Vascular endothelial growth factor (VEGF) in cartilage neovascularization and chondrocyte differentiation: auto-paracrine role during endochondral bone formation

• Published in: Journal of cell science Vol. 113 ( Pt 1); no. 1; pp. 59 - 69
• Main Authors: Carlevaro, M F, Cermelli, S, Cancedda, R, Descalzi Cancedda, F
• Format: Journal Article
• Language: English
• Published: England 01.01.2000
• Subjects: Animals; Ascorbic Acid - metabolism; Autocrine Communication; Bone Development - drug effects; Bone Development - physiology; Cartilage - blood supply; Cartilage - cytology; Cartilage - embryology; Cartilage - metabolism; Cell Differentiation - drug effects; Cells, Cultured; Chemotaxis - drug effects; Chick Embryo; Chondrocytes - cytology; Chondrocytes - drug effects; Chondrocytes - metabolism; Conalbumin - pharmacology; Culture Media, Conditioned - pharmacology; Endothelial Growth Factors - antagonists & inhibitors; Endothelial Growth Factors - chemistry; Endothelial Growth Factors - metabolism; Endothelial Growth Factors - pharmacology; Lymphokines - antagonists & inhibitors; Lymphokines - chemistry; Lymphokines - metabolism; Lymphokines - pharmacology; Mice; Molecular Weight; Neovascularization, Physiologic - drug effects; Paracrine Communication; Phosphorylation - drug effects; Receptor Protein-Tyrosine Kinases - antagonists & inhibitors; Receptor Protein-Tyrosine Kinases - chemistry; Receptor Protein-Tyrosine Kinases - metabolism; Receptors, Growth Factor - antagonists & inhibitors; Receptors, Growth Factor - chemistry; Receptors, Growth Factor - metabolism; Receptors, Vascular Endothelial Growth Factor; Tibia - cytology; Tibia - drug effects; Tibia - embryology; Tibia - metabolism; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors
• ISSN: 0021-9533; 1477-9137
• DOI: 10.1242/jcs.113.1.59

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) induces endothelial cell migration and proliferation in culture and is strongly angiogenic in vivo. VEGF synthesis has been shown to occur in both normal and transformed cells. The receptors for the factor have been shown to be localized mainly in endothelial cells, however, the presence of VEGF synthesis and the VEGF receptor in cells other than endothelial cells has been demonstrated. Neoangiogenesis in cartilage growth plate plays a fundamental role in endochondral ossification. We have shown that, in an avian in vitro system for chondrocyte differentiation, VEGF was produced and localized in cell clusters totally resembling in vivo cartilage. The factor was synthesized by hypertrophic chondrocytes and was released into their conditioned medium, which is highly chemotactic for endothelial cells. Antibodies against VEGF inhibited endothelial cell migration induced by chondrocyte conditioned media. Similarly, endothelial cell migration was inhibited also by antibodies directed against the VEGF receptor 2/Flk1 (VEGFR2). In avian and mammalian embryo long bones, immediately before vascular invasion, VEGF was distinctly localized in growth plate hypertrophic chondrocytes. In contrast, VEGF was not observed in quiescent and proliferating chondrocytes earlier in development. VEGF receptor 2 colocalized with the factor both in hypertrophic cartilage in vivo and hypertrophic cartilage engineered in vitro, suggesting an autocrine loop in chondrocytes at the time of their maturation to hypertrophic cells and of cartilage erosion. Regardless of cell exposure to exogenous VEGF, VEGFR-2 phosphorylation was recognized in cultured hypertrophic chondrocytes, supporting the idea of an autocrine functional activation of signal transduction in this non-endothelial cell type as a consequence of the endogenous VEGF production. In summary we propose that VEGF is actively responsible for hypertrophic cartilage neovascularization through a paracrine release by chondrocytes, with invading endothelial cells as a target. Furthermore, VEGF receptor localization and signal transduction in chondrocytes strongly support the hypothesis of a VEGF autocrine activity also in morphogenesis and differentiation of a mesoderm derived cell.