October 9, 2001
First there were dogs in space. Back in the 1950s and 60s, a cadre of Soviet canines traveled on rocket ships. In the United States, chimps preceded John Glenn into orbit. In the early days of the space program, no one was sure how earth-bound life forms would be affected by the conditions in space. Today, scientists are still studying what happens to living things in space.
But now they're looking at changes on the cellular and molecular level. One Tulane researcher is sending human kidney cells into orbit. Tim Hammond is in charge of the Tulane Environmental Astrobiology Center, which is a part of the Center for Bioenvironmental Research.
Hammond also is a kidney doctor who's interested in how medicines target certain tissues while leaving other organs unaffected. But when kidney cells are isolated in a petri dish, they lose many of the features that make them kidney cells, including the receptors that are affected by medications. So their usefulness in the lab is limited.
Scientists had long known that cells in suspension, spinning in devices that reduce gravity, grow and regain many of the features that they had in the body. Hammond found that when he put kidney cells in suspension, they regained tiny hairs, or microvilli, which help them absorb water and nutrients, as well as many of the receptors that had been missing.
Genes that were dormant in a petri dish were expressed in suspension. So the question was how to maximize suspension. That question was also being asked by the National Aeronautics and Space Administration, which wanted to find out more about how longer periods in microgravity would affect human tissues.
NASA engineers designed and built a rotating wall vessel that provides the closest thing to a microgravity environment available on earth. But even this is limited by gravity. As cell cultures grow, their growth is eventually distorted by shear from the rotating wall itself. Hammond wanted to go a step further and send the cells into space.
Hammond and his collaborators first got the chance to send some rat kidney cells to the Russian space station, Mir. Researchers got back images that show that the cells grew back much more microvilli than cultures grown in suspension on the ground. Researchers next got a chance to send an experiment up on the Neurolab mission in 1998. They grew human kidney cells in space for six days, with another sample in the rotating wall vessel and a control sample in normal gravity.
More than 900 genes were expressed in the rotating wall vessel that were not expressed in the static control sample. But 1,600 genes were expressed in the sample on the space shuttle. The results were stunning. The next step was to take a closer look at what happened in the cells and when. This time the researchers partnered with a biotech company that wants to use their discoveries to make commercial products.
They were able to secure a spot on space shuttle Atlantis in fall 2000. The cells spent 12 days in space, and researchers made more detailed observations of what changed. This year, Hammond and his colleagues sent up an antibiotic to study how it affects kidney cells. They will send another experiment up this November in order to look at the vitamin D receptor in kidney cells.
"The vitamin D receptor is a key player in the changes we see both on the ground and in space," Hammond said. He is interested in pinpointing the optimum level of shear stress. One of the reasons this may work so well is were mimicking conditions of the body. In the body, blood is pumping, things are moving and there's lots of shear. And kidney cells seem to get best expression of their receptors at the level of shear that seems to match what we have in the body.
Hammond's work has received widespread attention, and was the focus of a feature story in the September issue of Discover magazine. While his colleagues speculate that this work may lead to the ability to grow spare parts for the human body, Hammond's focus is on the most immediate tools that may come from this work--new medicines and new ways to test them.
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