Molecular Analysis of Endothelial-mesenchymal Transition Induced by Transforming Growth Factor-β Signaling
Summary
A protocol for in vitro induction of endothelial-mesenchymal transition (EndMT), which is useful for investigating cellular signaling pathways involved in EndMT, is described. In this experimental model, EndMT is induced by treatment with TGF-β in MS-1 endothelial cells.
Abstract
Phenotypic plasticity of endothelial cells underlies cardiovascular system development, cardiovascular diseases, and various conditions associated with organ fibrosis. In these conditions, differentiated endothelial cells acquire mesenchymal-like phenotypes. This process is called endothelial-mesenchymal transition (EndMT) and is characterized by downregulation of endothelial markers, upregulation of mesenchymal markers, and morphological changes. EndMT is induced by several signaling pathways, including transforming growth factor (TGF)-β, Wnt, and Notch, and regulated by molecular mechanisms similar to those of epithelial-mesenchymal transition (EMT) important for gastrulation, tissue fibrosis, and cancer metastasis. Understanding the mechanisms of EndMT is important to develop diagnostic and therapeutic approaches targeting EndMT. Robust induction of EndMT in vitro is useful to characterize common gene expression signatures, identify druggable molecular mechanisms, and screen for modulators of EndMT. Here, we describe an in vitro method for induction of EndMT. MS-1 mouse pancreatic microvascular endothelial cells undergo EndMT after prolonged exposure to TGF-β and show upregulation of mesenchymal markers and morphological changes as well as induction of multiple inflammatory chemokines and cytokines. Methods for the analysis of microRNA (miRNA) modulation are also included. These methods provide a platform to investigate mechanisms underlying EndMT and the contribution of miRNAs to EndMT.
Introduction
Endothelial-mesenchymal transition (EndMT) is the process by which a differentiated endothelial cell undergoes a variety of molecular changes, resulting in a fibroblast-like mesenchymal cell1. EndMT was initially described as an endothelial cell transformation during development of the heart2,3. In early heart development, the heart tube consists of an inner endocardium and an outer myocardium. These two layers are separated by a layer of extracellular matrix called the cardiac jelly. The embryonic endocardial cells, which acquire endothelial cell markers, transit into mesenchymal cells, invade the underlying cardiac jelly, and promote formation of the cardiac cushions, providing the foundation for the atrioventricular valves and septum and the semilunar valves. Furthermore, EndMT has been suggested to be sources of pericytes and vascular smooth muscle cells in other embryonic vascular systems including coronary vessels, abdominal aorta, and pulmonary artery4,5,6. In addition, EndMT is implicated in physiological angiogenic sprouting7.
Accumulating evidence has suggested that EndMT is also involved in multiple cardiovascular diseases and other diseases1,8. EndMT-associated conditions include vascular calcification, atherosclerosis, pulmonary arterial hypertension, cavernous malformation, organ fibrosis, vein graft remodeling, allograft dysfunction in kidney transplantation, and cancer8,9,10,11,12,13,14,15,16,17,18. A recent report described that several molecular EndMT markers can be a tool for diagnosis and prognosis prediction of renal graft dysfunction in kidney transplantation17. Modulation of EndMT-related cellular signaling pathways have been shown to ameliorate several disease conditions including cardiac fibrosis and vein graft remodeling in animal models8,15. Therefore, understanding the mechanisms underlying EndMT is important to develop diagnostic and therapeutic strategies targeting EndMT.
EndMT is characterized by loss of cell-cell junctions, increase in migratory potential, downregulation of endothelial-specific genes such as VE-cadherin, and upregulation of mesenchymal genes including α-smooth muscle actin (α-SMA). In addition, EndMT and epithelial-mesenchymal transition (EMT), a similar process that converts epithelial cells to mesenchymal cells, are associated with altered production of various extracellular matrix components, which may contribute to the development of tissue fibrosis8,19.
