Effects of IL-1β, IL-20, and BMP-2 on Intervertebral Disc Inflammation under Hypoxia

Intervertebral disc (IVD) is an avascular tissue under hypoxic condition after adulthood. Our previous data showed that inflammatory cytokines (interleukin (IL)-1β), IL-20, and bone morphogenetic protein-2 (BMP-2) play important roles in the healing process after disc injury. In the current study, we investigated whether IL-1β, IL-20, or BMP-2 modulate the expression of pro-inflammatory cytokines, chemotaxis factor, and angiogenesis factor on IVD cells under hypoxia. IVD cells were isolated from patients with intervertebral disc herniation (HIVD) at the levels of L4–5 and L5–S1. We found that the expression of IL-1β, IL-20, BMP-2, hypoxia-inducible factor (HIF)-1α, IL-6, IL-8, angiogenetic factor (vascular endothelial growth factor (VEGF)), chemotactic factor (monocyte chemoattractant protein 1 (MCP-1)), and matrix metalloproteinase-3 (MMP-3) was upregulated in IVD cells under hypoxia conditions. In addition, IL-1β upregulated the expression of pro-inflammatory cytokines (IL-6 and IL-8), VEGF, MCP-1, and disc degradation factor (MMP-3) in IVD cells under hypoxia conditions. IL-20 upregulated MCP-1 and VEGF expression. BMP-2 also upregulated the expression of MCP-1, VEGF, and IL-8 in IVD cells under hypoxia conditions. Treatment with antibody against IL-1β decreased VEGF and MMP-3 expression, while treatment with IL-20 or BMP-2 antibodies decreased MCP-1, VEGF, and MMP-3 expression. Moreover, IL-1β modulated both the expression of IL-20 and BMP-2, but IL-20 only modulated BMP-2 either under a hypoxic or normoxic condition. Therefore, we concluded that the inflammation, chemotaxis, matrix degradation, and angiogenesis after disc herniation are influenced by the hypoxic condition and controlled by IL-1β, IL-20, and BMP-2.