Norepinephrine stimulation downregulates the β2 -adrenergic receptor-nitric oxide pathway in human pulmonary artery endothelial cells.

BACKGROUND: Norepinephrine (NE)-mediated vasoconstriction plays an important role in pulmonary hypertension associated with left heart disease (PH-LHD). However, the role of NE-mediated endothelial cell dysfunction in the pathogenesis of PH-LHD remains to be elucidated.

METHODS AND RESULTS: An enzyme-linked immunosorbent assay showed that the NE concentration in the plasma of patients with PH-LHD was higher and the nitrate-nitrite concentration was lower than those in the control group. NE treatment decreased phospho-Ser633-eNOS and β2 -adrenergic receptor (β2 -AR) levels in the membrane of human pulmonary artery endothelial cells (HPAECs) analysed by western blot analysis. Consistently, fluorescence microscopy and flow cytometry showed that nitric oxide (NO) production was also decreased in HPAECs. Coimmunoprecipitation confirmed a direct interaction between β2 -AR and endothelial NO synthase (eNOS). Overexpression of β2 -AR attenuated the decline in phospho-Ser633-eNOS and NO production. Additionally, the expression of phospho-Ser633-eNOS and β2 -AR was decreased in human pulmonary artery endothelium. Finally, our results indicate that NE stimulated HPAEC proliferation, which was blocked by protein kinase A inhibitor or protein kinase B (PKB-AKT) inhibitor.

CONCLUSIONS: These data provide a novel mechanism for NE-decreased endothelium-derived NO and NE-induced HPAEC proliferation that leads to PH-LHD, suggesting a potential therapeutic target for PH-LHD.