Identification, localization and expression of NHE isoforms in the alveolar epithelial cells.

Safa Kinaneh,Emad E Khoury,Yara Knany,Zaid Abassi,Gidon Berger,Reem Ismael-Badarneh,Shadi Hamoud,Zaher S Azzam,Michael Bader

doi:10.1371/journal.pone.0239240

Abstract

Na+/H+ exchangers (NHEs), encoded by Solute Carrier 9A (SLC9A) genes in human, are ubiquitous integral membrane ion transporters that mediate the electroneutral exchange of H+ with Na+ or K+. NHEs, found in the kidney and intestine, play a major role in the process of fluid reabsorption together via Na+,K+-ATPase pump and Na+ channels. Nevertheless, the expression pattern of NHE in the lung and its role in alveolar fluid homeostasis has not been addressed. Therefore, we aimed to examine the expression of NHE specific isoforms in alveolar epithelial cells (AECs), and assess their role in congestive heart failure (CHF). Three NHE isoforms were identified in AEC and A549 cell line, at the level of protein and mRNA; NHE1, NHE2 and mainly NHE8, the latter was shown to be localized in the apical membrane of AEC. Treating A549 cells with angiotensin (Ang) II for 3, 5 and 24 hours displayed a significant reduction in NHE8 protein abundance. Moreover, the abundance of NHE8 protein was downregulated in A549 cells that were treated overnight with Ang II. NHE8 abundance in whole lung lysate was increased in rats with 1-week CHF compared to sham operated rats. However, lower abundance of NHE8 was observed in 4-week CHF group. In conclusion, we herein show for the first time, the expression of a novel NHE isoform in AEC, namely NHE8. Notably, Ang II decreased NHE8 protein levels. Moreover, NHE8 was distinctly affected in CHF rats, probably depending on the severity of the heart failure.

Highlights

Alveolar fluid clearance has been shown to be an important mechanism in keeping the airspaces free of edema in both cardiogenic and non-cardiogenic states [1,2]
Our major focus was on Na+/H+ exchangers (NHEs) isoforms that are primarily localized to cell membranes, can potentially contribute to the alveolar active sodium transport, and eventually alveolar fluid clearance
These exchangers, namely NHE1, NHE2 and NHE8 are expressed in A549 cell line, known to have characteristic features of AECII (Fig 1C)

Summary

Introduction

Alveolar fluid clearance has been shown to be an important mechanism in keeping the airspaces free of edema in both cardiogenic and non-cardiogenic states [1,2]. There is a large body of evidence that the removal of alveolar fluid is attained by the alveolar epithelial active sodium transport; by which sodium passively enters the alveolar epithelial cells (AEC) via apical amiloride-sensitive Na+ channel (ENaC) or other Na+ channels and is pumped out of the cells by basolateral Na+, K+-ATPase, an energy consuming process. Identification of NHEs in the alveolar epithelium manuscript. The other authors received no specific funding for this work

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Conclusion