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

Abstract

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...

Stimulation of Na+/H+ Exchanger Isoform 1 Promotes Microglial Migration

“…Despite that NHE-1 has been shown to be involved in migration of smooth muscle and fibroblast cells [14,31], it remains unknown whether NHE-1 regulates microglial migration. In this study, we first detected that microglial lamellipodia at the leading edge displayed highly motile dynamics upon BK stimulation.…”

Intracellular pH in the Resistance Vasculature: Regulation and Functional Implications

“…Considering the importance of acid-base transport for altering fundamental cell functions (e.g. cell proliferation and migration) implicated in changes of artery morphology [28,60,61] (see also ‘Hypertension’), it may moreover be very relevant to study pH i -regulatory pathways in VSMCs from arteries with atherosclerotic or restenotic lesions.…”

“…Knockout mice for NHE1 have been shown to be unsusceptible to developing pulmonary hypertension and pulmonary artery remodeling [60]. In accordance with a role for NHE1 in pulmonary artery remodeling, siRNA-mediated knockdown of NHE1 was subsequently shown to inhibit proliferation, migration and hypertrophy of VSMC-derived cells [61]. …”

Whole-Exome Sequencing Reveals TopBP1 as a Novel Gene in Idiopathic Pulmonary Arterial Hypertension

“…This was of particular interest to us given recent reports alluding to the presence of abnormalities in the DNA repair machinery found in both pulmonary endothelial (40) and smooth muscle cells (41) from patients with IPAH. Furthermore, TopBP1 has been shown to interact with E2F1 (42), a gene reported to promote pulmonary smooth muscle cell proliferation in the setting of hypoxia (43,44). In our patient population, we found three singlenucleotide variants (SNVs) (Figure 2A) located in close proximity to both the TopBP1 transactivation domain (rs55633281) and the topoisomerase II interacting domain (rs17301766 and rs10935070) ( Figure 2B).…”