Increased Regeneration Following Stress-Induced Lung Injury in Bleomycin-Treated Chimeric Mice with CD44 Knockout Mesenchymal Cells.

Zvi Fridlender,Raphael Breuer,Dmytro Petukhov,Shulamit B Wallach-Dayan,Mark Richter-Dayan

doi:10.3390/cells8101211

Zvi Fridlender, Raphael Breuer + Show 3 more

Open Access

https://doi.org/10.3390/cells8101211

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Journal: Cells	Publication Date: Oct 7, 2019
Citations: 7	License type: CC BY 4.0

Affiliation: Hadassah Medical Center, Boston University

Abstract

CD44, an adhesion-molecule promoting cell-migration, is shown here to increase in stress conditions following bleomycin-induced apoptosis in alveolar epithelial cells (AECs), a main target of lung injury. In vivo, it inhibits tissue regeneration and leads to fibrosis. We show that some AECs survive by the ataxia-telangiectasia mutated kinase/ATM pathway, and undergo a CD44-mediated epithelial-mesenchymal transdifferentiation (EMT) with migratory capacities in vitro, and in vivo. We assessed apoptosis vs. proliferation of AECs following bleomycin, ATM/P53 signaling pathway in AECs, and CD44 involvement in EMT, cell motility and tissue regeneration in vitro and in vivo. Expression of survival genes, CD44, and ATM/p53 pathway was elevated in AECs surviving bleomycin injury, as were the markers of EMT (downregulation of E-cadherin, upregulation of N-cadherin and vimentin, nuclear translocation of β-catenin). Inhibition of CD44 decreased AECs transdifferentiation. Bleomycin-treated chimeric CD44KO-mice had decreased EMT markers, ATM, and mesenchymal cells (α-SMA+) accumulation in lung, increased surfactant-b, diminished lung mesenchymal cell motility, and increased lung tissue regenerative capacity following bleomycin injury, as indicated by lung collagen content and semiquantitave morphological index scoring. Thus, AECs surviving lung injury are plastic and undergo ATM-mediated, CD44-dependent transdifferentiation, preventing tissue regeneration and promoting fibrosis. Synthetic or natural compounds that downregulate CD44 may improve tissue regeneration following injury.

Highlights

We previously detected bleomycin-induced reactive oxygen species (ROS) resulting in oxidative stress, mitochondrial leakage, DNA damage response (DDR), and apoptosis, in normal alveolar epithelial cells (AECs) [1]
Annexin-V(−) cells showed the upregulation of survival genes which are known to be expressed in response to oxidative-stress and DNA-damage, such as GADD45, P21 and others, and of genes involved in apoptosis regulation, such as Ataxia Telangiectasia Mutated (ATM), IAP’s and survivin (Table 1)
We have previously shown [21] that young mice injured with bleomycin (0.03–0.05 mU/mouse) evolve pulmonary fibrosis by day 14 but as opposed to aged mice [10], we show that lung tissue regenerates by day 56 [21]

Summary

Introduction

We previously detected bleomycin-induced reactive oxygen species (ROS) resulting in oxidative stress, mitochondrial leakage, DNA damage response (DDR), and apoptosis, in normal alveolar epithelial cells (AECs) [1]. E-cadherin, increasing vimentin and α–smooth muscle actin (αSMA) [3], a set of incidences that promote accumulation of myofibroblasts in injured tissues, which characterizes fibrotic diseases [5], including idiopathic pulmonary fibrosis (IPF). Involvement of CD44 in EMT during pulmonary fibrosis as opposed to tissue regeneration (both in clinic and in experimental animals) is more scant [9]. IPF in aging, which as opposed to juvenile subjects, lack the possibility of tissue regeneration and do not resolve fibrosis [10], correlates with increments in oxidative stress [11]

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