IGF-I production by mouse osteoblasts.
Mouse osteoblasts contain and secrete insulinlike growth factor I (IGF-I), which can be measured by radioimmunoassay after separation from endogenous IGF-I binding activity. Our studies indicate that IGF-I is produced by all bone cell populations prepared by sequential digestion of mouse calvaria with collagenase and protease. Furthermore, relatively small amounts of IGF-I are cell associated, and IGF-I is recovered primarily in the cell medium after 24 h of culture. Basal IGF-I secretion is also density dependent, and secretion per cell is approximately 20-fold higher when cultures are inoculated at 0.125 versus 1.0 x 10(5) cells per cm2. Growth hormone increased the secretion of IGF-I only in cells released in the earlier stages of digestion. These growth hormone-responsive populations were previously shown to differ from late released cells in that they show a lower expression of the osteoblastic phenotype, harbor more EGF receptors per cell, and have a higher proliferative response to low doses of exogenous IGF-I and EGF. These data reaffirm the presence of different subclasses of bone cells in populations obtained by sequential digestion of bone and suggest that growth hormone stimulates IGF-I secretion by immature osteoblasts.
Wong
G L
GL
University of Colorado, Colorado Springs 80933-7150.
Kotliar
D
D
Schlaeger
D
D
Brandes
S J
SJ
D000818:Animals; D002352:Carrier Proteins / Q000302:isolation & purification; D002452:Cell Count; D002478:Cells, Cultured; D002850:Chromatography, Gel; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D013006:Growth Hormone / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000494:pharmacology; D013002:Somatomedins / Q000096:biosynthesis*
D002352:Carrier Proteins; D011994:Recombinant Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D004247:DNA; D003513:Cycloheximide