IL-1β, but not BMP-7 leads to a dramatic change in the gene expression pattern of human adult articular chondrocytes-Portraying the gene expression pattern in two donors

Anabolic and catabolic cytokines and growth factors such as BMP-7 and IL-1β play a central role in controlling the balance between degradation and repair of normal and (osteo)arthritic articular cartilage matrix. In this report, we investigated the response of articular chondrocytes to these factors IL-1β and BMP-7 in terms of changes in gene expression levels. Large scale analysis was performed on primary human adult articular chondrocytes isolated from two human, independent donors cultured in alginate beads (non-stimulated and stimulated with IL-1β and BMP-7 for 48 h) using Affymetrix gene chips (oligo-arrays). Biostatistical and bioinformatic evaluation of gene expression pattern was performed using the Resolver software (Rosetta). Part of the results were confirmed using real-time PCR. IL-1β modulated significantly 909 out of 3459 genes detectable, whereas BMP-7 influenced only 36 out of 3440. BMP-7 induced mainly anabolic activation of chondrocytes including classical target genes such as collagen type II and aggrecan, while IL-1β, both, significantly modulated the gene expression levels of numerous genes; namely, IL-1β down-regulated the expression of anabolic genes and induced catabolic genes and mediators. Our data indicate that BMP-7 has only a limited effect on differentiated cells, whereas IL-1β causes a dramatic change in gene expression pattern, i.e. induced or repressed much more genes. This presumably reflects the fact that BMP-7 signaling is effected via one pathway only (i.e. Smad-pathway) whereas IL-1β is able to signal via a broad variety of intracellular signaling cascades involving the JNK, p38, NFkB and Erk pathways and even influencing BMP signaling.