Synergistic Effect of Nerve Growth Factor and Insulin-Like Growth Factor-1 on Anti-Apoptosis and Extracellular Matrix Synthesis of Rat Intervertebral Disc Cells

Abstract

Introduction: Decreased cellularity due to excessive apoptosis of disc cells is a major predisposing factor for disc degeneration. Therefore, the inhibition of apoptosis of disc cells might be a possible therapeutic approach for modulating the process of disc degeneration. The purpose of the current study was to investigate the effect of nerve growth factor (NGF) and insulin-like growth factor-1 (IGF-1) in preventing apoptosis and increasing extracellular matrix synthesis in rat intervertebral disc cells. Material and Methods: Expression of tropomyosin-related kinase A (TrkA) receptor for NGF and IGF-1 receptor (IGF-1R) for IGF-1 was examined in rat annulus fibrosus cells. In addition, rat annulus fibrosus cells were isolated, cultured, and placed in either 10% (normal control) or 0% (apoptosis-promoting condition) fetal bovine serum (FBS). We identified and quantified the degree of expression of TrkA and IGF-1R and apoptosis of the cells. Finally, we analyzed the effect of NGF (100 ng/ml) and IGF-1 (500 ng/ml) in preventing apoptosis and increasing synthesis of extracellular matrix proteins, such as aggrecan, collagen-1 and -2, in the cells, in 0% FBS. Results: In situ expression of TrkA and IGF-1R was identified in rat annulus fibrosus cells. In addition, the degree of expression of TrkA and IGF-1R was decreased in the cells treated with 0% FBS but some degree of expression was still maintained. Apoptosis of the cells was increased in 0% FBS compared with 10% FBS (p < 0.001). Despite extreme survival condition (0% FBS), each application of NGF (100 ng/ml) and IGF-1 (500 ng/ml) reduced apoptosis of the cells by 2% and 5%, respectively, which led to subsequently increased synthesis of aggrecan, collagen-1 and -2 (all, p < 0.05). The combined application of NGF (100 ng/ml) and IGF-1 (500 ng/ml) more significantly decreased apoptosis of the cells by 9% and increased synthesis of aggrecan, collagen-1 and -2 in the cells (all, p < 0.01). Conclusion: The current findings demonstrate that apoptosis of intervertebral disc cells can be attenuated by NGF and IGF-1, which lead to increased extracellular matrix synthesis. Combined application of NGF and IGF-1 has a synergistic effect than single use of NGF and IGF-1. Our result suggests that NGF and IGF-1 may play a therapeutic role in slowing disc degeneration, which is due to inappropriate or excessive apoptosis of intervertebral disc cells.