Expression and function of aquaporin 1 in hypoxia-induced pulmonary hypertension

Abstract

Background. Excessive proliferation of human pulmonary artery endothelial (HPAEC) and smooth muscle cells (HPASMC) is a major factor in vascular remodeling associated with the development of hypoxia-induced pulmonary hypertension (PH). Exposure to hypoxia (Hx) also results in upregulation of aquaporin 1 (Aqp1), an integral membrane water channel protein involved in several physiological processes such as cell migration, proliferation and angiogenesis. This study aims to investigate the interplay between Aqp1, Hx and PH. Methods: The hypoxic mouse model (10% O 2 for 5 weeks) was used to induce PH in vivo . For in vitro experiments, HPAEC were exposed to Hx (1% O 2 ). Expression of Aqp1 in tissue and cell lysates were analysed by quantitative PCR and Western blotting. Migratory response and apoptosis of HPAEC were assessed by wound healing and caspase assays, respectively, upon siRNA transfection targeting Aqp1 (siAqp1). Results: The expression levels of Aqp1 in HPAEC were 400 times higher for mRNA and 4 times higher for protein as compared to HPASMC. In mice, both mRNA and protein levels of Aqp1 were significantly elevated upon exposure to Hx (p≤0.01, respectively). Short term Hx (4h) increased mRNA as well as protein levels in HPAEC, whereas long term Hx (72h) decreased their levels. HPAEC transfected with siAqp1 migrated to a lesser extent and showed more apoptosis when compared to control siRNA. Conclusion: Hx modulates the expression of Aqp1 in vivo and in vitro . Inhibition of Aqp1 through siRNA resulted in less migration and more apoptosis. These data suggest an important functional role of Aqp1 in the development of hypoxia-induced PH.