Uniaxial mechanical strain: an in vitro correlate to distraction osteogenesis.
BACKGROUND
Distraction osteogenesis is a valuable clinical tool; however the molecular mechanisms governing successful distraction remain unknown. We have used a uniaxial in vitro strain device to simulate the uniaxial mechanical environment of the interfragmentary distraction gap.


METHODS
Using the Flexcell system, normal human osteoblasts were subjected to different levels of cyclical uniaxial mechanical strain. Cellular morphology, proliferation, migration, and the expression of angiogenic (vascular endothelial growth factor [VEGF] and fibroblast growth factor-2 [FGF-2]) and osteogenic (osteonectin, osteopontin, and osteocalcin) proteins and extracellular matrix molecules (collagen IalphaII) were analyzed in response to uniaxial cyclic strain.


RESULTS
Osteoblasts exposed to strain assumed a fusiform spindle-shaped morphology aligning parallel to the axis of uniaxial strain and osteoblasts exposed to strain or conditioned media had a 3-fold increase in proliferation. Osteoblast migration was maximal (5-fold) in response to 9% strain. Angiogenic cytokine, VEGF, and FGF-2, increased 32-fold and 2.6-fold (P < 0.05), respectively. Osteoblasts expressed greater amounts of osteonectin, osteopontin, and osteocalcin (2.1-fold, 1.8-fold, 1.5-fold respectively, P < 0.01) at lower levels of strain (3%). Bone morphogenic protein-2 production increased maximally at 9% strain (1.6-fold, P < 0.01). Collagen I expression increased 13-, 66-, and 153-fold in response to 3, 6, and 9% strain, respectively.


CONCLUSIONS
Uniaxial cyclic strain using the Flexcell device under appropriate strain parameters provides a novel in vitro model that induces osteoblast cellular and molecular expression patterns that simulate patterns observed in the in vivo distraction gap.
Bhatt
Kirit A
KA
Institute of Reconstructive Plastic Surgery, New York University School of Medicine, New York, New York, USA.
Chang
Eric I
EI
Warren
Stephen M
SM
Lin
Shin-E
SE
Bastidas
Nicholas
N
Ghali
Shadi
S
Thibboneir
Aurelia
A
Capla
Jennifer M
JM
McCarthy
Joseph G
JG
Gurtner
Geoffrey C
GC
D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D002465:Cell Movement / Q000502:physiology; D048430:Cell Shape / Q000502:physiology; D024042:Collagen Type I / Q000235:genetics / Q000378:metabolism; D024043:Collagen Type II / Q000235:genetics / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D010006:Osteoblasts / Q000166:cytology* / Q000502:physiology*; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D019857:Osteogenesis, Distraction; D015676:Osteonectin / Q000235:genetics / Q000378:metabolism; D053495:Osteopontin / Q000235:genetics / Q000378:metabolism; D013314:Stress, Mechanical; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism
D024042:Collagen Type I; D024043:Collagen Type II; D016326:Extracellular Matrix Proteins; D015676:Osteonectin; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D016222:Fibroblast Growth Factor 2; D015675:Osteocalcin; D053495:Osteopontin