Mitochondrial Rac1 GTPase Import and Electron Transfer from Cytochrome c Are Required for Pulmonary Fibrosis

• Published in: The Journal of biological chemistry 2012-01, Vol.287 (5), p.3301-3312
• Main Authors: Osborn-Heaford, Heather L., Ryan, Alan J., Murthy, Shubha, Racila, Ana-Monica, He, Chao, Sieren, Jessica C., Spitz, Douglas R., Carter, A. Brent
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Aged; Animals; Asbestos - toxicity; Carcinogens - toxicity; Cytochrome c; Cytochromes c - genetics; Cytochromes c - metabolism; Electron Transport - drug effects; Electron Transport - genetics; Electrons; Female; Fibrosis; Humans; Macrophages; Macrophages, Alveolar - enzymology; Macrophages, Alveolar - pathology; Male; Mice; Mice, Mutant Strains; Middle Aged; Mitochondria; Mitochondrial Proteins - genetics; Mitochondrial Proteins - metabolism; Molecular Bases of Disease; Neuropeptides - genetics; Neuropeptides - metabolism; Protein Prenylation - drug effects; Protein Prenylation - genetics; Pulmonary Fibrosis - chemically induced; Pulmonary Fibrosis - enzymology; Pulmonary Fibrosis - genetics; rac GTP-Binding Proteins - genetics; rac GTP-Binding Proteins - metabolism; Rac1; rac1 GTP-Binding Protein - genetics; rac1 GTP-Binding Protein - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.308387

The generation of reactive oxygen species, particularly H2O2, from alveolar macrophages is causally related to the development of pulmonary fibrosis. Rac1, a small GTPase, is known to increase mitochondrial H2O2 generation in macrophages; however, the mechanism by which this occurs is not known. This study shows that Rac1 is localized in the mitochondria of alveolar macrophages from asbestosis patients, and mitochondrial import requires the C-terminal cysteine of Rac1 (Cys-189), which is post-translationally modified by geranylgeranylation. Furthermore, H2O2 generation mediated by mitochondrial Rac1 requires electron transfer from cytochrome c to a cysteine residue on Rac1 (Cys-178). Asbestos-exposed mice harboring a conditional deletion of Rac1 in macrophages demonstrated decreased oxidative stress and were significantly protected from developing pulmonary fibrosis. These observations demonstrate that mitochondrial import and direct electron transfer from cytochrome c to Rac1 modulates mitochondrial H2O2 production in alveolar macrophages pulmonary fibrosis. Background: Rac1 activation is linked to H2O2 generation in macrophages. Results: Two cysteine residues in Rac1 modulate mitochondrial H2O2 generation via import and electron transfer from cytochrome c. Conclusion: Mitochondrial Rac1 activity in alveolar macrophages is associated with oxidative stress. Significance: Rac1 directly mediates mitochondrial H2O2 production in alveolar macrophages, which is linked to pulmonary fibrosis.