Bone formation during distraction osteogenesis is dependent on both VEGFR1 and VEGFR2 signaling.
BACKGROUND
Distraction osteogenesis (DO) is characterized by the induction of highly vascularized new bone formation through an intramembranous process largely devoid of the formation of cartilage.


METHODS
To test the hypothesis that DO is strictly dependent on vascualrization, we inhibited vascular endothelial growth factor (VEGF) activity by antibody blockade of both receptors VEGFR1 (Flt-1) and VEGFR2 (Flk-1) or only VEGFR2 (Flk-1) in a previously developed murine tibia DO model. During normal DO, VEGFR1 (Flt-1), VEGFR2 (Flk-1), VEGFR3 (Flt4) and all four VEGF ligand (A, B, C, and D) mRNAs are induced.


RESULTS
The expression of mRNA for the receptors generally paralleled those of the ligands during the period of active distraction. Bone formation, as assessed by muCT, showed a significant decrease with the double antibody treatment and a smaller decrease with single antibody treatment. Vessel volume, number, and connectivity showed progressive and significant inhibition in all of these of parameters between the single and double antibody blockade. Molecular analysis showed significant inhibition in skeletal cell development with the single and double antibody blockade of both VEGFR1 and 2. Interestingly, the single antibody treatment led to selective early development of chondrogenesis, whereas the double antibody treatment led to a failure of both osteogenesis and chondrogenesis.


CONCLUSIONS
Both VEGFR1 and VEGFR2 are functionally essential in blood vessel and bone formation during DO and are needed to promote osteogenic over chondrogenic lineage progression.
Jacobsen
Kimberly A
KA
Orthopaedic Research Laboratory Department of Orthopedic Surgery, Boston University School of Medicine, Boston, Massachusetts, USA.
Al-Aql
Zainab S
ZS
Wan
Chao
C
Fitch
Jennifer L
JL
Stapleton
Stephanie N
SN
Mason
Zachary D
ZD
Cole
Robert M
RM
Gilbert
Shawn R
SR
Clemens
Thomas L
TL
Morgan
Elise F
EF
Einhorn
Thomas A
TA
Gerstenfeld
Louis C
LC
D000818:Animals; D001846:Bone Development; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019857:Osteogenesis, Distraction; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2