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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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 5

IPF BAL cells have reduced GGDP levels.

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IPF BAL cells have reduced GGDP levels. (A) Schematic diagram of the mev...
(A) Schematic diagram of the mevalonate pathway. Representative mass spectrometric chromatography of FDP and GGDP in (B) normal (n = 7) and (C) IPF (n = 8) BAL cells. Levels of (D) FDP and (E) GGDP in BAL cells from healthy subjects (n = 7) and patients with IPF (n = 8) determined by mass spectrometry. (F) Representative immunoblot analysis of BAL cells from healthy subjects (n = 4) and patients with IPF (n = 5). Quantification of immunoblot in F of expression of (G) GGDPS and (H) GGTase 1 in BAL cells from healthy subjects (n = 9–11) and patients with IPF (n = 11). (I) Representative immunoblot analysis of MDMs from WT mice s.c. treated with vehicle or GGOH 10 days after exposure to saline or bleomycin (n = 5/group). Quantification of (J) GGDPS and (K) GGTase 1 expression in I (n = 5/group). (L) Acetyl-CoA concentration (n = 4–5). (M) OCR and (N) acetyl-CoA concentration in BAL cells isolated from WT or Rac1–/– Lyz2-Cre mice exposed to saline or bleomycin for 21 days (n = 5 mice/group). Inset in N shows Rac1 immunoblot analysis. (O) OCR in transfected MH-S cells (n = 3–4). FCCP, ; Oligo, oligomycin; FCCP, Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; Rot/Anti A, rotenone/antimycin A. (P) Acetyl-CoA concentration and (Q) Rac1 activity in THP-1 cells expressing scrambled siRNA or siPGC-1α together with empty or Rac1WT and treated with GGOH (n = 3/group). Inset in P shows PGC-1α immunoblot analysis. (R) Pearson’s correlation of acetyl-CoA to Rac1 activity. Values indicate the mean ± SEM. *P < 0.05, **P < 0.001, and ***P < 0.0001, by 2-tailed Student’s t test statistical analysis (D, E, G, and H), 1-way ANOVA followed by Tukey’s multiple comparisons test (J–L, N, P, and Q), and Pearson’s correlation analysis (R).