Proinflammatory cytokines modulate the chemokine CCL2 (MCP-1) in human annulus cells in vitro: CCL2 expression and production

• The role of the chemokine CCL2 (MCP-1, monocyte chemoattractant protein-1) in the human disc is poorly understood.
• We hypothesized exposure of human annulus cells to proinflammatory cytokines might alter expression and production of CCL2.
• CCL2 gene expression was upregulated following IL-1ß or TNF-α exposure (5.5 and 7.7 fold increases, respectively).
• Grade II-III cells exposed to IL-1ß or TNF-α secreted higher levels of CCL2 into the culture media vs. controls.
• Cells from more degenerated grade IV-V discs, however, only increased production following IL-1ß exposure.

Chemokines are important secondary inflammatory mediators released in response to stimuli which act as second-order cytokines with specialized functions in inflammation. The role of many of these specialized mediators is as yet poorly understood in the human intervertebral disc. Here we investigated CCL2 (chemokine (C–C motif) ligand 2, also known as monocyte chemotactic protein-1 (MCP-1)) in a study of its immunolocalization in disc tissue, and then hypothesized that exposure of cultured human annulus cells to proinflammatory cytokines might alter CCL2 gene expression and CCL2 production. CLL2 was localized to many disc cells in both herniated and non-herniated tissue specimens. Molecular analyses showed that cells exposed to IL-1β showed a 5.5 fold upregulation in CCL2 gene expression vs. controls, p = 0.017. Cells exposed to TNF-α showed a 7.7 fold upregulation vs. controls, p = 0.005. Cultured cells (grades II–V) showed increased MCP-1 production in IL1-β-treated cells vs. controls (p = 0.016), with no significant difference in production in TNF-α-treated cells. Local production of CCL2 in vivo and vitro suggests that annulus cells may be primary effector cells (as well as target cells), with the ability to mediate physiological immune-related processes during disc degeneration by both autocrine and paracrine signaling.