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Loss of Apelin Signaling Impairs Nitric Oxide Synthesis and Exacerbates Pulmonary Hypertension (Winner - Basic Science Category)

Hyung Chun


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Conference: 2010 International PHA Conference and Scientific Sessions

Release Date: 06.22.2010

Presentation Type: Scientific Sessions

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Lung Development

Abstract winnter chosen for oral presentation from the 2010 PHA International Conference and Scientific Sessions.

Chun HJ1,5, Chandra SM1, Razavi H2, Agrawal R3, Kundu R1, de Jesus Perez V4, Zamanian RT4, Quertermous T1.
1 Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA, USA
2 Department of Bioengineering, Stanford University School of Medicine, Stanford, CA, USA
3 Department of Anesthesia, Stanford University School of Medicine, Stanford, CA, USA
4 Division of Pulmonary and Critical Care Medicine, Stanford University School of Medicine, Stanford, CA, USA
5 Present address: Section of Cardiovascular Medicine, Yale University School of Medicine, New Haven, CT, USA

BACKGROUND. Apelin is a peptide ligand for APJ, a G-protein coupled receptor highly expressed in the vascular wall. Although both apelin and APJ are highly expressed in the pulmonary vasculature, their function in this vascular bed is unknown. Given the known vasodilatory and vasculoprotective roles of this pathway, we hypothesized that its disruption would lead to worsening of the vascular remodeling that occurs in pulmonary hypertension.

METHODS. Apelin deficient (KO) mice were used to assess right ventricular systolic pressures after 3 weeks of hypoxia. Lungs were perfused with contrast agent (Microfil), and imaged using micro-computed tomography (CT) imaging. NO levels were measured in the serum and lungs were evaluated for expression of endothelial nitric oxide synthase (eNOS) and KLF2 using quantitative real-time polymerase chain reaction (RT-PCR) and western blots.

RESULTS. We found that apelin null mice developed more severe pulmonary hypertension in response to hypoxia compared to wildtype mice (34.1 vs 28.3 mm Hg, p<0.001). Micro-computed tomography of the lungs demonstrated significant vascular abnormalities in the hypoxia-treated apelin null mice, including marked pruning of the smaller vessels (Figure). Apelin null mice had a significant reduction of serum nitric oxide (NO) levels. This was associated with a decrease in pulmonary endothelial nitric oxide synthase (eNOS) expression, in conjunction with a decrease in expression of KLF2, a known transcriptional regulator of eNOS. In vitro knockdown of apelin mRNA in pulmonary artery endothelial cells led to a marked decrease in eNOS and KLF2 transcript levels. Moreover, serum apelin levels from patients with pulmonary hypertension were significantly lower than those in healthy controls (1.25 vs 0.89 ng/mL, p=0.037).

CONCLUSIONS. These data demonstrate that disruption of apelin signaling can exacerbate pulmonary hypertension, secondary to vascular remodeling in the context of decreased expression of KLF2 and eNOS, and identify this pathway as a potentially important therapeutic target for treatment of this refractory human disease.