CCN2 Suppresses Catabolic Effects of Interleukin-1β through α5β1 and αVβ3 Integrins in Nucleus Pulposus Cells IMPLICATIONS IN INTERVERTEBRAL DISC DEGENERATION

Background: The relationship between inflammatory cytokines TNF- and IL-1 and CCN2 in nucleus pulposus cells is unknown. Results: Cytokines suppress CCN2 expression, whereas CCN2 represses catabolic action of IL-1. Conclusion: In nucleus pulposus, cytokines and CCN2 form a negative regulatory circuit. Significance: CCN2 may play an important role in pathogenesis of intervertebral disc degeneration. The objective of the study was to examine the regulation of CCN2 by inflammatory cytokines, IL-1, and TNF- and to determine whether CCN2 modulates IL-1-dependent catabolic gene expression in nucleus pulposus (NP) cells. IL-1 and TNF- suppress CCN2 mRNA and protein expression in an NF-B-dependent but MAPK-independent manner. The conserved B sites located at -93/-86 and -546/-537 bp in the CCN2 promoter mediated this suppression. On the other hand, treatment of NP cells with IL-1 in combination with CCN2 suppressed the inductive effect of IL-1 on catabolic genes, including MMP-3, ADAMTS-5, syndecan 4, and prolyl hydroxylase 3. Likewise, silencing of CCN2 in human NP cells resulted in elevated basal expression of several catabolic genes and inflammatory cytokines like IL-6, IL-4, and IL-12 as measured by gene expression and cytokine protein array, respectively. Interestingly, the suppressive effect of CCN2 on IL-1 was independent of modulation of NF-B signaling. Using disintegrins, echistatin, and VLO4, peptide inhibitors to v3 and 51 integrins, we showed that CCN2 binding to both integrins was required for the inhibition of IL-1-induced catabolic gene expression. It is noteworthy that analysis of human tissues showed a trend of altered expression of these integrins during degeneration. Taken together, these results suggest that CCN2 and inflammatory cytokines form a functional negative feedback loop in NP cells that may be important in the pathogenesis of disc disease.