Effects of platelet-derived growth factor on chondrocyte proliferation, migration and apoptosis via regulation of GIT1 expression.

The formation of fibrocartilage, cartilaginous and bony calluses is vital for bone healing following a fracture. Fibroblasts, chondrocytes and osteoblasts are critical functional cells that are involved in these three processes, respectively. Platelet­derived growth factor (PDGF), a growth factor that is released from platelet particles and appears during the early stages at the site of fractures, is essential in bone healing via regulation of cell proliferation and differentiation. However, the effects of PDGF on the chondrocytes remain unclear. In the present study, PDGF promoted phosphorylation of Src and upregulated the expression level of G­protein­coupled receptor kinase interacting protein­1 (GIT1) according to the results of the cell culture of chondrocytes in vitro and western blotting. However, the effect of PDGF on the upregulation of GIT1 expression was mostly inhibited by the Src inhibitor, PP2. After knocking down GIT1 expression using siRNA, the phosphorylation of Src continued to be induced by PDGF, although the expression of GIT1 was inhibited. Furthermore, the results indicated that PDGF promoted chondrocyte proliferation and migration, however, the effect on cell apoptosis induction was suppressed after adding the Src inhibitor, PP2. Additionally, when knocking down GIT1 using siRNA, the expression level of GIT1 decreased, which is similar to the effect of the Src inhibitor, PP2. The current study demonstrates that PDGF may initially activate the phosphorylation of Src, and subsequently induce GIT1 expression to promote chondrocyte proliferation and migration, but suppress cell apoptosis.