Pulmonary epithelial cells as central players in chronic lung disorders

Division 3: Respiratory & Age-related Health
Department of Respiratory Medicine
Department of Pharmacology and Toxicology
Department of Medical Microbiology

Background

According to estimates from the WHO and the Global Burden of Disease study, a staggering number of 500-600 million people worldwide suffer from chronic lung/airway diseases such as Chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), asthma and bronchopulmonary dysplasia (BPD). Chronic and repetitive exposure of the lungs and airways to insults such as noxious particles, allergens and infectious agents is considered the most important risk factor for developing these diseases.

Our overall aim is to obtain insight in the underlying causes of maladaptive responses of respiratory epithelial cells to these insults from a molecular, cellular and whole tissue perspective with the ultimate goal of developing novel therapeutic strategies to reverse or halt disease progression. We focus on the following triggers: (components of) cigarette smoke, emissions from novel tobacco products (i.e. heated tobacco products), microplastics and wood smoke, allergens and infectious agents (Figure 1). 

Our experimental models include state-of-the art human in vitro and ex vivo models as depicted in Figure 2, as well as primary human and murine stem cells, and precision cut lung slices. 

The Primary Lung Culture facility (PLUC) developed at the MUMC+ is essential for deployment of these models as it provides a unique biobank of well-characterized primary bronchial stem cells, alveolar stem cells, peripheral human lung tissues and primary fibroblasts (Figure 3).

Clinical evidence is obtained from these materials and, in addition, systemic biomarkers that can be used to monitor pulmonary processes are examined in clinical samples (mostly from the circulation and urine) which are available via our collaboration with the pulmonary rehabilitation center CIRO (Horn, the Netherlands). In addition, we use an extensive array of experimental animal models of disease and exposures mainly through our large network of collaborators (see below). An important read-out in our models is cellular metabolism (including glycolysis and mitochondrial function) as it is a key regulator of critical cellular processes and responses. We furthermore focus on the mediating role of redox signalling, the extracellular matrix (ECM), and intercellular communication via secreted factors such as extracellular vesicles (EVs)(Figure 1). Importantly, new therapeutic strategies, including pharmacological or cell-based therapies are tested.

Major breakthroughs

Cellular metabolism

Using peripheral lung tissue as well as primary human bronchial epithelial cells (PBECs) isolated from COPD and non-COPD donors, we have identified abnormalities in mitochondrial biogenesis and mitophagy in COPD likely induced by exposure of these cells to cigarette smoke (components). Furthermore, as a step towards future regulation of specific chemicals in cigarette smoke by governmental bodies, we have identified aldehydes, a harmful class of chemicals formed during the combustion and pyrolysis of tobacco, as compounds responsible for smoke-induced mitochondrial dysfunction in these cells. We are also working on extending these studies to include new, currently non-regulated, tobacco products such as heated tobacco products and are directing research efforts to explore the potential negative impact of inhaled microplastics and wood smoke (from woodstoves, a large contributor to airborne particulate matter in the Netherlands). In addition to these findings, we have identified abnormalities in the glycolysis pathway in animal models and clinical samples of asthmatics, and have demonstrated its crucial role in the pathogenesis of allergic airways disease by increasing IL-1β-induced proinflammatory signaling.

Redox signaling

We have shown the importance of redox regulation in general, and of the redox-based post-translational modification S-glutathionylation in particular, in modulating inflammation, cellular metabolism, and innate epithelial responses in relation to the diseases mentioned above. Importantly, we focus on modifiable redox events, offering the possibility to be (personalized) therapeutically targeted. In IPF, emphasis lies on the role of the pulmonary ROS-producing enzyme NOX4 and the redox-sensitive Src kinase family. Additionally, we study the effect of the only two FDA-approved anti-IPF drugs on the market hereon, as well as new treatment options including kinase inhibitors and dietary antioxidants, supported by comprehensive genomic and gene expression profiling of IPF lungs. Finally, we examine the potential use of volatile organic compounds (VOCs) as biomarkers of disease diagnosis, progression and response to therapy in both in vitro systems and in vivo in naïve patients suffering from IPF and other ILDs. 

Extracellular matrix (ECM)

We have identified an important role for epithelial cells in ECM remodeling in vitro, in animal models and in COPD patients. The contribution of this remodeled ECM to the hostile micro-environment to lung repair in emphysema is currently being examined. Of particular attention are the contribution of elastin degradation and its modulation by vitamin K, and the shifted metabolism of the glycosaminoglycan hyaluronan. 

Extra-cellular vesicles

In another (related) research line, we investigate the role of secreted factors, particularly extracellular vesicles (EVs), in mediating lung inflammation. We have demonstrated that cigarette smoke extract (CSE) induces increased release of EVs as well as changes in their proteomic composition. Specifically, CSE-induced EVs were enriched in proteins related to hemostasis and could promote activation of coagulation factor X and thrombingeneration. Like mitochondrial dysfunction, induction of procoagulant EVs was mediated by reactive aldehydes and furthermore preventable by antioxidants such as glutathione. Currently, we work with patient materials to investigate whether and how procoagulant EVs contribute to lung inflammation and comorbid cardiovascular disease in patients with COPD. Finally, we showed that EVs contribute to innate immunity during infections with respiratory pathogens and are currently investigating whether this defense mechanism is impaired in COPD.