Matrix Vesicles are carriers of Bone Morphogenetic Proteins (BMPs),

Abstract

Matrix vesicles (MVs) are well-positioned in the growth plate to serve as a carrier of morphogenetic information to nearby chondrocytes and osteoblasts. Bone morphogenetic proteins (BMPs), carried in MVs could promote differentiation of the above skeletal cells. Vascular endothelial growth factor (VEGF) in MVs could stimulate angiogenesis. Therefore, a study was undertaken to confirm the presence of bone morphogenetic proteins (BMPs) 1 through 7, VEGF and the non-collagenous matrix proteins, bone sialoprotein (BSP), osteopontin (OPN), osteocalcin (OC) and osteonectin (ON) in isolated rat growth plate. Methods:MVs were isolated from collagenase-digested rachitic rat tibial and femoral growth plates. The presence of BMPs 1-7, VEGF, OPN and OC was evaluated by western blot, plus ELISA analyses for BMP-2 and 4 content. The alkaline phosphatase-raising ability of MV extracts upon cultured rat growth plate chondrocytes was measured as a reflection of the MVs ability to promote chondro-osseous differentiation.Results:BMP-1 through 7, VEGF, BSP, OPN and OC were all detected by western blot analyses. Chondrocytes treated with MV extracts showed a two to three-fold increase in alkaline phosphatase activity over control, indicating increased differentiation.Significant amounts of BMP-2and 4 were detected in MVs by ELISA. Combined, these data, suggest that MVs could play an important morphogenetic role in growth plate and endochondral bone formation.