AGGRECAN IN BOVINE TENDON

Large proteoglycans were purified by ion-exchange chromatography, gel filtration and CsCl gradient centrifugation from the compressed and tensional regions of adult bovine deep flexor tendon. Tryptic peptide maps of proteoglycan from the compressed region were very similar to maps of aggrecan from bovine articular cartilage, with evidence for the presence of all fifteen previously identified markers from the G1, G2 and G3 domains. The presence of aggrecan in these samples was confirmed by sequencing the G1 peptide YPIHTPR. The equivalent maps for large proteoglycan from tensional tendon were also consistent with the presence of aggrecan, and this was confirmed by sequencing three marker peptides from each of the G2 and G3 domains. However, G1 marker peptides were conspicuously absent from tensional samples. Northern blots for aggrecan mRNA showed high levels in cells from compressed tendon and articular cartilage. Extended exposure revealed a lower level of hybridization to RNA from tensional tendon as well. The results confirm that aggrecan, which is similar in core protein structure to articular cartilage aggrecan, is the predominant chondroitin sulfate-bearing large proteoglycan of compressed tendon. The results also indicate that aggrecan fragments lacking the G1 domain can account for the small amounts of chondroitin sulfate-bearing large proteoglycan in tensional regions of adult tendon.