Insulin-like growth factor I stimulates proliferation and Fas-mediated apoptosis of human osteoblasts.
In vitro studies have shown that insulin-like growth factor I (IGF-I) is a potent growth factor for osteoblasts, although both bone formation and resorption are upregulated by IGF-I in vivo. To understand the difference in the action of IGF-I observed in vitro and in vivo experiments, we examined the effect of IGF-I on the proliferation and Fas-mediated apoptosis of human osteoblasts in vitro. Human osteoblastic cell line MG63 and human primary osteoblast-like cells obtained from biopsy specimens were used as human osteoblasts. Cells were cultured with or without various concentrations of IGF-I followed by determination of the proliferative response and Fas-mediated apoptosis. IGF-I dose dependently stimulated the proliferation of cultured human osteoblasts. Both Fas expression and the degree of anti-Fas IgM-induced apoptosis of human osteoblasts was also augmented by IGF-I. Furthermore, the cytotoxicity of Fas ligand (FasL) cDNA transformants against human osteoblasts was increased when IGF-I-stimulated osteoblasts were used as target cells, indicating that stimulation of IGF-I increased functional Fas expression on human osteoblasts as well as their proliferation. The addition of DEVD-CHO, a specific inhibitor of CPP32, to the culture resulted in a significant inhibition of Fas-mediated apoptosis of both unstimulated and IGF-I-stimulated osteoblasts, although it did not affect the proliferative response or Fas expression. Our data suggest that activation of CPP32 is necessary for Fas-mediated apoptosis of human osteoblasts, and treatment of IGF-I increased this signaling pathway. In contrast, regulation of proliferation and Fas expression of the cells were probably not affected by CPP32 activation. Our results suggest that IGF-I acts on cultured human osteoblasts by increasing their proliferation and induction of Fas-mediated apoptosis by neighbouring FasL+ cells such as osteoclasts, thus probably functioning as a local coupling factor in the bone in vivo, stimulating both bone formation and resorption.
Kawakami
A
A
First Department of Internal Medicine, Nagasaki University School of Medicine, Japan.
Nakashima
T
T
Tsuboi
M
M
Urayama
S
S
Matsuoka
N
N
Ida
H
H
Kawabe
Y
Y
Sakai
H
H
Migita
K
K
Aoyagi
T
T
Nakashima
M
M
Maeda
K
K
Eguchi
K
K
D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics / Q000276:immunology; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002478:Cells, Cultured; D003601:Cytotoxicity Tests, Immunologic; D053222:Fas Ligand Protein; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D004915:Leukemia, Erythroblastic, Acute; D008024:Ligands; D008562:Membrane Glycoproteins / Q000235:genetics / Q000633:toxicity; D009842:Oligopeptides / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000187:drug effects / Q000235:genetics / Q000502:physiology*
C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008024:Ligands; D008562:Membrane Glycoproteins; D009842:Oligopeptides; C108637:aspartyl-glutamyl-valyl-aspartal; D019014:fas Receptor; D007334:Insulin-Like Growth Factor I