- Title
- Contribution of cell death to the pathogenesis of chronic obstructive pulmonary disease (COPD)
- Creator
- Lu, Zhe
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Chronic obstructive pulmonary disease (COPD) affects millions of people worldwide. However, none of the existing treatments can halt or reverse the long-term decline in lung function that drives COPD. Therefore there is an urgent requirement for research into the pathogenesis of COPD in order to drive the development of much-needed therapeutics. COPD is characterized by chronically and gradually worsened airflow limitation. The poor airflow is the result of a number of pathologies in the lung. These pathologies include chronic bronchiolitis which involves the irritation and inflammation of the airways resulting in airway mucus hypersecretion. Additionally, remodelling of small airways also contributes to decreased lung function. Finally, breakdown of the alveolar structures, known as emphysema, leads to a collapse of alveoli and trapping of air, all of which reduce lung function. Cigarette smoke is the primary risk of COPD; it can trigger oxidative stress, protease/anti-protease imbalance and inflammation. All of these factors are known to contribute to the development of COPD. In addition, all these factors can cause cell death. My project will explore the possibility that cell death could contribute to the pathogenesis of COPD by driving inflammation and alveolar destruction. Improved understanding of the contribution of cell death to the pathogenesis of COPD might lead to the development of novel therapeutic strategies. The way in which a cell dies has important implications in terms of inflammatory responses during disease. Until recently, most of the mechanisms of cell death are defined as apoptotic or necrotic. Apoptosis is a form of cell death that follows defined molecular pathways. Apoptotic cells remain intact and are targeted for phagocytosis. Apoptosis results in no inflammatory response or an anti-inflammatory response in neighbouring cells. In contrast, necrosis results in the rupture of the plasma membrane; releasing damage associated molecular patterns (DAMPs) from the cell. DAMP release can trigger a pro-inflammatory effect which may drive further destruction of surrounding tissue. Thus necrotic death might play a more important role in the pathogenesis of COPD. Until recently, necrosis was thought to be unregulated. Recently, it has emerged that in some cases necrosis is subject to regulation by extracellular and intracellular signals. Necroptosis is a genetically encoded mechanism of necrotic cell death mediated by signalling pathways involving RIPK (receptor interacting protein kinases) 1, RIPK 3 and MLKL (mixed lineage kinase domain-like). First, the contribution of necroptosis and related signalling to the pathogenesis of COPD was tested in our mouse model of experimental COPD. Necroptosis may contribute to the pathogenesis of COPD by driving inflammation, and causing tissue destruction and emphysema. Evidence of apoptosis-independent cell death and activation of necroptosis signaling in experimental COPD were found by histological, gene expression and protein analysis. The effects of pharmaceutical inhibition of necroptosis with the RIPK1 inhibitor Nec-1s were evulated in our CS exposure model. Nec-1s administration had protective effects against inflammation both in acute and chronic CS exposure models; however, it did not affect the remodelling or emphysema in experimental COPD. The effect of genetic ablation of necroptosis pathway components was tested in our acute and chronic CS exposure models by using RIPK3 or MLKL deficient mice. Importantly, RIPK3 and MLKL deficient mice were protected against inflammation in acute and chronic models, and they both showed some protection against CS-induced airway remodelling and emphysema. Secondly, the contribution of necroptosis and apoptosis to the pathogenesis of COPD was evaluated in our mouse model of experimental COPD. The effect of genetic ablation of necroptosis mediator RIPK3 was tested on activation of the inflammasome pathway in our COPD model, and the relationship between necroptosis and pyroptosis. Necroptosis may contribute to the pathogenesis of COPD by driving inflammation and by causing tissue destruction in emphysema. Mouse lung epithelial cells (LA-4), mouse alveolar macrophages (MH-S) and human lower respiratory tract epithelial cells (A549) underwent a mixture of apoptotic and necrotic cell death in vitro when exposed to CSE. CSE-induced cell death of MH-S macrophages was reduced by inhibiting apoptosis (using a pan-caspase inhibitor Z-VAD-FMK) and necroptosis (using Nec-1s). By inhibiting apoptosis (using another pan-caspase inhibitor qVD-OPh) and necroptosis (using Nec-1s), CSE-induced cell death of human lower respiratory tract epithelial cells (A549) was reduced. However, a RIPK3 inhibitor (GSKʹ872) and an MLKL inhibitor (NSA) did not protect from CSE-induced death. MLKL deficiency and/or qVD-OPh treatment reduced airway inflammation in experimental COPD. Importantly, MLKL deficiency protected against CS-induced emphysema and airways remodelling, but apoptosis inhibition by qVD-OPh treatment did not. The relationship between necroptosis signalling and caspase-1 activation were analysed in experimental COPD using RIPK3-deficient mice by flow cytometry. The deficiency of RIPK3 rescued CS-induced decreases in mDC and increases in T cell and pDC numbers after chronic CS exposure. RIPK3 deficiency also rescued monocytes, T cells and NK1.1+ cells from cell death in experimental COPD. Interestingly, active caspase-1-positive cell ratio in γδ T cells was significantly lower in RIPK3-deficient mice compared to WT mice after chronic CS exposure. Moreover, RIP3 deficiency tended to reduce the pyroptosis of monocytes, T cells, CD4+ T, CD8+ T, γδ T and NK1.1+ T cells. Thirdly, a surrogate model of viral-induced exacerbation of CS-induced experimental COPD was developed by using the viral RNA mimetic PAMP, Poly I:C. Both RIPK3 and MLKL deficient mice were protected against Poly I:C + CS-induced inflammation, and were also protected against Poly I:C + CS-induced lung pathology. Neither RIP3 nor MLKL deficient mice were protected against influenza virus induced-airway inflammation and only RIPK3 deficiency protected against influenza-induced lung function alterations. Genetic inhibition of necroptosis on elastase-induced emphysema and inflammation was also evaluated. Only minor reductions in airway inflammation were observed in the MLKL-deficient mice. Taken together, our data extended our understanding of the pathogenesis and potential therapeutic approaches for COPD and showed that necroptosis may be a therapeutic target in COPD.
- Subject
- COPD; necroptosis; apoptosis; RIPK3 deficient mice; MLKL deficient mice; pulmonary inflammation; remodelling
- Identifier
- http://hdl.handle.net/1959.13/1410329
- Identifier
- uon:36167
- Rights
- Copyright 2019 Zhe Lu
- Language
- eng
- Full Text
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