Establishment of a coculture system with osteochondral and synovial explants as an ex vivo inflammatory osteoarthritis model

Abstract

Osteoarthritis (OA) is a whole-joint disorder involving inflammation in cartilage, synovium, and subchondral bone. An ex vivo inflammatory OA model incorporating various intra-articular tissues could facilitate the development of new OA therapeutics targeting whole joint tissue. In this study, an inflammatory ex vivo coculture system with bovine osteochondral explants (OCEs) and synovial explants (SEs) was induced using 1 ng/mL interleukin one beta and tumor necrosis factor alpha. Furthermore, 5-aminosalicylic acid (5-ASA), a promising OA drug reported previously, was assessed in the coculture system to evaluate the potential of the system to be applied in drug screening for OA treatment. Under inflammatory stimulation, cartilage and synovium tissues in monoculture displayed a strong inflammatory response transcriptionally, biochemically, and histologically. Under inflammatory conditions, coculture elevated the gene expression of IL-6 in synovium tissue compared with monocultured synovium. The synovium tissue in the coculture inflammatory group showed the highest synovitis score. The IL-8 release in the coculture medium was significantly higher than the additive amount in the OCE and SE monoculture groups under inflammatory microenvironment. For drug assessment, 5-ASA-treated group could promote the gene expression of CD163/CD86 and inhibit CD86 expression in synovium compared with inflammatory group. Moreover, the cumulative release of IL-6 into the medium was mitigated upon 5-ASA treatment. This study revealed the interaction between OCEs and SEs in an ex vivo coculture system. This preclinical coculture system could be used to evaluate the effects of novel OA drugs on both cartilage and synovium and explore the crosstalk mechanisms between intra-articular tissues.

Keywords

• coculture
• inflammation
• osteoarthritis model
• osteochondral explant
• synovium