NOX4 regulates macrophage apoptosis resistance to induce fibrotic progression

Our plain-English summary of NOX4 regulates macrophage apoptosis resistance to induce fibrotic progression, by J.L. Larson-Casey, L. Gu, J. Kang, et al (The Journal of Biological Chemistry, 2021).

The study

• Authors: J.L. Larson-Casey, L. Gu, J. Kang, A. Dhyani, A.B. Carter
• Journal: The Journal of Biological Chemistry
• Published: 2021;297(1):100810
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Pulmonary fibrosis is a progressive lung disease often occurring secondary to environmental exposure. Asbestos exposure is an important environmental mediator of lung fibrosis and remains a significant cause of disease despite strict regulations to limit exposure. Lung macrophages play an integral role in the pathogenesis of fibrosis induced by asbestos (asbestosis), in part by generating reactive oxygen species (ROS) and promoting resistance to apoptosis. However, the mechanism by which macrophages acquire apoptosis resistance is not known. Here, we confirm that macrophages isolated from asbestosis subjects are resistant to apoptosis and show they are associated with enhanced mitochondrial content of NADPH oxidase 4 (NOX4), which generates mitochondrial ROS generation. Similar results were seen in chrysotile-exposed WT mice, while macrophages from Nox4-/- mice showed increased apoptosis. NOX4 regulated apoptosis resistance by activating Akt1-mediated Bcl-2-associated death phosphorylation. Demonstrating the importance of NOX4-mediated apoptosis resistance in fibrotic remodeling, mice harboring a conditional deletion of Nox4 in monocyte-derived macrophages exhibited increased apoptosis and were protected from pulmonary fibrosis. Moreover, resolution occurred when Nox4 was deleted in monocyte-derived macrophages in mice with established fibrosis. These observations suggest that NOX4 regulates apoptosis resistance in monocyte-derived macrophages and contributes to the pathogenesis of pulmonary fibrosis. Targeting NOX4-mediated apoptosis resistance in monocyte-derived macrophages may provide a novel therapeutic target to protect against the development and/or progression of pulmonary fibrosis.

Copyright © 2021 The Authors. Published by Elsevier Inc. All rights reserved.

In plain English

This laboratory study combined human samples, mouse asbestos exposures and macrophage cell lines to ask how lung macrophages become resistant to apoptosis. Bronchoalveolar lavage macrophages were obtained from normal volunteers and from subjects with asbestosis; mice (wild-type, Nox4-/-, and mice with Nox4 deleted in macrophages or in monocyte-derived macrophages) received 100 micrograms of chrysotile asbestos or man-made vitreous fiber by the trachea. Macrophages from asbestosis subjects showed fewer TUNEL-positive cells and significantly lower caspase-3 activity than those from normal subjects, together with a 14-fold increase in NOX4 in the mitochondria. Chrysotile-exposed wild-type mice showed the same pattern, while macrophages from Nox4-/- mice showed increased TUNEL staining and caspase-3 activity. NOX4 acted through mitochondrial ROS, Akt1 activation and BAD phosphorylation at Ser136. Mice lacking Nox4 in monocyte-derived macrophages were protected from fibrosis, and deleting Nox4 after fibrosis was established reduced lung hydroxyproline. The authors concluded that NOX4 regulates apoptosis resistance in monocyte-derived macrophages and contributes to the pathogenesis of pulmonary fibrosis.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Experimental laboratory study using human bronchoalveolar lavage macrophages, genetically modified mouse models of chrysotile-induced lung fibrosis, and macrophage cell lines
• Who was studied: Bronchoalveolar lavage macrophages from normal volunteers (n = 5 in Fig. 1, n = 4 in Fig. 3) and asbestosis subjects (n = 4 in Fig. 1, n = 5 in Fig. 3) at UAB/Birmingham VAMC; 8- to 12-week-old male and female WT, Nox4-/-, Nox4-/-Lyz2-cre, Nox4fl/fl and Nox4-/-Csf1rMeriCreMer mice; THP-1 and MH-S macrophage cell lines
• Exposure: Chrysotile asbestos, 100 micrograms given intratracheally to mice, with man-made vitreous fiber (MMVF) as negative control; chrysotile also applied to cultured macrophages; human subjects had clinically diagnosed asbestosis
• Main results:
  • Lung macrophages from asbestosis subjects had fewer TUNEL-positive cells and significantly lower caspase-3 activity than those from normal subjects
  • Mitochondrial NOX4 was increased 14-fold in lung macrophages of asbestosis subjects compared with normal subjects
  • In mice, chrysotile-exposed WT macrophages lacked TUNEL staining and had decreased caspase-3 activity, while Nox4-/- macrophages showed increased TUNEL staining and caspase-3 activity
  • Deleting Nox4 in macrophages (Nox4-/-Lyz2-cre) prevented the chrysotile-induced increase in monocyte-derived macrophages, reduced BAL CCL2, and protected the mice from fibrosis, confirmed by hydroxyproline assay
  • NOX4 acted through Akt1-mediated BAD phosphorylation at Ser136; silencing Akt1 abolished BAD phosphorylation and increased caspase-3 activity in NOX4-expressing macrophages
  • In asbestosis subjects, lung macrophages showed increased NOX4, Akt1 activation and significantly increased BAD phosphorylation compared with normal volunteers
  • Mitochondrial ROS scavenging (MitoTEMPO) in chrysotile-exposed WT bone marrow-derived macrophages reduced NOX4, Akt1 activation and BAD phosphorylation and raised caspase-3 activity to control levels
  • Deleting Nox4 in monocyte-derived macrophages after fibrosis was established (tamoxifen from day 12) reduced hydroxyproline to the level of MMVF-exposed Nox4fl/fl mice
• The authors' conclusion: The authors concluded that NOX4 regulates apoptosis resistance in monocyte-derived macrophages and contributes to the pathogenesis of pulmonary fibrosis, and suggested it as a possible therapeutic target
• Limitations the authors state:
  • The authors state they cannot exclude that apoptosis in resident alveolar macrophages occurs through other proteins or pathways

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Apoptosis, Pulmonary Fibrosis, Environmental Exposure, Asbestos Exposure, Fibrosis, Reactive Oxygen Species (ROS), Chrysotile.

Related studies

• NOX4 modulates macrophage phenotype and mitochondrial biogenesis in asbestosis — C. He, J.L. Larson-Casey, et al. (2019)
• Apoptosis Resistance in Fibroblasts Precedes Progressive Scarring in Pulmonary Fibrosis and Is Partially Mediated by Toll-Like Receptor 4 Activation — K.M. Hanson, E.B. Hernady, et al. (2019)
• NOX4-TIM23 interaction regulates NOX4 mitochondrial import and metabolic reprogramming — J. Pandey, J.L. Larson-Casey, et al. (2023)
• Carbonic anhydrase 9 confers resistance to ferroptosis/apoptosis in malignant mesothelioma under hypoxia — Z. Li, L. Jiang, et al. (2019)
• Cu,Zn-Superoxide Dismutase-Mediated Redox Regulation of Jumonji Domain Containing 3 Modulates Macrophage Polarization and Pulmonary Fibrosis — C. He, J.L. Larson-Casey, et al. (2016)
• Pemetrexed induces apoptosis in malignant mesothelioma and lung cancer cells through activation of reactive oxygen species and inhibition of sirtuin 1 — K.E. Hwang, Y.S. Kim, et al. (2015)

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