CD73 alleviates osteoarthritis by maintaining anabolism and suppressing catabolism of chondrocytes extracellular matrix

Background: Osteoarthritis (OA) is the most common degenerative joint disease, with articular cartilage degeneration as primary manifestation. Intra-articular injection of exogenous liposomal adenosine in mice knee has been shown to alleviate OA progression. However, the role of CD73, the rate-limiting enzyme of extracellular adenosine synthesis, in OA is still unknown. Methods: In this work, we explored the expression changes of adenosine-related molecules via bioinformatic analysis. In addition, the expression level of these molecules was detected in OA cartilage. We also conducted a case–control study to investigate the genetic variants of selected SNPs on genes encoded adenosine-related molecules. To further explore the function of CD73 in chondrocytes, we knocked down the expression of CD73 with small interfering RNA and overexpressed CD73 with the use of lentivirus, and detected the expression of markers for anabolism and catabolism in mouse primary chondrocytes with or without IL-1β treatment. We also conducted in vivo experiments to explore the role of CD73 in OA. Results: We found that the expression of CD73 was upregulated in OA, and the variants of SNP rs2229523 (base A to G) on NT5E (the encoding gene of CD73) were significantly higher in OA population, which might cause the amino acid encoded by this SNP change from threonine to alanine. The original helix structure in the adjacent region of amino acid encoded by SNP rs2229523 would be deconstructed after its mutation. Furthermore, we found that CD73 promoting the expression of Col2a1 but suppressing the expression of Mmp13 expression in mouse primary chondrocytes under inflammatory environment. The overexpression of CD73 attenuated bone remodeling and alleviated cartilage degeneration in DMM mice. Moreover, the physical activities were also improved in DMM mice overexpressed CD73 with the use of adeno-associated virus. Conclusions: The variants of SNP rs2229523 (base A to G) on NT5E were significantly higher in OA population, and CD73 could alleviate OA by maintaining anabolism and suppressing catabolism of chondrocytes extracellular matrix.