Role of IL-17 in nucleus pulposus cell proliferation and metabolism cultured in vitro.

Objective: To explore the role of cytokine, interleukin-17 (IL-17) in human degenerative disc disease.

Methods: Through magnetic resonance imaging, human degenerative disc tissues were confirmed from the isolated nucleus pulposus cells, which were then cultured in vitro. The cells were cultured with and without different concentrations of IL-17. 2 ng/mL, 5 ng/mL, 10 ng/mL, 15 ng/mL and 20 ng/mL IL-17 concentrations were used for stimulation. After 72 hours, the inhibition rate of proliferation was measured by MTS method. For 48 and 96 hours, the nucleus pulposus cells were cultured with and without the appropriate IL-17 concentrations. The mRNA and protein expression levels of the matrix macromolecules and degrading tissue genes were measured by Real-time PCR and Western blot analysis.

Results: It was noted that nucleus pulposus cell proliferation was inhibited after culturing in vitro with IL-17 stimulation, and it was further observed that the inhibition effect was significantly stronger with 15 ng/mL IL-17 concentration. With the dosage of 15 ng/mL, IL-17 stimulation induced multiple cellular responses, such as the significant increase in mRNA expression for both aggrecan (ACAN) and type I collagen (COLLA1) genes (P<0.05), and the significant decrease in mRNA expression of both degrading tissue genes, MMP3 and TIMP3 (P<0.05). Western blot results also showed that the protein level of COL1A1 was significantly decreased (t=3.199, P=0.006), while the protein level of one peptidases (ADAMTS5) significantly increased (t=2.667, P=0.021).

Conclusions: These findings suggest that IL-17 can inhibit proliferation and affect the metabolism of the cultured nucleus pulposus cells in vitro, and these findings could possibly contribute to the degenerative changes that occur in DDD through extracellular matrix synthesis inhibition, promoting nucleus pulposus extracellular matrix degradation and disrupting the metabolic balance.