Osteoblast-derived VEGF regulates osteoblast differentiation and bone formation during bone repair
Kai Hu, Bjorn R. Olsen
Kai Hu, Bjorn R. Olsen
Published January 5, 2016
Citation Information: J Clin Invest. 2016;126(2):509-526. https://doi.org/10.1172/JCI82585.
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Research Article Bone biology

Osteoblast-derived VEGF regulates osteoblast differentiation and bone formation during bone repair

Abstract

Osteoblast-derived VEGF is important for bone development and postnatal bone homeostasis. Previous studies have demonstrated that VEGF affects bone repair and regeneration; however, the cellular mechanisms by which it works are not fully understood. In this study, we investigated the functions of osteoblast-derived VEGF in healing of a bone defect. The results indicate that osteoblast-derived VEGF plays critical roles at several stages in the repair process. Using transgenic mice with osteoblast-specific deletion of Vegfa, we demonstrated that VEGF promoted macrophage recruitment and angiogenic responses in the inflammation phase, and optimal levels of VEGF were required for coupling of angiogenesis and osteogenesis in areas where repair occurs by intramembranous ossification. VEGF likely functions as a paracrine factor in this process because deletion of Vegfr2 in osteoblastic lineage cells enhanced osteoblastic maturation and mineralization. Furthermore, osteoblast- and hypertrophic chondrocyte–derived VEGF stimulated recruitment of blood vessels and osteoclasts and promoted cartilage resorption at the repair site during the periosteal endochondral ossification stage. Finally, osteoblast-derived VEGF stimulated osteoclast formation in the final remodeling phase of the repair process. These findings provide a basis for clinical strategies to improve bone regeneration and treat defects in bone healing.

Authors

Kai Hu, Bjorn R. Olsen

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Figure 5

While 0.1 μg VEGF enhances, 1 μg recombinant VEGF fails to affect intramembranous bone formation in cortical defects of Vegfafl/fl Osx-Cre/ZsG mice at PSD10.

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While 0.1 μg VEGF enhances, 1 μg recombinant VEGF fails to affect intram...
(A) 3D reconstruction of mineralized bone in hole region of Osx-Cre/ZsG mice treated with PBS or 0.1 μg VEGF and Vegfafl/fl Osx-Cre/ZsG mice treated with PBS, 0.1 μg or 1 μg VEGF. (B and C) BV/TV, based on μCT of bone formed in hole region and wounded BM (red area in diagram). (D) Density of aniline blue staining and mineralization/collagen ratio in the hole region (yellow stippled rectangles) of Vegfafl/fl Osx-Cre/ZsG mice treated with PBS (6.3% ± 1.8% and 47.2% ± 9.0%, respectively) significantly reduced (P < 0.01) compared with Osx-Cre/ZsG mice treated with PBS (24.2% ± 3.2% and 88.5% ± 7.2%, respectively). Administration of 0.1 μg VEGF increases density of aniline blue staining in hole region of Vegfafl/fl Osx-Cre/ZsG mice (18.6% ± 3.5%; P < 0.05 vs. Vegfafl/fl Osx-Cre/ZsG + PBS), but fails to significantly enhance mineralization/collagen ratio (54.5% ± 10.8% when compared with Vegfafl/fl Osx-Cre/ZsG mice treated with PBS). Compared with PBS, 1 μg VEGF has little effect on aniline blue staining and mineralization/collagen ratio (8.2% ± 1.6% and 41.6% ± 9.5%) in Vegfafl/fl Osx-Cre/ZsG mice. (E) VEGF (0.1 μg) enhances anti-BSP staining with or without normalization to ZsG+ cells in hole region of Vegfafl/fl Osx-Cre/ZsG mice (8.9% ± 2.3% and 7.3% ± 1.4%) compared with Vegfafl/fl Osx-Cre/ZsG mice treated with PBS (1.8% ± 0.6% and 1.2% ± 0.4%); P < 0.01 with and P < 0.05 without normalization. VEGF (0.1 μg) has no significant effect (1.9% ± 0.9% and 1.0% ± 0.4%). (F) Density of ZsG+ cells and total cell number in hole region of Vegfafl/fl Osx-Cre/ZsG (CKO) mice not significantly altered by VEGF treatment. Scale bars: 100 μm (A), 200 μm (D), 50 μm (E); n= 5–6 mice for each group. Unpaired 2-tailed Student’s t test used. *P < 0.01; **,##P < 0.05. *,** vs. Osx-Cre/ZsG + PBS. ## vs. Vegfafl/fl Osx-Cre/ZsG + PBS.