title: Age-related changes in the response of human articular cartilage to IL-1alpha and transforming growth factor-beta (TGF-beta): chondrocytes exhibit a diminished sensitivity to TGF-beta.
abstract: Cartilage glycosaminoglycan (GAG) synthesis and composition, upon which its structural integrity depends, varies with age, is modified by anabolic and catabolic stimuli, and is regulated by UDP-glucuronate availability. However, how such stimuli, prototypically represented by transforming growth factor-beta1 (TGF-beta1) and IL-1alpha, modify GAG synthesis during aging of normal human articular cartilage is not known. Using explants, we show that chondroitin sulfate (CS):total GAG ratios decrease, whereas C6S:C4S ratios increase with cartilage maturation, and that chondrocytes in the cartilage mid-zone, but not the superficial or deep zones, exhibit uridine 5'-diphosphoglucose dehydrogenase (UDPGD) activity, which is also increased in mature cartilage. We also show that IL-1alpha treatment reduces both total GAG and CS synthesis, decreases C6S:C4S ratios (less C6S), but fails to modify chondrocyte UDPGD activity at all ages. On the other hand, TGF-beta1 increases total GAG synthesis in immature, but not mature, cartilage (stimulates CS but not non-CS), age-independently decreases C6S:C4S (more C4S), and increases chondrocyte UDPGD activity in a manner inversely correlated with age. Our findings show that TGF-beta1, but not IL-1alpha, modifies matrix synthesis such that its composition more closely resembles "less mature" articular cartilage. These effects of TGF-beta1, which appear to be restricted to periods of skeletal immaturity, are closely associated although not necessarily mechanistically linked with increases in chondrocyte UDPGD activity. The antianabolic effects of IL-1alpha are, on the other hand, likely to be independent of any direct modification in UDPGD activity and manifest equally in human cartilage of all ages.
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging; D002356:Cartilage / Q000378:metabolism; D002358:Cartilage, Articular / Q000378:metabolism*; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism; D002809:Chondroitin Sulfates / Q000378:metabolism; D005786:Gene Expression Regulation; D006025:Glycosaminoglycans / Q000378:metabolism; D006801:Humans; D007375:Interleukin-1 / Q000378:metabolism*; D008875:Middle Aged; D011509:Proteoglycans / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry; D013431:Sulfates / Q000378:metabolism; D013997:Time Factors; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D014530:Uridine Diphosphate / Q000378:metabolism; D014533:Uridine Diphosphate Glucose Dehydrogenase / Q000378:metabolism
chemical_list: D006025:Glycosaminoglycans; D007375:Interleukin-1; D011509:Proteoglycans; D011994:Recombinant Proteins; D013431:Sulfates; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D014530:Uridine Diphosphate; D002809:Chondroitin Sulfates; D014533:Uridine Diphosphate Glucose Dehydrogenase