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Title: Mechanisms to reverse impaired macrophage function in COPD
Author: Ryan, Eilíse M.
ISNI:       0000 0004 8509 4412
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2020
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COPD is major health problem and is set to become the third leading cause of death globally by 2030. To date we have no therapies which significantly alter the course of this debilitating disease. The lungs of COPD patients are characterised by chronic inflammation which results in airway narrowing and tissue destruction and persists even after smoking cessation. Patients with COPD experience defective innate immunity, characterized in part by macrophage dysfunction. In established disease, COPD macrophages have impaired phagocytosis of bacteria and apoptotic cells (efferocytosis). There is evidence that COPD macrophages have altered expression of a transcription factor, Nrf2, the master regulator of antioxidant defences. I hypothesised that impaired macrophage functions in COPD share common mechanistic defects. These defects may relate to cellular energetics and or antioxidant responses. To address if macrophage dysfunction in COPD was regulated by the lung microenvironment alone, I isolated macrophages from the airways [Alveolar macrophages (AM)], and from the peripherally circulating blood [Monocytederived macrophages (MDM)], of COPD and Healthy donors . I found that in COPD both AM and MDM had impaired bacterial phagocytosis and efferocytosis. I also found that efferocytosis and phagocytosis rates were closely correlated , suggesting a shared underlying mechanistic defect. Efferocytosis and phagocytosis rates also correlated with markers of disease severity in COPD. Dynamic metabolic profiling of macrophages, using Seahorse technology, revealed that AM and MDM from COPD patients have impaired energy reserves in both glycolysis and oxidative phosphorylation. Whilst experiencing reduced reserves in both of these central metabolic pathways , Seahorse evaluation also revealed an apparent over reliance on glycolysis in COPD macrophages . This was mirrored in LC-MS (liquid chromatography mass spectrometry) analysis of resting state macrophages. LC-MS revealed a global up regulation of the glycolytic intermediaries in resting state AM and MDM from COPD Donors. In parallel with this work , I established that COPD AM display an impaired transcriptional response to infection with Streptococcus pneumoniae, which primarily related to failure to mount an adequate anti-oxidant response. Manipulation of the anti-oxidant pathway with highly specific activators of Nrf2, enhanced bacterial phagocytosis and efferocytosis in COPD AM and MDM. Moreover ,treatment with Nrf2 agonists increased TCA cycle intermediaries, and restored redox balance to the cell, as assessed by LCMS. Using transcriptomics analysis we identified a number of key metabolic targets which differed at baseline between COPD AM and Healthy Donor AM, with key shifts in metabolism induced by Nrf2 activation in COPD AM. In summary I have established that there is a global defect in macrophage function in COPD, which is not singularly driven by tissue specific factors. I have determined that both AM and MDM from COPD patients have an impaired bioenergetic profile and I suggest that this may be the common underlying mechanism driving the phenotype. I have demonstrated a failure in COPD AM to mount an anti-oxidant response. I have subsequently shown a reversal of impaired macrophage function in COPD using a highly specific Nrf2 activator .Lastly, I have evidence that the Nrf2 mediated restoration of macrophage function in COPD is due, in part, to metabolic reprogramming, with a skewing towards oxidative phosphorylation. This highlights both the therapeutic potential for metabolic reprogramming in COPD and the role of Nrf2 activation in modulating disease behaviour in COPD.
Supervisor: Whyte, Moira ; Walmsley, Sarah Sponsor: Wellcome Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: chronic obstructive pulmonary disease ; COPD ; macrophages ; antioxidant signals ; macrophage dysfunction ; efferocytosis ; Alveolar macrophages ; Monocytederived macrophages