Deficiency of the NHE1 Gene Prevents Hypoxia-induced Pulmonary Hypertension and Vascular Remodeling

Abstract

Rationale: Our previous studies found that Na 1 /H 1 exchanger (NHE) activity played an essential role in pulmonary artery smooth muscle cell (PASMC) proliferation and in the development of hypoxiainduced pulmonary hypertension and vascular remodeling. Other investigators recently observed increased expression of the NHE isoform 1 (NHE1) gene in rodents with pulmonary hypertension induced by hypoxia. However, a causal role for the NHE1 gene in pulmonary hypertension has not been determined. Objectives: To determine the causal role of the NHE1 gene in pulmonary hypertension and vascular remodeling. Methods: We used NHE1-null mice to define the role of the NHE1 gene in the development of pulmonary hypertension and remodeling induced by hypoxia and to delineate the NHE1 regulatory pathway. Measurements and Main Results: After 2 weeks of exposure to hypoxia, in contrast to wild-type hypoxic littermates, there was no significant increase in right ventricular systolic pressure, in the ratio of right ventricular to left ventricular plus septal weight [RV/(LV 1 S)], or in medial wall thickness of the pulmonary arterioles in homozygous mice (NHE1 2/2 ). There was a significant decrease in Rho kinase (ROCK1 and ROCK2) expression, accompanied by an increase in p27 expression in NHE1 2/2 mice. Conclusions: Our study demonstrated that deficiency of the NHE1 gene prevented the development of hypoxia-induced pulmonary hypertension and vascular remodeling in mice and revealed a novel regulatory pathway associated with NHE1 signaling. Keywords: Na 1 /H 1 exchanger isoform 1; pulmonary hypertension; vascular remodeling; hypoxia; mouseThe Na 1 /H 1 exchanger (NHE) expressed in many mammalian cell types is a protein localized to the plasma and the mitochondrial inner membrane (1). The function of NHE is to regulate intracellular pH and cell volume by extruding H 1 from and taking up Na 1 into cells (2). Since NHE was first analyzed in 1976 (3) and the first NHE cDNA was cloned in 1989 (4), nine NHE isoforms have been identified and cloned (2), of which NHE isoform 1 (NHE1) is ubiquitously expressed.Pulmonary hypertension caused by many chronic lung diseases associated with prolonged hypoxia can result in right ventricular hypertrophy and heart failure (5). An important pathological feature of pulmonary hypertension is increased medial thickening of the pulmonary artery resulting from hypertrophy and hyperplasia of the pulmonary artery smooth muscle cells (PASMCs) (6, 7). In previous studies, we reported that NHE activity played a significant role in regulation of intracellular pH in PASMCs (8) and found that the inhibition of NHE activity was related to the inhibition of bovine PASMC proliferation induced by growth factors (9, 10). We also found that inhibition of NHE activity significantly reduced pulmonary hypertension and vascular remodeling induced by chronic hypoxia in rats (11). Our studies suggested that NHE activity might play an important role in development of pulmonary hypertension and vascular remodeling.Recently, incre...

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

“…Studies also showed that the inhibition of NHE1 by inhibitors attenuated the hypertrophy of cardiomyocytes (23)(24)(25)(26)(27). Because we also found a significant decrease in the medial wall thickness of pulmonary arteries in NHE1-deficient mice with decreased hypoxic pulmonary hypertension and vascular remodeling (11), we hypothesized that the effects of NHE1 on hypoxia-induced PASMC hypertrophy were also mediated via E2F1. In addition, the migration of PASMCs is reportedly involved in the pathogenesis of pulmonary hypertension (28), and hypoxia and smooth muscle growth-stimulating factors were shown to affect the migration of PASMCs (29)(30)(31).…”

“…We previously determined that p27, a cyclin-dependent kinase inhibitor and an upstream factor of E2F1, plays a critical role in inhibiting the proliferation of PASMCs and the pulmonary hypertension induced by hypoxia (17)(18)(19). We also observed a significantly decreased expression of cyclin D1, a downstream factor of p27 and upstream factor of E2F1, in PASMCs isolated from NHE1-deficient mice with decreased hypoxic pulmonary hypertension and vascular remodeling (11). We therefore assumed that the inhibition of NHE1 caused a reduction of PASMC proliferation via the E2F1 regulatory pathway.…”

“…Increased expression of the NHE1 gene was evident in animals with hypoxia-induced pulmonary hypertension and vascular remodeling (6)(7)(8)(9)(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.…”

Splice Cassette II of Na+,HCO3− Cotransporter NBCn1 (slc4a7) Interacts with Calcineurin A

“…A potential role for calcineurin in artery remodeling is interesting in the context of acid-base transport because we and others have reported that NHE1 is important for artery structure development and remodeling (10,49,50). Further investigations are required to determine whether changes in NBCn1 activity induced by calcineurin inhibitors contribute to the observed effects on artery remodeling.…”

Na+/H+ Exchange and Hypoxic Pulmonary Hypertension

“…In Nhe1 −/− mice, there was a decrease in ROCK expression and activity, an increase in the expression of p27 (a cyclindependent kinase inhibitor and known downstream factor of ROCK), and a decrease in cyclin D1 expression. 100 Moreover, expression of E2F1, a transcription factor important in cell cycle progression that is known to be downstream of p27, was upregulated by hypoxia in human PASMCs, and this upregulation was inhibited in the setting of in vitro NHE1 silencing. 67 The role of E2F1 as a downstream effector of NHE1 was further confirmed by the fact that overexpression of E2F1 prevented the decrease in PASMC proliferation and migration observed when NHE1 was silenced.…”