Microgravity and hypergravity effects on collagen biosynthesis of human dermal fibroblasts

Astronauts experiencing long periods of space flight suffer from severe loss of bone tissue, particularly in those bones that carry the body weight under normal gravity. It is assumed that the lack of mechanical load decreases connective tissue biosynthesis in bone-forming cells. To test this assumption, quantitative and qualitative aspects of collagen synthesis under microgravity, normal gravity, and hypergravity conditions were investigated by incubating human fibroblast cultures with [3H]-proline for 4, 7, 10, and 20 h during the Spacelab D2-mission in 1993. Quantitative analysis revealed an increase of collagen synthesis under microgravity conditions, being up to 143% higher than in 1 g controls. In contrast, hypergravity samples showed a decrease in collagen synthesis with increasing g, being at the 13% level at 10 g. The relative proportion of collagen in total synthesized protein showed a slight decrease with increasing g. The secretion of collagen by the cells, proline hydroxylation of individual collagen alpha-chains, and the relative proportions of synthesized collagens I, III, and V were not affected under any of the applied conditions.