Epithelial to mesenchymal transition in murine tracheal allotransplantation: an immunohistochemical observation.
ABSTRACT: Aberrant epithelial repair is a crucial event in the airway remodeling that characterizes obliterative bronchiolitis (OB) in transplanted lungs. Recent data from experiments using epithelial cell lines and human airway tissues from lung transplant recipients suggest that epithelial to mesenchymal transition (EMT) plays an important role in OB. The aim of this study was to clarify whether EMT is involved in airway remodeling in an animal model.We performed orthotopic tracheal transplantation from BALB/c to C57BL/6 mice with from BALC/c to BALB/c mouse grafts as controls. Five allogeneic and 3 syngeneic recipients were humanely killed at predetermined postoperative days 2-12 as well as 14 and 21. Histology was evaluated using hematoxylin-eosin (H&E) staining. We studied the expression of specific markers, including E-cadherin, an epithelial marker; ?-smooth muscle actin (SMA), and S100A4, mesenchymal markers, and zinc finger E-box-binding homeobox 1 (ZEB1), an EMT-related transcription factor.Histologic assessment of serial H&E stains of allogeneic grafts showed remarkable pseudostratified respiratory epithelium with subepithelial inflammatory cell infiltration, as well as denuded and flattened epithelium and subepithelial fibrosis. The dynamic epithelial changes occurred earlier than the subepithelial fibrosis. Immunohistochemical evaluation indicated the emergence of ?-SMA- positive epithelial cells that were most prominent on day 7. The expression of E-cadherin was attenuated in ?-SMA-positive epithelial cells. S100A4 was also expressed in epithelial cells. A few days before the intraepithelial expression of ?-SMA, ZEB1 emerged in the nuclei of epithelial cells.We observed expression of an EMT-related transcription factor and mesenchymal markers along with the attenuation of epithelial marker expression in epithelial cells, several days before prominent subepithelial fibrosis formation, results that suggest epithelial cells to play an important fibrosis role in airway remodeling during epithelial to mesenchymal transition.
Project description:Chronic allergic asthma is characterized by Th2-polarized inflammation and leads to airway remodeling and fibrosis but the mechanisms involved are not clear. To determine whether epithelial-mesenchymal transition contributes to airway remodeling in asthma, we induced allergic airway inflammation in mice by intranasal administration of house dust mite (HDM) extract for up to 15 consecutive weeks. We report that respiratory exposure to HDM led to significant airway inflammation and thickening of the smooth muscle layer in the wall of the large airways. Transforming growth factor beta-1 (TGF-?1) levels increased in mouse airways while epithelial cells lost expression of E-cadherin and occludin and gained expression of the mesenchymal proteins vimentin, alpha-smooth muscle actin (?-SMA) and pro-collagen I. We also observed increased expression and nuclear translocation of Snail1, a transcriptional repressor of E-cadherin and a potent inducer of EMT, in the airway epithelial cells of HDM-exposed mice. Furthermore, fate-mapping studies revealed migration of airway epithelial cells into the sub-epithelial regions of the airway wall. These results show the contribution of EMT to airway remodeling in chronic asthma-like inflammation and suggest that Th2-polarized airway inflammation can trigger invasion of epithelial cells into the subepithelial regions of the airway wall where they contribute to fibrosis, demonstrating a previously unknown plasticity of the airway epithelium in allergic airway disease.
