ISSLS PRIZE IN BASIC SCIENCE 2018: Growth differentiation factor-6 attenuated pro-inflammatory molecular changes in the rabbit anular-puncture model and degenerated disc-induced pain generation in the rat xenograft radiculopathy model

PURPOSE: To elucidate the effects of growth differentiation factor-6 (GDF6) on: (i) gene expression of inflammatory/pain-related molecules and structural integrity in the rabbit intervertebral disc (IVD) degeneration model, and (ii) sensory dysfunction and changes in pain-marker expression in dorsal nerve ganglia (DRGs) in the rat xenograft radiculopathy model. METHODS: Forty-six adolescent rabbits received anular-puncture in two non-consecutive lumbar IVDs. Four weeks later, phosphate-buffered saline (PBS) or GDF6 (1, 10 or 100 μg) was injected into the nucleus pulposus (NP) of punctured discs and followed for four weeks for gene expression analysis and 12 weeks for structural analyses. For pain assessment, eight rabbits were sacrificed at four weeks post-injection and NP tissues of injected discs were transplanted onto L5 DRGs of 16 nude rats to examine mechanical allodynia. The rat DRGs were analyzed immunohistochemically. RESULTS: In GDF6-treated rabbit NPs, gene expressions of interleukin-6, tumor necrosis factor-α, vascular endothelial growth factor, prostaglandin-endoperoxide synthase 2, and nerve growth factor were significantly lower than those in the PBS group. GDF6 injections resulted in partial restoration of disc height and improvement of MRI disc degeneration grades with statistical significance in rabbit structural analyses. Allodynia induced by xenograft transplantation of rabbit degenerated NPs onto rat DRGs was significantly reduced by GDF6 injection. Staining intensities for ionized calcium binding adaptor molecule-1 and calcitonin gene-related peptide in rat DRGs of the GDF6 group were significantly lower than those of the PBS group. CONCLUSION: GDF6 injection may change the pathological status of degenerative discs and attenuate degenerated IVD-induced pain.