Linking Fibrotic Remodeling and Ultrastructural Alterations of Alveolar Epithelial Cells after Deletion of Nedd4-2.

Theresa A Engelmann,Michael F Beers,Lars Knudsen,Matthias Ochs,Marcus A Mall,Julia Duerr,Dominik H W Leitz

doi:10.3390/ijms22147607

Abstract

Our previous study showed that in adult mice, conditional Nedd4-2-deficiency in club and alveolar epithelial type II (AE2) cells results in impaired mucociliary clearance, accumulation of Muc5b and progressive, terminal pulmonary fibrosis within 16 weeks. In the present study, we investigated ultrastructural alterations of the alveolar epithelium in relation to interstitial remodeling in alveolar septa as a function of disease progression. Two, eight and twelve weeks after induction of Nedd4-2 knockout, lungs were fixed and subjected to design-based stereological investigation at the light and electron microscopic level. Quantitative data did not show any abnormalities until 8 weeks compared to controls. At 12 weeks, however, volume of septal wall tissue increased while volume of acinar airspace and alveolar surface area significantly decreased. Volume and surface area of alveolar epithelial type I cells were reduced, which could not be compensated by a corresponding increase of AE2 cells. The volume of collagen fibrils in septal walls increased and was linked with an increase in blood–gas barrier thickness. A high correlation between parameters reflecting interstitial remodeling and abnormal AE2 cell ultrastructure could be established. Taken together, abnormal regeneration of the alveolar epithelium is correlated with interstitial septal wall remodeling.

Highlights

Idiopathic pulmonary fibrosis (IPF) is a progressively scarring lung disease with poor prognosis [1,2]
A recent study based on contrast enhanced dual energy computed tomography demonstrated that increased regional ventilation was a predictive parameter for future decline in lung function, and regions which were subject to higher regional ventilation were prone to fibrotic remodeling in follow-up, showing that mechanical stress is of relevance for disease progression [5,6,7]
We aimed to investigate the following questions: (1) Does the conditional deletion of Nedd4-2 have a direct effect on the ultrastructure of the alveolar epithelium, including the intracellular surfactant system? (2) Do ultrastructural abnormalities of the alveolar epithelium and the intracellular surfactant pool correlate with the interstitial remodeling? (3) In this animal model of progressive pulmonary fibrosis, is there any evidence for insufficient epithelial regeneration?

Summary

Introduction

Idiopathic pulmonary fibrosis (IPF) is a progressively scarring lung disease with poor prognosis [1,2]. The etiology of this disease is complex and poorly understood and appears to be multifactorial, including both genetic and environmental factors as well as aging [3]. A recent study based on contrast enhanced dual energy computed tomography demonstrated that increased regional ventilation was a predictive parameter for future decline in lung function, and regions which were subject to higher regional ventilation (deformation) were prone to fibrotic remodeling in follow-up, showing that mechanical stress is of relevance for disease progression [5,6,7]

Objectives

Methods

Results

Conclusion