Expression Of Vascular Endothelial Growth Factor And Its Effects On Bone Remodeling During Orthodontic Tooth Movement

Vasculature plays a key role in bone development remodeling and healing. Ferrara was the first to identify a growth factor for vascular endothelial cells in the media conditioned by bovine pituitary follicular cells. He had reported the purification of this endothelial-cell specific mitogen, and named it as vascular endothelial growth factor (VEGF). Extensive research has been done on members of VEGF family and receptors. There is strong evidence that this family exerts multiple biological functions in the pathological and physiological process of growth development tissue regeneration repair, and tumor genesis in addition. Recently, it has been demonstrated that angiogenesis plays a crucial role during enchondral bone formation and vascular invasion is a prerequisite for osteogenesis. It is also reported that VEGF is expressed in both bone tissue and cultured osteoblasts, moreover, the expression level of Flt-1 is high in the osteoclast. The family of VEGF-related molecules has grown and presently contain six members in mammalia: VEGF placenta growth factor (PLGF), VEGF-B, VEGF-C VEGF-D VEGF-E and neuropilin. VEGF may act as a central mediator for other bone growth factors.Currently, both therapeutic angiogenesis using recombinant VEGF gene trasnfer are being pursued in bone formation.Vascular endothelial growth factor (VEGF) has been long recognized to be a potent regulator of normal and abnormal angiogenesis. Bone formation is connected with angiogenesis, and vascular invasion is a prerequisite for osteogenesis. In bone develodment and regeneration, angiogenesis and bone/cartilage remodeling are essential processes and closely associated with each other. Histological findings indicate that osteoblasts and osteoprogenitor cells are always located adjacent to endothelial cells in blood vessels at sites of new bone remodeling. It is recognized that the vascular invasion is prerequisite for bone formation. These results suggest that there is a common mediator for these two biological events.VEGF is known to be an angiogenetic factor produced by many types of cells including fibroblasts, smooth muscle cells, hypertrophic chondrocytes, osteoblasts etc. Ferrara and Henzel were the first to identify a growth factor for vascular endothelial cells in the media conditioned by bovine pituitary follicular cells. Since then, extensive researches have been done on members of VEGF family and their receptors. There is a strong evidence that this family plays a fundamental role in the growth and differentiation of vascular endothelial cells as well asosteoblasts. Furthermore,VEGF-mediated angiogenesis is essential for bone formation.In particular,VEGF also is the major regulator of angiogenesis,since increased expression of the VEGF stimulates bone formation. In recent years, many rapid progresses have been made in understanding the molecular mechanism of the close association between angiogenesis and bone formation.Hence,VEGF may act as an essential mediator during these processes.A recent study has shown that VEGF administration leads to enchanced blood vessel formation and ossification in models of bone damage. Thus,VEGF has possible clinical applications for achieving bone formation and ongoing research is being pursued. Current studies about VEGF and osteogenesis focused on bone defect and repair, however, the study about the relationship between VEGF and orthodontic bone formation was not mentioned. Orthodontic tooth movement depends on the remodeling of periodontal tissues especially surrounding alveolar bone. This related tissue remodeling is achieved by osteoclastic bone resorption and osteoblastic new bone formation and mediated by many factors. It was reported that VEGF plays a role in the migration and differentiation of osteoblasts and has an obvious relationship with bone remodeling.To the best of our knowledge, such a molecular biology approach on the expression and distribution of VEGF in the periodontal tissue during orthodontic tooth movement has never been reported. Thus, we conducted this stud...