Increased flux through the mevalonate pathway mediates fibrotic repair without injury
Jennifer L. Larson-Casey, … , Veena B. Antony, A. Brent Carter
Jennifer L. Larson-Casey, … , Veena B. Antony, A. Brent Carter
Published November 1, 2019; First published October 14, 2019
Citation Information: J Clin Invest. 2019;129(11):4962-4978. https://doi.org/10.1172/JCI127959.
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Categories: Research Article Immunology Pulmonology

Increased flux through the mevalonate pathway mediates fibrotic repair without injury

Abstract

Macrophages are important in mounting an innate immune response to injury as well as in repair of injury. Gene expression of Rho proteins is known to be increased in fibrotic models; however, the role of these proteins in idiopathic pulmonary fibrosis (IPF) is not known. Here, we show that BAL cells from patients with IPF have a profibrotic phenotype secondary to increased activation of the small GTPase Rac1. Rac1 activation requires a posttranslational modification, geranylgeranylation, of the C-terminal cysteine residue. We found that by supplying more substrate for geranylgeranylation, Rac1 activation was substantially increased, resulting in profibrotic polarization by increasing flux through the mevalonate pathway. The increased flux was secondary to greater levels of acetyl-CoA from metabolic reprogramming to β oxidation. The polarization mediated fibrotic repair in the absence of injury by enhancing macrophage/fibroblast signaling. These observations suggest that targeting the mevalonate pathway may abrogate the role of macrophages in dysregulated fibrotic repair.

Authors

Jennifer L. Larson-Casey, Mudit Vaid, Linlin Gu, Chao He, Guo-Qiang Cai, Qiang Ding, Dana Davis, Taylor F. Berryhill, Landon S. Wilson, Stephen Barnes, Jeffrey D. Neighbors, Raymond J. Hohl, Kurt A. Zimmerman, Bradley K. Yoder, Ana Leda F. Longhini, Vidya Sagar Hanumanthu, Ranu Surolia, Veena B. Antony, A. Brent Carter

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Figure 2

Increasing Rac1 activity by augmentation of isoprenylation promotes lung fibrosis.

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Increasing Rac1 activity by augmentation of isoprenylation promotes lung...
(A) Schematic diagram of the mevalonate pathway. HMG-CoA, 3-hydroxy-3-methylglutaryl coenzyme A; MVADP, mevalonate 5-diphosphate. (B) Immunoblot analysis and (C) quantification of isolated mitochondria from THP-1 cells expressing empty control or Rac1WT and treated with vehicle or GGOH (50 μM) (n = 3). (D) Mitochondrial Rac1 activity in transfected MH-S cells treated with vehicle or GGOH (n = 3). (E) Immunoblot analysis of transfected macrophages expressing empty control or Rac1WT and treated with vehicle or GGOH. Cells were separated into aqueous (unprenylated) or detergent (prenylated) fractions. Ten days after exposure of WT mice to saline or bleomycin, pumps containing vehicle or GGOH were implanted s.c., and the mice were sacrificed 11 days later. (F) Mitochondrial Rac1 immunoblot analysis of isolated MDMs. (G) Isoprenylation status of Rac1 in isolated MDMs. (H) Mitochondrial Rac1 activity (n = 5/group). (I) Tgfb1 mRNA expression (saline, vehicle n = 4; saline, GGOH n = 6; bleomycin, vehicle n = 6; bleomycin, GGOH n = 4). (J) Active TGF-β1 and (K) Ym-1 expression in BALF (n = 5/group). (L) Representative lung histology images with Masson’s trichrome staining (n = 5/group). Original magnification, ×2.5. (M) Hydroxyproline content (n = 5/group). Values indicate the mean ± SEM. *P < 0.05, **P < 0.001, and ***P < 0.0001, by 1-way ANOVA followed by Tukey’s multiple comparisons test.