Induction of matrix metalloproteinase-2 and -3 activity in ovine nucleus pulposus cells grown in three-dimensional agarose gel culture by interleukin-1β: a potential pathway of disc degeneration

Degeneration of the intervertebral disc is an important clinical problem, which often contributes to low back pain. Since approximately 80–90% of the general population will be subject to back pain at some stage during their lifetime, this has major socioeconomic consequences. Matrix metalloproteinases (MMPs) have been implicated in the excessive breakdown of extracellular matrix components during disc degeneration. The aim of the present study was to evaluate the regulation of MMP-2 (gelatinase-A) and MMP-3 (stromelysin) produced by cultured ovine nucleus pulposus (NP) cells stimulated with interleukin-1β (IL-1β). NP cells were established in three-dimensional agarose culture and stimulated with IL-1β under serum-free conditions. Conditioned media samples were evaluated by gelatin and casein zymography and by fluorimetry using an MMP-specific substrate. Time-course and dose dependencies were established for MMP-2, -3 production by the NP cells in response to the IL-1β. Gelatin and casein zymography indicated that elevated levels of proMMP-2 and proMMP-3 were present in media samples in response to the IL-1β treatment. After 24–96 h culture, levels of the active 43 and 45 kDa active MMP-3 were significantly elevated, whereas MMP-2 was present mainly as its 72 kDa pro-form. Additional 36, 28 and 21 kDa MMP species were also present after prolonged incubation with IL-1β, probably representing MMP breakdown species. IL-1β was a potent catabolic mediator for the NP cells, resulting in the production of elevated levels of MMP-2 and -3 in culture. However, ~70% of the MMP-2 was present as the 72 kDa pro-form, which suggests that some additional steps are involved in its activation in vivo.