Fibronectin fragments alter matrix protein synthesis in cartilage tissue cultured in vitro.
We reported earlier that fibronectin fragments (Fn-f) added to bovine articular cartilage cultured in serum-free culture causes marked protease expression with resultant proteoglycan (PG) degradation and release into the culture media. We have further characterized the effects of Fn-f by studies of the effects on proteoglycan, collagen, general protein, and DNA synthesis and reversibility of the cartilage damage. We report here that the most active Fn-f, a 29-kDa amino-terminal Fn-f, when added to a 1 microM concentration, depressed PG and general protein synthesis in cartilage by over 50% within 24 h, as measured by sulfate and methionine/cysteine incorporation, respectively. This same Fn-f decreased PG synthesis throughout the full thickness cartilage section as shown by autoradiography. PG and general protein synthesis were significantly depressed within 24 h by 29-kDa Fn-f concentrations as low as 10 nM. Synthesis rates were effected by 100-fold lower Fn-f concentrations than was induction of proteinases. Removal of the 29-kDa Fn-f allowed a gain to supernormal levels of PG and protein synthesis. Cartilage damaged to the extent of removal of over 50% of the total PG did not replace PG after over 4 weeks in 10% serum-Dulbecco's modified Eagle minimum with or without added TGF-b1 and rIGF-a. These data show that while the effects of Fn-f on elevating protease expression and depressing PG synthesis are reversible, the resultant cartilage damage is apparently irreversible in vitro. Therefore, if Fn-f-mediated cartilage damage occurs as part of cartilage disease processes, the pathologic effects would be quite significant.
Xie
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D
Department of Biochemistry, Rush Medical College at Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612-3864.
Hui
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F
Homandberg
G A
GA
D000818:Animals; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D002846:Chromatography, Affinity; D004247:DNA / Q000096:biosynthesis; D005353:Fibronectins / Q000097:blood / Q000302:isolation & purification / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D009924:Organ Culture Techniques; D010446:Peptide Fragments / Q000494:pharmacology*; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism; D011509:Proteoglycans / Q000096:biosynthesis* / Q000378:metabolism; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D013997:Time Factors
D005353:Fibronectins; D010446:Peptide Fragments; D011506:Proteins; D011509:Proteoglycans; D012710:Serum Albumin, Bovine; D004247:DNA