Acta Pharmacologica Sinica (2009) 30: 1522–1528; doi: 10.1038/aps.2009.153

Aim:To investigate the molecular mechanism and signaling pathway by which fenoterol, a β₂-adrenergic receptor (β₂-AR) agonist, produces anti-inflammatory effects. 

Methods: THP-1, a monocytic cell line, was used to explore the mechanism of β₂-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 β₂-AR in the presence or absence of lipopolysaccharide (LPS) and small, interfering RNA (siRNA)-mediated knockdown of β-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 β₂-AR stimulation.  Furthermore, siRNA-mediated knockdown of β-arrestin-2 eliminated the anti-inflammatory effects and redistribution of CD14 and TLR4/CD14 complex stimulated by β₂-AR.

Conclusion: β₂-AR agonist exerts its anti-inflammatory effects by down-regulating TLR signaling in THP-1 cells, potentially resulting from β-arrestin-2 mediated redistribution of CD14 and TLR14/CD14 complex.

Keywords: β₂-adrenoceptor; toll-like receptors; β-arrestin-2; fenoterol; confocal microscopy;  lipopolysaccharide