COMPRESSION-INDUCED CHANGES IN THE SHAPE AND VOLUME OF THE CHONDROCYTE NUCLEUS

Changes in cell shape and volume are believed to play a role in the pr ocess of mechanical signal transduction by chondrocytes in articular c artilage. One proposed pathway through which chondrocyte deformation m ay be transduced to an intracellular signal is through cytoskeletally mediated deformation of intracellular organelles, and more specificall y, of the cell nucleus. In this study, confocal scanning laser microsc opy was used to perform in situ three-dimensional morphometric analyse s of the nuclei of viable chondrocytes during controlled compression o f articular cartilage explants from the canine patellofemoral groove. Unconfined compression of the tissue to a 15% surface-to-surface strai n resulted in a significant decrease of chondrocyte height and volume by 14.7 +/- 6.4 and 11.4 +/- 8.4%, respectively, and of nuclear height and volume by 8.8 +/- 6.2% and 9.8 +/- 8.8%, respectively. Disruption of the actin cytoskeleton using cytochalasin D altered the relationsh ip between matrix deformation and changes in nuclear height and shape, but not volume. The morphology and deformation behavior of the chondr ocytes were not affected by cytochalasin treatment. These results sugg est that the actin cytoskeleton plays an important role in the link be tween compression of the extracellular matrix and deformation of the c hondrocyte nuclei and imply that chondrocytes and their nuclei undergo significant changes in shape and volume in vivo.