Understanding mechanisms of lung destruction in patients with non-tuberculous mycobacterial pulmonary infection

Abstract

Non-tuberculous mycobacterial pulmonary disease (NTM-PD), primarily caused by Mycobacterium avium complex (MAC), is increasing globally. Characterised by cavitation and bronchiectasis, the mechanisms underlying lung tissue destruction in MAC infection remain poorly defined. Matrix metalloproteinases (MMPs), particularly MMP-1, are implicated in extracellular matrix degradation in chronic lung diseases such as tuberculosis (TB) and COPD. Recent evidence shows that MAC infection induces MMP-1 expression in macrophages, suggesting a similar pathogenic mechanism. Given that hypoxia is common in patients with preexisting lung conditions and is known to enhance MMP-1 activity in TB, we hypothesised that hypoxia exacerbates MMP-1 production in MAC-infected macrophages, contributing to disease progression.

Primary human monocyte-derived macrophages were infected with M. avium (reference and clinical isolates) and cultured under normoxic (21% O₂) or hypoxic (1% O₂) conditions. MMP-1 and TIMP-1 levels were measured by ELISA, and gene expression was assessed via RT-qPCR. HIF-1α involvement was evaluated using DMOG (stabiliser) and PX-478 (inhibitor), with protein expression analysed by Western blot. Pharmacological inhibitors targeting PI3K/Akt, MAPKs, NF-κB, and CREB were used to dissect regulatory pathways.

M. avium infection significantly increased MMP-1 transcription and secretion, with hypoxia further amplifying this response. Hypoxia also suppressed TIMP-1, shifting the MMP-1:TIMP-1 balance toward proteolysis. HIF-1α was stabilised by infection alone and further enhanced under hypoxia. HIF-1α stabilisation increased MMP-1 secretion, while inhibition reduced it dose-dependently. PI3K/Akt and p38 MAPK were key mediators of hypoxia-induced MMP-1 expression, while NF-κB inhibition suppressed MMP-1 under both oxygen conditions. Network analysis revealed crosstalk among PI3K, p38, NF-κB, and CREB, forming a coordinated regulatory axis.

In conclusion, M. avium infection and hypoxia synergistically drive MMP-1 overexpression in macrophages via HIF-1α and interconnected signalling pathways, contributing to lung matrix degradation in MAC-PD and identifying potential therapeutic targets.

Thesis is embargoed until 31 July 2030.

Date of Award	Jul 2025
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Cecilia O'Kane (Supervisor), Derek Brazil (Supervisor) & Gunnar Neels Schroeder (Supervisor)