Relationship between chondrocyte apoptosis and matrix depletion in human articular cartilage

Chondrocyte apoptosis has been described in studies of the pathogenesis of various arthritides. Since matrix degradation is important in the pathology of arthritis, we investigated the effect of matrix depletion on chondrocyte apoptosis.

Consecutive 1 mm sections of child's rib cartilage were cultured under 4 sets of conditions: (1) control; and treatment with (2) hyaluronidase, (3) collagenase, (4) hyaluronidase/collagenase alternately. Sections were harvested on Days 5, 8, and 11, and the proportion of apoptotic cells was measured by propidium iodide staining and flow cytometry. Changes of Fas and Fas ligand expression were verified by immunohistochemistry and Western blot.

Collagenase treatment led to an increase of apoptosis, which began on Day 8, whereas hyaluronidase treatment had no effect on chondrocyte viability up to Day 11. Alternating hyaluronidase and collagenase treatment induced chondrocyte death earlier, but the difference in apoptotic rate was not significant on Days 8 or 11 compared to collagenase treatment alone. Immunohistochemistry showed the expression of Fas ligand in all enzymatically treated specimens. Expression of Fas receptor was ubiquitous in both control and treated specimens.

The collagen framework is important in the maintenance of chondrocyte survival in human cartilage. Upregulation of Fas ligand in matrix depleted specimens suggested that the Fas pathway may have a role in apoptosis induced by matrix depletion.