Wilms' tumor 1 (Wt1) regulates pleural mesothelial cell plasticity and transition into myofibroblasts in idiopathic pulmonary fibrosis

Abstract

Pleural mesothelial cells (PMCs), which are derived from the mesoderm, exhibit an extraordinary capacity to undergo phenotypic changes during development and disease. PMC transformation and trafficking has a newly defined role in idiopathic pulmonary fibrosis (IPF); however, the contribution of Wilms' tumor 1 (Wt1)-positive PMCs to the generation of pathognomonic myofibroblasts remains unclear. PMCs were obtained from IPF lung explants and healthy donor lungs that were not used for transplantation. Short hairpin Wt1-knockdown PMCs (sh Wt1) were generated with Wt1 shRNA, and morphologic and functional assays were performed in vitro. Loss of Wt1 abrogated the PMC phenotype and showed evidence of mesothelial-to-mesenchymal transition (MMT), with a reduced expression of E-cadherin and an increase in the profibrotic markers α-smooth muscle actin (α-SMA) and fibronectin, along with increased migration and contractility, compared with that of the control. Migration of PMCs in response to active transforming growth factor (TGF)-β1 was assessed by live-cell imaging with 2-photon microscopy and 3D imaging, of Wt1-EGFP transgenic mice. Lineage-tracing experiments to map the fate of Wt1(+) PMCs in mouse lung in response to TGF-β1 were also performed by using a Cre-loxP system. Our results, for the first time, demonstrate that Wt1 is necessary for the morphologic integrity of pleural membrane and that loss of Wt1 contributes to IPF via MMT of PMCs into a myofibroblast phenotype.

Myofibroblastic Conversion and Regeneration of Mesothelial Cells in Peritoneal and Liver Fibrosis

“…Interestingly, a similar conversion of MCs was recently reported in fibrosis of the adult liver or lung. 12,13 In the mouse liver, MCs express WT1, cytokeratin 8 (KRT8), and vimentin (VIM) but not E-cadherin (CDH1) and a-smooth muscle actin (ACTA2). 12 On liver injury, Wt1 þ MCs give rise to hepatic stellate cells or ACTA2 þ myofibroblasts, depending on causes.…”

Contribution of Fetal, but Not Adult, Pulmonary Mesothelium to Mesenchymal Lineages in Lung Homeostasis and Fibrosis

“…Among the proposed sources has been the mesothelial lining of the lung (3). The mesothelium is a polarized epithelial sheet that covers the surface of most visceral organs and is required for their normal development.…”

“…These cells, like other mesothelial cells, express the transcription factor, Wilms' tumor 1 (Wt1), and Wt1-driven expression of constitutive Cre or inducible CreERT2 alleles has been used to trace the fate of PMCs during lung development, postnatal lung homeostasis, and lung disease, with conflicting results (3,(9)(10)(11). During lung development, one study using a constitutive Wt1-Cre transgene reported that PMCs contribute to vascular SMCs (11).…”

Ezh2 restricts the smooth muscle lineage during mouse lung mesothelial development

“…Expression of the lung mesothelial marker WT1 has been observed in lung fibrotic lesions, suggesting that mesothelial cells or their differentiated progeny may contribute to lesion formation (Mubarak Karki et al, 2014). Mesothelial contribution to fibrosis has also been demonstrated in the liver, where the lineage-traced mesothelium invades into the submesothelial region and differentiates into fibroblasts following chemical injury (Asahina et al, 2011;Li et al, 2013).…”

“…Mesothelial cells differentiate into fibroblasts upon exposure to Tgfβ, a pro-fibrotic signaling molecule, which is upregulated in IPF lungs (Batra and Antony, 2015). Additionally, a mouse model of fibrosis by intratracheal Tgfβ1 instillation induces expression of the mesothelial-specific transcription factor Wilms tumor 1 (WT1) in the lung parenchyma (Karki et al, 2014). These data suggest that the mesothelium and mesothelial-derived cells might reactivate their developmental plasticity during lung injury and repair processes, and contribute to inappropriate fibrosis.…”