Acquisition of hyaluronate-binding affinity in vivo by newly synthesized cartilage proteoglycans.
We have studied the hyaluronate-binding properties of aggregating cartilage proteoglycans synthesized in vivo by immature (6-week), mature (25-week) and aged (75-week) rabbits. Precursor isotope (35SO4) was given by intra-articular injection and articular cartilage was removed from rabbits after periods ranging from 1.5 h to 168 h. Proteoglycans were extracted with 4 M-guanidinium/HCl and monomers were isolated by CsCl gradient centrifugation under dissociative conditions. The percentages of both radiolabelled and total tissue monomers with a high affinity for hyaluronate [that is, capable of forming aggregates on Sepharose CL-2B in the presence of 0.8% (w/w) hyaluronate] were then determined. For all samples about 30% of the tissue monomers were high-affinity; however, less than 5% of the radiolabelled monomers were high-affinity at 1.5 h after injection, and this figure increased gradually with time in vivo. The increase was rapid in immature rabbits, such that after 24 h, about 30% of the radiolabelled monomers were high-affinity; on the other hand for mature and aged rabbits the increase was markedly slower such that 30% high-affinity was attained only after about 72 h. The results show that aggregating cartilage proteoglycans are secreted in vivo in a 'precursor' form with a low affinity for hyaluronate, and suggest that conversion of these monomers to a form with a higher binding affinity occurs with a half-time of about 12 h in immature cartilages but greater than 24 h in mature cartilages. The possible relationship of these findings to the process of proteoglycan aggregation in vivo is discussed.
Sandy
J D
JD
Department of Orthopedics, Brown University, Rhode Island Hospital, Providence 02902.
O'Neill
J R
JR
Ratzlaff
L C
LC
D000367:Age Factors; D000818:Animals; D002358:Cartilage, Articular / Q000378:metabolism*; D002847:Chromatography, Agarose; D016326:Extracellular Matrix Proteins; D006820:Hyaluronic Acid / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism*; D011817:Rabbits; D000099249:Proteoglycan Link Protein
D016326:Extracellular Matrix Proteins; D006820:Hyaluronic Acid; D011506:Proteins; D011509:Proteoglycans; D000099249:Proteoglycan Link Protein