Coculture of bovine cartilage with synovium and fibrous joint capsule increases aggrecanase and matrix metalloproteinase activity

Abstract

BackgroundA hallmark of osteoarthritis is increased proteolytic cleavage of aggrecan. Cross talk between cartilage and the synovium + joint capsule (SJC) can drive cartilage degradation by activating proteases in both tissues. We investigated aggrecan proteolysis patterns in cartilage explants using a physiologically relevant explant model of joint injury combining cartilage mechanical compression and coincubation with SJC.MethodsBovine cartilage explants were untreated; coincubated with SJC; or subjected to mechanical injury and coincubated with SJC, mechanical injury alone, or mechanical injury and incubated with tumor necrosis factor-α (TNF-α). To compare the patterns of aggrecan proteolysis between 6 h and 16 days, release of sulfated glycosaminoglycans and specific proteolytic aggrecan fragments into medium or remaining in cartilage explants was measured by dimethylmethylene blue and Western blot analysis.ResultsAggrecanase activity toward aggrecan was observed in all conditions, but it was directed toward the TEGE↓ARGS interglobular domain (IGD) site only when cartilage was coincubated with SJC or TNF-α. Matrix metalloproteinase (MMP) activity at the aggrecan IGD site (IPES↓FFGV) was not detected when cartilage was exposed to TNF-α (up to 6 days), but it was in all other conditions. Compared with when bovine cartilage was left untreated or subjected to mechanical injury alone, additional aggrecan fragment types were released into medium and proteolysis of aggrecan started at an earlier time when SJC was present.ConclusionsIndicative of different proteolytic pathways for aggrecan degradation, the SJC increases both aggrecanase and MMP activity toward aggrecan, whereas TNF-α inhibits MMP activity against the IGD of aggrecan.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-017-1318-9) contains supplementary material, which is available to authorized users.

Development of in vitro joint tissue co-culture models for evaluating transport and biological crosstalk

“…In the presented study, cartilage tissue was co-incubated with synovium and/or meniscus tissue to observe and quantify the effects of biological crosstalk. The results produced did not show a significant difference in sGAG loss with the addition of synovium which supported the findings of Swärd et al [36]. However, addition of synovium and/or meniscus caused collagen degradation in cartilage implying catabolic effects of these tissues.…”

“…Conversely, chondrocytes and the ECM could release enzymes that can affect the synovium. In a study conducted by Swärd et al, increased aggrecanase and MMP activity was observed upon coincubating bovine cartilage and synovial joint capsule tissue compared to cartilage alone in both a normal and injury model [36].…”

“…Tissues such as the synovium, meniscus and infrapatellar fat pad have been used in combination with cartilage tissues in order to mimic the in vivo environment [35,36]. In addition to being more comparable to the native joint, co-culture models provide several other advantages over mono-cultures.…”

“…coincubated bovine cartilage with synovial joint capsule tissue and reported increase in aggrecanase and MMP activity compared to cartilage alone in both a normal and injury model [36]. Addition of synovial joint capsule caused the FFGV, G1-KEEE and ARGS-CS2 aggrecan fragments to become cleaved and released into media [36].…”

“…Addition of synovial joint capsule caused the FFGV, G1-KEEE and ARGS-CS2 aggrecan fragments to become cleaved and released into media [36]. Beekhuizen et al cultured human OA cartilage and synovium to determine cytokines released by the synovium [55].…”