Phosphodiesterase 6 subunits are expressed and altered in idiopathic pulmonary fibrosis

Sevdalina Nikolova,Melanie Konigshoff,Andreas Guenther,Rajkumar Savai,Oliver Eickelberg,Soni S Pullamsetti,Robert Voswinckel,Walter Klepetko,Norbert Weissmann,Hossein A Ghofrani,Ralph T Schermuly,Friedrich Grimminger,Werner Seeger

doi:10.1186/1465-9921-11-146

Abstract

BackgroundIdiopathic Pulmonary Fibrosis (IPF) is an unresolved clinical issue. Phosphodiesterases (PDEs) are known therapeutic targets for various proliferative lung diseases. Lung PDE6 expression and function has received little or no attention. The present study aimed to characterize (i) PDE6 subunits expression in human lung, (ii) PDE6 subunits expression and alteration in IPF and (iii) functionality of the specific PDE6D subunit in alveolar epithelial cells (AECs).Methodology/Principal FindingsPDE6 subunits expression in transplant donor (n = 6) and IPF (n = 6) lungs was demonstrated by real-time quantitative (q)RT-PCR and immunoblotting analysis. PDE6D mRNA and protein levels and PDE6G/H protein levels were significantly down-regulated in the IPF lungs. Immunohistochemical analysis showed alveolar epithelial localization of the PDE6 subunits. This was confirmed by qRT-PCR from human primary alveolar type (AT)II cells, demonstrating the down-regulation pattern of PDE6D in IPF-derived ATII cells. In vitro, PDE6D protein depletion was provoked by transforming growth factor (TGF)-β1 in A549 AECs. PDE6D siRNA-mediated knockdown and an ectopic expression of PDE6D modified the proliferation rate of A549 AECs. These effects were mediated by increased intracellular cGMP levels and decreased ERK phosphorylation.Conclusions/SignificanceCollectively, we report previously unrecognized PDE6 expression in human lungs, significant alterations of the PDE6D and PDE6G/H subunits in IPF lungs and characterize the functional role of PDE6D in AEC proliferation.

Highlights

Idiopathic Pulmonary Fibrosis (IPF) is a progressive interstitial lung disease of unknown etiology associated with high morbidity and mortality [1], and further characterized by abnormal alveolar epithelial and fibro-proliferative responses, excessive extra-cellular matrix deposition, patchy inflammatory infiltrations and progressive loss of normal lung structure [2]
PDE6D subunit was significantly down-regulated in the IPF lungs as compared to the donor lungs and PDE6H showed a tendency of down-regulation in the IPF lungs as compared to the donor lungs
The PDE6D and PDE6G/H subunits were significantly down-regulated in the IPF lungs as compared to donor lungs, whereas PDE6A and PDE6B showed no significant alterations between donor and IPF-derived lung tissues (Figure 2B)

Summary

Introduction

IPF is a progressive interstitial lung disease of unknown etiology associated with high morbidity and mortality [1], and further characterized by abnormal alveolar epithelial and fibro-proliferative responses, excessive extra-cellular matrix deposition, patchy inflammatory infiltrations and progressive loss of normal lung structure [2]. At present there is no effective therapy for blocking or reversing the progression of the disease [3]. This situation demands a better understanding of the molecular and cellular mechanisms involved in the pathogenesis of IPF. A significant increase of Wnt signaling in ATII cells derived from IPF patients and its involvement in epithelial cell injury and hyperplasia has been documented [15]. Lung PDE6 expression and function has received little or no attention. The present study aimed to characterize (i) PDE6 subunits expression in human lung, (ii) PDE6 subunits expression and alteration in IPF and (iii) functionality of the specific PDE6D subunit in alveolar epithelial cells (AECs)

Methods

Results

Conclusion