The β2-subtype of adrenoceptors mediates inhibition of pro-fibrotic events in human lung fibroblasts

Abstract

Fibrosis is part of airway remodelling observed in bronchial asthma and COPD. Pro-fibrotic activity of lung fibroblasts may be suppressed by β-adrenoceptor activation. We aimed, first, to characterise the expression pattern of β-adrenoceptor subtypes in human lung fibroblasts and, second, to probe β-adrenoceptor signalling with an emphasis on anti-fibrotic actions. Using reverse transcription PCR, messenger RNA (mRNA) encoding β(2)-adrenoceptors was detected in MRC-5, HEL-299 and primary human lung fibroblasts, whereas transcripts for β(1)- and β(3)-adrenoceptors were not found. Real-time measurement of dynamic mass redistribution in MRC-5 cells revealed β-agonist-induced G(s)-signalling. Proliferation of MRC-5 cells (determined by [(3)H]-thymidine incorporation) was significantly inhibited by β-agonists including the β(2)-selective agonist formoterol (-logIC(50), 10.2) and olodaterol (-logIC(50), 10.6). Formoterol's effect was insensitive to β(1)-antagonism (GCP 20712, 3μM), but sensitive to β(2)-antagonism (ICI 118,551; apparent, pA (2), 9.6). Collagen synthesis in MRC-5 cells (determined by [(3)H]-proline incorporation) was inhibited by β-agonists including formoterol (-logIC(50), 10.0) and olodaterol (-logIC(50), 10.3) in a β(2)-blocker-sensitive manner. α-Smooth muscle actin, a marker of myo-fibroblast differentiation, was down-regulated at the mRNA and the protein level by about 50% following 24 and 48h exposure to 1nM formoterol, a maximally active concentration. In conclusion, human lung fibroblasts exclusively express β(2)-adrenoceptors and these mediate inhibition of various markers of pro-fibrotic cellular activity. Under clinical conditions, anti-fibrotic actions may accompany the therapeutic effect of long-term β(2)-agonist treatment of bronchial asthma and COPD.