Effect of glucocorticoid-induced osteoporotic-like conditions on osteoblast cell attachment to implant surface microtopographies.
OBJECTIVE
The objectives of this work were to: (1) establish methodology for pretreating osteoblast-like cells in vitro with dexamethasone to cause glucocorticoid-induced osteoporosis, (2) perform quantitative and qualitative assessments of cellular attachment of osteoporosis-like osteoblasts when grown on implant surfaces of differing roughness, (3) and explore the hypothesis that dexamethasone-treated osteoblasts have altered cell attachment properties by focal adhesion disassembly and decreased tyrosine phosphorylation of the focal adhesion tyrosine kinase.


METHODS
Osteoblasts were cultured with dexamethasone (10(-7) and 10(-6) M) for up to 4 days of incubation to induce osteoporosis-like conditions. Cellular attachment assays demonstrated the effect of dexamethasone treatments on cellular attachment properties of osteoblasts. Qualitative data were obtained utilizing immunofluorescent microscopy and Western blotting. Focal adhesion kinase (FAK) immunoprecipitation and tyrosine-phosphorylation Western blots were obtained from dexamethasone-treated human embryonic palatal mesenchymal- 1486 osteoblast cultures supplemented with ascorbate and beta-glycerol phosphate medium.


RESULTS
Cellular attachment was significantly greater (P < 0.05) with non-dexamethasone-treated osteoblasts (92%) as compared to dexamethasone-treated osteoblasts after 1 (72%), 2 (63%), and 4 days (53%) of exposure. Dexamethasone-treated osteoblasts were viable and capable of proliferation, suggesting that the reduction of cellular attachment may be related to these cell adhesion processes. Immunofluorescent microscopy of both dexamethasone-treated osteoblasts and non-dexamethasone-treated osteoblasts failed to show any relative difference in the disassembly of focal adhesions and actin filaments. Extended dexamethasone treatment periods (up to 3 weeks) showed changes in the levels of FAK and FAK-phosphotyrosine in human embryonic palatal mesenchymal-1486 osteoblasts.


CONCLUSIONS
The protocol used in this study demonstrated a glucocorticoid-induced osteoporosis-like suppression of osteoblasts. FAK disassembly was not a significant factor in short period; however, FAK protein levels and phosphotyrosine signaling on FAK were affected after 1-week exposure to dexamethasone. Phosphorylated FAK was not associated with the rise in the level of FAK, further indicating the possibility of FAK involvement in reduced cell attachment.
Cho
Peter
P
College of Dentistry, University of Iowa, Iowa City, IA. 522420-1010, USA.
Schneider
Galen B
GB
Kellogg
Bradley
B
Zaharias
Rebecca
R
Keller
John C
JC
D016475:3T3 Cells; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000494:pharmacology; D015153:Blotting, Western; D002448:Cell Adhesion / Q000187:drug effects; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D015921:Dental Implants; D003907:Dexamethasone / Q000009:adverse effects*; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000187:drug effects; D005938:Glucocorticoids / Q000009:adverse effects*; D005994:Glycerophosphates / Q000494:pharmacology; D006801:Humans; D047468:Immunoprecipitation; D051379:Mice; D008855:Microscopy, Electron, Scanning; D010006:Osteoblasts / Q000187:drug effects*; D010024:Osteoporosis / Q000139:chemically induced* / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D014443:Tyrosine / Q000187:drug effects
D000975:Antioxidants; D015921:Dental Implants; D005938:Glucocorticoids; D005994:Glycerophosphates; D014443:Tyrosine; D003907:Dexamethasone; D014025:Titanium; D051416:Focal Adhesion Protein-Tyrosine Kinases; D001205:Ascorbic Acid; C031463:beta-glycerophosphoric acid