Soluble VEGF isoforms are essential for establishingepiphyseal vascularization and regulating chondrocyte development and survival
Christa Maes, … , Roger Bouillon, Geert Carmeliet
Christa Maes, … , Roger Bouillon, Geert Carmeliet
Published January 15, 2004
Citation Information: J Clin Invest. 2004;113(2):188-199. https://doi.org/10.1172/JCI19383.
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Article Bone biology

Soluble VEGF isoforms are essential for establishingepiphyseal vascularization and regulating chondrocyte development and survival

Abstract

VEGF is crucial for metaphyseal bone vascularization. In contrast, the angiogenic factors required for vascularization of epiphyseal cartilage are unknown, although this represents a developmentally and clinically important aspect of bone growth. The VEGF gene is alternatively transcribed into VEGF120, VEGF164, and VEGF188 isoforms that differ in matrix association and receptor binding. Their role in bone development was studied in mice expressing single isoforms. Here we report that expression of only VEGF164 or only VEGF188 (in VEGF188/188 mice) was sufficient for metaphyseal development. VEGF188/188 mice, however, showed dwarfism, disrupted development of growth plates and secondary ossification centers, and knee joint dysplasia. This phenotype was at least partly due to impaired vascularization surrounding the epiphysis, resulting in ectopically increased hypoxia and massive chondrocyte apoptosis in the interior of the epiphyseal cartilage. In addition to the vascular defect, we provide in vitro evidence that the VEGF188 isoform alone is also insufficient to regulate chondrocyte proliferation and survival responses to hypoxia. Consistent herewith, chondrocytes in or close to the hypoxic zone in VEGF188/188 mice showed increased proliferation and decreased differentiation. These findings indicate that the insoluble VEGF188 isoform is insufficient for establishing epiphyseal vascularization and regulating cartilage development during endochondral bone formation.

Authors

Christa Maes, Ingrid Stockmans, Karen Moermans, Riet Van Looveren, Nico Smets, Peter Carmeliet, Roger Bouillon, Geert Carmeliet

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Figure 3

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Altered response of VEGF188/188 chondrocytes to hypoxia. Hind limbs from...
Altered response of VEGF188/188 chondrocytes to hypoxia. Hind limbs from WT and VEGF188/188 embryos were cultured in normoxia (21% O2) or hypoxia (0.5% O2) for 48 hours. (a) Sections were stained with TUNEL (green) and DAPI (blue). Measurements were performed in fixed areas in the resting and proliferating chondrocyte zones, as indicated. Scale bar: 150 μm. (b) Magnified view of TUNEL-stained resting chondrocyte zone of limbs cultured in hypoxia (turned 90° clockwise). (c) Quantification of total cell number and percentage of apoptotic cells (of total cell number) showing lack of growth inhibition in hypoxia and increased hypoxia-induced apoptosis in the resting chondrocyte zone of VEGF188/188 limbs as compared with WT; n = 4–5; significant differences are §P < 0.05 versus normoxia of the same genotype (effect of condition); *P < 0.05 versus WT in the same condition (effect of genotype). These effects could be partially or completely rescued, respectively, by supplementation of rmVEGF164 to the mutant limbs (n = 4–5; *P < 0.05 versus WT and °P < 0.05 versus VEGF188/188 in the same condition (effect of supplementation).