Tumor necrosis factor alpha (TNFα) is a multifunctional cytokine that is elevated in inflammatory diseases such as atherosclerosis, diabetes and rheumatoid arthritis. Recent evidence has suggested that β2 adrenergic receptor(β2AR) activation in osteoblasts suppresses osteogenic activity. In the present study, we explored whether TNFα modulates βAR expression in osteoblastic cells and whether this regulation is associated with the inhibition of osteoblast differentiation by TNFα. In the experiments, we used C2C12 cells, MC3T3- E1 cells and primary cultured mouse bone marrow stromal cells. Among the three subtypes of βAR, β2 and β3AR were found in our analysis to be upregulated by TNFα. Moreover, isoproterenol-induced cAMP production was observed to be significantly enhanced in TNFα-primed C2C12 cells, indicating that TNFα enhances β2AR signaling in osteoblasts.TNFα was further found in C2C12 cells to suppress bone morphogenetic protein 2-induced alkaline phosphatase(ALP) activity and the expression of osteogenic marker genes including Runx2, ALP and osteocalcin. Propranolol, aβ2AR antagonist, attenuated this TNFα suppression of osteogenic differentiation. TNFα increased the expression ofreceptor activator of NF-κB ligand (RANKL), an essential osteoclastogenic factor, in C2C12 cells which was againblocked by propranolol. In summary, our data show that TNFα increases β2AR expression in osteoblasts and that ablockade of β2AR attenuates the suppression of osteogenic differentiation and stimulation of RANKL expression byTNFα. These findings imply that a crosstalk between TNFα