The stimulation of adenosine 2A receptor reduces inflammatory response in mouse articular chondrocytes treated with hyaluronan oligosaccharides

The adenosine 2A receptor (A2AR) is greatly involved in inflammation pathologies such as rheumatoid arthritis. 24 By interacting with A2AR, the purine nucleoside adenosine acts as a potent endogenous inhibitor of the inflam- 25 matory process in a variety of tissues. Hyaluronan (HA) fragments act to prime inflammation via CD44 and the 26 toll-like receptor 4 (TLR-4). The aim of this study was to investigate whether the inhibition/stimulation of 27 A2AR modulates the inflammation cascade primed by small HA fragments in mouse articular chondrocytes. 28 6-mer HA treatment induced up-regulation of CD44, TLR4 and A2AR mRNA expression and the related protein 29 levels, and NF-kB activation, that in turn increased TNF-α, IL-1β, and IL-6 and production. Treatment with a 30 selective 2A adenosine receptor agonist (2-phenylaminoadenosine) enhanced A2AR increase, as well as the 31 inhibition of CD44 and TLR4 activity using two specific antibodies, abolished up-regulation of CD44 and 32 TLR4, and significantly reduced, especially by antibody inhibition, NF-kB activation and pro-inflammatory 33 cytokine production. Furthermore, the exposure of chondrocytes to A2AR specific interference mRNA (A2AR 34 siRNA) enhanced HA 6-mer induced NF-kB activation and inflammatory cytokine increase. Finally, the use 35 of an exchange protein activated by cAMP (EPAC) siRNA and a specific PKA inhibitor showed a predominant 36 EPAC involvement in the mediation of the anti-inflammatory activity exerted by A2AR stimulation. 37 These data suggest that HA depolymerization occurring during inflammation contributes to priming of the 38 inflammatory cascade, while endogenous adenosine, by exerting anti-inflammatory response via A2AR, 39 could be a modulatory mechanism that attempts to attenuate the inflammation process.