Targeted Induction of Lung Endothelial Cell Apoptosis Causes Emphysema-like Changes in the Mouse

Ricardo J Giordano,Johanna Lahdenranta,Lijie Zhen,Ugonma Chukwueke,Irina Petrache,Robert R Langley,Isaiah J Fidler,Renata Pasqualini,Rubin M Tuder,Wadih Arap

doi:10.1074/jbc.m804595200

Abstract

Pulmonary gas exchange relies on a rich capillary network, which, together with alveolar epithelial type I and II cells, form alveolar septa, the functional units in the lung. Alveolar capillary endothelial cells are critical in maintaining alveolar structure, because disruption of endothelial cell integrity underlies several lung diseases. Here we show that targeted ablation of lung capillary endothelial cells recapitulates the cellular events involved in cigarette smoke-induced emphysema, one of the most prevalent nonneoplastic lung diseases. Based on phage library screening on an immortalized lung endothelial cell line, we identified a lung endothelial cell-binding peptide, which preferentially homes to lung blood vessels. This peptide fused to a proapoptotic motif specifically induced programmed cell death of lung endothelial cells in vitro as well as targeted apoptosis of the lung microcirculation in vivo. As early as 4 days following peptide administration, mice developed air space enlargement associated with enhanced oxidative stress, influx of macrophages, and up-regulation of ceramide. Given that these are all critical elements of the corresponding human emphysema caused by cigarette smoke, these data provide evidence for a central role for the alveolar endothelial cells in the maintenance of lung structure and of endothelial cell apoptosis in the pathogenesis of emphysema-like changes. Thus, our data enable the generation of a convenient mouse model of human emphysema. Finally, combinatorial screenings on immortalized cells followed by in vivo targeting establishes an experimental framework for discovery and validation of additional ligand-directed pharmacodelivery systems.

Highlights

A “vascular hypothesis” for emphysema originated ϳ40 years ago based on the observation of scarcity of pulmonary capillaries in remaining alveolar septa in emphysematous human lungs [4]
We have shown that disruption of vascular endothelial growth factor (VEGF) receptor signaling alters the cellular and molecular maintenance program in the lung and sets up a destructive cycle involving the mutual interaction of oxidative stress and apoptosis of alveolar cells [6], under the control of the proapoptotic lipid ceramide [10]
First we evaluated whether temperature affected the binding of the dominant CGSPGWVRC phage clone to ImmortoMouse-derived lung endothelial cells

Summary

Introduction

A “vascular hypothesis” for emphysema originated ϳ40 years ago based on the observation of scarcity of pulmonary capillaries in remaining alveolar septa in emphysematous human lungs [4]. We have shown that disruption of VEGF receptor signaling alters the cellular and molecular maintenance program in the lung and sets up a destructive cycle involving the mutual interaction of oxidative stress and apoptosis of alveolar cells [6], under the control of the proapoptotic lipid ceramide [10] These observations were further confirmed with the report of emphysema in mice in which the VEGF gene has been deleted by lung expression of CRE recombinase [8] and our finding of emphysema in mice treated with the combination of VEGF-R1 and -R2 blocked with neutralizing MF1 and DC101 antibodies, respectively [11]. Given the phenotypic attributes of lung vasculature, we hypothesized that the expression of unique lung endothelial cell-specific peptide ligands will serve as molecular tools to interrogate the role of lung capillary endothelial cells in maintaining in vivo alveolar integrity

Methods

Results

Conclusion