TRPV4 mediates myofibroblast differentiation and pulmonary fibrosis in mice
Shaik O. Rahaman, … , Daniel J. Tschumperlin, Mitchell A. Olman
Shaik O. Rahaman, … , Daniel J. Tschumperlin, Mitchell A. Olman
Published November 3, 2014
Citation Information: J Clin Invest. 2014;124(12):5225-5238. https://doi.org/10.1172/JCI75331.
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Research Article Pulmonology

TRPV4 mediates myofibroblast differentiation and pulmonary fibrosis in mice

Abstract

Idiopathic pulmonary fibrosis (IPF) is a fatal fibrotic lung disorder with no effective medical treatments available. The generation of myofibroblasts, which are critical for fibrogenesis, requires both a mechanical signal and activated TGF-β; however, it is not clear how fibroblasts sense and transmit the mechanical signal(s) that promote differentiation into myofibroblasts. As transient receptor potential vanilloid 4 (TRPV4) channels are activated in response to changes in plasma membrane stretch/matrix stiffness, we investigated whether TRPV4 contributes to generation of myofibroblasts and/or experimental lung fibrosis. We determined that TRPV4 activity is upregulated in lung fibroblasts derived from patients with IPF. Moreover, TRPV4-deficient mice were protected from fibrosis. Furthermore, genetic ablation or pharmacological inhibition of TRPV4 function abrogated myofibroblast differentiation, which was restored by TRPV4 reintroduction. TRPV4 channel activity was elevated when cells were plated on matrices of increasing stiffness or on fibrotic lung tissue, and matrix stiffness–dependent myofibroblast differentiation was reduced in response to TRVP4 inhibition. TRPV4 activity modulated TGF-β1–dependent actions in a SMAD-independent manner, enhanced actomyosin remodeling, and increased nuclear translocation of the α-SMA transcription coactivator (MRTF-A). Together, these data indicate that TRPV4 activity mediates pulmonary fibrogenesis and suggest that manipulation of TRPV4 channel activity has potential as a therapeutic approach for fibrotic diseases.

Authors

Shaik O. Rahaman, Lisa M. Grove, Sailaja Paruchuri, Brian D. Southern, Susamma Abraham, Kathryn A. Niese, Rachel G. Scheraga, Sudakshina Ghosh, Charles K. Thodeti, David X. Zhang, Magdalene M. Moran, William P. Schilling, Daniel J. Tschumperlin, Mitchell A. Olman

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Figure 1

Trpv4 KO mice are protected from the profibrotic effects of bleomycin.

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Trpv4 KO mice are protected from the profibrotic effects of bleomycin. W...
WT or Trpv4 KO mice were instilled with (A–F) 4 U/kg or (G and H) 1 U/kg bleomycin or saline. (A) Hydroxyproline content in the lungs of WT and Trpv4 KO mice (day 14; n ≥ 5 per group, *P < 0.05). (B) Representative immunoblots of total lung protein lysates show reduced expression of collagen-1. Bar graphs show collagen-1 band density normalized to GAPDH. *P < 0.05, WT vs. Trpv4 KO; n > 5 per group. (C) Representative photomicrographs of trichrome-stained lung tissue (original magnification, ×10). The bar graph shows the percentage of fibrotic area. **P < 0.01, WT vs. Trpv4 KO; n = 5 per group. (D) Static lung compliance (Cst) was measured using the FlexiVent (day 14, static P-V loop; *P < 0.05, WT vs. Trpv4 KO; n = 5 per group). (E) Representative immunoblots of total lung protein lysates show reduced expression of α-SMA protein. The bar graph shows α-SMA band density normalized to GAPDH. *P < 0.05; n > 5 per group. (F) Cells counts and differentials from lung lavage from mice given bleomycin (4 U/kg, day 7, n ≥ 5 per group). Macs, macrophages; PMNs, polymorphonuclear leucocytes; Lymphs, lymphocytes. (G) Hydroxyproline as in A. WT, 203% ± 67% vs. KO, 143% ± 44% of WT IT saline; *P < 0.004; n = 5 per group. (H) Lung compliance as in D. *P < 0.05, WT vs. Trpv4 KO mice; n = 5 per group. (A, F, and G) Results are expressed as mean ± SD. (B–E and H) Results are expressed as mean ± SEM.