High concentrations of fibronectin fragments cause short-term catabolic effects in cartilage tissue while lower concentrations cause continuous anabolic effects.
We reported earlier that Fn fragments (Fn-f) added to bovine articular cartilage cultured in serum-free DMEM cause marked elevated release of protease activity within a few days. This results in greatly elevated rates of release of proteoglycan (PG). We have now extended our studies to 4-week cultures of cartilage in the presence of 10% serum. We report here that cartilage cultured with 0.01, 0.1, and 1 microM of an amino terminal 29-kDa Fn-f in 10% serum accelerated the loss of PG from the tissue during the first few days in a concentration-dependent manner. However, beyond this period PG content decreased much more slowly. During this early period, the 29-kDa Fn-f decreased rates of protein and PG synthesis up to 50% in a concentration-dependent fashion. Beyond this period, the synthesis rates began to increase in a mode inversely related to 29-kDa Fn-f concentration, up to 135% of Fn-f free control values. However, during the entire culture period, cartilage cultured with 1 nM 29-kDa Fn-f had higher PG contents and had enhanced rates of protein and PG synthesis. Since 1 nM 29-kDa Fn-f stabilized cartilage against decreases in PG content, we tested its ability to block the activity of higher 29-kDa Fn-f concentrations. Cartilage was preincubated for 7 days with 1 nM 29-kDa Fn-f, and then the culture adjusted to 100 nM 29-kDa Fn-f to cause PG depletion. The preincubated cartilage showed markedly enhanced resistance to PG depletion. Since the protective effect was similar to known properties of IGF-1, the ability of 20 ng/ml IGF-1 to block against the effects of 100 nM Fn-f was tested and shown to be similar in magnitude to that of 1 nM 29-kDa Fn-f. We propose that the initial catabolic effects of higher concentrations of Fn-f, followed by the later anabolic effects, may aid in tissue repair. Also, the continuous anabolic effects of lower concentrations may be involved in tissue homeostasis.
Homandberg
G A
GA
Department of Biochemistry, Rush Medical College at Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612-3864.
Hui
F
F
D000595:Amino Acid Sequence; D000818:Animals; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism*; D002417:Cattle; D003545:Cysteine / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D005353:Fibronectins / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007700:Kinetics; D008715:Methionine / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009924:Organ Culture Techniques; D010446:Peptide Fragments / Q000494:pharmacology*; D011509:Proteoglycans / Q000096:biosynthesis*; D011994:Recombinant Proteins / Q000494:pharmacology; D013431:Sulfates / Q000378:metabolism; D013462:Sulfur Radioisotopes; D013997:Time Factors
D005353:Fibronectins; D010446:Peptide Fragments; D011509:Proteoglycans; D011994:Recombinant Proteins; D013431:Sulfates; D013462:Sulfur Radioisotopes; D007334:Insulin-Like Growth Factor I; D004247:DNA; D008715:Methionine; D010450:Endopeptidases; D003545:Cysteine