Abstract
Matrix metalloproteinase-3 (MMP-3) plays an important role in intervertebral disc degeneration, a ubiquitous condition closely linked to low back pain and disability. Elevated expression of syndecan 4, a cell surface heparan sulfate proteoglycan, actively controls disc matrix catabolism. However, the relationship between MMP-3 expression and syndecan 4 in the context of inflammatory disc disease has not been clearly defined. We investigated the mechanisms by which cytokines control MMP-3 expression in rat and human nucleus pulposus cells. Cytokine treatment increased MMP-3 expression and promoter activity. Stable silencing of syndecan 4 blocked cytokine-mediated MMP-3 expression; more important, syndecan 4 did not mediate its effects through NF-κB or mitogen-activated protein kinase (MAPK) pathways. However, treatment with MAPK and NF-κB inhibitors resulted in partial blocking of the inductive effect of cytokines on MMP-3 expression. Loss-of-function studies confirmed that NF-κB, p38α/β2/γ/δ, and extracellular signal-regulated kinase (ERK) 2, but not ERK1, contributed to cytokine-dependent induction of MMP3 promoter activity. Similarly, inhibitor treatments, lentiviral short hairpin-p65, and short hairpin-IκB kinase β significantly decreased cytokine-dependent up-regulation in MMP-3 expression. Finally, we show that transforming growth factor-β can block the up-regulation of MMP-3 induced by tumor necrosis factor (TNF)-α by counteracting the NF-κB pathway and syndecan 4 expression. Taken together, our results suggest that cooperative signaling through syndecan 4 and the TNF receptor 1-MAPK-NF-κB axis is required for TNF-α-dependent expression of MMP-3 in nucleus pulposus cells. Controlling these pathways may slow the progression of intervertebral disc degeneration and matrix catabolism.