Project description:BACKGROUND: Epithelial to mesenchymal transition (EMT) in alveolar epithelial cells (AECs) has been widely observed in patients suffering interstitial pulmonary fibrosis. In vitro studies have also demonstrated that AECs could convert into myofibroblasts following exposure to TGF-beta1. In this study, we examined whether EMT occurs in bleomycin (BLM) induced pulmonary fibrosis, and the involvement of bronchial epithelial cells (BECs) in the EMT. Using an alpha-smooth muscle actin-Cre transgenic mouse (alpha-SMA-Cre/R26R) strain, we labelled myofibroblasts in vivo. We also performed a phenotypic analysis of human BEC lines during TGF-beta1 stimulation in vitro. METHODS: We generated the alpha-SMA-Cre mouse strain by pronuclear microinjection with a Cre recombinase cDNA driven by the mouse alpha-smooth muscle actin (alpha-SMA) promoter. alpha-SMA-Cre mice were crossed with the Cre-dependent LacZ expressing strain R26R to produce the double transgenic strain alpha-SMA-Cre/R26R. beta-galactosidase (betagal) staining, alpha-SMA and smooth muscle myosin heavy chains immunostaining were carried out simultaneously to confirm the specificity of expression of the transgenic reporter within smooth muscle cells (SMCs) under physiological conditions. BLM-induced peribronchial fibrosis in alpha-SMA-Cre/R26R mice was examined by pulmonary betagal staining and alpha-SMA immunofluorescence staining. To confirm in vivo observations of BECs undergoing EMT, we stimulated human BEC line 16HBE with TGF-beta1 and examined the localization of the myofibroblast markers alpha-SMA and F-actin, and the epithelial marker E-cadherin by immunofluorescence. RESULTS: betagal staining in organs of healthy alpha-SMA-Cre/R26R mice corresponded with the distribution of SMCs, as confirmed by alpha-SMA and SM-MHC immunostaining. BLM-treated mice showed significantly enhanced betagal staining in subepithelial areas in bronchi, terminal bronchioles and walls of pulmonary vessels. Some AECs in certain peribronchial areas or even a small subset of BECs were also positively stained, as confirmed by alpha-SMA immunostaining. In vitro, addition of TGF-beta1 to 16HBE cells could also stimulate the expression of alpha-SMA and F-actin, while E-cadherin was decreased, consistent with an EMT. CONCLUSION: We observed airway EMT in BLM-induced peribronchial fibrosis mice. BECs, like AECs, have the capacity to undergo EMT and to contribute to mesenchymal expansion in pulmonary fibrosis.
Project description:Eosinophilic inflammation and remodeling of the airways including subepithelial fibrosis and myofibroblast hyperplasia are characteristic pathological findings of bronchial asthma. Epithelial to mesenchymal transition (EMT) plays a critical role in airway remodelling. In this study, we hypothesized that infiltrating eosinophils promote airway remodelling in bronchial asthma. To demonstrate this hypothesis we evaluated the effect of eosinophils on EMT by in vitro and in vivo studies. EMT was assessed in mice that received intra-tracheal instillation of mouse bone marrow derived eosinophils and in human bronchial epithelial cells co-cultured with eosinophils freshly purified from healthy individuals or with eosinophilic leukemia cell lines. Intra-tracheal instillation of eosinophils was associated with enhanced bronchial inflammation and fibrosis and increased lung concentration of growth factors. Mice instilled with eosinophils pre-treated with transforming growth factor(TGF)-?1 siRNA had decreased bronchial wall fibrosis compared to controls. EMT was induced in bronchial epithelial cells co-cultured with human eosinophils and it was associated with increased expression of TGF-?1 and Smad3 phosphorylation in the bronchial epithelial cells. Treatment with anti-TGF-?1 antibody blocked EMT in bronchial epithelial cells. Eosinophils induced EMT in bronchial epithelial cells, suggesting their contribution to the pathogenesis of airway remodelling.
Project description:Chronic epithelial injury triggers a TGF-?-mediated cellular transition from normal epithelium into a mesenchymal-like state that produces subepithelial fibrosis and airway remodeling. Here we examined how TGF-? induces the mesenchymal cell state and determined its mechanism. We observed that TGF-? stimulation activates an inflammatory gene program controlled by the NF-?B/RelA signaling pathway. In the mesenchymal state, NF-?B-dependent immediate-early genes accumulate euchromatin marks and processive RNA polymerase. This program of immediate-early genes is activated by enhanced expression, nuclear translocation, and activating phosphorylation of the NF-?B/RelA transcription factor on Ser276, mediated by a paracrine signal. Phospho-Ser276 RelA binds to the BRD4/CDK9 transcriptional elongation complex, activating the paused RNA Pol II by phosphorylation on Ser2 in its carboxy-terminal domain. RelA-initiated transcriptional elongation is required for expression of the core epithelial-mesenchymal transition transcriptional regulators SNAI1, TWIST1, and ZEB1 and mesenchymal genes. Finally, we observed that pharmacological inhibition of BRD4 can attenuate experimental lung fibrosis induced by repetitive TGF-? challenge in a mouse model. These data provide a detailed mechanism for how activated NF-?B and BRD4 control epithelial-mesenchymal transition initiation and transcriptional elongation in model airway epithelial cells in vitro and in a murine pulmonary fibrosis model in vivo. Our data validate BRD4 as an in vivo target for the treatment of pulmonary fibrosis associated with inflammation-coupled remodeling in chronic lung diseases.
