Adenosine A2A receptor activation reduces chondrocyte senescence

Osteoarthritis (OA) pathogenesis is associated with reduced chondrocyte homeostasis and increased levels of cartilage cellular senescence. Chondrosenescence is the development of cartilage senescence that increases with aging joints and disrupts chondrocyte homeostasis and is associated with OA. Adenosine A2A receptor (A2AR) activation in cartilage via intra‐articular injection of liposomal A2AR agonist, liposomal‐CGS21680, leads to cartilage regeneration in vivo and chondrocyte homeostasis. A2AR knockout mice develop early OA isolated chondrocytes demonstrate upregulated expression of cellular senescence and aging‐associated genes. Based on these observations, we hypothesized that A2AR activation would ameliorate cartilage senescence. We found that A2AR stimulation of chondrocytes reduced beta‐galactosidase staining and regulated levels and cell localization of common senescence mediators p21 and p16 in vitro in the human TC28a2 chondrocyte cell line. In vivo analysis similarly showed A2AR activation reduced nuclear p21 and p16 in obesity‐induced OA mice injected with liposomal‐CGS21680 and increased nuclear p21 and p16 in A2AR knockout mouse chondrocytes compared to wild‐type mice. A2AR agonism also increased activity of the chondrocyte Sirt1/AMPK energy‐sensing pathway by enhancing nuclear Sirt1 localization and upregulating T172‐phosphorylated (active) AMPK protein levels. Lastly, A2AR activation in TC28a2 and primary human chondrocytes reduced wild‐type p53 and concomitantly increased p53 alternative splicing leading to increase in an anti‐senescent p53 variant, Δ133p53α. The results reported here indicate that A2AR signaling promotes chondrocyte homeostasis in vitro and reduces OA cartilage development in vivo by reducing chondrocyte senescence. A2AR agonism induces cartilage regeneration in OA. A2AR ligation activates a pathway involving Sirt1/AMPK in human TC28a2 chondrocytes. There is decrease in expression of senescence genes p21, p16, and p53. In contrast, expression increased for anti‐senescent p53 splice variant Δ133p53⍺. A2AR ligation‐induced cytoplasmic localization of p21 and p16 and increased levels of the Δ133p53⍺ protein. Our study suggests that A2AR activation with intra‐articular injection of liposomal‐CGS21680 can reduce senescence and enhance cartilage regenerative potential to ameliorate OA.