The Matrikine PGP in Lung Diseases: A Translational Study

Abstract

In this thesis two long conditions are investigated: chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). COPD is a progressive disorder characterized by the development of airflow limitation. It encompasses chronic bronchitis (chronic inflammation and obstruction of small airways) and emphysema (parenchymal destruction), which lead to progressive narrowing of the airways and shortness of breath. ARDS is characterized by an increase in the permeability of the alveolar-capillary barrier leading to impaired gas exchange. In both COPD and in ARDS, neutrophils play a key role. A better understanding of the underlying pathophysiology of these diseases is needed to eventually develop new therapies. Several models are described in this thesis which comprise in vitro experiments in human cells, in vivo preclinical models for COPD and ARDS, and translational analysis in clinical samples such as blood and primary cells from patients and healthy individuals. Since cigarette smoking is the major risk factor for developing COPD, most of the in vivo models were tested in mice after cigarette smoke exposure. In all the models, the role of the neutrophil chemoattractant proline-glycine-proline (PGP) or the more potent form acetylated PGP (acPGP) was investigated. PGP peptides are derived from collagen after a sequential cleavage by matrix metalloproteinases and prolyl endopeptidase (PE). Furthermore, the role of PGP peptides in ARDS and cardiovascular diseases was investigated. The main aim of this thesis is to get a better understanding on the role of PGP peptides during pathological conditions by using models for lung conditions such as COPD and ARDS. The PE inhibitor valproic acid (VPA) was tested in vitro and in vivo on PGP generation in an acute model for cigarette smoke-induced pulmonary inflammation and showed to significantly reduce the neutrophil influx into the lungs. Using a different approach to inhibit the PGP pathway, the PGP neutralizing peptide L-arginine-threonine-arginine (RTR) was used in sub chronic and chronic models of cigarette smoke-induced inflammation. Effects of PGP inhibition on the pathophysiology in lungs and heart were measured. In addition, effects of acPGP on activation of primary epithelia from COPD and healthy subjects were tested. RTR showed very promising anti-inflammatory results in all cases. Mice receiving RTR were protected from developing right ventricular hypertrophy (RVH) of the heart and emphysema of the lungs. Using a different PE inhibitor, the effect of PGP on the heart and pulmonary artery in a murine model for subchronic cigarette smoke exposure was investigated. Utilizing techniques such as echocardiography showed a protective effect on the heart after PGP depletion in this model. Finally, we describe the role of PGP in ARDS. Several in vitro and in vivo models are described together with the use of clinical samples with a focus on endothelial cells. We describe a novel role for acPGP in regulating paracellular permeability during inflammatory disease and demonstrate the potential to target this ligand in various disorders characterized by excessive matrix turnover and vascular leak such as ARDS. In conclusion, the findings in this thesis strongly underscore an important role for PGP in the development of a COPD phenotype such as emphysema and RVH. Furthermore, we have identified a novel role for acPGP as an activator of endothelial cell signaling which actively couples vascular permeability and tissue injury. This study indicates that PGP-induced inflammation may be an interesting therapeutic target.