Endothelin-1-induced potentiation of human airway smooth muscle proliferation: an ETA receptor-mediated phenomenon
Pulmonary and Critical Care Division, Department of Medicine, University of Pennsylvania School of Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104-4283, U.S.A
- 1. In this study the mitogenic effects in human cultured tracheal smooth muscle cells of endothelin-1 (ET-1), ET-3, and sarafotoxin S6c (S6c), the ETB receptor-selective agonist, were explored either alone or in combination with the potent mitogen, epidermal growth factor (EGF).
- 2. In confluent, growth-arrested human airway smooth, neither ET-1 (0.01 nM-1μm) nor ET-3 (0.001 nM-1 μm) or S6c (0.01 nM-1 μm) induced cell proliferation, as assessed by [3H]-thymidine incorporation. In contrast, EGF (1.6 pM − 16 nM) produced concentration-dependent stimulation of DNA synthesis (EC50 of about 0.06 nM). The maximum increase of about 60 fold above control, elicited by 16nM EGF, was similar to that obtained with 10% foetal bovine serum (FBS). EGF (0.16-16 nM) also produced a concentration-dependent increase in cell counts, whereas ET-1 (1 − 100 nM) was without effect on this index of mitogenesis.
- 3. ET-1 (1–100 nM) potentiated EGF-induced proliferation of human tracheal smooth muscle cells. For example, ET-1 (100 nM), which alone was without significant effect, increased by 3.0 to 3.5 fold the mitogenic influence of EGF (0.16 nM). The potentiating effect of ET-1 on EGF-induced proliferation was antagonized by BQ-123 (3 μm), the ETA receptor antagonist, but was unaffected by the ETB receptor antagonist BQ-788 (10 μm).
- 4. Neither ET-3 (1 − 100 nM) nor S6c (1 − 100 nM) influenced the mitogenic effects of EGF (0.16-1.6 nM).
- 5. [125I]-ET-1 binding studies revealed that on average the ratio of ETA to ETB receptors in human cultured tracheal smooth muscle cells was 35:65 (±3; n=4), confirming the predominance of the ETB receptor subtype in human airway smooth muscle.
- 6. These data indicate that ET-1 alone does not induce significant human airway smooth muscle cell proliferation. However, it potently potentiated mitogenesis induced by EGF, apparently via an ETA receptor-mediated mechanism. These findings suggest that ET-1, a mediator detected in increased amounts in patients with acute asthma, may potentiate the proliferative effects of mitogens and contribute to the airway smooth muscle hyperplasia associated with chronic severe asthma.