Localization of bone morphogenetic protein 13 in human intervertebral disc and its molecular and functional effects in vitro in 3D culture.

Our laboratory has demonstrated that bone morphogenetic protein 13 prevented the effects of annular injury in an ovine model, maintaining intervertebral disc height, cell numbers and increasing extracellular matrix production compared to degenerated controls. The present study sought to examine the molecular effects of bone morphogenetic protein 13 on human degenerated disc cells and localize its expression in both human degenerate and scoliotic disc tissue. Effect of bone morphogenetic protein 13 on human derived nucleus pulposus, annulus fibrosus and endplate cells cultured in alginate beads was evaluated by changes in proteoglycan and collagen content. Migratory potential of disc cells towards bone morphogenetic protein 13 was also examined. Bone morphogenetic protein 13 induced significant proteoglycan accumulation in nucleus (18%), annulus (21%) and endplate (23%) cells cultured in alginate beads (p<0.05) compared to controls. Further bone morphogenetic protein 13 increased collagen I and II protein expression in nucleus and endplate cells. Nucleus cells displayed a significant chemotactic response towards bone morphogenetic protein 13. The endogenous expression of bone morphogenetic protein 13 in degenerate disc tissue was not different to scoliotic disc. Bone morphogenetic protein 13 has the potential to enhance extracellular matrix accumulation and induce cell migration in certain disc cells.