Abstract
The aim of the study was to delineate regulation of CTGF/CCN2 expression by cytokines, IL-1β and TNF-α. In addition, we addressed if CCN2 modulates cytokine action on NP cells. Our studies showed that cytokines suppress CCN2 expression and that this effect was mediated in an NF-κB dependent but MAPK independent fashion. Site-directed mutagenesis and genomic chromatin immunoprecipitation (ChIP) analyses showed that the conserved κB sites located at −93/−86 and −546/−537 bp in the CCN2 promoter interacted with p65/RelA and mediated this suppressive effect of cytokines on CCN2 expression. Concerning role of CCN2 under inflammatory state, it was seen that the treatment of NP cells with IL-1β along with CCN2 blocked the stimulatory effect of IL-1β on MMP-3, ADAMTS5, prolyl hydroxylase 3 and syndecan 4 expression. Furthermore, silencing of CCN2 in human NP cells resulted in increased expression of catabolic genes and inflammatory cytokines such as IL-6, IL-4, and IL-12 as measured by gene expression analysis and cytokine protein array, respectively, under basal state. However, reporter analysis clearly showed that the inhibitory effect of CCN2 on IL-1β was independent of regulation of NF-κB signaling pathway. Using echistatin and VLO4, peptide inhibitors to αvβ3 and α5β1 integrins, we also showed that CCN2 interaction with these integrins was necessary for the inhibition of IL-1β-induced catabolic gene expression. Finally, analysis of human tissues showed a trend of altered expression of these integrins during degeneration. Collective, our results suggest that CCN2 and cytokines may form a functional negative feedback loop in NP cells important in the pathogenesis of disc degeneration. Disclosure of Interest None declared
Published Version
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