INHIBITION OF NF-kB ACTIVATION BY BETA-ARRESTIN 2 IN IL-1BETA-INDUCED INFLAMMATION IN MOUSE CHONDROCYTES

Hyaluronan (HA) degradation occurring during pathological state produced small HA oligosaccharides that may induce an inflammatory response by interacting with the toll-like receptor 4 (TLR-4) and CD44. TLR-4 stimulation activates different pathways that culminate with the activation of the transcriptional nuclear factor kappaB (NF-kB). The translocation of NF-kB into the nucleus may induce a pathway that involve the transforming growth factor activated kinase-1, (TAK-1), that in turn primes the expression of different inflammatory mediators. Beta-arrestin 2 is an adaptor protein that alter signalling of G protein and seems to be involved in the down-regulation of the inflammation response. In this study we investigated the role of Beta-arrestin 2 in mouse chondrocytes exposed to interleukin-1beta. Chondrocyte stimulation with IL-1beta enhanced HA levels and its degradation, up-regulated cyclic adenosine monophosphate (cAMP), beta-arrestin 2, TAK-1, protein 38 mitogen-activated protein kinase (p38MAPK), and protein kinase A (PKA) mRNA expression and of the related protein levelsb eta treatment also induced NF-kB activation, with a consequent transcription of pro-inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha), and inducible nitric oxide synthase (iNOS). The treatment of IL-1beta-stimulated chondrocytes with beta-arrestin 2 inhibitor, significantly increased the inflammatory response, while the treatment with a specific TAK-1 inhibitor significantly reduced the inflammatory response. The anti-inflammatory action exerted by beta-arrestin-2 was mediated both through a direct inhibition of TRAF-6, that prevent NF-kB activation, and in part through cAMP and PKA activation mediated by p38MAPK up-regulation. The treatment of IL-1beta-stimulated chondrocytes with a p38MAPK and PKA specific inhibitors increased the inflammatory mediators levels, confirming the involvement of the p38MAPK pathways activation induced by beta-arrestin 2. Taken together, these results could be useful for future anti-inflammatory strategies