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1 Department of Orthopedics, Mayo Clinic, Rochester, Minnesota 55905; and 2 National Aeronautics and Space Administration Ames Research Center, Moffett Field, California 94035
In the present
study, we evaluated the possibility that the abnormal bone matrix
produced during spaceflight may be associated with reduced expression
of bone matrix protein genes. To test this possibility, we investigated
the effects of a 14-day spaceflight (SLS-2 experiment) on steady-state
mRNA levels for glyceraldehyde-3-phosphate dehydrogenase (GAPDH),
osteocalcin, osteonectin, and prepro-
(1) subunit of type I collagen
in the major bone compartments of rat femur. There were pronounced
site-specific differences in the steady-state levels of expression of
the mRNAs for the three bone matrix proteins and GAPDH in normal
weight-bearing rats, and these relationships were altered after
spaceflight. Specifically, spaceflight resulted in decreases in mRNA
levels for GAPDH (decreased in proximal metaphysis), osteocalcin
(decreased in proximal metaphysis), osteonectin (decreased in proximal
and distal metaphysis), and collagen (decreased in proximal and distal
metaphysis) compared with ground controls. There were no changes in
mRNA levels for matrix proteins or GAPDH in the shaft and distal
epiphysis. These results demonstrate that spaceflight leads to site-
and gene-specific decreases in mRNA levels for bone matrix proteins.
These findings are consistent with the hypothesis that
spaceflight-induced decreases in bone formation are caused by
concomitant decreases in expression of genes for bone matrix proteins.
bone histomorphometry; Northern analysis; bone formation; weightlessness; osteoporosis
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