Fenoterol, a beta(2)-adrenoceptor agonist, inhibits LPS-induced membrane-bound CD14, TLR4/CD14 complex, and inflammatory cytokines production through beta-arrestin-2 in THP-1 cell line.

AIM: To investigate the molecular mechanism and signaling pathway by which fenoterol, a beta(2)-adrenergic receptor (beta(2)-AR) agonist, produces anti-inflammatory effects.

METHODS: THP-1, a monocytic cell line, was used to explore the mechanism of beta(2)-AR stimulation in LPS-induced secretion of inflammatory cytokines and changes of toll-like receptors (TLRs). We labeled TLR4 and CD14 using monoclonal anti-TLR4 PE-conjugated and anti-CD14 FITC-conjugated antibodies in THP-1 cells stimulated by beta(2)-AR in the presence or absence of lipopolysaccharide (LPS) and small, interfering RNA (siRNA)-mediated knockdown of beta-arrestin-2, and then analyzed their changes in distribution by flow cytometry, Western blotting and confocal analysis.

RESULTS: LPS-induced membrane-bound CD14, TLR4/CD14 complex levels and elevation of inflammatory cytokines were all significantly reduced by pre-incubation of fenoterol (P<0.05). However, the total level of CD14 and TLR4 was not significantly changed. Interestingly, confocal microscopy revealed redistribution of CD14 and TLR4/CD14 complex under beta(2)-AR stimulation. Furthermore, siRNA-mediated knockdown of beta-arrestin-2 eliminated the anti-inflammatory effects and redistribution of CD14 and TLR4/CD14 complex stimulated by beta(2)-AR.

CONCLUSION: beta(2)-AR agonist exerts its anti-inflammatory effects by down-regulating TLR signaling in THP-1 cells, potentially resulting from beta-arrestin-2 mediated redistribution of CD14 and TLR14/CD14 complex.