Comparisons of fibronectin fragment-mediated alteration of metabolism in human ankle, human knee and bovine articular cartilages

The cartilage matrix protein, fibronectin (Fn) is proteolytically fragmented to fibronectin fragments (Fn-f) in cartilage and synovial fluid of osteoarthritis patients. The resultant Fn-f have unique chondrocyte regulatory properties of relevance to disease processes. It has been shown that the Fn-f are capable of causing severe cartilage damage to bovine metacarpophalangeal cartilage in explant culture. In contrast, human ankle cartilage is more resistant to Fn-f mediated damage than is human knee cartilage while bovine cartilage shows similar PG depletion to human knee cartilage in terms of PG content. The objectives of this study were to explore Fn-f mediated catabolic differences among these three types of cartilages and to determine whether the endogenously generated cytokines, TNF-α and IL-1 are involved in Fn-f activity. We found that both 1 μM Fn-f treated human knee and ankle cartilage showed significantly higher PG degradation rates as compared to control levels in serum free culture, although the rates were lower than those in bovine cartilage by about 6–7 fold. The half-lives of newly synthesized 35S-labeled PG were affected by Fn-f in human knee and bovine cartilage but not in human ankle cartilage in serum culture. Matrix metalloproteinase (MMP)-3 protein levels in the cultured media of Fn-f treated human ankle cartilage were similar to those of human knee cartilage, suggesting the differences between ankle and knee cartilage cannot be explained by differences in MMP-3 expression. The Fn-f suppressed PG synthesis of these cartilages in a dose dependent manner. The threshold of Fn-f concentration to significantly inhibit bovine and human knee cartilage PG synthesis was lower than that to inhibit PG synthesis in human ankle cartilage. These results suggest that the differential susceptibility of ankle and knee cartilages to the Fn-f mediated cartilage damage may be mainly due to PG synthesis suppression differences. Bovine cartilage appears to be damaged by Fn-f by the additional contribution of more greatly enhanced proteolytic activity. Antisense oligonucleotides (ASO) to TNF-α and interleukin-1 receptor antagonist protein (IRAP) partially reversed Fn-f activity in some ankle donor cartilages, suggesting TNF-α and IL-1β may be involved in the Fn-f mediated human ankle cartilage PG synthesis suppression.