Osteogenic Protein-1 Induced Gene Expression: Evaluation in a Posterolateral Spinal Pseudarthrosis Model

STUDY DESIGN: Molecular study of gene expression in rabbit lumbar pseudarthrosis repairs using reverse transcriptase polymerase chain reaction. OBJECTIVE: To evaluate differential gene expression of no graft, autograft, and osteogenic protein-1 treated pseudarthroses. SUMMARY OF BACKGROUND DATA: Osteogenic protein-1 is a potential bone graft alternative that has achieved high fusion rates in a rabbit lumbar fusion model, including in the repair of nicotine-induced pseudarthroses. A previous study established a correlation between osteogenic protein-1 fusion outcomes and an enhanced level of cytokine gene expression. The expression of such cytokines is known to be decreased in nicotine-exposed rabbit fusion masses. METHODS: Messenger ribonucleic acid was isolated from nicotine-exposed New Zealand white rabbit lumbar pseudarthroses following attempted no graft, autograft, and osteogenic protein-1 pseudarthrosis repairs. Reverse transcriptase polymerase chain reaction was used to assess the expression of angiogenin, angiopoietin, intercellular adhesion molecule, platelet-derived growth factor-beta, vascular endothelial growth factor, bone morphogenetic proteins 2 and 7, type I collagen, and osteonectin. Glyceraldehyde-3-phosphate dehydrogenase was used as a constitutively expressed control. RESULTS: Levels of gene expression in the osteogenic protein-1 group were higher than those of the autograft group, which were higher than the no graft group for the majority of the genes studied. CONCLUSIONS: In the rabbit pseudarthrosis model, gene expression data supported the hypothesis that successful pseudarthrosis repair is related to the induction of osteogenic and angiogenic cytokines by osteogenic protein-1.