Effect of hypoxic exposure on Na<sup>+</sup>/H<sup>+</sup>antiport activity, isoform expression, and localization in endothelial cells

Cutaia, Michael; Parks, Nancy; Centracchio, Jason; Rounds, Sharon; Yip, Kay‐Pong; Sun, Ang

doi:10.1152/ajplung.1998.275.3.l442

Cited by 24 publications

(29 citation statements)

References 32 publications

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“…Although the expression of NHE3 was evident in PASMCs, the proliferation of cells was not significantly affected by either the NHE3 inhibitor S-3226 or NHE3 siRNA. Previous reports showed that no expression of NHE2 and NHE3 was evident in human lung tissue (48) and pulmonary endothelial cells (49). Therefore, we did not investigate the effects of E2F1 on NHE2 and NHE3 in this study.…”

Section: Discussionmentioning

confidence: 82%

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

Hales

2011

Am J Respir Cell Mol Biol

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We previously found that deficiency of the sodium-hydrogen exchanger 1 (NHE1) gene prevented hypoxia-induced pulmonary hypertension and vascular remodeling in mice, which were accompanied by a significantly reduced proliferation of pulmonary artery smooth muscle cells (PASMCs), and which decreased the medial-wall thickness of pulmonary arteries. That finding indicated the involvement of NHE1 in the proliferation and hypertrophy of PASMCs, but the underlying mechanism was not fully understood. To define the mechanism by which the inhibition of NHE1 decreases hypoxic pulmonary hypertension and vascular remodeling, we investigated the role of E2F1, a nuclear transcription factor, in silencing the NHE1 gene-induced inhibition of the proliferation, hypertrophy, and migration of human PASMCs. We found that: (1) silencing of NHE1 by short, interfering RNA (siRNA) significantly inhibited PASMC proliferation and cell cycle progression, decreased hypoxia-induced hypertrophy (in terms of cell size and protein/DNA ratio) and migration (in terms of the wound-healing and migration chamber assays); (2) hypoxia induced the expression of E2F1, which was reversed by NHE1 siRNA; and (3) the overexpression of E2F1 blocked the inhibitory effect of NHE1 siRNA on the proliferation, hypertrophy, and migration of PASMCs. The present study determined that silencing the NHE1 gene significantly inhibited the hypoxia-induced proliferation, hypertrophy, and migration of human PASMCs via repression of the nuclear transcription factor E2F1. This study revealed a novel mechanism underlying the regulation of hypoxic pulmonary hypertension and vascular remodeling via NHE1.Keywords: sodium-hydrogen exchanger 1; E2F1; PASMC proliferation; hypertrophy; hypoxia Pulmonary hypertension is caused by many chronic lung diseases associated with prolonged hypoxia, and can result in right ventricular hypertrophy and heart failure. An important pathological feature of pulmonary hypertension involves an increase in medial thickening of pulmonary arteries, resulting from the hyperplasia and hypertrophy of pulmonary artery smooth muscle cells (PASMCs) (1-3). The Na 1 -H 1 exchanger (NHE), a protein localized to plasma and the mitochondrial inner membrane (4), has nine isoforms (5), of which NHE isoform 1 (NHE1) is ubiquitously expressed. We previously reported on the inhibitory effect of reduced NHE activity in the proliferation of PASMCs (6) and on chronic hypoxia-induced pulmonary hypertension and vascular remodeling (7). Increased expression of the NHE1 gene was evident in animals with hypoxia-induced pulmonary hypertension and vascular remodeling (6-10). Moreover, we recently found that deficiency of the NHE1 gene prevented hypoxia-induced pulmonary hypertension and vascular remodeling in mice (11), accompanied by a significantly reduced proliferation of PASMCs and decreased medial wall thickness of the pulmonary arteries. Our findings indicated the involvement of NHE1 in the proliferation and hypertrophy of PASMCs. However, the mechanism by which NHE1 regul...

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Section: Discussionmentioning

confidence: 82%

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

Hales

2011

Am J Respir Cell Mol Biol

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“…pH i modulates a number of important cell functions, including volume regulation, signal transduction pathways involved in cell proliferation, and mediator release (8,32). A role for alkaline pH i in hypoxic regulation of vascular caliber is indicated by studies demonstrating that 1) acute hypoxia induces an increase in pulmonary vascular smooth muscle pH i (20), 2) late hypoxic contraction is accompanied by an increase in pH i (18), 3) activation of NHE and alkalinization is required for PASMC proliferation in response to growth factors (33), and 4) pulmonary vascular remodeling during chronic hypoxia can be prevented by inhibiting NHE (34).…”

Section: Discussionmentioning

confidence: 99%

“…Very low expression of NHE6 -9 has been reported in whole lung tissue, but localization of these isoforms is restricted to subcellular organelles (12,23,26,28,29). The cell-specific expression of NHEs in the pulmonary vasculature has not been studied, although cultured pulmonary endothelial cells have been shown to possess only NHE1 (8).…”

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confidence: 99%

Chronic hypoxia elevates intracellular pH and activates Na⁺/H⁺exchange in pulmonary arterial smooth muscle cells

