Vascular endothelial growth factor plays an important autocrine/paracrine role in the progression of osteoarthritis

Vascular endothelial growth factor (VEGF) plays an essential role in the angiogenesis of growing cartilage. Although VEGF expression in cartilage vanishes in normal adults, VEGF is known to be expressed in chondrocytes of osteoarthritic (OA) cartilage. As little information is available on the VEGF expression in the cartilage of OA-like lesions of the temporomandibular joint (TMJ), VEGF expression in the condylar cartilage of TMJs of rats affected with OA was examined. To evoke OA, mechanical stress was applied by forced jaw opening for 10 or 20 days. After 20 days, marked OA-like lesions were observed in the condyle. VEGF was expressed in the chondrocytes of the mature and hypertrophic cell layers of the intermediate and posterior region of the condyle. The percentage of VEGF immunopositive chondrocytes significantly increased with the period of applied mechanical stress. Furthermore, tartrate-resistant acid phosphatase (TRAP) staining of the condylar cartilage showed significant increment of osteoclasts in the mineralized layer subjacent to the hypertrophic layer where high VEGF expression could be detected. The results suggest that VEGF plays an important role in the progression of OA.Eiji Tanaka and Junko Aoyama contributed equally to this work.