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Abstract
Low back pain (LBP) is a major health problem and one of the main sources of LBP is intervertebral disc (IVD) degeneration. IVD degeneration is characterised by loss of disc cells and increased catabolism of extracellular matrix (ECM). The use of anabolic growth factors to regenerate the ECM of the IVD continues to be evaluated in preclinical studies. Bone morphogenetic protein 13 (BMP-13) stimulates proteoglycan production in chondrocyte-like cells and could be a potential therapeutic agent in regenerating the degenerate disc. However, the molecular effects of recombinant protein (rh) BMP-13 on IVD cells are not known. The effect of different doses of rhBMP-13 on nucleus pulposus, annulus fibrosus and end plate cells derived from degenerate human intervertebral discs cultured in alginate beads was evaluated by studying the changes in cell viability, cell proliferation and proteoglycan accumulation. Temporal responses were also evaluated by cellular proliferation and proteoglycan accumulation. Furthermore, the effect of rhBMP-13 stimulation on the expression of selected chondrogenic and osteogenic genes and proteins by IVD cells was determined. The findings show that rhBMP-13 induced significant proteoglycan accumulation in nucleus pulposus, annulus fibrosus and end plate cells at a concentration of 400ng/ml after 7 days. In nucleus pulposus cells, rhBMP-13 may have an anti-osteogenic effect, by potentially increasing sox9 gene expression and repressing runx2 and osteocalcin gene expression. In annulus fibrosus cells, rhBMP-13 increased collagen I gene and protein expression, enhancing the fibrocytic phenotype of the cells. In end plate cells, rhBMP-13 may have a chondrocytic effect, by increasing aggrecan, collagen II and sox9 gene expression. There was, however, an increase in runx2 and osteocalcin gene expression in both annulus fibrosus and end plate cells suggests a potential for bone formation and warrants further investigation. RhBMP-13 stimulation had a limited effect on the cellular viability and proliferation of IVD cells in vitro. The findings from the present study suggest that rhBMP-13 may enhance the expression of critical ECM genes that are characteristic of the cells in each region of the disc. Therefore, further exploration of BMP-13 as a potential therapeutic agent to ameliorate IVD degeneration is warranted.