Recently, several in vitro studies of EndMT have elucidated details of molecular mechanisms of EndMT15,20. EndMT is induced by various signaling pathways including transforming growth factor (TGF)-β, Wnt, and Notch1. Among them, TGF-β plays pivotal roles in the induction of both EMT and EndMT. In EndMT, prolonged exposure to TGF-β results in EndMT in various endothelial cells, while short exposure appears to be insufficient21. We here described a straightforward protocol for EndMT induction, in which MILE SVEN 1 (MS-1) mouse pancreatic microvascular endothelial cells undergo EndMT in vitro after prolonged exposure to TGF-β20. In this model, multiple downstream analyses can be performed to investigate hallmark features of EndMT, including morphological changes, downregulation of endothelial markers, upregulation of mesenchymal markers and inflammatory genes, cytoskeletal rearrangements, and collagen gel contraction.
MicroRNAs (miRNAs) are ~22 nt small regulatory RNAs that direct posttranscriptional repression of various mRNA targets22,23. Through seed sequence-mediated target recognition, miRNAs suppress hundreds of target genes and modulate diverse cellular functions such as cell differentiation, proliferation, and motility. This is also the case for regulation of EMT and EndMT, and several miRNAs have been reported as regulators of EMT and EndMT24,25. The EndMT model presented in this review can be easily combined with miRNA modulation procedures to test the roles of miRNAs in EndMT. The present review summarizes our experimental procedures to investigate TGF-β-induced EndMT in MS-1 cells and also includes comparison of conditions of EndMT induction by TGF-β in other endothelial cells.
Protocol
Representative Results
Discussion
It has been reported that activated Ras and TGF-β treatment for 24 h induced EndMT in MS-1 cells, while TGF-β alone failed to induce EndMT in this short period21. Consistently, we observed that TGF-β substantially induced EndMT after longer treatment (48–72 h) in MS-1 cells20. EndMT has been repeatedly observed after prolonged treatment with TGF-β (2–6 days) in various endothelial cells such as human umbilical vein endothelial cells (HUVEC), …
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
We thank Zea Borok and Kohei Miyazono for suggestions in preparation of manuscript. H.I.S. and M.H. are supported by the Uehara Memorial Foundation Research Fellowship, and H.I.S. is supported by the Osamu Hayaishi Memorial Scholarship for Study Abroad. This work was supported by a grant from Takeda Science Foundation (A.S.).
Materials
| MS-1 cells | American Type Culture Collection | CRL-2279 | |
| MEM-alpha | Thermo Fisher Scientific | 32571036 | |
| TGF-beta2 | R&D | 302-B2-002 | |
| 4 well Lab-Tek II Chamber Slide | Thermo Fisher Scientific | 154526 | |
| Y-27632 | Sigma-Aldrich | Y0503 | |
| Blocking One | nacalai tesque | 03953-95 | |
| phalloidin-tetramethylrhodamine B isothiocyanate | Sigma-Aldrich | P1951 | |
| TOTO-3 iodide | Thermo Fisher Scientific | T3604 | |
| VE cadherin monoclonal antibody (BV13) | Thermo Fisher Scientific | 14-1441-82 | |
| alpha-SMA Cy3 monoclonal antibody (1A4) | Sigma-Aldrich | C6198 | |
| Alexa Fluor 488 goat anti-mouse IgG (H+L) | Thermo Fisher Scientific | A-11001 | |
| Cover slip | Thermo Fisher Scientific | 174934 | |
| Collagen solution | Nitta gelatin Inc. | Cellmatrix I-P | |
| Collagen dilution buffer | Nitta gelatin Inc. | Cellmatrix I-P | |
| LNA miRNA inhibitor | EXIQON | miRCURY LNAmicroRNA Power Inhibitor (Negative Control B and target miRNA) | |
| synthetic miRNA duplex | Qiagen | miScript miRNA Mimic | |
| Lipofectamine RNAiMAX | Thermo Fisher Scientific | 13778030 | |
| Lipofectamine 2000 | Thermo Fisher Scientific | 11668027 | |
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