Project description:BACKGROUND: Obliterative bronchiolitis in chronic rejection of lung allografts is characterised by airway epithelial damage and fibrosis. The process whereby normal epithelium is lost and replaced by fibroblastic scar tissue is poorly understood, but recent findings suggest that epithelial cells can become fibroblasts through epithelial-mesenchymal transition (EMT). It is hypothesised that EMT occurs in lung allografts and plays a potential role in airway remodelling. METHODS: Sixteen stable lung transplant recipients underwent bronchoscopy with bronchoalveolar lavage (BAL), endobronchial biopsies, and bronchial brushings. Biopsy sections were stained for the fibroblast marker S100A4. Brushings were cultured on collagen, stained with anti-S100A4, and examined for further EMT markers including matrix metalloproteinase (MMP) zymographic activity and epithelial invasion through collagen coated filters. RESULTS: A median 15% (0-48%) of the biopsy epithelium stained for S100A4 in stable lung transplant recipients and MMP-7 co-localisation was observed. In non-stimulated epithelial cultures from lung allografts, S100A4 staining was identified with MMP-2 and MMP-9 production and zymographic activity. MMP total protein and activity was increased following stimulation with transforming growth factor (TGF)-beta1. Non-stimulated transplant epithelial cells were invasive and penetration of collagen coated filters increased following TGF-beta1 stimulation. CONCLUSIONS: This study provides evidence of EMT markers in lung allografts of patients without loss of lung function. The EMT process may represent a final common pathway following injury in more common diseases characterised by airway remodelling.
Project description:Whether or not cholangiocytes or their hepatic progenitors undergo an epithelial-to-mesenchymal transition (EMT) to become matrix-producing myofibroblasts during biliary fibrosis is a significant ongoing controversy. To assess whether EMT is active during biliary fibrosis, we used Alfp-Cre × Rosa26-YFP mice, in which the epithelial cells of the liver (hepatocytes, cholangiocytes, and their bipotential progenitors) are heritably labeled at high efficiency with yellow fluorescent protein (YFP). Primary cholangiocytes isolated from our reporter strain were able to undergo EMT in vitro when treated with transforming growth factor-?1 alone or in combination with tumor necrosis factor-?, as indicated by adoption of fibroblastoid morphology, intracellular relocalization of E-cadherin, and expression of ?-smooth muscle actin (?-SMA). To determine whether EMT occurs in vivo, we induced liver fibrosis in Alfp-Cre × Rosa26-YFP mice using the bile duct ligation (BDL) (2, 4, and 8 weeks), carbon tetrachloride (CCl(4) ) (3 weeks), and 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC; 2 and 3 weeks) models. In no case did we find evidence of colocalization of YFP with the mesenchymal markers S100A4, vimentin, ?-SMA, or procollagen 1?2, although these proteins were abundant in the peribiliary regions.Hepatocytes and cholangiocytes do not undergo EMT in murine models of hepatic fibrosis.
Project description:Chronic oxidative injury produced by airway disease triggers a transforming growth factor-? (TGF-?)-mediated epigenetic reprogramming known as the epithelial-mesenchymal transition (EMT). We observe that EMT silences protective mucosal interferon (IFN)-I and III production associated with enhanced rhinovirus (RV) and respiratory syncytial virus (RSV) replication. Mesenchymal transitioned cells are defective in inducible interferon regulatory factor 1 (IRF1) expression by occluding RelA and IRF3 access to the promoter. IRF1 is necessary for the expression of type III IFNs (IFNLs 1 and 2/3). Induced by the EMT, zinc finger E-box binding homeobox 1 (ZEB1) binds and silences IRF1. Ectopic ZEB1 is sufficient for IRF1 silencing, whereas ZEB1 knockdown partially restores IRF1-IFNL upregulation. ZEB1 silences IRF1 through the catalytic activity of the enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), forming repressive H3K27(me3) marks. We observe that IRF1 expression is mediated by ZEB1 de-repression, and our study demonstrates how airway remodelling/fibrosis is associated with a defective mucosal antiviral response through ZEB1-initiated epigenetic silencing.
