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Fibronectin is a survival factor for differentiated osteoblasts
R K Globus1, S B Doty, J C Lull
1NASA-Ames Research Center, Moffett Field, CA 94035, USA; Departments of Medicine, Stomatology and Anatomy, University of California, San Francisco, CA 94143, USA. rglobus@mail.arc.nasa.gov
Journal of Cell Science
|May 7, 1998
Summary
Osteoblasts rely on fibronectin for differentiation. Mature osteoblasts, however, depend on fibronectin for survival, as blocking it triggers apoptosis, suggesting a role in bone formation.
Area of Science:
- Cell Biology
- Biochemistry
- Skeletal Biology
Background:
- Osteoblasts produce the skeletal extracellular matrix, which includes fibronectin.
- Fibronectin regulates cell adhesion, differentiation, and function.
- Fibronectin interactions are crucial for osteoblast differentiation in vitro.
Purpose of the Study:
- To investigate the role of fibronectin in fully differentiated osteoblasts.
- To determine if fibronectin has a unique function in mature osteoblasts.
- To explore fibronectin's impact on osteoblast survival.
Main Methods:
- Treatment of mature osteoblast cultures with fibronectin antagonists (antibodies and fragments).
- Assessment of cell apoptosis using morphological features and DNA laddering.
- Evaluation of the effect of transforming growth factor-beta1 on fibronectin antagonist-induced apoptosis.
Main Results:
- Fibronectin antibodies induced apoptosis (>95%) in mature osteoblasts within 24 hours.
- Immature osteoblasts were resistant to fibronectin antibody-induced apoptosis.
- Fibronectin fragments and intact fibronectin induced apoptosis in mature but not immature osteoblasts.
- Transforming growth factor-beta1 partially protected cells from apoptosis.
Conclusions:
- Mature osteoblasts shift from fibronectin dependence for differentiation to dependence for survival.
- Fibronectin plays a critical role in maintaining the survival of differentiated osteoblasts.
- Fibronectin and transforming growth factor-beta1 may regulate bone formation by controlling osteoblast survival.