SPACEFLIGHT MODULATES INSULIN-LIKE-GROWTH-FACTOR BINDING-PROTEINS ANDGLUCOCORTICOID RECEPTOR IN OSTEOBLASTS

Rat osteoblasts were cultured for 4 or 5 days during a Space Shuttle m ission. After 20-h treatment with 1 alpha,25-dihydroxyvitamin DB, cond itioned media were harvested and cellular DNA and/or RNA were fixed on board. The insulin-like growth factor binding protein (IGF BP)-3 leve ls in the media were three- and tenfold higher than in ground controls on the fourth and fifth flight days, as quantitated by Western ligand blotting and radioimmunoassay, respectively. The increased ICF BP-3 p rotein levels correlated with two- to threefold elevation of IGF BP-3 mRNA levels, obtained by reverse transcription-polymerase chain reacti on. The IGF BP-5 mRNA levels in flight cultures were 33-69% lower than in ground controls. The IGF BP-4 mRNA levels in flight cultures were 75% lower than in ground controls on the fifth day but were not differ ent on the fourth day. The glucocorticoid receptor mRNA. levels in fli ght cultures were increased by three- to eightfold on the fourth and f ifth days compared with levels in ground controls. These data suggest potential mechanisms underlying spaceflight-induced osteopenia.