Autocrine lysophosphatidic acid signaling activates β-catenin and promotes lung allograft fibrosis
Pengxiu Cao, … , Eric R. Fearon, Vibha N. Lama
Pengxiu Cao, … , Eric R. Fearon, Vibha N. Lama
Published February 27, 2017
Citation Information: J Clin Invest. 2017;127(4):1517-1530. https://doi.org/10.1172/JCI88896.
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Research Article Cell biology

Autocrine lysophosphatidic acid signaling activates β-catenin and promotes lung allograft fibrosis

Abstract

Tissue fibrosis is the primary cause of long-term graft failure after organ transplantation. In lung allografts, progressive terminal airway fibrosis leads to an irreversible decline in lung function termed bronchiolitis obliterans syndrome (BOS). Here, we have identified an autocrine pathway linking nuclear factor of activated T cells 2 (NFAT1), autotaxin (ATX), lysophosphatidic acid (LPA), and β-catenin that contributes to progression of fibrosis in lung allografts. Mesenchymal cells (MCs) derived from fibrotic lung allografts (BOS MCs) demonstrated constitutive nuclear β-catenin expression that was dependent on autocrine ATX secretion and LPA signaling. We found that NFAT1 upstream of ATX regulated expression of ATX as well as β-catenin. Silencing NFAT1 in BOS MCs suppressed ATX expression, and sustained overexpression of NFAT1 increased ATX expression and activity in non-fibrotic MCs. LPA signaling induced NFAT1 nuclear translocation, suggesting that autocrine LPA synthesis promotes NFAT1 transcriptional activation and ATX secretion in a positive feedback loop. In an in vivo mouse orthotopic lung transplant model of BOS, antagonism of the LPA receptor (LPA1) or ATX inhibition decreased allograft fibrosis and was associated with lower active β-catenin and dephosphorylated NFAT1 expression. Lung allografts from β-catenin reporter mice demonstrated reduced β-catenin transcriptional activation in the presence of LPA1 antagonist, confirming an in vivo role for LPA signaling in β-catenin activation.

Authors

Pengxiu Cao, Yoshiro Aoki, Linda Badri, Natalie M. Walker, Casey M. Manning, Amir Lagstein, Eric R. Fearon, Vibha N. Lama

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Figure 7

LPA1 antagonist AM095 treatment decreases lung allograft fibrosis in murine orthotopic lung transplant model.

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LPA1 antagonist AM095 treatment decreases lung allograft fibrosis in mur...
(A) Time line of two durations of AM095 treatment. (B) Decreased airway remodeling and fibrosis in allografts treated with AM095 by trichrome and H&E staining. Lung allografts were treated with AM095 during days 14–28 or days 14–40, both harvested on day 40 after transplantation (n = 5 for placebo, 4 for AM095 treatment during days 14–28, and 5 for AM095-treated allografts during days 14–40). An Olympus BX41 microscope with an Olympus DP20 camera was used to take images. Scale bars: 200 μm for ×40 images and 40 μm for ×200 images. (C) Morphometric analysis of airway wall thickness in transplanted placebo allografts, AM095-treated allografts for days 14–28, and AM095-treated allografts for days 14–40 (n = 4/group with ANOVA). Data are represented by floating bars ranging from minimum to maximum, with a line showing the mean value of each graft. (D) Hydroxyproline assay in lung grafts was conducted for collagen content quantitation. Both durations of AM095 treatment significantly reduced hydroxyproline content in allografts (n = 7 for isograft and 6 for the rest of the groups, with ANOVA). *P < 0.05, **P < 0.01, ****P < 0.0001. (E) Dephosphorylated (dephospho) NFAT1, ATX, and total and active β-catenin proteins was decreased in allografts treated with AM095 (n = 4/group) by immunoblot.