Fig. 2Senescence-associated β-galactosidase staining in human knee articular cartilage. Samples of osteoarthritic human knee cartilage were stained for senescence-associated β-gal as described in the Experimental procedures. Staining was present in chondrocytes close to the lesion site in osteoarthritic cartilage with (A), a mild lesion and (B), a severe lesion; (C), β-gal staining was often localized to chondrocytes in chondrocyte clusters; original magni?cation ×40. (D) No staining was observed in intact regions of osteoarthritic knee cartilage. Sections were counterstained with eosin; AS, articular surface of the cartilage; #, chondrocyte cluster.
will also be an important factor in determining telomere length and a number of studies have correlated telomere length with
., 2000; Martin & Buckwalter, 2001;
., 2001). Martin & Buckwalter (2001) have recently reported that average telomere length in cartilage chondrocytes decreases with age, with lengths ranging from approximately 12 to 8 kilobase pairs in samples from patients across an age range of 1–87 years. These researchers expanded chondrocytes brie?y in culture prior to isolating genomic DNA for Southern blot; moreover, no information was given concerning disease status of the donors, and therefore a direct comparison with our data is impossible. However, these authors predict that local variations in average telomere length will exist across the joint with mechanical stress and injury, and this is borne out by our data. Overall, these results suggest that telomere shortening may be responsible for senescence in cartilage chondrocytes. Two recent reports provide data on this point: Piera-Velazquez et al. (2002) describe increased survival in vitro of cultured osteoarthritic chondrocytes by exogenous expression of the catalytic subunit of telomerase; Martin et al. (2002) argue that both telomere length and telomerase-independent pathways are required for the inde?nite extension of chondrocyte survival in vitro.
The high percentage of cultured chondrocytes that stain for SA-β-gal when isolated from intact cartilage from osteoarthritic patients or even normal cartilage was unexpected from the in
a b A B C D