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Khawaja AA, Chong DLW, Sahota J, Mikolasch TA, Pericleous C, Ripoll VM, Booth HL, Khan S, Rodriguez-Justo M, Giles IP, Porter JC. Identification of a Novel HIF-1α-α Mβ 2 Integrin-NET Axis in Fibrotic Interstitial Lung Disease. Front Immunol 2020; 11:2190. [PMID: 33178179 PMCID: PMC7594517 DOI: 10.3389/fimmu.2020.02190] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 08/11/2020] [Indexed: 12/18/2022] Open
Abstract
Neutrophilic inflammation correlates with mortality in fibrotic interstitial lung disease (ILD) particularly in the most severe form, idiopathic pulmonary fibrosis (IPF), although the underlying mechanisms remain unclear. Neutrophil function is modulated by numerous factors, including integrin activation, inflammatory cytokines and hypoxia. Hypoxia has an important role in inflammation and may also contribute to pulmonary disease. We aimed to determine how neutrophil activation occurs in ILD and the relative importance of hypoxia. Using lung biopsies and bronchoalveolar lavage (BAL) fluid from ILD patients we investigated the extent of hypoxia and neutrophil activation in ILD lungs. Then we used ex vivo neutrophils isolated from healthy volunteers and BAL from patients with ILD and non-ILD controls to further investigate aberrant neutrophil activation in hypoxia and ILD. We demonstrate for the first time using intracellular staining, HIF-1α stabilization in neutrophils and endothelial cells in ILD lung biopsies. Hypoxia enhanced both spontaneous (+1.31-fold, p < 0.05) and phorbol 12-myristate 13-acetate (PMA)-induced (+1.65-fold, p < 0.001) neutrophil extracellular trap (NET) release, neutrophil adhesion (+8.8-fold, <0.05), and trans-endothelial migration (+1.9-fold, p < 0.05). Hypoxia also increased neutrophil expression of the αM (+3.1-fold, p < 0.001) and αX (+1.6-fold, p < 0.01) integrin subunits. Interestingly, NET formation was induced by αMβ2 integrin activation and prevented by cation chelation. Finally, we observed NET-like structures in IPF lung sections and in the BAL from ILD patients, and quantification showed increased cell-free DNA content (+5.5-fold, p < 0.01) and MPO-citrullinated histone H3 complexes (+21.9-fold, p < 0.01) in BAL from ILD patients compared to non-ILD controls. In conclusion, HIF-1α upregulation may augment neutrophil recruitment and activation within the lung interstitium through activation of β2 integrins. Our results identify a novel HIF-1α- αMβ2 integrin axis in NET formation for future exploration in therapeutic approaches to fibrotic ILD.
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Affiliation(s)
- Akif A. Khawaja
- Centre for Inflammation and Tissue Repair, University College London, London, United Kingdom
- Centre for Rheumatology, University College London, London, United Kingdom
| | - Deborah L. W. Chong
- Centre for Inflammation and Tissue Repair, University College London, London, United Kingdom
| | - Jagdeep Sahota
- Centre for Inflammation and Tissue Repair, University College London, London, United Kingdom
| | - Theresia A. Mikolasch
- Centre for Inflammation and Tissue Repair, University College London, London, United Kingdom
- Interstitial Lung Disease Service, University College London Hospital NHS Foundation Trust, London, United Kingdom
| | - Charis Pericleous
- National Heart and Lung Institute, Imperial College London, London, United Kingdom
| | - Vera M. Ripoll
- Centre for Rheumatology, University College London, London, United Kingdom
| | - Helen L. Booth
- Interstitial Lung Disease Service, University College London Hospital NHS Foundation Trust, London, United Kingdom
| | - Saif Khan
- Institute of Nuclear Medicine, University College London, London, United Kingdom
| | - Manuel Rodriguez-Justo
- Department of Histopathology, University College London Hospital NHS Foundation Trust, London, United Kingdom
| | - Ian P. Giles
- Centre for Rheumatology, University College London, London, United Kingdom
| | - Joanna C. Porter
- Centre for Inflammation and Tissue Repair, University College London, London, United Kingdom
- Interstitial Lung Disease Service, University College London Hospital NHS Foundation Trust, London, United Kingdom
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