The SWI/SNF-Related, Matrix Associated, Actin-Dependent Regulator of Chromatin A4 Core Complex Represses Respiratory Syncytial Virus-Induced Syncytia Formation and Subepithelial Myofibroblast Transition.

Xiaofang Xu,Chenyang Dong,Roberto P Garofalo,Allan R Brasier,Sunduz Keles,Morgan Mann,Dianhua Qiao

doi:10.3389/fimmu.2021.633654

Abstract

Epigenetics plays an important role in the priming the dynamic response of airway epithelial cells to infectious and environmental stressors. Here, we examine the epigenetic role of the SWI/SNF Related, Matrix Associated, Actin Dependent Regulator of Chromatin A4 (SMARCA4) in the epithelial response to RSV infection. Depletion of SMARCA4 destabilized the abundance of the SMARCE1/ARID1A SWI/SNF subunits, disrupting the innate response and triggering a hybrid epithelial/mesenchymal (E/M) state. Assaying SMARCA4 complex-regulated open chromatin domains by transposase cleavage -next generation sequencing (ATAC-Seq), we observed that the majority of cleavage sites in uninfected cells have reduced chromatin accessibility. Paradoxically, SMARCA4 complex-depleted cells showed enhanced RSV-inducible chromatin opening and gene expression in the EMT pathway genes, MMP9, SNAI1/2, VIM, and CDH2. Focusing on the key MMP9, we observed that SMARCA4 complex depletion reduced basal BRD4 and RNA Polymerase II binding, but enhanced BRD4/Pol II binding in response to RSV infection. In addition, we observed that MMP9 secretion in SMARCA4 complex deficient cells contributes to mesenchymal transition, cellular fusion (syncytia) and subepithelial myofibroblast transition. We conclude the SMARCA4 complex is a transcriptional repressor of epithelial plasticity, whose depletion triggers a hybrid E/M state that affects the dynamic response of the small airway epithelial cell in mucosal remodeling via paracrine MMP9 activity.

Highlights

The human airway is lined with a contiguous mucosal surface composed of highly differentiated airway epithelial cells that play important role in gas exchange, maintenance of fluid balance, control of vascular reactivity and initiation of the innate response [1]
We selected highly differentiated Scgb1a1-expressing small human airway epithelial cells for this study because Human small airway epithelial cells (hSAEC) are a site of Respiratory syncytia virus (RSV) replication in lower respiratory tract infection (LRTI) [46]; inhibition of the innate pathway in this cell type in vivo blocks RSV-induced airway inflammation and airway obstruction [6]; and, Scgb1a1+ hSAECs produce pathogenic mucin- and T helper 2 lymphocyteactivating cytokines that mediate disease [47]
Wild type (WT) hSAECs were infected with sucrose-purified RSV [multiplicity of infection (MOI) =1] for 24 h, and SMARCA4/Brg1 transcripts were quantified by Q-RT-PCR

Summary

Introduction

The human airway is lined with a contiguous mucosal surface composed of highly differentiated airway epithelial cells that play important role in gas exchange, maintenance of fluid balance, control of vascular reactivity and initiation of the innate response [1]. Within minutes of mucosal denudation, nearby epithelial cells de-differentiate, enabling them to migrate to repopulate the injured area [7]. This epithelial injury-repair process is a sterotypic genomic response that results in loss of epithelial differentiation features [cadherin (CDH1)] and acquisition of mesenchymal properties [vimentin (VIM) and extracellular matrix (ECM)-remodeling matrix metalloproteinases (MMP)]. This genomic reprogramming is known as “type II” (nononcogenic) epithelial-to-mesenchymal transition (EMT) [8, 9]. Cellular reprogramming produced by EMT disrupts mucosal innate immunity [13, 14] and promotes ECM deposition, characteristic of obstructive lung diseases

Methods

Results

Conclusion