MICROGRAVITY AND HYPERGRAVITY EFFECTS ON COLLAGEN BIOSYNTHESIS OF HUMAN DERMAL FIBROBLASTS

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