Endothelin receptor B protects GM-CSF mRNA from degradation in human airway smooth muscle cells

Introduction: There are two different therapeutic concepts of endothelin receptor antagonism: blocking receptor subtype A (ET A R; selective antagonism) and blocking subtypes A and B (ET B R) (dual antagonism). Anti-inflammatory effects of endothelin receptor antagonists (ERA) have been shown, but little is known about the differences of selective versus dual antagonism. We used ambrisentan (selective ERA) and bosentan (dual ERA) as both are used in therapy. Aims: To assess the anti-inflammatory potential of ERA and to find out whether one concept is superior to the other. We studied the influence of ERA on pro-inflammatory cytokines in human airway smooth muscle cells (HASMCs). Methods: HASMC culture, ELISA, qRT-PCR. Results: TNFα induced transcription and expression of CXCL2, CXCL3, GM-CSF and MMP12 in HASMCs. In concentration-response experiments, bosentan led to a significantly greater reduction of GM-CSF and MMP12 protein release than ambrisentan while there was no significant difference in their effect on GM-CSF and MMP12 mRNA; they had no influence on CXCL2 and equally reduced CXCL3. Blocking MAP kinases with specific inhibitors revealed that both ET A R and ET B R signal through p38 MAPK , but only ET B R also signals through ERK-1/-2 to induce GM-CSF expression. After stopping transcription with actinomycin D, bosentan but not ambrisentan reduced GM-CSF but not MMP12 and CXCL3 mRNA. Conclusions: Both ERA hold anti-inflammatory potential which should be investigated in clinical trials. Bosentan led to a significantly stronger reduction of GM-CSF and MMP12 expression. ET B R protects GM-CSF mRNA from degradation via ERK-1/-2; this explains the greater reduction of GM-CSF expression by bosentan.