Genetic knockout and pharmacologic inhibition of NCX1 attenuate hypoxia-induced pulmonary arterial hypertension

https://doi.org/10.1016/j.bbrc.2020.06.045Get rights and content

Highlights

  • NCX1 is upregulated in pulmonary arteries of mice exposed to chronic hypoxia.

  • Hypoxia-induced pulmonary arterial hypertension (PAH) is significantly attenuated in NCX1+/− mice compared to wild-type mice.

  • Specific NCX1 inhibitor effectively suppresses hypoxia-induced PAH in mice.

  • Upregulation of NCX1 contributes to the development of hypoxia-induced PAH.

Abstract

The Na+/Ca2+ exchanger type-1 (NCX1) is a bidirectional transporter that is controlled by membrane potential and transmembrane gradients of Na+ and Ca2+. Vascular smooth muscle NCX1 plays an important role in intracellular Ca2+ homeostasis and Ca2+ signaling. We found that NCX1 was upregulated in the pulmonary arteries of mice exposed to chronic hypoxia (10% O2 for 4 weeks). Hence, we investigated the pathophysiological role of NCX1 in hypoxia-induced pulmonary arterial hypertension (PAH), using NCX1-heterozygous (NCX1+/−) mice, in which NCX1 expression is reduced by half, and SEA0400, a specific NCX1 inhibitor. NCX1+/− mice exhibited attenuation of hypoxia-induced PAH and right ventricular (RV) hypertrophy compared with wild-type mice. Furthermore, continuous administration of SEA0400 (0.5 mg/kg/day for 4 weeks) to wild-type mice by osmotic pumps significantly suppressed hypoxia-induced PAH and pulmonary vessel muscularization, with a slight reduction in RV hypertrophy. These findings indicate that the upregulation of NCX1 contributes to the development of hypoxia-induced PAH, suggesting that NCX1 inhibition might be a novel approach for the treatment of PAH.

Introduction

Pulmonary arterial hypertension (PAH) is a progressive and intractable disease characterized by increased pulmonary arterial tone and vascular remodeling, eventually resulting in right heart failure [1,2]. Histologically, patients with severe PAH exhibit small pulmonary arterial wall thickening, occlusive neointima, and formation of plexiform lesions originating from remodeled pulmonary arteries [3]. Such pulmonary arteriopathy can be triggered by a wide spectrum of genetic and environmental stimuli, including chronic hypoxia and inflammation [4,5]. Chronic hypoxia-induced PAH is clinically caused by chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea. Actually, in experimental animals, prolonged exposure to hypoxia generates the most commonly used PAH models [5,6]. Currently, several vasodilating drugs are used for preventing the progression of PAH, but their therapeutic effects are still insufficient [1]. Therefore, there is an urgent need for finding novel therapeutic targets of PAH.

Increased intracellular Ca2+ concentration in pulmonary arteries is a critical trigger for pulmonary arterial hypercontraction and vascular remodeling [7], leading to the initiation and progression of PAH. Previous studies have shown that chronic hypoxia causes abnormally enhanced Ca2+ signaling in pulmonary arteries, although the underlying molecular mechanisms are still controversial [5,7].

The Na+/Ca2+ exchanger type-1 (NCX1) is a bidirectional Ca2+ transporter controlled by membrane potential and transmembrane gradients of Na+ and Ca2+, which plays an important role in intracellular Ca2+ homeostasis and Ca2+ signaling [8,9]. NCX1 is ubiquitously expressed in several tissues, and is especially abundant in heart and blood vessels. Previous studies utilizing genetically altered mice and selective inhibitors for NCX1 revealed that NCX1 is pathophysiologically involved in the development of ischemic diseases of various organs [[10], [11], [12]] and salt-sensitive hypertension [13]. In this study, we found that NCX1 is excessively expressed in the pulmonary arteries of hypoxia-induced PAH model mice. However, the role of NCX1 in the pathogenesis of hypoxia-induced PAH is clearly unknown. Our studies with NCX1-heterozygous mice and specific NCX1 inhibitor provide compelling evidence that upregulation of NCX1 contributes to the development of hypoxia-induced PAH.

Section snippets

Animals

NCX1-heterozygous (NCX1+/−) mice were generated as reported previously [14,15]. C57BL/6J mice were purchased from Japan SLC (Japan). All mice used were males and they were housed under diurnal lighting conditions (light period 8:00 a.m. to 8:00 p.m.) and allowed access to normal raw chow and plain drinking water ad libitum. The experimental designs and all procedures were conducted in accordance with the Animal Care Guidelines of the Animal Experimental Committees of Fukuoka University.

Drugs

SEA0400

Upregulation of NCX1 in pulmonary arteries of mice exposed to chronic hypoxia

Prolonged exposure to normobaric hypoxia in experimental animals generates the most commonly used PAH models [5,6]. We initially examined the expression and localization of NCX1 in lung tissues of C57BL/6J mice after exposure to chronic hypoxia (10% O2 for 4 weeks) by immunostaining. As shown in Fig. 1A, immunofluorescence staining of NCX1 was observed in the distal pulmonary arteries of mice. Interestingly, the immunofluorescence intensities of NCX1 were strongly localized in the distal

Discussion

PAH is a progressive and intractable disease characterized by pulmonary arterial constriction and vascular remodeling [1,2]. Prolonged exposure to hypoxia in experimental animals is commonly used as a PAH model [5,6]. Previous studies have shown that hypoxic exposure causes abnormally enhanced Ca2+ signaling in pulmonary artery smooth muscle cells (PASMCs), which is a major trigger for pulmonary arterial constriction and vascular remodeling [5,7], but its molecular mechanisms remain clearly

Declaration of competing interest

The authors have declared no conflicts of interest.

Acknowledgments

We thank I. Komuro (Tokyo University) for providing NCX1+/− mice. This work was supported by JSPS KAKENHI Grant Numbers JP17K08610 (T.I.), JP19K07132 (S.K.), JP19K16509 (H.T.), JP19K18230 (A.N.) and a grant from Salt Science Research Foundation (No.1540).

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  • 1

    These two authors contributed equally.

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