title: A short pulse of mechanical force induces gene expression and growth in MC3T3-E1 osteoblasts via an ERK 1/2 pathway.
abstract: Physiological mechanical loading is crucial for maintenance of bone integrity and architecture. We have calculated the strain caused by gravity stress on osteoblasts and found that 4-30g corresponds to physiological levels of 40-300 microstrain. Short-term gravity loading (15 minutes) induced a 15-fold increase in expression of growth-related immediate early gene c-fos, a 5-fold increase in egr-1, and a 3-fold increase in autocrine bFGF. The non-growth-related genes EP-1, TGF-beta, and 18s were unaffected by gravity loading. Short-term physiological loading induced extracellular signal-regulated kinase (ERK 1/2) phosphorylation in a dose-dependent manner with maximum phosphorylation saturating at mechanical loading levels of 12g (p < 0.001) with no effect on total ERK. The phosphorylation of focal adhesion kinase (FAK) was unaffected by mechanical force. g-Loading did not activate P38 MAPK or c-jun N-terminal kinase (JNK). Additionally, a gravity pulse resulted in the localization of phosphorylated ERK 1/2 to the nucleus; this did not occur in unloaded cells. The induction of c-fos was inhibited 74% by the MEK1/2 inhibitor U0126 (p < 0.001) but was not affected by MEK1 or p38 MAPK-specific inhibitors. The long-term consequence of a single 15-minute gravity pulse was a 64% increase in cell growth (p < 0.001). U0126 significantly inhibited gravity-induced growth by 50% (p < 0.001). These studies suggest that short periods of physiological mechanical stress induce immediate early gene expression and growth in MC3T3-E1 osteoblasts primarily through an ERK 1/2-mediated pathway.
authors.affiliation: Northern California Institute for Research and Education, San Francisco, California, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Hatton
authors.forename: Milad
authors.initials: M
authors.lastname: Pooran
authors.forename: Chai-Fei
authors.initials: CF
authors.lastname: Li
authors.forename: Chris
authors.initials: C
authors.lastname: Luzzio
authors.forename: Millie
authors.initials: M
authors.lastname: Hughes-Fulford
mesh_terms: D016475:3T3 Cells; D000818:Animals; D016723:Bone Remodeling / Q000235:genetics / Q000502:physiology; D002455:Cell Division; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005786:Gene Expression Regulation; D006112:Gravitation; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology* / Q000502:physiology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D013314:Stress, Mechanical; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496051:Ptk2 protein, mouse; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases