- Title
- Galectin-3 and phagocyte function in asthma
- Creator
- Erriah, Melanie
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Asthma is a chronic obstructive airway condition that is thought to affect 300 million people globally including around 2.5 million Australians. Asthma-related expenditure in Australia alone is estimated to be over $600 million dollars annually, half of which is spent on prescription medications. The symptoms include wheezing and shortness of breath which can be managed through the use of inhaled bronchodilators and corticosteroids in mild cases and oral corticosteroids for more severe forms of the condition. These medications relax airway smooth muscles and suppress inflammation, thus reducing swelling and allowing air to circulate more freely. However a proportion of patients with neutrophilic asthma (NA) characterised by significant airway neutrophil infiltration and normal eosinophil numbers have been found to experience persistent symptoms despite the use of bronchodilators and inhaled corticosteroids for reasons which are not fully understood yet. It is likely that the presence of neutrophils in the airway influences airway inflammation in asthma possibly through alteration of macrophage function, but a deeper understanding of these mechanisms would be required in order to better target treatments. This thesis examined the expression of the protein galectin-3 in macrophages and neutrophils in asthma as well as its effect on macrophage efferocytosis of apoptotic granulocytes. Galectin-3 is a 32 kDa protein secreted by macrophages in response to cell activation. It is involved in processes such as chemotaxis, cell proliferation and phagocytosis and its production is usually increased at the site of inflammation. Galectin-3 levels were found to be lower in sputum supernatant from patients with NA compared with other subtypes which could explain the cellular dysfunction observed in this subtype. However the exact role of galectin-3 in immune cells in asthma still remains to be elucidated. Chapter 3 assessed the expression and distribution of galectin-3 and its receptor CD98 in blood monocyte-derived macrophages (MDMs) and airway macrophages (AMs) from participants with asthma. Galectin-3 expression in MDMs and AMs was higher in non-eosinophilic asthma (NEA) compared with eosinophilic asthma (EA). Secreted and intracellular levels of galectin-3 in MDMs and AMs respectively were associated with FEV₁% predicted suggesting potential significance of galectin-3 in asthma. These findings suggest that macrophage galectin-3 expression may be abnormally low in NA but also that higher galectin-3 levels may be associated with better lung function and outcomes in asthma. Galectin-3 has also been reported to be expressed in neutrophils where it is believed to regulate apoptosis and phagocytosis. However its expression in neutrophils in asthma is to date still largely unknown. In Chapter 4, the expression of galectin-3 and its receptor CD66b were assessed in viable and apoptotic blood granulocytes by flow cytometry. Galectin-3 and CD66b expression in neutrophils was similar between the asthma and healthy participants but decreased as the cells underwent apoptosis. Finally, a positive association was observed between CD66b expression in apoptotic neutrophils and sputum neutrophils which may indicate increased priming of neutrophils at the systemic level in NA. Galectin-3 has been reported to play a vital role in the clearance of dead cells and debris by macrophages, a process known as efferocytosis. This process is vital to prevent accumulation of dead cells that could potentially undergo secondary necrosis and damage surrounding tissues, in turn generating more inflammation and causing persistence of the asthma symptoms. AM efferocytic capacity has previously been reported to be reduced in chronic respiratory conditions such as asthma and COPD. However, the exact reason behind this defect is still unclear. In Chapter 5, a method of measuring macrophage efferocytosis of apoptotic granulocytes using MDMs as an AM model was developed. MDMs were used as a model as they are easier to isolate in large numbers and can be kept in culture without any significant loss of viability. This assay developed in Chapter 5 was used to compare the efferocytic ability of MDMs derived from participants with asthma and healthy controls. MDM efferocytosis was similar between the two participants however a negative correlation was observed between efferocytosis and sputum lymphocytes. These findings indicate that at the systemic level, the function of macrophages is unchanged in asthma but also that the airway cellular infiltrate may be having an effect on circulating leucocytes. Addition of galectin-3 was hypothesised to improve efferocytosis and potentially reduce the inflammation and symptoms associated with asthma. In Chapter 6, efferocytosis was measured in asthma and its subtypes and the effect of exogenous recombinant galectin-3 addition on MDM efferocytosis was assessed. Efferocytosis was lowest in NEA compared with EA. Moreover, galectin-3 significantly increased efferocytosis in participants with asthma, particularly in NEA, but not in the healthy controls. A negative correlation between efferocytosis in the presence of galectin-3 and sputum macrophage numbers was detected. These findings indicate that patients with NEA may have an innate macrophage defect observable at the systemic level, which can be reversed through addition of galectin-3. The link between MDM efferocytosis and sputum macrophages suggests that efferocytosis may also be impaired in AMs, which may in turn stimulate the recruitment and proliferation of macrophages in the airways. The findings presented in this thesis illustrate the important role that galectin-3 plays within macrophages and neutrophils and highlight its potential as a modulator of efferocytosis in asthma. Further studies on galectin-3 regulation in macrophages may facilitate the development of new non-steroidal medications targeting the root cause of the airway inflammation in asthma, particularly in NEA.
- Subject
- galectin-3; macrophages; asthma; neutrophils; inflammation
- Identifier
- http://hdl.handle.net/1959.13/1388351
- Identifier
- uon:32745
- Rights
- Copyright 2018 Melanie Erriah
- Language
- eng
- Full Text
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|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 4 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 160 KB | Adobe Acrobat PDF | View Details Download |