Profibrotic epithelial phenotype: a central role for MRTF and TAZ

Janne Folke Bialik,Caterina Di Ciano-Oliveira,Mei Ding,András Kapus,Michael M Kofler,Stine F Pedersen,Maria Zena Miranda,Pam Speight,Ori D Rotstein,Qinghong Dan,Katalin Szászi

doi:10.1038/s41598-019-40764-7

Janne Folke Bialik, Caterina Di Ciano-Oliveira + Show 9 more

Open Access

https://doi.org/10.1038/s41598-019-40764-7

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Abstract

Epithelial injury is a key initiator of fibrosis but - in contrast to the previous paradigm - the epithelium in situ does not undergo wide-spread epithelial-mesenchymal/myofibroblast transition (EMT/EMyT). Instead, it assumes a Profibrotic Epithelial Phenotype (PEP) characterized by fibrogenic cytokine production. The transcriptional mechanisms underlying PEP are undefined. As we have shown that two RhoA/cytoskeleton-regulated transcriptional coactivators, Myocardin-related transcription factor (MRTF) and TAZ, are indispensable for EMyT, we asked if they might mediate PEP as well. Here we show that mechanical stress (cyclic stretch) increased the expression of transforming growth factor-β1 (TGFβ1), connective tissue growth factor (CTGF), platelet-derived growth factor and Indian Hedgehog mRNA in LLC-PK1 tubular cells. These responses were mitigated by siRNA-mediated silencing or pharmacological inhibition of MRTF (CCG-1423) or TAZ (verteporfin). RhoA inhibition exerted similar effects. Unilateral ureteral obstruction, a murine model of mechanically-triggered kidney fibrosis, induced tubular RhoA activation along with overexpression/nuclear accumulation of MRTF and TAZ, and increased transcription of the above-mentioned cytokines. Laser capture microdissection revealed TAZ, TGFβ1 and CTGF induction specifically in the tubular epithelium. CCG-1423 suppressed total renal and tubular expression of these proteins. Thus, MRTF regulates epithelial TAZ expression, and both MRTF and TAZ are critical mediators of PEP-related epithelial cytokine production.

Highlights

Chronic kidney disease (CKD), affecting 12% of the North-American population is considered an “epidemic”[1]
We tested whether mechanical stress, a relevant inducer of fibrosis[54,55], alters fibrogenic cytokine expression in kidney tubular cells, and if so whether such responses might be dependent on Myocardin-related transcription factor (MRTF) and/or transcriptional co-activator with PDZ-binding motif (TAZ) signaling
Since cyclic stretch is an adequate mimic of pathophysiologic tubular mechanostress[56,57], and we have previously shown that it induces robust MRTF and TAZ translocation in LLC-PK1 proximal tubular cells[35], we used this stimulus for these proof-of-principle experiments

Summary

Introduction

Chronic kidney disease (CKD), affecting 12% of the North-American population is considered an “epidemic”[1]. Ever since the myofibroblast was recognized as the central cellular mediator of fibrogenesis[6], understanding the origins and activation of this mesenchymal cell type have become the focus of fibrosis research[7,8]. The previous paradigm attributed a direct role to the tubular epithelium in (myo)fibroblast generation via epithelial-mesenchymal transition. This notion was based on histological “snapshots” showing the co-existence of epithelial and mesenchymal markers in the injured epithelium in vivo (reviewed in14–16) and the undebated capacity of tubular cells to transition to myofibroblasts in vitro[17,18]. The representative Western blots (inset in panel a) document the downregulation of MRTF and TAZ by the corresponding siRNAs

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