Cultured human ankle and knee cartilage differ in susceptibility to damage mediated by fibronectin fragments

According to numerous cadaveric, radiographic, and clinical studies, ankle and knee joints differ in susceptibility to osteoarthritis. To test for biochemical differences in susceptibility to damage, a chondrocytic chondrolysis system has been utilized. In this system, fibronectin fragments are added to cultured cartilage explants, resulting in enhanced release of catabolic cytokines, induction of matrix metalloproteinases, temporary suppression of proteoglycan synthesis, and consequently, severe loss of cartilage proteoglycan. We found that the addition of an amino-terminal thrombin-generated 29-kDa fibronectin fragment to cultured knee cartilage from 14 donors (average age: 53 years) usually caused a 30-50% decrease in proteoglycan content by day 7. However, of the ankle cartilage specimens examined from 21 donors (average age: 50 years), only three showed damage by day 7, one by day 14, and six by day 21, and 11 were not damaged until day 28. For eight of the donors (average age: 44 years), both knee and ankle cartilages were obtained: this allowed comparison between tissues from the same donor. The analysis showed that the ankle cartilage was much more refractory to damage than was the knee cartilage from the same donor. These data clearly show differences between ankle and knee cartilage in susceptibility to the fibronectin fragments and suggest the feasibility of use of these fragments for discerning differences in homeostasis of the ankle and knee cartilage.