Microarray analysis from two independent experiments deter mined that 629 genes were regulated by TNF signalling in both sets of experiments by at least 1. 45 fold, the majority of which were increased in response to TNF. Of these genes, alterations of 138 were attenuated with U0126. Furthermore, of the remaining genes that were not regulated by TNF, 62 genes were regulated by U0126 alone, indicating that basal MEKERK activity may also play a role in chondrocyte gene regulation. Complete microarray data have been deposited in the Gene Expression Omnibus public repository. Selective extracellular matrix and proteinase genes are regulated by TNF induced MEKERK signalling We further analysed the lists of genes that were induced by TNF using specific gene ontologies.
Analysis of the list of TNF induced, MEKERK dependent and MEKERK inde pendent probe sets indicated that there was significant repre sentation of genes whose protein products localize to the extracellular space within both lists. kinase inhibitor Further analysis of the list of TNF regulated, MEKERK dependent geneswhose products are found in the extracellular spaceindicated that some of these genes were significantly cate gorized by the molecular function of their protein products into categories that included hyaluronic acid binding activity and proteinase activity. Analysis of the TNF regulated, MEK ERK independent list of genes whose protein products were localized to the extracellular space determined that many of the protein products of these genes were involved in a variety of activities, including chemokinecytokine activityincluding macrophage Csf 1and various protease activities.
The inflammatory genes, however, appeared to be primarily U0126 insensitive. To validate the changes in gene expression supplier EMD 121974 in response to TNF induced MEKERK signalling determined by the micro array analysis, we identified the relative changes in transcript levels of the extracellular matrix components Agc1, Hapln1, and Col2a1, proteases Mmp 9 and Mmp 12, as well as the inflammatory cytokine macrophage Csf 1. TNF decreased Agc1 and Hapln1 and increased Mmp 9 and Mmp 12 in a MEKERK dependent manner. In addition, Col2a1a gene not identified as MEK ERK sensitive by microarray analysiswas also determined to be MEKERK sensitive.
Pretreatment with U0126, however, only partially attenuated the TNF induced reduc tions in Agc1, Hapln1 and Col2a1 transcript levelsto a level only moderately, but not significantly, lower than control treated cultures, suggesting the possible involvement of other pathways. Conversely, TNF induced increases in macrophage Csf 1 were independent of MEK ERK signalling. As anticipated, the inactive U0126 analogue U0124 had no effect in any of the assays tested. Taken together, these results suggest that U0126 may atten uate the changes in chondrocyte gene expression towards a catabolic phenotype while allowing for inflammatory proc esses to be undisturbed.