ASBMR 30th Annual Meeting SA001–SA572

Abstract

In order to examine if autogenous BMP-2 expression is necessary for the osteogenic differentiation of marrow stromal cells, BMP-2 expression was inhibited using lentiviral transfection of a BMP2 shRNA. Inhibition of BMP2 expression decreased the expression of markers of terminal osteoblasts (osteocalcin, Runx2, osterix, APase activity, and mineral deposition), while the expression of transcription factors (Sox 9 and Msx2) that are seen in skeletal lineage progenitors were not effected. Rescue of osteogenic differentiation by the exogenous addition of either BMP7 or BMP2 recovered the levels of expression of osterix and APase and enhanced Sox9 and Msx2. However, BMP7 did not recover the expression of Runx2 and only partially recovered mineral deposition while the exogenous addition of BMP2 recovered all of these phenotypic properties. The effect of the loss of BMP2 expression on bone formation after marrow ablation lead to 80% loss of mineralized bone formation as assayed by microCT at day seven after surgery. Assay of same set of mRNAs as examined in vitro showed transient ~2 fold increase of Sox9 at day three after surgery in the shRNA BMP2 samples while at day seven osterix, Runx2, osteocalcin and Sox9 all showed ~50 to ~80% inhibition compared to expression in the NT (scrambled) treated samples. Interestingly, Msx2 showed ~10 fold elevation expression at seven days post surgery. Immunohistological examination of the cell populations found in the meduallary space three days after surgery with antibodies for CD146 and Sox9, showed equal numbers of cells expressing these skeletal stem markers in both control and shRNA treated specimens. These results demonstrate that: 1) BMP-2 is a central morphogenetic factor for the post natal osteogenic differentiation: 2) BMP2 does not effect the initial recruitment or expansion of skeletal stem cells in vivo: 3) Both BMP2 and BMP7 can both induce osterix and this transcription factor can promote ostegenic differentiation: 4) Expression of Runx2 is dependent on BMP2: 5) Both osterix and Runx2 are needed to fully promote osteogenic development. SA002See Friday Plenary number F002. SA003 Clinical Application of Resorbable Polymers in Guided BoneRegeneration. W. IP*. Orthopaedics & Traumatology, The University of Hong Kong, Hong Kong, Hong Kong. INTRODUCTION:Long segmental diaphyseal bone loss often results from high energy trauma like blast injury, osteomyelitis or wide excision of malignant conditions. Treatment of this long segmental diaphyseal defects remain a difficult clinical problem. In the literature, many authors have reported that bone loss more than 2.5 cm always require bone grafting. This is probably the critical size defect in human. Non-vascularized bone graft frequently fails if the defect is longer than 6-7 cm. 2.5 cm is probably the critical size defect in human and 7 cm is likely the critical size for non-vascularized bone graft. Various treatment methods are adopted currently to address this problem, including vascularized bone graft, distraction osteogene...