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Am J Respir Crit Care Med. 2018 Aug 15;198(4):486-496. doi: 10.1164/rccm.201709-1823OC.

Dicer1 Deficiency in the Idiopathic Pulmonary Fibrosis Fibroblastic Focus Promotes Fibrosis by Suppressing MicroRNA Biogenesis.

Author information

1
1 Department of Medicine.
2
2 Department of Pediatrics.
3
3 Clinical and Translational Science Institute, Biorepository & Laboratory Services, Histology and Research Laboratory.
4
4 Department of Biomedical Engineering, and.
5
5 Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis, Minnesota.

Abstract

RATIONALE:

The lung extracellular matrix (ECM) in idiopathic pulmonary fibrosis (IPF) mediates progression of fibrosis by decreasing fibroblast expression of miR-29 (microRNA-29), a master negative regulator of ECM production. The molecular mechanism is undefined. IPF-ECM is stiffer than normal. Stiffness drives fibroblast ECM production in a YAP (yes-associated protein)-dependent manner, and YAP is a known regulator of miR-29. Therefore, we tested the hypothesis that negative regulation of miR-29 by IPF-ECM was mediated by mechanotransduction of stiffness.

OBJECTIVES:

To determine how IPF-ECM negatively regulates miR-29.

METHODS:

We decellularized lung ECM using detergents and prepared polyacrylamide hydrogels of defined stiffness by varying acrylamide concentrations. Mechanistic studies were guided by immunohistochemistry of IPF lung and used cell culture, RNA-binding protein assays, and xenograft models.

MEASUREMENTS AND MAIN RESULTS:

Contrary to our hypothesis, we excluded fibroblast mechanotransduction of ECM stiffness as the primary mechanism deregulating miR-29. Instead, systematic examination of miR-29 biogenesis revealed a microRNA processing defect that impeded processing of miR-29 into its mature bioactive forms. Immunohistochemical analysis of the microRNA processing machinery in IPF lung specimens revealed decreased Dicer1 expression in the procollagen-rich myofibroblastic core of fibroblastic foci compared with the focus perimeter and adjacent alveolar walls. Mechanistically, IPF-ECM increased association of the Dicer1 transcript with RNA binding protein AUF1 (AU-binding factor 1), and Dicer1 knockdown conferred primary human lung fibroblasts with cell-autonomous fibrogenicity in zebrafish and mouse lung xenograft models.

CONCLUSIONS:

Our data identify suppression of fibroblast Dicer1 expression in the myofibroblast-rich IPF fibroblastic focus core as a central step in the mechanism by which the ECM sustains fibrosis progression in IPF.

KEYWORDS:

extracellular matrix; idiopathic pulmonary fibrosis; yes-associated protein

PMID:
29579397
PMCID:
PMC6118029
[Available on 2019-08-15]
DOI:
10.1164/rccm.201709-1823OC

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