Mechanical loading and delta12prostaglandin J2 induce bone morphogenetic protein-2, peroxisome proliferator-activated receptor gamma-1, and bone nodule formation in an osteoblastic cell line.
OBJECTIVE
We have previously reported that mechanical strain applied at a 1% level to an osteoblastic cell line induces the transcription of prostaglandin D2 synthase and increases the levels of prostaglandin D2 and its Delta12prostaglandin J2 metabolite. Mechanical strain also induces the expression of peroxisome proliferator-activated receptor gamma-1 and bone nodule formation. We hypothesized that mechanical load induces bone formation via Delta12prostaglandin J2-dependent synthesis of bone morphogenetic proteins. Our goal was to investigate the molecular events involved in osteogenesis induced by mechanical loading and Delta12prostaglandin J2, namely the induction of bone morphogenetic proteins and peroxisome proliferator-activated receptor gamma-1, a nuclear receptor for Delta12prostaglandin J2.


METHODS
Osteoblast monolayers were stretched for 1 h with a 1-h resting period and stretched for another hour at 1 Hz with 1% elongation. Cells were collected 0, 1, 6 and 16 h after stretching. Cyclooxygenase inhibitors and Delta12prostaglandin J2 were added in some experiments. Relative quantitative reverse transcriptase-polymerase chain reaction was used to examine whether the mRNA of bone morphogenetic protein-2, -4, -6, -7 and peroxisome proliferator-activated receptor gamma-1 was induced. Immunohistochemistry was used to evaluate bone morphogenetic protein expression in cells.


RESULTS
Mechanical strain significantly increased the mRNA expression of bone morphogenetic protein-2, -6, -7 and of peroxisome proliferator-activated receptor gamma-1, but not of bone morphogenetic protein-4. In stretched cells, bone morphogenetic protein-2 and peroxisome proliferator-activated receptor gamma-1 expression was blocked by cyclooxygenase inhibitors, but restored by exogenous Delta12prostaglandin J2. Delta12Prostaglandin J2 significantly enhanced bone nodule formation and bone morphogenetic protein-2 expression when added alone to resting osteoblasts.


CONCLUSIONS
These results suggest that the osteoblastic biomechanical pathways that trigger bone formation involve cyclooxygenase and prostaglandin D2 synthase activation, induction of Delta12prostaglandin J2 and its nuclear receptor, peroxisome proliferator-activated receptor gamma-1, and increased expression of bone morphogenetic protein-2. These data suggest that the Delta12prostaglandin J2/peroxisome proliferator-activated receptor gamma-1/bone morphogenetic protein-2 pathway plays an important role in osteogenesis.
Siddhivarn
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C
Center for Oral and Systemic Diseases and Department of Periodontology, School of Dentistry, University of North Carolina, Chapel Hill, NC 27599-7455, USA.
Banes
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A
Champagne
C
C
Riché
E L
EL
Weerapradist
W
W
Offenbacher
S
S
D016475:3T3 Cells; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D055418:Bone Morphogenetic Protein 6; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000187:drug effects* / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects* / Q000502:physiology; D010012:Osteogenesis / Q000187:drug effects* / Q000502:physiology; D047495:PPAR gamma / Q000187:drug effects* / Q000378:metabolism; D015230:Prostaglandin D2 / Q000494:pharmacology*; D013314:Stress, Mechanical; D016212:Transforming Growth Factor beta / Q000187:drug effects* / Q000378:metabolism
C525719:Bmp2 protein, mouse; C525810:Bmp4 protein, mouse; C525817:Bmp6 protein, mouse; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D055418:Bone Morphogenetic Protein 6; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D047495:PPAR gamma; D016212:Transforming Growth Factor beta; C499810:delta(12)-prostaglandin J(2); D015230:Prostaglandin D2