|M.Sc Student||Kinaneh Safa|
|Subject||Na+/H+ exchangers in alveolar epithelial cells and their|
involvement in lung edema clearance
|Department||Department of Medicine||Supervisor||Clinical Professor Zaher Azzam|
Background: Active alveolar fluid clearance (AFC) is important for keeping the airspaces free of edema, mainly due to the contribution of alveolar epithelial Na,K-ATPase pump and Na channels (ENaC). Notably, these two players alongside with a third partner, the Na/H-exchanger (NHE) contribute to the process of fluid reabsorption in the kidney and intestine. Nevertheless, the expression pattern of NHE isoforms in the lung, and their role in alveolar fluid homeostasis were not addressed yet.
Angiotensin II (Ang II), a multifunctional hormone, that supports arterial blood pressure and renal function, was recently investigated in our lab, and demonstrated to impair alveolar fluid clearance, by negatively regulating Na, K-ATPase and ENaC.
The Na/H-exchanger (NHE), which exchanges Na for H, regulates cell pH, contributes to ion transport and was recently addressed as a target protein for Ang II receptors.
To date, nine isoforms (NHE1-NHE9) have been identified within the mammalian NHE family. Mammalian NHEs consist of isoforms that occur primarily in the plasma membrane and those that appear to primarily reside in intracellular organelles.
Hypothesis: We hypothesized that alveolar epithelial cells (AEC) express at least one apical NHE isoform which may participate in sodium vectorial transport and hence influence alveolar fluid clearance process.
Methods: In order to investigate our hypothesis, AEC, A549 cells and lung tissue were subjected to western blot analysis, RT-PCR/qPCR, and immunofluorescence staining.
Results: The expression of three NHE isoforms was demonstrated in AEC and A549; NHE1, NHE2 and NHE8. Herein we report the expression of novel NHE isoform by alveolar epithelial cells which is NHE8. It is presumably localized to the apical membrane of AECI, and may contribute to the vectorial sodium transport in alveolar epithelial cells. However, another cell type, suspected to be interstitial macrophages, exhibits strong membrane expression of NHE8. Notably, Ang II regulates NHE8 protein abundance in a dose- and time- dependent manner, and NHE8 protein and mRNA expression are distinctly regulated in rats with induced Congestive Heart Failure (CHF).
Conclusion: The expression of NHE isoforms was validated in AEC; conceivably, our study demonstrated a possible role of NHE8 isoform in AFC process. However, future additional confirmatory studies are needed to validate and strengthen our findings.