Basal and IL-1beta enhanced chondrocyte chemotactic activity on monocytes are co-dependent on both IKKalpha and IKKbeta NF-kappaB activating kinases

IKKalpha and IKKbeta are essential kinases for activating NF-kappaB transcription factors that regulate cellular differentiation and inflammation. By virtue of their small size, chemokines support the crosstalk between cartilage and other joint compartments and contribute to immune cell chemotaxis in osteoarthritis (OA). Here we employed shRNA retroviruses to stably and efficiently ablate the expression of each IKK in primary OA chondrocytes to determine their individual contributions for monocyte chemotaxis in response to chondrocyte conditioned media. Both IKKalpha and IKKbeta KDs blunted both the monocyte chemotactic potential and the protein levels of CCL2/MCP-1, the chemokine with the highest concentration and the strongest association with monocyte chemotaxis. These findings were mirrored by gene expression analysis indicating that the lowest levels of CCL2/MCP-1 and other monocyte-active chemokines were in IKK?KD cells under both basal and IL-1beta stimulated conditions. We find that in their response to IL-1beta stimulation IKKalphaKD primary OA chondrocytes have reduced levels of phosphorylated NFkappaB p65pSer536 and H3pSer10. Confocal microscopy analysis revealed co-localized p65 and H3pSer10 nuclear signals in agreement with our findings that IKKalphaKD effectively blunts their basal level and IL-1beta dependent increases. Our results suggest that IKKalpha could be a novel OA disease target.