Endothelin receptor B protects granulocyte macrophage colony-stimulating factor mRNA from degradation

Evidence is lacking on the differential effects of the two therapeutic concepts of endothelin receptor antagonists (ERAs): the blockade of only the endothelin receptor A (ETAR; selective antagonism) versus both ETAR and endothelin receptor B (ETBR; dual blockade). Ambrisentan, a selective ERA, and bosentan, a dual blocker, are both available for therapy. We hypothesized that there are differences in the potential of ERAs to ameliorate inflammatory processes in human airway smooth muscle cells (HASMCs) and aimed to unravel underlying mechanisms. We used HASMC culture, enzyme-linked immunosorbent assay, and quantitative reverse-transcription polymerase chain reaction. Tumor necrosis factor α (TNFα) induced transcription and expression of chemokine (C-X-C motif) ligand 2 (CXCL2), chemokine (C-X-C motif) ligand 3 (CXCL3), granulocyte macrophage colony-stimulating factor (GM-CSF), and matrix metalloproteinase 12 (MMP12) in HASMCs. In concentration-response experiments, bosentan led to a significantly greater reduction of GM-CSF and MMP12 protein release than ambrisentan, whereas there was no significant difference in their effect on GM-CSF and MMP12 mRNA. Both ERAs reduced CXCL3 protein and mRNA equally but had no effect on CXCL2. Blocking mitogen-activated protein kinases revealed that both ETAR and ETBR signal through p38 mitogen-activated protein kinase, but ETBR also signals through extracellular signal-regulated kinase (ERK) 1/2 to induce GM-CSF expression. In the presence of the transcription inhibitor actinomycin D, bosentan, but not ambrisentan, reduced GM-CSF but not MMP12 or CXCL3 mRNA. In conclusion, blockade of each endothelin receptor subtype reduces GM-CSF transcription, but blocking ETBR additionally protects GM-CSF mRNA from degradation via ERK-1/2. Accordingly, blocking both ETAR and ETBR leads to a stronger reduction of TNFα-induced GM-CSF protein expression. This mechanism might be specific to GM-CSF. Our data stress the anti-inflammatory potential of ERA and warrant further investigation of their utility in chronic inflammatory airway diseases.