Induction of proinflammatory cytokine production in intervertebral disc cells by macrophage-like THP-1 cells requires mitogen-activated protein kinase activity

OBJECTIVE To determine the role played by mitogen-activated protein kinase (MAPK) signaling in the interactions between macrophages and intervertebral disc (IVD) cells, it was hypothesized that MAPK inhibition would modulate the production of the proinflammatory cytokines associated with inflammatory reaction in IVD cells. METHODS Human annulus fibrosus (AF) and nucleus pulposus (NP) cells were cocultured with phorbol myristate acetate stimulated macrophage-like THP-1 cells, with and without SB202190 (a p38-alpha and -beta inhibitor), SP600125 (a c-Jun N-terminal kinase [JNK] inhibitor), and PD98059 (an extracellular signal-regulated kinase [ERK] 1/2 inhibitor). The cytokines in conditioned media from cocultured and macrophage-exposed (nemotic) cells were assayed using enzyme-linked immunosorbent assays (ELISAs). RESULTS Interleukin (IL)-6 and IL-8 were secreted in greater quantities by the cocultured cells compared with naive IVD cells and macrophages (M phi) cultured alone. The tumor necrosis factor (TNF)-alpha and IL-6 levels produced by the NP cells cocultured with MOs (NP-M phi) were significantly lower than those produced by AF cells cocultured with M phi s (AF-M phi). SB202190 dose-dependently suppressed IL-6 secretion by AF-M phi and NP-M phi cocultures, and 10 mu M SB202190 significantly decreased IL-6 and IL-8 production in nemotic AF and NP pellets. SP600125 at 10 mu M significantly suppressed the production of TNF alpha, IL-6, and IL-8 in AF-M phi and NP-M phi cocultures and significantly suppressed IL-1 beta production in the NP-M phi coculture. Administration of 10 mu M PD98059 significantly decreased IL-6 levels in the AF-M phi coculture, and decreased the levels of TNF alpha and IL-8 in both the AF-M phi) and NP-M phi cocultures. CONCLUSIONS The present study shows that inhibitors of p38 MAPK effectively controlled IL-6 production during inflammatory reactions and that JNK and ERK1/2 inhibitors successfully suppressed the production of major proinflammatory cytokines during interactions between macrophages and IVD cells. Therefore, selective blockade of these signals may serve as a therapeutic approach to symptomatic IVD degeneration.