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Abstract
The treatment of human articular chondrocytes with Streptomyces hyaluronidase (St-HA′ase) or hyaluronan hexasaccharides (HA6) provides two approaches to the selective depletion of specific components of the extracellular matrix, and an opportunity to follow the reparative responses initiated by these changes. In this study, changes in the relative expression of messenger RNA for hyaluronan synthase-2, CD44, and aggrecan were determined by competitive, quantitative reverse transcriptase–polymerase chain reaction. Changes in the size of the cell-associated matrix surrounding live chondrocytes were analyzed by the particle exclusion assay, and hyaluronan accumulation was characterized using a biotin-labeled hyaluronan-specific binding protein. Both Streptomyces hyaluronidase as well as hyaluronan hexasaccharide treatment of chondrocytes resulted in an approximately 2-fold increase in hyaluronan synthase-2 mRNA copy numbers, together with a 1.8-fold increase in the mRNA copy number for the proteoglycan aggrecan. However, although matrix biosynthesis was enhanced, the chondrocytes failed to retain these components. Both treatments resulted in a diminished accumulation of extracellular hyaluronan as well as a loss of the chondrocyte proteoglycan-rich cell-associated matrix. Thus, this model is similar to the early stages of osteoarthritis. Upon removal of the Streptomyces hyaluronidase or hyaluronan hexasaccharides, the normal, healthy, adult human chondrocytes used in this study regained their capacity to retain extracellular hyaluronan and to reassemble and retain a cell-associated matrix. This stimulation of hyaluronan synthase-2 (HAS-2) and aggrecan mRNA expression, and the subsequent capacity to retain the newly synthesized extracellular matrix, illustrate the events which are necessary for adult human articular chondrocytes to undergo effective repair.
