Enhanced IL-1β Release Following NLRP3 and AIM2 Inflammasome Stimulation Is Linked to mtROS in Airway Macrophages in Pulmonary Fibrosis.

Athina Trachalaki,Katerina Antoniou,Toby M Maher,Eleni Bibaki,Rachele Invernizzi,Nikolaos Tzanakis,Eliza Tsitoura,Semeli Mastrodimou,Eirini Vasarmidi,Philip L Molyneaux

doi:10.3389/fimmu.2021.661811

Athina Trachalaki, Katerina Antoniou + Show 8 more

Open Access

https://doi.org/10.3389/fimmu.2021.661811

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Abstract

Fibrotic Interstitial lung diseases (ILDs) are complex disorders of variable clinical behaviour. The majority of them cause significant morbidity, whilst Idiopathic Pulmonary Fibrosis (IPF) is recognised as the most relentless. NLRP3, AIM2, and NLRC4 inflammasomes are multiprotein complexes driving IL-1β release; a proinflammatory and profibrotic cytokine. Several pathogenetic factors associated with IPF are identified as inflammasome activators, including increases in mtROS and bacterial burden. Mitochondrial oxidation and alterations in bacterial burden in IPF and other ILDs may lead to augmented inflammasome activity in airway macrophages (AMs). IPF (n=14), non-IPF-ILDs (n=12) patients and healthy subjects (n=12) were prospectively recruited and AMs were isolated from bronchoalveolar lavage. IL-1β release resulting from NLRP3, AIM2 and NLRC4 inflammasomes stimulation in AMs were determined and baseline levels of mitochondrial ROS and microbial burden were also measured. Our results showed that NLRP3 was more inducible in IPF and other ILDs compared to controls. Additionally, following AIM2 activation IL-1β release was significantly higher in IPF compared to controls, whereas similar trends were observed in Non-IPF-ILDs. NLRC4 activation was similar across groups. mtROS was significantly associated with heightened NLRP3 and AIM2 activation, and mitochondrial antioxidant treatment limited inflammasome activation. Importantly, microbial burden was linked to baseline IL-1β release and AIM2 and IL-18 relative expression independently of mtROS. In conclusion, the above findings suggested a link between the overactivation of NLRP3 and AIM2 inflammasomes, driven by mitochondrial oxidation, in the pathogenesis of lung fibrosis while changes in the microbiota may prime the inflammasome in the lungs.

Highlights

Interstitial Lung Disease (ILD) is a broad term used to describe multiple complex disorders with different aetiologies and disease behaviours
We assessed the mRNA expression of genes encoding core inflammasome components NLRP3, NOD-Like receptor (NLR) Family CARD Domain Containing 4 (NLRC4), and Absent in melanoma 2 (AIM2) as well as the gene encoding IL-18 in Bronchoalveolar Lavage Fluid (BALF) cells (Figures 1C–F)
In this study we demonstrated that airway macrophages (AMs) in pulmonary fibrosis secrete abundantly IL-1b following stimulation of the NLRP3 and AIM2 inflammasomes compared to healthy subjects

Summary

INTRODUCTION

Interstitial Lung Disease (ILD) is a broad term used to describe multiple complex disorders with different aetiologies and disease behaviours. The two antifibrotic treatments are effective in other progressive ILDs [6,7,8] This suggests progressive fibrosis arises from common underlying mechanisms, despite the initial cause, but the exact pathways remain to be identified [9]. In Chronic Hypersensitivity Pneumonitis (CHP), bacterial burden is higher, albeit at lower levels compared to IPF [38] These alterations have been linked to host immune response transcriptional changes [39] and variable cytokine secretion [40]. In this study we hypothesised that alterations in the lung microenvironment including microbiome changes and mitochondrial dysfunction in AMs could drive excessive inflammasome activation with possible implications in the pathogenesis of ILD disease. We sought to determine whether increased mtROS and microbial burden were associated with inflammasome activity in AMs from ILDs, including IPF

MATERIALS AND METHODS

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RESULTS

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