Rios¹,

Fallon²,

Wang³

et al. 2005

American Journal of Physiology-Lung Cellular and Molecular Phys

116

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(CH), caused by many lung diseases, results in pulmonary hypertension due, in part, to increased muscularity of small pulmonary vessels. Pulmonary arterial smooth muscle cell (PASMC) proliferation in response to growth factors requires increased intracellular pH (pH i) mediated by activation of Na ϩ /H ϩ exchange (NHE); however, the effect of CH on PASMC pH i homeostasis is unknown. Thus we measured basal pH i and NHE activity and expression in PASMCs isolated from mice exposed to normoxia or CH (3 wk/10% O 2). pHi was measured using the pH-sensitive fluorescent dye BCECF-AM. NHE activity was determined from Na ϩ -dependent recovery from NH 4-induced acidosis, and NHE expression was determined by RT-PCR and immunoblot. PASMCs from chronically hypoxic mice exhibited elevated basal pH i and increased NHE activity. NHE1 was the predominate isoform present in mouse PASMCs, and both gene and protein expression of NHE1 was increased following exposure to CH. Our findings indicate that exposure to CH caused increased pH i, NHE activity, and NHE1 expression, changes that may contribute to the development of pulmonary hypertension, in part, via pH-dependent induction of PASMC proliferation. pulmonary hypertension MANY CHRONIC LUNG DISEASES cause prolonged alveolar hypoxia, resulting in the development of pulmonary hypertension. The elevation in pulmonary arterial pressure is due to both active contraction of vascular smooth muscle and structural remodeling (21,24,36,38). Pulmonary vascular remodeling in response to chronic hypoxia has been well characterized and includes pulmonary arterial smooth muscle cell (PASMC) hypertrophy and hyperplasia, intimal thickening, and extension of smooth muscle into previously nonmuscular arterioles (21, 36). The exact cellular mechanisms governing hypoxia-induced PASMC growth are not completely known; however, changes in intracellular pH (pH i ) have been demonstrated to be required for cell growth and/or proliferation in pulmonary (33) and systemic tissue (6,17,22), suggesting a possible pivotal role for H ϩ homeostasis in mediating this response.

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“…pH i modulates a number of important cell functions, including signal transduction pathways involved in the regulation of cell size and proliferation (5,36,37). Alterations in pH i are also associated with hypoxic pulmonary vasoconstriction (20,21,23).…”

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confidence: 99%

HIF-1 regulates hypoxic induction of NHE1 expression and alkalinization of intracellular pH in pulmonary arterial myocytes

Shimoda¹,

Fallon²,

Pisarcik³

et al. 2006

American Journal of Physiology-Lung Cellular and Molecular Phys

186

178

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. HIF-1 regulates hypoxic induction of NHE1 expression and alkalinization of intracellular pH in pulmonary arterial myocytes. Am J Physiol Lung Cell Mol Physiol 291: L941-L949, 2006. First published June 9, 2006 doi:10.1152/ajplung.00528.2005.-Vascular remodeling resulting from altered pulmonary arterial smooth muscle cell (PASMC) growth is a contributing factor to the pathogenesis of hypoxic pulmonary hypertension. PASMC growth requires an alkaline shift in intracellular pH (pHi) and we previously showed that PASMCs isolated from mice exposed to chronic hypoxia exhibited increased Na ϩ /H ϩ exchanger (NHE) expression and activity, which resulted in increased pHi. However, the mechanism by which hypoxia caused these changes was unknown. In this study we tested the hypothesis that hypoxia-induced changes in PASMC pH homeostasis are mediated by the transcriptional regulator hypoxiainducible factor 1 (HIF-1). Consistent with previous results, increased NHE isoform 1 (NHE1) mRNA and protein, enhanced NHE activity, and an alkaline shift in pHi were observed in PASMCs isolated from wild-type mice exposed to chronic hypoxia (3 wk at 10% O2). In contrast, these changes were absent in PASMCs isolated from chronically hypoxic mice with partial deficiency for HIF-1. Exposure of PASMCs to hypoxia ex vivo (48 h at 4% O2) or overexpression of HIF-1 in the absence of hypoxia also increased NHE1 mRNA and protein expression. Our results indicate that full expression of HIF-1 is essential for hypoxic induction of NHE1 expression and changes in PASMC pH homeostasis and suggest a novel mechanism by which HIF-1 mediates pulmonary vascular remodeling during the pathogenesis of hypoxic pulmonary hypertension.hypoxia-inducible factor 1; pulmonary arterial smooth muscle cell

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Effect of hypoxic exposure on Na⁺/H⁺antiport activity, isoform expression, and localization in endothelial cells

Cited by 24 publications

References 32 publications

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

Chronic hypoxia elevates intracellular pH and activates Na⁺/H⁺exchange in pulmonary arterial smooth muscle cells

HIF-1 regulates hypoxic induction of NHE1 expression and alkalinization of intracellular pH in pulmonary arterial myocytes

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Effect of hypoxic exposure on Na+/H+antiport activity, isoform expression, and localization in endothelial cells

Cited by 24 publications

References 32 publications

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

Silencing of Sodium–Hydrogen Exchanger 1 Attenuates the Proliferation, Hypertrophy, and Migration of Pulmonary Artery Smooth Muscle Cells via E2F1

Chronic hypoxia elevates intracellular pH and activates Na+/H+exchange in pulmonary arterial smooth muscle cells

HIF-1 regulates hypoxic induction of NHE1 expression and alkalinization of intracellular pH in pulmonary arterial myocytes

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Effect of hypoxic exposure on Na⁺/H⁺antiport activity, isoform expression, and localization in endothelial cells

Chronic hypoxia elevates intracellular pH and activates Na⁺/H⁺exchange in pulmonary arterial smooth muscle cells