Project description:Nickel (Ni) is an environmental and occupational carcinogen, and exposure to Ni is associated with lung and nasal cancers in humans. Furthermore, Ni exposure is implicated in several lung diseases including chronic inflammatory airway diseases, asthma, and fibrosis. However, the mutagenic potential of Ni is low and does not correlate with its potent toxicity and carcinogenicity. Therefore, mechanisms underlying Ni exposure-associated diseases remain poorly understood. Since the health risks of environmental exposures often continue post exposure, understanding the exposure effects that persist after the termination of exposure could provide mechanistic insights into diseases. By examining the persistent effects of Ni exposure, we report that Ni induces epithelial-mesenchymal transition (EMT) and that the mesenchymal phenotype remains irreversible even after the termination of exposure. Ni-induced EMT was dependent on the irreversible upregulation of ZEB1, an EMT master regulator, via resolution of its promoter bivalency. ZEB1, upon activation, downregulated its repressors as well as the cell-cell adhesion molecule, E-cadherin, resulting in the cells undergoing EMT and switching to persistent mesenchymal status. ZEB1 depletion in cells exposed to Ni attenuated Ni-induced EMT. Moreover, Ni exposure did not induce EMT in ZEB1-depleted cells. Activation of EMT, during which the epithelial cells lose cell-cell adhesion and become migratory and invasive, plays a major role in asthma, fibrosis, and cancer and metastasis, lung diseases associated with Ni exposure. Therefore, our finding of irreversible epigenetic activation of ZEB1 by Ni exposure and the acquisition of persistent mesenchymal phenotype would have important implications in understanding Ni-induced diseases.
Project description:Recent studies have shown that cancer-associated fibroblasts (CAFs) and the epithelial-mesenchymal transition (EMT) contribute to invasive and metastatic abilities of ovarian cancer (OC) cells. In the present study, we attempted to identify the role of CAF- and EMT-related proteins in OCs, including serous carcinoma, mucinous carcinoma, endometrioid carcinoma and clear cell carcinoma using an immunohistochemical approach. The following CAF-related markers were used: CD10, podoplanin, fibroblast activating protein (FAP), platelet derived growth factor receptor (PDGFR?), PDGFR?, S100A4 and ?-smooth muscle actin (?-SMA). In addition, the following EMT-related markers were investigated: Slug, TWIST1 and ZEB1We performed hierarchical cluster analysis to group the samples according to their scoring. Subgroup 1 was characterized by high expression of CD10, podoplanin, ?-SMA, Slug and ZEB1, whereas subgroup 2 was closely associated with high expression of podoplanin, PDGFR?, PDGFR?, ?-SMA, and Slug. In addition, marked expression of CD10 was observed in subgroup 3. High expression of ?-SMA was a distinctive feature in subgroup 4, and expression of podoplanin and ?-SMA characterized subgroup 5. Each subgroup was correlated with a histological type. The fact that different histological types were associated with different subgroups suggests the presence of distinct and heterogeneous subpopulations of CAFs in OC.
Project description:Epithelial-mesenchymal transition (EMT) is essential in asthma airway remodeling. IL-33 from epithelial cells is involved in pulmonary fibrosis. CD146 has been extensively explored in cancer-associated EMT. Whether IL-33 regulates CD146 in the EMT process associated with asthma airway remodeling is still largely unknown. We hypothesized that EMT in airway remodeling was regulated by the IL-33/CD146 axis. House dust mite (HDM) extract increased the expression of IL-33 and CD146 in epithelial cells. Increased expression of CD146 in HDM-treated epithelial cells could be blocked with an ST2-neutralizing antibody. Moreover, HDM-induced EMT was dependent on the CD146 and TGF-?/SMAD-3 signaling pathways. IL-33 deficiency decreased CD146 expression and alleviated asthma severity. Similarly, CD146 deficiency mitigated EMT and airway remodeling in a murine model of chronic allergic airway inflammation. Furthermore, CD146 expression was significantly elevated in asthma patients. We concluded that IL-33 from HDM extract-treated alveolar epithelial cells stimulated CD146 expression, promoting EMT in airway remodeling in chronic allergic inflammation.