title: Fibulin-1 suppresses endothelial to mesenchymal transition in the proximal outflow tract.
abstract: Endothelial to mesenchymal transition (EMT) that occurs during cardiac outflow tract (OFT) development is critical for formation of the semilunar valves. Fibulin-1 (Fbln1) is an extracellular matrix protein that is present at several sites of EMT, including the OFT (i.e., E9.5-10.5). The aim of this study was to determine the role of Fbln1 in EMT during the earliest events of OFT development. Examination of proximal OFT cushions in Fbln1 null embryos detected hypercellularity at both E9.5 (93% increase; p = 0.002) and E10.5 (43% increase; p = 0.01) as compared to wild type, suggesting that Fbln1 normally suppresses OFT endocardial cushion EMT. This was supported by studies of proximal OFT cushion explants, which showed that explants from Fbln1 null embryos displayed a 58% increase in cells migrating from the explants as compared to wild type (p = 0.005). We next evaluated the effects of Fbln1 deficiency on the expression of factors that regulate proximal OFT EMT. At E9.5, Fbln1 null proximal OFT endocardium and EMT-derived mesenchyme showed increased TGFβ2 (58% increase; p = 0.01) and increased Snail1-positive nuclei (27% increase; p = 0.0003). Histological examination of OFT cushions in Fbln1 null embryos (E9.5) also detected cells present in the cushion that were determined to be erythrocytes based on round morphology, autofluorescence, and positive staining for hemoglobin. Erythrocytes were also detected in Fbln1 null OFT cushions at E10.5. Together, the findings indicate that Fbln1 normally suppresses proximal OFT EMT preventing proximal cushion hypercellularity and blood cell accumulation.
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Keerthi
authors.initials: K
authors.lastname: Harikrishnan
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Marion A
authors.initials: MA
authors.lastname: Cooley
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Sugi
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: Barth
authors.affiliation: Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, Odense, Denmark.
authors.forename: Lars M
authors.initials: LM
authors.lastname: Rasmussen
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Christine B
authors.initials: CB
authors.lastname: Kern
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA. Electronic address: argravek@musc.edu.
authors.forename: Kelley M
authors.initials: KM
authors.lastname: Argraves
authors.affiliation: Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: W Scott
authors.initials: WS
authors.lastname: Argraves
mesh_terms: D000818:Animals; D017209:Apoptosis; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D054089:Endocardial Cushions / Q000166:cytology / Q000378:metabolism*; D004699:Endocardium / Q000166:cytology / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*
chemical_list: D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; C060820:fibulin
keywords: EMT; Endocardial barrier; Endocardial cushions; Extracellular matrix; Fibulin-1; Proximal outflow tract; endothelial barrier