Mitochondrial Cu,Zn-superoxide dismutase mediates pulmonary fibrosis by augmenting H2O2 generation

Our plain-English summary of Mitochondrial Cu,Zn-superoxide dismutase mediates pulmonary fibrosis by augmenting H2O2 generation, by C. He, S. Murthy, M.L. McCormick, et al (The Journal of Biological Chemistry, 2011).

The study

• Authors: C. He, S. Murthy, M.L. McCormick, D.R. Spitz, A.J. Ryan, A.B. Carter
• Journal: The Journal of Biological Chemistry
• Published: 2011;286(17):15597-607
• Cited by: 66 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The release of H(2)O(2) from alveolar macrophages has been linked to the development of pulmonary fibrosis, but little is known about its source or mechanism of production. We found that alveolar macrophages from asbestosis patients spontaneously produce high levels of H(2)O(2) and have high expression of Cu,Zn-superoxide dismutase (SOD). Because Cu,Zn-SOD is found in the mitochondrial intermembrane space (IMS), we hypothesized that mitochondrial Cu,Zn-SOD-mediated H(2)O(2) generation contributed to pulmonary fibrosis. Asbestos-induced translocation of Cu,Zn-SOD to the IMS was unique to macrophages and dependent on functional mitochondrial respiration and the presence of at least one of the conserved cysteines required for disulfide bond formation. These conserved cysteine residues were also necessary for enzyme activation and H(2)O(2) generation. Cu,Zn-SOD-mediated H(2)O(2) generation was inhibited by knockdown of the iron-sulfur protein, Rieske, in complex III. The role of Cu,Zn-SOD was biologically relevant in that Cu,Zn-SOD(-/-) mice generated significantly less H(2)O(2) and had less oxidant stress in bronchoalveolar lavage fluid and lung parenchyma. Furthermore, Cu,Zn-SOD(-/-) mice did not develop pulmonary fibrosis, and knockdown of Cu,Zn-SOD in monocytes attenuated collagen I deposition by lung fibroblasts. Our findings demonstrate a novel mechanism for the pathogenesis of pulmonary fibrosis where the antioxidant enzyme Cu,Zn-SOD translocates to the mitochondrial IMS to increase H(2)O(2) generation in alveolar macrophages.

In plain English

This laboratory study combined human samples, cell culture and mouse experiments to examine how hydrogen peroxide (H2O2) is produced in asbestos-induced lung fibrosis. The authors obtained alveolar macrophages by bronchoalveolar lavage from patients with asbestosis and from lifetime non-smoking normal volunteers, and reported that macrophages from asbestosis patients had a 10-fold greater rate of spontaneous H2O2 generation, with similar Mn-SOD expression and activity but significantly more Cu,Zn-SOD expression and activity. In THP-1 monocytes, chrysotile asbestos exposure moved Cu,Zn-SOD into the mitochondrial intermembrane space; this did not occur in MLE-12 alveolar epithelial cells. Translocation required at least one of the conserved cysteines (57, 146), and both were needed for multimer formation and H2O2 generation; knockdown of the Rieske iron-sulfur protein of complex III inhibited H2O2 production and Cu,Zn-SOD activation. Mice lacking Cu,Zn-SOD given intratracheal chrysotile had less lipid peroxidation and oxidized glutathione and less collagen deposition than wild-type mice. The authors concluded that Cu,Zn-SOD translocation to the intermembrane space increases H2O2 and, in part, mediates 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: human alveolar macrophage samples, cell-line transfection/knockdown experiments, and chrysotile asbestos exposure of wild-type and Cu,Zn-SOD knockout mice
• Who was studied: Alveolar macrophages from patients with asbestosis and from normal non-smoking volunteers (6 per group for H2O2; 3 patients and 4 normal subjects for immunoblot), human THP-1 monocytes, MLE-12 mouse alveolar epithelial cells, human lung fibroblasts, and wild-type and Cu,Zn-SOD-deficient C57BL/6 mice; University of Iowa
• Exposure: Chrysotile asbestos (from the NAIMA Fiber Repository): 3-hour exposure of cultured cells; 100 micrograms intratracheally in mice, studied 1 or 21 days later
• Main results:
  • Alveolar macrophages from asbestosis patients generated spontaneous H2O2 at a rate 10-fold greater than those from normal subjects (6 per group, p less than 0.05)
  • Asbestosis patients' macrophages had Mn-SOD expression and activity similar to normal subjects, but significantly more Cu,Zn-SOD expression and activity
  • In THP-1 monocytes, chrysotile increased Cu,Zn-SOD in mitochondria, whereas in MLE-12 epithelial cells mitochondrial Cu,Zn-SOD decreased after asbestos exposure
  • Translocation to the intermembrane space required at least one conserved cysteine; the double mutant C57S,C146S was not detected in the IMS with or without asbestos
  • In THP-1 monocytes, knockdown of the Rieske iron-sulfur protein of complex III inhibited H2O2 generation and reduced the activated, disulfide-linked mitochondrial Cu,Zn-SOD
  • After asbestos exposure, wild-type mice had more than 6-fold higher lipid peroxidation in BAL fluid than Cu,Zn-SOD-deficient mice (4 per group, p less than 0.01), and higher percentage of glutathione in disulfide form in lung tissue (p less than 0.02)
  • At 21 days, wild-type lungs showed widespread peribronchial and parenchymal collagen deposition while deposition in Cu,Zn-SOD-deficient mice was significantly attenuated; collagen Ia1 mRNA was more than 5-fold higher in wild-type lungs
  • BAL cells from asbestos-exposed wild-type mice expressed more than 4-fold more TGF-beta mRNA than those from Cu,Zn-SOD-deficient mice; knockdown of Cu,Zn-SOD in THP-1 cells reduced procollagen I and collagen I secreted by human lung fibroblasts
• The authors' conclusion: The authors concluded that Cu,Zn-SOD translocates to the mitochondrial intermembrane space of monocytes/macrophages, where its activation increases H2O2 generation and, in part, mediates the development of pulmonary fibrosis after asbestos exposure, offering a potential therapeutic target

Topics

Medical terms in this study, explained in our Lexicon: Superoxide, Pulmonary Fibrosis, Alveolar Macrophage, Translocation, Macrophage, Bronchoalveolar Lavage (BAL), Parenchyma, Collagen.

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