causing these issues at a cellular level," said Burns.

Associate Professor Ernst Wolvetang of the Australian Institute for Bioengineering and Nanotechnology at the University of Queensland said while it's difficult to judge the research prior to publication, it is a "novel idea".

"If the right controls were done, and they find 75 percent different protein expression, especially if they include bone morphogenic proteins [such as those that regulate bone density], that would be a significant discovery," said Wolvetang.

He said as far as he knows microgravity studies had been done mostly on functional bone building cells, and in that sense the research is novel.

"How relevant this will be to space flight itself is a whole different matter, because we don't have embryonic stem cells in our adult bodies anymore," he said.

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