AJP - Endocrinology and Metabolism, Vol 266, Issue 4 E567-E573, Copyright © 1994 by American Physiological Society

ARTICLES

Spaceflight results in reduced mRNA levels for tissue-specific proteins in the musculoskeletal system

P. Backup, K. Westerlind, S. Harris, T. Spelsberg, B. Kline and R. Turner
Department of Orthopedic Surgery and Biochemistry, Mayo Graduate School, Rochester, Minnesota 55905.

The purpose of the present study in growing rats was to investigate the effects of short-term spaceflight on gene expression in bone and muscle and on cortical bone histomorphometry. Two experiments were carried out; Physiological Systems Experiments 1 and 2 were 4- and 10-day flights, respectively. Radial bone growth in the humerus was unchanged during the 4-day flight and decreased during the 10-day flight. Expression of mRNA for glyceraldehyde-3-phosphate dehydrogenase was unchanged in biceps, calvarial periosteum, and long-bone periosteum after spaceflight. Similarly, no changes in ribosomal RNA levels were observed in long-bone or calvarial periosteum after spaceflight. In contrast, spaceflight decreased steady-state mRNA levels for actin in muscle (4-day flight). Osteocalcin (both spaceflights) and the prepro-alpha 2[I] chain of type I precollagen (10-day flight) mRNA levels were decreased in long-bone and calvarial periosteum after spaceflight. These results indicate that the effects of spaceflight on the musculoskeletal system include decreased expression of some muscle- and bone-specific genes as well as decreased bone formation. Interestingly, detectable reductions in gene expression for bone matrix proteins preceded histological evidence for decreased bone formation.

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