Shear and Compression Differentially Regulate Clusters of Functionally Related Temporal Transcription Patterns in Cartilage Tissue

Jonathan B. Fitzgerald, Moonsoo Jin, Alan J. Grodzinsky
2006 Journal of Biological Chemistry  
Chondrocytes are subjected to a variety of biophysical forces and flows during physiological joint loading, including mechanical deformation, fluid flow, hydrostatic pressure, and streaming potentials; however, the role of these physical stimuli in regulating chondrocyte behavior is still being elucidated. To isolate the effects of these forces, we subjected intact cartilage explants to 1-24 h of continuous dynamic compression or dynamic shear loading at 0.1 Hz. We then measured the
more » ... n levels of 25 genes known to be involved in cartilage homeostasis using real-time PCR and compared the gene expression profiles obtained from dynamic compression, dynamic shear, and our recent results on static compression amplitude and duration. Using clustering analysis, we determined that transcripts for proteins with similar function had correlated responses to loading. However, the temporal expression patterns were strongly dependent on the type of loading applied. Most matrix proteins were up-regulated by 24 h of dynamic compression or dynamic shear, but down-regulated by 24 h of 50% static compression, suggesting that cyclic matrix deformation is a key stimulator of matrix protein expression. Most matrix proteases were up-regulated by 24 h under all loading types. Transcription factors c-Fos and c-Jun maximally responded within 1 h to all loading types. Pre-incubating cartilage explants with either a chelator of intracellular calcium or an inhibitor of the cyclic AMP pathway demonstrated the involvement of both pathways in transcription induced by dynamic loading. Mechanical forces within synovial joints are known to influence the metabolic behavior of chondrocytes, the sole cell type of cartilage (1-3). Chondrocytes are responsible for the maintenance and turnover of the cartilage extracellular matrix, in Downloaded from 4 The abbreviations used are: BAPTA-AM, bis-(aminophenoxy)ethanetetraacetic acid acetoxymethyl; PCA, principal component analysis; TIMP, tissue inhibitor of matrix protease; MMP, matrix metalloproteinase; ADAMTS, a disintegrin and metalloprotease with thrombospondin motifs; COX-2, cyclooxygenase-2; TGF, transforming growth factor; TNF␣, tumor necrosis factor ␣; NFB, nuclear factor B.
doi:10.1074/jbc.m510858200 pmid:16782710 fatcat:ltiu66ch35ditlkknqotknj4ue